ELECTRONIC SPECKLE PATTERN INTERFEROMETRIC MEASUREMENT OF FLEXTENSIONAL TRANSDUCER VIBRATION PATTERNS - IN AIR AND WATER

Flextensional transducers have become established recently as compact high power underwater sound sources operating at around 1 kHz. However, their elliptical shape means that they are difficult to analyze by equivalent circuit modelling, and finite element techniques are more useful. Electronic Speckle Pattern Interferometry (ESPI) is a valuable method for validating finite element models in that it measures displacements, which can be compared directly with model outputs. It also has the advantage that it can be used to map displacements of a whole surface by non-contacting means in a single measurement operation. This paper describes out-of-plane and in-plane measurements of a flextensional transducer on a laboratory bench and out-of-plane measurements on transducers immersed in a large test tank. Uniform reflection from the transducer was difficult to achieve and this severely limited the fringe quality, but adequate data were generated to demonstrate that the vibration patterns of the transducers radiating into water were significantly different from those measured in air, and good finite element transducer models must include a mechanism for water acoustic loading. © 1994 Academic Press Limited.