A Miniature Optical Acoustic Emission Transducer

Abstract

The optical transduction of acoustic emission signals offers many advantages over piezoelectric devices. These include high bandwidth, no modification to the signal as well as providing contactless measurement. The major difficulties associated with optical devices are stability against low frequency vibrations and the generally complex nature of an optical interferometer. This paper describes the attempts to miniaturize a Michelson interferometer while at the same time overcoming some of the stability problems associated with these devices.

Active stability of an interferometric transducer with dimensions of ∿ 5cm (2″) cube has been achieved over 8 fringes of red light at 100Hz and 4 fringes at 300Hz. The range of active stabilization of the interferometer is limited by the frequency response of the large amplitude piezoelectric element and the filter characteristics of the feedback electronics. A sensitivity of 0.5Å (0.5 × 10^-10m) has been achieved.