A DOUBLE DC-SQUID BASED MAGNETOMETER

We have developed a double de SQUID based magnetometer with a direct r ead-out circuit and measured its signal and noise characteristics. The inductances of the input SQUID and SQUID-preamplifier were 120 and 25 0 pH. Thin-film flux transformers on the separate substrates had an in ductance of the order of 1 mu H each and a current sensitivity of 0.54 and 0.32 mu A/Phi(0) for the first and the second SQUIDs, respectivel y. The intrinsic energy resolution of the fabricated magnetometer for an optimal gain of 58 for the first stage was close to 1.6x10(-32) J/H z. The dynamic range and the slew rate were about 126 dB and 4x10(4) P hi(0)/s.