Resonator probe for photoacoustic measurement

McLaughlin, David (2014) Resonator probe for photoacoustic measurement. [USQ Project]

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Abstract

Despite major technological advances in photoacoustic spectroscopy over the past four decades, a widely-applicable solution to compensating for ambient temperature sensitivity has not been documented. Temperature changes cause the resonant frequency of the cell to drift, resulting in a suboptimal signal. If the resonant frequency of a photoacoustic cell is detectable in real time, the laser frequency can be modulated to match the adjusted frequency.

To detect and track the change in resonant frequency of a photoacoustic cell in real time, a generalised algorithm is developed using a computer soundcard and MATLAB software.

The relationship between resonator dimensions, temperature, and the speed of sound is described for the case of an open-cell resonator, and the process of developing a software model with constraints imposed by prototype construction limitations is discussed. Following initial positive results from simulations, the physical resonator cell is constructed to validate the theoretical results against measured values.

Initial results indicating that the performance of the prototype was poorer than anticipated by simulations were attributed to distortions introduced by windowing frames for FFT processing. A novel method of pre-processing windowed frames of an audio signal to rectify this problem is detailed, and the speed and accuracy of the developed frequency detection algorithm under varying conditions is analysed.

Although the algorithm developed is shown to track frequency changes with a high degree of accuracy, the technique adopted to determine changes in resonant frequency of a photoacoustic cell is ultimately found to be unsuccessful.


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Item Type: USQ Project
Item Status: Live Archive
Additional Information: Bachelor of Electrical and Electronic Engineering project.
Faculty / Department / School: Current - Faculty of Health, Engineering and Sciences - School of Mechanical and Electrical Engineering
Supervisors: Leis, John
Date Deposited: 09 Sep 2015 05:04
Last Modified: 04 Mar 2016 05:28
Uncontrolled Keywords: photoacoustic spectroscopy, digital signal processing, multivariate gas analysis.
Fields of Research : 09 Engineering > 0913 Mechanical Engineering > 091301 Acoustics and Noise Control (excl. Architectural Acoustics)
URI: http://eprints.usq.edu.au/id/eprint/27238

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