Date of Award

1978

Degree Type

Thesis

Degree Name

Master of Science in Ocean Engineering

Department

Ocean Engineering

First Advisor

Peter Stepanishen

Abstract

This thesis describes the procedures and results of research conducted on pulsed ultrasonic piezoceramic transducers and arrays which operate in the megahertz range. These transducers and arrays are typical of the types employed currently in biomedical diagnostic systems. Two areas were addressed: The verification of the Impulse Response Approach as a method to predict the spatial and temporal characteristics of the acoustic field pressures of ultrasonic transducers of general shapes and excitations, and the investigation of the element interaction and spatial resolution of field pressures of arrays of piezoceramic elements.

An automated computer controlled high frequency acoustic measuring system was constructed. Several high frequency transducers were built to obtain acoustic nearfield data with this system. The data were subsequently processed using computer programs which were created to obtain impulse responses via the deconvolution of the far field on axis and nearfield time dependent pressures. The acoustic fields of an array driven under focused and unfocused conditions were also extensively mapped.

The experimentally derived impulse responses were in good agreement with the theoretical responses and thus provided important new verification of the Impulse Response Approach. The results of the experiment also indicated that extraneous modes of vibration of piezoceramic discs were, in this case, insignificant. A multi-element transducer array was constructed and operated in such a manner as to focus the acoustic energy, confining it to a narrow region as opposed to a continuous beam. The element to element interaction effects caused by electrical and acoustic coupling were found to be of significant importance in the single driven element case. The effects of interaction were not great enough to cause a perturbation from the expected field pressure pattern when the array was driven for focusing.

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