DC squids as ratio frequency amplifiers and application to the detection of nuclear quadrupole resonance
The high sensitivity of dc SQUID amplifiers is extended to the radio-frequency range. The dynamic input impedance of tightly coupled dc SQUIDs and the influence of parasitic capacitance between the SQUID and the input circuit on the SQUID characteristics were investigated. The reactive part of the dynamic input impedance is found to be determined by the inductive coupling, whereas the resistive part is found to be dominated by capacitive feedback. Optimization of the input circuits for both tuned and untuned amplifiers is discussed, and expressions for the optimum source resistance, gain, and noise temperature are derived for a given frequency, input coil, and coupling. Performance of the amplifiers designed according to these prescriptions is measured. The gain of an untuned amplifier operated at 100 MHz at 4.2 K is 16.5 +/- 0.5 dB, with a noise temperature of 3.8 +/- 0.9 K; at 1.5 K, the gain increases to 19.5 +/- 0.5 dB while the noise temperature decreases to 0.9 +/- 0.4 K. A tuned amplifier operated at 93 MHz and 4.2 K has a gain of 18.6 +/- 0.5dB and a noise temperature of 1.7 +/- 0.5 K. These results are in good agreement with predicted values. The usefulness of these sensitive amplifiers for the detection of magnetic resonance is demonstrated. A SQUID system for pulsed nuclear quadrupole resonance at about 30 MHz was developed.
- Research Organization:
- California Univ., Berkeley (USA)
- OSTI ID:
- 5239558
- Resource Relation:
- Other Information: Thesis (Ph. D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
DC AMPLIFIERS
PERFORMANCE
SQUID DEVICES
MAGNETIC RESONANCE
DETECTION
ELECTRIC IMPEDANCE
GAIN
TEMPERATURE NOISE
TUNING
AMPLIFICATION
AMPLIFIERS
ELECTRONIC EQUIPMENT
EQUIPMENT
FLUXMETERS
IMPEDANCE
MEASURING INSTRUMENTS
MICROWAVE EQUIPMENT
NOISE
RESONANCE
SUPERCONDUCTING DEVICES
420201* - Engineering- Cryogenic Equipment & Devices