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Description
Viscoelastic materials are widely used in industrial structures, cultural heritage objects, and biomedical applications. Monitoring their mechanical properties is essential, as these properties may evolve due to mechanical loading, aging, or environmental variations such as humidity and temperature fluctuations. Such changes can indicate potential degradation or loss of structural integrity.For isotropic viscoelastic materials, a complete mechanical characterization requires identifying the frequency dependence of the complex Lamé coefficients. This is commonly achieved by analyzing wave–material interactions. Ultrasonic acoustic waves are particularly suitable for this purpose because they are non-invasive and can be generated and measured remotely. In most existing approaches, the estimation of the complex Lamé coefficients is performed in two steps: shear wave analysis is first used to determine the second Lamé coefficient, followed by longitudinal wave analysis to estimate the first coefficient.This work proposes a method to estimate both coefficients simultaneously by studying the multi-component interaction of surface acoustic waves (SAWs) with viscoelastic materials. SAWs exhibit elliptical polarization characterized by the H/V ratio and the orientation angle of the particle motion ellipse. These polarization parameters are estimated using the Quaternion Fourier Transform (QFT), while the complex wavenumber is extracted using the Prony algorithm. The inverse problem is solved using theoretical models of SAW propagation in viscoelastic media. The method is validated using both numerical simulations and experimental measurements.