1. |
Teruyoshi Sasayama, Shuji Taue, Takashi Yoshida, AC susceptibility measurement of magnetic nanoparticles using an optically pumped magnetometer and a flux transformer, *AIP Advances*, 10.1063/9.0000634, 14, 015029, 2024.01. |

2. |
Naoya Futagawa, Misaki Fujimoto, Kohta Higashino, Teruyoshi Sasayama, Takashi Yoshida, Imaging of Magnetic Nanoparticles Using AC Susceptibility Data, *IEEE Transactions on Magnetics*, 10.1109/TMAG.2023.3293542, 5101205, 2023.11. |

3. |
Ziwei Guo, Teruyoshi Sasayama, Detection of Surface and Back-Surface Defects on Metal Plate via Rectangular Wave Eddy Current Testing Using Magnetoresistive Sensor, *IEEE Transactions on Magnetics*, 10.1109/TMAG.2023.3279832, 6200505, 2023.11. |

4. |
Ziwei Guo, Teruyoshi Sasayama, Compensate Method for Excitation Field in Rectangular Wave Eddy Current Testing, *Proc. International Symposium on Applied Electromagnetics and Mechanics (ISEM)*, PA-1a: 10, 2023.11. |

5. |
Teruyoshi Sasayama, Shuji Taue, Takashi Yoshida, AC Susceptibility Measurement of Magnetic Nanoparticles Using an Optically Pumped Magnetometer, *Proc. Magnetism and magnetic materials (MMM)*, CS-01, 2023.11. |

6. |
Misaki Fujimoto, Naoya Futagawa, Kohta Higashino, Teruyoshi Sasayama, Takashi Yoshida, Direct Magnetic Field Compensation Circuit for Improved Stability of Magnetic Nanoparticle Tomography, *IEEE Magnetics Society's Xplore Digital Library*, 10.1109/INTERMAG50591.2023.10265073, 2023.10. |

7. |
Yi Sun, Zhongzhou Du, Haochen Zhang, Haozhe Wang, Teruyoshi Sasayama, Takashi Yoshida, Simultaneous estimation of magnetic moment and Brownian relaxation time distributions of magnetic nanoparticles based on magnetic particle spectroscopy for biosensing application, *Nanoscale*, 10.1039/d3nr02860g, 15, 39, 16089-16102, 2023.09. |

8. |
Reiji Okawa, Yuta Takizawa, Shuji Taue, Yukinobu Hoshino, Teruyoshi Sasayama, Single-pixel imaging with optically pumped magnetometer for magnetic particle imaging, *Proc. the Fourteenth Japan-Finland Joint Symposium on Optics in Engineering*, 2023.08. |

9. |
Misaki Fujimoto, Naoya Futagawa, Kohta Higashino, Teruyoshi Sasayama, Takashi Yoshida, Investigation to Improve Stability in Magnetic Nanoparticle Tomography Using Direct Magnetic Field Compensation Circuit, *Proc. Intermag*, YPA-05, 2023.05. |

10. |
Naoya Futagawa, Misaki Fujimoto, Kohta Higashino, Teruyoshi Sasayama, Takashi Yoshida, Imaging of Magnetic Nanoparticle Using Magnetic Particle Spectroscopy Data, *Proc. Intermag*, YPA-03, 2023.05. |

11. |
Ziwei Guo, Teruyoshi Sasayama, Detection of Metal Surface and Back Surface by Rectangular Wave Eddy Current Testing with Magneto Resistive Sensor, *Proc. Intermag*, PPC-02, 2023.05. |

12. |
Haochen Zhang, Yi Sun, Shuya Yamamura, Teruyoshi Sasayama, Takashi Yoshida, Dipolar Interaction Effect on Harmonics in Liner Chain Magnetic Nanoparticles, *Proc. Intermag*, EOB-11, 2023.05. |

13. |
Teruyoshi Sasayama, Ziwei Guo, Signal Enhancement of Rectangular Wave Eddy Current Testing via Compensation using Digital-to-Analog Converter, *International Journal of Applied Electromagnetics and Mechanics*, 10.3233/JAE-220106, 71, S1, S39-S46, 2023.04. |

14. |
Teruyoshi Sasayama, Application of HTS Coil as High Sensitivity Magnetic Sensor to Non-Destructive Testing, *Proceedings of East Asia Symposium on Superconductor Electronics (EASSE)*, 38-38, 2023.03. |

15. |
Teruyoshi Sasayama, Classification of Corrosion Flaws on Front and/or Back Surfaces of Non-magnetic Metal Plates Using a Rectangular Wave Eddy Current Testing System, *Materials Transactions*, 10.2320/matertrans.MT-I2022002, 220-226, 2023.01. |

16. |
Teruyoshi Sasayama, Naoki Okamura, Kohta Higashino, Takashi Yoshida, Improvement in magnetic nanoparticle tomography estimation accuracy by combining sLORETA and non-negative least squares methods, *Journal of Magnetism and Magnetic Materials*, 10.1016/j.jmmm.2022.169953, 563, 169953, 2022.12. |

17. |
Haochen Zhang, Yi Sun, Zhongzhou Du, Teruyoshi Sasayama, Takashi Yoshida, Numerical Study on the Magnetization Characteristics of Chainlike Magnetic Nanoparticles, *IEEE Magnetics Letters*, 10.1109/LMAG.2022.3231819, 64, 3100104, 2022.12. |

18. |
Hiromasa Sasa, Shun Miura, Hiroshi Miyazaki, Teruyoshi Sasayama, Takashi Yoshida, Kaoru Yamamoto, Masataka Iwakuma, Yoshiji Hase, Yuichiro Sasamori, Hirokazu Honda, Masayuki Konno, and Teruo Izumi, Electromagnetic-Thermal Coupled Analysis Considering AC Losses in REBCO Windings at 65 K of 10 MW Fully-Superconducting Synchronous Generators for Electric Aircraft, *IEEE Transactions on Applied Superconductivity*, 32, 6, 5201806, 2022.09. |

19. |
Yuta Okade, Hiroshi Miyazaki, Hiromasa Sasa, Koichi Yoshida, Shun Miura, Teruyoshi Sasayama, Takashi Yoshida, Akifumi Kawagoe, and Masataka Iwakuma, REBCO Trapezoidal Armature Windings for Superconducting Induction Motors, *IEEE Transactions on Applied Superconductivity*, 32, 6, 5201706, 2022.09. |

20. |
Kaito Noda, Hiromasa Sasa, Hiroshi Miyazaki, Shun Miura, Takashi Yoshida, Teruyoshi Sasayama, Masataka Iwakuma, Akifumi Kawagoe, Teruo Izumi, Masayuki Konno, Yuichiro Sasamori, Hirokazu Honda, Yoshiji Hase and Masao Shutoh, Numerical simulation of a high-power density 10 MW REBCO superconducting synchronous generator cooled by sub-cooled LN2 for low AC loss, *Journal of Physics: Conference Series*, 10.1088/1742-6596/2323/1/012037, 240, 012037, 2022.08. |

