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Electrical Insulation and Dielectric Phenomena, 2003. Annual Report. Conference on

Date 19-22 Oct. 2003

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Displaying Results 1 - 25 of 180
  • PD characteristics of thin void between LDPE and electrode

    Publication Year: 2003 , Page(s): 612 - 615
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    PD measurements have been used in the after laying test for high voltage XLPE power cable lines because PD is sensitive to defects in a cable system. However, the PD characteristics for defects in XLPE cables or joints strongly depend-upon the type or the size of defects. They also change with time. Their details are not well understood yet. In this paper, the PD characteristics of a thin void between low-density polyethylene and electrode have been investigated. Especially, the change in PD characteristics with time and the time delay of the PD detection in the after laying test of XLPE cable line were discussed. View full abstract»

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  • Partial discharge activity at the intercept between solid and air insulation: Qualitative interpretation of the ultrasonic signatures

    Publication Year: 2003 , Page(s): 430 - 435
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    A discharge regime could be described based on the recording and analysis of digitized real-time sequences of the electrical signals. These signals were compared with the ones obtained using an ultrasonic diagnostic. The ultrasonic transducer easily detected partial discharges at corona threshold having a charge in the range of 200 pC. Discharge events consisting of a single pulse had a very consistent and reproducible ultrasonic signature. A single oscillating wave was produced exhibiting a fast damping over periods ranging from 30 to 50 ms. The ultrasonic method does-not permit the discrimination of multiple discrete isolated discharge events consisting of several single pulses occurring over the 1-ms frame. However, pulse sequences were observed to greatly affect the signatures. View full abstract»

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  • Electrical insulation characteristics of CO2 and CO2 gas mixtures under non-uniform electric field

    Publication Year: 2003 , Page(s): 538 - 541
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    Since SF6 gas has been specified as one of the greenhouse gases, we attempt to develop new insulation gases or gas mixtures alternative to SF6 gas for gas insulated switchgears (GIS). In this paper, we investigated partial discharge (PD) and breakdown (BD) characteristics of CO2 gas and CO2 gas mixtures as one of the promising candidates without using SF6 gas. Experimental results revealed PD inception and BD strengths for different gas pressure and CO2 content under lightning impulse voltage and ac high voltage application. View full abstract»

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  • Experimental investigations on electrohydrodynamic phenomena at single droplets on insulating surfaces

    Publication Year: 2003 , Page(s): 133 - 136
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (358 KB) |  | HTML iconHTML  

    Polymeric insulating material can lose its hydrophobic proper-ties when is stressed by various environmental factors under service conditions. Humidity is one very important factor for ageing phenomena. This paper reports investigations on single droplets which are electrically stressed on hydrophobic polymer surfaces. With the help of two digital optical diagnostic systems deformations and movements of the droplets can be recorded and analyzed in an electrical ac and dc field. The experiments show several electrohydrodynamic phenomena which have an effect on the process of the very early stage of ageing of polymer insulating surfaces. When a critical field stress is exceeded different phenomena occur, such as transient structures on the surface, creation of filaments, formation of water paths between droplets, collapsing of several droplets, separation of droplets and ejection of very small droplets from bigger ones. These effects lead to a deformation and rearrangement of the original droplets. As a result the droplets cover a wider area of the insulating surface and minimize the dry zones of the solid surface. Thus, bridging by a water path between the electrodes becomes more probable. View full abstract»

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  • Time-domain analysis of nonlinear stress-grading systems for high voltage rotating machines

    Publication Year: 2003 , Page(s): 482 - 485
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (304 KB) |  | HTML iconHTML  

    This paper introduces a new approach for the design and analysis of nonlinear stress-grading systems for high voltage rotating machines. The method is based on the simulation and modeling of stress-grading systems using a nonlinear lumped circuit model. The nonlinear model is analyzed in the time domain using the describing function method. The model generates the time variation of the resistances as well as the surface electric field and potential and ultimately converges to the optimal design parameters of the stress-grading system. The model is iterative and adaptive where a deviation from the nominal uniform field and the upper and lower bounds on the resistance values as well as bounds on the nonlinearity factor can be set to generate optimal design parameters of the stress-grading system. View full abstract»

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  • Prediction of remaining life of the paper insulation by the analysis of new oil-soluble compounds in power transformers

