A 35-SERIES SUPERCONDUCTING QUANTUM INTERFERENCE DEVICE ARRAY FOR HIGH-DYNAMIC-RANGE MAGNETIC MEASUREMENTS

A 35-Series Superconducting Quantum Interference Device Array has been developed for a magnetometer with a high dynamic range. The coherence of each SQUID was observed in a double-shielded tube made of cryoperm and lead; a maximum voltage swing of 2 mV and flux noise of 0.6 mu Ph i(0)/root Hz were obtained. The nonuniform inductance of the SQUIDs in the array, which causes Phi-V curve modulation, is decreased by using dummy SQUIDs at each end of the array. A gradiometer for biomagnetic measurement was constructed using a 35-SQUID array and a 10 x 10-mm pl anar pick-up coil. A magnetic-field sensitivity of 5.4 fT/root Hz, a m aximum slew rate of 1.9 mT/s, and a maximum feedback amplitude of +/-2 .23 mu T were achieved by using a direct-coupled Bur-locked-loop circu it. The dynamic range of the magnetometer input field was +/-4.13 x 10 (8) root Hz.