21. |
Teruyoshi Sasayama, Naoki Okamura, Kohta Higashino, Takashi Yoshida, Estimation Accuracy Improvement Of Magnetic Nanoparticle Tomography By Combining Inverse Solution Methods, *Proc. International Conference on the Scientific and Clinical Applications of Magnetic Carriers*, 2022.06. |

22. |
Teruyoshi Sasayama, Ziwei Guo, Signal Enhancement of Rectangular Wave Eddy-Current Testing by Compensation with D/A Converter, *Proc. International Symposium on Applied Electromagnetics and Mechanics (ISEM)*, 57-58, 2022.06. |

23. |
Kohta Higashino, Naoki Okamura, Teruyoshi Sasayama, Takashi Yoshida, Application of Square-Wave Inverter in Excitation System for Magnetic Nanoparticle Tomography, *AIP Advances*, 10.1063/9.0000266, 12, 3, 035012, 2022.03. |

24. |
Naoki Okamura, Teruyoshi Sasayama, Takashi Yoshida, Inverse Problem Analysis in Magnetic Nanoparticle Tomography using Minimum Variance Spatial Filter, *IEEE Transactions on Magnetics*, 10.1109/TMAG.2021.3078748, 58, 2, 6500305, 2022.02. |

25. |
Kohta Higashino, Naoki Okamura, Teruyoshi Sasayama, Takashi Yoshida, Square-Wave Inverter Excitation for Magnetic Nanoparticle Tomography, *Proc. MMM-Intermag*, IPD-03, 2022.01. |

26. |
K. Enpuku, A. L. Elrefai, J. Gotou, S. Yamamura, T. Sasayama, and T. Yoshida, Difference in AC magnetization between suspended and immobilized magnetic nanoparticles in Néel-relaxation dominant case: Effect of easy axis alignment in suspended nanoparticles, *Journal of Applied Physics*, 10.1063/5.0056481, 130, 11, 113903, 2021.09. |

27. |
Hiromasa Sasa, Masataka Iwakuma, Koichi Yoshida, Seiki Sato, Teruyoshi Sasayama, Takashi Yoshida, Kaoru Yamamoto, Shun Miura, Akifumi Kawagoe, Teruo Izumi, Akira Tomioka, Masayuki Konno, Yuichiro Sasamori, Hirokazu Honda, Yoshiji Hase, Masao Syutoh, Sergey Lee, Shinya Hasuo, Miyuki Nakamura, Takayo Hasegawa, Yuhji Aoki, Takahiro Umeno, Experimental Evaluation of 1 kW-class Prototype REBCO Fully Superconducting Synchronous Motor Cooled by Subcooled Liquid Nitrogen for E-Aircraft, *IEEE Transactions on Applied Superconductivity*, 10.1109/TASC.2021.3055452, 31, 5, 5200706, 2021.08. |

28. |
Naoki Okamura, Teruyoshi Sasayama, Takashi Yoshida, Inverse Problem Analysis in Magnetic Nanoparticle Tomography with Minimum Variance Spatial Filter, *2021 IEEE International Magnetics Conference, INTERMAG 2021*, CQ-04, 2021.04. |

29. |
Ahmed L. Elrefai, Teruyoshi Sasayama, Takashi Yoshida, Keiji Enpuku, AC Magnetization of Immobilized Magnetic Nanoparticles with Different Degrees of Parallel Alignment of Easy Axes, *IEEE Transactions on Magnetics*, 10.1109/TMAG.2020.3024864, 57, 2, 5200105, 2021.02. |

30. |
Teruyoshi Sasayama, Naoki Okamura, Takashi Yoshida, Sensitivity Improvement of Magnetic Nanoparticle Imaging by Compensation with Digital-to-Analog Converter, *IEEE Transactions on Magnetics*, 10.1109/TMAG.2020.3014375, 57, 2, 5300605, 2021.02. |

31. |
Teruyoshi Sasayama, Wataru Yoshimura, Keiji Enpuku, Rectangular wave eddy current testing using for imaging of backside defects of steel plates, *International Journal of Applied Electromagnetics and Mechanics*, 10.3233/JAE-209329, 64, 1-4, 255-262, 2020.12. |

32. |
Lijian Yang, Ping Huang, Shi Bai, Songwei Gao, Teruyoshi Sasayama, An effective method for differentiating inside and outside defects of oil and gas pipelines based on additional eddy current in low-frequency electromagnetic detection technique, *Japanese Journal of Applied Physics*, 10.35848/1347-4065/abaf0c, 59, 9, 096505, 2020.09. |

33. |
Teruyoshi Sasayama, Takashi Yoshida, Keiji Enpuku, Two-dimensional magnetic nanoparticle imaging using multiple magnetic sensors based on amplitude modulation, *Journal of Magnetism and Magnetic Materials*, 10.1016/j.jmmm.2020.166765, 505, 166765, 2020.07, We propose an imaging system for magnetic nanoparticles (MNPs) using multiple magnetic sensors based on amplitude modulation. The system was used to obtain two-dimensional images of two MNP samples spaced 15 mm apart at a depth of 30 mm. An AC magnetic field was used at an operating frequency of 5.4 kHz, and a third-harmonic signal generated by the MNP samples was detected using 16 pickup coils. To increase the position information of the MNP samples, the amplitude of the AC magnetic field was changed from 0.24 to 4.8 mT. The third-harmonic signals were subsequently analyzed using nonnegative least squares to image the MNP samples. The results show that the positions of the two MNP samples were estimated with good accuracy.. |

34. |
Ryota Sugouchi, Hirokazu Honda, Yoshiji Hase, Masao Shuto, Masayuki Konno, Teruo Izumi, Masataka Komiya, Shun Miura, Masataka Iwakuma, Koichi Yoshida, Teruyoshi Sasayama, Takashi Yoshida, Kaoru Yamamoto, Yuichiro Sasamori, Conceptual Design and Electromagnetic Analysis of 2 MW Fully Superconducting Synchronous Motors with Superconducting Magnetic Shields for Turbo-Electric Propulsion System, *IEEE Transactions on Applied Superconductivity*, 10.1109/TASC.2020.2974705, 30, 4, 3601905, 2020.06, With air traffic predicted to increase in the future, CO_{2} 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.. |

