Electrostatic Energy Harvester Research Articles

Biomechanical MEMS Electrostatic Energy Harvester for Pacemaker Application: A Study of Optimal Interface Circuit.

The leadless pacemaker is the most recent pacemaker concept, developed to overcome conventional pacemakers' limitations. This technology offers better comfort to the patients, lower risk from implantation, and higher reliability. However, these devices suffer from limited battery lifetime due to the extreme miniaturization required for implantation inside the heart cavities. This work proposes extending the battery lifetime by converting biomechanical heartbeat energy into electricity using an innovative electrostatic MEMS energy harvesting device. Based on theoretical models and experiments, we propose a general approach to choosing the optimal interface circuit which considers the parasitic capacitance of the circuit, as it is an imperfection that significantly affects the power performance. According to the energy consumed by the last generation commercial leadless pacemakers, the proposed MEMS solution with optimal interface circuit experimentally showed the possibility of extending the pacemaker battery lifetime by up to 44%.

Synchronized switch charge constrained conditioning circuit for electrostatic energy harvesting

Electrostatic energy harvesting conditioning circuits usually rely on triangular or rectangular shaped energy cycles. While the former enables significant converted energy, its complexity raises significant issues in realistic applications. Rectangular cycles can be implemented using purely passive components but feature limited conversion abilities. This study bridges the gap between these two approaches, presenting a semi-passive technique consisting of charging and discharging the transducer synchronously with the structure motion, using controlled switches that can be easily implemented while ensuring triangular cycles. Theoretical analysis and experimental validation of such an electrostatic energy harvesting circuit with synchronized controlled switches confirm that this technique provides a simple configuration while ensuring the efficiency of the triangular cycle. To validate the proposed circuit design, a system was employed featuring a rotating metallic variable capacitor designed to mechanically open two magnetic reed switches. This system seamlessly integrates with the devised circuit. The total energy converted by the entire system is estimated to be approximately 1 μJ per cycle, considering a storage component comprising a precharged 1 μF capacitor at 60 V. Yet, results demonstrated that efficiently transferring this energy to the storage stage requires transducers with low losses. While in the presented experimental test an off-the-shelf generic transducer showed high losses, resulting in only 24 nJ per cycle to be harvested, it is believed that specific high quality electrostatic device can benefit from this approach for efficient energy harvesting systems.

Design, Optimization, and Application of Nonlinear Energy Sink in Energy Harvesting Device

Vibration control has been of great interest to scientists and engineers for many years. Although linear vibration absorbers have been shown to be effective in mitigating vibrations at specific frequencies, their vibration reduction effect is usually limited to a narrow frequency bandwidth. Nonlinear energy sinks have attracted attention due to their better vibration reduction effect over a wider frequency bandwidth. In practical applications, the nonlinear energy sink devices can effectively absorb, dissipate, and convert energy from broadband excitation, so as to achieve vibration reduction and energy harvesting. However, research on energy harvesting based on the nonlinear energy sink is less mature than in linear systems. Multiple parameters of device design (e.g., damping size) affect the actual performance of the nonlinear energy sinks, but there is no exact method to simplify the design of the multiparameter nonlinear energy sinks. Since it is more difficult to implement electromagnetic and electrostatic energy harvesters, more research has focused on piezoelectric energy harvesters. This paper summarizes the research on the nonlinear energy sink and energy harvesting technology, including the introduction of the nonlinear energy sink, energy harvesting based on the nonlinear energy sink, and its application in various fields of energy harvesting. The paper also summarizes some important methods for solving the dynamical equations, as well as their advantages and disadvantages. The conclusions provide an outlook on the subsequent research of the nonlinear energy sink technology, such as the introduction of piezoelectric materials with high energy density, the benefits of balanced vibration suppression and harvesting of vibration energy, and the self-tuning of parameters in complex environments. It provides a powerful reference for the popularization and application of energy harvesting technology based on nonlinear energy sinks.

