Papers by Keyword: Electrets

Abstract: Kidney or gall-bladder stones are solid accretions (crystals) of dissolved minerals in urine or bile juice found inside the kidneys or urethras and gall bladder, with varying size from as small as a grain of sand to as large as a golf ball, the occurrence whose in the human is well known, although its pathogenesis is not well understood. According to literature, a number of biomaterials, such as collagen, blood vessel walls, DNA, RNA etc., are found to possess the property of electrets which is an electric analogue of a permanent magnet having the capability to retain quasipermanently, an induced polarization. In order to understand about the occurrence and the physical properties of stone formation in the human tissues, the study of its electret behaviour and conductivity becomes imperative which implies the fact of indulging in its growth inhibition, if their deposition is identified using scans. Thus, in this paper, in order to understand the mechanism of growth of these nephrolithiasis, we enumerated the electrical behaviour of the stone, by using the XRD (X-Ray Diffraction) analysis after their collection from different patient in and around the region and subsequently the dielectric constant of the stone was interpreted.

Abstract: 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.

Abstract: In this paper, we studied the method of electrets electrode which formed to accumulate negative electric charge by corona discharge. The breakdown voltage sample and damaged sample by various corona discharges have made material stabilization and improved characteristics of electric charge storage throughout the annealing process. After the experiment made material stabilization nearly melting point by many kinds of annealing conditions, we did the corona discharge again by the charged high voltage, a discharge electrode gap, and a discharged time. As we compared it with the best condition, we confirmed that characteristics of electric charge storage were improved.

Abstract: Thermoelectrets of poly(acrylonitrile) have been prepared for various electric field polarization strengths. The thermally stimulated discharge current technique has been used to study the remanent charge (dipolar and/or trapped charge) stability. The measurements were carried out in a vacuum. Two overlapping peaks and a significant increase of the current at high temperature have been observed. The first peak is centered around 372 K and the second one is centered around the polarization temperature. When the polarizing field increases from 0.47 to 1.2 MV m-1 the apparent activation energy varies from 1.08 to 1.40 eV, revealing a weak polarization field strength dependence, while the relaxation time at infinite temperature τ0 decreases from 2.05 x10 –15 to 1.05 x 10-18 s. The relaxation time at 300 K increases from 3.48 x 106 to 1.7 x 109 s indicating that the trapped electric charge may be stable at room temperature for the given polarization conditions.

Abstract: Polyethylene terephthalate (PET) is one of the major electret materials which has been studied and widely used in charge storage applications for a long time. The homo-charge and hetero-charge formation responsible for the electret effect of PET can be explained by the dipolar polarization, space charge separation and charge injection respectively as a result of contact poling or corona charging. These processes are also verifiable from studies of surface charges and thermally stimulated depolarization current (TSDC) of the PET films. Now consider a stack of PET films charged under the same condition as a single film. It would be intuitively expected that the electret effects of the individual films of the stack should be different due to their different positions in the stack. However, in a recent study on charged PET stacks, it was found that the electret effects of the individual films are quite similar. The surface charges of the individual films are about the same and they sum to make same total as a single charged PET film. On the other hand, the TSDC thermograms of individual films show similar characteristics in the thermal relaxation processes where homo- and hetero- charge effects are still observed. From the TSDC results, especially for the film in the middle of a triple layer sandwich, it shows clearly dipolar polarization and charge injection related peaks. These findings agree with the results of surface charge studies of the individual films.