Search

A compact and lightweight sensor is always expected to be embedded with the traditional micro-vibration isolator in spacecraft. It helps to detect the subtle disturbances the isolator encounters and alerts for potential harm. In this work, we developed a self-sensing micro-vibration isolator using an electret transducer. The theoretical models of the electret-based self-sensing isolator are derived from Hamilton's principle to investigate the coupled dynamics of the system and guide a model-based design. Simulations via the finite element method were also conducted to verify and extend the effectiveness of the proposed model. The results show that the electret transducer is an excellent candidate for the embedded sensor of the micro-vibration isolator. With the proper size and appropriate deployment pattern, the electret sensors can precisely detect the translation and rotation of the unsprung load. [ABSTRACT FROM AUTHOR]

This study explores the fabrication of electret nonwoven structures for high-efficiency air filtration, utilizing the blow spinning technique. In response to the growing need for effective filtration systems, we aimed to develop biodegradable materials capable of capturing fine particulate matter (PM2.5) without compromising environmental sustainability. Polylactic acid (PLA) was used as the primary polymer, with the addition of SiO2 and MoS2 to enhance the fibers' charge retention and filtration performance. The fibers were charged electrostatically to improve particle capture efficiency. The experimental results showed that fibers containing 5% MoS2 exhibited the highest filtration efficiency, surpassing those with SiO2, despite MoS2 being a semiconductor and SiO2 a dielectric. Furthermore, the addition of MoS2 improved the filtration efficiency across a range of particle sizes (0.2–1 µm) while maintaining a manageable pressure drop. These findings suggest that incorporating MoS2 in electret nonwoven structures can significantly improve filtration performance, making it a promising material for advanced air filtration applications. This study contributes to the development of eco-friendly filtration materials with high performance, essential in reducing exposure to airborne pollutants. [ABSTRACT FROM AUTHOR]

Confronting the limitations of traditional von Neumann architectures—chiefly their inability to process unstructured data efficiently, this work proposes a new in‐memory sensing and computing paradigm exemplified by introducing a pioneering tin oxide nanowire‐based photoelectric synaptic transistor (PST) with a floating gate replicating biological synapses' functionality. Capitalizing on the nanowire structure's high surface area to volume ratio, the PST overcomes the challenges of photo response in metal oxide semiconductors. Integrating metal oxides' Photoelectric‐Phenomenon‐Coupling effect with the charge storage capacity of field‐effect transistors enables effective optical detection and weight storage. The PST performs exceptional optoelectrical and synaptic properties, including capabilities for long‐term memory, short‐term memory, paired‐pulse facilitate, and synaptic plasticity. Furthermore, by incorporating a learning mechanism, the PST achieves an impressive 94.65% accuracy in recognizing patterns in the Modified National Institute of Standards and Technology's(MNIST) handwritten digit dataset within 50 epochs. This research indicates a significant step toward intelligent computing systems closely mimicking the human brain's computational prowess. [ABSTRACT FROM AUTHOR]

Abstract The pursuit for advanced magnetoelectric field sensors has gained momentum, driven by applications in various fields, ranging from biomedical applications to soft robotics and the automotive sector. In this context, a capacitive read-out based magnetostrictive polymer composite (MPC) sensor element is introduced, offering a new perspective on magnetic field detection. The sensor element’s unique feature is the possibility to independently tailor its mechanical and magnetic properties. When compared to other composite-based magnetic field sensors, the limit of detection (LoD) is three orders of magnitude lower (95.6 nT/√Hz at a resonance frequency of 160.5 Hz). In contrast to other electret-based ME sensors, the LoD is reduced by a factor of 20. To the best of the authors’ knowledge, this work marks the first comprehensive attempt to characterize a sensor magnetically, aligning with the thorough assessment standards of ME sensors. This study aims to narrow the disparity between established magnetic field sensors, featuring consistent characterization protocols, and the novel MPC sensors, which often undergo limited magnetic characterization as part of their evaluation. The presented sensor, built from readily available materials, offers a versatile and tuneable platform for magnetic field detection, and ongoing research aims to unlock its full potential in diverse applications.

In recent years, the demand for sustainable and degradable materials and electronic devices has increased significantly. Among a range of biodegradable polymers, poly(lactic acid) (PLA) is a good alternative to conventional petrol-based polymers because of its attractive mechanical properties and its easy processability. Recently, PLA has also been described as a promising dielectric material with piezoelectric and electret properties. We expect that PLA—after further optimization—will play an important role as a material for environmentally friendly sensors in the future, where first applications such as air filters and pressure sensors have already been proposed. However, degradation under normal ambient conditions is very slow, and an accelerated and controllable degradation process is highly desirable for any type of PLA-based sensors. Enzymatic hydrolysis with embedded enzymes has been proposed as an approach to accelerate and control degradation. In this work, we investigate the properties of PLA in terms of dielectric and mechanical properties with a focus on its ability to store charges after the enzyme proteinase K (Trit. album) has been incorporated. Results reveal that proteinase K has a positive effect on the charge stability of solvent-cast PLA electrets after complete evaporation of the solvent. Furthermore, we observed a concentration-dependent acceleration of mass loss in a Tris-HCl buffer. A fast degradation within only one day occurred at a concentration of 6 wt% proteinase K. [ABSTRACT FROM AUTHOR]

