Linear ultrasonic array design for echosonography

Phased-array echosonographic systems, currently in use in medical diagnosis, employ pulses that are a few wavelengths long at the center frequency. Design of such systems requires that arrays be composed of as few elements as are consistent with acceptable resolution and low side lobes. This paper outlines the development of a model for the field of an idealized phased array. The model is an extension of elementary array theory which includes pulse parameters and beam steering. It is specialized for the generation of simple and useful directivity patterns that are applicable at point focal regions and in the farfield. The directivity-pattern function provides the basis for a method of designing linear arrays by nonuniform element spacing. Arrays designed by this method offer advantages over uniform linear arrays because of the smaller number of elements required for given azimuthal resolution and side-lobe level, and because of reduced element interaction.