Quality factor enhancement for resonant MEMS applying an analogue feedback circuit driven by a lock-in amplifier

In this study, an analogue Q-control circuit is presented, based on a digital feedback loop. In this approach, a self-actuated and self-sensing piezoelectric microstructure is used in combination with a lock-in amplifier to extract the Q-control feedback signal amplitude which is proportional to the piezoelectric current. In the next step, the DC-value supported by the lock-in amplifier is multiplied with a sine signal on a custom-designed analogue circuit board containing an analogue amplifier IC. This generated analogue feedback signal allows to drive a complete analogue feedback loop enabling faster response of the Q-control and further faster measurements can be performed. Using this Q-factor enhancement technique, the Q-factor was increased from 397 to about 5357 in air without driving the used Q-control approach to its limits. These promising results will push further activities in measuring the viscosity of liquids in the future.