Dual bias current operation of 2-SQUID directly coupled magnetometers

High-T-c directly coupled magnetometers made from thin films of single laye r YBa2Cu3Oy deposited on bicrystal substrates were investigated. A series 2 -SQUID structure with a common pickup coil was designed to increase voltage modulation depth (DeltaV), A second bias current was introduced to compens ate for the disagreement between the two optimal bias currents and the volt age peak positions. The distribution of the second bias current was control led by selecting the proper electrodes formed on the pickup roil, thus elim inating the difference in the voltage peak positions. The value of DeltaV w as doubled. The white noise in the magnetometer decreased by using this 2-S QUID design, but the low-frequency noise increased slightly, In addition, a nother type of the 2-SQUID magnetometer was proposed, This magnetometer has SQUIDs with different inductances. The overlapped V-Phi curve showed the m odulation beat caused by the difference in V-Phi periodicity, and a high De ltaY was observed at several Phi (0) intervals.