Search

Background: Previous studies showed that hydroxyapatite electret (HAE) accelerates the regeneration of vascular endothelial cells and angiogenesis. This study investigated the effects of HAE in myocardial infarction (MI) model mice. Methods and Results: MI was induced in mice by ligating the left anterior descending artery. Immediately after ligation, HAE, non-polarized hydroxyapatite (HAN), or water (control) was injected into the infarct border myocardium. Functional and histological analyses were performed 2 weeks later. Echocardiography revealed that HAE injection preserved left ventricular systolic function and the wall thickness of the scar, whereas HAN-injected mice had impaired cardiac function and thinning of the wall, similar to control mice. Histological assessment showed that HAE injection significantly attenuated the length of the scar lesion. There was significant accumulation of CD31-positive cells and increased expression of vascular endothelial growth factor (Vegf), intercellular adhesion molecule-1 (Icam1), vascular cell adhesion molecule-1 (Vcam1), hypoxia-inducible factor-1α (Hif1a), and C-X-C motif chemokine ligand 12 (Cxcl12) genes in the infarct border zone of HAE-injected mice. These effects were not induced by HAN injection. Anti-VEGFR2 antibody canceled the beneficial effect of HAE. In vitro experiments in a human cardiovascular endothelial cell line showed that HAE dose-dependently increased VEGFA expression. Conclusions: Local injection of HAE attenuated infarct size and improved cardiac function after MI, probably due to angiogenesis. The electric charge of HAE may stimulate angiogenesis via HIF1α-CXCL12/VEGF signaling.

In this article, a novel approach that mitigates partial discharge (PD) by neutralizing local electric fields with the incorporation of electrets is presented. The surface charge density requirement of electret films that enable electric field neutralization is derived and numerical analysis is performed to validate them. The fabrication process of electrets is introduced, and we experimentally demonstrate the electret films reducing PD caused by the high dv/dt of power electronics switching voltage stimuli for the first time. The PD measurements of an uncharged polyvinylidene fluoride (PVDF) film and a charged PVDF (electret) film are compared as a function of the rise time of square voltage stimuli. In addition, we compare the PD inception voltage of the two films while maintaining dv/dt at a constant value to regulate the impact of capacitive current pulses falsely being detected as PD. The results show great promise in the electret-based approach and suggest that further development of the technology may be able to completely solve PD that has been both chronic and emerging issues in the power industry.

In its main definition, piezoelectrets are polymeric structures with electric charged internal cavities. The bipolar-trapped charges form macro-dipoles that can be mechanically deformed, thus presenting a high piezoelectric coefficient in the order of hundreds of pC/N. Such results outperform most of the traditional piezoelectric polymers. As piezoelectrets can be manufactured by different methods, some of the techniques allow the inner cavities to be geometrically controlled, therefore providing some degree of freedom in the piezoelectric behavior. This report provides a description of the most relevant methods, starting with a brief introduction of piezoelectret origin and reaching recent achievements in piezoelectret production, such as additive manufacturing (3D printing). Materials that are frequently employed in piezoelectret fabrication and methods for improving their characteristics are also presented.

Electrostatic generators as a kind of effective energy harvesters have attracted intensive attention. However, the output of the generators is highly dependent on the charge density. Here, we demonstrate an all-in-one rotary electrostatic nanogenerator based on the charge pumping and voltage multiplying strategy (CV-ESG), which achieves high output power in SF6 atmosphere. CV-ESG integrates a pumping electret generator, a main generator, and a voltage multiplying and stabilization circuit on a pair of rotator and stator. We analyze the breakdown effect and its influence on the insulating layer covered on the electrodes through experiments. The breakdown voltage is high in SF6 atmosphere, and the maximum average power of CV-ESG in SF6 is 37.29 mW at 750 rpm, which is 3.29 times that in air. There is no surface friction in CV-ESG, which avoids abrasion and reduces friction damping. And the pumping generator is integrated with the main generator, making CV-ESG compact and easy to assemble. This work provides the design strategy for a high-power rotary electrostatic generator with good performance.

Purpose. Investigation of the effect of electric polarization of polymeric fibrous materials on the sorption of oil and petroleum products. Methods. Melt blowing of Borealis brand polypropylene. Polarization of samples in a corona discharge field of positive and negative polarity with a strength of 25 kV/cm. Sample processing in low-temperature oxygen plasma of a glow discharge with a frequency of 35 kHz. Weighting method for determining sorption characteristics. Scanning electron microscopy method. Electret thermal analysis method. Findings. The dependence of sorption parameters of materials on the type of physical modification – corona discharge of different polarity and low-temperature plasma of a glow discharge – has been established. It is shown that the modification of fibrous-porous materials in a corona discharge field to impart electret properties to them somewhat reduces the sorption characteristics of these materials in relation to oil. In the manufacture of sorption materials for the collection of crude oil, the original unmodified fibrous-porous material should be used. It has been experimentally established that in the manufacture of sorption materials for the collection of light oil fractions, the preferred method is the modification of fibers in a corona discharge field of negative polarity. Electrization has a significant effect on the processes of sorption by fibers of its lipophilic components. A physical model of the sorption of petroleum products by electret samples of polymeric fibrous-porous materials is proposed. Application field of research. Fibrous-porous polymeric materials subjected to physical modification with the formation of an electret state can be used for: sorption of some oil fractions, filtration of liquids from contaminants of a dielectric nature, purification of air from ionized dust containing radioactive particles, targeted separation of biological fluids containing dielectric and (or) electret components.