The escalating environmental impact of pollution and the imperative to reduce carbon emissions have heightened the significance of developing biobased materials from natural biomass for electronic devices. This study investigates the utilization of biofermentation‐produced recombinant spider silk and animal‐derived hemin to create a novel biobased electret for field‐effect transistor memory. A critical challenge arises from the incompatibility between natural photoresponsive molecules and insulating biomaterials, resulting in severe phase separation that compromises film quality and morphology uniformity. This study systematically examines the effects of various film deposition and manufacturing techniques on the biobased electret's morphology, phase separation, and performance. Different methods demonstrate distinct advantages in terms of molecular aggregation/segregation, morphological homogeneity, and device performance. Phototransistor memory devices fabricated using spin coating and spray coating techniques exhibit robust aggregations and high memory windows of ≈30 V. Conversely, devices produced through solution shearing and electrospinning methods display enhanced smooth morphologies and high photoresponsivity. The phototransistor memory comprising electrospun fibers holds the potential to achieve the highest memory ratio, reaching ≈105. These findings not only highlight the applications of biobased materials through scalable film deposition processes but also underscore the importance of refining their morphology, phase separation, and performance in optoelectronic devices. [ABSTRACT FROM AUTHOR]

Objective To investigate the effects and possible mechanism of electret and 5-fluorouracil（ 5-FU） on the growth of scar fibroblasts. Methods The effect of +5000 V electret combined with different concentrations of 5-FU on the proliferation of scar fibroblasts was detected by automatic enzyme labeling instrument. The apoptosis of scar fibroblasts and the mRNA expression of p53 and other apoptotic genes were studied by fluorescence microscopy and RT-PCR technology under the action of electrostatic field. Results ① After the treatment of positive electret and different concentrations of 5-FU for 72 h, the cell proliferation rate decreased, and the inhibition rate of scar cells in the +5000 V electret+160 μg/ml 5-FU group was (0.15±0.051)%. ②+5000 V electret group could promote the apoptosis of scar fibroblasts; The number of apoptotic cells in +5000 V electret and 5-FU group was higher than that in 5-FU group. ③The mRNA expression levels of four apoptotic genes in the +5000 V electret group were increased, and the expression levels of four signature genes in the +5000 V electret and 5-FU group were increased compared with those in the 5-FU group. Conclusion The combination of positive electret and 5-FU had a synergistic effect on inhibiting cell growth. The mechanism of positive electret inhibiting scar cell growth may be through promoting the expression of apoptosis gene, and then affecting the growth state of cells to inhibit cell growth. [ABSTRACT FROM AUTHOR]

The potential risk of bacteria‐induced prosthetic infection during implantation/post‐operative healing raises a serious concern about the success of implant/surgery. In this context, the present study successfully established the antibacterial efficacy of the electret form of Mg1‐xCaxSi1‐xZrxO3 (x = 0, 0.1, 0.2, 0.3, 0.4 [MCSZO‐X]) bioceramics, toward both, Escherichia Coli and Staphylococcus aureus bacteria with reference to those of hydroxyapatite (HAP). MCSZO‐X bioceramics were synthesized using a solid‐state route. The influence of Ca‐ and Zr co‐doping on the crystallite size of MCSZO‐X has been analyzed using X‐ray peak profile analyses. The electrets were developed by corona poling of sintered MCSZO‐X samples at voltage and temperature of 20 kV and 500°C (30 min), respectively. The charge, stored on the surface of MCSZO‐X electret samples was calculated to be 0.253, 0.294, 0.320, 0.173, and 0.161 µC/cm2 via thermally stimulated depolarized current measurement. The positive and negative ends of MCSZO‐ X electrets exhibited a reduction in the viability of E. coli bacteria by (24%, 25%, 30%, 43%, and 42%) and (29%, 37%, 39%, 51%, and 48%), respectively, in comparison to those of HAP. On the contrary, the viability of S. aureus bacteria has decreased by (26%, 33%, 35%, 46%, and 42%) and (21%, 22%, 27%, 395, and 37%) on the surfaces of the positive and negative ends of MCSZO‐ X electrets, respectively, with the reference of those of HAP. The mechanism of electret‐induced antibacterial activity has been revealed via various assays, such as catalase activity, superoxide production (SOD), , protein estimation, and lipid peroxidation (LPO) assays. The positive ends of MCSZO‐X electrets demonstrate antibacterial efficacy by means of more reactive oxygen species generation as compared to their negative ends of electrets and uncharged surfaces of MCSZO‐X samples, as revealed by SOD, protein estimation, catalase activity, and LPO assays. However, the negative ends of electrets prevent the adhesion of bacterial cells via electrostatic repulsion. [ABSTRACT FROM AUTHOR]

