Publishing type：Research paper (scientific journal)   Publisher：AIP Advances  

Magnetic particle imaging (MPI) is an imaging diagnostic method that uses magnetic nanoparticles (MNPs). In this method, the magnetic field that excites the MNPs induces fundamental components in the detection coils owing to the direct magnetic field linkage, which adversely affects the measurements. In previous studies, this effect was mitigated by using a single-channel digital-to-analog (D/A) converter and instrumentation amplifier for compensation. Because multiple detection coils were used, variable resistors were employed to adjust the fundamental components of each channel. However, this process is time-consuming and does not allow phase adjustment, leading to reduced accuracy. This study proposes a compensation circuit using a multichannel D/A converter, that enables voltage adjustment for each channel via software. The proposed signal processing circuit significantly improved the compensation accuracy and successfully enabled position estimation within a 10 mm error when the sample was located 40 mm deep in the z-direction relative to the detection coils. These results demonstrate the feasibility of performing MPI using the proposed circuit.

DOI： 10.1063/9.0000863

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Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：AIP Advances  

Magnetic nanoparticle imaging (MPI) with a detection coil array can be used to estimate the position and quantity of magnetic nanoparticles (MNPs) via inverse problem analysis. In MPI studies, a system matrix is experimentally acquired for inverse problem analysis. However, a long acquisition time causes large temperature fluctuations in the excitation coil and electric circuit, and drift noise is present in the system matrix. In this study, we propose the generation of a system matrix by fitting a simulated system matrix using AC susceptometry to fewer experimental measurement points. Even when an inverse problem analysis was performed using a system matrix fitted with 1/100th the number of measurement data, the accuracy was higher than that obtained using an experimental matrix. This contributed to shortening the acquisition time.

DOI： 10.1063/9.0000865

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Language：English   Publisher：Frontiers in Bioengineering and Biotechnology  

DOI： 10.3389/fbioe.2024.1545581

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Publisher：International Journal on Magnetic Particle Imaging  

Multi-color Magnetic Particle Imaging (MPI) offers the ability to distinguish magnetic nanoparticles (MNPs) based on their physical states, enhancing its use in functional imaging and interventional guidance. This study explores the limits of solid-liquid phase differentiation in multi-color MPI. A customized MPI setup was used to test mixed-phase samples, highlighting the relationship between the solid-liquid phase differentiation resolution and system detection resolution. Results show that improving solid-liquid phase differentiation requires both point spread function (PSF) optimization and increased system detection resolution.

DOI： 10.18416/IJMPI.2025.2503052

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Publisher：International Journal on Magnetic Particle Imaging  

In this work, the fundamental imaging performance of the developed high temperature superconductor (HTS) MPI system with 120 mm bore diameter was investigated. The full width at half maximum, which is related to the spatial resolution of the image, was 30 mm under the gradient field of 0.34 T/m. Note that the gradient field can be easily increased by increasing the number of turns of the HTS selection field coils since the power consumption and the mass of the HTS coils are very low. The reasonable limit of detection of 48 µg(Fe) was also obtained. Since the power consumption and the mass of MPI scanner can be dramatically reduced by using HTS tape compared with those made of Cu wire, a HTS MPI scanner is one of the promising candidates for the realization of human-body-sized MPI scanner.

DOI： 10.18416/ijmpi.2025.2503018

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Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：IEEE Transactions on Magnetics  

Rectangular wave eddy current testing (RECT) identifies flaws in conductive materials by acquiring signals at multiple frequencies simultaneously. In eddy current testing, magnetoresistive (MR) sensors are used for low-frequency eddy current testing due to the high sensitivity of low-frequency inspection for detecting deep flaws. Therefore, a tunnel MR (TMR) sensor, which is less affected by temperature, was used as the detection element in this study. However, because the output signal of an MR sensor is a differential voltage signal, it is susceptible to the offset voltage of the MR element. To address this, we developed a compensation method using an indirect current feedback instrumentation amplifier with a digital-to-analog converter to eliminate the effect of offset voltage. A 12-mm-thick aluminum plate with an artificial flaw measuring 3 mm in diameter and 2, 4, and 6 mm in height was used as a specimen. The measurement results show that the offset was successfully eliminated using this compensation method, allowing smaller flaws on the backside to be identified with low-frequency excitation (10 Hz).

DOI： 10.1109/TMAG.2025.3540160

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Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

Room-temperature magnetization dynamics of multicore magnetic nanoparticles often account for intrinsic dipolar magnetism to behave as a single macrospin at low-frequency regime. Either magnetic particle imaging or hyperthermia benefits from the resulting superparamagnetism in terms of nonlinear magnetization response and relaxation losses at frequencies where the rotation of magnetic moments dominates over Brownian motion for a given sinusoidal field. For this situation, spontaneous thermal relaxation (in the absence of external fields) of each composing particle moment within the cluster is critical to define effective Néel time constant and may intersect with ferromagnetic resonance (FMR) at GHz range. Here, we performed broadband AC susceptometry on both immobilized single-core and multicore iron-oxide nanoparticles up to 26.5GHz under DC bias fields. For each solid sample, we confirmed FMR frequency, where large single-core nanoparticle systems demonstrated typical resonance blueshift as DC field increased. Interestingly, high DC field induced the secondary satellite peak in the imaginary part of AC susceptibility spectra for the case of multicore nanoparticle systems. We further highlighted that a synchronous precession of the polarized macrospins under nonuniform effective fields was responsible for splitting FMR peaks at nearby microwave frequencies. Upon curve fitting of the field-dependent FMR frequency spectra, the Landau-Lifshitz-Gilbert-Kittel model later elaborates on the complex moment dynamics of multicore nanoparticle systems in correlation with distribution functions.

Published by the American Physical Society 2024

DOI： 10.1103/PhysRevB.110.064421

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Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.110.064421/fulltext

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AIP Advances  

Magnetic particle imaging (MPI) is used to detect small magnetic fields in magnetic nanoparticles (MNPs). As a first step in MPI systems, we proposed an AC susceptibility measurement system with an optically pumped magnetometer (OPM) based on a flux transformer. First, the magnetic frequency response of the OPM was obtained for calibration. Second, the AC susceptibility of the Resovist MNPs in liquid and solid phases was obtained using the calibration data. These results are consistent with those of previous studies. Therefore, the proposed method is useful for detecting weak MNP magnetic signals in relatively strong magnetic fields and is expected to be applicable to MPI.

DOI： 10.1063/9.0000634

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Publishing type：Research paper (scientific journal)   Publisher：International Journal on Magnetic Particle Imaging  

Magnetic particle imaging (MPI), in which harmonic magnetization signals from magnetic nanoparticles are detected to image diseased regions with high sensitivity, is attracting attention. In MPI, the spatial resolution of the image is mainly determined by the DC magnetic field gradient of the scanner, and MPI scanners only for small animal size were commercialized at the present stage. In this work, we developed magnetic particle imaging modules with 120 mm bore diameter using yttrium barium copper oxide (YBCO) high temperature superconducting (HTS) tape as a selection field coil. The gradient field of 0.63 T/m is realized with the developed YBCO HTS coil cooled with liquid nitrogen (LN). The power consumption and the mass of the HTS selection field coil could be reduced compared with a Cu coil and it indicates that utilizing a HTS selection field coil is one of the best options toward the realization of human-body-sized MPI scanner.

DOI： 10.18416/IJMPI.2024.2403038

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Authorship：Lead author,　Corresponding author   Publishing type：Research paper (international conference proceedings)   Publisher：Conference Record - IEEE Instrumentation and Measurement Technology Conference  

We propose a magnetic particle imaging (MPI) scanner using an optically pumped magnetometer (OPM) and a flux transformer. OPM has high sensitivity, however, it does not operate in the excitation magnetic field to magnetize magnetic nanoparticles owing to a narrow dynamic range. Hence, a flux transformer is employed to overcome the problem. The results demonstrate that a 100 μg-Fe Resovist magnetic nanoparticle sample could be successfully detected even when the magnetic nanoparticle sample is located 25-50 mm from the pickup coil.

DOI： 10.1109/I2MTC60896.2024.10561229

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE Transactions on Magnetics  

Magnetic nanoparticle tomography (MNT) can estimate the position of magnetic nanoparticles (MNPs) via inverse problem analysis. In MNT studies, a system matrix is experimentally acquired for inverse problem analysis. However, the long acquisition time causes large temperature fluctuations in the excitation coil and electric circuit, resulting in noise in the system matrix. In this study, to remove this noise, the system matrix was calculated using ac susceptibility (ACS) data experimentally obtained via magnetic particle spectroscopy (MPS). The inverse problem was solved using the calculated system matrix. As a result, spatial fluctuation was suppressed. Moreover, the position of MNPs was accurately estimated. These results confirmed that the proposed method is useful for estimating the position of MNPs in MNT systems.

DOI： 10.1109/TMAG.2023.3293542

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Language：English   Publishing type：Research paper (bulletin of university, research institution)  

Language：English   Publishing type：Research paper (bulletin of university, research institution)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE Transactions on Magnetics  

Eddy current testing (ECT) at different frequencies can identify surface and back-surface defects caused by the skin effect. Traditional ECT uses a pickup coil to measure the magnetic-field signal caused by eddy current. However, according to Faraday's law of electromagnetic induction, the voltage signal detected at low frequencies is weak; thus, the signal is susceptible to interference from noise. By contrast, magnetoresistive (MR) sensors have high sensitivity at low frequencies. Therefore, we developed a rectangular wave ECT (RECT) system using an MR sensor. The system uses rectangular wave excitation, which can generate both low- and high-frequency signals, and the MR sensor detects the magnetic-field components. A 12 mm-thick aluminum plate with an artificial circular defect 10 mm in diameter and 4 mm in height was used as a specimen. The measurement results indicated that the developed system can accurately and quickly distinguish between surface and back-surface defects.

