Electronic balancing of multichannel SQUID-magnetometers

An electronically balanced three-channel SQUID magnetometer is presented. The electronic balancing reduces the imbalance of the gradiometers by at least a factor of 100. The authors realised in this way an imbalance of 10-5, without the necessity of prebalancing by means of superconducting tabs. Details of the design considerations and the construction of the three-channel system are given, focusing especially on the electronic balancing unit. Some illustrating experiments are also described and the possibilities of electronic balancing discussed