A 35-Series Superconducting Quantum Interference Device Array for High-Dynamic-Range Magnetic Measurements

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Abstract
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 µΦ0/√ Hz were obtained. The nonuniform inductance of the SQUIDs in the array, which causes Φ–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 10×10-mm planar pick-up coil. A magnetic-field sensitivity of 5.4 fT/√ Hz, a maximum slew rate of 1.9 mT/s, and a maximum feedback amplitude of ±2.23 µ T were achieved by using a direct-coupled flux-locked-loop circuit. The dynamic range of the magnetometer input field was ±4.13×108 √ Hz.

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