Electrostatic Vibration Energy Harvester Research Articles

Broadband Vibration-Based Energy Harvesting for Wireless Sensor Applications Using Frequency Upconversion.

Silicon-based kinetic energy converters employing variable capacitors, also known as electrostatic vibration energy harvesters, hold promise as power sources for Internet of Things devices. However, for most wireless applications, such as wearable technology or environmental and structural monitoring, the ambient vibration is often at relatively low frequencies (1-100 Hz). Since the power output of electrostatic harvesters is positively correlated to the frequency of capacitance oscillation, typical electrostatic energy harvesters, designed to match the natural frequency of ambient vibrations, do not produce sufficient power output. Moreover, energy conversion is limited to a narrow range of input frequencies. To address these shortcomings, an impacted-based electrostatic energy harvester is explored experimentally. The impact refers to electrode collision and it triggers frequency upconversion, namely a secondary high-frequency free oscillation of the electrodes overlapping with primary device oscillation tuned to input vibration frequency. The main purpose of high-frequency oscillation is to enable additional energy conversion cycles since this will increase the energy output. The devices investigated were fabricated using a commercial microfabrication foundry process and were experimentally studied. These devices exhibit non-uniform cross-section electrodes and a springless mass. The non-uniform width electrodes were used to prevent pull-in following electrode collision. Springless masses from different materials and sizes, such as 0.5 mm diameter Tungsten carbide, 0.8 mm diameter Tungsten carbide, zirconium dioxide, and silicon nitride, were added in an attempt to force collisions over a range of applied frequencies that would not otherwise result in collisions. The results show that the system operates over a relatively wide frequency range (up to 700 Hz frequency range), with the lower limit far below the natural frequency of the device. The addition of the springless mass successfully increased the device bandwidth. For example, at a low peak-to-peak vibration acceleration of 0.5 g (peak-to-peak), the addition of a zirconium dioxide ball doubled the device's bandwidth. Testing with different balls indicates that the different sizes and material properties have different effects on the device's performance, altering its mechanical and electrical damping.

A hybrid vibration energy harvester with integrated piezoelectric and electrostatic devices

In recent years, energy harvesting technology has become a promising power supply method for low-power wireless sensor nodes. According to the application requirements of energy acquisition, a piezoelectric and electrostatic hybrid vibration energy harvester (HVEH) is proposed in this paper. Compared with other vibration energy harvesters, the proposed hybrid harvester is easier to miniaturize and integrate into a MEMS. The electromechanical coupling model of the hybrid harvester is established. The optimal design of the proposed harvester is carried out based on numerical simulation. The optimal matching impedance of piezoelectric and electrostatic modules are calculated based on numerical simulation and validated through experiments, which are 80–90 kΩ and 15–20 MΩ, respectively. The output power of the HVEH is increased by 0.04%, 0.08%, 0.102%, and 0.097%, when the excitation acceleration is 0.1 g, 0.15 g, 0.2 g, and 0.25 g, respectively, compared with the single piezoelectric module.

Electrostatic Vibration Energy Harvester With a Self-Rechargeable Electret

The electrostatic vibration energy harvester (e-VEH) typically comprises a variable capacitor, whereas the electret layer provides a bias voltage during vibration. However, the charge stored in electret may significantly decay in high temperature or other harsh environments. Recovering the surface charge in electret without taking apart the brittle packaged device remains a technical challenge. In this work, e-VEHs are designed and fabricated with built-in silicon tips and perforated electrode based on MEMS technology. The integrated micro-tips could effectively recharge the electret surface without separating the assembled device. Through-holes on the fixed electrode also optimize the energy harvesting performance. After self-charging, the fabricated device yields an output voltage of 6.2 V at a low driving frequency of 75 Hz, suggesting promising applications for self-powered electronics.

