Modelling of the coupling structure of a HTC DC SQUID amplifier

In order to estimate self- and mutual inductances of the input coil and the pick-up loop of a YBCO SQUID amplifier operating at 77K, a simple method b ased on the determination of the current and flux distributions into the su perconductors is presented. The cases of inductors (single loop and spiral) and induced circuits (closed and open loop) are considered, The authors st ress the difference between a SQUID pick-up loop and a directly coupled mag netometer depending upon their action on the input inductance. Finally, the coupling efficiency and the ground plane effect are calculated and measure d for various patterns.