A Reduced Three Dimensional Model for SAW Sensors Using Finite Element Analysis

Mohamed El Gowini,Walied Moussa

doi:10.3390/s91209945

Abstract

A major problem that often arises in modeling Micro Electro Mechanical Systems (MEMS) such as Surface Acoustic Wave (SAW) sensors using Finite Element Analysis (FEA) is the extensive computational capacity required. In this study a new approach is adopted to significantly reduce the computational capacity needed for analyzing the response of a SAW sensor using the finite element (FE) method. The approach is based on the plane wave solution where the properties of the wave vary in two dimensions and are uniform along the thickness of the device. The plane wave solution therefore allows the thickness of the SAW device model to be minimized; the model is referred to as a Reduced 3D Model (R3D). Various configurations of this novel R3D model are developed and compared with theoretical and experimental frequency data and the results show very good agreement. In addition, two-dimensional (2D) models with similar configurations to the R3D are developed for comparison since the 2D approach is widely adopted in the literature as a computationally inexpensive approach to model SAW sensors using the FE method. Results illustrate that the R3D model is capable of capturing the SAW response more accurately than the 2D model; this is demonstrated by comparison of centre frequency and insertion loss values. These results are very encouraging and indicate that the R3D model is capable of capturing the MEMS-based SAW sensor response without being computationally expensive.

Highlights

Surface Acoustic Wave (SAW) devices are considered to be one of the early examples ofMicro-Electromechanical systems (MEMS) [1] due to the coupling needed between electrical and mechanical properties during wave propagation on the surface of these devices
The propagation of the wave along the surface allows it to be sensitive to changes in the external environment; SAW sensors have been developed for numerous applications such as gas detection [2], fluid viscosity changes [3], and pressure changes [4], determination of stiffness constants [5] and detection of the onset of ice formation on aerospace structures [6]
The frequency response is obtained from the Fourier transform of the transient response and the values of the centre frequency are compared with the dispersion data from Caliendo et al [26]

Summary

Introduction

Micro-Electromechanical systems (MEMS) [1] due to the coupling needed between electrical and mechanical properties during wave propagation on the surface of these devices. These devices’ high reliability and relative simplicity in fabrication and integration motivated MEMS researchers to utilize it in a broad range of applications such as TVs, VCRs, radar systems, wireless headsets, alarm systems and mobile phones. The propagation of the wave along the surface allows it to be sensitive to changes in the external environment; SAW sensors have been developed for numerous applications such as gas detection [2], fluid viscosity changes [3], and pressure changes [4], determination of stiffness constants [5] and detection of the onset of ice formation on aerospace structures [6]. To optimize the design phase various numerical and analytical techniques have been developed and some are used concurrently

Results

Discussion

Conclusion