Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： 10.1109/CEIDP49254.2020.9437492

Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： 10.5220/0007341800210025

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s10404-018-2051-7

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s10404-018-2051-7

Language：Japanese   Publishing type：Research paper (scientific journal)  

This paper provides electrical and dielectric properties of artificial snow produced at a defined condition in a climatic chamber. Complex impedance of the artificial snow block was measured varying its Liquid Water Content (LWC). An equivalent circuit of the electrode system was also discussed. It was revealed that the complex impedance of artificial snow decreased with increasing LWC. Moreover, it was suggested that the change in LWC would provide a change in dielectric properties of artificial snow depending on the source frequency.

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3390/bios7040044

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3390/bios7040044

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1049/iet-nbt.2016.0186

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： 10.1109/TENCON.2016.7848606

Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： 10.1109/TENCON.2016.7848608

Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： DOI: 10.1109/TENCON.2016.7848262

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1049/iet-nbt.2016.0186

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Rapid and sensitive detection of pathogenic bacteria has been an important concern in various fields such as bioscience research, medical diagnosis and hazard analysis in the food industry. The requirement for highly efficient bacterial detection has pointed to the need for new and innovative sample concentration technologies. In this study, a new microfluidic device was demonstrated to enable concentration of bacteria by using negative dielectrophoresis (n-DEP) in high conductive medium. A special design of the electrode system, which was covered with patterned dielectric films, was tested in order to control the electric field distribution in the device so that n-DEP force could drive cells to a point for concentration as well as Joule heating of the suspension medium could be suppressed to avoid heat-induced cell damage. The electrode design was optimized using numerical calculation results of cell motion trajectories and the suspension medium temperature in the device. It was experimentally proved that proposed microfluidic device could concentrate E. coli cells in a continuous flow of cell suspension.

DOI： 10.1109/ICIT.2015.7125592

Language：English   Publishing type：Research paper (international conference proceedings)  

Wide-gap semiconductors with nanostructures such as nanoparticles, nanorods, nanowires are promising as a new type of gas sensor. Recently, ZnO (zinc oxide) nano-structures have been extensively investigated for acetylene (C2H2) gas sensing device applications. In this paper, a new fabrication method of a C2H2 gas sensor based on ZnO nanowires using dielectrophoresis is demonstrated. Dielectrophoresis (DEP) is the electrokinetic motion of dielectrically polarized materials in nonuniform electric fields. ZnO nanowires were trapped in the microelectrode gap where the electric field became higher. The trapped ZnO nanowires were aligned along the electric field line and bridged the electrode gap. Upon exposure to C2H2 gas, the conductance of the DEP-trapped ZnO nanowires increased. The ZnO nanowire gas sensor response to C2H2 gas was dependent on the temperature and the maximum response was obtained at 250 °C. It was confirmed that the sensor response was considerably improved by electrochemically decorating the ZnO nanowires with platinum nanoparticles.

DOI： 10.1109/ICIT.2015.7125298

Language：English   Publishing type：Research paper (international conference proceedings)  

Polymerase chain reaction (PCR) is a powerful tool for diagnostic procedures in bacterial and viral infections. We have developed a new electrical technique for rapid detection of DNA amplified by PCR using dielectrophoresis (DEP) of microbeads that are chemically labeled with the amplicons. The DNA immobilization on the microbeads alters their DEP behavior in such a way that they are trapped on a microelectrode under the action of positive DEP, whereas pristine microbeads are not. Combining the dramatic alteration in DEP characteristics with impedance measurement leads to rapid and quantitative detection of amplicons. The method is based on the surface conductivity dependence of microbeads DEP characteristics. It was expected that the surface conductivity would depend on the length of DNA fragments immobilized on a microbeads. In this study, it was found that the crossover frequency was dependent on the length of DNA.

DOI： 10.1109/ICIT.2015.7125593

Language：English   Publishing type：Research paper (international conference proceedings)  

Polymerase chain reaction (PCR) is one of the most sensitive and specific detection methods of bacterial and viral infections. The authors proposed a new electrical technique for rapid detection of DNA amplified by PCR using dielectrophoresis (DEP) of microbeads. The method is based on dramatic alteration of DEP characteristics of microbeads caused by DNA labelling. DNA labeled microbeads are trapped on a microelectrode under the action of positive DEP, whereas pristine microbeads are not. DEP-trapped microbeads can be measured impedimetrically to realize rapid and quantitative detection of the amplified DNA. In this study, it was aimed to reveal how DNA length affects DEP characteristic of DNA-labeled microbeads. Dielectrophoretic crossover from the negative to the positive was measured for microbeads labeled with DNA length in 204 bp, 391 bp and 796 bp. After theoretical fitting of DEP crossover data, it was revealed that the surface conductance increased when the length of labeled DNA increased.

Language：English   Publishing type：Research paper (international conference proceedings)  

A new electrical technique for rapid detection of DNA amplified by polymerase chain reaction (PCR) using dielectrophoresis (DEP) of microbeads was demonstrated. The amplicons were chemically immobilized on the microbeads. The DNA immobilization on the microbeads alters their DEP behavior in such a way that they are trapped on a microelectrode under the action of positive DEP, whereas pristine microbeads are not. Combining the dramatic alteration in DEP characteristics with impedance measurement leads to rapid and quantitative detection of the amplicon in a few seconds. The proposed microbead-based assay could be applicable for rapid, quantitative, and automated detection of virus infection.

DOI： 10.1109/ICSENS.2014.6985174

Language：English   Publishing type：Research paper (scientific journal)  

Polymerase chain reaction (PCR) is a powerful tool for diagnostic procedures in bacterial and viral infections. The authors propose a new electrical technique for rapid detection of DNA amplified by PCR using dielectrophoresis (DEP) of microbeads. The method is based on dramatic alteration of DEP characteristics of microbeads caused by DNA labeling. DNA-labeled microbeads are trapped on a microelectrode under the action of positive DEP, whereas pristine ones are not. DEP-trapped microbeads are measured impedimetrically to realize rapid and quantitative detection of the amplified DNA. The validity of the proposed method was demonstrated by detection of PCR-amplified DNA of viruses.

DOI： 10.1209/0295-5075/108/28003

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)  

In this study, a bacterial detection technique and device that utilizes advantages of both positive and negative dielectrophoresis (DEP) has been proposed and demonstrated. The device has two microelectrodes, which serve as a bacteria concentrator using negative DEP (n-DEP) and as a bacteria detector using positive DEP (p-DEP), respectively. Bacteria flowing into the device are repelled under action of n-DEP force exerted by the first microelectrode, and are pushed toward the second microelectrode situated at the downstream. Then concentrated bacteria are finally captured by p-DEP on the second microelectrode and detected by dielectrophoretic impedance measurement (DEPIM) method. The numerical simulations and experiments proved that n-DEP concentrator could make DEPIM sensitivity two times higher than that without n-DEP as a result of increased number of bacteria trapped on the p-DEP microelectrode.

DOI： 10.1016/j.snb.2013.02.030

Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1541/ieejfms.132.978

Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1541/ieejfms.132.980

Language：English   Publishing type：Research paper (international conference proceedings)  

In this work, we demonstrated an electrical detection technique of norovirus capsid in liquid by using dielectrophoretic impedance measurement (DEPIM). DEPIM is a method composing of capturing target particles by dielectrophoresis (DEP) in the gap of microelectrodes and measuring the impedance change of the microelectrodes caused by the captured particles. DEPIM has been successfully applied to bacteria detection by the present authors. This is the first report to extend scope of DEPIM inspection from bacteria to norovirus. Recombinant norovirus capsid was employed as target particles in experiments due to safety concerns. First, we showed virus capturing by DEP using fluorescent labeled norovirus capsid. Then, DEPIM of the capsid was carried out. As the result, DEPIM detected 2.5 ng/ml of the norovirus capsid in 300 sec. This implies that DEPIM has comparable sensitivity but shorter detection time than immunochromatography.

DOI： 10.1109/ICSENS.2012.6411163

Language：English   Publishing type：Research paper (scientific journal)  

We improved our previously reported highly sensitive bacteria detection method called
electropermeabilization-assisted dielectrophoretic impedance measurement (EPA-DEPIM), which
counts the number of bacteria by measuring changes in impedance. EPA-DEPIM involves two processes:
collection of bacteria by dielectrophoresis (DEP), followed by electropermeabilization (EP) of the
cell membranes. In DEP, bacterial cells in aqueous solution are collected on microelectrodes by the
dielectrophoretic force. In EP, a pulse-like rectangular wave is applied to the collected cells to disrupt
their membranes. This increases the signal sensitivity because the disrupted membranes release
intracellular ions that increase the change in impedance. However, the pulse-like EP wave creates a
strong electric field that causes metal ions to be released from the microelectrodes, increasing the blank
signal to levels comparable to that for a low-concentration Escherichia coli suspension (102 cells/ml). To
address this problem, we demonstrated the efficacy of two types of pretreatment applied before the EP
wave: chemical pretreatment by exposure to hydrogen peroxide, and physical pretreatment by a small
pulse-like voltage. Both pretreatments successfully intensified the change in impedance even at a lower
EP voltage.

DOI： 10.1016/j.snb.2012.07.078

Other Link： http://dx.doi.org/10.1016/j.snb.2012.07.078

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1109/TDEI.2012.6180262

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1143/JJAP.51.045102

Other Link： http://jjap.jsap.jp/link?JJAP/51/045102/

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

In this study, a bacteria detection apparatus based on dielectrophoretic impedance measurement (DEPIM) method was
demonstrated for rapid evaluation of oral hygiene. The authors integrated a micro electrode chip on which bacteria were captured
by dielectrophoresis (DEP), an AC voltage source to induce DEP force, and an impedance measurement circuit to a portable
instrument that enables rapid and automated oral bacterial inspection in hospitals and clinics. Special considerations have
been made on effects of high electrical conductivity of oral samples on DEP force and DEPIM results. It was shown
experimentally and theoretically that using a higher electric field frequency for the DEP bacteria trap and the impedance
measurement could realise DEPIM application to bacteria inspection from oral samples with higher conductivity. Based on
these investigations, the authors optimised the frequency condition of the DEPIM suitable for inspecting an oral sample along
with the design and development of a portable DEPIM apparatus for on-site inspection of oral bacteria. Under the optimised
frequency condition, DEPIM results were in good agreement with the conventional culture method showing significant
applicability of the DEPIM apparatus for practical rapid oral bacteria inspection.

DOI： 10.1049/iet-nbt.2010.0011

Other Link： http://dx.doi.org/10.1049/iet-nbt.2010.0011

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1143/JJAP.49.086203

Other Link： http://dx.doi.org/10.1143/JJAP.49.086203

Language：English   Publishing type：Research paper (scientific journal)  

Dielectrophoresis DEP is an electrokinetic motion of dielectrically polarized materials in nonuniform electric fields. DEP has been successfully applied to manipulation of nanomaterials including carbon nanotubes CNTs, metallic nanoparticles, and semiconducting nanowires. Under positive DEP force, which attracts nano materials toward the higher field region, nanomaterials are trapped in the electrode gap and automatically establish good electrical connections between them and the external measuring circuit. This feature allows us a fast, simple, and low-cost fabrication of nanomaterial-based sensors based on a bottom-up approach. This paper first presents a theoretical background of DEP phenomena and then reviews recent works of the present author, which were aimed to develop nanomaterial-based sensors, such as a CNT gas sensor and a ZnO nanowire photosensor, using DEP fabrication technique. It is also demonstrated that DEP technique enables self-formation of interfaces between various nano materials, which can be also applicable as novel sensing transducers.

