Characteristics and prediction of magnetic noise due to DC electric railcars for biomagnetic measurements

A magnetically shielded room for biomagnetism should be designed taking account of the S/N ratio of the biomagnetic signal to the environmental magnetic noise generated mainly by dc electric railcars at an installed location. This paper describes the characteristics of the fluctuation of magnetic noise and a method of prediction of its amplitude. The distance dependence of the magnetic noise is measured at three locations near railroad by using fluxgate-magnetometers. A decay factor of the magnetic noise vs. the distance from a railroad can be obtained from such a measurement. The decay factors measured are in fairly good agreement with those calculated. The amplitude of the fluctuation of magnetic noise at any distance from the railroad can be easily predicted if the decay factor is measured.