Electret Charge Research Articles

Penetration Performance of Melt-Blown Polypropylene Electret Nonwoven Web against DEHS Aerosols

High filtration efficiency of melt-blown polypropylene nonwoven web used as air filter extremely depends on its elelctret characteristics. In this paper, penetration performance of DEHS(diethyl hexyl sebacate) aerosol while flowing through melt-blown polypropylene electret nonwoven web is studied by the method of aerosol penetration measurement as a function of particle size, and the contribution of mechanical and electrostatic mechanism to its capture ability is proposed. The stability of filtration performance after exposure to DEHS for a period of time is measured and the impact of DEHS and other challenge aerosols with different chemical properties on filtration performance is compared. The results show that the higher filtration efficiency of melt-blown polypropylene electret nonwoven web mainly depends on its high electret charge. Aerosol penetration drops off with the increase of aerosol particle size and decreases in the order of basic weight sequence of 20, 40 and 60 g/m2. The most penetration particle size (MPPS) appears at 0.08 m in diameter. The electret charge of the web was cleared away during the course of exposure to challenge aerosol after 5 minutes. The electriferous property of aerosol particle also influences the filtration performance of polypropylene electret nonwoven web. The electret web displays the best filtration performance for ionized aerosol.

First DEIS student essay competition

Includes the award paper, "Relating physics of electret charging using vacuum UV photo-ionization to seed electron production during high altitude plasma breakdown" (Laity, G.R.).

High-speed electret charging using vacuum UV photoionization [Reprint

In this letter, we propose a high-speed charging method using vacuum ultraviolet (vuv) irradiation, which can increase the charging rate by two orders of magnitudes than corona/soft-x-ray charging methods. So far, vuv has been used for neutralization of electrostatic charge in semiconductor process. However, the large ion current obtained with the VUV irradiation has never been used for charging electrets.

Electret effect in Pb5Ge3O11 crystals

The short-circuit thermally stimulated depolarization current (TSDC) through lead germanate single crystals has been measured as a function of temperature (100–800 K) and time. The results indicate that poling of the crystals at elevated temperatures (t ≥ 150°C) produces an electret state related to the spacecharge mechanism of polarization. Relatively mild poling conditions (E = 0.75 kV/cm, t = 150°C) produce a well-defined, long-lived electret with an abnormally large electret charge (1400 μC/cm2). The electret discharge leads to heating of the crystal, in the form of a peak in the range 520–570 K, whose height exceeds that of the pyroelectric peak near T C by two to three orders of magnitude. From the TSDC data, we evaluated the stored electret charge, its density, and the activation energy of traps for electret charges, and made preliminary conclusions as to the nature of the traps. We demonstrate that neglect of the electret discharge current (which depends on a number of factors) when determining the pyroelectric coefficient p σ above 280 K leads to a significant scatter in data.

The study of thermal silicon dioxide electrets formed by corona discharge and rapid-thermal annealing

A silicon dioxide (SiO2) electret passivates the surface of crystalline silicon (Si) in two ways: (i) when annealed and hydrogenated, the SiO2–Si interface has a low density of interface states, offering few energy levels through which electrons and holes can recombine; and (ii) the electret’s quasipermanent charge repels carriers of the same polarity, preventing most from reaching the SiO2–Si interface and thereby limiting interface recombination. In this work, we engineer a charged thermal SiO2 electret on Si by depositing corona charge onto the surface of an oxide-coated Si wafer and subjecting the wafer to a rapid thermal anneal (RTA). We show that the surface-located corona charge is redistributed deeper into the oxide by the RTA. With 80 s of charging, and an RTA at 380 °C for 60 s, we measure an electret charge density of 5 × 1012 cm–2, above which no further benefit to surface passivation is attained. The procedure leads to a surface recombination velocity of less than 20 cm/s on 1 Ω-cm n-type Si, which is commensurate with the best passivation schemes employed on high-efficiency Si solar cells. In this paper, we introduce the method of SiO2 electret formation, analyze the relationship between charge density and interface recombination, and assess the redistribution of charge by the RTA.

Electret properties of polyethylene and polytetrafluoroethylene films with chemically modified surface

This paper investigates the effect of chemical surface modification of polytetrafluoroethylene (PTFE) and low density polyethylene (LDPE) films on their electret properties. PTFE films were subjected to wet treatment with three different chemicals: orthophosphoric acid, tetrabutyl titanate and tetraethoxysilane. The technique based on the principles of molecular layer deposition (MLD) method was used to modify the surface of LDPE films with phosphorus trichloride vapors. The surfaces of the films were then corona charged, and the electret charge stability was studied by means of isothermal and thermally stimulated surface potential decay. Both PTFE and LDPE films, after the surface treatment, displayed a considerable enhancement in the charge stability compared to the virgin samples. It is important to note that the enhancement of the charge stability was achieved in the positively charged PTFE films, a result important to practical applications. We attribute this effect of charge stabilization to the formation of new energetically deep traps on the modified surface. Decrease in molecular mobility, due to attachment of new chemical structures to the surface macro molecules, may also contribute to the overall growth of the charge stability.

