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The use of a line-focus ultrasonic transducer in a vertical scanning reflection acoustic microscope system is well known for quantitative materials characterization [1]. The technique relies on the measurement of the reflected radio frequency tone burst echo amplitude, V, as a fonction of amount of defocus, z, and analysis of the interference minima of the V(z) curve to obtain various interface wave speeds. The technique uses well developed theory [2,3,4] representing fixed frequency ultrasound generated and detected by a cylindrical lens in the frequency domain. We have developed a large aperture lensless line-focus transducer which is highly efficient and has a bandwidth wide enough to allow the generation and detection of narrow transient pulses [5]. From this transducer placed in water near a solid sample, the resulting echo waveforms have multiple features which can be interpreted as the arrival of a specularly reflected axial ray and leaky surface waves. Using this transducer, we have developed a time-resolved and polarization-sensitive testing technique for materials characterization [6]. The objective of this paper is to provide a theoretical basis for interpretation and analysis of these time domain waveforms. |
