Study on shear stress measurement with LCR wave from surface based on LFMCW

The critically refracted longitudinal (L_CR) wave, which is a bulk longitudinal mode that travels within an effective depth underneath the surface, suits to be used to detect both surface stress and body stress. Strain inside the object would change the propagation velocity of the L_CR wave in the direction of the stress field. But in fact the alteration of the travel time of L_CR wave is so negligible that it´s difficult to measure. Usually, the pulse wave is used to drive L_CR wave, which may lead two difficulties. One is how to guarantee the power of the transmitting waves, the other is how to separate the L_CR wave from the receiving waves which contains many other common-frequency waves. In this paper, a special way for driving the L_CR wave which is called linear frequency modulated continuous wave (LFMCW) is discussed, which could overcome the problems mentioned above. And a method for the shear stress measurement with L_CR wave based on LFMCW is also introduced. The simulation of the system turns out that the method could provide high accurate for the measurement of shear stress with L_CR wave.