Research on Polypropylene Electret Melt-Blown Nonwoven Doped with Nano-Tourmaline

Electret filter composed of permanently charged electret fibers is a good material for environmental protection. A novel kind of electret melt-blown nonwovens (EMNs) doped with nano-tourmaline was developed by corona charging in this paper. The structure of web, mechanical properties, surface charge density and filtration efficiency of samples were discussed. The results showed that the structure of EMNs became loose and the initial surface charge density was increased markedly. Furthermore, the EMNs exhibited higher filtration efficiency and lower pressure drop, especially the content of nano-tourmaline was about 6 wt. %.

High-speed electret charging using vacuum UV photoionization

We propose a high-speed charging method of electrets using vacuum ultraviolet irradiation. Due to a large amount of the ionization current at reduced pressure, it takes only a few seconds to charge 15-μm-thick polymer electret film to the surface potential of −900 V. This charging rate is two orders of magnitudes larger than corona/soft-x-ray charging methods. The purity of N2 gas depends on the charging rate since the O2 quenching mechanisms of exited N2 molecule would exist. No charge decay is observed for 3000 h, which indicates charged electrets are as stable as those by other charging methods.

MP-21 環境振動発電器のためのX線光電離を用いたエレクトレット荷電法(ポスターセッション)

We propose a novel charging method of electret using X-ray irradiation for MEMS power generator. Since X-rays can penetrate inside of the generator and make ions from gas molecules by photoiozation effect, charging of electret would be possible even after assembling/packaging process. In Ar atmosphere, surface potential of electret increases with irradiation time of X-rays and becomes constant as much as applied bias voltage. It is found that the charging rate much depends on the introduced gas species and pressure, which means the present charging principle should be different from conventional radiation-based charging methods. TSD spectrum of the charged electret with X-rays shows the stability of charged electret with X-ray irradiation is approximately the same as that of corona-charged electrets.

Effect of the Electret Charge of Polyethylene–starch Composites on their Biodegradability

The influence of the state of polymeric materials on the process of their biodegradation was studied. The biodegradation of polyethylene–starch composites increases in intensity with increasing starch content.

Electrically active centers of capture of charge carriers and electret effect in polymeric dielectrics and mica

The results of an experimental investigation of the electret effect and electrically active centers of capture in polymeric dielectrics modified by radiation and subjected to deformation (X-ray radiation of electric gas barrier discharge using the EGBD technique), as well as mica after δCo60 radiation and heat treatment, have been presented. It has been shown that electrically active centers of capture in polymeric electrets are polar C-H bonds and, in mica crystals, these centers are radiation defects of K+-OH− ionic crystalline sublattice. It was shown that the process of the formation of polymeric and mica electrets is described by the wave-current model of polarization.

Selective Discharge of Electrostatic Charges on Electrets Using a Patterned Hydrogel Stamp

Paint with water: A topographically patterned agarose hydrogel stamp transfers and prints water onto uniformly charged PMMA electrets for selectively discharging electrostatic charges. The high-resolution electrostatic charge patterns produced by this simple approach can induce the reduction of metal ions and allow the fabrication of micro- and nanoscale metallic arrays.

Patterned piezo-, pyro-, and ferroelectricity of poled polymer electrets

Polymers with strong piezo-, pyro-, and ferroelectricity are attractive for a wide range of applications. In particular, semicrystalline ferroelectric polymers are suitable for a large variety of piezo- and pyroelectric transducers or sensors, while amorphous polymers containing chromophore molecules are particularly interesting for photonic devices. Recently, a new class of polymer materials has been added to this family: internally charged cellular space-charge polymer electrets (so-called “ferroelectrets”), whose piezoelectricity can be orders of magnitude higher than that of conventional ferroelectric polymers. Suitable patterning of these materials leads to improved or unusual macroscopic piezo-, pyro-, and ferroelectric or nonlinear optical properties that may be particularly useful for advanced transducer or waveguide applications. In the present paper, the piezo-, pyro-, and ferroelectricity of poled polymers is briefly introduced, an overview on the preparation of polymer electrets with patterned piezo-, pyro-, and ferroelectricity is provided and a survey of selected applications is presented.