DOI： 10.1063/1.3430535

Other Link： http://dx.doi.org/10.1063/1.3430535

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1143/JJAP.49.055002

Other Link： http://jjap.ipap.jp/link?JJAP/49/055002/

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1143/JJAP.49.055002

Other Link： http://dx.doi.org/10.1143/JJAP.49.055002

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1143/JJAP.49.055002

Other Link： http://dx.doi.org/10.1143/JJAP.49.055002

Language：English   Publishing type：Research paper (scientific journal)  

Other Link： http://www.jspf.or.jp/JPFRS/PDF/Vol8/jpfrs2009_08-0603.pdf

Language：Japanese   Publishing type：Research paper (scientific journal)  

Manipulation and Detection of Bacteria Using Dielectrophoresis

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Dielectrophoretic manipulation of nanomaterials and its application to device fabrication

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)  

Other Link： http://dx.doi.org/10.1049/iet-nbt.2008.0011

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Other Link： http://dx.doi.org/10.1143/JJAP.48.065004

Language：English   Publishing type：Research paper (scientific journal)  

Other Link： http://dx.doi.org/10.1007/s10404-008-0276-6

Language：English   Publishing type：Research paper (scientific journal)  

Other Link： http://dx.doi.org/10.1016/j.surfcoat.2008.06.068

Language：English   Publishing type：Research paper (scientific journal)  

http://dx.doi.org/10.1109/TDEI.2008.4543097

Other Link： http://dx.doi.org/10.1109/TDEI.2008.4543097

Language：English   Publishing type：Research paper (scientific journal)  

Other Link： http://dx.doi.org/10.1016/j.snb.2007.05.002

Language：English   Publishing type：Research paper (international conference proceedings)  

Other Link： http://dx.doi.org/10.1109/ICSENS.2007.4388458

Language：English   Publishing type：Research paper (scientific journal)  

Other Link： http://dx.doi.org/10.1088/0957-4484/18/33/335602

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Other Link： http://dx.doi.org/10.1016/j.apsusc.2007.02.152

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Other Link： http://dx.doi.org/10.1109/TDEI.2007.369536

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Other Link： http://dx.doi.org/10.1109/TDEI.2006.258191

Language：English   Publishing type：Research paper (scientific journal)  

Other Link： http://dx.doi.org/10.1016/j.snb.2005.12.027

Language：English   Publishing type：Research paper (scientific journal)  

Other Link： http://dx.doi.org/10.1088/0957-4484/17/14/013

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Other Link： http://dx.doi.org/10.1016/j.elstat.2005.11.001

Language：English   Publishing type：Research paper (scientific journal)  

Other Link： http://dx.doi.org/10.1088/0957-4484/17/10/021

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Other Link： http://dx.doi.org/10.1016/j.tsf.2005.08.024

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Other Link： http://dx.doi.org/10.1109/TDEI.2006.1624280

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Other Link： http://dx.doi.org/10.1016/j.snb.2005.08.043

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DOI： 10.1016/j.snb.2004.09.048

Other Link： http://dx.doi.org/10.1016/j.snb.2004.09.048

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DOI： 10.1016/j.snb.2004.12.048

Other Link： http://dx.doi.org/10.1016/j.snb.2004.12.048

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DOI： 10.1016/j.snb.2004.05.050

Other Link： http://dx.doi.org/10.1016/j.snb.2004.05.050

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1143/JJAP.42.L1483

Other Link： http://dx.doi.org/10.1143/JJAP.42.L1483

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/S0925-4005(03)00517-3

Other Link： http://dx.doi.org/10.1016/S0925-4005(03)00517-3

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1088/0022-3727/36/21/L01

Other Link： http://dx.doi.org/10.1088/0022-3727/36/21/L01

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1109/TIA.2003.816535

Other Link： http://dx.doi.org/10.1109/TIA.2003.816535

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/S0304-3886(03)00062-7

Other Link： http://dx.doi.org/10.1016/S0304-3886(03)00062-7

Language：English   Publishing type：Research paper (scientific journal)  

Other Link： http://dx.doi.org/10.1016/S0304-3886(02)00124-9

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DOI： 10.1109/TDEI.2002.1115484

Language：English   Publishing type：Research paper (international conference proceedings)  

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DOI： 10.1109/TDEI.2002.1024436

Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： 10.1109/ICDL.2002.1022703

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DOI： 10.1109/94.971460

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DOI： 10.1109/94.919953

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1109/77.920079

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.1322576

Language：English   Publishing type：Research paper (scientific journal)  

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DOI： 10.1109/94.839344

Language：English   Publishing type：Research paper (scientific journal)  

Other Link： http://dx.doi.org/10.1088/0022-3727/32/21/316

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DOI： 10.1109/77.783496

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DOI： 10.1109/77.783486

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DOI： 10.1109/94.752008

Language：English   Publishing type：Research paper (international conference proceedings)  

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DOI： 10.1016/S0011-2275(98)00079-4

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DOI： 10.1088/0022-3727/31/22/019

Other Link： http://dx.doi.org/10.1088/0022-3727/31/22/019

Language：English   Publishing type：Research paper (international conference proceedings)  

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DOI： 10.1016/S0011-2275(97)00134-3

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DOI： 10.1109/77.614630

Language：English   Publishing type：Research paper (international conference proceedings)  

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DOI： 10.1109/77.614630

Language：English   Publishing type：Research paper (international conference proceedings)  

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DOI： 10.1109/94.536729

Language：English   Publishing type：Research paper (international conference proceedings)  

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DOI： 10.1109/LSENS.2023.3297315

Language：English   Publishing type：Research paper (scientific journal)  

An all-solid-state pH sensing system utilizing a stainless steel vessel (SUS304) and a pH-insensitive diamond solution-gate field-effect transistor (SGFET) is presented here to explain the interaction between stainless steel vessel and field-effect transistor (FET) pH sensors for the first time. A pH-sensitive ion-sensitive field-effect transistor (ISFET) was first used to show the change of the sensing behavior from 47.78 to −4.73 mV/pH when using an Ag/AgCl electrode and stainless steel vessel as the gate. This intriguing sensing behavior was investigated by developing large- and small-signal equivalent circuit models in a transistor circuit for both the Ag/AgCl and the stainless steel vessel gate. The result shows that the targeted ion change ΔQh corresponding to the pH sensitivity has been offset, which explains the phenomenon observed when using the pH-sensitive ISFET with the stainless steel vessel. We then hypothesize that combining a pH-insensitive device with the stainless steel vessel gate should show a pH sensitivity close to the Nernst response. To validate this, a pH-insensitive diamond SGFET was then fabricated and combined with the stainless steel vessel for pH measurements. The system demonstrates a high pH sensitivity at −54.18 mV/pH across a wide range of pH solutions (pH 2–12) and remains stable in elevated temperatures when measured with a potentiostat setup at 80 °C. The results also suggest that this all-solid-state sensing system has great potential to be used in the food and beverage industry where stainless steel is widely employed due to its excellent corrosion resistance, low cost, and high sensing capabilities.

DOI： 10.1109/JSEN.2023.3257348

Language：English   Publishing type：Research paper (scientific journal)  

Global warming and rising energy demands have increased renewable energy (RE) usage globally. Wind energy has become the most technologically advanced renewable energy source. Wind turbines (WTs) must ride through faults to ensure power system stability. On the flip side, permanent magnet synchronous generators (PMSG)-based wind turbine power plants (WTPPs) are susceptible to grid voltage fluctuations and require extra regulations to maintain regular operations. Due to recent changes in grid code standards, it has become vital to explore alternate fault ride-through (FRT) methods to ensure their capabilities. This research will ensure that FRT solutions available via the Web of Science (WoS) database are vetted and compared in hardware retrofitting, internal software control changes, and hybrid techniques. In addition, a bibliometric analysis is provided, which reveals an ever-increasing volume of works dedicated to the topic. After that, a literature study of FRT techniques for PMSG WTs is carried out, demonstrating the evolution of these techniques over time. This paper concludes that additional research is required to enhance FRT capabilities in PMSG wind turbines and that further attention to topics, such as machine learning tools and the combination of FRT and wind power smoothing approaches, should arise in the following years.

DOI： 10.3390/en15239116

Language：English   Publishing type：Research paper (scientific journal)  

Wind power penetration is growing, posing considerable technological challenges for developing electrical grid systems. Gearless permanent magnet synchronous generator (PMSG) wind energy conversion systems (WECS) are becoming more popular. On the flip side, they are susceptible to grid failures. The use of Superconducting Magnetic Energy Storage (SMES) to enhance fault ride-through in PMSG wind turbines is investigated. Per the current Grid code trends, WECS are not to be disconnected from the grid; rather, they should provide reactive power support during such situations. This work incorporates machine and grid side converters to manage reactive, active power and DC-link voltage during grid failures. To improves system performance, lessen voltage dips at the point of common coupling (PCC), provide reactive power support and reduce the transient length, a DC-link capacitor is used with SMES. SMES reserve energy capacity is necessary for FRT operation when the wind turbine's inertial response range is insufficient. Finally, a 1.5 MW PMSG-based WTG with SMES is developed. The Pre-fault, fault-period, and post-fault performance are all assessed. They confirm the system's efficiency, speed, and stability.

Language：English   Publishing type：Research paper (scientific journal)  

In this paper, a new diagnosis method for SF6 gas-insulated switchgear (GIS) is proposed based on decomposition gas analysis. We focus on residual CF4 gas in GIS, which is a decomposition gas generated in GIS via partial or arc discharge. Unlike other decomposition gases, which can be removed by the gas absorbent, CF4 accumulates during in-service operation, enabling trend-based GIS condition monitoring. Because direct CF4 detection using commercially available gas sensors is difficult, we propose a novel indirect detection method in which CF4 is converted into CO and CO2 by a dielectric barrier discharge (DBD). A DBD-treated artificial gas mixture composed of CF4, O2, and SF6 was analyzed via Fourier transform infrared spectroscopy (FTIR). It was found that CO and CO2 are simultaneously generated when the CF4 gas concentration is higher than 100 ppm, which is close to the target CF4 concentration for GIS diagnosis. To demonstrate rapid, simple, and on-site diagnostic capabilities, a commercial electrochemical CO gas sensor was employed to detect DBD-converted CO gas. The CO concentration quantified by the calibrated gas sensor was almost identical to that obtained via FTIR. As the CF4-to-CO conversion rate is expected to improve with an optimum DBD reactor design, the proposed scheme could be applicable to GIS diagnosis.

DOI： doi.org/10.34343/ijpest.2021.15.e02010

Other Link： https://doi.org/10.34343/ijpest.2021.15.e02010

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/d0an02349c

Language：English   Publishing type：Research paper (international conference proceedings)  

This paper presents a new scheme for the detection of residual carbon tetrafluoride (CF 4 ) gas in gas-insulated switchgear (GIS) for its diagnosis. For the diagnosis of GIS, the decomposition gas species including CF 4 generated by partial discharges or breakdown are analyzed. Accumulation of the gas species indicates the history of the failure of GIS. However, most of the gas species are removed by an absorbent placed in a GIS vessel. The only CF 4 stays in GIS vessel for the long term. In this study, it is aimed to develop an easy and rapid CF 4 detection method. Because direct detection of CF 4 is difficult, an indirect detection method of CF 4 is proposed, in which CF 4 is processed by non-thermal plasma (NTP). In this paper, the conversion of CF 4 using dielectric barrier discharge (DBD) was examined. The infrared absorption band among SF 6 , CF 4 , and CO 2 was observed by Fourier transform infrared (FT-IR) spectroscopy. The amount of CO 2 generated in the case of CF 4 (10,000 ppm) and O 2 (10,000 ppm) diluted in Ar or SF 6 was analyzed. In the case of Ar dilution, CO 2 gradually increased with increasing time of DBD application by using a compact CO 2 NDIR sensor. In the case of SF 6 dilution, CO 2 , CO, O 2 , and SO 2 were detected by using a portable gas analyzer. The latter case showed a higher CO 2 generation rate of 400 ppm/hr, whereas the other showed 50 ppm/hr. In addition, a zeolite-filled column was installed for removing SO 2 from the processed gas.

DOI： 10.1109/CMD48350.2020.9287294

Language：Japanese   Publishing type：Research paper (scientific journal)  

Applications of dielectrophoresis in life science

DOI： 10.2198/electroph.64.15

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/5.0008188

Language：English   Publishing type：Research paper (scientific journal)  

Dielectrophoretic (DEP) manipulation of a diamond particle has potential application in the detection of DNA or other bio-molecules. We investigate the fundamental DEP and surface properties of submicron diamond particles. Diamond particles were dispersed in a NaCl solution and dropped on a castle-walled electrode. An AC electric field was applied to determine the DEP crossover frequency as a function of the solution conductivity. The surface conductance of the diamond particles was then evaluated from the parametrical fitting of the crossover frequencies. The diamond surface layer was shown to exhibit a rather high conductance, although bulk diamond is insulative.

DOI： 10.35848/1347-4065/ab7baf

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.5129725

Language：English   Publishing type：Research paper (other academic)  

A recent trend in the integration of electric power devices has caused problems of heat management because of high heat generation from the device. Therefore, studies of new materials having high thermal conductivity have been motivated. Polymer-based composites have been paid attention because of its flexibility and energy-saving productivity. In this study, nitride fillers, which have excellent thermal conductivity and electric insulating property, were used as a component of the polymer-based composites. To achieve high thermal diffusion with a small fraction of the fillers, the fillers were aligned by an electric field. Aluminum nitride (AlN) or boron nitride (BN) particles were dispersed in an acrylic polymer. An array of wire electrodes was used to form widely spread electric field. In-plane and through-plane alignment were carried out with varying arrangements of the electrode arrays. Thermal diffusivity in-plane direction of the AlN and BN composites increased about 1.2- and 1.7-fold by aligning the fillers as comparing with those without the alignment, respectively. To align the filler in through-plane detection, several kinds of the electrode arrangements were examined. As the best result, the through-plane thermal diffusivity of the aligned AlN composites became 30-fold compared to that without the alignment.

