Frequency Component Analysis of Back-Reflected Surface Acoustic Wave on Diamond-Coated Silicon

When ultrasound propagates on the surface of a layered substrate, the phase and group velocities of a surface acoustic wave (SAW) depend on the frequency, and the dispersion of the SAW can be obtained from its critical angles, for various frequencies. In the present work, a broadband SAW was generated by an oblique incident wave, and the wave reflected at the edge of a specimen was detected by a pulse–echo setup. Detected signals were decomposed into rf waveforms of different frequencies by digital filtering, and the critical angle was determined as a function of frequency. Two specimens with different coating thicknesses were investigated and the dispersion of the SAW was obtained. The results obtained in the present work showed good agreement with those in previous works.