A shielded facility for low-level magnetic measurements

Abstract

A facility has been constructed for the detection and measurement of time-varying magnetic fields of ∼10-9 G amplitude, in a bandwidth of 0.5 to 100 000 cps. The facility includes a shielded room and magnetic detector, which now consists of a copper coil, eventually to be cooled in liquid helium, feeding a parametric amplifier; it will initially be used to investigate bioelectric current flow in human heart muscles by mapping the time-varying fields outside the body. The shielded room now has two layers of 0.060 in. Moly-Permalloy, and a third inner layer of 0.19 in. aluminum enclosing a 86 in.×88 in.×88 in. volume will soon be installed. Measured shielding factors are given; at present magnetic "shaking" is used to produce a shielding factor of ∼400 in the 0-5 cps range, which rises rapidly with increasing frequency. © 1967 The American Institute of Physics.