Determination of elastic constants in layered media using surface acoustic waves

• Main Authors: CHIA HAO HSU, 許家豪
• Other Authors: 尹慶中
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/05563542354243228325

碩士 === 國立交通大學 === 機械工程系所 === 93 === This thesis studies determination of material constants in a thin film deposited on a half space through the measurement of phase velocities of surface acoustic waves propagating in layered media using laser-based ultrasonic technique. Based on the Stroh formulation, the phase velocity dispersion equation of surface acoustic waves is derived and numerically calculated. The experimental specimens made of a thin film sputtered on a substrate or a layer of piezoelectric material are fabricated by micro-electro- mechanical system (MEMS) process. The inter-digital transducer (IDT) deposited on the surface of specimen is used to launch narrow-band surface acoustic waves. A system of confocal Fabry-P�臆ot interferometer was developed during this research and used to measure the Doppler frequency shifts due to surface particle oscillations during surface acoustic wave propagation. The phase spectrum method is used to calculate phase velocities of the surface acoustic waves, which depend on the material properties of the thin film and substrate, frequencies and directions of wave propagation. The quasi-Newton method with and/or without constraints and simplex method are employed to search the minimum values of sum of the squared roots of errors. The augmented Lagrange multipliers are introduced to replace the equality and inequality constraints on material properties in inversion scheme. A process of multiple initial guess selected by random number is adopted for reliability assessment.