This work presents an automatic threshold shock sensor and actuator, including a bi-stable triggering mechanism as an actuator, and a levitation-based MEMS switch as the sensor. As a brief exposition, the bi-stable mechanism is sensitive to mechanical shock and releases an impact energy in case the shock is strong enough. Then, the bridge between the actuation and sensing components is the use of triboelectric materials for voltage generation. The voltage is transferred to the sensor that releases the pulled-in switch. 

The MEMS switch of interest consists of two electrostatic parallel plate electrodes with attractive force, and two side electrodes producing a levitation force. Levitation phenomenon rises from the side electrodes resulting in detachment of a microbeam from the substrate and opening the switch. High voltage requirement is a drawback of the levitation technique, which can be overcome with the connection of the triboelectric generator.

The bi-stable mechanism is a clamped-clamped beam buckled under an axial force attached to a triboelectric generator in the middle. Transition of the bi-stable mechanism from one stable position to another causes a collision between triboelectric generator layers. This impact creates a large voltage as a result of conversion of mechanical energy to electrical energy. Triggering the transition requires sufficient shock that is defined as the sensor threshold. The voltage is then transferred to the side electrodes of the MEMS switch. The MEMS switch is initially closed and if the generator voltage on the side electrodes is strong enough, it can overcome the stiction forces and open the microswitch. The main contribution of this paper is employing a bi-stable mechanism to tune the threshold shock when the switch can open. This tuning capability is enabled from changing the axial force on the clamped-clamped beam. The actuation in macro-scale is thus directly connected to a sensor-switch mechanism in micro-scale. This chain makes an autonomous actuation and sensing stand-alone system with potential application on air bag deployment devices and powerline protection systems. We will provide a theoretical frame work of the entire system validated by experimental results.


Bi-Stable Triboelectric Generators and Autonomous Shock Sensing

Division / Sponsors: 
Aerospace Division

Paper Proceedings: https://asmedigitalcollection.asme.org/SMASIS/SMASIS2020/volume/84027

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