Biomimicry, biomimesis and bioinspiration define distinctly different approaches for deepening the understanding of how living systems work and employing this knowledge to meet pressing demands in engineering. Biomimicry involves shear imitation of biological structures that most often do not reproduce the functionality that they have while in the living organisms. Biomimesis aims at reproduction of biological structure-function relationships and advances our knowledge of how different components of complex living systems work. Bioinspiration employs this knowledge in abiotic manners that are optimal for targeted applications. This article introduces and reviews these concepts in a global historic perspective. Representative examples from charge-transfer science and solar-energy engineering illustrate the evolution from biomimetic to bioinspired approaches and show their importance. Bioinspired molecular electrets, aiming at exploration of dipole effects on charge transfer, demonstrate the pintail impacts of biological inspiration that reach beyond its high utilitarian values. The abiotic character of bioinspiration opens doors for the emergence of unprecedented properties and phenomena, beyond what nature can offer.

A nonlinear interface circuit, known as synchronized switch harvesting on inductor (SSHI), for in-plane rotational electret kinetic energy harvesters (EHs) was developed. An explicit generator model is derived to verify the applicability of SSHI, which was originally proposed for the piezoelectric EH, on an in-plane electret EH. Experimentally, 505 μW was harvested with SSHI at a rectified voltage of 142 V for an in-plane rotational electret EH rotating at 1 rps, which is 2.47 times of that with a full-bridge rectifier, and which is in good agreement with the simulation result. The circuit efficiency and criteria for the inductor selection were clarified through circuit analysis based on spice simulation. It is found that the power dissipation of voltage-divider and rectification diodes becomes pronounced as the load voltage increases, constraining the efficiency. The inductor, which usually dominates the circuit volume, can be miniaturized for electret EHs, because the voltage inversion ratio, a benchmark of the SSHI performance, turns out to be insensitive to the series resistance of the inductor. The self-powering ability of the proposed circuit is also presented.

The nature of and the ability to control biasing across dielectrics is a key area of research for the design of more versatile organic field-effect transistors (OFETs). One important technique to a...

In this paper, electret based vibration energy harvesters are designed and fabricated with perforated electrode based on MEMS technology. Through-holes are distributed on the fixed electrode in the device to optimize the energy harvesting process. The effect of the holes on the output power of the device are analyzed and discussed both in the finite element method (FEM) simulation and the experiments. It can be noticed that the through-holes can effectively lower the squeeze-film air damping force on the moveable proof mass at the atmosphere. Therefore, the energy loss due to the air damping could be reduced, and the output power of the device increases. The effects of the hole diameter and numbers on the output power of our device are also investigated in detail. By optimizing the configuration of the holes, the perforated device with the hole diameter of $400~\mu \text{m}$ and depth of $100~\mu \text{m}$ exhibits the highest power output at the low acceleration of 1.84 m/s2, which proves promising application for self-powered electronics in the future. [2020-0380]

An electret‐based electrostatic energy harvester featuring tuneable resonance frequency, small size, light weight, and high output power was designed and its performance predicted by the finite element method and verified by experiment. The device consists of a resilient fluorinated polyethylene propylene (FEP) electret film that is metallised on one side with a small seismic mass attached to its centre and an arc‐shaped counter electrode. In principle, such an energy harvester is mechanically a mass‐spring system and electrically a self‐bias voltage variable capacitor and converts vibrational energy into electrical energy by electromechanical coupling. For an energy harvester sample with dimensions of 30 × 10 × 9 mm for which the last dimension denotes the initial depth of the centre of the harvester, the resonance frequency can be tuned from 17 to 70 Hz by stretching the length of the FEP film loaded with a given seismic mass of 0.06 g. For a seismic mass of 0.1 g, the harvester generated a power up to 797 μW to a matching resistor at its resonance frequency of 17 Hz at an acceleration of 1×g, where g is the gravity of the earth. Such energy harvesters are promising candidates for use in self‐powered electronic devices and wireless sensor network nodes.

Stricter requirements for the quality and reliability of manufactured products, as well as the need to increase the service life of machines, mechanisms and various devices, the operation of which is associated with the use of liquid or gas-air media, is the reason for the emergence of new and improvement of traditional methods for obtaining filter materials with higher performance characteristics. A method for a comprehensive analysis of the properties of regenerated filter materials for fine air purification is proposed. The overwhelming majority of filters, after their service life is exhausted, cannot be regenerated, since this, as a rule, is associated with high energy costs. At the same time, the development of methods for such regeneration is quite relevant from the point of view of resource conservation. In this regard, the purpose of this work is to use a number of physical research methods for the purpose of a comprehensive analysis of polymeric fibrous filter materials for air purification that have undergone regeneration. Filtration materials obtained by the «melt-blowing» method from polymer granules by processing the granulate in an extruder, aerodynamic spraying of the melt and the formation of a fibrous-porous layer on a forming mandrel were selected for research. The main filtration characteristics of the original and regenerated filter materials (breakthrough coefficient, aerodynamic drag),as well as the electrophysical properties of the primary and secondary filter materials, the presence of a spontaneous electret charge have been investigated. The main stages of regeneration and evaluation of physicochemical, mechanical and operational properties of fibrous-porous materials that have undergone secondary thermo-aerodynamic processing in comparison with the original ones are described. It is shown that the studied materials retain their basic properties, while the structure of the fibers changes and the electret effect is enhanced.