DOI： 10.1109/TMAG.2023.3279832

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Digests of the Intermag Conference  

Magnetic nanoparticle tomography (MNT) is an imaging technique that uses magnetic nanoparticles (MNPs). When acquiring signals from MNPs, the detection coil is affected by the magnetic field that excites the MNPs. In the conventional method, a digital-To-Analog converter and a voltage divider circuit are used to remove the fundamental signal from the excitation magnetic field. In this study, we propose a circuit that uses a fundamental wave extraction circuit to remove the fundamental wave signal and reduce the influence of direct magnetic field fluctuations. The proposed circuit reduces the influence of direct magnetic field fluctuation and successfully detects a signal of the MNP sample at a depth of 50 mm, confirming the feasibility of MNT.

DOI： 10.1109/INTERMAG50591.2023.10265073

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Language：English   Publishing type：Research paper (bulletin of university, research institution)   Publisher：Nanoscale  

Magnetic nanoparticles (MNPs) exhibit unique physicochemical characteristics owing to their comparable dimensions with important biological substances, high surface-to-volume ratios, size-dependent magnetic properties, and temperature sensitivity. In this study, we present a novel method for simultaneously estimating the magnetic moment and Brownian relaxation time distribution of MNPs based on AC magnetization harmonics. We provide a detailed description of the theoretical framework and experimental procedures. The dynamics of MNP magnetization are described using the Fokker-Planck equation, and a matrix equation is established to connect the magnetic moment, Brownian relaxation time, and magnetization harmonics. By employing a non-negative linear least squares algorithm with constraints, the magnetic moment and Brownian relaxation time distributions are inversed, which are then converted into the distributions of core sizes and hydrodynamic sizes. Finally, the estimated core size distribution reconstructed from M-H curves is consistent with the hydrodynamic size distribution measured by dynamic light scattering. This method is particularly useful for facilitating quantitative magnetic immunoassays.

DOI： 10.1039/d3nr02860g

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Language：English   Publishing type：Research paper (bulletin of university, research institution)  

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

Language：English   Publishing type：Research paper (bulletin of university, research institution)  

Language：English   Publishing type：Research paper (bulletin of university, research institution)  

Language：English   Publishing type：Research paper (bulletin of university, research institution)  

Language：English   Publishing type：Research paper (bulletin of university, research institution)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOS PRESS  

Rectangular wave eddy current testing (RECT), which is performed using a rectangular wave excitation current, can simultaneously obtain multiple datasets. However, the high-frequency harmonic signal detected by the detection coil interferes with the low-frequency signal based on Faraday's law of induction. The method proposed in this study is a type of electronic bridge, wherein a compensation method is implemented to enhance the low-frequency signal of the RECT using a digital-to-analog converter (DAC). The compensation wave generated by the DAC is determined such that the output signal becomes zero when the probe does not detect any flaws. A 12 mm thick aluminum plate with flat-bottom drill holes on the backside is used as the specimen. The holes have a diameter of 3 mm and depths of 2, 4, and 6 mm, respectively. The results demonstrate that the flaw signal cannot be detected without compensation. However, the flaw signal can be successfully detected around these holes with compensation.

DOI： 10.3233/JAE-220106

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Language：English   Publishing type：Research paper (bulletin of university, research institution)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Institute of Metals and Materials  

<p>If a rectangular wave excitation current is used for eddy current testing (ECT) instead of a sinusoidal wave, multifrequency testing can be performed directly because rectangular waves contain a fundamental wave as well as harmonic waves. Furthermore, considering the skin effect, it is possible to determine whether the specimen has a corrosion flaw on the front surface, back surface, or flaws on both surfaces. In this study, we first evaluate a method to classify these flaws on non-magnetic metal plates using rectangular wave ECT (RECT) systems with a linear amplifier. Here, we present an indicator in which each harmonic amplitude is divided by its fundamental amplitude. The results indicate that the amount of attenuation of the indicator in relation to the frequency depends on the type of flaw; therefore, we can classify the type of flaw using the indicator. Subsequently, we developed a RECT system with an inverter and conducted the same experiment. The results indicate that the tendency is the same as that when using the RECT system with a linear amplifier, which contributes to high efficiency, low cost, and weight reduction.</p><p> </p><p>This Paper was Originally Published in Japanese in J. JSNDI <b>71</b> (2022) 215–221.</p>

DOI： 10.2320/matertrans.MT-I2022002

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

This work investigated chainlike magnetic nanoparticles (CMNPs), which are a type of magnetic nanoparticle (MNP) with a dipole-dipole interaction in which individual nanoparticles are connected to form a chainlike structure. We numerically analyzed the ac magnetization characteristics of the CMNP and the single-core MNP (SMNP) using the Landau-Lifshitz-Gilbert equation. Owing to the magnetic dipole-dipole interaction, the magnetization of the CMNP is approximately 10 times that of the SMNP under a certain excitation field. MNPs with a chainlike structure are thus expected to have enhanced magnetization characteristics and better performance in medical applications. Additionally, it was found that stronger magnetization can be expected from a CMNP connecting 10 or more magnetic cores with a size of approximately 10-12 nm.

DOI： 10.1109/LMAG.2022.3231819

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Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

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

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

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

A large AC loss is generated in armature windings composed of a REBa2Cu3Oy (REBCO, RE = rare earth, Eu, Gd, etc.) wire in a fully superconducting synchronous generator. In aircraft applications, liquid nitrogen is suitable for cooling windings because of its specific heat capacity and dielectric strength. The evaporation of liquid refrigerant significantly decreases the dielectric strength, which results in an increase in the risk of accidents by discharging. For safe operation, the temperature in the generator is set below the boiling point of nitrogen (∼77 K). We calculated the temperature rise caused by the AC loss and others by applying a method that estimates the AC loss from the experimental results. This paper addresses the electromagnetic-thermal analysis in finite element method to calculate the temperature rise and proves the feasibility of a fully superconducting generator cooled by liquid nitrogen, that is, the temperature is maintained below 77 K. The output power is 10 MW. The temperature of liquid nitrogen was assumed to be 65 K, and its flow speed was set as a parameter. Additionally, we confirmed that designing a method that determines the number of parallel conductors of REBCO windings considering the temperature rise can enhance the output power density.

DOI： 10.1109/TASC.2022.3160660

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of Physics: Conference Series  

Generators used in electric aircraft require a high-power density, and AC loss is also a significant problem. We designed 10 MW REBCO superconducting synchronous generators at 64 K to achieve a power density of 20 kW/kg and low AC loss. In this study, electromagnetic analyses were performed using finite element method software. Consequently, the thickness of the back yoke is 50 mm or less so that the generator can meet the target power density. The method of decreasing the magnetic field of the armature winding and increasing that of the field winding was used to effectively reduce the AC loss. As a result, the generator achieved a high-power density of 21.0 kW/kg, reducing the AC loss from over 600 kW to 415 kW.

DOI： 10.1088/1742-6596/2323/1/012037

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Language：English   Publishing type：Research paper (bulletin of university, research institution)  

Language：English   Publishing type：Research paper (bulletin of university, research institution)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japanese Society for Non-Destructive Inspection  

<p>If a rectangular wave excitation current is used for eddy current testing (ECT) instead of a sinusoidal wave, multi-frequency testing can be directly performed, because rectangular waves contain a fundamental wave as well as harmonic waves. Furthermore, taking skin effect into account, it would be possible to identify whether the specimen has a corrosion flaw on the front surface, back surface, or flaws on both surfaces. In this study, we first investigate the method to classify these flaws on non-magnetic metal plates using rectangular wave ECT (RECT) systems with a linear amplifier. Here, we introduce an indicator that each harmonic amplitude is divided by the fundamental amplitude. The results indicate that the amount of the attenuation of the indicator, with respect to frequency, depends on the type of the flaw, and so, we can classify the type of the flaw using the indicator. Subsequently, we develop a RECT system with an inverter, and the same experiment is conducted. The results indicate that the tendency is the same as that using the RECT system with a linear amplifier, which contributes to the high efficiency, low cost, and weight reduction of the RECT.</p>

DOI： 10.11396/jjsndi.71.215

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：{AIP} Publishing  

To collect the signals of magnetic nanoparticles (MNPs) at a distance from a magnetic nanoparticle tomography, a strong ac magnetic field should be generated by applying a high current to the excitation coil. To this end, sinusoidal excitation using a linear amplifier-type ac power source has been applied to the tomography. Although this source can provide a high-quality sinusoidal voltage, its low power efficiency is not suitable for generating the required high current. To overcome this limitation, we use an H-bridge voltage source inverter to achieve high efficiency by generating a square-wave voltage. However, the third harmonic component in the square wave, undermines the acquisition of MNP signals. Thus, we suppress the third harmonic by shifting the switching phase of the inverter transistors. As a result, the third harmonic in the excitation current is reduced to less than one-tenth of that obtained after conventional suppression. We verify the distribution of MNP signals at depths up to 50 mm using the proposed excitation approach. The results demonstrate the effectiveness of the proposed approach based on square-wave inverter excitation for magnetic nanoparticle tomography.