The harmful effects of air pollution on humans are multifaceted and are closely linked to outbreaks of various infectious viruses. Thus, design of high‐performance air filters that are lightweight, flexible, and easy to prepare is urgent. The electret air filter can utilize the electrostatic force of charge to capture dust particles, making it efficient and convenient, which is highly favored by people. In this study, a summary of the research on electret filters for highly efficient air purification is presented. First, this study outlines the mechanisms of air filtration methods and discusses three factors that evaluate filter performance. The methods of manufacturing electret air filters are then presented, and the advantages and limitations of different methods are discussed. Then, electrification, including corona discharge, friction electrification, electrospinning, thermal electrification, and water electrification as methods, enhances the physical charge adsorption performance of materials, while the use of fluorinate polymer, non‐fluorinate polymer, and biobased polymer as functional substrates exhibits varying degrees of electrification effects. Different materials and manufacturing techniques give the filters additional advantages, such as being self‐degradable and antibacterial. Finally, the challenges that remain in the development of electret filters for use in air purification are also discussed in terms of material type and fabrication technology. It is expected that highly efficient air purification with low energy consumption can be achieved by electret filters with multifunctional capabilities. [ABSTRACT FROM AUTHOR]

Electrical stimulation has recently received attention as noninvasive treatment in skin wound healing with its outstanding biological property for clinical setting. However, the complexity of equipment for applying appropriate electrical stimulation remains an ongoing challenge. Here, we proposed a strategy for skin scar inhibition by providing electrical stimulation via a multilayer stacked electret (MS‐electret), which can generate direct current (DC) electric field (EF) without any power supply equipment. In addition, the MS‐electret can easily control the intensity of EFs by simply stacking electret layers and maintain stable EF with the surface potential of 3400 V over 5 days owing to the injected charges on the electret surface. We confirmed inhibition of type 1 collagen and α‐SMA expression of human dermal fibroblasts (hDFs) by 90% and 44% in vitro, indicating that the transition of hDFs to myofibroblasts was restricted by applying stable electrical stimulation. We further revealed a 20% significant decrease in the ratio of myofibroblasts caused by the MS‐electret in vivo. These findings present that the MS‐electret is an outstanding candidate for effective skin scar inhibition with a battery‐free, physiological electrical microenvironment, and noninvasive treatment that allows it to prevent external infection. [ABSTRACT FROM AUTHOR]

Abstract Electrical stimulation has recently received attention as noninvasive treatment in skin wound healing with its outstanding biological property for clinical setting. However, the complexity of equipment for applying appropriate electrical stimulation remains an ongoing challenge. Here, we proposed a strategy for skin scar inhibition by providing electrical stimulation via a multilayer stacked electret (MS‐electret), which can generate direct current (DC) electric field (EF) without any power supply equipment. In addition, the MS‐electret can easily control the intensity of EFs by simply stacking electret layers and maintain stable EF with the surface potential of 3400 V over 5 days owing to the injected charges on the electret surface. We confirmed inhibition of type 1 collagen and α‐SMA expression of human dermal fibroblasts (hDFs) by 90% and 44% in vitro, indicating that the transition of hDFs to myofibroblasts was restricted by applying stable electrical stimulation. We further revealed a 20% significant decrease in the ratio of myofibroblasts caused by the MS‐electret in vivo. These findings present that the MS‐electret is an outstanding candidate for effective skin scar inhibition with a battery‐free, physiological electrical microenvironment, and noninvasive treatment that allows it to prevent external infection.

In the paper, the studies of electret properties of polypropylene with different percentages of montmorillonite have been carried out by methods of thermally stimulated potential relaxation and thermally stimulated currents. A significant effect of filler concentration on the electret state stability was revealed. The parameters of electrically active defects and the storage time of the electret state were determined. It was established that polypropylene with a 4% mass content of montmorillonite exhibited the best electret properties.

Electromechanically active nano/microfibers are promising components of sensors and actuators; however, piezoelectric polymers are normally expensive. To address this issue, this study examined the geometrical and electrostatic densities of an inexpensive highly sparse as-electrospun atactic polystyrene microfiber mat. The densities of porous individual fibers and the highly sparse fiber mat were experimentally determined to be 0.88 and 0.051 g cm−3, respectively, with corresponding material filling ratios of 80 % and 4.7 %, respectively. A high theoretical surface charge density of approximately 1.4 × 10−3 C m−2 was determined for the fiber mat after excluding air spaces in both individual fibers and the mat. These findings provide a pathway to outstanding electrets that are ultra-lightweight and have high charge densities.

