IMPROVED INTERFEROMETRIC TECHNIQUES FOR MEASURING FLEXTENSIONAL TRANSDUCER VIBRATION PATTERNS UNDERWATER

The design of flextensional transducers involves a two-stage process. Firstly finite element analysis (FE) is used to model the transducers in order to predict behaviour and the influence of design alterations; and secondly experimental methods are employed to assess the performa nce of the transducers, providing data with which the FEA models may b e corrected, updated or validated. Whole-field laser-based interferome tric techniques are ideal for analysis of the transducers within the c ontrolled environment of the laboratory, providing information concern ing the spatial and temporal characteristics of the resonant modes of vibration. However, there has been uncertainty concerning the validity of this data with respect to the transducers operating in water. Elec tronic speckle pattern interferometry (ESPI) has previously been appli ed to the analysis of flextensional transducers both in air and in wat er. Whilst the laboratory displacement data provided a detailed analys is of behaviour, the underwater results were of insufficient quality t o allow effective post-processing. ESPI has been developed and applied to the dynamic analysis of transducer behaviour. Using a Nd: YAG puls ed laser, laboratory and underwater-based experimentation has been per formed, producing quality subtraction correlation fringe patterns depi cting transducer mode behaviour. (C) 1996 Academic Press Limited