DOI： 10.1063/9.0000266

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Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers ({IEEE})  

In magnetic nanoparticle tomography (MNT), the reduction of artifacts and the calculation time can be used to estimate the position of magnetic nanoparticles (MNPs). A non-negative least-squares (NNLS) inverse problem analysis has been used in MNT systems for this task. However, due to the presence of measurement noise and the high sensitivity of the NNLS method, it often estimates certain MNPs inaccurately, i.e., it generates artifacts. In addition, its calculation time is very high. In this study, we applied the minimum variance spatial filter (MV-SF) inverse problem analysis to MNT and estimated the position of an MNP sample containing 100 mu g of Fe. Using the MV-SF method, MNP samples placed at a depth of 25-40 mm were observed to have no artifacts. Moreover, the MV-SF method was also observed to be faster than the NNLS method by a factor of approximately 20. These results verify the feasibility of the MV-SF method for estimating the MNP positions in an MNT system.

DOI： 10.1109/TMAG.2021.3078748

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DOI： 10.1063/5.0056481

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DOI： 10.1109/TASC.2021.3055452

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Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

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DOI： 10.1109/TMAG.2020.3024864

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DOI： 10.1109/TMAG.2020.3014375

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DOI： 10.3233/JAE-209329

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

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DOI： 10.35848/1347-4065/abaf0c

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

With air traffic predicted to increase in the future, CO₂ emission must be decreased to prevent global warming. Our research group previously proposed electric propulsion systems based on superconducting technology, which is promising for reducing emissions. In this study, propulsive 2 MW fully superconducting motors were conceptually designed. At operating temperatures of 20 and 64 K, we observed the influence of the superconducting magnetic shield on the electromagnetic properties, especially the output power density, AC loss, and efficiency. The superconducting magnetic shield can reduce leakage magnetic field to the outside of the motor by inducing a current, and the shield is reproduced with a conductor of extremely high conductivity for simplicity in electromagnetic analysis. As a result, at an operating temperature of 20 K, the superconducting motors with the superconducting magnetic shields showed a high power density greater than 40 kW/kg and high efficiency of 99.7%. Even at an operating temperature of 64 K, the motors with the superconducting shield showed a power density and efficiency of 20 kW/kg and 99.4%, respectively.

DOI： 10.1109/TASC.2020.2974705

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High power density motors are required for electric propulsion aircrafts. The highest power density of the conventional motor is reported as 5.2 kW/kg up to now. Superconducting rotating machines have a potential to realize higher power density due to its high current density and a large magnetic field property. In this study, the induction motor with air-cored superconducting armature windings was conceptually designed. The output power range was 3 to 6 MW and the output power density aimed to be over 20 kW/kg. The armature voltage should be below kV-class and joule loss below 122 kW. The target efficiency was over 95%. The electromagnetic design and analysis were carried out by JMAG Designer. The number of magnetic poles and operating temperatures were set as two poles and liquid hydrogen temperature of 20 K, respectively. The parameter was power frequency in the range of 100-250 Hz. As a result, all the requirements were satisfied when the power frequency was 130 Hz. The feasibility of the MW-class superconducting induction motor was investigated, and in conclusion, the superconducting induction motor can be applied to the aircraft propulsion system.

DOI： 10.1109/TASC.2020.2971671

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DOI： 10.1109/TASC.2020.2989746

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

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

We studied the properties of a magnetometer using high-T_c superconducting coils and an inductance modulation scheme. First, we obtained analytical expressions for the responsivity and magnetic field noise of the magnetometer that could be used for the design of a magnetometer. Next, a prototype magnetometer was fabricated and its performance was measured in liquid nitrogen. It was observed that the measured results agreed well with the calculated results, which indicated the validity of the present design method. We obtained a magnetic field noise of 0.8 pT/Hz^1/2 above 25 Hz when using a pickup coil with 50 turns and an average diameter of 25 mm. At low frequencies, the field noise increased when decreasing the frequency, and reached 9 pT/Hz^1/2 at 1 Hz. We also discuss the improvement of the magnetometer performance when the size of the pickup coil is increased.

DOI： 10.1016/j.jmmm.2020.166525

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

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

We demonstrate the wash-free detection of biological targets based on the Brownian relaxation of magnetic markers. The Brownian relaxation time of bound markers was prolonged by using a cluster (or agglomerate) of bound markers that was formed via the binding reaction between markers and targets. Thus, bound and free markers were differentiated magnetically by using the difference in their relaxation times. Two types of magnetic properties, i.e., third-harmonic signal and magnetic relaxation, were used for measurement. The concentration of target was detected from the decrease in the third-harmonic signal and the increase in the magnetic-relaxation signal. We demonstrated the detection of C-reactive proteins using these two properties. In both cases, a good correlation was obtained between the measured signal and the concentration of target. It was also shown that the two methods had different concentration dependences, which will be caused mainly by the distribution of cluster size of the bound markers.

DOI： 10.1016/j.jmmm.2019.166356

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

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

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)  

Eddy current testing (ECT) usually employs a sinusoidal current that flows through an excitation coil. If a square wave instead of a sinusoidal wave is used for excitation, i.e., a square-wave inverter instead of linear amplifiers is used for an ECT system, a handheld ECT system can be developed and the cost can be reduced. In this study, we developed a low-frequency ECT (LF-ECT) system with a square-wave inverter to determine whether an inverter is applicable to estimating the thickness of a thick steel plate in the range from 6 to 19 mm. The developed ECT system has a differential excitation coil and a pickup coil, and these coils are arranged on the steel plate. A square-wave voltage is applied to the excitation coil, and the voltage of the pickup coil is measured. Subsequently, the mutual equivalent resistance and inductance are calculated. Results indicate that the fundamental component of the resistance increases with the thickness when the frequency is approximately 4 Hz. Furthermore, we determined whether the harmonic signals generated by the inverter are also useful. Results indicate that the harmonic components of the resistance also tend to increase with a sufficiently small increase in thickness, i.e., ≤12 mm. This implies that surface and back-surface defects can be simultaneously obtained.

DOI： 10.18494/SAM.2019.2318

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

10 MW fully superconducting generators, comprising REBCO superconducting tapes with various armature winding configurations, were designed. The influences of these configurations, such as a distributed-winding and a concentrated-winding configuration, on AC loss, output power density, and output voltage waveform were evaluated. As a result, the short-pitch distributed-winding model exhibited the best properties among all the models. In particular, the AC loss of the armature winding was approximately half that of the concentrated winding. Furthermore, the distortion factor was lower than 10%.

DOI： 10.1088/1742-6596/1293/1/012074

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

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

Future aircraft are expected to have low noise pollution, low emission, and low fuel consumption. A fully turbo-electric propulsion system was proposed by NASA with these aims. The advantages of fully superconducting rotating machines are their weight and efficiency, owing to a high current density resulting in no iron core and no joule heat. In this paper, 10-MW fully superconducting generators with REBa₂Cu₃O_y (RE: Rare Earth, Y, Gd, Eu, and others, REBCO) superconducting tapes were studied in relation to their output power density and efficiency. The target output power density is over 20 kW/kg. Fully superconducting generators of 10 MW were designed, then a numerical simulation of the rated operation was conducted. The ac loss of the superconducting windings, iron loss of the yoke, total efficiency, dry weight, and output power density were evaluated, and their dependence on the operating temperature and the synchronous rotating speed were investigated. Here laser-scribing of the wires into a multifilamentary structure and transposed parallel conductors were introduced for ac loss reduction and current capacity enhancement. Consequently, the efficiency reached 99.2% in the case where the REBCO superconducting tapes were scribed into a 10-filament structure. The best model achieved a power density of 26.7 kW/kg. The iron yoke accounts for approximately half the total weight of all the models. The result suggests that the development of superconducting shields brings significant improvement to the output power density.

DOI： 10.1109/TASC.2019.2906655

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

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

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Defect detection on the backside of thick steel plates is essential for the safety maintenance of most infrastructures in which they are used. Eddy-current testing (ECT) is a promising method to detect the defects in a steel plate, and inspections at low frequencies are necessary to suppress the skin effect. However, if the frequency is reduced further, the signal from the detection coil also becomes smaller. Therefore, we assessed the optimal frequency for the detection of slit defects on the backside of a 10 mm thick steel plate based on experiments and electromagnetic simulations using the finite-element method. The results suggest that the optimal frequency to detect the defects is approximately 8-10 Hz when the height of the slit exceeds 6 mm. Similarly, in the simulation, the signal was maximized when the frequency was 8-10 Hz, which validates the experimental results. Furthermore, we propose a method to emphasize the deeper defects using multi-frequency data as a fundamental study. The results show that the backside defects are depicted more clearly.

DOI： 10.1109/TMAG.2019.2896590

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

We performed three-dimensional detection of magnetic nanoparticle (MNP) samples using the combination of a field-free line (FFL) and multiple pickup coils. In this method, two-dimensional maps of the signal fields generated by the MNP samples were used to reconstruct a three-dimensional image of the MNP concentration. In the experiment, a weak field gradient of the FFL (0.06-0.13 T m^-1) was used. The degradation of the imaging quality owing to the weak field gradient was compensated using ten field maps. We successfully demonstrated the three-dimensional detection of two MNP samples. The Fe content of each sample was 10 and 20 μg and the spacing for both samples was 16 mm. The results confirm the effectiveness of the present method for MNP detection using a weak field gradient. We also quantitatively discuss how the imaging quality degrades when the field gradient is decreased.

