A physical model describing the propagation of lowfrequency surface waves in relation to the viscoelastic behavior of porcine skin is presented, along with a series of empirical studies testing the performance of the model. The model assumes that the skin behaves as a semi-infinite, locally isotropic, viscoelastic halfspace. While the assumption of a semi-infinite body is violated, this violation does not appear to have a significant impact on the performance of the model based on the empirical

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... studies. 1-Hz surface waves in the skin propagate primarily as Rayleigh waves with a wavelength and velocity of approximately 3 m and 3.0 m/s, respectively. The amplitude of the acoustic wave, as measured by tracking the acoustic stress wave-induced shift in a backscattered laser speckle pattern, decreases exponentially with lateral distance from the acoustic source. Using this model of surface wave propagation, the mechanical loss factor or tan ␦ of the skin is measured to be on the order of 0.14Ϯ0.07. The results presented are consistent with earlier works on the propagation of low-frequency acoustic waves in biological tissues, and should serve as a theoretical and empirical basis for using the wave characteristics of propagating surface waves in combination with the mechanical behavior of the tissue for biomechanical studies and for potential diagnostic applications.