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Electrical Insulation, IEEE Transactions on

Issue 4 • Date Aug. 1992

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Displaying Results 1 - 25 of 31
  • Second-harmonic generation of light in ferroelectric polymer films with a spatially nonuniform distribution of polarization

    Page(s): 849 - 855
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    A spatial distribution of the spontaneous polarization P s(z) results in a similar spatial distribution of the nonlinear optical coefficients d 31(z), d 32(z), and d 33(z). Large errors in the determination of the coherence length and of the nonlinear optical coefficients can occur if the distribution of the polarization is not taken into account. A proper analysis of second-harmonic data thus requires in any case the knowledge of the polarization distribution, which can be measured by a piezo- and a pyroelectric technique. The optical transfer matrix formalism further allows the study of quasi-phase-matching techniques, optical resonance enhancement techniques for the fundamental or for the harmonic beams and planar waveguide structures.<> View full abstract»

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  • Photoconductivity in polysilanes with attached pi -conjugated chromophores

    Page(s): 856 - 860
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    The photogeneration of charge carriers and the electronic transport in new derivatives of polymethylphenylsilane was studied. The strong increase in the photoelectric sensitivity of the polysilanes with attached nitro substituted pi -conjugated pendant groups was observed. The transport of charge carriers was found to be dispersive.<> View full abstract»

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  • Design and properties of a microcalorimeter

    Page(s): 861 - 866
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    A pyroelectric microcalorimeter is introduced for the measurement of the specific heat of films. It consists of a pyroelectric sensor with the sample directly deposited onto one of the electrodes of the sensor. The arrangement is heated by the absorption of intensity-modulated radiation at the other electrode. For a homogeneously poled pyroelectric sensor, the quotient for the pyroelectric current, obtained at modulation frequencies omega below and above omega =2D/d 2, with D the thermal diffusivity and d the thickness of the pyroelectric sensor material, directly yields the quotient of the heat capacity of the pyroelectric material and the sample. Experimental results show that with the pyroelectric microcalorimeter it is possible to measure the specific heat of film samples with a thickness in the submicron range and with a sample mass of several micrograms.<> View full abstract»

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  • Silicon subminiature microphones with organic piezoelectric layers-fabrication and acoustical behavior

    Page(s): 867 - 871
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    A silicon subminiature microphone, based on the piezoelectric effect of organic films such as aromatic polyurea, PVDF, and PVDF/TrFE, is proposed. The acoustical sensor is fabricated using a slightly modified integrated circuit technology process and a standard micromechanical fabrication procedure. The main production steps of this hybrid sensor are given, including the fabrication of the mechanical part of the sensor, the deposition or spin coating of the films, and the poling of the polymer layers. Measurements of the transverse piezoelectric charge constant d 31 yield values up to > View full abstract»

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  • Direct observation of space charge evolution in e-irradiated Kapton films

    Page(s): 763 - 767
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    The pressure wave propagation method was applied to analyze in a vacuum the evolution of the space charge in electron-irradiated Kapton H films. The 125 μm thick films were irradiated in a vacuum chamber with a monoenergetic electron beam in the 10 to 50 keV energy range. The method allows direct observation of the depth of penetration of electrons and first results on Kapton are presented. The space charge generated in the irradiated and nonirradiated regions was observed during and after the irradiation process. The space charge is influenced by electric field-assisted detrapping of incident electrons and their interaction with the lattice as they drift. Interfacial effects are indicated by the buildup of a negative charge layer at the metal-polymer interface View full abstract»

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  • Thermal depolarization of PVDF: anomaly at 180°C

    Page(s): 768 - 772
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    PVDF samples with high β content (80%), prepolarized at room temperature, were heated to higher temperatures. The polarization was measured first under open circuit conditions at the high temperature and then after cooling down again to room temperature For elevated temperatures up to 175°C the polarization was reduced to 2% of the original value, yet recovered roughly to 8% of the original value after cooling down to room temperature In contrast to this, when heating the films to 180°C, a significantly different behavior was observed in cooling down to room temperature again the polarization returned from ~1% at 180°C to ~40% of the original prepolarized value View full abstract»

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  • Piezoelectricity of PVDF/PUE, PVDF/PMMA and PVDF/PMMA+BaTiO3 laminates