Recent Progress on Mechanical Optimization of MEMS Electret-Based Electrostatic Vibration Energy Harvesters

In recent years, self-powered energy harvesting technology has been widely studied, which may provide supplementary power for wireless sensing networks with low power consumptions. The energy harvester could reduce the use of conventional power supply of batteries, and even eliminate the challenge of battery replacement for large scale networks. In this review, the fundamentals and theories of energy conversion from mechanical vibration to electrical current via variable capacitor are introduced, followed by the discussion of frequency bandwidth broadening, structural parameters, such as surface potential, initial air gap, and stopper heights, as the aspects for controlling squeeze-film air damping force and the output power. Representative examples of the design optimizations of vacuum operating pressure and perforated holes on bottom electrode are presented. Also, special electret processing and built-in corona needles for enhanced space charge stability and self-recharging capability are briefed. This review can provide the research community with a better understanding of the MEMS-compatible electrostatic vibration energy harvester, and further facilitate its development for future potential applications.

Double-Deck MEMS Electrostatic Vibrational Energy Harvester with Airborne Interconnection

Double-Deck MEMS Electrostatic Vibrational Energy Harvester with Airborne Interconnection

Power Generation Demonstration of Electrostatic Vibrational Energy Harvester with Comb Electrodes and Suspensions Located in Upper and Lower Decks

Power Generation Demonstration of Electrostatic Vibrational Energy Harvester with Comb Electrodes and Suspensions Located in Upper and Lower Decks

A Fully Integrated AC-DC Converter in 1 V CMOS for Electrostatic Vibration Energy Transducer with an Open Circuit Voltage of 10 V

This paper proposes an AC-DC converter for electrostatic vibration energy harvesting. The converter is composed of a CMOS full bridge rectifier and a CMOS shunt regulator. Even with 1 V CMOS, the open circuit voltage of the energy transducer can be as high as 10 V and beyond. Bandgap reference (BGR) inputs a regulated voltage, which is controlled by the output voltage of the BGR. Built-in power-on reset is introduced, which can minimize the silicon area and power to function normally found upon start-up. The AC-DC converter was fabricated with a 65 nm low-Vt 1 V CMOS with 0.081 mm2. 1 V regulation was measured successfully at 20–70 °C with a power conversion efficiency of 43%.

Electrostatic Vibrational MEMS Energy Harvester with Thin Film Electrets

Electrostatic Vibrational MEMS Energy Harvester with Thin Film Electrets

High-efficiency Electrostatic Vibrational MEMS Energy Harvester for IoT Sensors

1．背景

New modifications of a Bennet doubler circuit-based electrostatic vibrational energy harvester

In this work, theoretical and experimental studies of the conditioning circuit based on the Bennet doubler with a power source in a variable capacitor branch having one, two and three variable capacitors are carried out for electrostatic vibrational energy harvesters (e-VEHs). Analytical expressions for evaluation of the e-VEH conditioning circuit main parameters are derived. All three modifications of the conditioning circuit have two operation modes: autostabilization and the mode of unlimited capacitors charge and voltage growth. The change between the operation modes for one-, two- and three-capacitor circuits with switches takes place when the maximal-to-minimal capacitance ratio η is equal to 2, 1.618 and 1.414, respectively. For e-VEHs with switches in the autostabilization regime, a three-capacitor circuit will be the most efficient when the capacitance modulation depth η is less than 1.414, a two-capacitor circuit will be the most efficient when 1.414 <η < 1.618, and, for 1.618 <η < 2, the most efficient will be a one-capacitor circuit. In the steady-state autostabilization mode, the saturation voltage will be greater than the primary voltage source V0 if the capacitance modulation depth η is greater than 1.5, 1.366 and 1.302 for the circuit with one, two and three variable capacitors, respectively. The use of diodes instead of switches in the circuits results in the decrease of saturation voltage and leads to the increase of the critical values of ηcr when the change between the operation modes occurs. As the diode inverse currents increase, the effect of the saturation voltage reduction in the autostabilization mode becomes stronger and can even lead to the circuit nonoperabilities. The employment of the Bennet doubler based conditioning circuit modifications considered here enables solving its two main problems: operation only for the capacitance modulation depth more than 2 and the uncontrolled capacitors charge and voltage growth. It should be noted that the observed two conditioning circuit operation regimes will be also inherent for electret vibrational microgenerators and for microgenerators based on using electrodes with materials having different work functions. In addition, the considered two- and three-capacitor circuits make it possible to use e-VEHs at lower values of an external mechanical force or with greater stiffness of spring suspensions minimizing the pull-in effect probability.