35. |
Masataka Komiya, Ryota Sugouchi, Hiromasa Sasa, Shun Miura, Masataka Iwakuma, Takashi Yoshida, Teruyoshi Sasayama, Kaoru Yamamoto, Akira Tomioka, Masayuki Konno, Teruo Izumi, Conceptual Design and Numerical Analysis of 10 MW Fully Superconducting Synchronous Generators Installed with a Novel Casing Structure, *IEEE Transactions on Applied Superconductivity*, 10.1109/TASC.2020.2989746, 30, 4, 5206607, 2020.06. |

36. |
Koichiro Ozaki, Yuma Doi, Koichi Yoshida, Shun Miura, Teruyoshi Sasayama, Takashi Yoshida, Kaoru Yamamoto, Masataka Iwakuma, Akifumi Kawagoe, Akira Tomioka, Masayuki Konno, Teruo Izumi, Conceptual Design of Superconducting Induction Motors Using REBa_{2}Cu_{3}O_{y} Superconducting Tapes for Electric Aircraft, *IEEE Transactions on Applied Superconductivity*, 10.1109/TASC.2020.2971671, 30, 4, 8984315, 2020.06, 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.. |

37. |
Teruyoshi Sasayama, Naoki Okamura, Takashi Yoshida, Sensitivity Improvement of the Imaging of Magnetic Nanoparticle Distribution by Compensation Circuit with D/A Converter, *Proceedings of Joint European Magnetic Symposia (JEMS)*, FS-04, 2020.05. |

38. |
Teruyoshi Sasayama, Low-frequency Eddy current Testing Using a Magneto-impedance Sensor and Flux Transformer, *Proceedings of Joint European Magnetic Symposia (JEMS)*, FS-05, 2020.05. |

39. |
Ahmed L. Elrefai, Teruyoshi Sasayama, Takashi Yoshida, Keiji Enpuku, AC Magnetization of Immobilized Magnetic Nanoparticles with Different Degree of Parallel Alignment of Easy Axes, *Proceedings of Joint European Magnetic Symposia (JEMS)*, CQ-09, 2020.05. |

40. |
Shigeya Yamashita, Masaaki Matsuo, Takashi Yoshida, Teruyoshi Sasayama, Keiji Enpuku, Properties of magnetometer utilizing high-T_{c} superconducting coil and inductance modulation scheme, *Journal of Magnetism and Magnetic Materials*, 10.1016/j.jmmm.2020.166525, 502, 2020.05, 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.. |

41. |
Kazuki Akiyoshi, Takashi Yoshida, Teruyoshi Sasayama, Ahmed L. Elrefai, Misato Hara, Keiji Enpuku, Wash-free detection of biological target using cluster formation of magnetic markers, *Journal of Magnetism and Magnetic Materials*, 10.1016/j.jmmm.2019.166356, 500, 2020.04, 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.. |

42. |
Teruyoshi Sasayama, Takashi Yoshida, Keiji Enpuku, 2D Imaging of Magnetic Nanoparticles using Multiple Pickup Coils and Amplitude Modulation , *Proceedings of International Workshop on Magnetic Bio-Sensing*, P-10, 2019.11. |

43. |
Kazuki Akiyoshi，Takashi Yoshida, Teruyoshi Sasayama, Keiji Enpuku, Wash-Free Detection of C-reactive Protein Utilizing Cluster Formation of Magnetic Markers, *Proceedings of International Workshop on Magnetic Bio-Sensing*, P-3, 2019.11. |

44. |
Shigeya Yamashita, Masaaki Matsuo, Takashi Yoshida, Teruyoshi Sasayama, Keiji Enpuku, Magnetometer Based on Inductance Modulation of High-Tc Superconducting Coil, *Proceedings of International Workshop on Magnetic Bio-Sensing*, P-6, 2019.11. |

45. |
Teruyoshi Sasayama, Keiji Enpuku, Eddy Current Testing Using Square-wave Inverter for Thickness Inspection of Steel Plate, *Sensors and Materials*, 10.18494/SAM.2019.2318, 31, 10, 3023-3032, 2019.10, 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.. |

46. |
Masataka Komiya, Ryota Sugouchi, Hiromasa Sasa, Shun Miura, Masataka Iwakuma, Takashi Yoshida, Teruyoshi Sasayama, Kaoru Yamamoto, Akira Tomioka, Masayuki Konno, Teruo Izumi, Conceptual Design and Numerical Analysis of 10 MW Fully Superconducting Synchronous Generators Installed with a Novel Casing Structure, *31st International Symposium on Superconductivity, ISS 2018
Journal of Physics: Conference Series*, 10.1088/1742-6596/1293/1/012074, 1293, 1, 2019.10, 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%.. |

47. |
Teruyoshi Sasayama , Takashi Yoshida, Keiji Enpuku, Spatial distribution imaging of magnetic nanoparticles using pickup coil array, *Proceedings of Joint European Magnetic Symposia (JEMS)*, P10, 2019.08. |

48. |
Kazuki Akiyoshi , Takashi Yoshida, Teruyoshi Sasayama, Keiji Enpuku, Wash-free detection of biological target utilizing agglomerate formation of magnetic markers, *Proceedings of Joint European Magnetic Symposia (JEMS)*, P14, 2019.08. |

49. |
Shigeya Yamashita , Masaaki Matsuo, Takashi Yoshida, Teruyoshi Sasayama, Keiji Enpuku, Properties of magnetometer utilizing high-Tc superconducting coil and inductance modulation scheme, *Proceedings of Joint European Magnetic Symposia (JEMS)*, P71, 2019.08. |

50. |
Teruyoshi Sasayama , Wataru Yoshimura, Keiji Enpuku, Eddy current testing using square wave excitation current for detection of backside defect of steel plate, *International Symposium on Applied Electromagnetics and Mechanics (ISEM)
*, 36, 2019.08. |

51. |
Masataka Komiya, Takuya Aikawa, Hiromasa Sasa, Shun Miura, Masataka Iwakuma, Takashi Yoshida, Teruyoshi Sasayama, Akira Tomioka, Masayuki Konno, Teruo Izumi, Design Study of 10 MW REBCO Fully Superconducting Synchronous Generator for Electric Aircraft, *IEEE Transactions on Applied Superconductivity*, 10.1109/TASC.2019.2906655, 29, 5, 2019.08, 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 REBa_{2}Cu_{3}O_{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.. |

52. |
Wataru Yoshimura, Teruyoshi Sasayama, Keiji Enpuku, Optimal Frequency of Low-Frequency Eddy-Current Testing for Detecting Defects on the Backside of Thick Steel Plates, *IEEE Transactions on Magnetics*, 10.1109/TMAG.2019.2896590, 55, 7, 2019.07, 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.. |

53. |
Shohei Hamanaga, Takashi Yoshida, Teruyoshi Sasayama, Ahmed L. Elrefai, Keiji Enpuku, Three-dimensional detection of magnetic nanoparticles using a field-free line with weak field gradient and multiple pickup coils, *Japanese Journal of Applied Physics*, 10.7567/1347-4065/ab1950, 58, 6, 2019.05, 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.. |