DOI： 10.7567/1347-4065/ab1950

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

When testing ferromagnetic materials such as iron, low-frequency eddy-current testing (LF-ECT) is used to avoid the skin effect. However, the drawback of LF-ECT is that the signal becomes weak at low frequencies. Furthermore, when the specimen is covered with protective materials, the signal becomes even weak, owing to the large lift-off. To overcome these drawbacks, we utilize a high-temperature superconducting (HTS) coil and a pulse-width modulation (PWM) inverter in the LF-ECT method. Using an HTS coil and a PWM inverter, strong currents are conducted, and the change in the coil resistance can be easily measured. The small impedance change of the HTS coil is detected by using a Maxwell bridge. The result demonstrates that a steel plate thickness of up to 20 mm can be estimated based upon the measurements of the change in the coil resistance, even when the lift-off is 98 mm.

DOI： 10.3233/JAE-171117

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

The structure of magnetic nanoparticles affects the signal intensity and resolution of magnetic particle imaging, which is derived from the harmonics caused by the nonlinear response of magnetization. To understand the key effects of particle structures on the magnetization harmonics, the dependence of the harmonics on the size and anisotropy of different structures was investigated. We measured the harmonic signals with respect to different magnetic nanoparticle structures by applying an AC field with a gradient field for magnetic particle imaging, which was compared with the numerically simulated magnetization properties. In addition, the dynamics of the easy axis of magnetic nanoparticles in the liquid state were evaluated. The difference between the harmonics in the solid and liquid states indicates the effective core size and anisotropy due to particle structures such as single-core, chainlike, and multicore particles. In the case of the chainlike structure, the difference between the harmonics in the solid and liquid states was larger than other structures. In the numerical simulations, core diameters and anisotropy constants were considered as the effective values, such as the increase in anisotropy in the chainlike structure due to dipole interaction. The multicore particles showed high harmonics owing to their large effective core diameters. The superparamagnetic regime in the multicore structure despite the large effective core diameter was derived from the small effective anisotropy. The effective core size and the effective anisotropy of each particle structure and their impacts on the harmonic signals were revealed.

DOI： 10.1016/j.jmmm.2018.11.043

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

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

We have developed a new type of magnetometer using a high-critical-temperature superconductor (HTS) coil. This magnetometer consists of pickup and input coils made from HTS tape. The two coils are connected with very low joint resistance, and the signal flux that is collected by the pickup coil is transferred to the input coil. The signal at the input coil is then read out using a newly developed inductance-modulation scheme. The inductance of the input coil is modulated over time using a magnetic wire that is inserted into the input coil, and the magnetic flux is converted into a signal voltage using this time-dependent inductance. It is demonstrated that this magnetometer can measure low-frequency signal fields down to 0.03 Hz without any reduction in responsivity. The noise level was measured to be 0.85 pT/Hz ^1/2 at frequencies above 25 Hz and reached 11 pT/Hz ^1/2 at 1 Hz when using a pickup coil with 50 turns and an average diameter of 25 mm.

DOI： 10.1109/TASC.2019.2892481

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

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

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

The evaluation of opposite-side defects in thick ferromagnetic objects (for example, steel plates) is essential for safety maintenance. Eddy-current testing (ECT) can detect defects in metallic specimens; however, owing to the skin effect, its use is limited to the evaluation of surface or subsurface defects. Therefore, in this paper, we propose a non-contacting inspection system that consists of two excitation coils and a detection coil to detect slit defects on the backside of a steel plate using low-frequency ECT (LF-ECT). Using the proposed system, we examine whether LF-ECT mainly detects the leakage or the flux induced by the eddy current, and also examine which direction of the excitation currents in the two excitation coils is suitable for detecting slit defects. The results suggest that the method to drive the current in the same direction and to detect the imaginary part of the magnetic flux density, which corresponds to the flux induced by the eddy current, is suitable for detecting slit defects. Subsequently, we examine the detection limit of the height of the slit defect when the thickness of the steel plate is 10 mm and the width and length of the slit defect are constant, at 50 and 1 mm, respectively. The results demonstrate that the slit defect can be detected by using the proposed system when the height is greater than or equal to 4 mm. Therefore, the proposed system is a promising tool to detect critical defects on the backside of steel plates.

DOI： 10.1109/TMAG.2018.2847729

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

To guide gastric tubes into the stomach correctly, we propose the position-guidance system of a permanent magnet attached to the tip of the tube using high-sensitivity magnetoresistance (MR) sensors placed outside the patient's body. To enhance the sensitivity of the magnetic sensors and improve the position-estimation performance, we employ a small offset coil surrounding the magnetic sensor to compensate the geomagnetic field and evaluate the effect of the geomagnetic field compensation. The results show that the mean value of the position-estimation error with the compensation was less than 10 mm, even when the distance between the permanent magnet and MR sensors is 190 mm, whereas the mean value without the compensation exceeds 10 mm when the distance is greater than 150 mm. This suggests that the proposed compensation method improves the performance and broadens the scope of application for different users, e.g., pregnant or obese patients, of the guide system.

DOI： 10.1109/TMAG.2018.2846267

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

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

Naso- or oro-gastric tubes are used for patients who have difficulty swallowing, to deliver nutrients or medicines to the stomach. To observe whether the tube is inserted into the stomach correctly, we have proposed a method that estimates the position of the permanent magnet attached to the tip of the tube using several magnetic sensors placed outside the patient's body [1], [2]. The mean of the tip position estimation error is less than 10 mm when the distance between the sensor plane and the permanent magnet is 150 mm [2]. However, if the system is used on pregnant or fat patients, the system needs to perform accurately even for distances greater than 150 mm. To achieve the requirement mentioned above, the sensitivity of the magnetic sensors should be enhanced. Although high-sensitivity magnetoimpedance (MI) and magnetoresistance (MR) sensors can detect signals of the order of nT, the performance is only achieved in a magnetically shielded room due to the limitation of the measurement range and the existence of the geomagnetic field; this creates a problem for the system's practical use in hospitals. Therefore, we propose a method to compensate the geomagnetic field using offset coils.

DOI： 10.1109/INTMAG.2018.8508131

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

Ferromagnetic materials such as steel have high magnetic permeability, and thus their skin depth is shallower than that of non-ferromagnetic materials. Therefore, inspection at low frequency is required to examine a thick steel plate using eddy current testing (ECT) [1], [2]. Previously, we have demonstrated, using an electromagnetic simulation in conjunction with the finite element method, that the slit defect in the backside of the steel plate can be detected when the excitation frequency is low enough [3]. In this study, we propose a system that detects slit defects in the backside of the steel plate using low-frequency-ECT (LF-ECT).

DOI： 10.1109/INTMAG.2018.8508192

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

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

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

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

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

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

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

We developed a new type of magnetometer to measure low-frequency magnetic fields with an operational principle based on magnetic flux transfer and modulation. This magnetometer consists of three coils: pickup, input and readout coils. The pickup and input coils were made from high-critical-temperature superconductor (HTS) tape and were connected with very low connection resistance to form a closed loop. The magnetic flux that is collected by the pickup coil can be transferred to the input coil even at low frequencies below 1 Hz. The magnetic flux at the input coil is then detected by the readout coil using a readout scheme based on modulation of the mutual inductance M between the input and readout coils. To modulate M over time, a magnetic wire was inserted into the readout coil and a time-varying current was supplied to the wire. Using this time-varying M, the magnetic flux is converted into an amplitude-modulated voltage across the readout coil for measurements. A prototype magnetometer was fabricated for demonstration. This magnetometer can operate at low frequencies down to f = 0.5 Hz without responsivity degradation. The magnetic field noise levels were 8 and 60 pT/Hz^1/2 at 50 and 1 Hz, respectively.

DOI： 10.1088/1742-6596/1054/1/012058

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

We developed a magnetometer based on inductance modulation of a coil made from a high-critical-temperature superconducting material. The coil inductance was modulated over time via a modulation current applied to a magnetic wire that was inserted into the coil. The magnetic field was then converted into a signal voltage using this time-dependent inductance. The relationship between magnetometer performance and the modulation current conditions was studied. Under appropriate conditions, the magnetometer had responsivity of 885 V/T. The magnetic field noise was 1.3 pT/Hz1/2 in the white noise region and 5.6 pT/Hz1/2 at f = 1 Hz.

DOI： 10.7567/JJAP.57.060314

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

We studied the magnetization (M-H) curve of immobilized magnetic nanoparticles (MNPs) used for biomedical applications. First, we performed numerical simulation on the DC M-H curve over a wide range of MNPs parameters. Based on the simulation results, we obtained an empirical expression for DC M-H curve. The empirical expression was compared with the measured M-H curves of various MNP samples, and quantitative agreements were obtained between them. We can also estimate the basic parameters of MNP from the comparison. Therefore, the empirical expression is useful for analyzing the M-H curve of immobilized MNPs for specific biomedical applications.

DOI： 10.1063/1.5004725

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

We performed three-dimensional magnetic particle imaging using third-harmonic signal detection. The measurement system consists of three coil types, i.e., an ac excitation coil, a dc gradient coil, and five pickup coils cooled to 77 K. In the experiment, two magnetic nanoparticle samples containing 10 μg (Fe) of magnetic nanoparticles were arranged three-dimensionally with a spacing of 16 mm. An ac excitation field with a strength of 1.6 mT at 3 kHz and a dc gradient field with a field gradient of 0.2 T/m were used. A third-harmonic signal generated from the magnetic nanoparticle samples was detected using the five pickup coils. The noise of the detection system was as low as S_B ^1/2 = 7 fT/Hz^1/2 at a signal frequency of 9 kHz. A magnetic field map generated from the two magnetic nanoparticle samples was obtained by scanning the samples two-dimensionally. Field maps obtained with the five pickup coils were analyzed to reconstruct a three-dimensional distribution image of the magnetic nanoparticle sample. A mathematical technique called the nonnegative least squares method was used for this purpose. We successfully demonstrated three-dimensional magnetic particle imaging. Namely, we reconstructed the three-dimensional positions of the two magnetic nanoparticle samples with good accuracy. Quantities of the two magnetic nanoparticle samples were also estimated reasonably well. These results indicate the feasibility of the present system for three-dimensional magnetic particle imaging.

