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Electrets, 1999. ISE 10. Proceedings. 10th International Symposium on

Date 22-24 Sept. 1999

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Displaying Results 1 - 25 of 191
  • 10th International Symposium on Electrets (ISE 10). Proceedings (Cat. No.99 CH36256)

    Publication Year: 1999
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  • Why the First Industrial Revolution Did Not Take Place in Alexandria

    Publication Year: 1999 , Page(s): 1 - 8
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    First Page of the Article
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  • Author index

    Publication Year: 1999 , Page(s): 801 - 806
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  • Subject index

    Publication Year: 1999 , Page(s): 807 - 812
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    The index contains an entry for all items that appeared in this publication. View full abstract»

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  • Photoinduced anisotropy in chalcogenide glasses

    Publication Year: 1999 , Page(s): 705 - 708
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    A model is formulated that allows one to explain some basic characteristic features of photoinduced anisotropy in glassy semiconductors. The model assumes the occurrence of correlated pairs of localized states for electrons and holes and relates photoinduced anisotropy to generation of geminate electron-hole pairs trapped by these localized states View full abstract»

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  • Dielectric and spectral characteristics of some aromatic polyether films and tablets

    Publication Year: 1999 , Page(s): 721 - 724
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    The authors study a series of polyethers and polyesters based on chloromethyl oxetane embedded in polymer matrices of polymethyl metacrylate (PMMA) and polyvinyl alcohol (PVA) type. These polymers have been studied both in solid state as thin films deposed on quartz disks and in solution. The electronic absorption spectra and photochromic effects in such materials are discussed and the polarisation current density is measured View full abstract»

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  • The study of the open-circuit thermally stimulated discharge on the guest-host nonlinear optical polymer electret DR1/PMMA film

    Publication Year: 1999 , Page(s): 383 - 386
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    In this paper the charge dynamic characteristic of the guest-host NLO polymer electret DR1/PMMA films after corona poling is investigated by means of the thermally stimulated discharge (TSD) technology. The results indicate that in the sample poled by the constant voltage corona charging near the glass transition temperature (Tg) there are two kinds of charges: space charge trapped by the traps of sample and dipole charge originating from the oriented dipole, and the dipole charge is completely compensated by the space charge. Most of trap energy levels of the space charges are higher than the bound levels of dipole charges at the suitable poling temperature. The breadth B of site distribution in the KWW stretched exponential expression applied to fit the relaxation of the oriented dipole is correlated to the interaction between dipole and space charge. Aging can lead to the space charge transferring to deeper traps due to the fast retrapping effect, which makes the space charge more stable, and consequently improves the orientation stability of the dipole and optical nonlinear stability View full abstract»

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  • Study of dielectric relaxation processes of PET by Dynamic Dielectric and ThermoStimulated spectroscopies

    Publication Year: 1999 , Page(s): 289 - 292
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    During the last decades, the frequency range of investigation of dielectric materials has been extended by many order of magnitude in the high frequency side. Actually, the reasonable accessible frequency range of dynamic dielectric spectrometers is about [10-2 - 109 Hz]. However, the main problem occurring in polymer relaxation analysis is the overlapping of relaxation modes when the frequency of measurement is increased, each being associated with a typical kind of motion. The purpose of the investigation reported in this paper is to enlarge the accessible range of dielectric studies of amorphous polymers like amorphous PET, taken as model polymer. For this aim, two dielectric techniques have been used : Dielectric Spectroscopy (DS) and Thermally Stimulated Currents (TSC). This paper presents a comparison of both techniques on results obtained on the secondary (β) and main (α) relaxation regions View full abstract»

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  • Optical constants and dielectric permittivity of lutetium oxide films deposited with an electron gun