54. |
Teruyoshi Sasayama, Keiji Enpuku, Low-frequency eddy current testing using HTS coil driven by PWM inverter, *International Journal of Applied Electromagnetics and Mechanics*, 10.3233/JAE-171117, 59, 4, 1275-1282, 2019.03, 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.. |

55. |
Satoshi Ota, Yuki Matsugi, Takeru Nakamura, Ryoji Takeda, Yasushi Takemura, Ichiro Kato, Satoshi Nohara, Teruyoshi Sasayama, Takashi Yoshida, Keiji Enpuku, Effects of size and anisotropy of magnetic nanoparticles associated with dynamics of easy axis for magnetic particle imaging, *Journal of Magnetism and Magnetic Materials*, 10.1016/j.jmmm.2018.11.043, 474, 311-318, 2019.03, 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.. |

56. |
Wataru Yoshimura, Teruyoshi Sasayama, Keiji Enpuku, Optimal Frequency of Low-frequency Eddy Current Testing for Detecting Cracks on the Posterior Side of Steel Plates, *Proc.MMM-Intermag*, AQ-06, 2019.01. |

57. |
Keiji Enpuku, Masaaki Matsuo, Yujiro Yoshida, Shigeya Yamashita, Teruyoshi Sasayama, Takashi Yoshida, Magnetometer Using Inductance Modulation of High-Critical-Temperature Superconducting Coil for Low-Frequency Field Measurement in Presence of Excitation Fields, *IEEE Transactions on Applied Superconductivity*, 10.1109/TASC.2019.2892481, 29, 5, 2019.01, 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.. |

58. |
Wataru Yoshimura, Ryo Tanaka, Teruyoshi Sasayama, Keiji Enpuku, Detection of Slit Defects on Backside of Steel Plate Using Low-Frequency Eddy-Current Testing, *IEEE Transactions on Magnetics*, 10.1109/TMAG.2018.2847729, 54, 11, 2018.11, 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.. |

59. |
Teruyoshi Sasayama, Yuji Gotoh, Keiji Enpuku, Improving tip position-estimation performance of gastric tube by compensating geomagnetic field with offset coils, *IEEE Transactions on Magnetics*, 10.1109/TMAG.2018.2846267, 54, 11, 2018.11, 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.. |

60. |
S. Hamanaga, T. Sasayama, T. Yoshida, K. Enpuku, Three Dimensional Imaging of Magnetic Nanoparticles Utilizing Field Free Line and Multiple Pickup Coils, *Proceedings of International Workshop on Magnetic Bio-Sensing*, P-1, 2018.10. |

61. |
K. Irie, K. Akiyoshi, T. Yoshida, T. Sasayama, K. Enpuku, Wash Free Detection of Biological Target Utilizing Magnetic Markers and MR Sensor, *Proceedings of International Workshop on Magnetic Bio-Sensing*, P-7, 2018.10. |

62. |
A. L. Elrefai, T.Sasayama, T. Yoshida, K. Enpuku, Effect of Viscosity on Harmonic Signals of Magnetic Nanoparticles for Temperature Measurement, *Proceedings of International Workshop on Magnetic Bio-Sensing*, O4-2, 2018.10. |

63. |
Wataru Yoshimura, Teruyoshi Sasayama, Keiji Enpuku, Detection of slit defects on backside of steel plate using low-frequency eddy-current-testing, *2018 IEEE International Magnetic Conference, INTERMAG 2018
2018 IEEE International Magnetic Conference, INTERMAG 2018*, 10.1109/INTMAG.2018.8508192, 2018.10, 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).. |

64. |
Teruyoshi Sasayama, Yuji Gotoh, Keiji Enpuku, Improving tip position estimation accuracy of gastric tube by compensating geomagnetic field with offset coils, *2018 IEEE International Magnetic Conference, INTERMAG 2018
2018 IEEE International Magnetic Conference, INTERMAG 2018*, 10.1109/INTMAG.2018.8508131, 2018.10, 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.. |

65. |
Teruyoshi Sasayama, Keiji Enpuku, Back-Side Flaw Detection of Thick Steel Plate Using Three-Axis MR Sensor, *Proceedings of The Sixth Japan-US NDT Symposium*, 146-151, 2018.07. |

66. |
K. Enpuku, M. Matsuo, Y. Yoshida, S. Yamashita, T. Sasayama, T. Yoshida, Magnetometer based on transfer and modulation of magnetic flux using high-critical-temperature superconductor coils, *30th International Symposium on Superconductivity, ISS 2017
Journal of Physics: Conference Series*, 10.1088/1742-6596/1054/1/012058, 1054, 1, 2018.07, 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.. |

67. |
Keiji Enpuku, Masaaki Matsuo, Yujiro Yoshida, Shigeya Yamashita, Teruyoshi Sasayama, Takashi Yoshida, Low-noise magnetometer based on inductance modulation in high-critical-temperature superconductor coil, *Japanese Journal of Applied Physics*, 10.7567/JJAP.57.060314, 57, 6, 060314, 2018.06, 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.. |

68. |
Ahmed L. Elrefai, Teruyoshi Sasayama, Takashi Yoshida, Keiji Enpuku, Empirical expression for DC magnetization curve of immobilized magnetic nanoparticles for use in biomedical applications, *AIP Advances*, 10.1063/1.5004725, 8, 5, 2018.05, 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.. |

69. |
M. Muta, Y. Tsujita, M. Matsuo, Teruyoshi Sasayama, Takashi Yoshida, Keiji Enpuku, Three-Dimensional Magnetic Particle Imaging Utilizing Multiple Pickup Coils and Field-Free Line, *16th International Superconductive Electronics Conference, ISEC 2017
2017 16th International Superconductive Electronics Conference, ISEC 2017*, 10.1109/ISEC.2017.8314234, 2018-January, 1-3, 2018.03, 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.. |

70. |
Masahiro Muta, Shohei Hamanaga, Naoki Tanaka, Teruyoshi Sasayama, Takashi Yoshida, Keiji Enpuku, Three-dimensional imaging of magnetic nanoparticles using multiple pickup coils and field-free line, *Japanese Journal of Applied Physics*, 10.7567/JJAP.57.023002, 57, 2, 2018.02, 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.. |

71. |
Ahmed Lotfy Elrefai, Teruyoshi Sasayama, Takashi Yoshida, Keiji Enpuku, Empirical Expression for DC Magnetization Curve of Immobilized Magnetic Nanoparticles for Use in Biomedical Applications, *Proc. Magnetism and Magnetics Materials Conference*, CU-04, 2017.11. |

