Viscosity–density sensor with resonant torsional paddle for direct detection in liquid

Abstract

A novel micro-machined biosensor based on the resonant torsional paddle with electromagnetic excitation which can work in liquid directly is presented. The sensor designed consists of two paddles with resonant torsional mode, in which the energy loss of the resonator during the vibration is so lower that it can be suitable for detection in liquid. Finite element method analysis was carried out to guarantee the sensitivity of the sensor. Micro electro-mechanical system (MEMS) bulk silicon processes were adopted to accomplish the fabrication. A positive-feedback circuit with energy compensation is designed to improve the characteristics of the sensor in liquid. Experiments show that the resonant torsional paddle can work directly in liquid and the Q-factor of the sensor in liquid can be improved from 2.65 to 40 with energy compensation. Viscosity tests and density tests for the sensor show that the decrease in frequency and the decrease in Q-factor are related to density and viscosity of the solutions, respectively.

Piezoelectirc Rotational Mode Disk Resonators for Liquid Viscosity Monitoring

“…Such devices exhibit very low quality factors (in the order of 2-3) in liquid due to their out of plane vibration causing significant damping. Using such devices also involves a complex sensing and actuation mechanism [1]. Puchades and Fuller introduced a thermally actuated resonating plate which senses kinematic viscosity (the ratio of dynamic viscosity and density) [2].…”