A low-cost magnetic shield consisting of nonoriented silicon steel

This paper presented a double cylindrical magnetic shield with nonoriented silicon steel plate rings. The total weight of cylinders was about 14 kg, and its corresponding material cost was less than 50 USD. A relatively low magnetic noise of 2 pT/Hz/sup -1/2/ at 10 Hz and 20 pT/Hz/sup -1/2/ at 1 Hz was measured with a HTS dc-SQUID sensor inside the shield. The transverse shielding factor was measured with a fluxgate sensor, and the value was about 500 when the ranges of frequency and amplitude were 10 Hz-1 kHz and 100 nT-10 /spl mu/T. The value dramatically improved to as high as 20 000 by magnetic shaking enhancement. If magnetic shaking was not applied to the inner cylinder, this cylinder would reduce the leakage field of the magnetic shaking from the outer cylinder to less than 300 nT. The cost performance of the multicylindrical shield was also discussed. To provide the most outer cylinder with magnetic shaking allowed the cost performance to be twice as good as cylinders that did not use magnetic shaking.