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Abstract

A model for the propagation of ultrasonic pulses in fluids using a conventional circular transducer is discussed, and it is shown that diffraction effects limit the range and lateral resolution of such pulse-echo systems. The variation in amplitude and shape of the echo responses which result, can make interpretation of the results difficult.

The diffraction effects are explained in terms of a model which sees a circular transducer as a piston source radiating a direct plane wave in the geometric region straight ahead of the source, together with diffracted toroidal waves from the edge of the source.

An impulse response method is used to make calculations of the echo waveforms reflected from point targets. The forms of the echo responses are used to demonstrate the effects of diffraction on the overall resolution of the transducer. The impulse response method is extended so that the echo response from any arbitrary geometry targets, including non-planar, can be modelled.

New high-resolution transducers are designed to overcome some of the limitations due to the diffraction effects, by radiating either solely plane waves, or solely edge waves, in a non- uniform manner across the transducer’s surface. The results show that such non-uniformly excited transducers have both improved resolution and simpler field structures than conventional transducers.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > TK Electrical engineering. Electronics Nuclear engineering
Departments:	Doctoral Theses School of Science & Technology > School of Science & Technology Doctoral Theses School of Science & Technology > Engineering > Electrical & Electronic Engineering

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