Airborne ultrasound is currently used for a variety of applications, including distance ranging, level monitoring, broken ply detection and for the limited non-destructive testing of low Z materials (such as green-state ceramics, rubber and carbon fiber composite). Ideally we would like to be able to use airborne ultrasound for high quality non-destructive testing of high Z materials, as this would allow testing of parts without contamination by a couplant, and could potentially allow very rapid testing. The testing of most materials using airborne ultrasound is impeded by the high acoustic impedance mismatch between air and the test-piece, giving a very high reflection coefficient. This, (combined with other factors such as the high attenuation of ultrasound in air, and the slow velocity of ultrasound in air) make testing with airborne ultrasound very difficult.