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.5124419

Language：English   Publishing type：Research paper (other academic)  

Partial and arc discharge in gas insulated switchgear (GIS), such as a switching component or circuit breaker, can lead decomposition gas generation of sulphur hexafluoride (SF₆), which is generally used as an electrical insulation medium. The authors had demonstrated that SF₆ decomposition products, such as HF, SO₂, SOF₂, can be detected by using a carbon nanotube (CNT) gas sensor, which was fabricated by dielectrophoresis. In this study, we selected carbon tetrafluoride (CF₄) as a target decomposition gas to be detected by nanomaterial-based gas sensors. Because CF₄ is hard to be removed by using a molecular sieve or absorbent, the decomposition product accumulates in a long time and can be used for GIS diagnosis. Three kinds of semiconducting nanomaterial, carbon nanotube, SnO₂ nanoparticle, ZnO nanowires, were integrated on a microelectrode by dielectrophoresis respectively to fabricate a gas sensor. It was found that SnO₂ gas sensor showed the highest response to CF₄ gas at 1% concentration in SF₆. The conductance of the SnO₂ sensor gradually decreased with elapsed time after exposure to the CF₄ gas depending on the operating temperature.

DOI： 10.1007/978-3-030-31676-1_46

Language：English   Publishing type：Research paper (other academic)  

In this study, we focus on the alteration of negative dielectrophoresis (n-DEP) caused by small amount of DNA labeling on the microbeads and propose a new design of microfluidic device for more sensitive DNA detection. In previous study, we proposed a new electrical technique for rapid detection of DNA amplified by polymerase chain reaction (PCR). The method is based on dramatic alteration of dielectrophoresis (DEP) characteristics of microbeads caused by DNA labeling. The DNA labeling of microbeads alters their DEP behavior in such a way that they are trapped on a microelectrode under the action of positive DEP (p-DEP), whereas bare microbeads are not, due to the n-DEP. However, this method requires at least 10⁵ copies of DNA labelling on a microbead to alter the DEP behavior of microbeads from negative to positive. As a result, we are able to distinguish bare microbeads and microbeads labeled with DNA at DNA to microbead ratio of 3×10³: 1 and 3×10⁴: 1, based on the n-DEP alteration.

DOI： 10.1109/ICSENS.2017.8234345

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.elstat.2017.04.010

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (other academic)  

Oil-insulated transformer is one of the important equipments in the current high-voltage transmission system and it has contributed to the reduction of transmission power loss. However, abnormal phenomena, such as over-heat, discharge and so on, would appear in the oil-insulated transformer. Currently, gas chromatography is the most common diagnosis technique for the transformer diagnosis which is not suitable for rapid detection in the operation field. Therefore, it is necessary to develop a more efficient diagnostic method to identify the abnormal phenomena. In this paper, we demonstrated a platinum modified ZnO gas sensor, which was fabricated by dielectrophoresis (DEP) integration method, to detect acetylene gas dissolved in the insulating oil after arc discharge occurred inside the insulating oil. In addition, the influence of discharge voltage to sensor response was investigated and the response was compared to quantitative analysis obtained by gas chromatography. Relationship between the sensor response and the concentration of acetylene gas dissolved suggested a possibility of quantitative analysis of acetylene by platinum (Pt) decorated ZnO sensor.

DOI： 10.1109/TENCON.2016.7848262

Language：English   Publishing type：Research paper (scientific journal)  

This paper provides electrical and dielectric properties of artificial snow produced at a defined condition in a climatic chamber. Complex impedance of the artificial snow block was measured varying its Liquid Water Content (LWC). An equivalent circuit of the electrode system was also discussed. It was revealed that the complex impedance of artificial snow decreased with increasing LWC. Moreover, it was suggested that the change in LWC would provide a change in dielectric properties of artificial snow depending on the source frequency.

DOI： 10.1541/ieejfms.137.590

Language：English   Publishing type：Research paper (scientific journal)  

Dielectrophoretic impedance measurement (DEPIM) is a method to detect bacteria in an aqueous solution. DEPIM consists of two simultaneous processes: dielectrophoretic trapping of the target bacteria onto a microelectrode and measurement of impedance change caused by trapping bacteria. In this study, a new bacterial concentration process was combined with DEPIM to improve its sensitivity. The concentration process was based on negative dielectrophoresis of bacteria caused by specific configuration of parallel electrodes. A ditched dielectric thin layer deposited on one of the parallel electrodes causes non-uniform electric field resulting in occurring negative dielectrophoresis. Two electrode configurations, one is for the bacteria concentration and the other is for DEPIM, were fabricated in a microchannel. As a result, the detection sensitivity of DEPIM increased about 1.6 times by combining the concentration.

DOI： 10.1541/ieejsmas.136.148

Language：English   Publishing type：Research paper (scientific journal)  

The aim of this study is the electrical detection of pathogenic viruses, namely, adenovirus and rotavirus, using dielectrophoretic impedance measurement (DEPIM). DEPIM consists of two simultaneous processes: dielectrophoretic trapping of the target and measurement of the impedance change and increase in conductance with the number of trapped targets. This is the first study of applying DEPIM, which was originally developed to detect bacteria suspended in aqueous solutions, to virus detection. The dielectric properties of the viruses were also investigated in terms of their dielectrophoretic behavior. Although their estimated dielectric properties were different from those of bacteria, the trapped viruses increased the conductance of the microelectrode in a manner similar to that in bacteria detection. We demonstrated the electrical detection of viruses within 60 s at concentrations as low as 70 ng/ml for adenovirus and 50 ng/ml for rotavirus.

DOI： 10.7567/JJAP.55.017001

Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： 10.1109/ICSENS.2015.7370216

Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： 10.1109/TRANSDUCERS.2015.7181228

Language：English   Publishing type：Research paper (other academic)  

Polymerase chain reaction (PCR) is one of the most sensitive and specific detection methods of bacterial and viral infections. The authors proposed a new electrical technique for rapid detection of DNA amplified by PCR using dielectrophoresis (DEP) of microbeads. The method is based on dramatic alteration of DEP characteristics of microbeads caused by DNA labelling. DNA labeled microbeads are trapped on a microelectrode under the action of positive DEP, whereas pristine microbeads are not. DEP-trapped microbeads can be measured impedimetrically to realize rapid and quantitative detection of the amplified DNA. In this study, it was aimed to reveal how DNA length affects DEP characteristic of DNA-labeled microbeads. Dielectrophoretic crossover from the negative to the positive was measured for microbeads labeled with DNA length in 204 bp, 391 bp and 796 bp. After theoretical fitting of DEP crossover data, it was revealed that the surface conductance increased when the length of labeled DNA increased.

DOI： 10.5220/0005280701850189

Language：English   Publishing type：Research paper (other academic)  

Hot spots produced by gas-puff z-pinch plasma which are high energy density plasma regions radiate intensive soft x-rays. Gas-puff z-pinch is expected to industrial applications such as soft x-ray lithography, microscopy and laser. In these cases, the scattering of hot spots is important when the gas-puff z-pinch plasma is used as a point source of soft x-ray. Previous results in our study showed the reduction of radial displacement of hot spots in positive voltage shots by using an IPP (Inductive Pulsed Power) system. In this paper, the voltage polarity effects on the gaspuff z-pinch plasma behavior, spatial distribution of hot spots and soft x-ray emission are described.

DOI： 10.1109/PPPS.2001.01002207

Language：English   Publishing type：Research paper (other academic)  

We proposed a new DNA detection method based on microbeads dielectrophoresis (DEP). In the method, the DNA-labeled microbeads are electrically detected. Only the DNA-labeled microbeads are trapped on a microelectrode by positive DEP, whereas the pristine ones are repelled In this paper, size selective detection of DNA using the method is described. It was found that the frequency response of DEP of the DNA-labeled microbeads depended on the DNA length. At high frequency only the long DNA-labeled microbeads were trapped, whereas the short DNA-labeled microbeads were repelled. This phenomena can realize selective detection of DNA with different length.

Language：English   Publishing type：Research paper (other academic)  

Aim of this paper is to demonstrate virus detection by dielectrophoretic impedance measurement (DEPIM). DEPIM consists of two processes of dielectrophoretic trapping of target particles and measuring impedance change with increasing the number of trapped particles. DEPIM has been used to detect bacteria suspended in aqueous solution. In this study, norovirus and rotavirus, which cause gastroenteritis in human, were used as the target viruses. As the results, 50 ng/ml of norovirus and 10 ng/ml of rotavirus were detected within 100 s.

DOI： 10.1109/ICSensT.2013.6727678

Language：English   Publishing type：Research paper (other academic)  

The authors have proposed a new method to concentrate bacteria flowing in a microchannel by using negative dielectrophoretic force generated by using a thin dielectric layer. In this study, it was demonstrated application of the bacteria concentration to improve throughput of optical detection of bacteria in microchannel.

DOI： 10.1109/ICSensT.2013.6727658

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.4028/www.scientific.net/AMR.699.915

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.4028/www.scientific.net/AMR.699.513

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.4028/www.scientific.net/AMR.699.251

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.4028/www.scientific.net/AMR.699.909

Language：English   Publishing type：Research paper (other academic)  

We have previously demonstrated a fabrication method of single-walled carbon nanotubes (SWCNTs) based gas sensor by employing dielectrophoresis. Because this method uses the SWCNTs that are synthesized in bulk, it is a cheaper and more flexible method than that of on-site synthesized. This method can quantify the amount of trapped nanotubes on a real time basis by monitoring the electrical impedance of the sensor simultaneously with its fabrication. In this study, semiconducting SWCNTs, which served as transducer in gas detection, were separated from commercially available mixture of semiconducting and metallic ones, and were further enriched by using a spin column and dextran-based gel. The separation and enrichment of the semiconducting SWCNTs were confirmed by measuring their optical and electrical properties. The CNT gas sensor fabricated using separated semiconducting SWCNTs was highly sensitive against nitrogen dioxide gas, - more sensitive by two times than that fabricated using the pristine SWCNTs mixture.

DOI： 10.1109/NMDC.2011.6155387

Language：English   Publishing type：Research paper (scientific journal)  

Application of high electric field is effective for the alignment of carbon nanotube (CNT) in a nanocomposite film. The conventionally used single pair of parallel plate electrodes is not applicable to large-sized nanocomposite fabrication due to limited output voltage of the high-voltage source. We have proposed an array of parallel wire electrodes to address this issue. The composite material was spread over a thin dielectric layer placed on the wire electrodes. The high electric field region can be extended over a wider area just by increasing the number of electrode pairs. Discrete electric field distribution bordered by the wire electrodes was avoided by linearly oscillated motion of the composite film. A CNT/epoxy resin composite film with a size of 15 cm × 15 cm was successfully fabricated.

DOI： 10.1088/0022-3727/44/44/445303

Language：English   Publishing type：Research paper (scientific journal)  

This paper describes a realizable fabrication method to manufacture chemical gas sensors by using single-walled carbon nanotubes (SWCNTs). The sensors were tested for the monitoring of SF ₆ decomposition gas produced by partial discharge (PD) in GIS tank. The results showed a superior sensitivity, favorable reliability and good reproducibility. For further clarifying the relativity between sensor response and partial discharge activity, the discharge in GIS tank was monitored simultaneously through conventional pulse current method and a SWCNTs gas sensor, and the measurement results were put together for comparative analysis in this paper. The sensor response showed a great dependence on partial discharge characteristics. The sensor response increased nearly linearly with limits when the energy of discharge was persistently accumulated. Partial discharge power had a great influence on the response rate and the time delay. With the increase of partial discharge power, the response rate augmented almost in proportion while the time delay gradually becomes shorter with limits. The results were quite favorable to assess the partial discharge intensity and duration to some extent. Compared with pulse current method, the sensor was predominant to detect partial discharge exposed to constantly high levels of noise. It was capable of detecting partial discharge which was too weak to be detected with pulse current method. However, the sensor response didn't show much dependency on the apparent discharge of partial discharge.

Language：English   Publishing type：Research paper (other academic)  

A simple and rapid bacteria detection device for on-site evaluation of oral hygiene in hospitals and clinics was demonstrated. The developed device utilizes dielectrophoretic impedance measurement (DEPIM) method. We integrated a micro electrode chip on which bacteria were captured by dielectrophoresis (DEP), an AC voltage source to induce DEP force, and an impedance measurement circuit to a portable instrument that enables rapid and automated oral bacterial inspection in hospitals and clinics. Special considerations have been made on effects of high electrical conductivity of oral samples on DEP force and DEPIM results. It was shown experimentally and theoretically that using a higher electric field frequency for the DEP bacteria trap and the impedance measurement could realize DEPIM application to bacteria inspection from oral samples with higher conductivity. Based on these investigations, we optimized the frequency condition of the DEPIM suitable for inspecting an oral sample along with the design and development of a portable DEPIM apparatus for on-site inspection of oral bacteria.

