ABSTRACT Micromachined capacitance transducers have been investigated in practical situations where air-coupled ultrasound has current application. Their ~2 MHz bandwidths lead to good performance in pulse-echo and through transmission operation at solid surfaces. Applications in surface profiling and distance measurement have been investigated. For the transduction of waves within solid media, the devices are shown to be capable of detecting longitudinal and shear waves at solid surfaces, as well as Rayleigh and Lamb waves. Examples are also given of fully noncontact, through transmission of carbon fibre reinforced polymer plates.
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