A suspended plate viscosity sensor featuring in-plane vibration and piezoresistive readout

Abstract

Miniaturized viscosity sensors are often characterized by high-resonance frequencies and low-vibration amplitudes. The viscosity parameter obtained by such devices is therefore not always comparable to those probed by conventional laboratory equipment. We present a novel micromachined viscosity sensor with relatively low operating frequencies in the kHz range. The sensor utilizes Lorentz force excitation and piezoresistive readout. The resonating part consists of a rectangular plate suspended by four beam springs. The first mode of vibration is an in-plane mode. Thus, the contribution of the moving plate to the device damping is low, whereas the overall mass is high. This principle improves the quality factor and gives additional freedom to the device designer. This paper presents the device concept, the fabrication process and a prototype of the viscosity sensor. Measurement results demonstrate the feasibility of the device and show that the damping of the device is an appropriate measure for the viscosity.

A micromachined suspended plate viscosity sensor featuring in-plane vibrations and integrated piezoresistive readout

“…The contribution of the plate to the damping of the device is therefore low [11]. Therefore, increasing the size of the plate only results in a small increase of the damping, whereas the higher moving mass enhances the quality factor of the device immersed in liquid.…”

Application of resonant steel tuning forks with circular and rectangular cross sections for precise mass density and viscosity measurements

“…(3)-(6) is presented in [26]. There, the model has been applied to the measurements obtained by eight different sensor setups showing good performance for all investigated sensors including tuning forks, silicon cantilevers [34], silicon platelets [35], U-shaped wires [36], and spiral spring sensors [37]. The investigation of the applicability of the model evaluating the relative root mean square deviations of modeled and measured resonance frequencies and quality factors yielded results better than 1.7 · 10 −3 for the resonance frequency and 3.3 · 10 −2 for the quality factor, respectively.…”

Vibrating wire rheometry

“…(8) ), they were able to measure the viscous modulus G to within 20% of the accepted value. Using nanofabrication techniques, Riesch et al fabricated a viscometer consisting of a suspended plate 100 × 100 μm in size with a resonance frequency of 16 kHz [15] . While this device was successfully used to measure viscosity, its use was not extended to complex fluids.…”