    Publication Year: 2003 , Page(s): 128 - 132
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (359 KB) |  | HTML iconHTML  

    The evaluation of the state of the paper insulation of a power transformer can be assessed by the analysis of specific degradation by-products of paper such as CO, CO2 and furanic compounds. However it is still difficult to differentiate an incipient fault from the normal aging of an equipment. There is a need to develop more precise diagnostic tools. An experimental accelerated aging test conducted on kraft paper and oil samples at 150°C, allowed us to observe the production of new oil-soluble species. New compounds analogous to furanic derivatives were detected by high performance liquid chromatography. Specific sugars such as rhamnose and mannose were also detected by high performance ionic chromatography. The evolution of some of these species are correlated with the aging of the paper (decrease of the paper polymerization degree). Their presence in samples obtained from the field leads us to believe that selected molecules could play an important role in the prediction of remaining life of power transformers. View full abstract»

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  • A comparative study of some design concepts for mechanically prestressed fiber-reinforced composite insulations

    Publication Year: 2003 , Page(s): 653 - 656
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (336 KB) |  | HTML iconHTML  

    In recent years, the accumulated research evidence in our group has demonstrated that the addition of mechanically prestressed fibers in epoxy resin will strengthen the microstructure and therefore improve the electrical insulation strength of the epoxy resin by increasing the electrical tree growth resistance. In this paper, a comparative study of the effect of some different design concepts on mechanically prestressed insulation is presented. Calculations of the effect of prestress in the resin and the optimized design for the composite insulation are based on fundamental stress analysis. The electrical treeing test results from prestressing specimens with multiple unidirectional and orthogonal fibers clearly demonstrate the beneficial effect of mechanical prestress and that enforced compressive stresses in the resin by optimized prestress design can significantly increase the electrical tree growth time to failure and therefore improve the electrical insulation. View full abstract»

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  • Comprehensive diagnostic and aging assessment method of solid insulation in transformer

    Publication Year: 2003 , Page(s): 137 - 140
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (340 KB) |  | HTML iconHTML  

    Up to now, the diagnostic methods and criteria for operating oil-immersed power transformers are still under research. Besides the investigation of diagnostic methods for solid insulation in transformer, quite a lot of data collected from the in-service transformers under different condition included the data of failed or defected transformers have been analyzed systematically in this paper, such as its furfural concentrations, dissolved gases in oil, the degree of polymerization of insulating paper and pressboard, etc. Statistic analyses or the membership functions had been carried out to reveal the relationship between the contents of furfural or gases in oil and the aging of solid insulation. And the life expectancy of power transformer is studied. Finally a comprehensive diagnostic method is put forward for the aging assessment of solid insulation. The examples of application show the method is effective and easy to apply for the operating transformers. View full abstract»

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  • Transient current and light emission associated to the propagation of pre-breakdown phenomena in water

    Publication Year: 2003 , Page(s): 542 - 545
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (385 KB) |  | HTML iconHTML  

    This paper presents a study of pre-breakdown phenomena in water. Streamer propagation is studied by the simultaneous recording of transient currents, and fast photographs. The light emitted by streamers is intense compared to hydrocarbons, and this allows us to visualize on the same photograph both the emitted fight and the shadow of gaseous channels. This allows us to observe the spatial and temporal development of streamers: fast luminous discharge first propagate (velocity about 30 km/s), and gaseous filaments develop afterwards in the hot track left by the discharge. The succession of fast discharges produces a stepped propagation. At very high voltage, a single fast discharge can lead to breakdown in a unique step. The initiation and propagation are both favored when the conductivity of water is increased. View full abstract»

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  • Dielectric properties of polar fluid mixtures at wide range of temperature and frequency

    Publication Year: 2003 , Page(s): 486 - 489
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    Dielectric property of a liquid is depends upon different parameters such as temperature, frequency, impurities, moisture content and presence of other liquids etc. In this experiment Silicone fluids of different viscosity were used as the dielectric liquid and analar graded dimethyl ketone was used as the solvent and measurements were carried out at various mixture proportions, temperature and frequencies. The experimental values have been verified with the existing literature through the determination of the dipole moments, polarizability. Fourier Transform Infrared Spectroscopy (FTIR) analysis also performed for the verification of the liquid purity. Thus the measured results were employed to arrive at a unified method of calculating the dielectric properties. View full abstract»