Language：English   Publishing type：Research paper (scientific journal)  

In this study, the concept design for the improvement of the bacterial detection sensitivity of the DEPIM (Dielectrophoretic Impedance Measurement) method has been proposed. The cells in the micro-chamber are repelled and concentrated by n-DEP (negative dielectrophosesis). The concentrated cells are captured by p-DEP (positive DEP) and detected by measuring the change in the electrical impedance. The numerical simulations and the preliminary test were performed to investigate the effectiveness of the n-DEP concentration. When n-DEP concentration was employed, the increase in the rate of the conductance became approximately two times higher than that obtained without n-DEP.

DOI： 10.1088/1742-6596/307/1/012031

Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： 10.1109/TENCON.2010.5686640

Language：English   Publishing type：Research paper (scientific journal)  

The Dielectrophoresis (DEP) is electrokinetic motion of dielectrically polarized materials in non-uniform electric fields. DEP has been successfully applied to manipulation of nanomaterials including carbon nanotubes, metallic nanoparticles and semiconducting nanowires. Under positive DEP force, which attracts nanomaterials toward the higher field region, nanomaterials are trapped in the electrode gap and automatically establish good electrical connections between them and the external measuring circuit. This feature allows us a fast, simple and low-cost fabrication of nanomaterial-based sensors based on a bottom-up basis. This paper firstly presents a theoretical background of DEP phenomena and then reviews recent works of the present author, which were aimed to develop nanomaterial-based sensors, such as a carbon nanotube gas sensor and a ZnO nanowire photosensor, using DEP fabrication technique.

DOI： 10.1541/ieejfms.129.435

Language：English   Publishing type：Research paper (scientific journal)  

In this study, the authors propose a new bacteria detection method using a carbon nanotube (CNT) gas sensor and a microheater, which were coupled into a Bio-MEMS (microelectromechanical systems)-type device. Bacteria were heated by the microheater in air so that ammonia (NH₃) gas can be generated by the oxidation reaction of organic components of bacteria. Thus generated NH ₃ gas was detected by using the CNT gas sensor, which was fabricated by dielectrophoresis (DEP) and combined with the microheater to form a small chamber. Cyclic pulsed heating operation was employed so that the CNT response to elevated temperature did not mask NH₃ response. It was demonstrated that the proposed device could detect and quantify 10⁷ bacteria cells (Escherichia coli). Possible application of DEP to trap and enrich target bacteria on the microheater was also discussed.

DOI： 10.1049/iet-nbt.2008.0011

Language：English   Publishing type：Research paper (scientific journal)  

The authors have previously proposed a novel technique for the preparation of water-soluble carbon nanotubes (CNT_s) using microplasma generated by a pulsed streamer discharge in water. This paper describes effects of pH values on water-solubility of single-walled CNT (SWCNT) treated by the microplasma. The SWCNT treated under basic conditions showed two times higher solubility compared to that treated under neutral condition, whereas the SWCNT solubility considerably decreased under acidic conditions. Based on optical emission measurements of microplasma showed that radical formation was not pH sensitive. Fourier transform infrared (FTIR) spectroscopy and Xray photoelectron spectroscopy (XPS) analysis showed that the microplasma treated SWCNT was functionalized with -COO- groups with little pH dependence. In contrary, clear pH dependence was observed for zeta potential of the microplasma-treated SWCNT. The lowest zeta potential was-46 mV, which was obtained with basic solution adjusted by NH₃ (pH≈9). The SWCNT treated under basic conditions was more negatively charged due to suppressed protonation of -COO- groups. As a result, the electrostatic repulsion force between SWCNTs could overcome van der Waals force improving their solubility and dispersibility in water.

DOI： 10.1143/JJAP.48.065004

Language：English   Publishing type：Research paper (scientific journal)  

In this study, influences of gas bubbling on water-solubility of single-walled carbon nanotubes (SWCNTs) based on microplasma treatment in water were investigated. Oxygen (O₂), argon (Ar), nitrogen (N₂) and carbon dioxide (CO₂) were used as the bubbling gases. Bubbling of O₂, Ar and N₂ enhanced the O* and H* radicals produced by the microplasma in water and the solubility of SWCNT was increased more than two times compared to that without gas bubbling. On the other hand, the solubility was very poor in case of CO₂. The negative effect of CO₂ on the solubility might be due to the decrease of radicals, which were scavenged by carbonate ion generated by dissociation of CO₂ in water, and caused by the reaction of radicals with CO₂ or CO rather than those with SWCNT.

DOI： 10.1016/j.surfcoat.2008.06.068

Language：English   Publishing type：Research paper (scientific journal)  

Composite insulation system of liquid nitrogen and solid insulator, which are widely employed in high 4TC superconducting equipment, can be deteriorated by partial discharge (PD) generated in highly stressed region. By subcooling the liquid nitrogen below the boiling point of 77 K at atmospheric pressure, the superconducting power device can obtain higher performance because the critical current density of the superconductor can be increased. The subcooled liquid nitrogen may also have better properties as electrical insulation medium than pool boiling one because gaseous bubble generation is suppressed. In this study, effects of subcooling temperature on PD characteristics were investigated at atmospheric pressure. Behavior of PD induced bubbles was optically investigated using a high speed digital imaging system as well as a laser light scattering method. These optical observations were synchronized with PD signal detection in order to clarify relationship between the PD intensity and bubble behavior. It was found that PD induced bubbles were strongly influenced by the PD energy as well as temperature of the subcooled liquid nitrogen.

DOI： 10.1109/TDEI.2008.4543097

Language：English   Publishing type：Research paper (scientific journal)  

Other Link： http://dx.doi.org/10.1007/s00340-007-2891-4

Language：English   Publishing type：Research paper (scientific journal)  

The authors have previously demonstrated the manipulation of bacteria and carbon nanotubes (CNTs) using dielectrophoresis (DEP) and its application for various types of biological and chemical sensors. This paper demonstrates simultaneous DEP handling of bacteria and CNTs, which are mixed and suspended in water. The CNTs were solubilized in water using microplasma-based treatment. When a microelectrode was energized with an ac voltage in the suspension of Escherichia coli (E. coli) cells and multi-walled CNTs (MWCNTs), both of them were simultaneously trapped in the microelectrode gap. Scanning electron microscopy (SEM) images revealed that E. coli cells were trapped on the surface or the tip of MWCNTs, where the electric field strength was intensified due to high aspect ratio of MWCNTs. As a result, bio/nano interfaces between bacteria and MWCNTs were automatically formed in a self-assembly manner. A potential application of the DEP-fabricated bio/nano interfaces is a drug delivery system (DDS), which is realized by transporting drug molecules from CNTs to cells across the cell membrane, which can be electroporated by the local high electric field formed on the CNT surface.

DOI： 10.1007/s10404-008-0276-6

Language：English   Publishing type：Research paper (scientific journal)  

Ordered ZnO nanowire arrays have been fabricated in N₂ background gas by catalyst-free nanoparticle-assisted pulsed-laser deposition. A single ZnO nanowire was collected in an electrode gap by dielectrophoresis. Under the optical pumping above an exciting laser (λ=∈355 nm) threshold of ∼ 334 kW/cm², ultraviolet lasing action in a single ZnO nanowire was observed at room temperature, indicating that the as-synthesized nanowires in pure N₂ background gas are of high quality. The crystalline facets of both ends of the nanowire acted to form an optical cavity. Therefore, the mode spacings corresponding to cavity lengths of the respective nanowires were observed in photoluminescence spectra.

DOI： 10.1007/s00340-007-2891-4

Language：English   Publishing type：Research paper (scientific journal)  

In this study, magnetic iron oxide nanoparticles were produced by thermal treatment of Fe(OH)₃ colloidal solution after graphite arc discharge in the solution. The X-ray diffraction (XRD) pattern of the heat-treated powders showed that magnetic iron oxide nanoparticles (γ-Fe₂O ₃ or Fe₃O₄) were produced by the phase transformation from α-Fe₂O₂ at the thermal treatment temperature over 500 °C. The XRD pattern also indicated that the graphite powders produced by the arc discharge were contained in the Fe(OH)₃ colloidal solution, suggesting that the graphite powders contributed to the reduction process of a-Fe2O₃.

DOI： 10.1002/ecj.10024

Language：English   Publishing type：Research paper (other academic)  

Palladium (Pd) has been widely employed for conventional hydrogen sensors due to the catalytic nature. Pd has been incorporated also with carbon nanotube (CNT) gas sensors for hydrogen sensing. In this study, a liquid-phase electrochemical reaction was proposed to realize a simple and inexpensive fabrication method of a Pd-functionalized CNT hydrogen sensor. The single-walled CNTs were trapped onto a microelectrode under positive dielectrophoresis. The CNT-retaining microelectrode was immersed in a palladium acetate solution together with a graphite rod. DC voltage was applied between the microelectrode (cathode) and the graphite rod (anode) so that palladium acetate could be reduced and catalytic Pd could be electrodeposited on the CNT surface. The CNT sensor could reversibly respond to hydrogen gas in the air in the range of 0.01 % -1 % concentration at room temperature. It was also demonstrated that the Pdfunctionalized CNT gas sensor could be fabricated just by dipping the CNT-retaining microelectrode into an aqueous Pd salt solution without applying DC voltage (electroless redox reaction).

DOI： 10.1109/ICSENS.2007.4388458

Language：English   Publishing type：Research paper (scientific journal)  

The authors have developed a novel fabrication method of a carbon nanotube (CNT) gas sensor using positive dielectrophoresis (DEP). One advantage of the DEP technique is that one can readily build up interfaces between electrodes and CNT, or between CNT and other nanomaterials. In this paper, the DEP technique was employed to fabricate interfaces between CNT and catalytic palladium (Pd) to realize a CNT-based hydrogen (H₂) gas sensor. Two types of CNT/Pd interfaces were proposed and tested. For one type, CNTs were trapped onto a microelectrode made of Pd so that the CNT/Pd interfaces were formed at both ends of CNTs lying over the Pd electrode surface. The other type of gas sensor was fabricated by simultaneously trapping CNTs and Pd nanoparticles under action of the positive DEP. It was found that both types of the CNT/Pd gas sensors could respond to hydrogen, while the CNT sensor without the Pd functionalization could not. For the hydrogen gas diluted with dry air, the electrical resistance of the CNT/Pd sensors increased at the moment of hydrogen exposure, and then turned to decrease in the later stage. The resistance increase just after the H₂ exposure was probably due to reduction of CNTs by H atoms, which were produced by dissociative adsorption of H₂ molecules on the catalytic Pd surface. In the later stage, the dissociated H atoms might react with dissociated oxygen atoms to create H₂O molecules accompanying heat generation.

DOI： 10.1016/j.snb.2007.05.002

Language：English   Publishing type：Research paper (scientific journal)  

The authors have previously proposed a novel technique for the preparation of water-soluble carbon nanotubes (CNTs) using microplasma generated by a pulsed streamer discharge in water. This paper describes an improvement in the method of the microplasma-based CNT solubilization process by the use of gas bubbling in water. Oxygen, argon and nitrogen were used as bubbling gas in order to clarify the effects of the gas species on the single-walled CNT (SWCNT) solubilization efficiency. Ultraviolet-visible absorption spectra of the SWCNT suspensions revealed that the SWCNT solubility was increased by more than two times by using gas bubbling together with microplasma treatment. No significant difference was observed among the three gas species tested. Fourier transform infrared (FTIR)spectroscopy and x-ray photoelectron spectroscopy (XPS) analysis showed that the number of -OH groups, introduced on the SWCNT surface by the microplasma treatment, was increased by gas bubbling. Optical emission measurements also showed that the number of highly oxidative oxygen and hydrogen radicals, which were generated by the microplasma, was also increased by gas bubbling. These results indicate that gas bubbling has positive effects on microplasma-based SWCNT solubilization as a result of enhanced radical formation and functionalization of the SWCNT surface.

DOI： 10.1088/0957-4484/18/33/335602

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

We describe the synthesis of nano-structured materials of ZnO and Pd by laser ablation and their applications to sensors. The synthesis of ZnO nano-wires was performed by nano-particle assisted deposition (NPAD) where nano-crystals were grown with nano-particles generated by laser-ablating a ZnO sintered target in an Ar background gas. The synthesized ZnO nano-wires were characterized with a scanning electron microscopy and the photoluminescent characteristics were examined under an excitation with the third harmonics of a Nd:YAG laser. The nano-wires with a diameter in the range from 50 to 150 nm and a length of up to 5 μm were taken out of the substrate by laser blow-off technique and/or sonication. It was confirmed that the nano-wires showed the stimulated emission under optical pumping, indicating a high quality of the crystalinity. Pd nano-particles were generated by laser-ablating a Pd plate in pure water. The transmission electron microscope observation revealed that Pd nano-particles with a diameter in the range from 3 nm to several tens of nanometers were produced. Using these nano-structured materials, we successfully fabricated sensors by the dielectrophoresis techniques. In the case of the ultraviolet photosensor, a detection sensitivity of 10 nW/cm ² was achieved and in the case of hydrogen sensing, the response time of less than 10 s has been demonstrated with Pd nano-particles.

