Soft material characterization through surface wave elastography using a laser Doppler vibrometer

This paper provides a comprehensive investigation into characterizing viscoelastic properties in soft materials, focusing on silicone. Conventional measurement techniques such as tensile testing and dynamic mechanical analysis prove inadequate for soft materials. The proposed method utilizes Rayleigh surface wave propagation, employing a laser Doppler vibrometer to measure phase speed and amplitude, induced by air jet pulses in a contactless manner. Usually, a contact probe is used for excitation, which results a higher signal to noise ratio. The study involves a regression analysis to obtain dispersion curves, filtering outcomes with a coefficient of determination threshold above 95% as a quality indicator for the measurements. Mechanical parameters, including complex dynamic modulus and shear modulus components, are determined from Rayleigh and shear complex wave-numbers. Repeatability assessments, including changes in measuring direction, underscore the stability of the experimental setup and sample uniformity. Noteworthy is the comparison of results from the Surface Wave Elastography (SWE) method through an experimental test, a novel aspect in this study. The evaluation method, based on a spring–damper model rooted in the exact solution of Newton’s second law differential equation, serves as a reference. The comparison of mean storage modulus values between the SWE method and the free-loading mass method revealed errors of 6.36% and 10.23% for two tested samples.