High-performance magnetically shielded room

An ultrahigh-performance magnetically shielded room was completed as a part of a biomagnetic measuring system using superconducting quantum interference device. From the difference between environmental magnetic noise and a signal, necessary shielding factor was decided to be 1/100000 at low frequencies and 1/1000 at high frequencies. The soccer ball shaped room consists of four layers of permalloy and a layer of aluminum, and provides a space 4 meters in diameter in which magnetic fields are very weak. An independent base was built and the room was fixed rigidly to it. Because permalloy is very sensitive to shocks, the materials for the room were cut in the factory, carried with care, and assembled with screws on site. Xenon lamps supply light via optical fibers and the room is ventilated by way of many small holes in the floor. The door is equipped with the air pressure system.