(Invited) SAE-MEMS Technology for Electrostatic Vibrational Energy Harvesters

Energy harvesting [1] is expected to be a self-powering technology for small wireless sensor nodes in the next generation Internet-of-Things (IoT). In particular, small vibrational energy harvesters (VEHs) based on micro-electro-mechanical systems (MEMS) technology, which are battery-free and can generate electricity even at night or in the dark, are being investigated worldwide for next-generation power sources for small wireless IoT nodes [2,3]. Electrostatic MEMS VEHs, which use semi-permanent charge-holding dielectrics called "electrets," are useful for power generation using environmental vibrations because they have a higher output power density at lower frequencies than other methods [4]. Further miniaturization, higher performance, and higher productivity will be required to use electret-type MEMS VEHs as power sources for compact wireless IoT nodes and other devices. Although the integration of MEMS VEHs with power management circuits enables miniaturization, higher performance, and improved productivity, the monolithic integration of electret-type MEMS VEHs and electronic circuits is an unexplored area in conventional technology. Conventional electrostatic MEMS VEHs involve corona discharge, electron beam irradiation, X-ray irradiation, or high-temperature treatment as electret charge processing, which imposes restrictions on the design and manufacturing of MEMS structures and the integration of MEMS and electronic circuits. Recently, self-assembled electrets (SAEs), which are electrets that do not require any charging process, have been developed using materials for organic electroluminescent devices [5]. The surface charge density of SAEs is equivalent to those of previously reported electrets for VEHs, and thus SAE is expected to improve the performance of VEH and simplify the manufacturing process. However, there have been no reports of MEMS devices using SAEs.Our proposed method is the first technology to form SAEs inside MEMS structures using only a vacuum evaporation process at room temperature, and we have succeeded in actual vibration power generation [6]. This technology can be integrated into existing semiconductor processes because the electret formation requires only room-temperature deposition, making it possible to monolithically integrate electret-type MEMS VEHs and electronic circuits on the same substrate. In addition, since the SAE surface potential is proportional to the film thickness, the amount of electricity generated can be further increased by increasing the thickness of the SAE film. Therefore, this technology is expected to accelerate the miniaturization, performance, and productivity improvement of MEMS environmental vibration power generation devices. Akinaga, “Recent advances and future prospects in energy harvesting technologies,” Jpn. J. Appl. Phys. 59 (2020) 110201.D. Mitcheson, E. M. Yeatman, G. K. Rao, A. S. Holmes, and T. C. Green, “Energy Harvesting from Human and Machine Motion for Wireless Electronic Devices” Proc. IEEE 96 (2008) 1457–1486.Suzuki, “Recent progress in MEMS electret generator for energy harvesting,” IEEJ Trans. Elec. Electron. Eng. 6 (2011) 101-111.Toshiyoshi, S. Ju, H. Honma, C.-H. Ji, and H. Fujita, “MEMS vibrational energy harvesters,” Sci. Technol. Adv. Mater. 20 (2019) 124-143.Tanaka, N. Matsuura, and H. Ishii, “Self-Assembled Electret for Vibration-Based Power Generator,” Sci. Rep. 10 (2020) 6648.Yamane, H. Kayaguchi, K. Kawashima, H. Ishii, and Y. Tanaka, “MEMS post-processed self-assembled electret for vibratory energy harvesters,” Appl. Phys. Lett. 119 (2021) 254102.

Dynamic analysis of a novel two-sided nonlinear MEMS electrostatic energy harvester

In this work, we investigate the frequency response of an electrostatic MEMS energy harvester with innovative gap-overlap transducer design. We prove theoretically and experimentally that this design solution gives rise to a strongly nonlinear behaviour in MEMS dynamics. This is the first time that this phenomenon is demonstrated in a gap-overlap electrostatic MEMS along with a theoretical explanation. When increasing the bias voltage, the frequency response shifts towards lower frequencies while bending towards higher ones. The main consequence of this bending is a significant increase of the system bandwidth (+280 % compared to a linear situation with no bias voltage for the same device) when the bias voltage increases up to 30 V. A proposed gap-overlap transducer configuration is demonstrated to be a simple and efficient solution for MEMS energy harvester bandwidth increase.

Optimal Heartbeat Energy Harvesting using Electrostatic Energy Harvesters

Microelectromechanical system of electrostatic energy harvesters is modeled using a nonlinear state–space approach in this research. The analytical models of in‐plane overlap, in‐plane gap closing, and their compound structures are used to analyze the energy harvesting performance from heartbeats‐generated vibrations. The detailed models of both electrical and mechanical subsystems including stopper function, motion drag, parasitic capacitors, and energy converter capacitors are developed in the format of state–space equations. To reach the optimal heartbeat energy harvesting, typical 1D harvesters are developed and allowed to move in x–y and x–y–z directions. Accordingly, the optimal harvester combines the features of in‐plane overlap and in‐plane gap closing energy conversions, and so allows efficient absorption of energy released by heartbeat in different directions. This 3D feature gives a considerable rise to power generation to 35.038 μw at the same size compared to the new rate of the in‐plane overlap or in‐plane gap‐closing electrostatic harvesters individually.