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  • Corona between point plane electrodes in air at atmospheric pressure

    Publication Year: 2003 , Page(s): 305 - 308
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (249 KB) |  | HTML iconHTML  

    Several theoretical investigations have been reported in literature on electric field nonuniformity between point plane electrodes. In the present investigations experiments have been performed to determine corona onset voltages in air at atmospheric pressure between point plane electrodes for DC voltage applications of both polarities. The diameter of hemispherical tip of point electrodes used in experiments varied from 1.2 mm to 3.0 mm and gap distances varied from 20 mm to 50 mm (approximately). For these electrode arrangements, calculated variation of electrical field non uniformity factor was from 18 to 48. The measured corona inception voltages were found to increase with increase in diameter of point electrodes and also with increase in gap distance between electrodes. The calculated maximum stresses at tip of point electrode at corona inception are in approximate range of 70kv/cm to 135 kv/cm. The maximum stress, which appears for tip diameter of 1.2 mm for point electrode, does not significantly influence the field variation in these gaps as to disturb Townsend mechanism of ionization growth. View full abstract»

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  • PD patterns in CIGRE II cells subjected to PWM voltages

    Publication Year: 2003 , Page(s): 604 - 607
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    This work reports the results of a basic research regarding the study of Partial Discharge (PD) behaviour in a flat cavity when the insulation is subjected to a square voltage waveform and to two different PWM-like voltage waveforms. Tests were performed on CIGRE II specimens realised using polyimide film samples. View full abstract»

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  • Displacement current and trapping mechanisms of electric charges in TiO2-rutile

    Publication Year: 2003 , Page(s): 221 - 224
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (330 KB) |  | HTML iconHTML  

    The Scanning Electron Microscopy Mirror Effect (SEMME) and the Induced Current Measurement (ICM) have been used to characterize insulators. The application of these methods to a semiconducting material of wide band gap (TiO2) reveals that the material presents a great leakage surface current and high anisotropy of dielectric properties. The goal of the present communication is to understand and study such a behaviour. View full abstract»

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  • Impulse voltage breakdown of argon+SF6 mixtures under non-uniform electric fields

    Publication Year: 2003 , Page(s): 448 - 450
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (270 KB) |  | HTML iconHTML  

    This experimental study addresses the behavior of binary mixtures of argon and sulfur hexafluoride in a rod-plane electrode configuration when subjected to impulse voltages. Positive-polarity, standard lightning impulse voltages (1.2-μs/50-μs) with different magnitudes were employed throughout the experiments. The percentage of SF6 in Ar was varied from 1% to 90% at a total gas pressure of 50 kPa and 100 kPa. The breakdown voltage of each gas mixture was recorded at 50% breakdown probability. Similar to our theoretical as well as experimental studies under static electric fields it is observed that the breakdown strength of Ar has increased dramatically when mixed with a small percentage of SF6. However, the breakdown voltages did increase monotonically but not dramatically for higher SF6 percentages. View full abstract»

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  • Influence of the properties of materials and the hydrostatic pressure on creepage discharge characteristics over solid/liquid interfaces

    Publication Year: 2003 , Page(s): 293 - 296
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (364 KB) |  | HTML iconHTML  

    The present work is aimed at the characterization of discharges propagating on solid/liquid interfaces under ac voltages using a point-plane electrode arrangement. Different types of solid insulating immersed in mineral oil, are tested. The influence of the thickness of solid samples, the voltage, and the hydrostatic pressure on the length and pattern of creepage discharges as well as on the associated currents and emitted light are analyzed. It is shown that the final length, Lf, and the number of discharge branches, the associated current and en-fitted light are reduced when a hydrostatic pressure is applied. For a given pressure, Lf increases quasi-linearly with the voltage, whatever the solid insulating. Lf tends to increase with the dielectric constant of solid insulating. View full abstract»

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  • Identification and location of breakdown in windings

    Publication Year: 2003 , Page(s): 518 - 521
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (307 KB) |  | HTML iconHTML  

