Optimization of dc SQUID voltmeter and magnetometer circuits

Journal Article · Thu Nov 01 04:00:00 EST 1979 · J. Low Temp. Phys.; (United States)

DOI:https://doi.org/10.1007/BF00119198· OSTI ID:5677756

Clarke, J; Tesche, C D; Giffard, R P

We calculate the signal-to-noise ratio in a dc SQUID system as a function of source impedance, taking into account the effects of current and voltage noise sources in the SQUID. The optimization of both tuned and untuned volmeters and magnetometers is discussed and typical sensitivities are predicted using calculated noise spectra. The calculations are based on an ideal symmetric dc SQUID with ..beta..=2LI/sub 0//Phi/sub 0/=1 and moderate noise rounding (GAMMA=2k/sub B/T/I/sub 0/Phi/sub 0/=0.05), where Phi/sub 0/ is the flux quantum, T is the temperature, L is the SQUID inductance, and I/sub 0/ is the critical current of each junction. The optimum noise temperatures of tuned and untuned voltmeters are found to be 2.8(..omega..L/R) T and 8(..omega..L/R) T (1+1.5..cap alpha../sup 2/ +0.7..cap alpha../sup 4/)/sup 1/2//..cap alpha../sup 2/ respectively, where ..omega../2..pi.. is the signal frequency, assumed to be much less than the Josephson frequency, and ..cap alpha.. is the coupling coefficient between the SQUID and its input coil. It is found that tuned and untuned magnetometers can be characterized by optimum effective signal energies given by (16k/sub B/TLB/..cap alpha../sup 2/R)(1+1l5..cap alpha../sup 2/ +0.7..cap alpha../sup 2/)/sup 1/2/+0.75..cap alpha../sup 2/) and 2k/sub B/T/sub i/R/sub i/B/..omega../sup 2/L/sub p/ respectively, where B is the bandwidth, R/sub i/ is the resistance representing the losses in the tuned circuit at temperture T/sub i/, and L/sub p/ is the inductance of the pickup coil.

• Research Organization: Department of Physics, University of California, and Materials and Molecular Research Division, Lawrence Berkeley Laboratory, University of California, Berkeley, California
• OSTI ID: 5677756
• Journal Information: J. Low Temp. Phys.; (United States), Journal Name: J. Low Temp. Phys.; (United States) Journal Issue: 3-4 Vol. 37:3; ISSN JLTPA
• Country of Publication: United States
• Language: English

Related Subjects

420201* -- Engineering-- Cryogenic Equipment & Devices
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ELECTRIC MEASURING INSTRUMENTS
ELECTRICAL EQUIPMENT
ELECTRONIC EQUIPMENT
EQUIPMENT
FLUXMETERS
MAGNETOMETERS
MEASURING INSTRUMENTS
MICROWAVE EQUIPMENT
NOISE
OPTIMIZATION
SQUID DEVICES
SUPERCONDUCTING DEVICES
VOLTMETERS