Speaker
Description
Magnetization dynamics by pulse excitation in amorphous wire is limited in the surface layer by skin effect due to magnetic rotation. We have constituted highly sensitive linear micro magnetic field sensors utilizing off-diagonal Magneto-Impedance (MI) effect [１]. Recently we have succeeded in producing pico-Tesla ($10^{-8}$ Oe) resolution MI sensors [2] due to ultra-low intrinsic magnetic noise of amorphous wire. Superconducting quantum interference deice (SQUID) have ultrasensitive, which have been utilized for bio-magnetic signals. For example, magnetocardiography (MCG) is a noninvasive technology that measures the magnetic field of the heart. We have tried to measure MCG signal using MI gradiometer. Figure 1 shows magnetic signal at 4 cm left the pit of the stomach. The subject was a man. A distance between from sensor head to a body surface is about 10 mm. The magnetic signal shown was averaged for 20 cycles. The magnetic wave form was well corresponding to the ECG wave form.
Meanwhile, we have also tried MEG (magnetoencephalography) measurements of spontaneous brain activity (alpha rhythm) via pico-tesla resolution MI sensor. It was evaluated that Alpha rhythm have a maximum amplitude of approximately 8 pT, with main frequency components at 9-13 Hz, which depends on state of eye closing or opening.
Fig. 1 MCG signals in averaging over 20 cycles at 25 mm to the left of the pit of the stomach.
Acknowledgements
This work was partly supported by JST A-STEP Grant Number JPMJTR221D, Japan.
References
[1] S. Gudoshnikov, N. Usov, A. Nozdrin, M. Ipatov, A. Zhukov, and V. Zhukova, “Highly sensitive magnetometer based on the off‐diagonal GMI effect in Co‐rich glass‐coated microwire,” physica status solidi (a), vol. 211, no. 5. Wiley, pp. 980–985, Feb. 14, 2014. doi: 10.1002/pssa.201300717.
[2] T. Uchiyama and J. Ma, “Development of pico tesla resolution amorphous wire magneto-impedance sensor for bio-magnetic field measurements,” Journal of Magnetism and Magnetic Materials, vol. 514. Elsevier BV, p. 167148, Nov. 2020. doi: 10.1016/j.jmmm.2020.167148.