DOI： 10.1016/j.apsusc.2007.02.152

Language：English   Publishing type：Research paper (scientific journal)  

We fabricated a gas sensor using single-walled carbon nanohorns (SWNHs) produced by the gas-injected arc-in-water method. This gas sensor consisted of agglomerated SWNHs as a coating film between Al electrodes on a glass substrate and the shift of the electric resistance of this coating film caused by gas adsorption was monitored. Its sensing property was examined for the detection of NH3 and O3 at room temperature. It was confirmed that the electrical resistance of the SWNHs film increases with adsorption of NH3, whereas the adsorption of O3 induced the decrease of the resistance. A model to correlate the gas concentration and the sensing property was proposed focusing on the detection of NH3 based on mono-layer adsorption and a second-order interaction of adsorbed gas molecules for charge transfer.

DOI： 10.1163/156855207781389447

Language：English   Publishing type：Research paper (scientific journal)  

The authors have previously demonstrated that a carbon nanotube (CNT) gas sensor can detect SF₆ decomposition byproducts generated by partial discharges (PDs). There are several factors to be considered, however, before applying the CNT gas sensor to practical diagnosis of a gas-insulated switchgear (GIS). In this paper, three major factors, namely, the effects of operating temperature and installation location of the CNT gas sensor and SF ₆/N₂ gas mixture, were investigated. The stability of sensor conductance and the sensor response to PD were improved by controlling the sensor operating temperature. The maximum sensor response was obtained at about 70 °C. The CNT gas sensor, which was installed in an external pipe connected to the GIS tank, could detect PD generated in the tank, although the sensor response became lower and slower as the sensor was located further away from the PD source. It was found that the sensor response to PD showed a clear dependence on the mixing ratio of the SFS/N2 gas mixture. The maximum sensor response was achieved for SF₆/N₂ (20%/80%) gas mixture. This result was discussed based on Fourier transformation infrared (FTIR) analysis of PD decomposition byproducts adsorbed on the CNT surface.

DOI： 10.1109/TDEI.2007.369536

Language：English   Publishing type：Research paper (other academic)  

ZnO nano-nails which consist of the nanowire at the top of nanorods have been synthesized by the nanoparticle-assisted deposition technique. When the nanowire was excited by the third harmonics of a Q-switched Nd:YAG laser, the ultraviolet stimulated emission was clearly observed from single nanowire, indicating the high crystalinity of the nanowire. The highly sensitive ultraviolet photo-detectors were successfully fabricated by trapping these nanowires between electrodes using the dielectrophoresis technique.

DOI： 10.1117/12.698854

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

This paper deals with ac particle-triggered corona discharge as a follow-up to our previous research with dc voltage to clarify the particle-triggered corona discharge process in SF₆ gas. Corona current pulses, charges associated with a corona current pulse, and corona light pulses were observed with an aluminum ellipsoidal particle suspended in a parallel plane electrode system under a SF₆ gas pressure range of 30 kPa ≤ P ≤ 50 kPa by changing the particle position. Corona mode, phase (Φ)-charge (q) characteristics as well as corona discharge processes were discussed and the following results were obtained. Ac corona mode depended on the instantaneous applied voltage, voltage gradient as well as the particle position and then, the Φ-q characteristics were also affected by those parameters. Charges flow into the floating particle due to coronas on the both tips of particle and excite field fluctuations around the opposite side of particle in addition to the applied ac field. The field fluctuation in SF₆ gas by the corona charges was about 4% of the applied field and much lower than that in air gap which was about 70%. That is, the corona development was suppressed effectively by high electron affinity of SF₆ gas even in the case of floating particle. The less effective interference between coronas on the both side of particle in SF₆ gas results in an obscure local minimum in the breakdown voltage characteristics as the particle is in the vicinity of electrode as contrasted with a drastic fall in the breakdown voltage by the particle in air.

DOI： 10.1109/TDEI.2007.302876

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

The final objective of this research project is clarification of the particle-triggered corona mechanism in SF₆ gas-insulated electrical equipment as well as development of high precision diagnostic method of foreign metallic particle in GIS insulated by SF₆ gas using the electrical signal due to corona discharge. The following research steps are conducting to achieve our goal: 1) clarification of particle-triggered corona phenomena in air which is well-understood corona mechanism, 2) clarification of particle-triggered corona phenomena under dc and ac applied voltage in SF ₆ gas at low pressure in which a stable corona occurred, and 3) clarification of the pressure effect on the particle-triggered corona mechanism. This study is the second step of our research series research, which focuses on characteristics and the mechanism of particle-triggered corona discharge in SF₆ gas on the basis of measurements of corona current pulses at a pressure range of 30 kPa to 50 kPa under dc applied voltage. The identification of positive and negative corona pulses in SF₆ gas from the waveform, amplitude and repetition rate of corona current pulses is difficult; thus, current and light pulses of coronas from the both tips of particle were measured simultaneously to discriminate the polarity of corona current pulses. Experiments showed that near the corona onset voltage, positive corona accompanied pulse current but negative corona tended to be glow-like corona. As the applied voltage was increased, negative corona changed into streamer type accompanying strong current pulse. Positive corona pulses maintained a small amplitude with an instantaneously high repetition rate, even if the field enhancement on the positive tip of particle occurred due to the positive-ion inflow to the particle produced by negative corona. On the basis of current pulse measurements, the mechanism of particle-triggered corona was discussed. Moreover, corona activity and breakdown voltage were investigated by changing the particle position. This study confirmed that the active corona development and fall in breakdown voltage were due to the effect of intermittent short-circuit arc in the minor gap between particle and electrode when the particle was in the vicinity of the electrode.

DOI： 10.1109/TDEI.2006.258192

Language：English   Publishing type：Research paper (scientific journal)  

Chemical byproducts analysis has been recognized as a powerful diagnosis method for SF₆ gas-insulated switchgear (GIS). The authors have previously demonstrated that a carbon nanotube (CNT) gas sensor could detect partial discharge (PD) generated in SF₆ gas. However, PD-generated decomposition gas species, which were responsible for the CNT gas sensor response, have not been identified yet. In this paper, two kinds of experiments were conducted in order to identify the responsible decomposition gas species. At first, the decomposition gas molecules adsorbed on CNTs were analyzed by Fourier transformation infrared (FTIR) spectroscopy. FTIR absorbance was observed around 735 cm^-1 after CNTs were exposed to PD generated in SF₆. In the second experiment, the CNT gas sensor responses to typical SF₆ decomposition products (HF and SF₄) were examined. The CNT gas sensor responded to these gases in the same way as to PD generated in SF₆. SF₄ response was larger than HF response. Based on these results, SF₄ and SOF₂ emerged as candidates for the responsible decomposition gases. Electrochemical interactions between adsorbed gas molecules and CNT were discussed based on theoretical predictions of molecular orbital calculations. The calculation results suggested that both of SOF₂ and SF₄ could increase the CNT gas sensor conductance.

DOI： 10.1109/TDEI.2006.258191

Language：English   Publishing type：Research paper (scientific journal)  

This paper describes a selective detection method for specific bacteria by using a dielectrophoretic impedance measurement method in conjunction with an antigen-antibody reaction. The authors have previously demonstrated a bacteria detection technique called DEPIM (dielectrophoretic impedance measurement) and EPA-DEPIM (electropermeabilization-assisted DEPIM) using a positive dielectrophoretic force to capture bacteria in suspension onto an interdigitated electrode chip. It has also been demonstrated that a selective DEPIM detection of specific bacteria could be realized by taking advantage of agglutination phenomena, which were caused by an antigen-antibody reaction. In the present study, other combinations of the antigen-antibody reaction with DEPIM or EPA-DEPIM were demonstrated. Antibody molecules were immobilized on the electrode chip before the preliminary bacteria trapping by positive dielectrophoresis (DEP). The bacteria were attracted to the electrode gap under the action of the positive DEP force and finally brought into contact with the glass surface to be bound with the immobilized antibody. By appropriately adjusting the balance between the DEP force and the drag force caused by liquid flow, the target bacteria (Escherichia coli) could be selectively retained on the chip surface avoiding undesired non-specific binding. The retained bacteria were electrically detected by EPA-DEPIM. It was also confirmed that the proposed method realized selective detection of the target bacteria from a mixed suspension with nontarget bacteria.

DOI： 10.1016/j.snb.2005.12.027

Language：English   Publishing type：Research paper (scientific journal)  

A novel technique for the preparation of water-soluble carbon nanotubes was demonstrated using a pulsed streamer discharge generated in water. The technique involved chemical reactions between radicals generated by the pulsed streamer discharge and carbon nanotubes. The pulsed streamer-treated carbon nanotubes were homogeneously dispersed and well solubilized in water for a month or longer. The mechanism of solubilization of carbon nanotubes by the pulsed streamer discharge is discussed based on FTIR spectroscopy and optical emission spectra measurements. FTIR spectroscopy revealed that -OH groups, which are known to impart a hydrophilic nature to carbon material, were introduced on the carbon nanotube surface. Optical emission spectra from the pulsed streamer plasma showed that highly oxidative O^* and H^* radicals were generated in water. These results suggest that the functionalization of the carbon nanotube surface by -OH group can be attributed to the O^* and H^* radicals. An advantage of the proposed method is that there is no need for any chemical agents or additives for solubilization. Chemical agents for solubilization are generated from the water itself by the electrochemical reactions induced by the pulsed streamer discharge.

DOI： 10.1088/0957-4484/17/14/013

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

This paper deals with the breakdown voltage characteristics of saturated liquid helium in the presence of a needle-shaped or spherical metallic particle to obtain insulation design data for pool-cooled, low-temperature superconducting coils and to find the predominant factor affecting the breakdown voltage of liquid helium at a given state. The results show the following. (1) The generation of bubbles at the instant of collision of a particle with an electrode is caused mainly by the kinetic energy released from the moving particle to the liquid helium, while the electrostatic energy accompanying the microdischarge between the particle and the electrode has a lesser effect on it. (2) The lowest breakdown voltage at different particle conditions appears in the case of a free needle particle. The low breakdown voltage is caused by the bubble triggered by the particle collision, the high electric field at the tip of the needle particle, and the rich initial electrons supplied by the microdischarge.

DOI： 10.1109/TDEI.2006.1657957

Language：English   Publishing type：Research paper (scientific journal)  

This paper describes an electrokinetic fabrication method for a gas sensor composed of single-wall carbon nanohorns (SWCNHs) using dielectrophoresis (DEP). The authors have previously demonstrated that DEP manipulation of carbon nanotubes (CNTs) can be applied to the fabrication of a CNT gas sensor. In the present study, we further explored the possibility of electrokinetic manipulation of SWCNHs. The latter have different structures and properties compared to CNTs. The SWCNHs were synthesized using the 'arc in water with gas injection' method. The SWCNH aggregates were dispersed in ethanol and trapped in an interdigitated microelectrode gap under the action of positive DEP. After the DEP process, the ethanol was evaporated and the microelectrode retaining the SWCNHs was exposed to nitrogen dioxide (NO₂) or ammonia (NH₃) gas while the electrode impedance was monitored. It was found that conductance of the DEP-fabricated SWCNH sensor increased or decreased upon exposure to ppm-levels of NO₂ or NH₃, respectively. These results were similar to those previously obtained for CNT gas sensors and suggest that the SWCNH aggregate behaves as a p-type semiconductor. The comparison reveals that intrinsic NO₂ sensitivity of the SWCNHs is lower than that of single-wall CNTs (SWCNTs) but comparable with the intrinsic sensitivity of multiple-wall CNTs (MWCNTs).

DOI： 10.1016/j.elstat.2005.11.001

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

In this study, magnetic iron oxide nanoparticles were produced by thermal treatment of Fe(OH) ₃ colloidal solution after graphite arc discharge in the solution. X-ray diffraction (XRD) pattern of the heat-treated powders showed that magnetic iron oxide nanoparticles (γ-Fe ₂O ₃ or Fe ₃O ₄) were produced by the phase transformation from α-Fe ₂O ₃ at the thermal treatment temperature over 500°C. The XRD pattern also indicated that the graphite powders produced by the arc discharge were contained in the Fe(OH) ₃ colloidal solution, suggesting that the graphite powders contributed to the reduction process of α-Fe ₂O ₃.

