Date of Award

1983

Degree Type

Thesis

Degree Name

Master of Science in Ocean Engineering

Department

Ocean Engineering

First Advisor

Peter Stepanishen

Abstract

The transient behavior of an ultrasonic transducer operating in a pulse-echo system is studied both analytically and experimentally. Mathematically, the acoustic field is described using an impulse response approach, while a distributed parameter model is used to represent the transducer dynamics. The harmonic pressure field from a circular piston is first presented using a Fourier integral representation of the impulse response. A pulse-echo model for an ultrasonic system is then developed and used to evaluate the pulsed acoustic field response from a transducer for a variety of field points and electrical excitations. A multipulse structure is clearly observed in both the field pressures and the receive voltages. A set of transducers having various matching conditions are fabricated and used to obtain pulse-echo responses from a spherical target placed at different points throughout the acoustic nearfield. Again a multiple pulse structure is noted. To minimize the effect of these acoustic transients, various focusing schemes are experimentally studied. Spherical, conical and toroidal apertures are examined for both shaped-element and lens systems. Transducers of identical diameters, frequencies and focal distances have been designed and fabricated for each case. Measurements of the pulsed acoustic field from these transducers indicate that where sharply focused fields are employed, acoustic transient effects can be effectively eliminated from the focal zone.

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