The bacterial contamination in implants has been recognized as one of the key issues in orthopedics. In this article, a new technique of electrical polarization of various non-piezoelectric and piezoelectric biocompatible ceramics has been explored to develop antibacterial implants. Optimally processed hydroxyapatite (HA), BaTiO3 (BT), CaTiO3 (CT), Na0.5K0.5NbO3 (NKN) and their composites have been used as model biomaterials to verify the concept. The phase evolution analyses and microstructural characterizations were performed for sintered samples. The samples were polarized at polarizing voltage and temperature of 20 kV and 500°C, respectively, for 30 min. The hydrophilicity of polarized surfaces was examined using deionized water and culture media. The polarization induced in-vitro antibacterial study was performed for both, gram positive and gram negative bacteria. The viability of Staphylococcus aureus ( S. aureus) and Escherichia coli ( E. coli) bacteria reduces significantly on the polarized surfaces. In addition, the influence of polarization on antibacterial response has been explored via various mechanisms such as development of reactive oxygen species (ROS), catalase activity and lipoperoxidation. Furthermore, the cellular response of polarized surfaces was also examined using SaOS2 and MG-63 cells. The viability of SaOS2 and MG-63 cells was observed to increase significantly on negatively polarized surfaces. Overall, the surface treatment enhances the antibacterial response of HA, NKN, BT, CT and their composites surfaces with positive influence on cellular response.

We report the synthesis, morphology and photo-memory device applications of a block copolymer (BCP) consisting of poly(9,9-dioctylfluorene) (PFO) and polystyrene (PS). Three BCPs were designed with various PS contents to manipulate the structure–performance relationship of the polymer electrets in a photonic field-effect transistor-type (FET) memory device. The memory device using the BCP electret exhibited a dynamic switching behaviour with photo-writing and electrical-erasing processes. We found that the BCPs with a high PS content provided improved device performance, which could be explained by two aspects: (1) the enhanced β-conformation of the PFO strengthened the electron-trapping capability, (2) the well-dispersed and microphase-separated morphology stabilized the trapped electrons on the interface of PFO and PS domains. Consequently, PFO5k-b-PS22k outperformed in terms of the photo-responding current along with having a high current on/off ratio of 104 and exhibited a retention time of more than 10 000 s. Our experimental results revealed the effectiveness of using the design based on a BCP for application in photonic FET memory devices.

The detection of mechanical stretching is usually based on piezoresistive effect made up of piezoelectric material. Here, we report a novel approach of autonomous contactless stretch sensor for detection of varying electric field based on electret technology. The present work proposes a novel approach that detects low-noise with high sensitivity for various stretch-based applications. Nanoparticle filled thin-film polymeric membrane are activated by corona injection to trap the charges and form a permanently charged electret and the contactless fixed electrode pair continuously monitors the change in electric field exerted by the tensile strain/deformation on the polymeric membrane. The sensor detects a peak output response of 4.7 V under 20% cyclic tensile strain with a sensitivity of 56 mV/%strain. By considering these merits of simple and scalable fabrication, outstanding performance and robust characteristic, we believe the autonomous contactless stretch sensor can open great opportunities not only for low-noise sensing/detection applications but can contribute to multitude large-scale applications such as intrusion detectors, microphones, pressure monitoring, sensing for security and safety applications.

Chemical doping is widely used in the electronic devices. In p-type semiconductor thin films, oxygen doping fills the hole traps and increases hole concentrations, improving the performance of the organic field-effect transistors (OFETs). Due to the low ionization potential for p-type semiconductors, the superfluous holes induced by the oxygen doping degrades the OFETs off-state leakage performance. On the other hand, for p-type semiconductors with high ionization potential (up to 5.5-6.0 eV), the limited oxidation of oxygen is hard to achieve satisfactory doping concentrations to fill the trap states. This refers to the well-known intrinsic incompatibility between the oxygen doping and high-performance OFETs. Herein, a novel strategy is introduced to overcome the incompatibility and achieve high-performance OFETs by using the structural polymer electret. That is, moderate hole concentrations induced by low-pressure (30 Pa) oxygen plasma fill the hole traps within semiconductor. And the built-in field resulted from polymer electret accumulates the holes inside semiconductor near the semiconductor/electret interface, thus improving the OFETs performance. Using a model organic semiconductor with high ionization potential-2,7-didodecyl[1]benzothieno [3,2-b][1]benzothiophene (C12-BTBT) as an example, the high-performance OFETs with field-effect mobility ( $\mu _{FET}$ ) of 3.5 cm2V−1 s−1, subthreshold-swing ( SS ) of 110 mV decade−1, on-off ratio of 104, and widely-tunable threshold voltage ( ${V} _{t}$ ) are realized at a low voltage below 2 V in the open air.

A simple versatile way of producing mini electret pieces with a handheld corona charging device is reported here. Its adaptability and suitability are demonstrated using a PVDF polymer. A quantitative assessment of the electret pieces is made by probing local charge distribution using electric force microscopy. The results are expected to be useful for polymer-based applications like dust filters that protect in the sub-micron range and for possible drug release devices.