DOI： 10.1541/ieejfms.126.349

Language：English   Publishing type：Research paper (scientific journal)  

An intermittent arc discharge in water, which has several millisecond pulse width, was used to produce carbon nanoparticles. High-resolution TEM observation revealed that the aggregated nanoonions were obtained as the floating powders on the water surface and the rest products which contains multiwalled carbon nanotubes were found at the base of the water. Production efficiency of carbon soot which contains the carbon nanoonions and multiwalled nanotubes to consumption mass of carbon electrodes was also investigated. Production efficiency of carbon soot was increased about 3 times in comparison with a direct current (DC) arc discharge method in water.

DOI： 10.1016/j.tsf.2005.08.024

Language：English   Publishing type：Research paper (scientific journal)  

Wide-gap semiconductors with nanostructures such as nanoparticles, nanorods, nanowires are promising as a new type of UV photosensor. Recently, ZnO (zinc oxide) nanowires have been extensively investigated for electronic and optoelectronic device applications. ZnO nanowires are expected to have good UV response due to their large surface area to volume ratio, and they might enhance the performance of UV photosensors. In this paper, a new fabrication method of a UV photosensor based on ZnO nanowires using dielectrophoresis is demonstrated. Dielectrophoresis (DEP) is the electrokinetic motion of dielectrically polarized materials in non-uniform electric fields. ZnO nanowires, which were synthesized by nanoparticle-assisted pulsed-laser deposition (NAPLD) and suspended in ethanol, were trapped in the microelectrode gap where the electric field became higher. The trapped ZnO nanowires were aligned along the electric field line and bridged the electrode gap. Under UV irradiation, the conductance of the DEP-trapped ZnO nanowires exponentially increased with a time constant of a few minutes. The slow UV response of ZnO nanowires was similar to that observed with ZnO thin films and might be attributed to adsorption and photodesorption of ambient gas molecules such as O₂ or H ₂O. At higher UV intensity, the conductance response became larger. The DEP-fabricated ZnO nanowire UV photosensor could detect UV light down to 10nWcm^-2 intensity, indicating a higher UV sensitivity than ZnO thin films or ZnO nanowires assembled by other methods.

DOI： 10.1088/0957-4484/17/10/021

Language：English   Publishing type：Research paper (scientific journal)  

The authors proposed a new type of gas sensor for high sensitive detection of decomposition products generated by partial discharge (PD) in SF ₆ gas. The sensor employed carbon nanotubes (CNTs) as gas sensing transducer and was fabricated by electrokinetic manipulation of CNTs using dielectrophoresis. Due to complicated gas decomposition process of SF ₆ gas, calibration of the CNT gas sensor is an essential and challenging subject in order to realize reliable and stable detection of PD under practical conditions. In this paper, two methods for the CNT gas sensor calibration were proposed and tested. The first method was based on initial conductance dependence of the CNT gas sensor response. The CNT gas sensor response to PD increased almost linearly with the amount of CNT trapped onto the sensor electrode, which could be quantified by the initial conductance of the sensor. However, the calibration accuracy of this method was about 50 % and was not high enough for practical use. The second method employed NO ₂ (nitrogen dioxide) as calibration gas because of the similarity in the CNT sensor response to PD decomposition products and NO ₂. It was found that the accuracy of the NO ₂ calibration was about 10 % and far better than the first method. Finally, effectiveness of the NO ₂ calibration was demonstrated by a PD monitoring test in which two CNT sensors were simultaneously exposed to SF ₆ decomposition products with identical concentration.

DOI： 10.1109/TDEI.2006.1624280

Language：English   Publishing type：Research paper (scientific journal)  

Single-walled carbon nanotube (CNT) gas sensors were fabricated by dielectrophoresis onto microelectrodes made of Cr, Pd or Al. The Al/CNT sensor response to NO ₂ (nitrogen dioxide) gas was characterized by fast and large resistance increase at the moment of NO ₂ exposure, whereas the resistance of the other metal/CNT sensors monotonously decreased. It was suggested that the adsorbed NO ₂ molecules might alter the Schottky barrier at the Al/CNT interface as well as the positive hole density in the p-type semiconducting CNT. The Al/CNT sensor response could be interpreted as a superposition of the Schottky contact resistance and the CNT resistance, which were differently influenced by the NO ₂ adsorption and contributed to the overall sensor response. The Schottky response of the Al/CNT sensor was approximately one order of magnitude faster than the CNT response obtained using the other metal electrodes.

DOI： 10.1016/j.snb.2005.08.043

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.cryogenics.2005.08.004

DOI： 10.1109/TDEI.2005.1522199

Language：English   Publishing type：Research paper (scientific journal)  

For electrical insulation diagnosis of gas-insulated switchgear (GIS), detection of partial discharge (PD) generated in sulfur hexafluoride (SF ₆) gas is important. This paper describes a new detection method of PD generated in SF₆ gas using a gas sensor composed of multiwall carbon nanotubes (MWCNTs). The gas sensor was fabricated by electrokinetic manipulation of semiconducting MWCNTs using positive dielectrophoresis. The MWCNT gas sensor and a point-to-plane electrode system were placed in a steel tank filled with SF₆ gas at atmospheric pressure. AC high voltage was applied to the point electrode in order to generate PD while the electrical impedance of the MWCNT sensor was monitored. When the PD was generated, the electrical conductance of the MWCNT sensor gradually increased. The sensor response was reversible and was influenced by the PD intensity as well as by the relative position of the sensor to the point electrode. It was suggested that the sensor conductance increase was caused by an electronic interaction between MWCNTs and non-identified oxidative decomposition products. The faint PD, which could not be sensed by gas detecting tubes, was successfully detected by the MWCNT sensor on a real time basis.

DOI： 10.1016/S0925-4005(04)00415-0

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

This paper deals with consideration of particle motion control and its trapping in the deactivation of foreign contaminating moving particle in simulated GIS. The particle motion behavior in non-uniform field gap without/with different shaped spacers was investigated experimentally under dc and 60 Hz ac voltages. The obtained results were confirmed experimentally as well as by calculating the electrostatic force acting on the particle in the non-uniform field gap and are reported elsewhere. Whereas, in this paper, the observed particle motion behavior around simple shaped spacer is simulated by solving the particle motion equations analytically in the presence of electrical gradient and image forces. The simulation agreed fairly well with the experimental results. Furthermore, in the non-uniform electric field, the effect of dielectric coating on the grounded electrode on the particle motion and particle deactivation is also briefly discussed. On the basis of the obtained results of particle motion behavior without/with different shaped spacers and the effect of dielectric coating on the ground electrode, different methods of particle deactivation are suggested as well as confirmed experimentally.

DOI： 10.1109/TDEI.2005.1394025

Language：English   Publishing type：Research paper (other academic)  

This paper deals with breakdown voltage characteristics of saturated liquid helium, in the presence of a metallic particle in shape of needle or sphere to obtain insulation design data for the pool-cooled low temperature superconducting coil and to find the factors dominating the breakdown voltage. The results show that the lowest breakdown voltage appears at a free needle particle which produces bubble-generation, rich initial electrons and high stress electric field.

Language：English   Publishing type：Research paper (other academic)  

The authors had proposed a new detection method for partial discharge (PD) occurring in sulfur hexafluoride (SF₆) gas using a carbon nanotube (CNT) gas sensor. In the previous study, we had investigated the dependency of gas sensor response on applied voltage and gas sensor position. In this paper, a series of experiments was performed to observe dynamic behavior of decomposition gas using the CNT gas sensor. The gas sensor responses to PD under several SF₆ gas pressures were measured. It was found that the sensor response normalized by PD power increased almost linearly with the gas pressure. The result is useful to understand the mechanism how the gas pressure influences the generation and diffusion of decomposition gas. Effects of absorbent placed inside the discharge chamber were also investigated. Finally, the gas sensor responses were measured with a time interval after PD was extinguished to check if an offline diagnosis was possible. Although the sensor response decreased with elapsed time after PD was extinguished, it was still possible to detect the residual decomposition gas using the CNT gas sensor.

DOI： 10.1109/CEIDP.2005.1560744

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

This paper describes a generation method of ozone using a silent discharge ozonizer, which is cooled down to cryogenic temperature by liquid nitrogen. The ozonizer was consisted of two metal electrodes and one dielectric barrier covering the lower electrode surface. In order to cool down the discharge space between the dielectric barrier and the upper electrode, the ozonizer was placed in an inner vessel of a metal cryostat whose outer vessel was filled with liquid nitrogen. It was found that the ozone concentration and ozone yield were increased with decreasing temperature. Especially, the cooling effects were remarkable in high specific energy region. The maximum ozone concentration of 146 g/m³ and ozone yield of 212.5 g/kWh were achieved at 170 K. Temperature distribution within the ozonizer was theoretically analyzed inorder to clarify the effects of the dielectric barrier material and the electrode gap space.

DOI： 10.1541/ieejfms.124.791

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

This paper deals with the effect of the magnitude and polarity on the particle initiated breakdown characteristics around a simple shaped spacer in quasi-uniform field gap under lightning impulse voltage superimposed on pre-stressed DC voltage. The results are discussed on the dust figure technique and also on the breakdown voltage / delay time characteristics, while keeping in view the magnitude of the pre-stressed DC applied voltage. Consequently, it was found that the surface charges accumulated on the spacer in the vicinity of the particle tip under the pre-stressed DC voltage play an important role in the particle initiated breakdown phenomenon.

DOI： 10.1541/ieejfms.124.547

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.cryogenics.2003.12.001

Language：English   Publishing type：Research paper (other academic)  

Partial discharge (PD) characteristics within an artificial air-filled void contained in a solid insulator were experimentally investigated under 60 Hz ac voltages at liquid nitrogen temperature (77 K) and room temperature of 298 K. The results show that the first PD inception voltage at 77 K is about twice higher than that at 298 K while successive values at both temperatures are almost the same. The results also show that PD charge magnitude noticeably decreases and PD pulse number remarkably increases with the decrease in the temperature from 298 K to 77 K. The latter results are further discussed based on the observed remarkable decrease in the charged area by a single PD on an inner void surface with the decrease in the temperature.

Language：English   Publishing type：Research paper (scientific journal)  

This paper is concerned with the pre-breakdown phenomena and the breakdown voltage characteristics, in the presence of a free moving conducting spherical particle, of saturated normal liquid helium (He I) and saturated superfluid liquid helium (He II) under uniform dc field. Experiments show that the particle lifts off around the theoretical value of the lift-off electric field, and the particle oscillates between the electrodes at higher applied voltages. In that case, the microdischarge appears just before the charged particle collides with the oppositely charged electrode, and the bubble is generated at the moment of every collision of the particle with the electrode. It is confirmed theoretically as well as experimentally that the maximum bubble radius in He II is nearly proportional to the E_in^1/3, which is the released energy from the particle for the bubble generation. The insulation environment before the electrical breakdown suddenly changes at the λ-point since the bubble behavior in He I and He II greatly differs. In the characteristics of the breakdown voltage vs. liquid pressure, a clear discontinuity appears at the λ-point. Furthermore, the breakdown voltage in the parallel plane gap contaminated by a particle is lower than that in the rod-plane gap without a particle. It is found that the breakdown voltage characteristics are closely related to the trigger effect of the microdischarge and the bubble generation.

DOI： 10.1109/TDEI.2003.1255780

Language：English   Publishing type：Research paper (scientific journal)  

This paper describes a simple production method for carbon nanoparticles by pulsed arc discharge in water, which is triggered by the electrical breakdown of water between graphite electrodes. High-resolution transmission electron microscopy (HRTEM) observation revealed that the main products obtained by the proposed method were onion-like nanoparticles; while carbon nanotubes were not formed. The carbon nanoonions uniformly dispersed in water forming micron-sized aggregates. The effects of the arc discharge mode (dc or pulse) on the nanoparticle formation mechanism are discussed.

DOI： 10.1143/jjap.42.l1483

Language：English   Publishing type：Research paper (scientific journal)  

Partial discharge (PD) characteristics within an artificial air-filled void contained in a solid insulator were experimentally investigated under superimposed sinusoidal voltages of 60 and 600Hz at liquid nitrogen temperature (77K) to find the effects of the waveforms of distorted sinusoidal voltages on PD characteristics at 77K. The results show that PD inception voltage at 77K is independent of the applied voltage waveform. The results also show that, when the 600Hz component of the superimposed voltage is increased with its constant peak value, PD intensity seems to be independent of the voltage waveform, whereas PD pulse number increases. Since PD charge magnitude and pulse number at 77K were remarkably different from those at 298K, their mechanisms are discussed based on the observation results of residual charge distributions remaining on a void surface subjected to PDs under 60Hz ac voltages at both temperatures.