72. |
Teruyoshi Sasayama, Yuji Gotoh, Keiji Enpuku, A Gastric Tube Monitoring System for Clinical Applications, *IEEE Transactions on Magnetics*, 10.1109/TMAG.2017.2714683, 53, 11, 2017.11, 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.. |

73. |
Ahmed L. Elrefai, Teruyoshi Sasayama, Takashi Yoshida, Keiji Enpuku, Magnetic Core-Size Distribution of Magnetic Nanoparticles Estimated from Magnetization, AC Susceptibility, and Relaxation Measurements, *IEEE Transactions on Magnetics*, 10.1109/TMAG.2017.2700480, 53, 11, 2017.11, 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 10^{4} 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.. |

74. |
Keiji Enpuku, Masaaki Matsuo, Teruyoshi Sasayama, Takashi Yoshida, Magnetometer exploiting inductance modulation in coils made of high-critical-temperature superconductor, *Applied Physics Express*, 10.7567/APEX.10.113101, 10, 11, 2017.11, 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.. |

75. |
Teruyoshi Sasayama, Ahmed Lotfy Elrefai, Takashi Yoshida, Keiji Enpuku, Relaxation Measurement System for Magnetic Nanoparticles, *Proceedings of International Workshop on Magnetic Bio-Sensing*, T2-4, 2017.09. |

76. |
Takashi Yoshida, Yuki Matsugi, Takuru Nakamura, Teruyoshi Sasayama, Keiji Enpuku, Magnetic Fractionation of Magnetic Nanoparticles for Magnetic Particle Imaging, *Proceedings of International Workshop on Magnetic Bio-Sensing*, F1-4, 2017.09. |

77. |
Masahiro Muta, S. Hamanaga, N. Tanaka, Teruyoshi Sasayama, Keiji Enpuku, Three-dimensional Imaging of Magnetic Nanoparticles using Multiple Pickup Coils, *Proceedings of International Workshop on Magnetic Bio-Sensing*, P2, 2017.09. |

78. |
Y. Takafuji, K. Irie, K. Akiyoshi, Teruyoshi Sasayama, Takashi Yoshida, Keiji Enpuku, Liquid-Phase Detection of Biomaterial Using Magnetic Markers, *Proceedings of International Workshop on Magnetic Bio-Sensing*, P8, 2017.09. |

79. |
Teruyoshi Sasayama, Keiji Enpuku, Low-Frequency Eddy Current Testing using HTS coil and PWM Inverter, *Proc. International Symposium on Applied Electromagnetics and Mechanics (ISEM)*, SP_159, 2017.09. |

80. |
Teruyoshi Sasayama, Y. Gotoh, Keiji Enpuku, Development and evaluation of tip position estimation system of gastric tube for practical applications, *2017 IEEE International Magnetics Conference, INTERMAG 2017
2017 IEEE International Magnetics Conference, INTERMAG 2017*, 10.1109/INTMAG.2017.8007961, 2017.08, For patients who have difficulty swallowing, naso- or oro-gastric tubes are usually used to deliver nutrients to the stomach.. |

81. |
A. L. Elrefai, Teruyoshi Sasayama, Takashi Yoshida, Keiji Enpuku, Magnetic core-size distribution of magnetic nanoparticles estimated from magnetization, AC susceptibility and relaxation measurements, *2017 IEEE International Magnetics Conference, INTERMAG 2017
2017 IEEE International Magnetics Conference, INTERMAG 2017*, 10.1109/INTMAG.2017.8007882, 2017.08, Magnetic nanoparticles (MNPs) have been widely studied for use in biomedical applications such as magnetic immunoassay, magnetic particle imaging and hyperthermia.. |

82. |
R. Tanaka, T. Sasayama, M. Matsuo, K. Enpuku, Properties of signal caused by the Cracks on the back surface of steel plate in low frequency eddy current testing, *2017 IEEE International Magnetics Conference, INTERMAG 2017
2017 IEEE International Magnetics Conference, INTERMAG 2017*, 10.1109/INTMAG.2017.8007648, 2017.08, Ferromagnetic materials such as steel have high magnetic permeability and a smaller skin depth than non-ferromagnetic materials.. |

83. |
Takashi Yoshida, Yuki Matsugi, Naotaka Tsujimura, Teruyoshi Sasayama, Keiji Enpuku, Thilo Viereck, Meinhard Schilling, Frank Ludwig, Effect of alignment of easy axes on dynamic magnetization of immobilized magnetic nanoparticles, *Journal of Magnetism and Magnetic Materials*, 10.1016/j.jmmm.2016.10.040, 427, 162-167, 2017.04, 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.. |

84. |
Teruyoshi Sasayama, Yuya Tsujita, Manabu Morishita, Masahiro Muta, Takashi Yoshida, Keiji Enpuku, Three-dimensional magnetic nanoparticle imaging using small field gradient and multiple pickup coils, *Journal of Magnetism and Magnetic Materials*, 10.1016/j.jmmm.2016.10.107, 427, 144-150, 2017.04, We propose a magnetic particle imaging (MPI) method based on third harmonic signal detection using a small field gradient and multiple pickup coils. First, we developed a system using two pickup coils and performed three-dimensional detection of two magnetic nanoparticle (MNP) samples, which were spaced 15 mm apart. In the experiments, an excitation field strength of 1.6 mT was used at an operating frequency of 3 kHz. A DC gradient field with a typical value of 0.2 T/m was also used to produce the so-called field-free line. A third harmonic signal generated by the MNP samples was detected using the two pickup coils, and the samples were then mechanically scanned to obtain field maps. The field maps were subsequently analyzed using the nonnegative least squares method to obtain three-dimensional position information for the MNP samples. The results show that the positions of the two MNP samples were estimated with good accuracy, despite the small field gradient used. Further improvement in MPI performance will be achieved by increasing the number of pickup coils used.. |

85. |
Takashi Yoshida, Teruyoshi Sasayama, Keiji Enpuku, Effect of Core Size Distribution of Immobilized Magnetic Nanoparticles on Harmonic Magnetization, *International Journal on Magnetic Particle Imaging*, 3, 1, 1703002, 2017.03. |

86. |
Keiji Enpuku, Yuya Tsujita, Kota Nakamura, Teruyoshi Sasayama, Takashi Yoshida, Biosensing utilizing magnetic markers and superconducting quantum interference devices, *Superconductor Science and Technology*, 10.1088/1361-6668/aa5fce, 30, 5, 2017.03, 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.. |

87. |
Teruyoshi Sasayama, Takashi Yoshida, Keiji Enpuku, Relationship between harmonic spectra and coercive field of immobilized magnetic nanoparticles, *Japanese Journal of Applied Physics*, 10.7567/JJAP.56.025001, 56, 2, 2017.02, 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 H_{0}. First, we measured the dependences of the coercive field 〈H_{c}〉 on f and H_{0}. 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.. |

