Measurement of the Acoustic Nonlinearity Parameter using Laser Detection of an Ultrasonic Wave

Abstract

Nonlinear ultrasonic technique (NUT) has been widely studied by many researchers and the absolute acoustic nonlinearity parameter β has been considered as an important index for non-destructive evaluation (NDE). However, the piezoelectric detection technique conventionally used in the NDE has a limitation for application to industries because of the contact method and complicated calibration for different materials. In this study, an applicability of the laser interferometric detection technique based on two-wave mixing (TWM) in photorefractive crystal (PRC) is studied by means of the NDT. Two methods via the aforementioned technique are proposed for measuring absolute acoustic nonlinearity parameter. First, the indirect method, which is able to obtain the absolute parameter from the relative parameter without calibration, is proposed. Second, the direct method that is able to determine the absolute parameter with simple-calibration is proposed. Proposed methods are compared with the references and the results via the conventional method to identify the performance. The experimental results are successfully well matched with the references and show the superior than the conventional method with regard to not only the utility by non-contact but also application for different materials. From these results, the proposed technique is proper to measure the acoustic nonlinearity parameter and also can be applied regardless of the test materials for quantitative NDE industries.