The computer-aided, time-domain method is a proposal to determine the spatial pulse response for an arbitrarily shaped source and for arbitrary aperture velocity and delay distributions. The computational procedure ‘‘generates’’ the pulse response function by directly repeating the physical stages that accompany the creation of this phenomenon, such as radiation from the surface element, and propagation and summation in the observation point. The method is very simple mathematically, employing a simple algorithm, and can be easily implemented—even on a small minicomputer. The mathematical work required prior to the computation has been greatly simplified; the commonly studied behavior of the derivatives (arrival time/source point), as well as the exact temporal limits of the pulse response occurrence, need not be analyzed. The Dirac-type free-space Green’s function, as well as other arbitrary types of the causal Green’s function, can also be considered. The obtainable results are approximate, but computational precision depends only on the number of the elementary surfaces used to model the aperture, and, therefore, can be obtained practically, as desired. The method can also be easily used for computations of the transducer coupling functions and of the transient field diffracted by an arbitrary object. The nonplanar sources and objects can also be considered.

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In acoustics, the analysis of pressure distribution in a field of surface sources is most frequently performed using the assumption that the source constitutes a part of an infinite planar rigid baffle (Rayleigh’s approximation). However, in many practical cases of ultrasonic echography, assumption of a soft pressure-release baffle (the Rayleigh-Sommerfeld approximation) or of free-field conditions (the Kirchhoff approximation) seemed to be better matched to real conditions. A theoretical survey of the planar baffles problem is given in this paper, and its practical aspects in acoustic source radiation are discussed. Some experiments, showing the influence of different boundary conditions onto radiation patterns, verify the theoretical predictions.

In order to improve ultrasonic image quality, transducers, similar to those currently used in nondestructive testing and medical imaging applications, have been studied extensively. Attention has been given to single isolated transducers, for which anomalous radiation patterns have been obtained, and to transducers integrated in an array structure, where additional problems occur due to coupling effects between nearest neighbors. An experimental study of these phenomena has made it possible in both cases to find the origin of the perturbations with respect to the theoretical situations which occur in the radiation pattern. Solutions for increasing these perturbations are also suggested.

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