DOI： 10.1541/ieejpes.123.1280

Language：English   Publishing type：Research paper (scientific journal)  

Free wire particle motion behavior and particle triggered breakdown characteristics around different shaped spacers between diverging conducting plane electrodes are studied experimentally in the laboratory air under DC and 60Hz AC voltages. Wire particle motion behavior was observed experimentally and is discussed on the basis of the results of field calculations. Consequently, it was found that a particle around spacer tends to move toward or away from the spacer depending on the field strength around the spacer, under both DC or AC voltages. Moreover, it was observed that a particle can hardly adheres to the spacer in case of corona discharge at wire particle ends under DC voltage and/or an oscillating wire particle in case of AC voltage and vicevcrsa. Also, the wire particle adhesion phenomenon and the characteristics of surface flashover triggered by free conducting wire particle around a simple shaped spacer in quasi uniform field is briefly discussed.

DOI： 10.1541/ieejpes.123.1288

Language：English   Publishing type：Research paper (scientific journal)  

In this study, an argon gas-puff z-pinch plasma was produced by an inductive pulsed power system. The gap length dependence of plasma characteristics such as the pinch plasma behavior, soft x-ray emissions, and spatial distribution of hot spots, was investigated. The soft x-ray output decreased with gap length, and hot spots generated by sausage instability were distributed along the z-axis for shorter delay times of the discharge onset. However, hot spots were distributed in the center of the gap space with increased delay times, regardless of the gap length, and the number of hot spots decreased.

DOI： 10.1002/eej.10126

Language：English   Publishing type：Research paper (scientific journal)  

A new method of estimating partial discharge onset conditions in gases around a triple junction is proposed. The effectiveness of the method based on the Paschen curve and the potential distribution along the interface between a solid insulator and gas is confirmed experimentally in air at room temperature. The partial discharge onset conditions in air and SF₆ gas under different pressures at room temperature and in cryogenic nitrogen and helium gases at saturation temperature and atmospheric pressure are estimated. The partial discharge intensity is discussed on the basis of the proposed method.

DOI： 10.1002/eej.10175

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

This paper deals with free-conducting particle motion and particle-triggered breakdown in ac electric fields between non-parallel plane electrodes in atmospheric air. Spherical particle motion was investigated theoretically and experimentally under ac voltages with various frequencies, considering the effect of the electrical gradient force and the dependence of the Coulomb force magnitude on the distance between a particle and an electrode. The result shows that when the Coulomb force acting on a bouncing particle changes its direction periodically under ac voltage whose frequency is around commercial power frequency, the electrical gradient force can become effective in initiating particle motion toward decreasing electrode gap regions, causing the particle to trigger breakdown. Moreover, it was found that the direction in which a particle advances horizontally is greatly influenced by microdischarge occurrence when the particle bounces very near to the grounded electrode under high-frequency ac voltage, and that when a particle bounces on an electrode, particle-triggered breakdown voltage is decreased by the effect of microdischarge.

DOI： 10.1109/TDEI.2003.1207466

Language：English   Publishing type：Research paper (scientific journal)  

This paper deals with free conducting particle motion around different shaped spacers between diverging conducting plates under dc voltage in atmospheric air. Spherical particle motion was observed experimentally and the results were discussed on the basis of the electrostatic force acting on the particle with and without spacer. The results show that a particle around a spacer tends to move laterally towards or away from the spacer towards higher field regions, depending on the spacer configuration. It lifts at higher field positions and sometimes adheres to the spacer. The effects of spacer angle and spacer material (permittivity) on free conducting particle motion are also discussed. For comparing the results obtained with a sphere, a wire particle motion around different shaped spacers is also investigated. The obtained results suggest one of the methods to prevent/suppress the conducting particle from approaching or adhering to spacers, is to reduce the field strength in the vicinity of the triple junction of gas, solid dielectric and electrode in gas insulated system (GIS).

DOI： 10.1109/TDEI.2003.1207471

Language：English   Publishing type：Research paper (scientific journal)  

When a spherical conducting particle exists in an electrode system where electrical gradient force acts along the electrode surface, the particle tends to move towards the high field region as reported in [1]. The possibility of appearance of this phenomenon is experimentally investigated with wire particles, which can easily produce the corona discharge on their ends resulting the action of a reactive force on the particle by a corona wind. The results show that a hovering particle travels deeper into the high electric field regions regardless of the corona discharge. Moreover, it is found that wire particle with corona discharge hovers near the negative electrode under dc voltage in atmospheric air due to different characteristics of corona discharge by the polarity. But under the ac voltage, the particle hovers near the bottom electrode only and invades in the high field region deeper than under the dc voltage.

DOI： 10.1109/TDEI.2003.1207467

Language：English   Publishing type：Research paper (scientific journal)  

This paper describes a selective detection technique of viable bacteria based on dielectrophoresis and electrical impedance measurements. The authors have previously proposed a detection technique of biological particles called dielectrophoretic impedance measurement (DEPIM) method using positive dielectrophoretic force to capture biological cells in suspension onto an interdigitated microelectrode array. By combining antigen-antibody reaction with the DEPIM, selective detection of a particular species of bacteria was demonstrated. In this present work, the authors demonstrated another selective DEPIM method utilizing cell viability dependency of dielectrophoretic force without introducing the antigen-antibody reaction. It was found that dielectrophoresis of heat-treated Escherichia coli showed strong dependency on viability when applied field frequency was as high as 1 MHz. As a result, viable bacteria could be exclusively collected by positive dielectrophoresis and selectively detected by the DEPIM technique from a suspension also containing heat-treated nonviable cells. On the other hand, nonviable bacteria obtained by UV irradiation showed little dielectrophoresis dependency on viability. According to a theoretical analysis of the dielectrophoretic force, it is suggested that heat treatment alters the dielectric properties of treated cells. In particular, a decrease in cytoplasmic conductivity, which might be caused by heat-induced perforation of cell membrane, was expected to considerably affect dielectrophoresis characteristics. Proposed selective DEPIM method was also applied to evaluation of heat sterilization effect on a real time basis. It was experimentally proved that DEPIM could evaluate viable cell number variation with heat treatment time in a considerably shorter time than conventional microbiological method based on cell incubation.

DOI： 10.1016/S0304-3886(02)00124-9

Language：English   Publishing type：Research paper (scientific journal)  

This paper describes characteristics and generation mechanism of quench time lag of NbTi mechanical persist current switch (PCS). The quench time lag t_D was defined as a time delay between quench occurrence and the moment of the instantaneous value of the switch current exceeding a static quench current of the PCS. Quench time lag characteristics were investigated by using ramp current waveforms in order to clarify effects of the current sweep rate. It was found that the quench time lag decreased with increasing current sweep rate. A theoretical model was proposed in order to clarify the quench mechanism with a transient current waveform. In the model, the quench time lag was calculated by computing temperature rise of a superconducting connection bridge due to an AC loss and a flux flow loss. The simulation results of the quench time lag were in a good agreement with experimental data when cooling effects of liquid helium were taken into account.

DOI： 10.1016/S0011-2275(02)00150-9

Language：English   Publishing type：Research paper (scientific journal)  

dc pre-breakdown phenomena and breakdown characteristics in the presence of free conducting particles in liquid nitrogen are studied experimentally. The results show that a microdischarge occurs when a charged particle is approaching an oppositely charged electrode. An intense microdischarge can trigger a complete breakdown of the gap. The breakdown voltage of a uniform field gap with a free metallic particle of mm size might be reduced well below that of a point-to-plane gap without a particle in liquid nitrogen. Heavy contamination by a metallic powder produces a large reduction in the breakdown voltage, with a horizontal spacer surface. However carbon powder is less hazardous compared to metallic powder.

DOI： 10.1109/94.983880

Language：English   Publishing type：Research paper (scientific journal)  

Dielectrophoresis (DEP) is the electrokinetic motion of dielectrically polarized particles in nonuniform electric fields. DEP has found many useful technological applications including separation, levitation and characterization of dielectric particles such as biological cells. In this study, the authors propose a new type of liquid filter, which utilizes dielectrophoretic force (DEP force) to capture fine particles suspended in liquid. The DEP filter consists of an electrode system that is filled up with many dielectric particles. These particles modify the electric field distribution in the electrode system so that strong DEP force is generated on their surfaces. If the DEP force is stronger than drag force exerted by liquid flow in the filter, the suspended particles can be trapped and eliminated from the flowing liquid. The DEP filter can control trapping and releasing process just by changing electrode energizing ac signal and the resultant DEP force. It was experimentally confirmed that the DEP filter could continuously eliminate yeast cells suspended in water. The cell density decreased from 10⁶ cells/mL to 10¹ cells/mL in about an hour. The electrical conductivity of the medium was a crucial parameter that influenced the liquid temperature by Joule heating and DEP force. Further-more, the selective separation of viable and nonviable yeast cells was demonstrated by utilizing viability dependency of the DEP force.

Language：English   Publishing type：Research paper (scientific journal)  

Hot spots produced by gas-puff z-pinch plasma which are high energy density plasma regions radiate intensive soft x-rays. Gas-puff z-pinch is expected to industrial applications such as soft x-ray lithography, microscopy and laser, in these cases, the scattering of hot spots is important when the gas-puff z-pinch plasma is used as a point source of soft x-ray. Previous results in our study showed the reduction of radial displacement of hot spots in positive voltage shots by using IPP(inductive pulsed power) system. In this paper, the voltage polarities effect on the z-pinch plasma behaviour, soft x-ray emission and spatial distribution of hot spots are described.

Language：English   Publishing type：Research paper (scientific journal)  

This paper describes a new selective detection method of microorganisms such as bacteria by using dielectrophoresis together with antigen-antibody reaction. The authors had proposed the dielectrophoretic impedance measurement (DEPIM) method, which realized fast and easy detection of biological cells suspended in aqueous medium. However, highly selective detection of bacteria according to their species or strain, was rather difficult by utilizing only the dielectric property variation according to the cell type. In this paper, we propose a selective bacteria detection method using DEPIM combined with antigen-antibody reaction, which is widely used in clinical diagnosis. Two kinds of combinations of DEPIM with immunoassay are tested. In one method, agglutination of bacteria is employed to increase dielectrophoretic force. The other method utilizes antibody molecules immobilized onto the microelectrode surface. It is experimentally confirmed that both methods can leave peculiar bacteria on the electrode surface after preliminary dielectrophoretic enrichment. Furthermore, agglutinated bacteria can be electrically detected by residual increase of the electrode conductance. These findings suggest that target bacteria may be selectively detected from mixture of various bacteria by the improved DEPIM technique.

Language：English   Publishing type：Research paper (scientific journal)  

This paper describes effects of pulsed HV waveforms on biological cell inactivation. A simple RLC circuit with various inductance values was employed to investigate the waveform effects on the electrical sterilization of Escherichia Coli. It has been found that the minimum value of cell survivability can be realized by choosing an appropriate inductance value, even when the initial energy stored in a capacitor is constant. In order to realize the higher energy efficiency than a conventional RC discharging network, circuit parameters should be determined so that amplitude and width of each pulse become larger than the critical values 15 kV/cm and 50 μs, respectively.

DOI： 10.1109/94.892003

Language：English   Publishing type：Research paper (scientific journal)  

This paper deals with free-conducting particle motion and particle-triggered breakdown mechanism in AC and DC electric fields between non-parallel plane electrodes. Particle motion is divided into several modes, and particle-triggered breakdown mechanisms are discussed for each motion mode theoretically and experimentally. The obtained results suggest that several types of particle-triggered breakdown can occur in Gas Insulated System (GIS).

Language：English   Publishing type：Research paper (scientific journal)  

We describe a new technique that realizes the quantitative estimation of the biological cell concentration in an aqueous medium. The proposed dielectrophoretic impedance measurement method utilizes the positive dielectrophoretic force to capture suspended biological particles onto an interdigitated micro-electrode array in pearl-chain formation. Higher cell concentration results in faster development of the pearl chains, which are electrically connected in parallel within the electrode gap to increase the conductance and capacitance between the electrodes. By monitoring temporal variation of the electrical impedance, it is possible to quantitatively evaluate the cell population according to a theoretical model of the cell collection process. It has been demonstrated that a suspension liquid of Escherichia coli could be accurately assayed in about 10 min at 10⁵ cm^-3 concentration.

DOI： 10.1088/0022-3727/32/21/316

Language：English   Publishing type：Research paper (other academic)  

This paper deals with bubble behavior and electrical insulation at quenching state in superconducting coils. Bubble behavior in the simulated electrode system which consists of concentric coil layer-to-cylindrical electrode system with an insulation barrier and spacers immersed in liquid nitrogen was categorized into two types according to the cooling channel width (l_c). In this study, bubble behavior and partial breakdown (PBD) characteristics are investigated with l_c being narrower than the diameter of induced bubbles. Experimental results show that the bubbles are trapped in the groove between coil turns in the tested electrode system even at no applied voltage. Behavior of trapped bubbles depends on the applied voltage and shape of spacer which was installed for positioning of electrodes. The spacer having no aperture produces the most severe condition for electrical insulation: tight trap of bubble, excitation of electrohydrodynamic (EHD) instability on the surface of trapped bubble and lower inception voltage of partial breakdown in cooling channel than that with the spacer having an aperture. The pressurizing of liquid nitrogen is effective for suppression of active boiling and improvement of electrical insulation performance in the tested electrode system.

