Computer Aided Design and Eeffects of Beam Placement in Bulk Micromachined Piezoresistive MEMS Accelerometer for Concrete SHM Applications

Abstract

Structural Health Monitoring (SHM) using non destructive testing generally involves measurement of shift in natural frequency of the monitored structure. Vibration sensors play a crucial role in such SHM systems and the present day SHM systems use commercially available off the shelf MEMS accelerometers. In this work, an attempt has been made to design a MEMS accelerometer that is specifically intended for concrete SHM applications. This paper presents the design methodology of a MEMS silicon piezoresistive single axis accelerometer with the seismic mass (m) suspended by four symmetrical cantilever beams. The simulation and analysis results using CoventorWare MEMS design tool show that this newly designed accelerometer is capable of measuring vibrations up to 2g.The modal analysis results indicate that the accelerometers considered for this analysis (Device-A, Device-B, Device-C) using CoventorWare simulation tool has its first mode natural frequency of 1040Hz and 946Hz respectively against the specified 900Hz. The piezoresistive sensitivity of Device-A (with larger mass and optimum stiffness) is found to be the maximum thus demonstrates that the beam length and half side length of the mass should lie in the region (L<a). Further it has been shown that flexural beams placement as chosen in the Device-A is the best choice for achieving maximum sensitivity and desirable natural frequency with reasonably reduced cross axis sensitivity.