Evaluation of Directional Dependence of Sensitivity for Room-Temperature Magnetic Flux Sensors With Wide Sensitivity Region

Yoshiaki Adachi,Yasushi Terazono,Yuki Mizuhara

doi:10.1109/tmag.2020.3008912

Yoshiaki Adachi, Yasushi Terazono + Show 1 more

Open Access

https://doi.org/10.1109/tmag.2020.3008912

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Abstract

Recently, the room-temperature (RT) magnetic flux sensors have begun to be applied to biomagnetic measurements. The RT sensors have a large advantage that they can be placed closer to the magnetic sources and obtain larger signals, unlike the superconducting quantum interference device (SQUID) flux sensors. However, when an RT sensor is placed closer to the sources, the dimension of the sensitivity region cannot be negligible, and the directional dependence of sensitivity should be considered to estimate the theoretical magnetic signals for magnetic source analysis. We proposed a method to evaluate the directional dependence of the sensitivity of the RT sensors in response to adjacent magnetic sources using the array of coils arranged along a circular arc. Consequently, it was revealed that a specific magnetoresistance device-based flux sensor with a certain spatial extent had the directional dependence of sensitivity with a bell-shaped profile. We also proposed the multiple sensitivity points model for the bell-shaped profile and estimated the sensitivity distribution over the sensitivity region, which is expected to be effective in improving the accuracy of the magnetic source analysis using an RT sensor array.

Highlights

B IOMAGNETIC measurement is a promising tool for the non-invasive investigation of electric activities in body tissues such as neurons or muscles
We proposed a method to evaluate the directional dependence of the sensitivity of an RT magnetic flux sensor when the magnetic sources are located quite adjacent to the sensor
The specification of the directional dependence of commercially available sensors provided by their manufacturers is often evaluated in a uniform magnetic field and not suited for the biomagnetic applications because the distance between the sensor and the source is quite short and the magnetic field over the sensor sensitivity region cannot be regarded as uniform

Summary

Introduction

B IOMAGNETIC measurement is a promising tool for the non-invasive investigation of electric activities in body tissues such as neurons or muscles. The electric currents generated by these tissues induce weak magnetic fields that can be detected using highly sensitive magnetic flux sensors arranged over the body surface. The electric activities reflect the function of the tissues and provide significant clinical information. The two applications of the biomagnetic measurements magnetoencephalogram and magnetocardiogram that are effective for the non-invasive functional imaging of the brain and heart, respectively, are already commercialized and introduced to hospitals [1]. The magnetic field resolution of the RT sensors is still inferior to the SQUID sensors. The RT sensors have two well-known advantages for biomagnetic measurements other than the non-necessity of cooling. One is the flexibility of the sensor arrangement, and the other is that the sensor can be placed closer to the

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