Electret-Based Vibration Energy Harvesters with Tapered Comb Fingers and Curved-Beam Hinges

Abstract

Energy harvesting from ambient vibrations can be an attractive alternative to electrochemical cells for powering low-energy-driven electronics, such as wearable sensors, implantable medical devices, and environmental monitoring systems. Electret-based vibration energy harvesters (eVEHs) are advantageous for their compact size, process compatibility with electronics, and simple conditioning circuits; incorporating curved-beam springs in eVEHs broadens their spectra, making them suitable for random broadband vibration sources. This study delves into the effects of comb-drive designs on the performance of eVEHs with curved-beam hinges. More specifically, it is examined how the comb finger shapes influence the output power. Linear taper profiles are investigated for different polarities and rates. The results are obtained via numerical simulation based on stochastic differential equations. The study reveals that tapered finger designs can achieve higher output power than a standard, non-tapered finger design with the same at-rest capacitance. It also shows that the degree of improvement, as well as the specific design that achieves it, depends on the vibration strength. At low vibration strengths (<0.07 g), a gap-widening type (termed LinB) is more beneficial, with an improvement up to 2.45 times (@ 0.02 g) over the standard one. At high vibration strengths (>0.07 g), on the other hand, a gap-narrowing type (termed LinA) becomes more advantageous, producing as high as 11% more power (@ 0.1 g) than the reference. The results suggest that the comb-finger design dictates electrostatic damping, and its effects on motion dynamics depend on the input vibration strength.