88. |
Takashi Yoshida, Yuki Matsugi, Teruyoshi Sasayama, Keiji Enpuku, Effect of Alignment of Magnetic Easy Axes on AC Magnetization of Immobilized Magnetic Nanoparticles, *Proceedings of International Workshop on Magnetic Bio-Sensing*, 2016.10. |

89. |
Yuya Tsujita, Masahiro Muta, Teruyoshi Sasayama, Keiji Enpuku, Three-Dimensional Detection of Magnetic Nanoparticles Using Small Field Gradient and Multiple Pickup Coils, *Proceedings of International Workshop on Magnetic Bio-Sensing*, 2016.10. |

90. |
Kazushi Yamamoto, Teruyoshi Sasayama, Takashi Yoshida, Masaaki Matsuo, Keiji Enpuku, System Development for Single-Sided Magnetic Particle Imaging Using Electric Scanning of Field Free Point, *Proceedings of International Workshop on Magnetic Bio-Sensing*, 2016.10. |

91. |
Yuki Matsugi, Teruyoshi Sasayama, Takashi Yoshida, Keiji Enpuku, Evaluation of Harmonic Spectrum of Magnetic Nanoparticles for Magnetic Particle Imaging, *Proceedings of International Workshop on Magnetic Bio-Sensing*, 2016.10. |

92. |
Kota Nakamura, Yoshitsugu Takafuji, Teruyoshi Sasayama, Takashi Yoshida, and Keiji Enpuku, Highly Sensitive Liquid-Phase Immunoassays Using Brownian Relaxation of Magnetic Markers, *Proceedings of International Workshop on Magnetic Bio-Sensing*, 2016.10. |

93. |
Teruyoshi Sasayama, Takashi Yoshida, Keiji Enpuku, Harmonic Signals of Immobilized Magnetic Nanoparticles for Magnetic Particle Imaging, *Proceedings of International Workshop on Magnetic Bio-Sensing*, 2016.10. |

94. |
Takashi Yoshida, Teruyoshi Sasayama, Keiji Enpuku, Biological Applications of Magnetic Nanoparticles for Magnetic Immunoassay and Magnetic Particle Imaging - for magnetic immunoassay and magnetic particle imaging -, *ECS Transactions*, 75, 2, 39-47, 2016.10. |

95. |
Teruyoshi Sasayama, Tomoki Ishida, Masaaki Matsuo, Keiji Enpuku, Thickness Measurement of an Iron Plate Using Low-Frequency Eddy Current Testing with an HTS Coil, *IEEE Transactions on Applied Superconductivity*, 10.1109/TASC.2016.2535366, 26, 5, 9001305, 2016.08, We applied low-frequency eddy current testing (ECT) using a high-temperature superconducting (HTS) coil in order to measure the thickness of an iron plate. Using this method, we measured changes in coil impedance when the iron plate was placed below the coil. Although low-frequency measurements were necessary to avoid the skin effect, changes in coil impedance became very small at low frequencies. For this reason, an HTS coil was used in order to sensitively measure these small changes. First, changes in the inductance L and the resistance R of the coil were measured when the iron plate was positioned 18 mm below the HTS coil, and the thickness of the plate was changed in increments from 6 to 22 mm. The results show that we were able to estimate the thickness of the plate up to 22 mm based on the changes in R when an excitation frequency of 4 Hz was used. Next, the effect of the liftoff between the iron plate and the HTS coil on the changes in L and R was studied while the liftoff was changed from 18 to 28 mm. The results show that the liftoff could be estimated from the changes in L. We were therefore able to determine the liftoff and the thickness of the iron plate by measuring changes in L and R, respectively. Results obtained from numerical simulation using the finite-element method were in agreement with the experimental results.. |

96. |
Teruyoshi Sasayama, Yuya Tsujita, Manabu Morishita, Masahiro Muta, Keiji Enpuku, Three-Dimensional Magnetic Nanoparticle Imaging Using a Small Gradient Field and Multiple Pickup Coils, *11th International Conference on the Scientific and Clinical Applications of Magntic Carriers*, 113, 2016.06. |

97. |
Masakazu Ura, Kohei Noguchi, Yuta Ueoka, Kota Nakamura, Teruyoshi Sasayama, Takashi Yoshida, Keiji Enpuku, Improved liquid-phase detection of biological targets based on magnetic markers and high-critical-temperature superconducting quantum interference device, *IEICE Transactions on Electronics*, 10.1587/transele.E99.C.669, E99C, 6, 669-675, 2016.06, 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.. |

98. |
K. Enpuku, T. Sasayama, T. Yoshida, Estimation of magnetic moment and anisotropy energy of magnetic markers for biosensing application, *Journal of Applied Physics*, 10.1063/1.4948951, 119, 18, 2016.05, 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.. |

99. |
Kazuhiro Tanabe, Shi Bai, Kazushi. Yamamoto, Teruyoshi Sasayama, Takashi Yoshida, Keiji Enpuku, Planar Gradient Coil and Electric Scanning of Field Free Point for Single-Sided Magnetic Particle Imaging, *Proc.MMM-Intermag*, AW-09, 2016.01. |

100. |
Takashi Yoshida, Teruyoshi Sasayama, Keiji Enpuku, Biological Applications of Magnetic Nanoparticles for Magnetic Immunoassay and Magnetic Particle Imaging - for magnetic immunoassay and magnetic particle imaging -, *ECS Transactions*, 75, 2, 39-47, 2016.01. |

101. |
Teruyoshi Sasayama, Yusuke Yanamoto, Shunsuke Funaji, Takahiro Ao, Experimental and simulation study on inductance and equivalent resistance using equivalent circuit model and finite element method, *IEEJ Journal of Industry Applications*, 10.1541/ieejjia.5.392, 5, 5, 392-397, 2016.01, 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.. |

102. |
Tomoki Ishida, Teruyoshi Sasayama, Masaaki Matsuo, Keiji Enpuku, Measurement of iron-plate thickness using HTS coil, *15th International Superconductive Electronics Conference, ISEC 2015
2015 15th International Superconductive Electronics Conference, ISEC 2015*, 10.1109/ISEC.2015.7383469, SQ-P07, 2016.01, 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.. |

103. |
M. Ura, Y. Ueoka, K. Noguchi, K. Nakamura, T. Sasayama, T. Yoshida, K. Enpuku, New detection method of biological targets based on HTS SQUID and magnetic marker, *15th International Superconductive Electronics Conference, ISEC 2015
2015 15th International Superconductive Electronics Conference, ISEC 2015*, 10.1109/ISEC.2015.7383474, SQ-P06, 2016.01, 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^{-19}mol/ml, indicating the high sensitivity of the present method.. |