    It is possible to estimate the location of the fault based on a study of the resonant frequencies of the winding current. It is shown that the nearest neighbourhood rule based on a clustering approach provides a good framework for fault location. Additional signal acquisition in the form of the tank current can considerably simplify the identification of a fault to ground. Experimental investigations are performed in order to identify and locate breakdown in windings. View full abstract»

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  • Relationship between surface discharge of Gleitbuschel-type in an artificial void and pit formation

    Publication Year: 2003 , Page(s): 141 - 144
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (361 KB) |  | HTML iconHTML  

    In previous reports, pit formation in an artificial void has been discussed with the artificial void model which has been based on the Whitehead model. As a result, difference in surface discharge patterns in the artificial void was found to have a great effect on pit formation process. In this study, the further details am investigated, especially when the surface discharge pattern is Gleitbuschel. The pit formation processes are classified into two different types: degradation process of fatigue-failure-type in low voltage range and degradation process of early/random-failure-type in high voltage range. Assuming that the pit formation process in low voltage range is thermally activated degradation process of Arrhenius type, the activation energy is estimated to be 104.31 kJ/mol. This value is in good accord with activation energy for polymer bond scission caused by interaction with oxygen and ozone. Therefore, in low voltage range, oxidation reaction leads probably to the pit formation. In high voltage range, negative charges on the void surface have a sparse distribution. Furthermore, pit fort-nation occurs at an area on the void surface where negative charges accumulate. These results suggest that existing probability of structural defects at which a great deal of negative charges accumulates plays an important role in the pit formation process in high voltage range. View full abstract»

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  • Heat sink effects in thermal stability tests of ZnO arresters

    Publication Year: 2003 , Page(s): 473 - 477
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    The effect of heat sinks placed between the ZnO elements of a surge arrester is evaluated in the context of the IEC test for thermal stability. View full abstract»

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  • Pulsed electric field studies of bio-dielectrics

    Publication Year: 2003 , Page(s): 56 - 59
    Cited by:  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (356 KB) |  | HTML iconHTML  

    Chemical weed control accounts for oyer ℬ in costs to the American farmer. Non-chemical alternatives offer many advantages such as protecting the environment and safety for applicators. Studies have shown that high voltage, pulsed electric field (PEF) treatment of biodielectrics is an effective method to inactivate micro-organisms and bacteria. Therefore, the PEF technology might be used as an effective alternative to chemical weed control. In this work, we have studied the breakdown characteristics of weed seeds using single and repetitive pulsed electric fields. Breakdown of seeds as a function of various parameters of the pulsed system such as its duration, rise/fall time, repetition rate, and field strength, are studied. Two types of weed seeds, namely yellow foxtail and smallflower morningglory, were used in the experiment. Preliminary results suggest that the PEF method can reduce the percent germination of the yellow foxtail. Conversely, the smallflower morningglory had increased percent germination. This trend is most likely due to the presence or absence of a hardened seed coat of which the smallflower morninglory possesses. View full abstract»

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  • Breakdown pattern identification in high temperature dielectric films using scanning electron microscopy (SEM)

    Publication Year: 2003 , Page(s): 265 - 268
    Cited by:  Papers (2)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (540 KB) |  | HTML iconHTML  

    In this research paper DC breakdown patterns identification were carried out after applying high voltages across samples of 25 μm Kapton® (polyimide) and Mylar® polyester (poly(ethylene terephthalate), PET) films. For pattern identifications, Scanning Electron Microscopy (SEM) technique was employed for acquiring 150× and 300× magnified images. In both images the shape of breakdown area was almost identical to the shape of electrodes. The SEM results clearly revealed that the melting process during high voltage DC breakdown process is higher in case of Mylar® polyester than that of Kapton® (polyimide). In case of Mylar® at room temperature, observed hole diameter was approximately 265.5 μm with the total effected area of 55.3×10-9 m2 at DC breakdown strength of 326.7 MV/m as compared to Kapton®, which was 155.7 μm with total effected area of 19×10-9 m2 at breakdown strength of 364.9 MV/m. In these films for the measurement of electrical breakdown strength a new type of environmental chamber was used. Two-parameter Weibull distribution has been used to analyze the results. View full abstract»

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  • Activation energies and electron transport in LDPE

    Publication Year: 2003 , Page(s): 28 - 31
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (360 KB) |  | HTML iconHTML  

