An extrapolation procedure for transient reflection measurements made on thick acoustical panels composed of lossy, dispersive materials

Abstract

The underwater acoustic behavior of an elastomeric coating material is frequently evaluated by performing a reflection experiment on a sample, e.g., a rectangular panel, of the coating material. Extrapolation of the transient portion of the reflected wave in such measurements is required when steady-state conditions do not occur prior to interference from extraneous reflections. This article describes a technique for the extrapolation of measurements made on thick acoustical panels (the interrogating wave is assumed to be normally incident). The technique involves fitting a multiple-layer model to the experimental data via a least-squares process. The model assumes homogeneous and isotropic panel layers. The technique can perform the extrapolation using a much shorter leading portion of the reflected wave than is possible with other existing techniques. Experiments on three sample panels were conducted to investigate the usefulness of the technique. The first panel consists of three simple homogeneous layers. The second and third samples are fabricated from viscoelastic layers including macrovoids. The experiment covered the frequency range 2–20 kHz. The measurements on the simple three-layer panel are in reasonably good agreement with theoretical calculations based on the known acoustical properties of the layers. The acoustical properties of the more complicated panels are unknown. However, the extrapolations based on the measurements obtained from these panels appear to have reasonable behavior.