The design of a complete dc Superconducting Quantum Interference Device (SQUID) with a flux transformer input circuit is described. The flux coupling circuits introduce a substantial capacitance across the SQUID and give rise to many resonances which may couple strongly to the SQUID dynamics. Both effects lead to multiple modes in the SQUID dynamics and, consequently, to excess noise. For a low-noise SQUID with smooth characteristics, the analysis and practical considerations suggest signal coupling via an intermediary transformer. The method allows simultaneous optimization of the SQUID parameters, minimizing the parasitic capacitance, control over the resonances, and good inductance matching to practical magnetometer coils. A model is developed to optimize the structure; it describes the whole circuit with the help of a suitably modified autonomous SQUID, provided that the system is free from multiple modes due to resonances or large parasitic capacitance. Following these design principles, a dc SQUID was built. The fabrication of the SQUID and the high-quality electronics especially suitable for multiple-SQUID devices is presented.
NASA STI/Recon Technical Report N
- Pub Date:
- October 1987
- Design Analysis;
- Noise Reduction;
- Squid (Detectors);
- Electronics and Electrical Engineering