104. |
Takashi Yoshida, N. Tsujimura, K. Tanabe, Teruyoshi Sasayama, Keiji Enpuku, Evaluation of Complex Harmonic Signals from Magnetic Nanoparticles for Magnetic Particle Imaging, *IEEE Transactions on Magnetics*, 10.1109/TMAG.2015.2441750, 51, 11, 5101704, 2015.11, 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.. |

105. |
Teruyoshi Sasayama, Takashi Yoshida, Kazuhiro Tanabe, Naotaka Tsujimura, Keiji Enpuku, Hysteresis Loss of Fractionated Magnetic Nanoparticles for Hyperthermia Application, *IEEE Transactions on Magnetics*, 10.1109/TMAG.2015.2438080, 51, 11, 5101504, 2015.11, 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.. |

106. |
Teruyoshi Sasayama, Yuji Gotoh, Keiji Enpuku, Improving Estimation Accuracy of Nasogastric Tube Tip Position Using Predata, *IEEE Transactions on Magnetics*, 10.1109/TMAG.2015.2438858, 51, 11, 5101604, 2015.11, 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 |

107. |
S. Bai, A. Hirokawa, K. Tanabe, Teruyoshi Sasayama, Takashi Yoshida, Keiji Enpuku, Narrowband Magnetic Particle Imaging Utilizing Electric Scanning of Field Free Point, *IEEE Transactions on Magnetics*, 10.1109/TMAG.2015.2438029, 51, 11, 5101404, 2015.11, 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 mm^{2}. 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.. |

108. |
Shi Bai, Aiki Hirokawa, Kazuhiro Tanabe, Teruyoshi Sasayama, Takashi Yoshida, Keiji Enpuku, Narrow-Band Magnetic Particle Imaging using Orthogonal Gradient Field, *Journal of the Magnetics Society of Japan*, 39, 5, 216-219, 2015.09. |

109. |
Manabu Morishita, Takashi Miyazaki, Yuya Tsujita, Teruyoshi Sasayama, Keiji Enpuku, Narrowband Magnetic Particle Imaging Using Cooled Pickup Coil and Third Harmonic Detection, *Proc. ISEC*, SQ-P05, 2015.07. |

110. |
Teruyoshi Sasayama, Y. Yanamoto, S. Funaji, T. Ao, Comparison of experiment and simulation results for inductance and equivalent resistance obtained using multi-port transformer model and FEM, *2015 IEEE International Magnetics Conference, INTERMAG 2015
2015 IEEE International Magnetics Conference, INTERMAG 2015*, 10.1109/INTMAG.2015.7156803, 2015.07, 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].. |

111. |
T. Yoshida, N. Tsujimura, K. Tanabe, T. Sasayama, K. Enpuku, Evaluation of complex harmonic signals from magnetic nanoparticles for magnetic particle imaging, *2015 IEEE International Magnetics Conference, INTERMAG 2015
2015 IEEE International Magnetics Conference, INTERMAG 2015*, 10.1109/INTMAG.2015.7157571, 2015.07, 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].. |

112. |
Teruyoshi Sasayama, Takashi Yoshida, K. Tanabe, N. Tsujimura, Keiji Enpuku, Hysteresis loss of fractionated magnetic nanoparticles for hyperthermia application, *2015 IEEE International Magnetics Conference, INTERMAG 2015
2015 IEEE International Magnetics Conference, INTERMAG 2015*, 10.1109/INTMAG.2015.7157196, 2015.07, 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].. |

113. |
Teruyoshi Sasayama, Y. Gotoh, Keiji Enpuku, Improving estimation accuracy of nasogastric tube tip position using pre data, *2015 IEEE International Magnetics Conference, INTERMAG 2015
2015 IEEE International Magnetics Conference, INTERMAG 2015*, 10.1109/INTMAG.2015.7157195, 2015.07, 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].. |

114. |
K. Saito, T. Sasayama, M. Nakano, Measurement of hysteresis loop at the tip of the teeth of an inverter-driven squirrel-cage induction motor, *2015 IEEE International Magnetics Conference, INTERMAG 2015
2015 IEEE International Magnetics Conference, INTERMAG 2015*, 10.1109/INTMAG.2015.7157771, 2015.07, 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.. |

115. |
Kanade Saito, Teruyoshi Sasayama, Masanori Nakano, Measurement of Hysteresis Loop at the Tip of the Teeth of an Inverter-Driven Squirrel-cage Induction Motor, *Proc. Intermag*, HX-03, 2015.05. |

116. |
Teruyoshi Sasayama, Takashi Yoshida, Kazuhiro Tanabe, Naotaka Tsujimura, Keiji Enpuku, Hysteresis Loss of Fractionated Magnetic Nanoparticles for Hyperthermia Application, *Proc. Intermag*, EV-05, 2015.05. |

117. |
Teruyoshi Sasayama, Yuji Gotoh, Keiji Enpuku, Improving Estimation Accuracy of Nasogastric Tube Tip Position using Pre Data, *Proc. Intermag*, EV-04, 2015.05. |

118. |
Teruyoshi Sasayama, Yusuke Yanamoto, Shunsuke Funaji, Takahiro Ao, Comparison of Experiment and Simulation Results for Inductance and Equivalent Resistance Obtained using Multi-port Transformer Model and FEM, *Proc. Intermag*, BW-14, 2015.05. |

119. |
Shi Bai, Aiki Hirokawa, Kazuhiro Tanabe, Teruyoshi Sasayama, Takashi Yoshida, Keiji Enpuku, Narrowband Magnetic Particle Imaging Utilizing Electric Scanning of Field Free Point, *Proc. Intermag*, BI-04, 2015.05. |

120. |
Takashi Yoshida, Naotaka Tsujimura, Kazuhiro Tanabe, Teruyoshi Sasayama, Keiji Enpuku, Evaluation of Complex Harmonic Signals from Magnetic Nanoparticles for Magnetic Particle Imaging, *Proc. Intermag*, GV-02, 2015.05. |

121. |
M. M. Saari, K. Sakai, T. Kiwa, T. Sasayama, T. Yoshida, K. Tsukada, Characterization of the magnetic moment distribution in low-concentration solutions of iron oxide nanoparticles by a high- T _{c} superconducting quantum interference device magnetometer, *Journal of Applied Physics*, 10.1063/1.4919043, 117, 17, 17B321, 2015.05, 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.. |

122. |
Teruyoshi Sasayama, Takashi Yoshida, M. M. Saari, Keiji Enpuku, Comparison of volume distribution of magnetic nanoparticles obtained from M-H curve with a mixture of log-normal distributions, *Journal of Applied Physics*, 10.1063/1.4919268, 117, 17, 17D155, 2015.05, 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/m^{3} and 1×10-9 s, respectively, for Resovist MNPs.. |

