μ-Coriolis Mass Flow Sensor With Differential Capacitive Readout

In this paper we present a $\mu $ -Coriolis mass flow sensor with differential capacitive readout, which can reduce the effect of common mode vibrations caused by external disturbances. The device consists of two silicon nitride micro-channel loops mechanically connected through two membranes. The sensor is actuated using Lorentz forces, inducing rotation of the sensor's micro-channels. Coriolis forces of opposite sign are subsequently generated in the two channel loops. Thus, any common mode vibration can be distinguished from vibration induced by mass flow through the channels. Capacitive readout structures surround the sensor to detect these vibrations. A piezo-electric resonator is placed in close proximity to the sensor to generate artificial external disturbance. Flow measurements are executed to compare the differential readout method to a single ended readout with and without external disturbances. The flow sensitivity is unaffected. However, the mean deviation of the output signal is 60-70% lower when using the differential readout compared to single ended readout when external disturbances are induced. The effect of external disturbances on the zero flow stability is reduced by approximately 64% by using the differential readout. Full elimination of the effect is not possible due to non-linearity of the readout capacitors. Reducing non-linearity of the readout could further improve performance, e.g. by implementing (piezo-resistive) strain gauges on top of the micro-channel.