Reconstruction of the normal velocity distribution on the surface of an ultrasonic transducer from the acoustic pressure measured on a reference surface

In piezoceramic ultrasonic transducers, the thickness vibrations are usually accompanied by the excitation of Lamb waves, which are difficult to control. Therefore, the normal velocity distribution over the radiating surface is unknown. As a result, the ultrasonic field generated by the transducer cannot be predicted with the desired accuracy. The purpose of this study is to develop and experimentally validate a new method for evaluating the normal velocity distribution over the surface of an ultrasonic transducer. The method consists in measuring the amplitude and phase of the acoustic pressure field over a certain reference surface and then calculating the acoustic field at the transducer by using the Rayleigh integral. The accuracy and stability of the method are illustrated numerically. The method is tested experimentally with a focused piezoceramic transducer. In the experiment, the reference surface is represented by a plane perpendicular to the axis of the acoustic beam. The ultrasonic field is scanned by a needle hydrophone, which is moved by a micropositioner. The measurements show that the method provides an accurate prediction of the acoustic field generated by a source with an unknown nonuniform normal velocity distribution. (C) 2003 MAN "Nauka/Interperiodica".