Lightning peak current is one of the most important parameter concerning the studies of the lightning phenomena. Nowadays, with a continuous dissemination of elevated structures, such as telecommunication towers, the study of the lightning peak current could be intensified with the installation of measurement devices in large scale. Thus, it is useful to develop a device that is robust, compact, low cost, and allows data collection. This paper describes a high-current sensor operating in a range up to 100- and 7.7-kA resolution. The system consists of a self-integrating Rogowski coil connected to the electret sensor by a coaxial cable. The electret sensor is installed in a sturdy and inexpensive casing at the tower base. Measurements indicate a linear and precise correlation between the voltage generated by the coil, installed on the top of the tower, and the impulse current from lightning.

The triboelectric nanogenerator (TENG) is in the spotlight due to its advantages of material and processing diversity. Despite these advantages, for its practical utilization, the output performance of the TENG still needs to be enhanced. Unlike most of the previous approach to increase triboelectricity between two contact surfaces, in this paper, the output performance is significantly enhanced by improving the electrical charge induction through employment of a stably pre-charged electret. The main advantages of the proposed strategy is stable long term output enhancement of the TENG. For the first time, the eminent concept of “quality of electrical charges” on the electret is proposed as the degree of helpfulness of the electrical charges to enhance the electrical output performance of the TENG. In this regard, a procedure to develop the electret with high quality electrical charges in deep traps, which determines long-term performance of the TENG, is systematically investigated to maximize the amount of electrical charges and simultaneously minimize their escape to the external environment. In consequence, unlike existing studies only focusing on immediate enhancement of electrical output performance of the TENG with electret, this study provides the strategy to stably enhance the output performance for a long time. This strategy becomes dominant especially with weak contact force generating small oscillation without strong contact between two materials. Thus, using the developed electret, enhanced and reliable performance of the energy harvester is further demonstrated as a proof of niche application to effectively harvest energy from weak vibration of an automobile engine.

This paper presents an ultra-low power human proximity sensor using electrostatic induction. The analytical model of electrostatic induction current generated by human motion is derived and verified with measurement results. Based on the analytical model, we propose an ultra-low power integrated circuit to detect human motion using electrostatic induction. The test chip implementing the proposed circuit is fabricated in a commercial 250 nm CMOS process. The measurement results of this fabricated chip show that it consumes only 30 nW for detecting human motion, which is less than 1/100th of the power dissipated by the conventional human proximity sensors.

The development of highly durable, stretchable, and steady triboelectric nanogenerators (TENGs) is highly desirable to satisfy the tight requirement of energy demand. Here, we presented a novel integrated polymeric membrane that is designed by PEDOT:PSSa-naphthalene sulfonated polyimide (PPNSP)-EMI. BF4 Electronic skin (e-skin) for potential TENG applications. The proposed TENG e-skin is fabricated by an interconnected architecture with push-pull 3D ionic electrets that can threshold the transfer of charges through an ion-hopping mechanism for the generation of a higher output voltage (Voc) and currents (Jsc) against an electronegative PTFE film. PPNSP was synthesized from the condensation of naphthalene-tetracarboxylic dianhydride, 2, 2’-benzidine sulfonic acid, and 4,4’diaminodiphenyl ether through an addition copolymerization protocol, and PEDOT:PSSa was subsequently deposited using the dip-coating method. Porous networked PPNSP e-skin with continuous ion transport nano-channels is synthesized by introducing simple and strong molecular push-pull 3D interactions via intrinsic ions. In addition, EMI. BF4 ionic liquid (IL) is doped inside the PPNSP skin to interexchange ions to enhance the potential window for higher output Voc and Iscs. In this article, we investigated the push-pull dynamic interactions between PPNSP-EMI.BF4 e-skin and PTFE and tolerable output performance. The novel PPNSP- EMI.BF4 e-skin TENG produced upto 49.1 V and 1.03 µA at 1 Hz, 74 V and 1.45 µA at 2 Hz, 122.3 V and 2.21 µA at 3 Hz and 171 V and 3.6 µA at 4 Hz, and 195 V and 4.43 µA at 5 Hz, respectively. The proposed novel TENG device was shown to be highly flexible, highly durable, commercially viable, and a prospective candidate to produce higher electrical charge outputs at various applied frequencies.

With the rising demand for wearable, multifunctional, and flexible electronics, plenty of efforts aiming at wearable devices have been devoted to designing sensors with greater efficiency, wide environment tolerance, and good sustainability. Herein, a thin film of double-network ionic hydrogel with a solution replacement treatment method is fabricated, which not only possesses excellent stretchability (>1100%) and good transparency (>80%), but also maintains a wide application temperature range (−10~40 °C). Moreover, the hydrogel membrane further acts as both the flexible electrode and a triboelectric layer, with a larger friction area achieved through a micro-structure pattern method. Combining this with a corona-charged fluorinated ethylene propylene (FEP) film, an electret/hydrogel-based tactile sensor (EHTS) is designed and fabricated. The output performance of the EHTS is effectively boosted by 156.3% through the hybrid of triboelectric and electrostatic effects, which achieves the open-circuit peak voltage of 12.5 V, short-circuit current of 0.5 μA, and considerable power of 4.3 μW respectively, with a mentionable size of 10 mm × 10 mm × 0.9 mm. The EHTS also demonstrates a stable output characteristic within a wide range of temperature tolerance from −10 to approximately 40 °C and can be further integrated into a mask for human breath monitoring, which could provide for a reliable healthcare service during the COVID-19 pandemic. In general, the EHTS shows excellent potential in the fields of healthcare devices and wearable electronics.

