磁性体の移動に起因する磁気ノイズの考察  [in Japanese] Examination of Magnetic Noises due to Movement of Object Composed of Magnetic Materials  [in Japanese]

For biomagnetic measurements, it is important to understand the characteristics such as frequency dependence, fluctuation, and source of environmental lowfrequency magnetic field noises. Biomagnetic signals, especially magnetoencephalogram and magnetocardiogram signals, always exist in the frequency range below several ten Hz. These signals are very weak in comparison with those of environmental magnetic noises. Such noises at low frequency are generated mainly by the transmitting and return currents of streetcars, movements of automobiles and elevators in geomagnetism, and vibrations of magnetically shielded rooms. In this paper, magnetic noise due to the movement of an object composed of magnetic materils is investigated by using a newly developed method of analysis. That combines the finite element method and an analytical method of calculating the magnetic fields produced by the magnetization in the object. The proposed method is verified by a basic experiment using simple steel boxes.