    Publication Year: 1999 , Page(s): 709 - 712
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    Lu2O3 films deposited by electron-beam evaporation exhibit interesting optical properties in the range 0.2 - 2 μm. The films exhibit very good transparency over a wide spectral range. Only a very small influence of the deposition pressure as well as thermal annealing of specimens on optical properties was observed. Refractive index and its dispersion over a wide spectral region was determined. Films exhibit only a weak absorption in violet and ultraviolet ranges. The high-frequency dielectric permittivity was estimated. Thin films of LU2O3 can be useful for thin-film optics. Lu2O3-Si antireflection coatings were fabricated. These coatings reduce reflectivity of silicon-based photocells from 35% at λ=0.56 μm down to 0.9% View full abstract»

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  • Thermally stimulated current spectra of polypropylene thin films irradiated with pulsed CO2 laser light

    Publication Year: 1999 , Page(s): 419 - 422
    Cited by:  Papers (1)
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    There have been many reports on the laser light irradiation effects of polymers. Especially, ablation effect of polymers by irradiation with excimer laser light has been extensively studied by Srinivasan et al. Recently, interest in laser light irradiation to polymers has grown more and more in relation to the laser-induced pressure pulse method for measuring charge profiles in polymer thin films. However, irradiation effect of laser light on electrical properties of polymers has been hardly investigated yet. The electrical properties of insulating polymers strongly depend on charge traps in these polymers and the charge traps are best examined by thermally stimulated current (TSC) spectroscopy. For positively corona-charged polypropylene (PP), their TSC spectra were reported to have two main bands above room temperature: a low temperature band BL and a high temperature band BH, which peak around 60-70 °C and 130-140 °C, respectively. The charge traps responsible for the BL and BH bands were also reported to exist in the strained amorphous regions and the crystalline defects, respectively. Propagation of the laser-induced pressure pulse or thermal pulse through semi-crystalline polymer films is expected to induce defects in the crystalline regions and some of these defects can act as deep charge traps. Therefore, we tried in this experiment to introduce crystalline defects into PP by irradiation with pulsed CO2 laser light and detect these defects by TSC method View full abstract»

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  • On the electrical and dielectric properties of Nylon 11

    Publication Year: 1999 , Page(s): 671 - 674
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    The electrical and dielectric properties of ferroelectric Nylon 11 have been studied using alternating current (AC), thermally stimulated depolarization current (TSDC), direct current (DC) for a triangular signal with a very low period, and isothermal discharging current measurements. Measurements were carried out in a broad temperature range from -170 to 200°C. The primary α relaxation associated with the glass transition and two secondary relaxations were observed. In order to analyze the influence of water on the relaxation spectrum, the AC measurements have been carried out on dry, normal and humid samples, in the frequency range from 10 MHz to 1 MHz. Water increases the strength of secondary β relaxation and shifts the peaks to lower temperatures/higher frequencies. The agreement between the electrical conductivity of the material determined from DC and AC measurements is good and the activation energy of the conductivity is 1.4 eV View full abstract»

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  • Analysis of polarization and space charge in thermally poled PVDF

    Publication Year: 1999 , Page(s): 87 - 90
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    The spatial distribution of the space charge (SC) and polarization in thermally poled polyvinylidenefluoride (PVDF) can be studied using laser intensity modulation method (LIMM). The actual amount of charge existing in the poled specimen can be determined by hysteresis and thermally stimulated discharge current (TSDC) measurements. The hysteresis measurements are directly sensitive to polarization while the other method is sensitive to both the polarization and SC. PVDF is a ferroelectric polymer which contains polar crystals in which the direction of polarization can be reversed by an application of an appropriate electric field. It is interesting to try to determine the contribution of polarization charge and space charge to observed effects. Present work reports the results concerning the magnitude and spatial distribution of polarization/space charge in PVDF, determined from hysteresis, TSDC and LIMM measurements View full abstract»

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  • Thermally stimulated depolarization currents in corona poled doped polystyrene

    Publication Year: 1999 , Page(s): 335 - 338
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    In this study the samples of guest-host polystyrene/disperse red 1 (DR1) were poled in a corona triode by a constant current method and the efficiency of poling was probed by the thermally stimulated depolarization (TSD) method. The main objective of this work was to analyze the relative importance of the parameters selected as variables in order to improve the poling efficiency for the studied guest-host system View full abstract»