Wide bandgap (WBG) power electronics converters (PEC) that enable high voltage, high dv/dt, and high-power density inevitably contain sharp edges, triple points, and cavities in their design, which result in local electric field enhancements. The intensified local electric stresses cause partial discharge (PD) that erodes electrical insulators and causes accelerated device failure. In this study, a new approach that utilizes electrets for PD mitigation is presented. We experimentally show that incorporating electret fabricated from polyvinylidene fluoride (PVDF) film based on widely used triode-corona charging method neutralizes local electric fields and mitigates PD that occurs in and around triple points and cavities.

Fiber-based nanogenerators have great potential applications in wearable electronics such as portable nanodevices, e-skin, and artificial intelligence system. Here, we report a kind of fiber-based electret nanogenerator (FENG) with a semisupported core-shell structure. Owing to its unique structure, the open-circuit voltage and short-circuit current of the FENG reach 40 V and 0.6 μA, respectively, under a short working distance (∼25 μm). No obvious degradation of the output performance under a long-time continuous work (>16 h) and different humidity environments (20-95%) is observed, which demonstrates the FENG's good reliability and stability. Many universal materials, such as cotton rope, conductive sewing thread, and polyvinyl chloride tube, have been successfully used to fabricate FENG. Meanwhile, the FENG-based wearable fabric has been successfully developed to effectively harvest mechanical energy of human motion. The FENG is highly effective, reliable, and stable, promoting the development of fiber-based nanogenerators and their applications in self-powered wearable electronics.

A straightforward mechanism for the photorecovery behavior of photoresponsive nonvolatile organic field-effect transistor (OFET) memories is proposed by employing a commercially available conjugated polymer, the poly(9,9-dioctylfluorene) (PFO), the conjugated monomer fluorene (FO), and the nonconjugated poly(vinyl alcohol) (PVA), as charge storage layers beneath the semiconducting pentacene layer. As photoexcitons are generated upon light exposure, the respective charges recombine with the trapped charges in electrets and neutralize the memory device. However, whether the excitons are generated in the semiconducting layer or the electret part, the origin that mainly governs the photorecovery behavior remains unclear. In this study, we show that when PVA, a nonphotoactive electret, replaces PFO the photorecovery behavior is totally absent, and it confirms the photorecovery behavior dominated by the excitons in situ generated in a charged electret. Moreover, PFO as a photoactive electret, exhibiting an excellent hole-trapping ability over 24 h in the dark and high Ion/Ioff current ratio of 108, has successfully demonstrated rapid photoinduced recovery under UV light. The devices also display a reliable switching ability between electrical charge trapping and optical recovery cycles for optical-recording application. This report presents a clear understanding behind photorecovery phenomena that demonstrates useful guidance to boost the development of photoactive OFET memories based on conjugated polymer electrets.

Flexible triboelectric generators present a wide range of prospective applications owing to their small size, light weight, and wearability; in addition, they can convert external mechanical energy into electrical energy to provide an energy supply for wearable electronic products. In this study, a wearable textile triboelectric generator was developed by weaving polyurethane (PU) nanofiber core-spun yarn and Si3N4-electret-doped polyvinylidene fluoride (PVDF) nanofiber core-spun yarn into a double-layer fabric. Within the double-layer fabric, one layer was Si3N4-doped PVDF (denoted as Si3N4@PVDF) nanofiber fabric, and the other was PU nanofiber fabric. When subjected to an external mechanical force, PU nanofiber fabric and Si3N4@PVDF nanofiber fabric came into contact and were able to convert external mechanical energy into electrical energy. The most notable instantaneous electrical performance of this triboelectric nanogenerator was open circuit voltage of 71 V, short-circuit current of 0.7 μA, and output power of 56 μW. Additionally, the wearable textile triboelectric generator exhibited superior washability, stability, and cycle durability. More significantly, it was capable of driving some low-consumption electronic products, including capacitors, LED bulbs, and digital meters, thereby exhibiting a strong potential for flexible self-powered electronic devices and intelligent textiles.

The electrophysical characteristics of a multilayer memristive Au/Ta/ZrO2(Y)/TaOx/TiN structure have been studied. Electron and ion electret effects due to charge carrier trapping and ion migration polarization in the dielectric have been discovered. The influence of traps on electroforming processes and resistive switching has been established. The values of activation energy and ion and trap concentrations have been determined. The effect of resistive switching stabilization has been found, which is associated with the specific bilayer structure of TaOx and self-forming tantalum nanoclusters. The nanoclusters serve as electric field concentrators in the course of electroforming and subsequent resistive switching.

Charge/light-related advancements have greatly pushed the development of modern technology, and the relationship between charge and light is worth exploring. While research into the applications of light and charge flow (photoelectric current) is in full swing, studies on the reaction between light and electrostatic charge have made little progress on rare ways to realize photo-stimulated discharge. Herein, we link electrostatic charge and light using a bridge of intense heat, which is produced from the efficient photothermal conversion of Ti3C2Tx MXene. The in situ photothermal conversion and selective thermally stimulated discharge are successfully combined, then novel light-induced electrostatic lithography can be realized on both polymethyl methacrylate glasses and nanofilms. In this process the surface temperature of Ti3C2Tx film can be as high as 300 °C using 808 nm near-infrared irradiation at a power density of 1.7 W cm−2. The combination of light and electrostatic charge is also successfully applied to electrostatic printing and chemical reactions.

This work presents general studies of the influence of doping methods on the properties of elements with anomalous photovoltaic effects and the process of doping of semi-crystalline thin CdTe films with isovalent impurities is also investigated. The process of thermal diffusion has been studied.

