Modeling and characterization of electret based vibration energy harvesters in slot-effect configuration

Abstract

The purpose of this article is to elaborate a model and the optimization guidelines for electret based harvesters with a specific electret/electrodes configuration, namely the slot-effect configuration. Slot-effect configured harvesters have been investigated experimentally by several research groups. A model describing their dynamic behavior has also been recently proposed in the literature. However, the simplifications used in the existing model can lead to inaccuracies and a refined analysis is elaborated in the present article. The model is compared with experimental measurements on MEMS fabricated devices with a corrugated electret. The electrodes dimensioning in the MEMS device are chosen so that the harvester behaves in a quasi-linear manner over its full range of displacement. This quasi-linearity simplifies greatly the device optimization. Indeed, the behavior of the developed electrostatic harvester is shown to be very comparable to that of piezoelectric harvesters, which are very well understood and documented. The influence of several design parameters on output power performance is investigated. As long as pull-in and breakdown voltage effects can be avoided, the electret surface potential should be maximized and the air gap minimized. We also investigate theoretically the influence of three types of electret on the generated power: planar, corrugated with partial charge coverage, and corrugated with full charge coverage. With the dimensions corresponding to our MEMS devices, the output power characteristics for the three types of electret are similar. However, it is shown that this is not always true. In some conditions, corrugated electrets with full charge coverage are detrimental for the generated power.

Equivalent-circuit models for electret-based vibration energy harvesters

“…Figure 8 shows a connection scheme routing one of the two electrodes and the proof mass to ground [34,35,39,40]. The load is connected between the remaining electrode and the ground.…”

“…However, the effective permittivity ignores the effect of the remaining substrate and is not easy to obtain analytically for other geometries. Altena [38] and Renaud [39] classified the electrical configurations of electret-based harvesters into cross-wafer and slot-effect configurations based on how three electrical terminals are connected. They developed a full model for the slot-effect configuration and proposed a guideline to device optimisation.…”

A Novel Characterization Method for Accurate Lumped Parameter Modeling of Electret Electrostatic Vibration Energy Harvesters

“…In particular, its accuracy relies on the assumption of uniform charge distribution across the surfaces of the transducer's facing capacitor plates. This hypothesis is not always verified, depending on both the employed charging techniques and the transducer geometry [10], [11].…”

Optimization of a Piezoelectric Energy Harvester and Design of a Charge Pump Converter for CMOS-MEMS Monolithic Integration

“…This concept allows these devices to be self-sufficient. Ambient vibrations can be converted into electrical energy by using piezoelectric [8,9,10,11,12,13], triboelectric [14,15,16], electromagnetic [17], and electrostatic transducers [18,19,20]. Among them, piezoelectric transducers are considered an attractive option due to their high energy density, ease of integration, and durability.…”