Combined Analytical and Numerical Modeling of a Resonant MEMS Sensor for Viscosity and Mass Density Measurements

A resonant MEMS sensor for viscosity and mass density measurements of liquids was modeled. The device is based on Lorentz-force excitation and features an integrated piezoresistive readout [1]. The core sensing element is a rectangular vibrating plate suspended by four beam springs. Two of the plate-carrying springs comprise piezoresistors. With two additional resistors on the silicon rim, they form a half Wheatstone-bridge (Figure 1). Through the conductive layer of the beam springs a sinusoidal excitation current is driven. In the field of a permanent magnet, the Lorentz-force excites time-harmonic plate vibrations resulting in a bridge unbalance. Evaluating the properties of the resonant system allows estimation of the viscosity and the mass density of the fluids.