Electrets, referring to an insulating dielectric material carrying quasi-permanent neat charges, are attracting interest for their potential wide applications in electronic devices, filtration fabrics and biological/medical sterilization. Here we report a high-performance, optical transparent and solution-processible polymer electret, atactic poly(4-fluorostyrene) (FPS), synthesized by radical polymerization. The deep bulk traps of FPS could stably accommodate charges, and the hydrophobicity of this material prevents moisture invasion in ambient environments, both of which contribute to the high environmental-stability. Subsequently, the solution processed FPS film with a high sheet charge density of 6.8 × 1012 cm−2, high dielectric strength, good thermal stability and decreased leakage current is introduced as a gate dielectric for organic field effect transistors (OFETs) and non-volatile memories. Using FPS-coated SiO2 as the gate dielectric and 2,7-didodecyl[1]benzothieno[3,2-b][1]benzothiophene (C12-BTBT) as the semiconductor, OFETs can work with a high mobility of 11.2 cm2 V−1 s−1 and on/off ratio of 107, along with a large memory window of 108 V, and enhanced memory stability over one month during direct exposure to ambient air. Finally, we use a conjugated polymer blended with FPS to show the general improvement of OFET performance by our FPS electret.

Sections PDFPDF Tools Share Summary This study reports a new concept for power generation from thermal energy, which integrates a thermoacoustic engine (TAE) with a contact‐free electret‐based electrostatic transducer. The TAE converts thermal energy into high‐intensity acoustic energy, while the electret‐based electrostatic transducer converts the generated acoustic energy into electricity. The experiments demonstrate the feasibility and potential of the proposed electret‐based thermoacoustic‐electrostatic power generator (TAEPG). The dynamic response of the electrostatic transducer and energy conversion inside the TAE are further investigated using a lumped element model and a frequency‐domain reduced‐order network model. Good agreement is achieved between experimental measurements and theoretical predictions. Furthermore, a parametric study is performed to study the effect of key parameters including the external heating power, air gap, and resistive load on the performance of the TAEPG. Results show that an open‐circuit voltage amplitude of 4.7 V is produced at a closed‐end pressure amplitude of 480 Pa in the experiment, and it is estimated that 25.2% of the acoustic power generated by the TAE has been extracted by the electret‐based electrostatic transducer. In this case, the maximum electric power output is measured to be 2.91 μW at a resistive load of around 2.2 MΩ. By increasing the external heating power, the TAEPG can produce a maximum voltage amplitude of 8 V. This work shows that the proposed concept has great potential for developing miniature heat‐driven power generators.

Using amplified femtosecond pulses at a wavelength of 1028 nm, the second harmonic is generated at a wavelength of 514 nm by composite polymer films containing D-π-A (push–pull) chromophores with quadratic optical nonlinearity. It is shown that these films are photostable with respect to laser pulses having peak intensities of up to 11.6 GW/cm2. The effective generation of the second harmonic is observed in a wide range of pump beam incidence angles (20°–80°) with a maximum in the vicinity of 60°.

In this study, we explore different filter and contextual characteristics that influence effectiveness of high-efficiency filters in 21 residences in Toronto, Canada. The in situ effectiveness was assessed with decay tests at the beginning and the end of filter life with four different filters (MERV 8-14 from ASHRAE Standard 52.2) installed in operational HVAC systems, compared with either the system off or with no filter installed. There was considerable difference between median PM2.5 effectiveness of the non-electret filters when compared to electret filters (16% vs. 36%) of the same nominal efficiency (MERV 8). However, median PM2.5 effectiveness of electret filters only slightly improved (between 5% and 9% absolute increase) as MERV increased from 8 to 14. There was more variation in filter effectiveness between the same filter in different homes than there was between different filters in the same home. Variations in filter performance arose because home-specific particle loss rates (eg, ventilation rate) vary greatly in different buildings. The higher the loss rates due to non-filter factors, the lower the effectiveness of a filter. Given the relatively large variation in effectiveness for a given filter over time and in different homes, increasing system runtime may be a productive way to improve filter performance in many homes.

A novel electret sensor, made from a polytetrafluoroethylene (PTFE) foil, is proposed for monitoring of radon concentration in closed spaces. A triode air system was implemented to form the electret foil. In order to calibrate the electret sensor, the ionization chamber with the electret embedded at its bottom, was placed in an emanation chamber containing radon of known concentration. The change in the effective charge density of the electret resulting from the interaction of the electret sensor with ionizing radiation, make it possible to determine the degree of its response to the radon concentration in the examined environment. The electric charge of the electret sensor was evaluated at the beginning and at the end of the concentration measurement using a field chopper. The measurement of the value of the electric field between the electret and the reference electrode directly corresponds to the effective surface charge density of the electret. The measuring system was calibrated in values of the electret equivalent voltage of Uz. In order to assess the electret properties, both the thermostimulated charge relaxation (TSQ) method and the thermostimulated discharge current (TSDC) method were used to evaluate corresponding parameters. These investigations led to the optimization of the electret formation process for the maximum sensitivity to the effects of alpha particles resulting from radon radioactive decay.

