Electrostatic vibration energy harvester using an electret-charged mems transducer with an unstable auto-synchronous conditioning circuit

Abstract

A new autostabilization mechanism in the Bennet doubler circuit-based electrostatic vibrational energy harvester V.P. Abstract.This paper reports for the first time experiments using an electrostatic vibration energy harvester comprised of a low voltage electret-charged MEMS transducer joined to an unstable autosynchronous conditioning circuit with rectangular charge-voltage characteristic, also known as the Bennet's doubler conditioning circuit. The experimental results show that the electret voltage, even if of low value, can be used as the necessary pre-charge for these type of electrostatic vibration energy harvesters. Also, the use of such a conditioning circuit with a low-voltage electret capacitive MEMS tranducer instead of the previously-reported conditioning circuits with direct connection to load or through a rectifier, can be advantageous in terms of maximal harvested power for a low-voltage electret, showing up to 95% higher converted power. IntroductionIn the recent years, extensive research has been done on electret-based electrostatic vibration energy harvesters (e-VEHs). High-voltages electret have enabled the realization of e-VEHs with relatively high harvested power density from relatively high-gap and/or in-plane moving electrode capacitive transducers [1]. These electret e-VEHs have been experimentally tested using either a direct connection to an impedance-matched load -also known as the primitive conditioning circuit -, or simple conditioning circuits consisting of a diode bridge connected to an impedance-matched load, with or without the use of a smoothing capacitor.However, electrets may be subject to degradation resulting in the decrease of their built-in voltage over time. This problem is strongly linked to the materials and the technology used to implement the charged electret layer. As the electret voltage decreases, so does the converted power if using the previously-mentioned conditioning circuits.Notwithstanding this decrease of the electret built-in voltage, recently, a new class of conditioning circuits was discovered: inspired from the "Bennet's doubler of electricity", they allow an exponential self-increase of their biasing, and thus of the converted power, at the small cost of a low pre-charge voltage. In the electrical domain, these circuits show no saturation of the harvested power over time of operation. Moreover, these circuits are inductorless and do not require any external command for synchronization [2,3]. This paper presents the first experiment combining the Bennet's doubler conditioning circuit, which will be called the unstable auto-synchronous conditioning circuit in the rest of the paper,

Series-Parallel Charge Pump Conditioning Circuits for Electrostatic Kinetic Energy Harvesting

“…The application context is the following: suppose there exists a maximal allowable voltage V M across the transducer, η > N, and the transducer is supposed to use of electret charging to provide a built-in polarization of the transducer (see for example [12], [13]), with no external pre-charging of the circuit's fixed capacitors. This built-in bias also provides an initial voltage to e-KEHs using a conditioning circuit with exponential voltage increasing regime, as has been experimentally verified in [14]. A simple electrical model of the electret-charged transducer is represented in Fig.…”

“…Particularly, the dependence of the system's dynamics to the exact shape of the rectangular QV-cycle was highlighted. As examples have recently shown that exponential mode conditioning circuits often give better energy conversion figures than other conditioning circuits [14], it is of great interest to build a toolbox of conditioning circuits with different extreme bias ratio at the scale of one cycle (i.e., QV-cycle aspect ratios), that do not saturate in large time scale of autonomous operation in the electrical domain. It gives the designer a wider choice of conditioning schemes to fulfill the optimal conditioning determined by the coupled system's study.…”

Analysis and comparison of charge-pump conditioning circuits for capacitive electromechanical energy conversion

“…These results were used to compare the different circuits under different application constraints. Further work will have to include the impact of the electromechanical coupling in this comparison, as it can have a large impact on the system's dynamics [9].…”

Dynamic responses of an energy harvesting system based on piezoelectric and electromagnetic mechanisms under colored noise

“…[1][2][3][4] Vibration energy harvesters (VEHs) with ability to harvest electrical energy from environmental vibration are a good potential technology to provide continuous electrical energy instead of batteries with limited lifespan. [5] Piezoelectric, [6] electromagnetic, [7] electrostatic [8] and triboelectric [9] transductions are the main technologies for converting environmental vibration into electric energy. To increase the energy conversion efficiency, a hybrid piezoelectric and electromagnetic energy harvesting system (EHS) has been developed.…”