Faculty Profiles - KIWA Toshihiko

High-Resolution Laser-Assisted Magnetic Nanoparticle Imaging Using a High-T<inf>C</inf> SQUID Magnetometer

Toshihiko Kiwa, Koji Morita, Yasuaki Matsunaga, Mohd Mawardi Saari, Kenji Sakai, Keiji Tsukada

IEEE Transactions on Applied Superconductivity 27 ( 4 ) 1108 - 1114 2017.6

Language：English Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

© 2017 IEEE. A new type of magnetic nanoparticle imaging (MPI) system has been proposed and developed. The spatial resolution of MPI systems is generally determined and limited by the size of the magnetic sensors used and the magnetic properties of the nanoparticles detected. Here, high-resolution imaging of magnetic particles was realized by combining the MPI system with a high-TC SQUID magnetometer and laser scanning system. The spatial resolution of this system was not determined by the properties of the magnetic nanoparticles but was determined by the laser spot size focused on samples. Thus, the higher spatial resolution imparted by conventional MPI systems could be expected. As a demonstration of the imaging system, two cylindrical containers filled with magnetic particles solutions were fabricated and measured. Although the containers were spaced only 2 mm apart, they could be clearly distinguished by the obtained signals. A knife-edge analysis was also applied to the obtained signals, and the spatial resolution of our system was estimated to be approximately 0.9 mm.

DOI： 10.1109/TASC.2017.2656118

Magnetic characteristics measurements of ethanol-water mixtures using a hybrid-type high-temperature superconducting quantum-interference device magnetometer

Keiji Tsukada, Yasuaki Matsunaga, Ryota Isshiki, Yuta Nakamura, Kenji Sakai, Toshihiko Kiwa

AIP Advances 7 ( 5 ) 158 - 162 2017.5

Language：English Publisher：AMER INST PHYSICS

© 2017 Author(s). The magnetic characteristics of ethanol-water mixtures were investigated using our newly developed hybrid-type magnetometer based on a high-temperature superconducting quantum-interference device. The magnetization (M-H) curves of ethanol-water mixtures show good diamagnetic characteristics. The magnetic moments of the mixture show ethanol concentration dependence. However, the variation in magnetic moment differs from the characteristics expected by considering the magnetic moment ratio between water and ethanol, and volume-reduction rate. It showed two decrement regions separated at approximately 50-60% concentration values. It is also observed that the concentration dependence of the magnetic moment measured using the sample vibration method under a uniform magnetic field and that by the sample rotation method showed slightly different characteristics. These anomalies are attributed to the formation of clustered structures in the mixture.

DOI： 10.1063/1.4973950

Absolute-magnetic-field measurement using nanogranular in-gap magnetic sensor with second-harmonic and liquid-nitrogen-temperature operation

Keiji Tsukada, Takuya Yasugi, Yatsuse Majima, Kenji Sakai, Toshihiko Kiwa

AIP Advances 7 ( 5 ) 1257 - 1264 2017.5

Language：English Publisher：AMER INST PHYSICS

© 2017 Author(s). To detect the absolute magnetic field, such as the earth’s magnetic field, a linear magnetic response, a zero point, and thermal stability are required. We thus propose an operating method and sensor probe consisting of a nanogranular in-gap magnetic sensor (GIGS), an operational amplifier integrated circuit, and a modulation coil. The sensor probe was operated in second-harmonic mode at a liquid-nitrogen (Liq. N2) temperature. When an AC magnetic field was applied to GIGS, the second-harmonic signal was generated and modulated by the outer magnetic field to be measured. After lock-in detection, the modulated output signal showed good linearity and a zero point. Moreover, higher sensitivity and low noise with low thermal fluctuation was obtained by the cooling at Liq. N2 temperature.

DOI： 10.1063/1.4978217

Magnetic method for measuring moisture content using diamagnetic characteristics of water

Tsukada Keiji, Matsunaga Yasuaki, Nakamura Yuta, Isshiki Ryota, Fujimoto Kayo, Sakai Kenji, Kiwa Toshihiko

Measurement Science and Technology 28 ( 1 ) 3477 - 3487 2017.1

Language：English Publisher：IOP PUBLISHING LTD

© 2016 IOP Publishing Ltd. Moisture content measurements of rice kernels and soil are important for agriculture. Therefore, in this study, a new measurement method using the diamagnetic characteristics of water was developed for measurements of the moisture content of rice kernels and soil. The magnetic characteristics of the samples were determined using a magnetometer developed by us based on a superconducting quantum interference device. Because of the diamagnetic characteristics of water, the susceptibility of rice kernels became more negative with increasing moisture content. In the case of soil, which is a mixture of diamagnetic and ferromagnetic materials, a second-harmonic detection method using AC with DC bias magnetic field was applied to reduce the influence of the ferromagnetic signal. The intensity of the second-harmonic signal of a soil was determined to be proportional to its moisture content.

DOI： 10.1088/1361-6501/28/1/014010