Semester

Spring

Date of Graduation

2009

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Osama Mukdadi.

Abstract

Elastic wave propagation in layered media has been of interest in many disciplines including non-destructive material characterization, acoustic sensors and medical ultrasound imaging. A great variety of devices are based on the propagation of electromechanical waves in piezoelectric plates. Despite the diversity of applications, the principles and characteristics of wave propagation are the same regardless the design or configuration of the device. The aim of this study is to develop numerical and analytical tools to model and design devices based on the wave propagation in piezoelectric layered media; particularly, ultrasound transducers for medical imaging and acoustic sensors for biological applications.;Single-element ultrasound transducers can be modeled as infinite layered piezoelectric plates. A Semi-Analytical Finite Element (SAFE) method has been implemented and used to theoretically predict the resonant frequencies and the dispersion behavior of these plates. The analysis of piezoelectric layered plates showed that the resonant frequencies at the ZGV points of the Lamb wave modes are more significant than those at the cut-off frequencies. On the other hand, 1D array ultrasound transducers are modeled as periodic piezoelectric plates with finite cross-section using a modified SAFE method. Dispersion curves, group velocity spectra and mode shapes are obtained using this method. Geometric parameters of the piezoelectric element, such as, aspect ratio and subdicing width and depth of the piezoelectric element had an important effect on the dispersion behavior. In general, the lower aspect ratios, as well as lower subdicing depth, tend to increase the cut-off frequency and the resonance of all modes.;An analytical model is presented to study the dynamic behavior of single-element ultrasound transducers and acoustic sensors. This model is based on leaky Rayleigh and Lamb wave analysis, which has been widely used for NDT applications. A procedure to calculate the resonance frequencies for ultrasound transducers based on the dispersion curves has been derived and experimentally validated. This analytical solution has also been used to calculate and optimize the sensitivity and coupling coefficient of Rayleigh and Lamb wave sensors.;The procedures and results obtained in this study can be used to analyze and design devices based on the wave propagation on multilayered piezoelectric plates, i.e. ultrasound transducer and sensors. It is believed that an accurate characterization of the wave propagation and dynamic properties, as well as an optimized configuration of the device can substantially improve its performance. These developments can be applied on ultrasound biomicroscopy, medical imaging, NDT techniques, MEM devices and biosensors.

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