New Six-Layer Magnetically-Shielded Room for MEG

Abstract

A high performance magnetically-shielded room (MSR) has been built by Imedco, to house a 4-D MEG system, containing both gradiometers and magnetometers (Vectorview). The MSR consists of three nested enclosures, each consisting of a high-permeability magnetic layer plus an aluminum layer, where special care was given to the junctions of the inner aluminum layer. Measurements of the passive shielding factor yield 1,630 (64dB), 3,600 (71dB), 240,000 (107dB) , and 78,000,000 (158dB) at frequencies of 0.01 Hz, 0.10 Hz, 1.0 Hz, and 10 Hz respectively. Thus, our room is among the very good MSRs. In addition, an active system is being developed, now yielding an extra SF of 6-10 at 0.10 Hz; this needs improvement to reduce new electric train disturbances. Also, we plan to reduce disturbances generated by the inner high-permeability layer when it is mechanically perturbed, for example by walking in the room.