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

摘要

This thesis presents a multi-purpose sensor concept viable for the simultaneousmeasurement of pressure, temperature and thickness of plate structures. It alsoestablishes the knowledge base necessary for future sensor design. Thermal-AcoustoPhotonic Non-Destructive Evaluation (TAP-NDE) is employed to remotely initiate andacquire interrogating ultrasonic waves. Parameters including pressure, temperature andplate thickness are determined through exploring the dispersion features of theinterrogating waves. A theoretical study is performed, through which a modified wavepropagation theory applicable to homogeneous, isotropic, linear elastic materials isformulated along with an associated numerical model. A numerical scheme for solvingthe model is also developed using FEMLAB, a finite element based PDE solver. GaborWavelet Transform (GWT) is employed to map numerical time waveforms into the jointtime-frequency domain. Wave time-frequency information enables dispersion curves tobe extracted and material pressure, temperature and thickness to be determined. A sensorconfiguration design integrating the wave generation and sensing components of theproven TAP-NDE technology is also developed.Conclusions of the research are drawn from wave dispersion obtained correspondingto the following ranges of parameters: 300-500kHz for frequency, 25-300oC fortemperature, 1-3mm for plate thickness, and 6 10 1?? - 7 1 10 ?? N/m for pressure. Each ofthe three parameters considered in the study has a different level of impact on plate wavedispersion. 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 leastprominent among the three parameters considered. Plate thickness and temperature canbe 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 increasewith increasing temperature, but decrease with increasing pressure.