Electret based vibration energy harvester for sensor network

Abstract

Energy harvesting is an enabling technology for wireless sensor network and low-power-consumption wearable devices. Among various energy sources in the environment, structural vibration and human motion are most abundantly distributed. Since kinetic energy of the vibration is mainly concentrated in the low-frequency range, electrostatic induction generator using electrets attracts much attention. Here, recent progress of electret materials, charging methods, and device technologies are discussed for further developments of MEMS electret energy harvesters.

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].…”

“…An external interface has to let the circuit reach the optimal cycle and then sustain it, as will be discussed in Section V-D. Note that in the example presented above, the use of a saturating charge-pump conditioning circuit (e.g., the simple rectifier circuits presented in [13], that are widely used with electret e-VEHs) instead of the proposed circuit can only be comparatively disadvantageous. Indeed, the absolute maximal harvested power would intrinsically be limited by E and η, because of the saturation phenomenon.…”

“…In this case, the evolution laws derived in Section III lead to (evolution with no parallel configuration of C 1 and/or C 2 with C var ). As at each cycle, the switching in series will necessarily occur, since η > N ∀ n n 1 , V 1,n = V 1,n 1 + 1 with ΔQ k defined in (13). Thus ∀ n n 1 , Δ n = V 1,n − V 2,n = V 1,n 1 − V 2,n 1 +…”

“…with, from (12), and with ΔQ n defined in (13) ∀ n, V 1,n =V 1,n−1 + ΔQ n−1 C 1 ∀ n, V 2,n =V 2,n−1 + ΔQ n−1 C 2 .…”

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

“…This variable capacitor is called the capacitive transducer. In capacitive energy conversion applications, this transducer can be charged by a built-in voltage, by the deposition of an electret layer [1]. The energy conversion occurs when the electrostatic force between the transducer's plates opposes the movement induced by an external mechanical force on them.…”