Ultrasonic continuous wave particle monitor

Abstract

Apparatus for sensing particles in a fluid medium comprising an ultrasonic resonant cavity for containing a fluid medium. A first transducer on one side of the cavity continuously propagates thereacross ultrasonic compressional waves whose phase and amplitude are perturbed by the presence of particles in the fluid medium. A second transducer positioned on the opposite side of the cavity from the first transducer substantially parallel to and in registry therewith receives the ultrasonic waves and converts them to rf electric waves of the same frequency, the rf electric waves having their phases and amplitudes modulated in response to any perturbations in the ultrasonic waves. The rf waves are amplified and fedback to the first transducer thereby to establish an oscillatory circuit. An attenuator in the oscillatory circuit causes its operation to be marginally oscillatory whereby small changes in the amplitude of the rf waves caused by any perturbations in the ultrasonic waves produce relatively large changes in the amplitude thereof. A detector responsive to perturbations in the rf wave demodulates the amplified rf wave to produce signals indicative of the presence of particles in the fluid medium. Thus, enhanced sensitivity to small changes in the ultrasonic properties of the fluid medium caused by the presence of particles therein is achieved.