IDENTIFICATION OF PARAMETRIC MODELS FOR ULTRASONIC DOUBLE TRANSMISSION EXPERIMENTS ON VISCOELASTIC PLATES

In this paper, an identification method is proposed for the determinat ion of the acoustic properties of viscoelastic plates based on an imme rsion pulse-echo technique. A double transmission (DT) configuration i s used for the experiments, which facilitates the calibration of the m easurement setup. With the DT configuration, parametric models are est ablished for the ultrasonic plane-wave propagation through a viscoelas tic plate at both normal and oblique incidence. The effects of beam sp reading due to the finite aperture size of the ultrasonic transducer a re taken into account by introducing a diffraction correction factor i nto the plane-wave models. A maximum likelihood estimator, which takes into account the measurement noise on both the input and the output s ignals, is constructed for the estimation of the parameters of the DT models. From the estimated model parameters, the absorption and disper sion properties and velocities for both shear and longitudinal waves, as well as the density and the thickness of the plate, are obtained si multaneously. Using the estimated parameters, the prediction of the DT measurement can be made at different angles of incidence. The predict ed and measured transfer functions are then compared to validate the e stimates. Experiments performed on a Plexiglas plate confirm the effic iency and reliability of the method. (C) 1996 Acoustical Society of Am erica.