DC SQUIDs as radio-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. We perform a detailed investigation of the dynamic input impedance of tightly coupled dc SQUIDs and of the influence of parasitic capacitance between the SQUID and the input circuit on the SQUID characteristics. 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. We also discuss the optimization of the input circuits for both tuned and untuned amplifiers and derive expressions for the optimum source resistance, gain and noise temperature for a given frequency, input coil and coupling. The performance of the amplifiers designed according to these prescriptions is measured. The gain of an untuned amplifier operated at 100 MHz at 4.2K is 16.5 +- 0.5dB with a noise temperature of 3.8 +- 0.9K; at 1.5K the gain increases to 19.5 +- 0.5dB while the noise temperature decreases to 0.9 +- 0.4K. A tuned amplifier operated at 93 MHz and 4.2K has a gain of 18.6 +- 0.5dB and a noise temperature of 1.7 +- 0.5K. 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 is developed. 59 refs., 31 figs., 3 tabs.
- Research Organization:
- Lawrence Berkeley Lab., CA (USA)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 6433653
- Report Number(s):
- LBL-20636; ON: DE86005228
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
47 OTHER INSTRUMENTATION
AMPLIFIERS
DATA
ELECTRIC IMPEDANCE
ELECTROMAGNETIC RADIATION
ELECTRONIC EQUIPMENT
EQUIPMENT
EXPERIMENTAL DATA
FLUXMETERS
IMPEDANCE
INFORMATION
MAGNETIC RESONANCE
MEASURING INSTRUMENTS
MICROWAVE EQUIPMENT
NOISE
NUCLEAR MAGNETIC RESONANCE
NUMERICAL DATA
RADIATIONS
RADIO NOISE
RADIOWAVE RADIATION
RESONANCE
RF SYSTEMS
SQUID DEVICES
SUPERCONDUCTING DEVICES
USES