    Page(s): 782 - 786
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    Preparation of piezoelectric laminates by using PVDF polymer film (a), polyester urethane elastomer film (b), PMMA film (c), and (PMMA+BaTiO3) composite film (d) is proposed. Three-layered-structure systems of (aba), (aca), and (ada) have been made and conventional electrets based on these laminates have been prepared. The modification of internal layers in the systems leads to a change of their dielectric properties and also the mechanical parameters which determine the piezoelectricity. The origins of piezoelectricity in these systems have been considered on the basis of TSD thermograms View full abstract»

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  • On the charge storage and decay mechanism in silicon dioxide electrets

    Page(s): 691 - 697
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    A mechanism for both the storage and the decay of charge in a charged silicon dioxide layer is proposed. The oxide layer needs neutral electron traps to obtain stable trapped negative charge, after having been charged, resulting in an electret that can be applied in microphones. The deprotonization of the silanol groups, followed by charge injection, results in an electrochemical reaction with immobile SiO- as one of the reaction products. Decay of the stable charge thus obtained can occur by the clustering of water molecules at inner silanol groups, resulting in a conductive hydrogen bonded network, which eventually leads to the discharge of the electret. Measurement results are presented, showing a considerable decrease in surface conductivity, after having grafted the SiO2 surface, resulting in covalently bonded, relatively long octadecyl silane chains View full abstract»

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  • Piezo and pyroelectric radiation dosimetry

    Page(s): 835 - 842
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    The authors review the use of photoacoustic and pyroelectric radiation dosimeters. They compare the characteristics and results obtained with a photoacoustic radiation dosimeter (PARD) and a pyroelectric radiation dosimeter (PERD). The PARD and the PERD can be used to measure the energy fluence rate of continuous X-ray beams. In the same way, the single-pulse photoacoustic radiation dosimeter and the single-pulse pyroelectric radiation dosimeter (PPERD) were compared. They can measure the energy fluence of a single pulse of X-radiation. A theoretical model to explain the results obtained with the PPERD is presented and compared with experimental results View full abstract»

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  • Radiation-induced conductivity in electron-beam irradiated insulating polymer films

    Page(s): 843 - 848
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    The radiation-induced conductivity (RIC) in polypropylene, polyethylene terephthalate, and polyimide due to electron-beam irradiation is measured with an external bias method and, in the case of polypropylene, also with a short-circuit method, as a function of dose rate and time of irradiation or total dose. The results substantiate the power-law dependence of the RIC on dose rate in all cases, but indicate that the dependence on time is different for the materials under investigation. In addition, the delayed radiation-induced conductivity (DRIC) is determined. The DRIC shows a hyperbolic time dependence with different exponents for the different materials View full abstract»

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  • Thermally stimulated current study of amorphous oriented PPS

    Page(s): 795 - 800
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    The influence of aging on relaxation phenomena in poly-p-phenylene sulfide (PPS) has been investigated by TSC spectrometry. In the vicinity of the glass transition temperature, Tg, two relaxation peaks have been observed in amorphous oriented PPS: a secondary peak at 62°C in nonaged PPS and at 45°C in aged PPS; and a primary peak at 93°C in both films. According to differential scanning calorimetry data, they have been associated with the dielectric manifestation of the sub-Tg and Tg transitions, respectively. Each mode has been characterized by a distribution of relaxation times. For the sub-Tg mode with the relaxation times follow a Vogel equation while for the Tg mode they obey a compensation law. The sub-T g modes, which is strongly enhanced upon aging, has been attributed to a diffusion of free volume favored by local order in rigid domains. The Tg mode has been assigned to cooperative movements of sequences of various length in `true' amorphous regions View full abstract»

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  • Comparison of polarization distribution measurement by the LIMM and PWP methods

    Page(s): 751 - 757
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    Two different methods of measurement of polarization distributions in piezoelectric materials, the laser intensity modulation method (LIMM) and the pressure wave propagation (PWP) method, are compared. The two techniques are described, and measurements made on different PVDF-based samples, one with a symmetric and the other one with an antisymmetric structure, are reported. Although the LIMM responds to diffusion of heat and the PWP method to the propagation of a pressure wave, the direct observation of the raw data gives similar information in both cases as far as the symmetry of the polarization distribution is concerned. The specific characteristics of each method are analyzed View full abstract»

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  • Determination of charge density and charge centroid location in electrets with semiconducting substrates