Metal oxide semiconductors have been developed for ultraviolet–visible photodetectors, but improving sensitivity has remained a challenge due to poor mobility and carrier losses. In this study, a high‐performance photodetector is achieved by implementing a chargeable electret to regulate carrier transmission properties in the CuBi2O4 (CBO) conductive channel. As expected, the positively charged device shows improved performance, with a broadband detection range covering 250–600 nm, maximum responsivity and detectivity of around 10.65 A W−1 and 8.56 × 1012 Jones, and a fast rise and decay time of 50 and 300 µs, respectively. Mechanism analyses suggest two roles of the electret layer: 1) positive charges in the electret layer attract electrons and leave a pure hole conductive channel with less carrier recombination and trapping; 2) holes in the conductive channel move in one direction with less carrier collision and scattering. This work has demonstrated an effective strategy for providing a durable and stable ultra‐high electrostatic field to improve the sensitivity of photodetectors. [ABSTRACT FROM AUTHOR]

In this paper, we developed a lightweight, self-sensing electret-based dynamic vibration absorber (ESDVA) for micro-vibration suppressions. We modeled the electromechanical coupling procedure of the ESDVA based on the first principles and proposed a sensing model based on support vector regression machine (SVR). The SVR algorithm helps to linearize the original voltage generated by the electret for precise vibration sensing. A prototype of the ESDVA is fabricated, and the theoretical model and SVR algorithms are verified by experiments. According to experimental results, the ESDVA successfully reduced primary structure vibration amplitudes by up to 50% with a mass burden of 1.4% of the primary structure. The proposed sensing model achieve an accuracy rate of over 93.5% for vibration sensing and the robustness of the model was also assessed. Moreover, the advantages of the proposed electret-based sensing method over classical methods are discussed. [ABSTRACT FROM AUTHOR]

In this study, in an electret capacitor sensor (ECS), which is an electromechanical exchange device consisting of an electret sandwiched between two electrodes, ridges as spacers and grooves as gaps were formed in the PTFE (polytetrafluoroethylene) layer of the insulating electrode by laser ablation. The ECSs were then fabricated using PTFE electrets, and the charge retention and airborne ultrasonic wave transmitting and receiving characteristics were investigated. The charge retention characteristics of the ECS with laser‐patterned insulating electrodes were slightly lower than those of the silica‐aggregate electret. As the thickness of the insulating layer increased or the groove width decreased, the transmitting and receiving sensitivity increased significantly and then peaked and degraded at the measurements of transmitting and receiving. The ECS with the highest peak sensitivity obtained by laser patterning had a bandwidth comparable to that of the conventional ECS with silica aggregate electret, but the peak sensitivity was improved by up to 8 dB. Therefore, laser patterning could contribute to the improvement of ECS performance. [ABSTRACT FROM AUTHOR]

In this study, we focused on acoustic emission (AE) as a method for quantitative evaluation of fermentation. Since bubbling in the culture medium and detachment of the medium during fermentation are considered to be phenomena similar to corrosion, AE could be expected to be detected. Therefore, we conducted AE measurements using ECS during fermentation of yeast in sucrose solution, fermentation of yeast during sake brewing, and fermentation of sawdust in a hot bath facility, and investigated the possibility of evaluation of fermentation process using electret sensor (ECS). AE was detected during the fermentation of yeast. The peak frequency of AE detected during yeast fermentation was widely distributed. Cumulative number of AE, however, showed a strong correlation with the decrease in sugar content during fermentation, indicating the possibility of quantitative evaluation of the fermentation state by AE measurement if a time lag is considered. In the measurement of AE from the fermentation of sake malt, a large amount of AE was detected from the lower part of the tank immediately after brewing, and the number of AE gradually increased in the upper part of the tank. These AE measurements suggested that even in top fermentation, the initial fermentation may occur in the lower part of the tank. In the fermentation and warm bath facility, AE during fermentation could be detected even in powdered media. Although the durability of the ECS needs to be improved under high temperature and high humidity conditions, it is expected to be able to monitor the fermentation process better than temperature measurements. [ABSTRACT FROM AUTHOR]

Copyright of Cotton Textile Technology is the property of Cotton Textile Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Recently, vibration energy harvesting devices have gained growing interests. One of the main requirements for them is a broad bandwidth owing to stochastic spectral characteristics of the general vibration sources. Among various approaches for wide bandwidth, curved-beam hinges are quite attractive due to their simple structures. Although there have been several reports on curved beams, a more detailed study is needed. The device under study is an electret-based one with balanced comb-drive configuration. The whole system is modeled by using nonlinear stochastic differential equations. The numerical analysis results show that there is an optimum curve height for maximum power output, which depends on various conditions, such as external vibration strength, comb-drive dimensions, and initial electret charges. At the external acceleration magnitude of 0.02 g and 0.05 g, the device with curved beams can produce up to 2.9 times and 4.8 times higher power output, respectively, than one with straight beams for given device geometries. To the contrary, at lower and higher vibration magnitudes, straight-beam devices harvest more energy than curved-beam ones. Therefore, it can be concluded that the curved beam height needs to be carefully determined based on the conditions of the application, especially on the characteristics of the external vibration sources. [ABSTRACT FROM AUTHOR]

