Date of Award

12-2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical and Computer Engineering (Holcomb Dept. of)

Committee Member

Hai Xiao, Committee Chair

Committee Member

Lin Zhu

Committee Member

John Ballato

Committee Member

Pingshan Wang

Abstract

Endoscopic photoacoustic imaging probe is becoming increasingly important for many clinical photoacoustic imaging applications in which the target tissue can only be accessed by introducing an endoscopic probe percutaneously or through a natural orifice. Miniature fiber optic hydrophone (FOH) has become an attractive choice for endoscopic photoacoustic imaging application. Fiber optic hydrophone has many proven advantages, including small size, light weight, immunity to electromagnetic interference, low cost for single-use application and capability of integration of excitation light source and acoustic wave receiver.

This dissertation demonstrates an open cavity, micro-cantilever based fiber optic Fabry-Perot interferometer (FPI) hydrophone. A fused silica micro-cantilever beam as the sensing element is directly fabricated by femtosecond (fs) laser micromachining system. The theoretical analyses and experimental verifications were all applied for evaluation of the proposed cantilever based FOH.

A rectangular micro-cantilever based FOH is presented, which has a narrow bandwidth but high response and high sensitivity around its resonant frequency, and has many advantages as a good potential candidate for endoscopic photoacoustic imaging application. As a key parameter of the hydrophone, the resonant frequency can be adjusted by changing the dimensions and shapes of the micro-cantilever. In order to increase the resonant frequency of the rectangular micro-cantilever based FOH, and without loss in sensitivity, V-shaped and triangular cantilever based FOHs are investigated and compared with the rectangular cantilever based FOH theoretically and experimentally. The resonant frequency of the triangular cantilever based FOH has been doubled without loss in sensitivity compared with the rectangular cantilever based FOH.

Cantilever based 45° angled FOH was proposed for a new choice for sideway looking detection except forward looking detection for endoscopic imaging in vessels. It consists of a fiber with a 45° angled endface and an fs laser fabricated micro-cantilever. The 45° angled endface would steer the optical axis by 90° via total internal reflection, and send the input light to the sensing part. This configuration could be applied for cross-axial sensing application. The proposed FOHs were all theoretically analyzed and experimental tested. Experimental results agree well with the simulated frequency responses of the proposed FOHs.

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