Design, Modeling and Simulation of Micromechanical Suspension System for the Detection of Screech

Abstract

High performance military gas turbine engines are often equipped with augmenters to provide increased level of thrust for relatively short period of time. The augmentation level which can be supplied by engines, is limited by the combustion instabilities, screech and rumble. Screech is a loud, high pitched sound that can cause rapid failure of the mechanical components and also be a threat in combat situations when the military flights can be detected by the enemy due to the intense sound. For the avoidance of these consequences due to instabilities, a MEMS accelerometer herein is proposed and addressed that can detect screech frequencies. The current work deals with design and comparison of two different mechanical suspension systems of a single axis MEMS accelerometer, namely parallel beam and folded beam for its improved sensitivity based on SOI MUMPs fabrication process flow by MEMSCAP foundry. Correspondingly, the analytical modeling for designing the suspension system and combs is presented. Initially, a system level analytical modeling is done, followed by a device level design by building geometrical models using FE simulator COMSOL Multiphysics and MATLAB and a comparative analysis is carried out. Various design parameters like resonant frequency, mechanical and electrical sensitivity, static capacitance, cross axis sensitivity and Bandwidth Vs Sensitivity analysis are also attained and compared. The sensitivity of the parallel beam is found to be 9.925nm/g and folded beam is 17.1nm/g hence inferred that folded beam gives 1.7 times improved sensitivity and the mechanical stress detected by the folded beam is less than parallel beam suspension thus reflecting the better performance of a folded beam suspension. The novelty of the design lies in the fact that the device gives a stable performance over 1g to 1000g of acceleration due to gravity (g = 10 m/s2) and also provides fine sensitivity.