Steering triboelectric and mechanical properties of polymer fibers with carbon black

The development of wearable electronics has spurred an increased interest in self-powered systems and triboelectric nanogenerators (TENGs). To enhance the output performance of TENGs, researchers have dedicated significant efforts toward finding effective ways to increase triboelectric and mechanical performance. This study examined how conductive carbon black (CB) affects the mechanical and triboelectric properties of electrospun fibers made of polyurethane (PU), polystyrene (PS), and polycarbonate (PC). The addition of CB affected their mechanical properties, including increased tensile strength and decreased elongation at break. Importantly, triboelectric testing revealed that incorporating CB decreased the triboelectric output of PU and PS by over 90%, while it increased the output of PC by 260%. These findings indicate that CB's effects on triboelectric properties depend on the material and its content, underscoring the importance of selecting CB content carefully for optimal mechanical and triboelectric performance in electrospun fibers and composites. This research validates the development of advanced composite materials for electrostatic discharge protection and energy harvesting applications.

MEMS Electrostatic Energy Harvester Developed by Simultaneous Process for Anodic Bonding and Electret Charging

MEMS Electrostatic Energy Harvester Developed by Simultaneous Process for Anodic Bonding and Electret Charging

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 Energy Harvesting of Kinetic Motions Using a MEMS Device and a Bennet Doubler Conditioning Circuit

This work is concerned with the design of a microelectromechanical system (MEMS) device that can harvest kinetic energy from its environment using only classical microfabrication techniques. The device is composed of a cantilever beam, where a proof mass is linked to its tip in order to tune the natural frequency of the device. Two stationary electrodes are standing side by side with the cantilever beam to form two out-of-phase variable capacitances with a rotary interdigitated design suitable for flexural bending motions. A Bennet doubler is implemented as a conditioning circuit while taking advantage of the variable capacitances to harvest the kinetic energy of the beam. Finite element modeling is used to estimate the variation of the capacitance and deduce an analytical model from the results. For the dynamic response, a reduced-order model based on a single-mode projection is derived and numerically solved, from the equation of motion of the beam. The response of the system depicts a clear benefit regarding the harvested energy kept in a storage capacitance.

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.

Theoretical analysis of electrostatic energy harvester configured as Bennet's doubler based on Q‐V cycles

SummaryWe present a theoretical analysis of a MEMS electrostatic energy harvester configured as Bennet's doubler. The steady‐state operation of the circuit can be approximated by a rectangular Q‐V cycle in the ideal case or by a trapezoid diagram when the electrical losses are taken into account. A similarity between the voltage doubler and charge‐pump circuit is highlighted. The analytical solution of the saturation voltage is derived, providing a more insightful comprehension of the system performance and the influence of its parameters. The results obtained from studying the Q‐V diagram coincide with those of circuit simulations for both cases when using (i) a mathematically idealized diode or (ii) a realistic diode model that includes the electrical losses. A configuration employing a simple switch connected in series with one of the three diodes that can further increase the saturation voltage is investigated, providing an efficient alternative for boosting the output voltage of an electrostatic energy harvester.

Development and applicability of low-fidelity solutions for electret-based microcantilever energy harvesters

An electrostatic energy harvester is investigated where the reduced-order model is developed accounting for the electrical and mechanical nonlinearities. To overcome the difficulty of dealing with such a nonlinear model, an analytical approach based on the method of multiple scales is employed to create analytical solutions for displacement, electrical charge, and power of this harvester. The reduced-order model with the analytical solutions makes this approach novel and unique. The limits of applicability of this approach is determined by comparing the analytical solutions with solutions obtained using numerical integration. The results show that with estimating the effective nonlinearity as suggested in this approach, it is possible to interpret the behavior of harvester for a variety of operating conditions. The effective nonlinearity decreases more for a particular electrical load resistance as the electret voltage increases. However, the effective nonlinearity increases for a particular electret voltage as the electrical load resistance increases. When effective nonlinearity becomes very small, the behavior of the harvester turns into almost linear, and the matching of solutions of method of multiple scales with solutions of numerical integration is perfect. But, when the effective nonlinearity is significant, the deviation between solutions of method of multiple scales and solutions of numerical integration becomes noticeable. Moreover, increasing acceleration amplitude of the base excitation for cases of significant effective nonlinearity creates a bounded motion with softening behavior.

A hybrid piezoelectric and electrostatic energy harvester for scavenging arterial pulsations

Implantable and wearable biomedical devices suffer from a limited lifespan of on-board batteries which require change causing physical discomfort. In order to overcome this, various energy harvesters have been developed as the human body possesses several types of energy available for scavenging through appropriately designed energy harvesting devices, while the cardiovascular system in particular represents a constant reliable source of mechanical energy from vibration. Most conventional energy harvesters exploit only a single phenomenon, such piezo- or triboelectricity, thus producing reduced power density. As an improvement, hybridisation of energy harvesters intends to negate this drawback by simultaneously scavenging energy by multiple harvesters. In the present work, the reverse electrowetting on dielectric (REWOD) phenomenon is combined with the piezoelectric effect in a proof-of-concept hybrid harvester for scavenging biomechanical energy from arterial or other type pulsations. A mathematical model of the harvester was developed; and, an investigation using computational fluid dynamics simulations was carried out using the COMSOL Multiphysics software. The effect of the materials of piezoelectric film and geometrical features of the harvester on parameters such as the displacement, the frequency of pulsations and the energy produced were studied. An experimental setup that could model the time-varying pressures and displacements caused from arterial pulsations was designed and the characteristics of the produced piezoelectrical energy were analysed. A comparison between experimental and computational data was carried out demonstrating a good agreement. The dependencies between geometrical parameters and electrical output were determined and recommendations on piezoelectric materials and design solutions were provided.

