LTS SQUID sensor with a new configuration

We have developed highly sensitive SQUID-based magnetometers and gradiometers, fabricated in a standard Nb/AlO X /Nb technology. The SQUID itself is designed as a current sensor having an input coil and a feedback coil. The number of turns of the input coil can be adjusted to ensure optimal coupling to the pickup loops with an inductance in the range from 5 nH to 300 nH. Several types of planar pickup loop configurations have been realized. The magnetometer has a pickup loop with a size of 1 cm × 1 cm. With a typical white noise level better than 4 µ 0 Hz -1/2 and an effective area of 2.6 mm 2 a field resolution of 3.2 fT Hz -1/2 results for the magnetometer. Two loops connected in series with an area of 2 cm × 2 cm each and a baseline of 4 cm were used in the gradiometer. We measured a 7.5 mm 2 effective area for each loop and a field gradient resolution of 36 fT m -1 Hz -1/2 corresponding to a field resolution in the loop of 1.6 fT Hz -1/2 .