Cantilever-based electret energy harvesters

Abstract

Integration of structures and functions has permitted to reduce electric consumptions of sensors, actuators and electronic devices. Therefore, it is now possible to imagine low-consumption devices able to harvest energy in their surrounding environment. One way to proceed is to develop converters able to turn mechanical energy, such as vibrations, into electricity: this paper focuses on electrostatic converters using electrets. We develop an accurate analytical model of a simple but efficient cantilever-based electret energy harvester. Therefore, we prove that with vibrations of 0.1g (~1m/s²), it is theoretically possible to harvest up to 30µW per gram of mobile mass. This power corresponds to the maximum output power of a resonant energy harvester according to the model of William and Yates. Simulations results are validated by experimental measurements, raising at the same time the large impact of parasitic capacitances on the output power. Therefore, we 'only' managed to harvest 10µW per gram of mobile mass, but according to our factor of merit, this puts us in the best results of the state of the art.

Electret Length Optimization of Output Power for Double-End Fixed Beam Out-of-Plane Electret-Based Vibration Energy Harvesters

“…Boisseau [17] obtained the capacitance between the electrode and the counter-electrode by describing the deflection of cantilever over its length direction. He divided the beam in two parts due to the mass as Figure1 shows.…”

“…Electret-based vibration energy harvesters (E-VEHs) can be divided into two types, in-plane [14][15][16] and out-of-plane [17][18][19][20][21], depending on the vibration direction. In-plane E-VEHs operate under vibration parallel to the electret surface, whereas out-of-plane E-VEHs do so under vibration normal to the electret surface.…”

“…Boisseau [17] was the first to present a cantilever out-of-plane E-VEH employing an electret, and optimized several key parameters for example the air gap, the load, and the electret length. Cantilever beam have low stiffness coefficients compared with other beam structures, which means that the harvester can harvest more low-frequency vibration energy from the environment.…”

New DRIE-Patterned Electrets for Vibration Energy Harvesting

“…This induces a current across load R and part of the mechanical energy is then turned into electricity. The equivalent electric model of e-VEH is presented in figure 3(b) and consists in a variable capacitor in series with a voltage source [3]. The output power (P) of this converter is directly linked to the electret's surface voltage V and the capacitance variation of the structure dC/dt when it is subjected to vibrations [4].…”

Proximity sensing of electrostatic induction electret nanoparticles device using separation electrode

“…The electret capacitive proximity sensor is a device that can measure vertical position which depends on electrostatic effect. [19][20][21][22] Even though the coupling effect of the electret induced charge and the variable electrostatic capacitor have been recently reported for device geometries, 19 investigations have not been studied the separation electrode with structural patterned device.…”