Armine Karami

Electret-Free Micromachined Silicon Electrostatic Vibration Energy Harvester With the Bennet’s Doubler as Conditioning Circuit

This letter presents for the first time experiments combining a previously reported microelectromechanical system electrostatic vibration energy harvester (e-VEH) and the Bennets doubler circuit. A self-limiting effect on the harvested power, which was not reported before on macroscopic e-VEHs, has been observed. This effect is due to the nonlinear dynamics of the system and to the self-increase of the electromechanical damping that is typical for e-VEHs. With a few volts of initial precharge, the Bennets doubler progressively increases the voltage across the transducers terminals up to 23 V, where saturation occurs. A power of 2.3 μW is available for a load, when the harvester is excited by 1.5 g at 150 Hz of external acceleration.

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

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 Bennets 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.

MEMS electrostatic vibration energy harvester without switches and inductive elements

The paper is devoted to a novel study of monophase MEMS electrostatic Vibration Energy Harvester (e-VEH) with conditioning circuit based on Bennets doubler. Unlike the majority of conditioning circuits that charge a power supply, the circuit based on Bennets doubler is characterized by the absence of switches requiring additional control electronics, and is free from hardly compatible with batch fabrication process inductive elements. Our experiment with a 0.042 cm 3 batch fabricated MEMS e-VEH shows that a pre-charged capacitor as a power supply causes a voltage increase, followed by a saturation which was not reported before. This saturation is due to the nonlinear dynamics of the system and the electromechanical damping that is typical for MEMS. It has been found that because of that coupled behavior there exists an optimal power supply voltage at which output power is maximum. At 187 Hz / 4 g external vibrations the system is shown to charge a 12 V supply with a output power of 1.8 μW.

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

This paper presents a new family of conditioning circuits used in electrostatic kinetic energy harvesters (e-KEHs), generalizing a previously reported conditioning circuit known as the Bennets doubler. The proposed topology implements a conditioning scheme described by a rectangular charge-voltage cycle (QV-cycle) of tunable aspect ratio. These circuits show an exponential increase of the converted energy over operation time if studied in the sole electrical domain. The QV-cycles aspect ratio can be set to values that were previously inaccessible with other exponential conditioning circuits. After a brief intuitive presentation of the new topology, its operation is rigorously analyzed and its dynamics are quantitatively derived in the electrical domain. In particular, the aspect ratio of the rectangular QV-cycle describing the biasing scheme of the transducer is expressed as a function of the circuits parameters. Practical considerations about the use of the reported conditioning circuits in actual e-KEHs are also presented. These include a discussion on the applications of the proposed conditioning, a description of the effects of electrical nonidealities, and a proposition of an energy extracting interface.

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

This letter presents a new method for the characterization of electret transducers, which are typically used in electret electrostatic vibration energy harvesters (electret e-VEHs). This is the first method allowing to accurately measure the value of the equivalent voltage source representing the electret in lumped parameter models of a wide range of electret e-VEHs. An accurate value for this parameter is critical for design, analysis, and optimization, given the increasing complexity of e-VEHs electrical interfaces. Until now, there was no universal method allowing the measurement of this parameter, because of practical difficulties with some geometries, and because of charging non-uniformities. In this letter, the new method is presented, with insights on how to maximize the measurement accuracy. It is then applied to a state-of-the art MEMS electret e-VEH.

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

This work presents a rigorous electrical analysis of charge-pump conditioning circuits for capacitive energy converters (CEG) with built-in bias voltage. The subsequent implications on the selection of the optimal conditioning circuit are also presented. In particular, the determining role of the application context and constraints on the optimal conditioning circuit choice is discussed. This context is defined by the transducers capacitance variation amplitude, by the value of the built-in bias of the transducer, and by limitations on the operating voltages across the circuit elements and the transducer.

Characterization of the capacitance variation of electrostatic vibration energy harvesters biased following rectangular charge-voltage diagrams

This paper presents for the first time a method to measure the capacitance variation of electrostatic vibration energy harvesters (e-VEHs) that employ conditioning circuits implementing a biasing scheme that can be represented by a rectangular charge-voltage diagram. Given the increasing number of e-VEHs using such complex conditioning circuits and the complex dynamics that are induced from this type of biasing, a mean to assess this measurement is of primary importance for the analysis of e-VEHs. The proposed method is based on the inspection of the voltage evolution across two simple conditioning circuits implementing a rectangular charge-voltage diagrams biasing scheme. After the method is presented, it is carried out for the characterization of a state-of-the-art MEMS e-VEH.

Electrostatic Vibration Energy Harvester Pre-charged Wirelessly at 2.45 GHz

This paper reports the design, fabrication and experiments of an electrostatic vibration harvester (e-VEH), pre-charged wirelessly for the first time by using an electromagnetic waves harvester at 2.4 GHz. The rectenna uses the Cockcroft-Walton voltage doubler rectifier. It is designed and optimized to operate at low power densities and provides high voltage levels: 0.5 V at 0.5 μW/cm2 and 0.8 V at 1 μW/cm2 The e-VEH uses the Bennet doubler as conditioning circuit. Experiments show 23 V voltage across the transducer terminal when the harvester is excited at 25 Hz by 1.5 g of external acceleration. An accumulated energy of 275 μJ and a maximum power of 0.4 μW are available for the load.