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

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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.