DEVELOPMENT OF A COMPUTER-MODEL FOR AN ULTRASONIC POLYMER FILM TRANSDUCER SYSTEM

A piezoelectric polymer film such as polyvinylidene fluoride (PVDF) of fers the possibility of making cheap ultrasonic transducers which can be permanently bonded to structures for NDE applications. However, bef ore this can be achieved it is necessary to have a fu II understanding of the behaviour of PVDF in the context of a transducer application. This paper describes the development of an interactive computer progra m to implement a one-dimensional model of a thin film transducer syste m mounted on a solid substrate. Starting from a typical transducer equ ivalent circuit, this paper explains how that circuit can be expanded into a complete model representing a PVDF transducer with one or more backing layers bonded to an arbitrary solid substrate. The computer pr ogram uses this model to provide immediate predictions of electrical i nput impedence, acoustic response and pulse-echo response. A series of experiments has been performed using PVDF transducers bonded to a var iety of materials in order to validate the model. This has enabled the degree of accuracy required for various pa ra meters with in the mode l, such as mechanical and dielectric loss values, to be assessed. Once validated, the model has been used as a tool to predict the effect of physical parameters, such as bond and electrode thickness, on the per formance of a transducer. (C) 1997 Elsevier Science Ltd.