DOI： 10.1109/ISEC.2017.8314234

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

We performed three-dimensional detection of magnetic nanoparticle (MNP) samples using third-harmonic signal detection. In this method, a combination of five pickup coils and a gradient field with a field-free line was used to acquire three-dimensional MNP sample position information. The resulting two-dimensional maps of the signal fields generated by the MNP samples are sufficient for three-dimensional MNP image reconstruction. In the experiments, two MNP samples with different Fe contents were set at different positions. Two-dimensional field maps were measured using the five pickup coils, and the three-dimensional MNP sample distribution was then reconstructed from these field maps by solving an inversion problem. We demonstrated three-dimensional detection of two MNP samples where we reconstructed the three-dimensional positions and the Fe contents of these two MNP samples with reasonable accuracy. These results indicate the feasibility of the proposed system for three-dimensional magnetic particle imaging.

DOI： 10.7567/JJAP.57.023002

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

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

We developed a magnetometer for measuring low-frequency magnetic fields. The magnetometer consists of two coils, namely, pickup and modulation coils made of high-critical-temperature superconducting material. The inductance of the modulation coil is modulated with time, and the magnetic field signal is converted to an amplitude-modulated voltage across the modulation coil. The prototype magnetometer can operate at low frequencies down to f = 0.01 Hz without diminishing the response. The noise in the magnetic field signal is 40 pT/Hz^1/2 at 10 Hz. An order of magnitude improvement will be possible with a modulation coil of suitable geometry.

DOI： 10.7567/APEX.10.113101

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

The magnetic core-size distribution of magnetic nanoparticles (MNPs) was estimated from three independent measurements, i.e., magnetization, ac susceptibility (ACS), and magnetic relaxation (MRX). First, distribution of magnetic moment m in MNP sample was estimated by analyzing the static magnetization (M - H) curve of the MNP sample in suspension. Next, distribution of anisotropy energy E was estimated by analyzing the ACS of immobilized MNP sample measured from 10 Hz to 1 MHz. The ACS measurement in much lower frequency range was substituted by the MRX measurement. MRX of immobilized MNP sample was measured from 2 to 10⁴ s, corresponding to the frequency range from 10^-4 to 0.5 Hz in ACS measurement. The relaxation curve was analyzed using a newly developed analytical method to estimate the E distribution of the MNPs in the range of large E values. Then, the estimated distributions of m and E were transferred to the distributions of magnetic core size. Core-size distributions obtained from m and E distributions reasonably agreed with each other. Namely, we obtained similar core-size distribution from static and dynamic properties of MNP sample, confirming the validity of the present method. Therefore, the present method can be useful to estimate the core-size distribution of MNP sample.

DOI： 10.1109/TMAG.2017.2700480

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

To correctly insert a gastric tube into the stomach, the position of an attached permanent magnet is estimated by solving the inverse problem using measurement data obtained from magneto-impedance (MI) sensors placed outside the patient's body. The ubiquity and power of tablet computers make them promising tools to easily confirm the position of the tip of the gastric tube. However, a single mobile device may be insufficient for actually solving the inverse problem. Therefore, we propose a distributed cooperative local access network system for the estimation of the position of a permanent magnet attached to the tip of a gastric tube. In addition, we evaluate whether ferromagnetic materials near a sensor affect the performance of the system. Experimental results show that the position estimation error is less than 10 mm, even when the tip is 150 mm from a MI sensor, and that the tip position can be displayed on a tablet computer every 0.25 s. These results suggest that the proposed method holds promise for hospital applications.

DOI： 10.1109/TMAG.2017.2714683

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

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

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

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

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

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

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

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

For patients who have difficulty swallowing, naso- or oro-gastric tubes are usually used to deliver nutrients to the stomach.

DOI： 10.1109/INTMAG.2017.8007961

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

Ferromagnetic materials such as steel have high magnetic permeability and a smaller skin depth than non-ferromagnetic materials.

DOI： 10.1109/INTMAG.2017.8007648

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

Magnetic nanoparticles (MNPs) have been widely studied for use in biomedical applications such as magnetic immunoassay, magnetic particle imaging and hyperthermia.

DOI： 10.1109/INTMAG.2017.8007882

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

In some biomedical applications of magnetic nanoparticles (MNPs), the particles are physically immobilized. In this study, we explore the effect of the alignment of the magnetic easy axes on the dynamic magnetization of immobilized MNPs under an AC excitation field. We prepared three immobilized MNP samples: (1) a sample in which easy axes are randomly oriented, (2) a parallel-aligned sample in which easy axes are parallel to the AC field, and (3) an orthogonally aligned sample in which easy axes are perpendicular to the AC field. First, we show that the parallel-aligned sample has the largest hysteresis in the magnetization curve and the largest harmonic magnetization spectra, followed by the randomly oriented and orthogonally aligned samples. For example, 1.6-fold increase was observed in the area of the hysteresis loop of the parallel-aligned sample compared to that of the randomly oriented sample. To quantitatively discuss the experimental results, we perform a numerical simulation based on a Fokker-Planck equation, in which probability distributions for the directions of the easy axes are taken into account in simulating the prepared MNP samples. We obtained quantitative agreement between experiment and simulation. These results indicate that the dynamic magnetization of immobilized MNPs is significantly affected by the alignment of the easy axes.

DOI： 10.1016/j.jmmm.2016.10.040

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

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

Magnetic biosensing techniques that are based on the use of bio-functionalized magnetic nanoparticles (magnetic markers) and superconducting quantum interference devices (SQUIDs) are expected to have various advantages when compared with conventional biosensing methods. In this paper, we review the recent progress made in magnetic biosensing techniques. First, we describe the most important parameters of magnetic markers that are intended for use in biosensing, i.e., the magnetic signal and the relaxation time that are determined by the Brownian and/or Néel relaxation mechanisms. We note that these parameters are significantly dependent on the marker size, and as a result, commercial markers exhibit a wide variety of values for these key parameters. Next, we describe three measurement methods that have been developed based on the magnetic properties of these markers, i.e., AC susceptibility, relaxation and remanence-based measurement methods. The weak (picotesla-range) signals emitted by the markers can be measured precisely with a SQUID system using these methods. Finally, we give examples of biosensing for in vitro and in vivo medical diagnosis applications. For in vitro diagnosis, high-sensitivity detection of various biological targets has been demonstrated without use of any washing process to separate the bound and free markers. For in vivo applications, detection of the quantities and the three-dimensional positions of the markers that have been injected into the test subject are demonstrated. These results confirm the effectiveness of magnetic biosensing techniques.

DOI： 10.1088/1361-6668/aa5fce

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

We studied the AC hysteresis loop and the harmonic spectra of samples containing immobilized magnetic nanoparticles (MNPs) at different values of the excitation field frequency f and amplitude H₀. First, we measured the dependences of the coercive field 〈H_c〉 on f and H₀. The measured dependences agreed qualitatively with the numerically predicted values. Next, we studied the relationship between 〈H_c〉 and the harmonic spectra, and found strong correlation between 〈H_c〉 and the attenuation rate of these harmonic spectra. We obtained an empirical expression for the harmonic spectra using 〈H_c〉 and a static magnetization curve for the immobilized MNPs. The expression obtained explained the experimental data well. Finally, the harmonic spectra were measured for two MNP samples with different distributions of the magnetic moment m. The MNP sample with the lower m distribution produces richer harmonic spectra for use in magnetic particle imaging.

DOI： 10.7567/JJAP.56.025001

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

Language：English   Publishing type：Research paper (bulletin of university, research institution)  

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

Language：English   Publishing type：Research paper (bulletin of university, research institution)  

Language：English   Publishing type：Research paper (bulletin of university, research institution)  

Language：English   Publishing type：Research paper (bulletin of university, research institution)  

Language：English   Publishing type：Research paper (bulletin of university, research institution)  

Language：English   Publishing type：Research paper (bulletin of university, research institution)  

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

Language：English   Publishing type：Research paper (bulletin of university, research institution)  

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

In this paper, we propose improved methods of liquidphase detection of biological targets utilizing magnetic markers and a high-critical-temperature superconducting quantum interference device (SQUID). For liquid-phase detection, the bound and unbound (free) markers are magnetically distinguished by using Brownian relaxation of free markers. Although a signal from the free markers is zero in an ideal case, it exists in a real sample on account of the aggregation and precipitation of free markers. This signal is called a blank signal, and it degrades the sensitivity of target detection. To solve this problem, we propose improved detection methods. First, we introduce a reaction field, B_re, during the binding reaction between the markers and targets. We additionally introduce a dispersion process after magnetization of the bound markers. Using these methods, we can obtain a strong signal from the bound markers without increasing the aggregation of the free markers. Next, we introduce a field-reversal method in the measurement procedure to differentiate the signal from the markers in suspension from that of the precipitated markers. Using this procedure, we can eliminate the signal from the precipitated markers. Then, we detect biotin molecules by using these methods. In an experiment, the biotins were immobilized on the surfaces of large polymer beads with diameters of 3.3 μm. They were detected with streptavidin-conjugated magnetic markers. The minimum detectable molecular number concentration was 1.8 × 10^-19 mol/ml, which indicates the high sensitivity of the proposed method.

