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In this study, a combined threshold pressure sensor and switch is introduced. The sensor detects when the pressure drops below a threshold value and automatically triggers a switch without the need for any computational overhead to read the pressure or trigger the switch. This system exploits the significant fluid interaction of a MEMS beam undergoing a large oscillation from electrostatic levitation to detect changes in ambient pressure. The levitation electrode configuration is combined with a parallel-plate system by adding an extra voltage to an electrode that is traditionally grounded, giving the system the ability to simultaneously act as a switch by toggling to and from the pulled-in position. It is experimentally demonstrated that the pressure sensing/switching mechanism is feasible and the threshold pressure to trigger the switch can be controlled by adjusting the voltage applied to the switch electrode. 

We demonstrate a tunable air pressure switch. The switch detects when the ambient pressure drops below a threshold value and automatically triggers without the need for any computational overhead to read the pressure or trigger the switch. The switch exploits the significant fluid interaction of a MEMS beam undergoing a large oscillation from electrostatic levitation to detect changes in ambient pressure. If the oscillation amplitude near the resonant frequency is above a threshold level, dynamic pull-in is triggered and the switch is closed. The pressure at which the switch closes can be tuned by adjusting the voltage applied to the switch. The use of electrostatic levitation allows the device to be released from their pulled-in position and reused many times without mechanical failure. A theoretical model is derived and validated with experimental data. It is experimentally demonstrated that the pressure switching mechanism is feasible. 

This study illustrates the concept of threshold pressure sensing using the parametric resonance of an electrostatic levitation mechanism. The electrostatic levitation allows the oscillations in the opposite direction of the substrate, thereby not limited to small gaps. The pressure sensor detects the pressure drop below a threshold value by triggering the parametric resonance with significant peak to peak dynamic amplitude changes (~ 25 𝝁𝒎). This detection relies on the fact that the instability region expands when the pressure drop forces the amplitude jump up to the higher oscillation branch. This significant change in the resonator amplitude can be related to a large capacitance variation indicating the threshold pressure. A mathematical model of the resonator is presented to show the working principle of the sensor through frequency response. Our experimental results show that the threshold pressure the sensor detects, can be adjusted by the AC voltage it receives. 

We introduce a capacitive MEMS filter that uses electrostatic levitation for actuation and sensing. The advantage of this electrode configuration is that it does not suffer from the pull-in instability and therefore tremendously high voltages can be applied to this system. A large sensing voltage will produce a large output signal, which boosts the signal to noise ratio. The filter outputs about a 110mV peak-to-peak signal when operated at 175V, and can be boosted to 175mV by increasing the voltage to 250V. Because pull-in is eliminated, voltages much higher than 250V can be applied. An outline of the filter design and operating principle is discussed. A model of the filter is derived and analyzed to show the mechanical response and approximate peak-to-peak signal output. This study shows the feasibility of a capacitive sensor that is based on electrostatic levitation, and outlines the advantages it has over traditional parallel-plate electrode configurations. This design is promising for signal signal processing applications where large strokes are important. 

In this paper a novel electrostatic MEMS combined shock sensor and normally-closed switch is presented. The switch uses combined attractive and repulsive forcing to toggle a cantilever beam to and from the pulled-in position. The attractive force is generated through a parallel plate electrode configuration and induces pull-in. The repulsive force is generated through electrostatic levitation from a third electrode and serves to pull the beam out of its pulled-in position. A triboelectric transducer converts impact energy to electrical energy to provide voltage for the third electrode, which temporarily opens the switch if enough impact energy is supplied. Triboelectricity addresses the high voltage requirement for electrostatic levitation. The multi-electrode sensor also addresses the low current output from the generator because it acts as an open circuit between the parallel plate and levitation electrodes. A theoretical model of the switch is derived to analyze stability and the dynamic response of the cantilever. Threshold voltages to pull-in and release the beam through repulsive forcing is calculated. Output voltage plots from a prototype generator under a single impact are applied to the sensor-switch model to demonstrate the working principle of the sensor-switch is feasible. 

Parametric resonances in a repulsive-force MEMS resonator are investigated. The repulsive force is generated through electrostatic fringe fields that arise from a specific electrode configuration. Because of the nature of the electrostatic force, parametric resonance occurs in this system and is predicted using Mathieu’s Equation. Governing equations of motion are solved using numerical shooting techniques and show both parametric and subharmonic resonance at twice the natural frequency. The primary instability tongue for parametric resonance is also mapped. This is of particular interest for MEMS sensors that require high signal-to-noise ratios due to the large oscillation amplitudes associated with parametric resonance.