Inter-laboratory performance between two nanoparticle air filtration systems using scanning mobility particle analyzers

The performance of two aerosol testing systems, at two different laboratories (University of Nebraska Medical Center—UNMC and 3M Company), was compared to evaluate which calibration procedures minimized variability in filter testing of nanoparticles. Both charged electret and uncharged flat-web fibrous filters were used with Scanning Mobility Particle Sizers to give upstream and downstream size distributions and calculate filter penetration. Challenge aerosols were polydisperse nanoparticles of sodium chloride (NaCl) ranging from approximately 10–300 nm and monodisperse polystyrene latex (PSL) spheres of preselected sizes, including 40, 60, 100, and 200 nm. The implementation of optimized procedures resulted in comparable filtration performance at the two testing sites with challenges of NaCl particles and PSL spheres. The penetration results for the uncharged filter were nearly identical for both challenges, while lower penetration through the charged filter was observed with NaCl aerosol, probably due to differences in NaCl and PSL dielectric constants. Results showed that reproducible, comparable nanoparticle filtration data could be achieved between two separate laboratories when sources of error and proper calibration procedures were addressed.

軟Ｘ線照射によるシリコンマイクロホン用エレクトレットの作製

To develop an ultraminiature high-performance microphone for the next generation, we have been studying a silicon microphone. We previously fabricated a single-crystalline silicon microphone using original MEMS technology. The prototype microphone showed excellent acoustic characteristics such as high sensitivity and wide frequency range. Aiming at low-voltage operation, we have recently developed a novel electret charging technique using soft X-ray irradiation. This technique leads to removing the 48-V bias voltage. Experimental results show that an internal inorganic dielectric film keeps electric charges and has excellent heat resistance. This technique exhibits promise for developing a low-voltage operation silicon microphone for purposes ranging from broadcasting to consumer use.

Selective electret charging method for energy harvesters using biased electrode

A lot of energy harvesting devices using electret material has been developed. Since the power from the electret energy harvester is proportional to the surface charge concentration, i.e. charged voltage on the electret, frequency and dynamic range of the capacitance change. To fabricate the electret, the corona discharge is a very popular charging method that consists of a high voltage needle for corona ions generation, and a grid electrode applying a bias voltage that implants the electrons from corona ions to the electret material. In this study, we introduce a novel charging method with fine patterns using the buried gridelectrodes applied with a bias voltage. We also describe FEM analysis and experimental results.

Full-swing organic inverters using a charged perfluorinated electret fabricated by means of mass-printing technologies

We report on the successful fabrication of full-swing charged organic inverter circuits by means of continuous mass-printing technologies. Using an electrostatic charged perfluorinated gate dielectric (Cytop™), we demonstrate depletion-mode and enhancement-mode transistors with the same organic semiconductor in top-gate device structure. The threshold voltage of the printed p-type transistors can be shifted by injecting stable positive charges by means of a corona discharge or contact charging.

Electret state in Bi 4Ti 3O 12 ceramics

The effect of thermal treatment atmosphere (argon, air or oxygen) on the electret behavior of bismuth titanate (Bi 4Ti 3O 12) ceramics was investigated. Polycrystalline ferroelectric ceramics were prepared by reactive liquid phase sintering. Sintered samples were polarized applying an electric field, E p = 1 MV m −1 at 100 °C for 60 min. Effective surface density, σ eff of free charges was determined by compensation voltage measurements. Thermally treated samples in oxygen atmosphere exhibit a significant decrease of σ eff while those treated in argon exhibit an increase of σ eff accompanied by the improvement in stability of electret charge. In all cases homocharge with a time independent sign was obtained.

Effect of Solvent Exposure on the Filtration Performance of Electrostatically Charged Polypropylene Filter Media

Solvent-induced performance deterioration in corona charged polypropylene electret filter media was studied. Electret media, exposed to isopropanol (IPA) in the liquid phase, exhibited reduced filtration efficiency with negligible changes in the pressure drop across the media. Scanning electron microscopy imaging indicated no observable morphological changes after IPA exposure. Solvent-induced efficiency deterioration of electret filter media was hypothesized to originate from charge deterioration rather than charge masking. The charge of the individual fibers in filter media was characterized using electrostatic force microscopy (EFM). EFM investigation produced evidence that exposure to IPA in the liquid phase affected the electrostatic charges on fibers. Exposure to organic solvents such as xylene, toluene, and ethyl benzene has been reported to increase charge mobility in polypropylene fibers, thereby reducing the electrostatic charge and the ability of the fibers in the electret filter media to capture particulates.

M5-2 シリコンエレクトレットコンデンサマイクロホンの実現に向けた無機エレクトレット膜および着電技術の開発(M5 アクチュエータ/フィジカルセンサ)

Towards low-voltage and high-performance subminiature microphone, we are studying silicon electret condenser microphone. Recently, we developed a novel charging method for electret films using soft X-ray irradiation. In this paper, the principle of the charging method and the surface potential of a charged inorganic electret film are reported.