DOI： 10.1587/transele.E99.C.669

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

We present a method to evaluate the magnetic moment (m) and the anisotropy energy (E) of magnetic markers, which are the key parameters employed in biosensing applications. The distributions of the m and E values in the marker are evaluated by analyzing the static magnetization (M-H) curve of the suspended markers and the frequency dependence of the AC susceptibility of the immobilized markers, respectively. Then, we obtain the relationship between m and E. In the experiment, four markers made of multicore and single core nanoparticles are examined. We obtain distributions of the m and E values, which show the particular characteristics of each marker. Although the m and E values are widely distributed in the marker, a clear relationship is obtained between the values. Therefore, the obtained m-E curve, as well as the distribution of the m and E values, provides a framework to discuss the dynamic behavior of the immobilized markers. The difference in the estimated m-E curves between the markers is also discussed.

DOI： 10.1063/1.4948951

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

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

We developed improved methods of liquid-phase detection of biological targets using HTS SQUID and Brownian relaxation of magnetic markers. In a real sample, the aggregation and precipitation of free markers deteriorate their Brownian relaxation and cause so-called blank signals. In order to solve this problem, we developed two methods. First, we introduced a reaction field Bre during the binding reaction between the markers and targets. Using this method, we could obtain a strong signal from the bound markers without increasing the aggregation of the free markers. Next, we introduced a fieldreversal method in the measurement procedure in order to differentiate the signal from the markers in suspension from that from the precipitated markers. Using this procedure, we could eliminate the signal from the precipitated markers. Then, we detected biotin molecules by using these methods. The biotins were immobilized on the surfaces of large polymer beads with diameters of 3.3 μm and were detected with streptavidinconjugated magnetic markers. The minimum detectable molecular number concentration was 1.8 × 10^-19mol/ml, indicating the high sensitivity of the present method.

DOI： 10.1109/ISEC.2015.7383474

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

Eddy current testing (ECT) has been widely used for the nondestructive evaluation of metallic plates or pipes. One of the methods in ECT is to measure the change of coil impedance that is caused by the metallic plate below the coil. We applied this method to estimate the thickness of an iron plate. In this case, low-frequency measurement is required in order to avoid the skin effect. At low frequencies, however, coil resistance dominates the coil impedance, and it becomes difficult to measure small changes in coil impedance. Therefore, we applied a high-temperature superconducting (HTS) coil in order to realize low coil resistance. In the experiment, changes in inductance L and resistance R of the coil were measured when the iron plate was set at 20 mm below the HTS coil. The range of the measurement frequency was chosen from 2 to 15 Hz, and the thickness of the plate was changed from 6 to 22 mm. It was shown that changes in R were clearly related to the thickness of the iron plate. Therefore, we could determine the thickness of the iron plate. Numerical simulation using the finite element method was also performed to analyze the experimental results.

DOI： 10.1109/ISEC.2015.7383469

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

A zone-control induction heating (ZCIH) system heats workpieces using several induction coils. To design and control the ZCIH system, parameters such as the self/mutual inductance and self/mutual-equivalent resistance between coils should be obtained in advance. For this purpose, we have proposed a practical method called "multiport transformer model" to reduce the computation time in calculating these parameters. In this study, we compare the parametric result obtained by simulations using the multiport transformer model, with the result obtained through the finite element method (FEM) analysis results and experimental data to validate the computational accuracy of the multiport transformer model. The comparison result shows that the characteristics of the inductance and equivalent resistance calculated by the multiport transformer model are similar to those obtained from the FEM analysis and experimental result. This indicates that our proposed model can contribute to the design optimization and control of a ZCIH system.

DOI： 10.1541/ieejjia.5.392

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

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

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

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

We evaluated the complex harmonic signals from magnetic nanoparticles (MNPs) for magnetic particle imaging (MPI). We measured the complex harmonic signals from Resovist MNPs, one of the candidates for an MPI tracer, when only an ac excitation field and both the ac and the dc excitation fields were applied. To evaluate the complex harmonic magnetization spectra, we performed a numerical simulation accounting for the distributions of magnetic moments, anisotropy energy barriers, and hydrodynamic sizes of MNPs in the sample. The simulation results agreed well with experimentally obtained amplitude of the harmonic signals. The simulation results of the phase lag, which was caused by the finite relaxation time, agreed with the experiments for low harmonic numbers. The phase lag deviation between them became significant for higher harmonic numbers. For quantitative evaluation of the phase lag for higher harmonic numbers, a more accurate estimation of the Néel relaxation time is required.

DOI： 10.1109/TMAG.2015.2441750

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

We developed a narrowband magnetic particle imaging (MPI) system that uses third-harmonic signal detection and electrical scanning of the field free point (FFP). Comparing with mechanical scanning, we can decrease the measurement time significantly and increase the signal-to-noise ratio as well. For electrical scanning, we designed and constructed gradient and shift coils. The gradient coil consisting of four pieces of planar coils generated the gradient field with a field gradient of 0.4 T/m at a height of 25 mm from the coil surface. The FFP can be moved ±8 mm by supplying a current of ±6.6 A to the shift coil. Using the developed system, we detected two magnetic nanoparticle (MNP) samples located at a depth of 35 mm below the pickup coil with a spacing of 10 mm. By applying an excitation field of 1 mT at 22.75 kHz, we measured the third-harmonic signal from the MNP samples and obtained a contour map of the signal field in an area of 16 × 16 mm². Then, we converted the field map into an MNP distribution using singular value decomposition method. It was shown that the spatial resolution of the reconstructed MNP distribution was improved compared with that of the measured contour map of the signal field. The spatial resolution for MNP detection in MNP distribution was 5 mm and two MNP samples were distinguished clearly. This result indicated that MPI using electrical scanning of the FFP was successfully performed.

DOI： 10.1109/TMAG.2015.2438029

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

A nasogastric tube is commonly used to pour nutrients into the stomachs of patients who have difficulty swallowing in order to provide them with the required nutrition. However, it is possible to inadvertently insert the tube into the lungs. Thus, a method of obtaining the tip position of the tube is desired. In this paper, we use predata of magnetoimpedance (MI) sensors to estimate the position of the magnet attached to the tube tip using a minimum variance beamformer. Experimental results show that the position estimation error is <10 mm even when the distance from the MI sensors is 150 mm using the predata, whereas the error exceeds 10 mm when the predata is not used. These results suggest that the proposed method is a promising method for hospital applications.

DOI： 10.1109/TMAG.2015.2438858

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

Magnetic hyperthermia using magnetic nanoparticles (MNPs) draws significant interest for application in heat therapy for cancerous tumors, wherein it is important to improve the heating efficiency, i.e., to increase the hysteresis loss. In this paper, we examined the hysteresis loss of magnetically fractionated MNPs for hyperthermia application. Original Resovist MNPs were magnetically fractionated into three types, and their hysteresis loops were measured with an excitation field of 2.5 mT (rms) at a frequency of 20 kHz. The hysteresis loss of fractionated MNPs with the larger magnetic moment was approximately two times that of the original Resovist MNPs. A numerical simulation based on the Langevin function was performed to support the experimental results. From the experimental and simulation results, we can conclude that the efficiency of hyperthermia is improved by magnetically separating MNPs.

DOI： 10.1109/TMAG.2015.2438080

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

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

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

Induction motors are driven using pulse-width modulation (PWM) inverters because of the ease of control and energy saving that may be realized. When the iron loss of an induction motor is calculated using the finite element method (FEM), there are differences between experimental and simulation results obtained under PWM inverter excitation. To improve the accuracy using FEM, it is important to understand the behavior of the magnetic flux in the motor driven by the PWM inverter during the experiment. To the best of our knowledge, there are few reports regarding the magnetic flux in an induction motor [1]. In this study, we measure the magnetic flux and hysteresis loop in a squirrel-cage induction motor using search coils located on the tip of the teeth.

DOI： 10.1109/INTMAG.2015.7157771

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

Early and chronic stroke patients tend to have trouble swallowing [1]. To ensure that they are able to receive the required nutrition, a nasogastric tube is usually used to pour nutrients into the stomach. However, when the tube is inserted through the patient's nostril into their stomach, it may be accidentally inserted into the lungs, and this may be fatal if the nutrients are released into the lungs. To prevent this, a method to estimate the position of the tip of the tube has previously been proposed. This method involves attaching a permanent magnet to the nasogastric tube and arranging several magneto impedance (MI) sensors outside the body (Figs. 1 and 2) [1][2].

DOI： 10.1109/INTMAG.2015.7157195

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

Magnetic hyperthermia using magnetic nanoparticles (MNPs) is of significant interest for application in heat therapy of cancerous tumors. In this application, it is important to clarify the magnetic characteristics of the MNPs in order to estimate the heating efficiency. To achieve this objective, several studies have measured the AC hysteresis loops of MNPs under various AC magnetic field conditions [1][2].

DOI： 10.1109/INTMAG.2015.7157196

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

Magnetic nanoparticles (MNPs) have been widely studied for biomedical applications such as separation of biological targets, immunoassays, drug delivery, hyperthermia, and magnetic particle imaging (MPI). In particular, MPI is a new modality for imaging the spatial distribution of the MNPs, especially for in-vivo diagnostics [1].

DOI： 10.1109/INTMAG.2015.7157571

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

To ensure the rapid and uniform heating of a workpiece, the zone-control induction heating (ZCIH) system has been developed. This system has several coils, each of which is connected to an independent inverter unit. The frequencies and phases of the currents are treated as being equal to avoid interference between coils [1].

