K. Enpuku et H. Koch, WASHER RESONANCES OF DC SUPERCONDUCTING QUANTUM INTERFERENCE DEVICE COUPLED TO MULTITURN INPUT COIL, JPN J A P 1, 32(9A), 1993, pp. 3811-3816
Properties of washer resonances in dc superconducting quantum interfer
ence devices (SQUIDs) coupled to a multiturn input coil have been stud
ied using an expanded model of the coupled SQUID. The condition of res
istances required to suppress the washer resonance is clarified. In th
e coupled SQUID, junction shunt resistances should be determined by ta
king into account this condition in addition to the conventional condi
tion beta(c) < 1, where beta(c) is the McCumber parameter. In the case
of small junction capacitances, it is shown that the washer resonance
limits the value of junction shunt resistances, and prevents the use
of large resistances given by beta(c) < 1. In order to solve this prob
lem, a new washer geometry of the SQUID is proposed. From the experime
nt using the expanded model of the new washer, it is shown that the ne
w washer can control the washer resonances, and enables the use of lar
ge resistance in the coupled SQUID. Therefore, the new washer will be
useful for the improvement of the performance of the coupled SQUID.