We demonstrate a microelectromechanical systems (MEMS) electret-type vibrational energy harvester with a wide bandwidth between 25 and 60 Hz (span of 35 Hz) for a small sinusoidal acceleration of less than 10 mG (G = 9.8 m/s2). We have developed a method of tailoring the nonlinear characteristics by adjusting the mutual position of the opposing electrodes. Both soft- and hard-spring effects are realized, thereby further extending the frequency bandwidth between 25 and 95 Hz so that power can be effectively retrieved from extremely small vibrations of 10 mG. This reconfigurable nature of the developed harvester device is suitable for autonomous distributed sensors that obtain power from environmental vibrations. [ABSTRACT FROM AUTHOR]

In this paper, we present a new structure and a process for electrostatic energy harvesters fabricated using a silicon-on-glass wafer. Conventional electret-based MEMS energy harvesters are produced using a silicon-on-insulator (SOI) wafer, which is inevitably accompanied by parasitic capacitances across the buried oxide layer. The new harvester, on the other hand, can be formed by individually developing silicon and glass parts and subsequently putting them together by anodic bonding, thereby virtually eliminating parasitic capacitance. Special caution is taken not to cause the destruction of the electret layer during high-temperature anodic bonding. The device has been successfully fabricated and experimentally confirmed to function as an energy harvester. This silicon-on-glass structure is beneficial in not only suppressing the parasitic capacitance but also increasing its output power compared with those made by the conventional SOI-based process. [ABSTRACT FROM AUTHOR]

This is the first review of conductive electrets (unpoled carbons and metals), which provide a new avenue for low-power electronics. The electret provides low DC voltage (μV) while allowing low DC current (μA) to pass through. Ohm's Law is obeyed. The voltage scales with the inter-electrode distance. Series connection of multiple electret components provides a series voltage that equals the sum of the voltages of the components if there is no bending at the connection between the components. Otherwise, the series voltage is below the sum. Bending within the component also diminishes the voltage because of the polarization continuity decrease. The electret originates from the interaction of a tiny fraction of the carriers with the atoms. This interaction results in the charge in the electret. Dividing the electret charge by the electret voltage V' provides the electret-based capacitance C', which is higher than the permittivity-based capacitance (conventional) by a large number of orders of magnitude. The C' governs the electret energy (1/2 C'V'2) and electret discharge time constant (RC', where R = resistance), as shown for metals. The discharge time is promoted by a larger inter-electrode distance. The electret discharges occur upon short-circuiting and charge back upon subsequent opencircuiting. The discharge or charge of the electret amounts to the discharge or charge of C'. [ABSTRACT FROM AUTHOR]

Recently, electrical stimulation, as a non-pharmacological physical stimulus, has been widely exploited in biomedical and clinical applications due to its ability to significantly enhance cell proliferation and differentiation. As a kind of dielectric material with permanent polarization characteristics, electrets have demonstrated tremendous potential in this field owing to their merits of low cost, stable performance, and excellent biocompatibility. This review provides a comprehensive summary of the recent advances in electrets and their biomedical applications. We first provide a brief introduction to the development of electrets, as well as typical materials and fabrication methods. Subsequently, we systematically describe the recent advances of electrets in biomedical applications, including bone regeneration, wound healing, nerve regeneration, drug delivery, and wearable electronics. Finally, the present challenges and opportunities have also been discussed in this emerging field. This review is anticipated to provide state-of-the-art insights on the electrical stimulation-related applications of electrets. [ABSTRACT FROM AUTHOR]

Abstract Impedance matching is one outstanding issue for the electret‐based vibration energy harvester (eVEH) due to its small equivalent capacitance. In this paper, the authors developed a synchronized charge extraction (SCE) circuit for eVEH, to improve its performance in small load resistance conditions. An electromagnetic detector is embedded with the eVEH to detect its maximum vibration amplitude. The synchronized switch is controlled by a microcontroller unit. According to the authors’ simulation study, the power output of eVEH interfaced with the SCE circuit is three times larger than that of the standard circuit, which proved the effectiveness of our SCE circuit.

The protection effects of wearing masks against viruses and bacteria have been verified many times over previous pandemics and infectious diseases. However, the supply of the surgical masks can barely meet the surging demand at the early stage (first 12 months) of the outbreak of a pandemic. Thus, it is essential to use surgical masks wisely in such urgent times. In this work, we selected two types of surgical masks and systematically explored how actual wearing time influences the protective performances of the masks. Each type of surgical masks was worn for 4, 10, 24, 32 and 48 h, respectively, and the results show that with the increase of actual wearing time, both particulate filtration efficiency (PFE) and bacterial filtration efficiency (BFE) of the masks decline. After wearing for 32 h, the PFEs of both types of masks were still far above the corresponding standard (≥30%, according to YY0469-2011). After wearing for 10 h, the BFEs of both masks were over 95% (which is regarded as the safe value), whereas after 24 and 32 h of wearing, the BFE of one type of mask decreased obviously to 91.6% and 80.0%, respectively. Based on these results, it is rational to conclude that the wearing time of surgical masks should be no more than 10 h. [ABSTRACT FROM AUTHOR]