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  • Dielectric properties of ethyl cellulose and ethyl-cellulose acrylic acid system

    Publication Year: 1999 , Page(s): 343 - 346
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    Dielectric permittivities and losses were measured above room temperature in the frequency range 102-106 Hz for undoped and acrylic acid (AA) doped ethyl cellulose (EC) films (thickness about 20 microns) with progressively increasing AA concentration. The variation of permittivity with temperature is attributed to thermal expansion in the lower temperature region to the orientation of dipolar molecules in the neighbourhood of Tg and random thermal motion of molecules above Tg. The dielectric losses exhibit one peak. Doping with acrylic acid is found to affect the magnitude and position of the loss peak. An explanation for this has been attempted on the basis of charge transfer complex formation View full abstract»

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  • New methods of computer simulation of thermally stimulated depolarization (TSD) currents in dielectrics

    Publication Year: 1999 , Page(s): 387 - 390
    Cited by:  Papers (1)
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    The new methods of computer simulation of thermally stimulated depolarization (TSD) currents in dielectrics were elaborated. Some of the problems were analyzed by S.N. Koykov with the use of Fortran. These and other problems were also analyzed by two authors with the use of Mathcad PLUS 6.0. In some cases the results received by Fortran and by Mathcad PLUS 6.0 are compared. The examples of analysis of experimental data by these new methods are given View full abstract»

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  • Acoustic emission sensors based on ferroelectric composites

    Publication Year: 1999 , Page(s): 747 - 750
    Cited by:  Papers (1)
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    The authors develop an acoustic emission sensor using a Ca-modified PbTiO3 ceramic-PVDF copolymer composite as piezoelectric element. The sensor's experimental impedance and frequency bandwidth are determined and it is concluded that the device can operate over a large frequency range View full abstract»

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  • Electrical properties and percolation phenomena in carbon black filled polymer composites

    Publication Year: 1999 , Page(s): 529 - 532
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    The electrical conductivity and related percolation phenomena in polypropylene/carbon black (PP/CB) composite systems have been studied. The carbon black concentration was systematically varied in a wide range. The electrical and dielectric properties of these materials were investigated by means of broadband AC (10-1-106 Hz) dielectric relaxation spectroscopy techniques. By complex dielectric permittivity measurements, the dependence of AC conductivity, σ AC, and DC conductivity, σDC, on the frequency and on the concentration of the conductive filler was investigated. The dielectric behaviour of this system can be satisfactorily described in terms of percolation theory. According to our results, the percolation threshold was calculated to be 6.2 wt.% CB. The concentration and frequency dependence of the conductivity was studied in detail. Both, dielectric constant and dc conductivity, follow power-law behaviour yielding values for the critical exponents which are in good agreement with the theoretical ones View full abstract»

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  • Computer simulation of TSP and TSD current in dielectrics on the basis of some physical models of charge relaxation

    Publication Year: 1999 , Page(s): 423 - 426
    Cited by:  Papers (1)
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    In precious paper we proposed some new methods of computer simulation of thermally stimulated TSD currents on the basis of the traditional used simplest Debye model (or first order differential equation) of charge relaxation both with one relaxation time and by presence of distribution of electrical active centers on relaxation time. In this paper we give computer simulation of TSD, TSP current on another, physical models of charge relaxation (here will be given new results for the model of three-layer dielectric and for symmetrical model of charge distribution in dielectric which are compared with experimental data for polymer films) View full abstract»

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  • Effects of electric conduction on electrical response of electrorheological fluids

    Publication Year: 1999 , Page(s): 123 - 126
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    In the present study, the current-voltage characteristics and the electrical responses of the electrorheological (ER) fluids were measured under DC electric field conditions. The test fluids consisted of microsphere particles with various moisture levels dispersed in a silicone oil. The current density/electric field curves could roughly be fitted with sinh functions suggesting ionic conduction. The forces of cohesion between individual particles in the ER fluids were also determined using a mathematical model. The current-force relationship predicted by the theory was compared to experimental results for the test fluids View full abstract»