123. |
Keiji Enpuku, Takashi Miyazaki, Manabu Morishita, Yuya Tsujita, Masaaki Matsuo, Shi Bai, Teruyoshi Sasayama, Takashi Yoshida, Narrowband magnetic nanoparticle imaging using cooled pickup coil and gradient field, *Japanese Journal of Applied Physics*, 10.7567/JJAP.54.057002, 54, 5, 057002, 2015.01, 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.. |

124. |
Teruyoshi Sasayama, Yusuke Yanamoto, Shunsuke Funaji, Takahiro Ao, Theoretical and numerical examination of equivalent resistances in zone-control induction heating system, *IEEJ Journal of Industry Applications*, 10.1541/ieejjia.4.67, 4, 1, 67-73, 2015.01, 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.. |

125. |
Teruyoshi Sasayama, Takashi Yoshida, Mohd Mawardi Saari, Keiji Enpuku, Comparison of Volume Distribution of Magnetic Nanoparticles Obtained from M-H Curve with a Mixture of Log-normal Distributions, *Proceedings of 59th Annual Magnetism and Magnetics Materials Conference*, EU-06, 2014.11. |

126. |
Teruyoshi Sasayama, Yuji Gotoh, Keiji Enpuku, Application of minimum variance beamformer for estimation of tip position of a nasogastric tube, *IEEE Transactions on Magnetics*, 10.1109/TMAG.2014.2328651, 50, 11, 5101404, 2014.11, 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.. |

127. |
Teruyoshi Sasayama, Masataka Morita, Masanori Nakano, Experimental study on effect of load on iron loss of an electrical steel sheet under PWM inverter excitation, *IEEE Transactions on Magnetics*, 10.1109/TMAG.2014.2331358, 50, 11, 6000504, 2014.11, 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.. |

128. |
Keiji Enpuku, Shi Bai, Aiki Hirokawa, Kazuhiro Tanabe, Teruyoshi Sasayama, Takashi Yoshida, The effect of Neel relaxation on the properties of the third harmonic signal of magnetic nanoparticles for use in narrow-band magnetic nanoparticle imaging, *Japanese Journal of Applied Physics*, 10.7567/JJAP.53.103002, 53, 10, 103002, 2014.10, 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.. |

129. |
Teruyoshi Sasayama, Masataka Morita, Masanori Nakano, Experimental study on effect of load on iron loss of electrical steel sheet under PWM inverter excitation, *Proc. Intermag*, BV-02, 2014.05. |

130. |
Teruyoshi Sasayama, Yusuke Yanamoto, Shunsuke Funaji, Takahiro Ao, A practical method to calculate self- and mutual-inductance and equivalent resistance for a zone-control induction heating system, *Proc. Intermag*, AP-08, 2014.05. |

131. |
Teruyoshi Sasayama, Yuji Gotoh, Keiji Enpuku, Application of minimum variance beamformer for estimation of tip position of a nasogastric tube, *Proc. Intermag*, EW-01, 2014.05. |

132. |
Teruyoshi Sasayama, Yusuke Yanamoto, Norio Takahashi, Naoki Uchida, Takahiro Ao, Keiji Kawanaka, Nobuyasu Matsunaka, Proposal of Concept of Theoretical Formula for Equivalent Resistances for Zone-Control Induction Heating System and Theoretical and Numerical Examination, *Proc. Compumag*, PA6-1, 2013.06. |

133. |
Yusuke Yanamoto, Teruyoshi Sasayama, Norio Takahashi, Naoki Uchida, Takahiro Ao, Keiji Kawanaka, Nobuyasu Matsunaka, Examination on Equivalent Resistance and Coupling Coefficient of Zone-Control Induction Heating by Finite Element Method, *Proc. Compumag*, PA6-16, 2013.06. |

134. |
Norio Takahashi, Shuhei Okamura, Teruyoshi Sasayama, Yoshihiro Yamagami, Optimization of 3-D magnetic circuit of linear oscillatory actuator for diaphragm blower, *IEEE Transactions on Magnetics*, 10.1109/TMAG.2013.2238900, 49, 5, 2125-2128, 2013.05, 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).. |

135. |
Takayuki Okimura, Teruyoshi Sasayama, Norio Takahashi, Soichiro Ikuno, Parallelization of finite element analysis of nonlinear magnetic fields using GPU, *IEEE Transactions on Magnetics*, 10.1109/TMAG.2013.2244062, 49, 5, 1557-1560, 2013.05, 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.. |

136. |
Shuhei Okamura, Teruyoshi Sasayama, Norio Takahashi, Yoshihiro Yamagami, 3D Optimization of Magnetic Circuit of Linear Oscillatory Actuator of Diaphragm Blower, *Proc. Biennial IEEE Conference on Electromagnetic Field Computation (CEFC2012)*, 87-87, 2012.11. |

137. |
Teruyoshi Sasayama, Tetsuo Kobayashi, Movement-imagery brain-machine interface: EEG classification of beta rhythm synchronization based on cumulative distribution function, *IEICE Transactions on Information and Systems*, 10.1587/transinf.E94.D.2479, E94-D, 12, 2479-2486, 2011.12, 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 |

138. |
Teruyoshi Sasayama, Shoji Hamada, Tetsuo Kobayashi, Application of linearly-constrained prewhitening beamformer to reconstruction of highly correlated EEG signal sources, *2011 5th IEEE/ICME International Conference on Complex Medical Engineering, CME 2011
2011 IEEE/ICME International Conference on Complex Medical Engineering, CME 2011*, 10.1109/ICCME.2011.5876810, 593-598, 2011.07, 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.. |

139. |
Teruyoshi Sasayama, Tomoaki Iida, Takenori Oida, Shoji Hamada, Tetsuo Kobayashi, Construction of human head voxel models from MR images for EEG analysis based on EM algorithm, *2010 IEEE/ICME International Conference on Complex Medical Engineering, CME2010
2010 IEEE/ICME International Conference on Complex Medical Engineering, CME2010*, 10.1109/ICCME.2010.5558863, 100-105, 2010.10, 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.. |

140. |
Teruyoshi Sasayama, Jiuk. Jung, Tetsuo Kobayashi, Classifiers of EEG beta rhythms between right and left wrist-bending hand movements and their imageries, *Proc. 18th International Congress on Brain*, 167-170, 2009.10. |

141. |
Hirokazu Kawaguchi, Teruyoshi Sasayama, Jiuk Jung, Takenori Oida, Tetsuo Kobayashi, Spatial filtering of steady-state samatosensory evoked potentials toward the development of brain-machine interface, *Proc. 18th International Congress on Brain*, 175-178, 2009.10. |

142. |
T. Sasayama, T. Iida, J. Jung, and T. Kobayashi, Discrimination between right and left hand movements, *Proc. 2008 ICME International Conference on Complex Medical Engineering*, 109-112, 2008.05. |