Modeling and analysis of dual modules cantilever-based electrostatic energy harvester with stoppers

Based on the cantilever beam, this paper proposes and designs a novel electret-based electrostatic energy harvester (e-EEH) with dual modules: module I is a capacitor of nonparallel plate electrodes; module II is a multi-electrode array capacitor. Two stoppers are presented in concern with reliability by limiting the motion of proof mass to prevent capacitor breakdown and pull-in. Meanwhile the stoppers serve as a functional element to realize broadband harvesting. Considering the bending of the cantilever beam, the expression of the module Ⅰ capacitance is analytically derived as a function of the deflection. Conformal transformation is applied to obtain the expression of the module Ⅱ capacitance, simultaneously considering the change of distance and overlap area between movable and fixed electrodes. According to Hamilton's principle and Kirchhoff's circuit law, the electromechanical coupling nonlinear dynamics equations of the proposed energy harvesters are established. The output performance of the energy harvester is obtained and analyzed by numerical calculation. The results show that the double-model electrostatic energy harvester can output high power in low- frequency broadband.

Threshold Voltage Cancellation For Low Input Voltage of 65nm CMOS Rectifier of Energy Harvesting For Implantable Medical Devices in Telemedicine Embedded System

Telemedicine applications run at very low voltages, necessitating the use of a Great Precision Rectifier with high sensitivity to function at low input voltages. In this study, we used a 65 nm CMOS rectifier to achieve a 0.2V input voltage for Energy Harvesting Telemedicine application. The suggested rectifier, which has two-stage structure and operates at frequency of 2.4GHz, has been found to perform better in cases where the minimum operating voltage is lower than previously published papers, and the rectifier can operate over a wide range of low input voltage amplitudes. Full-Wave Fully gate cross-coupled Rectifiers (FWFR) CMOS Rectifier Efficiency at Freq of 2.4 GHz: With an input voltage amplitude of 2V, the minimum and maximum output voltages are 0.49V and 1.997V, respectively, with a peak VCE of 99.85 percent and a peak PCE of 46.86 percent. This enables the suggested rectifier to be used in a variety of vibration energy collecting systems, including electrostatic, electromagnetic, and piezoelectric energy harvesters. The proposed rectifier, which is built at 2.4GHz and has a two-stage structure, performs better in the event of low input voltage amplitude and has a lower minimum operation voltage than previously published papers. Full-wave fully gate cross-coupled rectifiers (FWFR) CMOS Rectifier Performance Summary at Freq of 2.4 GHz: With a 2V input voltage amplitude, the minimum and maximum output voltages are 0.49V and 1.997V, respectively, with a maximum VCE of 99.85% and a maximum PCE of 46.86%.

High Precision Low Input Voltage of 65nm CMOS Rectifier for Energy Harvesting using Threshold Voltage Minimization in Telemedicine Embedded System

Telemedicine applications run at very low input voltages, necessitating the use of Great Precision Rectifier with high sensitivity to function at low input voltages. In this study, we used a 65 nm CMOS rectifier to achieve a 0.2V input voltage for Energy Harvesting Telemedicine application. The suggested rectifier, which has two-stage structure and operates at frequency of 2.4GHz, has been found to perform better in cases where the minimum operating voltage is lower than previously published papers, and the rectifier can operate over a wide range of low input voltage amplitudes. Full-Wave Fully gate cross-coupled Rectifiers (FWFR) CMOS Rectifier Efficiency at Freq of 2.4 GHz: With an input voltage amplitude of 2V, the minimum and maximum output voltages are 0.49V and 1.997V, respectively, with a peak VCE of 99.85 percent and a peak PCE of 46.86 percent. This enables the suggested rectifier to be used in a variety of vibration energy collecting systems, including electrostatic, electromagnetic, and piezoelectric energy harvesters. The proposed rectifier, which is built at 2.4GHz and has a two-stage structure, performs better in the event of low input voltage amplitude and has lower minimum operation voltage than previously published papers. Full-wave fully gate cross-coupled rectifiers (FWFR) CMOS Rectifier Performance Summary at Freq of 2.4 GHz: With a 2V input voltage amplitude, the minimum and maximum output voltages are 0.49V and 1.997V, respectively, with a maximum VCE of 99.85% and a maximum PCE of 46.86%.

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