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  • The action potential of the plant Mimosa pudica under modulated microwave radiation

    Publication Year: 1999 , Page(s): 237 - 240
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    In vivo investigations of a possible influence of modulated microwave radiation on the action potential of the plant Mimosa pudica were carried out. In the preliminary results a tendency was observed for the potential pulse to be higher and of shorter duration. Further measurements are nevertheless necessary in order to rule out a coupling of the high frequency field to the electronic set-up View full abstract»

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  • Analysis of electret sub-miniature microphones

    Publication Year: 1999 , Page(s): 797 - 800
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    Previously a method of evaluation of electret microphones with a flexible diaphragm has been presented. It was based on taking into account electrostatic forces between a membrane and a back plate in the field of electret. However this method is not appropriate for a sub-miniature microphone with a rigid diaphragm. Besides this use of a double-layer dielectric with different sizes and dielectric constants of the back plate and a diaphragm is also a reason for such inapplicability. Usually an estimation of the microphone sensitivity is based on an evaluation of the voltage that is generated by diaphragm oscillations. Thus an alternating of field in a gap between the diaphragm and the back plate is a general basis for all types of microphone's evaluation View full abstract»

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  • Electromechanical response of cellular electret films

    Publication Year: 1999 , Page(s): 261 - 264
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    Charged films with a cellular structure show pseudo-piezoelectric properties with high transducer constants. The electromechanical response equations of such films are derived for their operation as sensors and actuators. Measurements of the direct and inverse transducer constants, the thermal stability of the charge, and Young's modulus are presented. By assuming reasonable charge distributions and charge densities, the calculated transducer constants are in good agreement with the measured values. Both the theoretical model and the measurements show the reciprocity of the transducer constants View full abstract»

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  • Molecular mobility and hydration properties in polyurethane and styrene-acrylonitrile blends

    Publication Year: 1999 , Page(s): 485 - 488
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    Dielectric measurements by means of thermally stimulated depolarization currents (TSDC) techniques in the temperature range 90-300 K were used to study molecular mobility and morphology in blends of polyurethanes based on branched polymer polyol (PUR) and styrene-acrylonitrile copolymer (SAN) with different SAN content. Water sorption/desorption isotherms both in equilibrium (ESI) and dynamic (DSI) were used to measure isothermal water uptake and diffusion coefficients. Water sorption has a significant influence on the γ and β relaxations. With increasing water content the MWS peak shifts to lower temperatures. For all samples studied the amount of water at saturation was found to decrease with increasing temperature and SAN content in the blends View full abstract»

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  • Charge relaxation in PTFE-Al structures having interfacial region modified by the glow discharge

    Publication Year: 1999 , Page(s): 91 - 94
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    It is known that glow discharge modifies the physical and chemical nature of polymer surfaces and in general enhances their adhesion to the metals. This effect finds wide use in a commercial technologies of polymer electrets. However, in polytetrafluoroethylene (PTFE) films treated by a glow discharge (prior to metallization and conventional corona-charging procedure) the surface voltage stability is reduced significantly. The first objective of the present paper is to study the charge relaxation mechanism in PTFE-Al structures having interfacial region modified by the glow discharge. The second is to obtain information about the electrophysical, chemical and structural properties of this region View full abstract»

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  • On the energy spectrum of electrically active defects in polyethylene terephthalate (PET) films

    Publication Year: 1999 , Page(s): 339 - 342
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    The TSD curves in PET films show two maxima: in the 80°C region (α-peak) and at 125°C (β-peak). From the thermally stimulated depolarization results in PET films the quasi-two-dimensional electrically active defect (EAD) distribution function is reconstructed, The distribution function maximum for the α-peak shifts to the region of lower values during the PET films depolarization in the ambient air at a pressure of 1100 mbar as compared to measurements in vacuum View full abstract»

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