    Page(s): 698 - 701
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    A method for determining the amount and the mean spatial depth of charge in electret-semiconductor systems is presented. It consists of two nondestructive measurements, from which the internal and external electric fields can be calculated independently. First, the surface potential at the electret-air interface is measured by an electrostatic voltmeter. Second, using a contacting front electrode, a metal-insulator-semiconductor structure is formed, on which capacitance or conductance voltage measurements are carried out. With these results, one obtains the surface potential at the electret-semiconductor interface. The charge centroid and the charge density can now be calculated. For SiO2-silicon structures, where the 1-μm-thick thermally wet-grown SiO2 layer acts as an electret, it was found that the charge centroid can be influenced strongly by temperature treatment prior to charging View full abstract»

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  • Influence of defects and substitutions on polarization phenomena of bioelectrets: apatites

    Page(s): 826 - 830
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    Nonstoichiometric hydroxyapatites and carbonated hydroxyapatites are characterized by the thermally stimulated current technique. Since dielectric energy losses are cooperative, the compensation temperature has been chosen as fingerprint of the local order. Relaxation map analysis shows the existence of either monophasic or biphasic structures and analysis of polarization phenomena gives information on localization and interaction of defects with structural ions of the apatites View full abstract»

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  • Bioelectrets and biopiezoelectricity

    Page(s): 813 - 819
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    Some biopolymers possess polar uniaxial orientation of molecular dipoles and show pyroelectricity and piezoelectricity. Some examples of bioelectrets are described. Shear piezoelectricity is observed for elongated films of poly-L-lactic acid (PLLA). Temperature relaxations in the complex piezoelectric constants, the elastic constant, and the permittivity are observed at the glass transition temperature, ~90°C. However, the piezoelectric constants for the crystalline phase of PLLA calculated from a spherical dispersion theory are independent of temperature. Thin layers of aromatic polyurea prepared by vacuum deposition polymerization show pyroelectricity and piezoelectricity after poling, which are stable to 200°C View full abstract»

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  • Effect of space charge on micro-macro domain transition of PLZT

    Page(s): 773 - 776
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    Space charge distributions of PLZT 8/65/35 were measured by the laser intensity modulation method. The effect of space charge on the micro-macro domain transition is shown. Large differences in the depolarization temperature Td measured on heating and cooling are due mainly to the effect of space charge View full abstract»

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  • Effect of dye-doping on photo-induced pyroelectric response in thin films of vinylidene fluoride/trifluoroethylene copolymers

    Page(s): 777 - 781
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    The time dependence of the current response induced by a chopped laser beam was measured for dye-doped vinylidene fluoride/trifluoroethylene copolymers spin coated on an ITO coated glass substrate. In addition to conventional pyroelectric response, an anomalous current was observed in the high dye concentration region. This effect was explained by the photoconductivity of dye molecules densely dispersed in the noncrystalline regions of the polymer matrix View full abstract»

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  • The trapping of electrons in polystyrene

    Page(s): 680 - 686
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    The trapping of electrons in localized states in polystyrene has been studied by means of an electron beam technique. A 2.2-kV beam is used to inject a short pulse of charge into the free surface of a thin film of the polymer, and a second electron beam monitors the surface potential of the film. The surface potential is related to trapped charge density and to the depth of charge penetration. By defining a trapping parameter α=1/μτE, one can relate the incremental buildup of surface potential to the injected charge density and carrier range. The release of electrons from traps is analyzed in terms of a time and temperature dependent demarcation energy E m. This energy is related to elapsed time since charge injection via the equation Em=kT1n(vt ). Time dependence of charge decay is thus related to the energy distribution of traps in the polymer View full abstract»

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  • Dielectric investigation of β-cyclodextrin hydrates and inclusion complexes

    Page(s): 801 - 806
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    The dielectric behavior of β-CD hydrates and β-CD inclusion complexes with various organic guest molecules has been studied mainly by the thermally stimulated depolarization current (TSDC) method in the temperature range 80 to 300 K. Some preliminary measurements have also been carried out by conventional AC techniques at room temperature. Results are discussed in relation to the corresponding structure as determined by X-ray diffraction and are compared with differential scanning calorimetry data reported in the literature. The main high-temperature (200 to 280 K) peak recorded with the TSDC method is shown to be directly related to a phase transition occurring near the peak temperature. Water enclosed in the β-CD cavity seems to play a very important role as far as this transition is concerned View full abstract»

