ANGULAR RESPONSE OF PIEZOELECTRIC ELEMENTS IN PHASED-ARRAY ULTRASOUND SCANNERS

In the design of phased linear array sector scanners for medical applications, it is important to preserve uniform response at each angle throughout the sector scan of ± 45°. Examination of linear array transducers showed reduced transmit pressure and receive sensitivity at angles beyond ± 200 by individual array elements. The angular response of piezoelectric elements, many wavelengths long and approximately one wavelength or less in width, do not agree with the predictions of simple diffraction theory for plane apertures. Continuous wave (CW) angular response measurements using the RCA Ultrasonovision of individual piezoelectric elements 0.6λ to 2λ wide indicated this behavior was independent of inter-element coupling and pulse excitation effects within a linear array transducer. Spectral analysis of isolated elements showed a significant amount of energy coupled into the transverse mode due to the small aspect ratio of width to thickness dimensions of the piezoelectric elements. A first-order two-dimensional numerical model, based on thickness mode and transverse mode vibrations, resulted in angular response functions which agree well with experimental measurements. Copyright © 1979 by The Institute of Electrical and Electronics Engineers, Inc.