Study on Lamb wave propagation in single crystal silicon wafer using large aperture line focusing ultrasonic transducer

Abstract

In this experiment, [100]. [110] and [111] single crystal silicon wafers were interrogated by line focused ultrasonic transducer with large aperture. Lamb waves generated in the wafers were detected by same transducer, and the rf signals, V (t, z) were acquired as varying defocusing distance. Since Lamb wave is dispersive, a numerous modes were mixed in the detected rf signal. A series of signal processing were carried out in order to separate mode. V (z) curve for a specific frequency were obtained from the V (ƒ, z) which is FFT of V (t, z). Phase velocity can be obtained from the V (z) curves as similar method as used in acoustic microscopy. Finally phase velocity as a function of propagation direction can be determined by rotating the silicon wafers. Angular dependences of wavenumber in [100], [110] and [111] silicon wafer were obtained and shown in the figures. The angular dependences of Lamb wave phase velocity in [100], [110] and [111] silicon wafer were also obtained and shown in the figures. These results show good agreements with the crystalline orientation of silicon wafers. As conclusion, line focusing ultrasonic transducer with large aperture is an epoch tool for the evaluating anisotropic plates.