Monolithic flux transformer-coupled high-T/sub c/ DC SQUID magnetometers

YBa/sub 2/Cu/sub 3/O/sub 7-x/ based monolithic flux transformer-coupled high-T/sub c/ DC SQUID magnetometers operating up to 73 K have been realized. The devices are characterized by high values of the modulation voltage, up to 32 /spl mu/V at 40 K. A minimal white noise level of 0.10 pT//spl radic/Hz was obtained above 200 Hz, and 0.64 pT//spl radic/Hz at 1 Hz and 55 K. The temperature dependence of the modulation voltage, the effective sensing area and the field sensitivity are discussed. Model-calculations have been performed to investigate high frequency resonances in the washer-input coil structure. Methods for damping are considered.<
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