Self-Rechargeable Electret based on Vibration Energy Harvester

In this paper, we propose a new method to corona charge the electret after device packaging, based on the common electret based electrostatic vibration energy harvester (e-VEH) with the out-of-the-plane gap closing scheme. Combined with a new portable corona charging system, the electret in the device has been charged successfully. Here, new portable corona charging system is designed to be powered by another e-VEH directly. In our demo, one e-VEH powers the portable corona charging system first, and then the system releases the energy to corona charge the electret in the other device through some build-in corona tips. After charging, the electret possesses a uniform surface potential, and the device shows a better power output then before charging. In the future, if the surface potential of the electret decays after the e-VEH has been working for a long time, we can also use this new method to recharge the electret directly.

Operation features of electrostatic vibrational energy harvester based on contact potential difference

The paper presents a theoretical study of the electrostatic vibrational energy harvester (e-VEH) operation features based on the work function difference between the variable capacitor electrodes. The analysis was carried out for two types of the conditioning circuits: half-wave rectifier and Bennet doubler circuits both with ideal switches and diodes. Both circuits are able to accumulate electrical energy even for low contact potential differences Vbi. Bennet doubler demonstrates higher efficiency than the half-wave rectifier. However, when the variable capacitance modulation depth η ⩾ 2 it is necessary to introduce special means to limit the voltages growth process and avoid an electrical breakdown for the Bennet doubler circuit. For both circuits with diodes the capacitor voltages become lower than those for the circuits with switches and depend now not purely on the built-in voltage Vbi and η, but also on the used diode parameters. When the values of Vbi increase the capacitor voltages for circuits with diodes tend to the corresponding voltages for the circuits with switches. There is also a strong dependence of the capacitor saturation voltage VC1,max on inverse current of the diodes IS. The optimal inverse current of the diodes when the highest saturation voltages are reached is found to be in the range from 50 pA to 100 pA.

Electrostatic MEMS Vibration Energy Harvesters inside of Tire Treads.

An electret electrostatic MEMS vibration energy harvester for tire sensors mounted inside of the tire tread is reported. The device was designed so as to linearly change an electrostatic capacitance between the corrugated electret and output electrode according to the displacement of the proof mass. The electromechanical linearity was effective at reducing the power loss. The output power reached 495 μW under sinusoidal vibration despite the footprint size being as small as 1 cm2. Under impact vibration inside of the tire tread, the output power reached 60 μW at a traveling speed of 60 km/h. It was revealed that a higher mechanical resonance frequency of the harvester adjusted within the frequency band of a low-power spectral density of impact vibration acceleration was effective for high efficiency harvest impact vibration energy.

Charge Doubler Vibration Energy Harvester Using Self-Synchronized mechanical switches

In this work, we study an electrostatic vibrational energy harvester e-VEH based on the charge doubler principle introduced by Bennet two centuries ago. We proof the advantages of using self-synchronized mechanical switches instead didoes, to avoid the problems of leakage current and threshold voltage. We made a new device as a proof of concept, which can work with mechanical switches or with diodes. To harvest the kinetic energy, an electrode moves between two fixed ones thanks to external vibration and creates an asymmetric variation of two variable capacitors. Due to his motion, this electrode also drives a sequence of contacts in the mechanical switch’s configuration. A comparison between this design and the one using diodes in the same conditions shows that the output voltage increase with an exponentially form for both design. However, the one using mechanical switches is faster by a factor of 80%. This induce a time reduction of 99% of harvested power at 40nW.

Comparative performance of voltage multipliers for MEMS vibration-based energy harvesters

This paper investigates by numerical simulation the performance of an electrostatic vibration energy harvester when it is electrically configured in two different diode-capacitor multiplier topologies. The complete lumped-model of an overlap-varying generator along with power electronic interface circuit is constructed for analysis using a crcuit simulator. Parasitic capacitance of the transducers and nonideal diode traits such as leakage current and junction capacitance are incorporated. We find that both configurations are able to efficiently operate with a ratio of capacitance variation much lower than 2, which overcomes a challenging obstacle of MEMS-based devices. Other advantages and disadvantages of the two topologies are compared and discussed.

