Degree Type

Dissertation

Date of Award

2005

Degree Name

Doctor of Philosophy

Department

Aerospace Engineering

First Advisor

Dale E. Chimenti

Second Advisor

Ron Roberts

Abstract

This research work is focused on the development of a spherically focused (no-mirror) capacitive-film air-coupled ultrasonic transducer and a leak location array sensor for long-endurance spacecraft. For the development of a spherically focused capacitive-film air-coupled ultrasonic transducer, two transducers have been designed, fabricated, and their performance characterized, using a spherically deformed backplate and film. One has a 10-mm diameter and 25.4-mm geometric focal length, and another has a 50-mm diameter and 50.8-mm geometric focal length. Both spherically focused transducers have frequency spectra centered at 805 kHz with -6-dB points at 400 kHz and 1200 kHz. By performing rigorous feasibility tests; a flexible copper/polyimide circuit board material is employed as a backplate in place of the conventional silicon substrate. Utilizing its deformability and ease of microfabrication, we have demonstrated that spherically focused air-coupled ultrasonic transducers can be made to function without the need of an external focusing device, such as a zone plate or an acoustic mirror. We have also invented a simple and easily applied method to conform the metalized polymer film onto a spherically curved backplate, while suppressing wrinkling on the film. Good agreement has been shown between measurement and theory, suggesting that our transducers behave as ideal spherically focused piston transducers;For the development of a leak location array sensor for long-endurance spacecraft, we have developed and experimentally demonstrated a sensitive and reliable means to locate an air leak in a plate-like structure. The goals of this work are accomplished by developing a sophisticated leak location algorithm and a two-dimensional PZT array sensor. The proposed leak location algorithm is highly effective in finding the direction of the leaks, using a minimal number of sensors, and needing less computation time while still achieving high accuracy. In addition, it accounts for the multi-mode dispersive characteristics in a plate-like structure, and utilizes structure-borne noise generated by turbulence at an air leak. This leak location algorithm is implemented by a prototype of a 64-element array sensor.

DOI

https://doi.org/10.31274/rtd-180813-15416

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Jun-Ho Song

Language

en

Proquest ID

AAI3200481

File Format

application/pdf

File Size

169 pages

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