Finite Element Simulation of Ultrasonic Guided Waves Generated by a Pulsed Laser in Human Skin

Author： Li Xingfei Wang Chi Xiang Hongbiao Zhang Guoxiong

ISSN： 1568-5543

Source： Composite Interfaces, Vol.34, Iss.6, 2006-11, pp. : 711-725

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Abstract

A high‐power, short laser, pulse incident on human skin generates a transient temperature field. As a rapid and localized thermal expansion occurs, energy is released in the form of propagating ultrasound in all directions. Laser‐generated ultrasound is non‐contact, broadband, and multiple propagation modes, and so, has been studied widely in the non‐destructive testing of structural materials. However, its application in human skin is still new. Considering human skin properties, the transient temperature distribution in human skin is simulated using the finite element method (FEM). A finite element model, a 2‐layer elastic, isotropic biomaterial model, is developed to simulate the laser thermo‐elastic generation and propagation of the laser ultrasound. Taking into consideration the fundamental understanding of the laser/material interface, the simulation comprises a set of boundary conditions that approximate a heat flux point source with Gaussian spatial variation located on top of the surface of the material. We obtained the temporal characteristics of the ultrasonic guided waves generated by the pulsed laser with different beam radius and the various rise times. The numerical results indicate the significant influence of pulsed laser beam radius and pulse‐width on laser‐generated ultrasound propagation features, and that the heat‐affected zone is very localized; such a distribution of the transient temperature is considered as a body source in the generation of ultrasound. Obviously, these results and the method discussed in this paper establish a qualitative basis for the thermo‐elastic mechanism in non‐destructive evaluation of the human skin properties, which is of great significance and applicability.