Velocity measurements of cylindrical surface waves with a large aperture line-focus acoustic transducer

Acoustic microscopy has been widely applied in the measurements of the mechanical properties. However, the measurement of wave velocity on a curved cylindrical surface by acoustic microscopy was seldom reported. In this paper, we adopted a large aperture line-focus PVDF transducer and a defocusing measurement system to measure the velocity of a cylindrical surface waves. The theoretical model was established to study the relationship among the propagation path of surface waves, the geometric parameters of a transducer, and the diameter of a shaft specimen. Based on theoretical deduction and mathematical modeling, theoretical oscillation curves of phase difference were obtained. According to the improved V(f,z) analysis method, the V(f,z) curves were obtained through analyzing experimental data at different frequencies by Fourier transform. Then the surface wave velocity of the cylindrical tungsten steel specimen (Ø 20 mm) could be determined by fitting the V(f,z) curves with the theoretical curves. The measurement results were consistent with the theoretical values, indicating that the measurement method was feasible. This study laid the basis for the ultrasonic measurement of the mechanical properties on the layer-coated cylinders.