Diffraction by planar targets of transient focused ultrasonic waves

Abstract

A theoretical study is proposed dealing with the acoustic pressure radiated into fluids by focused transducers and scattered by circular planar targets. In the case of small targets, the detected pressure has been expressed as a convolution in the time domain of the source velocity function with the transmit-receive impulse response. This result has been generalized to the case of targets with a finite size. For a point like target, many pulses are observed and are well resolved in time. The calculated pressure signal has been interpreted with the concept of direct and edge waves. The simulations shown that, in the case of targets of finite size, the different pulses corresponding to the edge waves are of lower amplitude. Consequently, the diffraction phenomenon and its effects are more noticeable for targets of small size. In the experimental set up, an ultrasonic plane transducer with a nominal frequency 2.25 MHz, and coupled to a lens is used. Cylindrical rods of different diameters have been used as targets. Some experimental results are presented, and a good agreement with the theoretical model is obtained.