Abstract
We have designed and fabricated a low noise, highTc superconducting quantum interference device (SQUID) magnetometer with animproved yield. In order to reduce the field noise level of the magnetometer, weincreased the voltage modulation depth with a series SQUID array and enhanced theeffective area with a flux focuser. Ten washer-type SQUIDs were connected inseries, thereby increasing the voltage flux transfer function by a factor of 10.An enhancement in effective area by a factor of 5 was achieved by coupling the10-SQUID array to a single-layered flux focuser. For the directly coupled SQUIDarray magnetometer, the yield was improved by selecting the best SQUIDs tohave in series in order to reduce the flux noise. The magnetic field sensitivity of40 fT Hz−1/2 in the whiteregime and 100 fT Hz−1/2 at 1 Hz is demonstrated by using a single layer of highTc film. The proposed high yield magnetometers would be suitable for building low noisemulti-channel magnetocardiographs.
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