ULTRASONIC EVALUATION OF DISPERSIVE POLYMERS BY THE PIEZOELECTRIC EMBEDDED ELEMENT METHOD - MODELING AND EXPERIMENTAL VALIDATION

In this paper, a one-dimensional model for the frequency evolution of the electric impedance of a thin piezoelectric disk is derived. II is established that this impedance depends on the acoustical properties o f the surrounding media. The Validity of such a model is improved by c omparing theoretical calculations with experimental electrical impedan ce measurements obtained when the piezoelectric element is bounded bet ween two dispersive plates, parallel faced and of finite thickness. By means of this model, the inverse problem consisting of determining th e acoustical properties of the surrounding media from an electrical im pedance measurement of the embedded sensor is solved. This is achieved through a nonlinear optimization numerical method. The corresponding results are successfully compared with those obtained by ultrasonic sp ectroscopy. (C) 1998 Elsevier Science B.V. All rights reserved.