Ultrasonic beam structures in fluid media

Abstract

Field patterns of short-pulse ultrasonic transducers are quite different from those of continuous- or quasicontinuous-wave sources and depend critically on the actual waveform emitted. The observed patterns, including those provided by using a small target to probe the field in the transmit–receive mode, are also dependent on the method of detection used—whether full- or half-wave. The structure of the field and the marked difference between the pulsed pressure beam pattern and the corresponding transmit–receive mode beam pattern are explained in terms of the plane and edge waves radiated by the source. The field radiated by a transducer is compared with measurements of the field structure of a circular aperture insonified by a plane wave. Consequences of the pulsed beam structure for ultrasonic pulse-echo evaluation are pointed out.