Laser Doppler vibrometer-based transfer-function method for bending wave characterization of viscoelastic panels

The dispersive nature of the bending waves is unique in plate structures or structure-borne wave propagation, such as sandwiched wall board systems in which incorporating viscoelastic panels as constrained damping layers drastically enhances sound transmission losses. To predict bending wave propagation through the constrained damping layers, bending wave parameters of the damping layers play a central role. A characterization method has been developed to determine the flexural wave properties, including the bending phase speed, Young's modulus and the loss factor of highly viscous panels. The transfer function is experimentally measured using a laser Doppler vibrometer with its laser beam shining on two locations radially away from a thin, light-weight flexural wave exciter on the viscoelastic panel under test. The laser beam senses bending vibration velocities in a non-contacting manner. This dynamic method experimentally determines the broadband bending phase speed, the Young's modulus, and the bending loss factor. After a brief introduction of the experimental method, this paper discusses further development of previously accomplished effort by Miller III & Xiang (InterNoise 2020). The discussion also addresses experimental challenges as well as an approach to mitigating boundary disturbances and improving measurement accuracy.