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RF Properties of the Coupling Circuit between dc SQUID and Multiturn Input Coil
Keiji ENPUKU Toshihiro TANAKA Keiji YOSHIDA
IEICE TRANSACTIONS on Electronics
Publication Date: 1991/07/25
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Issue on Low Temperature Electronics)
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Rf properties of the coupling circuit between the dc SQUID and the multiturn input coil have been studied in order to investigate the origin of the degradation of the SQUID characteristics due to the input coil. It is pointed out that rf properties of the coupling circuit become important due to the existence of the rf currents generated from Jasephson junctions. The rf properties of the coupling circuit have been measured by using the expanded model of the circuit with Cu electrodes. We observe that resonant structures appear in rf properties of the coupling circuit. This means that the SQUID coil coupled to the input coil can not be expressed by a simple inductance, as is not the case of the isolated SQUID. It is shown that the resonant structures result from the standing wave occurring in the coupling circuit. It is also shown that the resonant structures can be suppressed with the damping resistors. Based on the experimental results, a circuit model of the coupling circuit is obtained, which explains well the experimental results. The obtained results are useful to study the effect of the input coil on SQUID characteristics.