Integration of selective photodetection and signal storage in a single device, such as organic field-effect transistor (OFET) memories, meets the demands for radiation monitoring and protection. A new strategy is developed to achieve filter-free and selective light monitoring by adopting a solution-processed blend charge-trapping layer in OFET memories, where the charge-trapping layer is composed of phenyl-C61-butyric acid methyl ester (PCBM) dispersed in a polymer electret thin film. The OFET memory without PCBM shows response only to ultraviolet light, whereas the spectral response edges are extended to the visible and near-infrared regions in the corresponding devices with relatively low and high contents of PCBM in the charge-trapping layer, respectively. A set of OFET memories with different PCBM contents is used to qualitatively evaluate the light composition in an optical source. The tunable spectral response in the OFET memories is ascribed to the additional photoassisted charge-trapping paths depending on the blend ratio in the charge-trapping layer. This mechanism may inspire alternative approaches to organic-based optical sensing and monitoring in flexible and wearable electronics.

In this article, we have fabricated organic nonvolatile memory (ONVM) transistors using different thicknesses of poly( $\alpha $ -methyl styrene) ( $\text{P}\alpha $ MS) as tunneling layers on Si substrates with a SiO2 layer of 50 nm. With a tunneling layer thickness of 6 nm, the fabricated devices achieved an operation voltage of −12 V. To this structure, we added a 12-nm-thick poly(vinyl alcohol) (PVA) film as the charge trapping layer. Compared with the devices without an additional trapping layer, the bilayer devices showed a larger memory window of 9.8 V if a programming voltage of 28 V was applied for 1 s, and a memory window of 8 V is reached after a programming time of only 0.2 s. Furthermore, the retention and endurance properties of the bilayer devices were also improved. Above all, using the combination of non-polar and polar polymers as a bilayer electret provides an easy strategy to optimize charge trapping properties for ONVMs.

Recently, we reported on the preparation of Teflon AF 1600 based electret films with extremely high charge stability by thermal evaporation and corona discharge [Hirschberg et al. Organic Electronics 57 (2018) 146]. Here we present investigations on thermally evaporated electret films made of Teflon AF 2400 with even improved charge stability. Deposition of smooth films without micropores at rates exceeding 10 nm/s was achieved with a specially designed evaporator. The evaporated thin films exhibit an extraordinary dielectric breakdown strength, which is almost one order of magnitude above the bulk value for films thicknesses in the μm range. The resulting maximum charging potential is as high as 267 V for a 5.4 μm electret film. Films of 15 μm could be charged up to 600 V. The charge stability was investigated as function of charging potential, film thickness, and the polarity of the charges. Negative charging proved to provide a much higher charge stability. The charge stability decreases with increasing charging voltage, which is shown to be due to filling of more shallow traps upon at higher charging voltages. Thicker films exhibit higher charge stability. This observation is in line with the proposed internal charge decay mechanism and can be explained in terms of longer charge migration paths. The reproducibility of the fabrication process of the thin film was tested involving about 200 samples. An excellent standard deviation of 2.9% was found for a charging voltage of 250 V, which makes the preset fabrication method very attractive for industrial applications.

Micro mechanical energy harvester as a kind of micro power source for micro electro mechanical systems (MEMS) has been paid considerable attention. Electret-based vibration energy harvester (E-MVEH) has been a research highlight due to its high sensitivity, simplicity and compatibility to the fabrication process of MEMS. In this manuscript, a novel E-MVEH with multiple-air-gap structure based on bipolar electrets is comparatively investigated. The E-MVEH with single-air-gap structure consists of an electret membrane (EM) with an electrode on one surface and a counter-electrode supported by means of micro-springs. The E-MVEH with double air gaps is made of a bipolar electret membrane put in the middle of two counter-electrodes that are supported by means of micro-springs. It is essentially equivalent to two variable capacitors in series. The E-MVEH with four air gaps consists of two double-air-gaps E-MVEH in parallel connection. When an external vibration causes a relative displacement between the electret membrane (EM) and the counter-electrode, the capacitance varies, leading to re-organization of the charges on the counter-electrode. Thus, an alternating current is generated and the vibration energy is converted into electric energy. This alternating current can be changed into direct current through a full bridge rectifier. The bipolar EM used in this study is a sandwich FEP/THV/FEP perfluoropolymer EM reported previously by our group. It can display persistent and strong electrostatic field with both polarities on the top and bottom surface, respectively. The experimental results of the output characteristic for the proposed E-MVEH show that there exists a resonant frequency in the vibration frequency range of 30−180 Hz, at which the open-circuit voltage and short-circuit current and hence the output power reach their respective maximum. The resonant frequency moves towards the low frequency with increasing vibration intensity, whereas the effect of air-gap number on the resonant frequency is rather small. On the basis of experimental results and theoretical analysis, the maximum output power is positively correlated to the vibration driving force, the surface potential and the area of the electret membrane, and the air-gap number. When the surface potential of the electret membrane is 1200±50 V, the maximum output power is only 0.19 μW for single-air-gap structure and reaches 27.02 μW for the four-air-gap structures under a vibration driving force of 0.5 N and a load resistance of 55 MΩ. For the four-air-gap structures, the maximum output power increases to 59.12 μW when the surface potential of the electret membrane increases to 2150 V. The multi-air-gap energy harvester fabricated with bipolar electret membrane can produce larger variable capacitance; therefore, the output power is significantly enhanced. This novel E-MVEH provides an up-to-date strategy for the design of self-powered sensor systems.

