Excess noise in the dc SQUID; 4. 2K to 20mK

Thesis/Dissertation · Fri Jan 01 04:00:00 EST 1988

OSTI ID:7030167

Wellstood, F C

The design, construction, operation, and behavior of low-noise dc SQUID measuring systems are described for temperatures from 0.020 to 4.2 K. Evidence is presented for four different types of excess noise in dc SQUIDs operated in this temperature range. At temperatures between about 1 and 4 K, the spectral density of the low-frequency flux noise of a wide variety of thin-film dc SQUIDs scales as 1/f{sup m} where m - 1.0 {plus minus} 0.1. The origin of this noise depends upon the construction of the SQUID. In SQUIDs with Pb or PbIn bodies, the noise originates in critical-current fluctuations. In SQUIDs with Nb bodies, the nature of the noise depends upon the detailed manner in which the NB is deposited. One deposition technique produces a large level of flux noise, while another produces only the usual level of critical-current noise. When a SQUID is cooled below about 1 K, the behavior of the excess noise changes. Theoretical calculations are presented for the use of SQUIDs in high-sensitivity applications. The emphasis is on the optimal detection of pulse signals by a dc SQUID, taking into account the effect of the input circuit on the SQUID behavior, and making use of optimal filter theory.

• Research Organization: California Univ., Berkeley, CA (USA)
• OSTI ID: 7030167
• Country of Publication: United States
• Language: English

Related Subjects

426001* -- Engineering-- Superconducting Devices & Circuits-- (1990-)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
BACKGROUND NOISE
CURRENTS
DESIGN
DIRECT CURRENT
ELECTRIC CURRENTS
ELECTRONIC EQUIPMENT
EQUIPMENT
FLUXMETERS
FUNCTIONS
MEASURING INSTRUMENTS
MICROWAVE EQUIPMENT
NOISE
PULSES
SENSITIVITY
SIGNALS
SPECTRAL DENSITY
SPECTRAL FUNCTIONS
SQUID DEVICES
SUPERCONDUCTING DEVICES
ULTRALOW TEMPERATURE