DOI： 10.1109/INTMAG.2015.7156803

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

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

We studied the distributions of the magnetic moment and magnetic volume of magnetic nanoparticles (MNPs). These distributions were estimated by applying the singular value decomposition method to the M-H curve measured in the liquid phase. The estimated distributions were compared with a mixture of log-normal distributions, and two results agree well with each other. Using the estimated distribution of the magnetic moment, we also analyzed the M-H curve of immobilized MNPs in order to estimate the average value of the anisotropy energy constant Ku and the characteristic time τON that determines the Neel relaxation of immobilized MNPs. The values Ku and τON are estimated as 4 kJ/m³ and 1×10-9 s, respectively, for Resovist MNPs.

DOI： 10.1063/1.4919268

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

We developed a highly sensitive AC/DC magnetometer using a high-temperature superconductor superconducting quantum interference device for the evaluation of magnetic nanoparticles in solutions. Using the developed system, we investigated the distribution of magnetic moments of iron oxide multi-core particles of 100 nm at various iron concentrations that are lower than 96 μg/ml by analyzing the measured magnetization curves. Singular value decomposition and non-regularized non-negative least-squares methods were used during the reconstruction of the distribution. Similar distributions were obtained for all concentrations, and the iron concentration could be determined from the measured magnetization curves. The measured harmonics upon the excitation of AC and DC magnetic fields curves agreed well with the harmonics simulated based on the reconstructed magnetization curves, implying that the magnetization curves of magnetic nanoparticles were successfully obtained as we will show in the article. We compared the magnetization curves between multi-core particles of 100 nm and 130 nm, composed of 12-nm iron oxide nanoparticles. A distinctive magnetic property between the 100 nm and 130 nm particles in low-concentration solutions was successfully characterized. The distribution characteristic of magnetic moments suggests that the net magnetic moment in a multi-core particle is affected by the size of the magnetic cores and their degree of aggregation. Exploration of magnetic properties with high sensitivity can be expected using the developed system.

DOI： 10.1063/1.4919043

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

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

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

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

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

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

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

When a workpiece is heated by eddy currents using a zone-control induction heating (ZCIH) system, there exists both inductance and resistance in the induction heating circuit. To efficiently control a ZCIH system, the detailed behavior of the self inductance and equivalent resistance of each coil and the mutual inductance and equivalent resistance between the coils should be clarified beforehand. This paper proposes the concept of the self- and mutual-equivalent resistances in the eddy current circuit and discusses the theoretical physical meaning and properties of these parameters. We also derive a theoretical formula for these parameters using a simple assumption and then examine their properties.

DOI： 10.1541/ieejjia.4.67

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

Magnetic particle imaging (MPI) has been extensively studied for in-vivo biomedical diagnosis. We developed a narrowband MPI system utilizing third harmonic detection. The third harmonic signal from the magnetic nanoparticles (MNPs) was detected with a pickup coil cooled to 77K, and its output was read out with a resonant circuit. The noise of the detection system was S_B^1/2 = 12fT/Hz^1/2 at a signal frequency of 8.79 kHz. We also introduced the so-called gradient field with a field gradient of 0.3 T/m in order to improve the MPI spatial resolution. We first clarified the properties of MNPs, which provided the basis for MPI using the gradient field. Next, we measured the signal-field map generated from the MNPs when an excitation field with a root mean square value of 1.6 mT and frequency of 2.93 kHz was applied. Using a mathematical technique called singular value decomposition (SVD), we reconstructed an image of the MNP distribution from the measured map. We demonstrated the detection of MNP samples as small as 1μg at a distance of 50mm. The spatial resolution of the reconstructed MNP distribution was approximately 10mm. These results will indicate the feasibility of the system for the application to breast cancer detection.

DOI： 10.7567/JJAP.54.057002

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

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

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

This paper investigates the effects of a load on the iron loss of an electrical sheet using a ring specimen with a secondary coil under pulse width modulation inverter excitation. In this experiment, the resistance load is connected to the secondary coil to simulate the motor load. To investigate the iron loss under load, we derive two methods to calculate the iron loss: the current difference method (CDM) and the power difference method (PDM). In the CDM, the iron loss is determined using the differential between the input current from the power amplifier to the specimen and the output current from the specimen to the load and voltage of the B-coil. In the PDM, the iron loss is derived using the differential between the input and output power. The iron loss calculated using the CDM and PDM agrees well when the secondary coil is open circuit, whereas the difference in the iron loss between the CDM and PDM increases as the resistance of the load decreases, especially when the carrier frequency is high.

DOI： 10.1109/TMAG.2014.2331358

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

When a patient is not capable of eating a meal due to difficulty in swallowing, a nasogastric tube can be inserted through the nose to the stomach to provide nourishment in liquid form. However, it is possible to insert the tube into the lungs by mistake. In this paper, we apply a minimum variance beamformer that is commonly used in brain signal source detection to estimate the position of the magnet attached to the tip of a nasogastric tube. To reduce the computational cost, the signal source power is calculated with two different resolutions. Furthermore, the signal source power calculations are performed in parallel. The position may be estimated in less than 1.0 s, making this method suitable for detecting the tip position of a nasogastric tube in real time.

DOI： 10.1109/TMAG.2014.2328651

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

We study the third harmonic signal of magnetic nanoparticles (MNPs) for use in narrow-band magnetic nanoparticle imaging. We measured the properties of the third harmonic signal, such as frequency and magnetic field dependencies, when the behavior of MNPs was dominated by Neel relaxation. It was shown that the third harmonic signal had both real and imaginary parts, although only the real part is expected from the conventional Langevin function. The real and imaginary parts exhibited different dependences on the frequency and magnetic field. The dynamic behavior of MNPs was analyzed by taking into account the Neel relaxation of MNPs. It was shown that the imaginary part was generated due to Neel relaxation. We obtain an analytical expression for the third harmonic signal, in which distributions of magnetic moment and anisotropic energy of MNPs in the sample were also considered. We show that the analytical results quantitatively explain the experimental results. Our results indicate that the properties of the third harmonic signal of immobilized MNPs are significantly affected by Neel relaxation.

DOI： 10.7567/JJAP.53.103002

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

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

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

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

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

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

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

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

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)  

The efficiency and materials cost of a linear oscillatory actuator (LOA) for a diaphragm blower depends on the design of magnetic circuit. Therefore, it is necessary to optimize the magnetic circuit in order to develop a high efficiency and low price LOA by employing the magnetic field analysis method and an optimization method. In this paper, the 3-D multi-objective optimization of LOA with large magnetic force and small magnet volume is carried out using the combined 3-D finite element method (FEM), evolution strategy (ES), and particle swarm optimization (PSO).

DOI： 10.1109/TMAG.2013.2238900

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

The acceleration of a nonlinear magnetic field analysis by parallelizing the finite element method (FEM) is examined using the graphics processing unit (GPU). It is shown that the speedup of the magnetic field analysis is realized by parallelizing the variable preconditioned conjugate gradient (VPCG) method. The Jacobi over-relaxation (JOR) method, conjugate residual (CR) method and conjugate gradient (CG) method are also applied in the variable preconditioning. The results of computations demonstrate that VPCG using the GPU significantly improve the performance. Especially, CG applied by variable preconditioned on GPU is 39 times faster than ICCG on a CPU.

DOI： 10.1109/TMAG.2013.2244062

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

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

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

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

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

We developed a novel movement-imagery-based braincomputer interface (BCI) for untrained subjects without employing machine learning techniques. The development of BCI consisted of several steps. First, spline Laplacian analysis was performed. Next, timefrequency analysis was applied to determine the optimal frequency range and latencies of the electroencephalograms (EEGs). Finally, trials were classified as right or left based on β-band event-related synchronization using the cumulative distribution function of pretrigger EEG noise. To test the performance of the BCI, EEGs during the execution and imagination of right/left wrist-bending movements were measured from 63 locations over the entire scalp using eight healthy subjects. The highest classification accuracies were 84.4% and 77.8% for real movements and their imageries, respectively. The accuracy is significantly higher than that of previously reported machine-learning-based BCIs in the movement imagery task (paired t-test, p < 0.05). It has also been demonstrated that the highest accuracy was achieved even though subjects had never participated in movement imageries.

DOI： 10.1587/transinf.E94.D.2479

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

In this study, we compared the performances of minimum variance beamformer (MVBF), linearly-constrained (LC)-MVBF, prewhitening beamformer (PWBF), and LC-PWBF with regard to the estimation of signal location in the brain neocortex. Equivalent current dipoles were located in the primary motor cortex in performed numerical simulations by considering applications in brain-computer interfaces based on modulation of μ and β rhythms. It was confirmed that when the signals were highly correlated, the location bias of LC-PWBF was smaller than that of MVBF, LC-MVBF, and PWBF. Obtained results suggest that LC-PWBF is useful for estimating the location of signal sources that are highly correlated and have low signal-to-noise ratio.

DOI： 10.1109/ICCME.2011.5876810

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

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

In order to enhance the reliability of electroencephalogram (EEG) signal source analyses, utilizing EEG lead field matrices obtained by field analyses in custom-made real head models is effective technique. Custom-made models are usually constructed from voxel models derived from magnetic resonance (MR) images using a variety of image-processing techniques. We have improved one of the techniques that select threshold levels dividing signals and noises based on the EM (expectation-maximization) algorithm. This technique contributes to rapid and high-quality voxel model acquisition. We demonstrate the following operations: (a) voxel model construction, (b) lead field calculation, and (c) simulation of EEG electrode voltage measurement induced by an equivalent current dipole (ECD), which is set in the primary motor cortex by considering application of brain-machine interfaces. The proposed technique is compared with other techniques based on the voltage differences caused by the constructed model-shape differences.