Language：English   Publishing type：Research paper (other academic)  

Degradation and Lifetime characteristics of solid insulators with an artificial air-filled void was investigated experimentally at liquid nitrogen temperature. As a result, it was found that the lifetime of a test sample decreased suddenly with increase in applied voltage. Observation of the PD characteristics showed that the decrease in lifetime at a higher applied voltage had a close relationship with the PD activity. The void surface subjected to the PDs was observed with SEM, and the degradation mechanism was discussed taking the experimental results into consideration.

Language：English   Publishing type：Research paper (other academic)  

An inductive energy storage pulsed power generator needs an opening switch to immediately limit the circuit current and to achieve a high inductive voltage. Quench phenomena of a superconducting wire can be applicable to the opening switch because it provides a fast resistance increase of the wire. In this study, quench characteristics of a superconducting wire were investigated using pulsed current waveforms with various peak values. It has been found that quench of the wire occurred when the current exceeded a critical value. The resistance rise rate of the wire increases with the current peak and wire length. An inductive pulsed power generator, which used a solenoid coil of the superconducting wire as an opening switch, was constructed to demonstrate that the switch could principally work to generate pulsed voltage and power with a fast rising rate.

Language：English   Publishing type：Research paper (scientific journal)  

The dc breakdown strength and pulsed breakdown time lag of saturated superfluid liquid helium (HeII) at 1.4 and 1.85 K are measured over a wide range of electrode sizes and applied field strengths. The results of the measurements are statistically analyzed by using Weibull distribution functions. It is found that the area effect is dominant for dc and pulsed breakdown rather than the volume effect as in the case of liquid helium of 4.2 K (HeI). The shape parameter in the Weibull distribution function for dc breakdown strengths of HeII is smaller than that of HeI. As a result, dc breakdown in superfluid helium can take place in a wider electrode area than in normal liquid helium, while no remarkable differences in breakdown areas are observed between 1.85 and 1.4 K. On the other hand, the statistical time lag in HeII becomes shorter with a decrease in temperature. According to the Fowler-Nordheim theory, it is suggested that a higher electron mobility in HeII may increase the field-emitted electron kinetic energy to trigger liquid breakdown with a higher probability.

DOI： 10.1002/(SICI)1520-6416(199908)128:3<16::AID-EEJ3>3.0.CO;2-N

Language：English   Publishing type：Research paper (scientific journal)  

The effect of a thin insulation film on breakdown phenomena in liquid nitrogen in the presence of thermally induced bubbles is investigated with a cylinder-to-plane electrode. Bubbles were produced by a heater mounted in the cylinder, which is partially covered with an insulation film. The results show that the film's effect on the breakdown voltage is insignificant until a pore is formed on the film by a previous breakdown, but it becomes substantial after pore formation. The reduction rate in breakdown voltage after the pore formation depends on the gap length and heater power. The minimum breakdown voltage drops to the magnitude of the breakdown voltage in the gaseous phase at normal boiling temperature. The breakdown mechanism is discussed on the basis of bubble observation and numerical calculation of suspended-bubble motion.

DOI： 10.1002/(SICI)1520-6416(199906)127:4<18::AID-EEJ3>3.0.CO;2-J

Language：English   Publishing type：Research paper (scientific journal)  

This paper deals with magnetic field dependence of transition current of NbTi mechanical persistent current switch (PCS), which realizes zero contact resistance and consists of two contact pieces made of NbTi bulk, in parallel or perpendicular magnetic field. The transition current is defined as the quench current with which the contact resistance abruptly generates. It is found that the transition current decreases with the field strength. Using a theoretical model to explain the formation mechanism of a superconducting connection at the contact of the mechanical PCS, it is confirmed that the transition current varies according to J_c-B characteristics of the contact piece material NbTi. These findings prove that NbTi mechanical PCS has superconductive connection between the contact pieces in the closed state and can be operated in persistent current mode as a superconducting PCS.

DOI： 10.1016/S0011-2275(98)00122-2

Language：English   Publishing type：Research paper (scientific journal)  

A part of gas substances in a void in solid insulators becomes liquid or solid at cryogenic temperature and the reduction in gas pressure in it may cause a decrease in partial discharge (PD) inception voltage. In this study, PD inception voltage and PD characteristics around the PD inception in artificial air-filled voids are investigated experimentally at room and liquid nitrogen temperatures. The results show that PD inception voltage decreases with decrease in ambient temperature due to the liquefaction of oxygen. PD characteristics just after the PD inception at liquid nitrogen temperature are affected by arrangement of test sample. Based on the simultaneous measurement of the current pulses and light images, PD characteristic dependence on the sample arrangement is discussed, taking account of the phase change of oxygen in the void.

Language：English   Publishing type：Research paper (other academic)  

Magnetohydrodynamic (MHD) instabilities, such as kink and sausage instabilities, appeared on the gas-puff z-pinch plasma during the pinching process prevent spatial stability of hot spots, which are high energy density plasma regions produced by those instabilities on the z-pinch plasma column locally. Spatial stabilization of hot spots in the axial direction is very important to have practical applications. In this study, radius and velocity of the inwardly tilted gas-puff z-pinch plasma during the compression and efficiency of energy conversion were analyzed theoretically by solving one dimensional snowplow model (1D-SPM) and circuit equations which considered inductive pulsed power generator. Those results were compared with experimental results measured with framing photograph of the pinching plasma. Efficiency of energy conversion of an input energy supplied from the inductive pulsed power generator into kinetic energy of the z-pinch plasma and final pinching velocity of the plasma exceeded that in comparison with fast bank method. These results received benefit from the fast and large pinching current transferred from the inductive pulsed power generator.

DOI： 10.1109/BEAMS.1998.816929

Language：English   Publishing type：Research paper (scientific journal)  

This paper deals with the surge propagation characteristics in a superconducting magnet in which arc discharge can be generated and extinguished to produce a high frequency oscillating voltage. Special attention is paid to the effects of conductor resistance in the high frequency range, which decreases with a lowering of temperature. Based on the results of simulation tests and theoretical considerations, it is shown that waveform shaping during surge travelling depends on an attenuation process due to electrical loss, as well as transmission and reflection phenomena at junctions with external circuits.

DOI： 10.1016/0011-2275(95)98218-P

Language：English   Publishing type：Research paper (scientific journal)  

Information about breakdown time lags under pulsed voltage stress is prerequisite to the insulation design of superconducting devices. Experiments have been carried out using a pulse generator which provides a step voltage with 200 ns rise time and a long decay time constant of more than 1 ms. The present experiments may bridge the information gap between time lag measurements in the ns range using extremely high field strengths, and existing data found with usual lightning impulse voltage. The test device is described in the paper, and some typical results are discussed in detail.

DOI： 10.1109/94.300281

Language：English   Publishing type：Research paper (scientific journal)  

Reversible electrical breakdown of bilayer lipid membranes is observed by using the voltage-clamp method with ramped voltage waveforms. It is shown experimentally that the critical transmembrane voltage at which membrane conductance drastically increases depends on the ramp rate. The pore growing process is discussed quantitatively based on a transient pore model of the breakdown phenomena. The comparison between the experimental results and theoretical prediction shows that the model can describe the time course of the pore development and resultant increase in the membrane conductance. Effects of the voltage rising rate on the electroporation and the membrane conductance increase are discussed by using the transient pore model. (from Authors)

Language：English   Publishing type：Research paper (other academic)  

Information about breakdown time lags under pulsed voltage stress i is prerequisite to the insulation design of superconducting devices. Experiments have been carried out using a pulse generator with 200ns rise time and a long delay time constant of more than 1ms. This generator provides a step voltage to the gap in the μs range. The present experiments may bridge the information gap between time lag measurements in the ns range using extremely high field strengths, and existing data found with usual lightning impulse voltage. The test device is described in the paper, and some typical results are discussed in detail.

Language：English   Publishing type：Research paper (scientific journal)  

Streamer propagation on a dielectric film under transverse magnetic field produced by a superconducting magnet is investigated by using the Lichtenberg figure technique. The positive and negative streamer channels are deflected in the same direction due to the Lorentz force, which acts on electrons in the streamer head. The deflection angle of negative streamer is larger than that of the positive one and increases with the propagation in the radial direction. On the other hand, the deflection angle of positive streamer is almost constant along the path. A streamer propagation model is proposed taking account of the electric field in the space charge region left behind the streamer channel and the field enhancement effect at the streamer tip. Through comparison of the experimental results of the streamer deflection characteristics with the theoretical prediction, the electric field in the space charge region is supposed to reach a value of 2 to 3 kV/cm. The internal field causes voltage drop across the space charge region, while the electric field is enhanced in the concentrated positive streamer head. On the other hand, the negative steamer spreads uniformly and the field concentration effect at the tip is weak.

DOI： 10.1109/14.204869

Language：English   Publishing type：Research paper (other academic)  

The authors examine dielectric breakdown phenomena under some environments peculiar to superconducting coils, such as an internal high voltage and thermal bubbles in the coolant generated by the coil quench, as well as high magnetic field and low temperature. Breakdown mechanisms of vacuum, gaseous helium, and liquefied gas are also discussed.

Language：English   Publishing type：Research paper (scientific journal)  

This paper describes a new method of apparent mobility measurement in a space charge flow field generated by corona discharge. The positive helium ion mobility at cryogenic temperatures down to 4.2 K is newly measured and the results obtained agree well with theoretical values for the atomic helium ion He⁺. The mobility of negative charge carriers is also obtained at 4.3 K. The results suggest the transition from free electron to electronic bubble in dense helium gas and support the discharge mechanism of a negative pulse corona in which an electronic bubble has the same space charge effect as a negative ion in electronegative gas.

DOI： 10.1088/0022-3727/24/8/019

Language：English   Publishing type：Research paper (scientific journal)  

D.c. breakdown characteristics of gaseous helium in uniform and non-uniform electric fields down to 4.2 K at atmospheric pressure have been investigated. Although helium is a nonelectronegative gas, a negative pulse corona is observed only near the normal boiling point due to the abrupt appearance of quasi-bubble state electrons. Positive ion space charge modifies the electric field distribution in the gap space considerably. The electric field strength on the non-corona electrode in the ion flow field is measured satisfactorily and analysed theoretically using a numerical electric field calculation technique. On the basis of experimental results, methods are proposed to give corona onset criteria and the breakdown voltage preceded by a positive glow corona.

DOI： 10.1016/0011-2275(90)90276-I

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/eej.4391100204

Language：English   Publishing type：Research paper (scientific journal)  

A new dulling system for the work rolls used to roughen the surface of cold rolled steel sheet has been developed. Such sheets are used in various products, such as outer panels of automobiles, and decorative outer plates of electric appliances. In this process, several pulsed laser beams generated by Q switched Nd:YAG lasers produce small craters with rims around them. This process includes a longitudinal scanning system within the laser processing head and a rotation system for the work roll; consequently, the surface of the dulled roll consists of innumerable small craters. The main features of the system consist of: (1) a special way of controlling RF power applied to the acousto optic modulator for the Q switching to change the peak power, pulse duration, and low level CW power to fit the dulling condition, (2) a method to combine two or more pulse beams to control the profile of dulling craters. Immediate advantages of this process are: (1) timesaving (very high repetition rate of pulses by Q switching), (2) stable operation (without a mechanical chopper which is usually used with a CO₂ laser to make pulsed beam), and (3) cost saving. This newly developed system is effectively applied to the production of cold rolled steel sheets.

DOI： 10.2351/1.4745240

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1541/ieejfms1972.109.375

Language：English   Publishing type：Research paper (scientific journal)  

Electrical properties of liquid nitrogen and its vaporized gas have become of great interest again since the discovery of high-temperature superconducting materials. This paper presents breakdown characteristics of gaseous nitrogen from room temperature down to 74 K. With uniform field gap geometry, the validity of Paschen’s law is confirmed even under the saturated gas condition at 74 K. In the case of non-uniform field gap, there is a remarkable difference in the effect of positive and negative polarities on corona stabilization. A wider gap length is necessary for stable negative corona formation than for positive corona at temperatures < 100 K. Breakdown criteria are proposed on the basis of experimental results to give a practical and reliable procedure for the design of cryogenic insulating systems which use liquid nitrogen and the vaporized gas as the coolant.

DOI： 10.1109/14.34195

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/eej.4391080302

Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1541/ieejfms1972.107.379

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1541/ieejfms1972.107.233

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