    Space charge measurements were made on low density polyethylene samples to which dc fields had been applied. Some measurements were performed under isothermal conditions, and others with a temperature gradient established across the sample thickness. Isochronal current density. was also measured as a function of temperature and field. The activation energy associated with the hopping transport of electrons through the sample volume was around 0.09 eV, whereas the activation energies deduced from the temperature dependence of the isochronal current density were in the range 0.60-1.40 eV, depending on the applied field strength and the impurity content of the samples. It was concluded that the isochronal current densities were controlled by electron injection from the cathode, the most likely injection mechanism being tunnelling between the Fermi level of the metallic electrode and acceptor sites within the dielectric close to the interface. View full abstract»

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  • Voltage distortion effects on insulation systems behaviour in ASD motors

    Publication Year: 2003 , Page(s): 608 - 611
    Cited by:  Papers (2)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (334 KB) |  | HTML iconHTML  

    Adopting PWM-like voltage waves, the insulation systems of stator windings of medium voltage motors have been characterized in presence and in absence of partial discharges. In addition, the dielectric losses increase for similar test samples, stressed both by a quasi square voltage and by a sinusoidal voltage, have been evaluated and reported. View full abstract»

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  • Comparative study of dielectric relaxation spectra of electrically and thermally aged low density polyethylene

    Publication Year: 2003 , Page(s): 161 - 164
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB) |  | HTML iconHTML  

    Low-density polyethylene (LDPE) films were thermally aged in a sodium chloride aqueous solution at constant temperature (thermal aging). Some of the samples were simultaneously immersed in solution and subjected to an electric AC field (electrical aging). The dielectric relaxation spectra at 30°C in the range of 10-5 Hz to 105 Hz were obtained for unaged and aged samples. For the low frequency (LF) region (10-5 Hz to 10-1 Hz) the time domain technique was used. A lock-in amplifier was used for the 10-1 Hz to 101 Hz medium frequency (MF) region. While for the high frequency (HF), 10-1 Hz to 105 Hz, RLC bridge measurements were performed. The main differences can be seen between electrically, thermally aged and unaged LDPE in the HF and LF regions. The LF peak is a broad peak related to localized space charge injection driven by the electric field. For electrically aged samples this peak increases in an earlier stage of electrical aging, decreasing afterwards. While in thermally aged samples the peak amplitude always increases with aging time. Finally the HF shows the beginning of a peak due to the γ and β transitions. This peak decreases with aging disappearing for the most aged samples. View full abstract»

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  • Optimization of the aluminium target thickness on space charge measurement using the LIPP technique

    Publication Year: 2003 , Page(s): 237 - 240
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (364 KB) |  | HTML iconHTML  

    In this paper, the influence of the Aluminium (Al) disc thickness on the acoustic reflection, spatial resolution of space charge measurements in 1.2mm and 2mm XLPE plaques using the LIPP system has been studied. Experimental results indicate that there exists a minimum thickness of Al for each sample, which requires eliminating the signal reflection. It is also revealed that the spatial resolution determinate with the thickness of Al. Using a optimal thickness of Al for the target, preliminary results obtained from 2mm as-received and degassed planar XLPE samples subjected to a dc electric stress of 30 kV/mm (at room temperature) for 24 hours are reported. View full abstract»

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  • Piezoelectricity of multi-layers space-charge electrets from Teflon FEP film with homogeneous voids distributed on its surface

    Publication Year: 2003 , Page(s): 225 - 228
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (322 KB) |  | HTML iconHTML  

    The development of new cellular and porous polymers has introduced new advances on the study of the piezoelectricity characteristics of electric charged polymers. Recently, a multi-layer space-charge electret was also fabricated using at least one "soft" porous and one "hard" nonporous Teflon PTFE film assembled in various multi-layer stacks. Now, in this paper we propose a new multi-layer space-charge electret fabricated using at least one Teflon-FEP film with small voids homogeneously distributed on its surface. The device has the same concept of the electret microphone mechanism. When these multi-layer setups are charged by impulse voltage process, it is possible to obtain samples with high piezoelectric coefficients. Controlling the size of the voids on the film interface, we can obtain a better control of the charging processes and, can determine a better value of the charging impulse voltage. View full abstract»

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