Effects on dc SQUID characteristics of damping of input coil resonances

Journal Article · Sat Aug 01 00:00:00 EDT 1987 · J. Low Temp. Phys.; (United States)

DOI:https://doi.org/10.1007/BF00683902· OSTI ID:5915292

Knuutila, J; Ahonen, A; Tesche, C

The possibility of improving dc SQUID performance by damping the input circuit resonances caused by parasitic capacitances is studied experimentally. A high-quality dc SQUID was coupled to a first-order axial gradiometer built for neuromagnetic research, and a resistor-capacitor shunt was connected in parallel with the input coil of the SQUID. Ten different RC shunts were studied with the SQUID operating in a flux-locked loop, carefully shielded against external disturbances. It was found that increasing the shunt resistance resulted in smoother flux-voltage characteristics and smaller noise. At best, the minimum obtainable equivalent flux noise level was one-fourth that for the unshunted SQUID. The noise level is a function of the shunt resistance R/sub s/ only, except for shunt capacitance values bringing the low-frequency resonance of the input coil close to the flux modulation frequency. At a constant bias current level, where the amplitude of the flux-voltage characteristics is at maximum, the equivalent flux noise varies as R/sub s//sup -0.7/. The results agree reasonably well with recently published predictions based on numerical simulations where the whole input circuit with parasitic capacitances was taken into account.

• Research Organization: Helsinki Univ. of Technology, Espoo, Finland
• OSTI ID: 5915292
• Journal Information: J. Low Temp. Phys.; (United States), Journal Name: J. Low Temp. Phys.; (United States) Vol. 68:3-4; ISSN JLTPA
• Country of Publication: United States
• Language: English

Related Subjects

420201* -- Engineering-- Cryogenic Equipment & Devices
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
CAPACITANCE
COMPUTERIZED SIMULATION
COUPLING CONSTANTS
DAMPING
ELECTRICAL PROPERTIES
ELECTRONIC EQUIPMENT
EQUIPMENT
FLUXMETERS
MAGNETIC FLUX
MEASURING INSTRUMENTS
MICROWAVE EQUIPMENT
NOISE
OPTIMIZATION
OSCILLATION MODES
PERFORMANCE
PERFORMANCE TESTING
PHYSICAL PROPERTIES
RESONANCE
SIMULATION
SPECTRA
SQUID DEVICES
SUPERCONDUCTING COILS
SUPERCONDUCTING DEVICES
TEST FACILITIES
TESTING