DOI： 10.1109/ICCME.2010.5558863

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

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

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

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

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

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

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

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

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

Event date： 2025.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京都中野区  

Event date： 2025.3

Language：English   Presentation type：Oral presentation (invited, special)  

Country：Germany  

Event date： 2025.3

Language：English   Presentation type：Poster presentation  

Country：Germany  

Event date： 2025.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京江東区  

Event date： 2025.1

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Venue： 高知  

Event date： 2025.1

Language：English  

Country：United States  

Event date： 2025.1

Language：English   Presentation type：Poster presentation  

Country：United States  

Event date： 2025.1

Language：English  

Country：United States  

Event date： 2025.1

Language：English  

Country：United States  

Event date： 2024.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：三重  

Event date： 2024.11

Language：English   Presentation type：Poster presentation  

Venue：福岡  

Event date： 2024.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：鹿児島  

Event date： 2024.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：京都  

Event date： 2024.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：京都  

Event date： 2024.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：京都  

Event date： 2024.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：鹿児島  

Event date： 2024.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：秋田  

Event date： 2024.9

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Venue：秋田  

Event date： 2024.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：長崎  

Event date： 2024.9

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Venue：栃木  

Event date： 2024.5

Language：English   Presentation type：Oral presentation (general)  

Venue：イギリス　グラスゴー   Country：United Kingdom  

Event date： 2024.4 - 2025.4

Language：English   Presentation type：Poster presentation  

Venue：神奈川  

Event date： 2024.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京  

Event date： 2024.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Flüeli-Ranft   Country：Switzerland  

Event date： 2024.3

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Venue：徳島  

Event date： 2023.12

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Venue：静岡  

Event date： 2023.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：静岡  

Event date： 2023.11

Language：English  

Venue：東京  

Event date： 2023.10 - 2023.11

Language：English  

Venue：Dallas   Country：United States  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：熊本  

Event date： 2023.8 - 2023.9

Language：English  

Venue：静岡  

Event date： 2023.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡  

Event date： 2023.5

Language：English   Presentation type：Oral presentation (general)  

Venue：宮城  

Event date： 2023.5

Language：English   Presentation type：Oral presentation (general)  

Venue：宮城  

Event date： 2023.5

Language：English   Presentation type：Oral presentation (general)  

Venue：宮城  

Event date： 2023.5

Language：English   Presentation type：Oral presentation (general)  

Venue：宮城  

Event date： 2023.3

Language：English   Presentation type：Oral presentation (general)  

Venue：岡山  

Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡   Country：Japan  

Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：愛知  

Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：愛知  

Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：愛知  

Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：愛知  

Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：愛知  

Event date： 2023.1

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：愛知   Country：Japan  

Event date： 2022.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：遠隔  

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京  

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：遠隔  

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：遠隔  

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：遠隔  

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：長野  

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：長野  

Event date： 2022.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：遠隔  

Event date： 2022.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：遠隔  

Event date： 2022.6

Language：English  

Venue：London  

Event date： 2022.6

Language：English   Presentation type：Oral presentation (general)  

Venue：遠隔  

Event date： 2022.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：遠隔  

Event date： 2022.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：遠隔  

Event date： 2022.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：遠隔  

Event date： 2022.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：遠隔  

Event date： 2022.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：遠隔  

Event date： 2022.1

Language：English  

Venue：遠隔   Country：United States  

Event date： 2021.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：遠隔  

Event date： 2021.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：遠隔  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：遠隔  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：遠隔  

Event date： 2021.8 - 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：遠隔  

Event date： 2021.8 - 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：遠隔  

Event date： 2021.8 - 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：遠隔  

Event date： 2021.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：遠隔  

Event date： 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：遠隔  

Event date： 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：遠隔  

Event date： 2021.4

Language：English   Presentation type：Oral presentation (general)  

Venue：遠隔   Country：Canada  

Event date： 2021.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：遠隔  

Event date： 2021.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：遠隔  

Event date： 2021.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：遠隔  

Event date： 2020.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：遠隔  

Event date： 2020.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：遠隔  

Event date： 2020.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：遠隔   Country：Japan  

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：遠隔  

Event date： 2020.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：遠隔  

Event date： 2020.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：遠隔  

Event date： 2020.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：静岡   Country：Japan  

Event date： 2019.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Taipei City   Country：Taiwan, Province of China  

Event date： 2019.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Taipei City   Country：Taiwan, Province of China  

Event date： 2019.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Taipei City   Country：Taiwan, Province of China  

Event date： 2019.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：京都  

Event date： 2019.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：京都  

Event date： 2019.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：京都  

Event date： 2019.8

Language：English  

Venue：Uppsala   Country：Sweden  

Event date： 2019.8

Language：English  

Venue：Uppsala   Country：Sweden  

Event date： 2019.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：沖縄  

Event date： 2019.3

Language：Japanese   Presentation type：Symposium, workshop panel (public)  

Venue：北海道  

Event date： 2019.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北海道   Country：Japan  

Event date： 2019.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北海道   Country：Japan  

Event date： 2019.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北海道  

Event date： 2019.1

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京  

Event date： 2019.1

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京  

Event date： 2019.1

Language：English  

Venue：Washington DC   Country：United States  

Event date： 2018.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大分  

Event date： 2018.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大分  

Event date： 2018.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：兵庫  

Event date： 2018.11

Language：English   Presentation type：Oral presentation (general)  

Venue：神奈川  

Event date： 2018.11

Language：English   Presentation type：Oral presentation (general)  

Venue：神奈川  

Event date： 2018.11

Language：English   Presentation type：Oral presentation (general)  

Venue：神奈川  

Event date： 2018.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大分  

Event date： 2018.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大分  

Event date： 2018.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：愛知  

Event date： 2018.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：愛知  

Event date： 2018.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京  

Event date： 2018.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京  

Event date： 2018.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京  

Event date： 2018.9

Language：English   Presentation type：Oral presentation (general)  

Venue：島根  

Event date： 2018.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：愛知  

Event date： 2018.7

Language：English   Presentation type：Oral presentation (general)  

Venue：Honolulu, Hawaii, USA  

Event date： 2018.4

Language：English  

Venue：Singapore   Country：Singapore  

Event date： 2018.4

Language：English  

Venue：Singapore   Country：Singapore  

Event date： 2018.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡  

Event date： 2018.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡  

Event date： 2018.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡  

Event date： 2017.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：新潟  

Event date： 2017.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：新潟   Country：Japan  

Event date： 2017.11

Language：English  

Venue：Pittsburgh, Pennsylvania   Country：United States  

Event date： 2017.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Bio-lake, Wuhan   Country：China  

Event date： 2017.10

Language：English  

Venue：Bio-lake, Wuhan   Country：China  

Event date： 2017.10

Language：English  

Venue：Bio-lake, Wuhan   Country：China  

Event date： 2017.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Bio-lake, Wuhan   Country：China  

Event date： 2017.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡  

Event date： 2017.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：沖縄  

Event date： 2017.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：沖縄  

Event date： 2017.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：沖縄  

Event date： 2017.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：沖縄  

Event date： 2017.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：沖縄  

Event date： 2017.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡  

Event date： 2017.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡  

Event date： 2017.9

Language：English   Presentation type：Oral presentation (general)  

Venue：福岡  

Event date： 2017.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡  

Event date： 2017.9

Language：English  

Venue：Chamonix Mont-Blank   Country：France  

Event date： 2017.4

Language：English  

Venue：Dublin   Country：Ireland  

Event date： 2017.4

Language：English  

Venue：Dublin   Country：Ireland  

Event date： 2017.4

Language：English  

Venue：Dublin   Country：Ireland  

Event date： 2017.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：神奈川  

Event date： 2017.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：岡山  

Event date： 2017.1

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京  

Event date： 2017.1

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京  

Event date： 2016.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京  

Event date： 2016.10

Language：English   Presentation type：Oral presentation (general)  

Venue：福岡  

Event date： 2016.10

Language：English   Presentation type：Oral presentation (general)  

Venue：福岡  

Event date： 2016.10

Language：English  

Venue：福岡  

Event date： 2016.10

Language：English  

Venue：福岡  

Event date： 2016.10

Language：English  

Venue：福岡  

Event date： 2016.10

Language：English  

Venue：福岡  

Event date： 2016.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Honolulu   Country：United States  

Event date： 2016.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡  

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：宮崎  

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：宮崎  

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：宮崎  

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：宮崎  

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：福岡  

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：金沢  

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：金沢  

Event date： 2016.5 - 2016.6

Language：English  

Venue：Vancouver   Country：Canada  

Event date： 2016.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京  

Event date： 2016.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京  

Event date： 2016.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京  

Event date： 2016.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：仙台  

Event date： 2016.1

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京  

Event date： 2016.1

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京  

Event date： 2016.1

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京  

Event date： 2016.1

Language：English  

Venue：San Diego   Country：United States  

Event date： 2015.11

Language：English  

Venue：Daejeon   Country：Korea, Republic of  

Event date： 2015.11

Language：English  

Venue：Daejeon   Country：Korea, Republic of  

Event date： 2015.11

Language：English  

Venue：Daejeon   Country：Korea, Republic of  

Event date： 2015.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡  

Event date： 2015.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡  

Event date： 2015.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡  

Event date： 2015.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：愛知  

Event date： 2015.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：愛知  

Event date： 2015.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：愛知  

Event date： 2015.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：愛知