Finite-difference Time-domain Method In Ultrasonic Electronics

Surface acoustic wave(SAW) devices are widely used in many areas, especially in communication systems such as radar and mobile-phones. Although a number of analytical and numerical techniques such as equivalent circuit model, P-Matrix model and coupling-of-modes modeling have been used to model surface acoustic wave filters, the present modeling schemes seem to be difficult to predict the characteristics of SAW filters with complex inter-digital transducers(IDT) and fabricates on multilayered substrates accurately. Among these methods, only finite element method(FEM) can predict the characteristics of SAW filters in high frequency accurately. However, FEM itself also has shortcomings. It takes a long time to model the devices and the computers on which the programs run should be in a high level.In this research, the finite difference time domain method (FDTD) is used to model SAW devices. In this method, Newton equation and piezoelectric equation are discretized and the result can be get in iteration of space and time. The perfectly matched layer(PML) boundary condition is set to reduce reflections of wave. In this way, the characteristic of these devices will be modeled and analyzed. the electric field intensity is calculated by an electrostatic field simulator named ANSOFT Maxwell 2D. The distribution of the field components can be predicted by this method. Finally we can get the frequency response of the device by the input and output of voltage signal.