Measured characteristics of an acoustic microscope having a bow-tie transducer

Point focus acoustic microscope lenses have been constructed with bow-tie transducers to operate at 50 MHz. The authors report on the characteristics observed for the lenses. The bow-tie transducer was conceived as providing a way to achieve angular resolution in the measurement of the Rayleigh wave velocity on anisotropic substrates, while retaining the lateral resolution of the spherical point focus lens. When used to measure the Rayleigh wave velocity on y-cut quartz, these transducers show strong variation of the deduced velocity with orientation and exhibit the correct symmetry. Agreement however, with the generally accepted velocity variation is poor. It is proposed that diffraction effects in the lens rod result in Rayleigh waves being excited with significant amplitude in direction on the object surface that lie outside the sector of the bow tie. Spatial resolution was also examined in the directions along and across the bow tie and was found to be similar for both cases