Research On New Measurement Technology By Using Ultrasonic Speckle Correlation Method

When a rough interface is insonified by coherent waves, there will be a speckle field in the space because of the interference between the refraction waves and the back-scattered waves. Speckles can be viewed as a kind of noise, which affects the quality of image and leads to signal distortion, whereas it can also be viewed as an information carrier of the characteristics of the interface. Ultrasound scattering is similar to laser, mircrowave and stress wave scattering. Not only the research on the properties of ultrasound scattering field will be helpful to search for the common properties of the scattering fields of various kinds of material waves, but also the analyzing of the basic properties of ultrasonic scattering field will lead to found the ultrasonic speckle interferometry, which will be used more widely than laser speckle interferometry.Supported jointly by the National Natural Science Foundation of China (No. 10074017) and the Excellent Doctoral Thesis Foundation of Huazhong University of Science and Technology (No. 2004-21), in this thesis, the first-order and second-order statistic properties of ultrasonic speckles back-scattered from a rough interface,the ultrasonic speckle in space and the in-plane and out-of-plane displacement measurement by ultrasonic speckle correlation method are studied theoretically and experimentally. In the theoretical analyses of the ultrasonic scattering field, we consider the measuring system as a linear system with ignoring the effect of ultrasonic dispersion and attenuation. Then based on the Kirchhoff diffraction theory and the random signal process theory, we deduced and achieved some results about the properbility density functions of ultrasonic speckle amplitude and phase, the transversal and longitudinal self-correlation length and the relationship between the speckle motion, the incident direction and the receiving direction of the ultrasound, and the displacement of the interface. In the studying of the measurement of in-plane and out-of-plane displacement using the basic principle of digital speckle correlation method (DSCM), the theoretical analysies and experimental studies vertify that the combination of the movement regular of ultrasound speckle with the DSCM is a feasible and effective method to measure the in-plane and out-of-plane displacement. The maximum rotation angle which could be measured using ultrasonic speckle digital correlation method was obtained by experiment.