Passive Pressure Transducer Utilizing Acoustic Emission

Abstract

A passive pressure transducer has been developed which utilizes the acoustic emission effect. This effect is noted when a suitable solid material is placed under increasing stress, causing permanent deformation processes to occur which are accompanied by emission of acoustic energy. These processes are irreversible, so if the stress is released and then reapplied, no acoustic energy will be emitted on the second cycle until the stress reaches its previous maximum level. The instrument described here contains a diaphragm of anodized aluminum which is first exposed to the pressure that is to be measured and then withdrawn and read by subjecting it to steadily increasing known pressure while monitoring it for acoustic emission. The pressure at which acoustic emission begins is taken as the pressure originally measured by the instrument. Pressure transducers of this type are inexpensive and require no calibration. Accuracy is within a few percent and can probably be improved. Possible applications include deep ocean depth measurements, measurements of peak acceleration, and tellatale uses for monitoring peak pressures.