Under the first-order approximation of Taylor expansion, the analytic expression for the defect mode frequency is derived, from which the coupling factor is deduced.
利用泰勒展式的一级近似，得到了缺陷模频率的解析表达式，进而得到紧束缚理论中的耦合因子。
2
By oil immersion coupling. the system can be used to detect near surface defects with focussing probe. find surface cracks with surface wave probe and determine defect size with computerized C-scan.