Computational Analysis of a Spiral Vibrating Beam for the MEMS-Viscosity Sensor

Abstract

A MEMS-viscosity sensor with dual spiral structure has been developed based on a novel measurement method unlike traditional method for viscosity measurement. This viscosity sensor, passing completely through a silicon wafer using MEMS (Micro Electro Mechanical Systems) fabrication processing, was made up the spiral structure with a vibrating body and a sensing body. When a large deflection was generated toward each direction of the vibration body of spiral structure due to the applied external load, it can be the cause of performance deterioration of the MEMS-viscosity sensor. And the analytical methods were proposed to fine the deflections by a computational analysis using FEM (Finite Element Method). A computational analysis was carried out by coupled analysis using modal analysis method and harmonic response analysis assuming air environment. In the spiral model of the MEMS-viscosity sensor on which normal loads of Fz=100 [µN] and Fz=1000 [µN] were applied, the maximum resonance points occurred at about 1400[Hz] of 1st mode along with vertical direction (Z-direction) respectively. When Fz=1000 [µN] was applied, the maximum value of deflection was obtained about 3.0x10-4 [m] in vertical direction, but the normal load of more than Fz=1000 [µN] should be avoided for safety and reliability of this MEMS-viscosity sensor because the deflections of horizontal directions (X and Y-direction) were near to limit of the design values. We found that the deflections of horizontal direction were small enough to be negligible compared to the vertical direction, and the spiral structure can be stably maintained against less than Fz=1000 [µN] of the external load. We also found out the waviness phenomenon in the deflections along the spiral beam. As a solution of the waviness phenomenon in the spiral structure with rectangular shape beam, it seems that the spiral beam must be given so that the spiral radius is continuously compensated by using other beam shapes. It was demonstrated that the approach using computational analysis allows us to deduce visually the deflection of the spiral structure for viscosity sensor.