Characterization of fluorinated nematic liquid crystal for high-power electrostatic energy harvester

The use of fluorinated nematic liquid crystal (NLC) as the medium in between the stator and the rotor of electrostatic vibration energy harvester is proposed for output power enhancement. Fluorine terminal group of 3,4,5-Trifluoro-4’-(trans-4-pentylcyclohexyl)-1,1’-biphenyl (BCH-5F.F.F) offers high resistivity that is two-order-of-magnitude higher than that of 5CB used in our previously study. In a power generation experiment, output power as high as 490 µW is obtained at 10 Hz and 1.00 mmpeak-peak vibration, while keeping the leakage current as low as a few µA.

Nonlinear electrostatic energy harvester using compensational springs in gravity field

This paper presents an experimental proof-of-concept of an innovative design of electrostatic vibration energy harvester based on a double bistable curved beam whose mechanical behaviour is significantly modified by additional linear springs. The basic analytical model for a curved beam with dynamical and quasi static behaviour is introduced and validated by finite element modelling. It is shown that the static force offset due to the gravity field can provide an important increase in the sensitivity to external acceleration. The device is fabricated using silicon on glass technology without the need of a wafer bonding technique. Energy harvesting experiments are performed with various orientations of the device relative to the gravity field direction. The electrical power output is derived from the output voltage measured across a storage capacitor. It is shown that the maximum power output of the energy harvester reaches 10 µW under 50 Hz, 10 m s−2 sine excitation, and is sensible at accelerations with amplitudes less than 1 g (down to 3 m s−2) and operating at a very low frequency range (5–100 Hz) with an overall device size of 1 cm × 1.5 cm × 200 µm.

Improvement of energy conversion effectiveness and maximum output power of electrostatic induction-type MEMS energy harvesters by using symmetric comb-electrode structures

We introduce symmetric comb-electrode structures for the electrostatic vibrational MEMS energy harvester to lower the electrostatic constraint force attributed to the built-in electret potential, thereby allowing the harvester device to operate in a small acceleration range of 0.05 g or lower (1 g = 9.8 m s−2). Given the same device structure, two different potentials for the electret are tested to experimentally confirm that the output induction current is enhanced 4.2 times by increasing the electret potential from −60 V to −250 V. At the same time, the harvester effectiveness has been improved to as high as 93%. The device is used to swiftly charge a 470 µF storage capacitor to 3.3 V in 120 s from small sinusoidal vibrations of 0.6 g at 124 Hz.

Low Frequency High Power Energy Harvester

The vibration energy harvester has become a hot spot because it can supply energy to device without battery. Four types of vibration energy harvesters with different operation modes are introduced in low frequency and high power aspects. They are electromagnetic, magnetostrictive, electrostatic and piezoelectric vibration energy harvester. Their developments are illustrated in detail. Meanwhile, the advantages and disadvantages of the four different structures are compared, and the performances are summarized. Among them, piezoelectric vibration energy harvester was studied the earliest. So, it has better performance and can be used widely.

A new autostabilization mechanism in the Bennet doubler circuit-based electrostatic vibrational energy harvester

In this work, the theoretical and experimental study of the electric circuit is carried out for the electrostatic microgenerators based on the Bennet doubler with a power source in a variable capacitor branch. It is established that the circuit is able to operate at different capacitance modulation depth values. For the circuit with one variable capacitor, when the maximal-to-minimal capacitance ratio is less than 2, one can observe a saturation of the storage capacitor voltage (voltage autostabilization process). The equation for the saturation voltage evaluation is derived. As it is revealed for a maximal-to-minimal capacitance ratio more than 1.5, the saturation voltage is higher than power source voltage V0. When the maximal-to-minimal capacitance ratio is greater than 2, one can observe a continuous growth of the capacitor voltages as for the basic Bennet doubler conditioning circuit. A similar change of the regimes in the same circuit, but with two variable capacitors, takes place when a maximal-to-minimal capacitance ratio is about 1.618. The employment of the considered Bennet doubler conditioning circuit enables solving two main problems: operation only for a capacitance modulation depth above 2 (1.618) and the uncontrolled capacitors voltages growth. The circuit under study can be also used for electret microgenerators and for microgenerators based on using electrodes with materials having different work functions.