Noncontact method applied to determine thickness of thin layer based on laser ultrasonic technique

This paper describes a novel method to non-destructively determine the thickness of thin layer in a non-contact way. A model of wave interference was established based on the multireflection of shear wave in layered system. Furthermore, its expression of reflection coefficient phase was deduced to provide the principle of thickness measurement. A formed laser source by focusing a line on the layer surface was used to generate shear wave, while an electromagnetic acoustic testing (EMAT) sensor was proposed to receive the wave. An example of the method and experimental measurement for comparison is given for a thin steel sheet with the thickness of approximate 0.4 mm. The relative error between the present method and metallography method is less than 4%, which shows laser-EMAT technique is very suitable to non-destructive assess the thickness of the layer