Copyright of Polymer Materials Science & Engineering is the property of Sichuan University, Polymer Research Institute and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Impedance matching is one outstanding issue for the electret‐based vibration energy harvester (eVEH) due to its small equivalent capacitance. In this paper, the authors developed a synchronized charge extraction (SCE) circuit for eVEH, to improve its performance in small load resistance conditions. An electromagnetic detector is embedded with the eVEH to detect its maximum vibration amplitude. The synchronized switch is controlled by a microcontroller unit. According to the authors' simulation study, the power output of eVEH interfaced with the SCE circuit is three times larger than that of the standard circuit, which proved the effectiveness of our SCE circuit. [ABSTRACT FROM AUTHOR]

Space charge accumulates near electrodes in insulating materials under high voltage direct current. Electric stress created by charge accumulation distorts electric field, reduces the remaining useful life of insulating materials, and decreases partial discharge inception voltage that are critical for ensuring the dielectric integrity of power applications. In this article, a novel approach that mitigates space charge accumulation using electrets is presented. Electrets are used to reduce electric fields that cause charge injection and space charge accumulation in dielectric materials. The validity of using electrets for preventing space charge accumulation is numerically and experimentally demonstrated. Bipolar charge transport model is developed to simulate space charge injection and accumulation in silicone rubber without and with the incorporation of electret. Space charge experiments are performed to confirm the numerical results. The results show that electrets can effectively mitigate space charge accumulation in dielectric materials. The results also show that the incorrect use of electret such as reversing the polarity can lead to more substantial space charge accumulation. [ABSTRACT FROM AUTHOR]

Solid-film electrets and cellular electrets are defined as promising insulating dielectric materials containing permanent electrostatic and polarizations. High-performance charging methods are critical for electret transducers. Unlike dielectric barrier discharge (DBD) charging, the soft X-ray charging method, with its strong penetration ability, has been widely used in electrets after packaging and has even been embedded in high-aspect-ratio structures (HARSs). However, the related charging model and the charging effect of the soft X-ray irradiation remain unclear. In this study, the charge carrier migration theory and the one-dimensional electrostatic model were employed to build the soft X-ray charging models. The influence of soft X-ray irradiation under deferent poling voltages was investigated theoretically and experimentally. The conducted space charge measurement based on a pulsed electro-acoustic (PEA) system with a soft X-ray generator revealed that soft X-ray charging can offer higher surface charge densities and piezoelectricity to cellular electrets under the critical poling voltage lower than twice the breakdown voltage. [ABSTRACT FROM AUTHOR]

Stent thrombosis (ST) is a catastrophic event and efforts to reduce its incidence by altering blood-stent interactions are longstanding. A new electret coating technology that produces long-lasting negative charge on stent surface could make them intrinsically resistant to thrombosis. We assessed the thrombogenicity of stents using an annular perfusion model with confocal microscopy, and determined the efficacy of electret coating technology to confer thrombo-resistant properties to standard stents. Using an annular perfusion chamber, Bare Metal Stent (BMS), standard uncoated DES (DES), and Electret-coated DES (e-DES) were exposed to human blood under arterial flow conditions. Deposits of fibrinogen and platelets on the stent surface were analyzed using immunofluorescence staining and confocal microscopy. Surface coverage by fibrinogen and platelets and the deposit/aggregate size were quantified using computerized morphometric analysis. The experimental methodology produced consistent, quantifiable results. Area of stent surface covered by fibrinogen and platelets and the average size of the deposits/aggregates were lowest for e-DES and highest on BMS, with DES in the middle. The size of fibrinogen–deposits showed no differences between the stents. The testing methodology used in our study successfully demonstrated that electret coating confers significant antithrombotic property to DES stents. These findings warrant confirmation in a larger study.

Abstract Space charge accumulates near electrodes in insulating materials under high voltage direct current. Electric stress created by charge accumulation distorts electric field, reduces the remaining useful life of insulating materials, and decreases partial discharge inception voltage that are critical for ensuring the dielectric integrity of power applications. In this article, a novel approach that mitigates space charge accumulation using electrets is presented. Electrets are used to reduce electric fields that cause charge injection and space charge accumulation in dielectric materials. The validity of using electrets for preventing space charge accumulation is numerically and experimentally demonstrated. Bipolar charge transport model is developed to simulate space charge injection and accumulation in silicone rubber without and with the incorporation of electret. Space charge experiments are performed to confirm the numerical results. The results show that electrets can effectively mitigate space charge accumulation in dielectric materials. The results also show that the incorrect use of electret such as reversing the polarity can lead to more substantial space charge accumulation.

