A new sensor concept for simultaneous measurement of pressure, temperature and thickness of plate structures using modified wave propagation theory

Abstract

This thesis presents a multi-purpose sensor concept viable for the simultaneous measurement of pressure, temperature and thickness of plate structures. It also establishes the knowledge base necessary for future sensor design. Thermal-Acousto Photonic Non-Destructive Evaluation (TAP-NDE) is employed to remotely initiate and acquire interrogating ultrasonic waves. Parameters including pressure, temperature and plate thickness are determined through exploring the dispersion features of the interrogating waves. A theoretical study is performed, through which a modified wave propagation theory applicable to homogeneous, isotropic, linear elastic materials is formulated along with an associated numerical model. A numerical scheme for solving the model is also developed using FEMLAB, a finite element based PDE solver. Gabor Wavelet Transform (GWT) is employed to map numerical time waveforms into the joint time-frequency domain. Wave time-frequency information enables dispersion curves to be extracted and material pressure, temperature and thickness to be determined. A sensor configuration design integrating the wave generation and sensing components of the proven TAP-NDE technology is also developed. Conclusions of the research are drawn from wave dispersion obtained corresponding to the following ranges of parameters: 300-500kHz for frequency, 25-300oC for temperature, 1-3mm for plate thickness, and 6 10 1?? - 7 1 10 ?? N/m for pressure. Each of the three parameters considered in the study has a different level of impact on plate wave dispersion. Plate thickness is found to have the most impact on wave dispersion, followed by temperature of the plate. The effect attributable to pressure is the least prominent among the three parameters considered. Plate thickness and temperature can be readily measured while simultaneously resolved using dispersion curves. However, pressure variation can only be differentiated when the plate is smaller than 1mm in thickness. It is observed that the thicker the plate, the faster the frequency group velocity. Also, the group velocities of all frequency components considered are seen to increase with increasing temperature, but decrease with increasing pressure.