Ben Salah Issam, Ben Amor Morched, Ben Ghozlen Mohamed Hédi
Laboratory of Physics of Materials, Faculty of Sciences of Sfax, BP 1171, 3000 University of Sfax, Tunisia.
Sfax Preparatory Engineering Institute, Menzel Chaker Road 0.5 km, BP 1172, 3000 Sfax, Tunisia.
Ultrasonics. 2015 Aug;61:145-50. doi: 10.1016/j.ultras.2015.04.011. Epub 2015 May 4.
Numerical examples for wave propagation in a three-layer structure have been investigated for both electrically open and shorted cases. The first order differential equations are solved by both methods ODE and Stiffness matrix. The solutions are used to study the effects of thickness and gradient coefficient of soft middle layer on the phase velocity and on the electromechanical coupling factor. We demonstrate that the electromechanical coupling factor is substantially increased when the equivalent thickness is in the order of the wavelength. The effects of gradient coefficients are plotted for the first mode when electrical and mechanical gradient variations are applied separately and altogether. The obtained deviations in comparison with the ungraded homogenous film are plotted with respect to the dimensionless wavenumber. The impact related to the gradient coefficient of the soft middle layer, on the mechanical displacement and the Poynting vector, is carried out. The numericals results are illustrated by a set of appropriate curves related to various profiles. The obtained results set guidelines not only for the design of high-performance surface acoustic wave (SAW) devices, but also for the measurement of material properties in a functionally graded piezoelectric layered system using Love waves.
针对三层结构中的波传播，研究了电开路和短路情况下的数值示例。通过常微分方程（ODE）和刚度矩阵这两种方法求解一阶微分方程。这些解用于研究软质中间层的厚度和梯度系数对相速度和机电耦合系数的影响。我们证明，当等效厚度处于波长量级时，机电耦合系数会显著增加。分别绘制了单独施加和同时施加电梯度变化与机械梯度变化时，一阶模式下梯度系数的影响。相对于无量纲波数，绘制了与未分级均匀薄膜相比所获得的偏差。研究了软质中间层的梯度系数对机械位移和坡印廷矢量的影响。数值结果通过与各种轮廓相关的一组适当曲线进行说明。所获得的结果不仅为高性能表面声波（SAW）器件的设计提供了指导方针，还为使用乐甫波在功能梯度压电层状系统中测量材料特性提供了指导方针。
