A RF superconducting electromechanical transducer for gravitational wave antennae

An electromechanical transducer based on a superconducting radiofrequency bridge circuit has been developed for use on a gravitational radiation detector. The low electrical loss of superconductors has made it possible to achieve electrical quality factors of several thousand in a lumped-element circuit which operates at 4 MHz. The bridge could be remotely balanced to one part in 50000, which led to a displacement noise level of 10/sup -15/ m/ square root Hz. It should be useful in measuring any physical quantity which can be made to change a capacitance. At the present stage of development, capacitance changes of 10/sup -20/ F could be detected in a 1-s integration time. One straightforward improvement, namely, the use of a low-phase-noise quartz crystal oscillator as the bridge excitation source will reduce the noise to 10/sup -17/ m/ square root Hz.>