Identification of parametric models for ultrasonic double transmission experiments on viscoelastic plates

Abstract

In this paper, an identification method is proposed for the determination of the acoustic properties of viscoelastic plates based on an immersion pulse-echo technique. A double transmission (DT) configuration is used for the experiments, which facilitates the calibration of the measurement setup. With the DT configuration, parametric models are established for the ultrasonic plane-wave propagation through a viscoelastic plate at both normal and oblique incidence. The effects of beam spreading due to the finite aperture size of the ultrasonic transducer are taken into account by introducing a diffraction correction factor into the plane-wave models. A maximum likelihood estimator, which takes into account the measurement noise on both the input and the output signals, is constructed for the estimation of the parameters of the DT models. From the estimated model parameters, the absorption and dispersion properties and velocities for both shear and longitudinal waves, as well as the density and the thickness of the plate, are obtained simultaneously. Using the estimated parameters, the prediction of the DT measurement can be made at different angles of incidence. The predicted and measured transfer functions are then compared to validate the estimates. Experiments performed on a Plexiglas plate confirm the efficiency and reliability of the method.