Miniature wideband ultrasonic transducers to measure compression and shear waves in solid

This paper reports on the characterisation of specially developed miniature ultrasonic transducers as receivers directly-coupled to a solid surface, to make field point measurements of the ultrasonic waves propagating from a pulsed transducer. The emitting transducer is water-coupled at various angles to steel test pieces, the miniature receiving transducer being coupled to an opposite surface. The receiver is fabricated as a needle-like probe using a lead metaniobate disc of diameter 0.3 mm as the active element. The 6 dB bandwidth of the miniature probe ranges from around 0.5 to 7 MHz, which is wide enough not significantly to change the shape of the ultrasonic pulses investigated. To a reasonable approximation, the probe responds to the normal component of the particle velocity of the incoming wave, and can be used to measure both the longitudinal (compression) and transverse (shear) waves. The measurement results obtained compare well to the results of calculations made using theoretical models recently developed by the authors.