Monitoring the bite force is valuable in the treatment of bruxism, an unconscious oral habit. Conventional bite force sensors used in clinical practice are unsuitable for wearable bite force measurement systems because of their size and measurement principles. In this study, a self-powered bite force sensor composed of an electret and a dielectric elastomer is proposed to realize a mouthguard-type wearable bite force measurement system. A theoretical model of the sensor was constructed to compensate for the nonlinearity between the applied bite force and sensor output voltage. A fabricated large-scale prototype sensor and theoretical model accurately estimated an applied force of up to 50 N. The proposed sensor is expected to realize a self-powered bite force monitoring system by making it thin and embedding it in a mouthguard. [ABSTRACT FROM AUTHOR]

Owing to magic charge storage behavior, an electret can exhibit an external electrostatic field, which is widely used in numerous domains such as electronics, energy, healthcare, and environment. However, the theory of the charge storage mechanism still needs further development to enhance the performance and stability of the electret. Herein, a stable charge storage model known as the heterocharge‐synergy model (HSM) in electrets is proposed and verified, and the electrostatic field superposition effect of electrets is also proved. Based on the HSM and superposition effect, the stable electrostatic field intensity (average of ≈22.49 kV cm−1 and maximum of ≈29.58 kV cm−1, which is close to the minimum air breakdown field intensity of ≈30 kV cm−1) of the composite electret film is multiplied by simple layer‐by‐layer stacking. Utilizing the multilayer composite electret films and designing a two‐sided electrostatic induction structure, a two‐sided bipolar single‐electrode non‐contact nanogenerator is constructed with transferred charge density up to ≈132.61 µC m−2, which is twice as large as that of the non‐contact nanogenerators with one‐sided electrostatic induction structure. Clearing and utilizing the charge behaviors of the electret can boost the performance and enhance the stability of electret‐based devices in various domains. [ABSTRACT FROM AUTHOR]

Electrets were prepared by spin‐coating the dispersion of fine silica powders, and their charge retention characteristics were investigated. Finer silica aggregates were formed on the PTFE surface layer by spin‐coating the dispersed solution of fine silica powder than those formed by spray‐coating colloidal silica. Electrets using fine silica powder also showed better charge retention characteristics than those using colloidal silica. Such an improvement in the charge retention might be due to the suppression of discharge in the excessive gap caused by coarse silica aggregates. Then, ECSs were fabricated using the prepared electrets, and their transmitting and receiving characteristics of airborne ultrasound were also investigated. The peak sensitivity of the ECS using a spin coating of fine powdered silica dispersion was slightly improved from those using spray coating of colloidal silica. On the other hand, the peak frequency and frequency band were greatly improved using spin coating of fine powdered silica dispersion. Therefore, ECS using fine silica powder is expected to be applied as a broadband airborne ultrasonic sensor. [ABSTRACT FROM AUTHOR]

Recently, electrical stimulation, as a non-pharmacological physical stimulus, has been widely exploited in biomedical and clinical applications due to its ability to significantly enhance cell proliferation and differentiation. As a kind of dielectric material with permanent polarization characteristics, electrets have demonstrated tremendous potential in this field owing to their merits of low cost, stable performance, and excellent biocompatibility. This review provides a comprehensive summary of the recent advances in electrets and their biomedical applications. We first provide a brief introduction to the development of electrets, as well as typical materials and fabrication methods. Subsequently, we systematically describe the recent advances of electrets in biomedical applications, including bone regeneration, wound healing, nerve regeneration, drug delivery, and wearable electronics. Finally, the present challenges and opportunities have also been discussed in this emerging field. This review is anticipated to provide state-of-the-art insights on the electrical stimulation-related applications of electrets.

Peripheral sensory nerves play critical roles in bone homeostasis and in repair of damaged bone. However, bone defects are generally accompanied by loss of ossification-promoting nerve endings. The cellular networks that connect bone and nerve regeneration are largely unknown, but an understanding of this cross-talk could enable selective modulation of these signals to promote regeneration of diseased or damaged bone. Here we identify myelinating Schwann cells (mSCs) as an essential microenvironmental component connecting bone and nerve regeneration. We found that mSCs accumulate in the region of bone defects, where they support bone regeneration by mediating regeneration of nerves in the vicinity. Consistently, in vivo depletion of mSCs greatly dampened bone regeneration in models of both cranial and femoral bone defects. To exploit this activity of mSCs, we fabricated an aligned self-powered silicon dioxide electret composite membrane (AS), and we showed that the combination of electrical stimulation and aligned topography of fibers on the membrane promoted nerve regeneration by driving myelination of SCs, which subsequently contributed to nerve-dependent bone regeneration. Mechanistically, AS membranes affected myelination of SCs by inhibiting Notch pathway signaling and by driving polarization of macrophages into the anti-inflammatory M2-like phenotype. Our study reveals that mSCs are essential for executing signals between damaged bone and nerves to support generation of both tissues and prompts further studies of biomembranes to stimulate mSCs and support bone regeneration. [Display omitted] • Identifying accumulation of myelinating Schwann cells (mSCs) in the region of bone defects. • Functionally demonstrating that mSCs support both nerve and bone regeneration. • Fabricating self-powered electret membranes (AS) to promote myelination of SCs by inhibiting Notch signaling. • Showing that AS can polarize macrophages into M2-like phenotype to support a microenvironment conducive to tissue repair. • Demonstrating AS membranes promote nerve-dependent bone regeneration in vivo , suggesting clinical potential. [ABSTRACT FROM AUTHOR]

