Evaluation of a high-performance magnetically shielded room for biomagnetic measurement

A spherical magnetically shielded room called COSMOS and a method for measuring the shielding factor of well-shielded rooms have been developed. A dc-superconducting quantum interference device is used to detect faint magnetic fields, and the detected signals are averaged to increase the signal-to-noise ratio. The measured magnetic shielding factor for COSMOS is 420000 at 1 Hz.