Design, optimization, and construction of a DC SQUID with complete flux transformer circuits

Journal Article · Wed Jun 01 04:00:00 EDT 1988 · J. Low Temp. Phys.; (United States)

DOI:https://doi.org/10.1007/BF00116869· OSTI ID:5947323

Knuutila, J; Kajola, M; Seppae, H; Mutikainen, R; Salmi, J

The design of a complete dc SQUID with a flux transformer input circuit is discussed. 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 authors analysis and practical considerations suggest signal coupling via an intermediary transformer. This 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, they have built a dc SQUID, primarily for use in biomagnetic research, but also well suited for other applications. The fabrication of the SQUID and the high-quality electronics especially suitable for multiple-SQUID devices is presented. The SQUID's showed smooth characteristics, and the lowest measured noise of their complete SQUID is 1.3 /times/ 10/sup /minus 6// /Phi//sub 0///radical/Hz, indicating the success of the design.

• Research Organization: Helsinki Univ. of Technology, Espoo (Finland)
• OSTI ID: 5947323
• Journal Information: J. Low Temp. Phys.; (United States), Journal Name: J. Low Temp. Phys.; (United States) Vol. 71:5-6; ISSN JLTPA
• Country of Publication: United States
• Language: English

Related Subjects

420201* -- Engineering-- Cryogenic Equipment & Devices
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
CAPACITANCE
CURRENTS
DAMPING
DESIGN
DIRECT CURRENT
ELECTRIC COILS
ELECTRIC CURRENTS
ELECTRICAL EQUIPMENT
ELECTRICAL PROPERTIES
ELECTRONIC CIRCUITS
ELECTRONIC EQUIPMENT
EQUIPMENT
EQUIVALENT CIRCUITS
FABRICATION
FLUXMETERS
INDUCTION
INTEGRATED CIRCUITS
JUNCTIONS
MAGNET COILS
MAGNETIC FLUX
MAGNETOMETERS
MATHEMATICAL MODELS
MEASURING INSTRUMENTS
MICROELECTRONIC CIRCUITS
MICROWAVE EQUIPMENT
OPTIMIZATION
PERFORMANCE
PHYSICAL PROPERTIES
RESONANCE
SENSITIVITY
SIGNAL-TO-NOISE RATIO
SQUID DEVICES
SUPERCONDUCTING DEVICES
SUPERCONDUCTING JUNCTIONS