It has been shown that plasma treatment of the surface of a polytetrafluoroethylene film in nonthermal plasma of atmospheric-pressure glow discharge makes it possible to obtain low values of the contact angle, to achieve high uniformity of the properties of the treated surface, and to significantly increase the work of adhesion. The treatment with nonthermal atmospheric-pressure glow-discharge plasma leads to the formation of an electret state stable over time on the polytetrafluoroethylene film surface. [ABSTRACT FROM AUTHOR]

Texture detection is one of the essential features requested for artificial tactile sensing to push the demand for flexible low-cost tactile sensors in the robotics sector. In this manuscript, we demonstrate the ability of a ferroelectret-based pressure sensor together with a patterned elastomer layer to detect surface textures. The ferroelectret sensor was fabricated using fluorinated ethylene propylene (FEP) sheets bonded with a patterned adhesive layer to create cavities, integrated with the elastomer bumped surface, and finally charged using a pyroelectric method developed by our group. The ferroelectret-based sensor showed a linear response to the applied force in the range of 0.5 to 2 N, a piezoelectric coefficient of 150.1 ± 3.2 pC/N in the range of 10–80 Hz, and a flat dynamic response in the range of 10–1000 Hz. The tactile sensing characterization of the sensor, performed at different scanning speeds (10 to 30 mm/s) and gratings with different periodicities (0 to 0.8 mm), showed that the fundamental frequencies observed ranged from 12 Hz to 75 Hz, as expected from the model. These results lay the foundation for the adoption of such sensors in different applications that need fine tactile information, such as an autonomous or teleoperated robotic hand, prostheses, and wearable devices. [ABSTRACT FROM AUTHOR]

Insulating oil is a pivotal component of power transformers, but it suffers from aging byproducts during service operation. The aging byproducts from the degradation of oil insulation tend to induce insulation failure, which poses a significant threat to the security of the power grid. Therefore, the regeneration of insulating oil is required to prolong the useful life of insulating oil and hence be of economic and ecological interests. Typical in-use oil regeneration routes employ multi-step procedures. In this work, a one-step regeneration method using a PVDF/BaTiO3 composite membrane is proposed. BaTiO3 endows the composite membrane with improved hydrophobicity and an electret state. The regeneration performance of the PVDF/BaTiO3 nanofiber membrane was assessed by considering the acid value, moisture content, dielectric loss factor tan δ, and the AC breakdown voltage of the refreshed oil. The test results showed that the filtration efficiencies toward formic acid and moisture were up to 77.5% and 60.6%, respectively. Moreover, the dielectric loss factor tan δ of the refreshed oil decreased evidently at a power frequency, and the AC breakdown voltage rose from 23.7 kV to 38.9 kV. This suggests that the PVDF/BaTiO3 composite membrane may be employed efficiently, and it minimizes aging byproducts via the one-step filtration. [ABSTRACT FROM AUTHOR]

Soft, low‐cost, high‐performance generators are highly desirable for harvesting ambient low frequency mechanical energy. Here, a dielectric elastomer nanogenerator (DENG) is reported, which consists of a dielectric elastomer capacitor, an electret electrostatic voltage source, and a charge pump circuit. Under biaxial stretching, DENG can convert tensile mechanical energy into electrical power without any external power supply. Different from traditional DEG with the charge outward transfer in direct current (DC), the DENG works based on shuttle movement of internal charges in an alternating current (AC). Through alternating current (AC) method, the charge density of the DENG can reach 26 mC m−2 per mechanical cycle, as well as energy density of up to 140 mJ g−1. Due to the all‐solid‐state structure without air gap, the DENG is capable of working stably under different ambient humidity (20 RH%–100 RH%). To demonstrate the applications, a water wave harvester based on the DENG is constructed. The integrated device powers a sensing communication module for self‐powered remote weather monitoring, showing the potential application in ocean wave energy harvesting. [ABSTRACT FROM AUTHOR]

The article describes the effect of fine mineral fillers (aerosil, bentonite, mica, and talc) on the properties of electret materials based on polylactide. Compositions of the polymer with 4% fillers content showed the best performances. Loading of the fillers results in a slight increase of specific volume resistivity of the samples. IR spectroscopy and differential scanning calorimetry show no significant change in chemical structure and glass transition temperature and flow (melting) point of the filler-loaded polylactide. Addition of fillers reduces melt flow index (MFI) and elongation at a break with almost no change in ultimate tensile strength. [ABSTRACT FROM AUTHOR]