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  • Transition from dispersive to non-dispersive hole transport in poly-N-vinylcarbazole/polycarbonate mixtures

    Page(s): 714 - 718
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    Isothermal time-of-flight (TOF) measurements carried out on films of a poly(N-vinyl carbazole)/polycarbonate mixture in the temperature range 220 to 370 K show that with increasing temperature a transition from dispersive (≲250 K) to nondispersive (>250 K) hole transport occurs. A comparison of thermally stimulated currents, thermoluminescence, isothermal TOF, and thermally stimulated TOF measurements indicates that the low-temperature dispersive transport results from frozen-in energetic disorder rather than from multiple trapping View full abstract»

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  • Constant-current corona charging of biaxially stretched PVDF films in humidity-controlled atmospheres

    Page(s): 744 - 750
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    A special version of a constant current corona triode has been developed for charging samples in controlled atmospheres. Measurements performed on biaxially stretched polyvinylidenefluoride (PVDF) samples show that the buildup of the surface potential is dependent on air humidity. In a dry air atmosphere, the polarization clearly shows the ferroelectric behavior of the PVDF sample. For samples charged under humid conditions, the surface potential vs. time curves pass through a maximum value which decreases with increasing relative humidity. A tentative explanation for the surface potential dependence on the humidity is given, based on the increase in conductivity originating from the dissociated water molecules absorbed into the sample View full abstract»

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  • Study of space-charge effects on dielectric breakdown of polymers by direct probing

    Page(s): 758 - 762
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    Direct and quantitative probing of space charge was carried out to study effects of space charge on dielectric breakdown of polymeric insulating materials. In poly-p-phenylene sulfide, in which dielectric-breakdown characteristics were explained in terms of space-charge formation, positive homo space charge was observed. The amount and the depth of space charge detected could explain the dependence of impulse breakdown strength on prestressing both qualitatively and quantitatively. In oxidized polyethylene, negative homo space charge was observed. This also agreed well with the prestress dependence of the breakdown characteristics. The injecting electrode during the prestressing or the region nearby was suggested to be important in the breakdown process of both materials View full abstract»

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  • Charge dynamics in Mylar films corona-charged at various temperatures

    Page(s): 702 - 707
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    The discharging behavior of Mylar polyethyleneterephthalate (PETP) films is investigated and discussed in terms of dipole relaxation at 85°C as well as conductivity and trap dynamics at higher temperatures. For comparison, the low-temperature peak due to positive real charge in nonpolar fluoropolymer Teflon FEP is also described. The shift of the mean charge depth in PETP samples charged at elevated temperatures, the transport of detrapped real charge in the bulk of PETP, and the compensation of detrapped charge in the bulk during thermally stimulated discharge are studied by means of heat-pulse experiments as well as measurements of the steady-state conduction current and the bulk conductivity glow curve View full abstract»

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  • A novel method for electret production using impulse voltages

    Page(s): 739 - 743
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    A method for producing electrets is proposed in which an electric discharge is produced by a negative impulse voltage in a small air gap. The dielectric film to be charged is placed between two planar electrodes, the film being in contact with one of the electrodes and separated from the other by the air gap. The electric discharge in the gap causes electric charges to deposit onto the dielectric surface where they are trapped, thus forming the electret. Measurements carried out with Teflon FEP show a very uniform deposition, and also that the sample surface potential increases linearly with increasing impulse peak voltage. This method appears to be as good as the corona discharge for the production of electrets, with regards to a high turn out and low cost View full abstract»

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  • Escape depth of secondary electrons from electron-irradiated polymers

    Page(s): 831 - 834
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    Measurements on polymers (Teflon, FEP and Mylar) have shown that the secondary electron emission from uncharged surfaces exceeds that from surfaces containing a positive surface charge. The reduced emission of charged surfaces is due to recombination between electrons undergoing emission and trapped holes within the charged layer. During the experiments the surface of the material was kept at a negative potential to assure that all secondary electrons reaching the surface from within the material are actually emitted. An analysis of the results yielded the maximum escape depth of the secondary electrons, and showed that the ratio of the maximum escape depth of the secondaries from Mylar to the maximum escape depth from Teflon is almost the same as the ratio of the corresponding second crossover energies of these polymers View full abstract»

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Aims & Scope

This Transactions ceased production in 1993. The current retitled publication is  IEEE Transactions on Dielectrics and Electrical Insulation.

Full Aims & Scope