Study on High Sensitivity Fluxgate Magnetometer for Measurement of Biomagnetic Information.

磁通门磁力仪具有灵敏度高、噪声低（<10^（-5）> A/m）、结构简单、可靠性高、可直接测量磁场矢量分量等优点，得到了广泛的应用。近年来，心磁图（MCG）等生物磁信息的测量越来越受到人们的关注，本文研究了用磁通门磁强计测量MCG和肺磁场的技术。在这项研究中获得的实验和理论结果如下。(1)在一对磁通门磁力仪中采用差分结构，将地磁起伏等外部噪声场降低到-40 dB，降低比小于<10^（-3）> A/m。采用二阶导数梯度计的双差分结构，降低比提高到-47dB。(2)在约30次平均以减少外部噪声之后，可以通过磁通门磁力计测量MCG。测量MCG的场强在<10^（-5）> A/m的量级。因此，应测量肺的磁场（<10^（-3）> A/m）。(3)由此推断，脑磁图（MEG：<10^（-6）> A/m）可能只能用SQUID测量，而不能用磁通门磁强计测量。

The fluxgate magnetometer has been widely used due to its high sensitivity, low noise performance ( <10^(-5)> A/m), simple construction, high reliability and the capability of directly measuring the vector component of magnetic field. Recently there has been an increasing interest in the measurement of biomagnetic information such as magnetocardiogram(MCG).We have investigated the techniques of the measurements of MCG and magnetic field of the lung using fluxgate magnetometer. Experimental and theoretical results obtained in this study are as follows.(1) External noise field such as the fluctuation of geomagnetic field were reduced to -40 dB in reduction ratio (less than <10^(-3)> A/m) using the differencial structure in a pair of fluxgate magnetometer. Futher, the reduction ratio was improved to -47 dB using the double differencial structuer (second-derivative gradiometer).(2) MCG could be measured by the fluxgate magnetometer after about 30 times averaging for external noise reduction. Measured field strength of MCG was in the order of <10^(-5)> A/m. Consequently, the magnetic field ( <10^(-3)> A/m) of the lung should be measured.(3) It is infered that the magnetoencephalogram(MEG: <10^(-6)> A/m) may be able to measured only by SQUID but not by the fluxgate magnetometer.