Future Naval shipboard power and energy management systems must coordinate the operation of all major components with the use of power electronic converters (PECs). However, the high electric field, repetitive pulses, and fast dv/dt in the PEC-based power systems causes partial discharge (PD) and surface flashover that result in accelerated material aging and system failure. In this study, an electret-based dielectric approach is proposed to address these issues by reducing the PD magnitude and improving critical flashover voltage (CFO). The charge trapped on the electret films neutralizes the locally enhanced electric field around the triple points, sharp edges, and cavities. We experimentally demonstrate the effectiveness of the electret films in solving the dielectric issues by conducting PD measurements and surface flashover experiments under square voltage waveforms that represents PEC switching voltages.

Electret-based vibrational energy generators (E-VEGs) are of particular interest since they can generate electrical power from ambient vibration. A challenge is that the charging process is required for making the electret from a dielectric material, and the process is one of the main factors that determine the manufacturing costs of the device. Recently, by utilizing the spontaneous orientation of polar molecules, which have been used for organic light -emitting diodes, we realized a novel E-VEG that does not require any charging process. In this paper, the operation mechanism and stability of the device are discussed. We believe that the E- VEG using spontaneous orientation enables us to reduce the costs, leading to the device's mass commercialization.

With the rapid development of the Internet of Things (IoT) and big-data technology, the higher requirement for the intelligence of bearings has been put forward. This paper reports a novel type of intelligent thrust ball bearing, called electret thrust ball bearing (ETBB), which has both self-powering and self-sensing capabilities. Due to the common characteristics of non-contact and relative rotational movement, the electret rotary power generator on the free-standing mode is embedded into the thrust ball bearing, which not only maintains the mechanical structural integrity of the thrust ball bearing, but also obtains the capabilities of self-powering and self-sensing. A localized selective corona charging method is developed for integrating both positive and negative charged electret into the rotor of the ETBB to improve output performance and the output power of the ETBB by bipolar charging is increased by 365% to 0.35mW. Through measuring the electrical output characteristics of the ETBB at different rotating speeds, it is found that the rotating speed of the ETBB can be characterized by the two values of output current and frequency, which has extremely high sensitivity and stability. This work proposes an electrostatic intelligent bearing with self-powering and self-sensing, which has widespread application prospects in the development of IoT and Intelligent machinery.

In this manuscript, the first pyroelectric-based rechargeable electret for continuous energy harvester is reported. The proposed pyroelectric-based electret preparation provides two main advantages 1) Wafer-scale electret production with uniform surface charge density and 2) On-chip rechargeable option for the electret-based energy harvesters and sensors. Pyroelectrically generated surface charges are transferred to the dielectric material placed in contact with the polarized surface of the pyroelectric crystal. A 5 mm thick lithium niobate crystal is used as a pyroelectric material with a temperature gradient of 2.3°C/sec. A Teflon dielectric is used as an electret material with a surface area of 1 cm2 and thickness of $75\mu m$ . Obtained results from the pyroelectrically prepared electret showed a surface potential of ∼540V with a charging efficiency of 8.9% from the pyroelectric surface potential of 6060V. Obtained results were in good agreement with repeatability and charge stability for >15 days. Our preliminary experiment of energy harvester showed an average power of $1.29\mu W$ at 4Hz.

Piezoelectret using space-charged porous polymers attracts much attention due to its high piezoelectric coefficient. In the present study, a novel all-polymer soft-X-ray-charged multilayer piezoelectret is proposed for push-button energy harvesting. The prototype is microfabricated using a parylene-C structural layer with patterned gap-control protrusions, dip-coated PEDOT:PSS electrode, and a dip-coated polymer electret layer. With the current prototype, up to 24.6 µJ electrical energy has been obtained with a single pushing force of only 1.3 N, corresponding to a record-high piezoelectric coefficient d33 of 105 nC/N, 30 times higher than conventional MEMS-based piezoelectrets.

There is a large amount of unused electric field energy around power lines. Due to the inherent low energy density around the power line, the traditional capacitive energy harvester adopts a large-volume strategy to increase the output power, which limits the application scenarios. This paper proposes a new type of electric field energy harvester based on electret electrostatic enhancement effect to harvest electric field energy. The electric field energy density is increased by adding an electret film to the double-layer disc structure. In the case of reducing the size of the harvester, the external electric field and the electric field generated by the electret form a coupling, which increases the vibration amplitude and thereby increases the output power. Using the Comsol finite element simulation tool, the simulation results show that the maximum output voltage can reach 530V at a resonance frequency of 300Hz. The acquisition power of harvester is up to 2.34mW in the electric field. The harvester can work for low-power wireless sensor nodes near the power line.

Triboelectric nanogenerators (TENGs), which hold great promise for sustainably powering wearable electronics by harvesting distributed mechanical energy, are still severely limited by their unsatisfactory power density, small capacitance, and high internal impedance. Herein, a materials optimization strategy is proposed to achieve a high performance of TENGs and to lower the matching impedance simultaneously. A permittivity-tunable electret composite film, i.e., a thermoplastic polyurethane (TPU) matrix with polyethylene glycol (PEG) additives and polytetrafluoroethylene (PTFE) nanoparticle inclusions, is employed as the triboelectric layer. Through optimizing the dielectric constant of the composite, the injected charge density and internal capacitance of the TENG are significantly enhanced, thus synergistically boosting the output power and reducing the impedance of the TENG. The optimal output power reaches 16.8 mW at an external resistance of 200 kΩ, showing a 17.3 times enhancement in output power and a 90% decline in matching impedance. This work demonstrates a significant progress toward the materials optimization of a triboelectric generator for its practical commercialization.