Development of semi-portable DC-SQUID magnetometer

A semi-portable DC-SQUID magnetometer with a liquid helium continuous flow cryostat has been developed. The cryostat is 340 mm long and 50 mm in outer diameter. The pick-up coil is a co-axial, first order, differential type, 20 mm in diameter and 30 mm in baseline. The distance between the pick-up coil and the outer surface of the cryostat is 5 mm. It is easy to set this cryostat on the chest wall or on a human head. The cool down time is about 20 minutes, which is much shorter than that for a conventional storage Dewar. The white noise level, measured in a magnetically shielded room, is 8.7 fT//spl radic/Hz at 30 Hz. Noise at 1 Hz is about 30 fT//spl radic/Hz. Noise from temperature fluctuations (<9 mK) and drift (4.22 K /spl sim/ 4.55 K) is negligible. The consumption rate of liquid helium is 10 l/h. Here, the authors show the measurement of a magnetocardiogram in a magnetically shielded room.<
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