Showing papers in "Ieej Transactions on Fundamentals and Materials in 2013"

Simultaneous Measurements of Space Charge Distribution and External Current in Low Density Polyethylene

Abstract: Space charge distribution and external current in low density polyethylene (LDPE) have been measured simultaneously using an improved PEA (pulsed electro-acoustic) measurement system. They are usually measured using different devices independently. However, to investigate the relationship between the space charge behavior and the conduction current, it is necessary to measure them simultaneously in the same sample. Therefore, we have developed an improved PEA system to measure them simultaneously. In this improved system, the space charge distribution and the external current measurements are carried out by switching connection of the lower electrode between electrometer and ground. As the result of simultaneous measurements, it is found that the external current increases during the injection and traveling of positive charge from the anode towards the cathode. To explain the phenomenon, we estimated displacement current, conduction current and conductivity distributions in the sample from the results of the measurements. Moreover, we examined the relationship between those distributions and charge behavior in LDPE.

Solutions of Wave Scattering Problems for a Class of the Modified Wiener-Hopf Geometries

Abstract: Among a number of analysis methods for wave scattering problems, the Wiener-Hopf technique is known as a rigorous approach for canonical geometries. In this paper, we shall investigate functional equations arising in scattering problems associated with the modified Wiener-Hopf geometries, and develop general methods for approximate solutions. Applications of the methods to specific scattering problems related to canonical, two-dimensional obstacles are also discussed. First we consider scattering problems involving the modified Wiener-Hopf geometry of the first kind. It can be shown that the Wiener-Hopf analysis often leads to the integral equation as in

Boron Nitride Based Poly(phenylene sulfide) Composites with Enhanced Thermal Conductivity and Breakdown Strength

Abstract: Dielectric polymer composites with high thermal conductivity and high breakdown strength have wide applications in electronic devices and electrical equipment. In this study, poly (phenylene sulfide) [PPS] and boron nitride (BN) were selected for preparing high thermal conductivity composites for high temperature insulation application. The composites were prepared by melt compounding to contain 0-40.0 wt% (BN). Laser flash method was used to measure the thermal conductivity. As a result, the composites exhibit significantly enhanced thermal conductivity when compared with the pure polymer. For instance, the composite sample shows an increase of thermal conductivity from 0.28 W/(m·K) (the pure PPS) to 1.21 W/(m·K) when it contains 40.0 wt% BN. Weibull statistical distribution was used to analyze the breakdown data and the characteristic breakdown strength was used to compare the breakdown strength of various samples. It was found that, except the sample containing the low concentration of BN filler, the composites show enhanced breakdown strength when compared with the pure PPS. Scanning electron microcopy (SEM) results show that the BN flakes are homogeneously distributed in the PPS matrix. Thermogravimetric analysis shows that the composites have increased thermal stability when compared with the pure PPS.

Analysis of an Eddy Current Speed Meter by Rectangular Coil System

Abstract: Eddy current measurement technology are widely used in instruments such as displacement meters, vibration meters, and non-destructive testing equipment. In this paper, we proposes eddy current speed meter using a rectangular coil and clarifies its speed characteristics using an analytical method. A rectangle has a shape effect not present in a circle and an improvement in characteristics due to the coil system aspect ratio and also improvement in the flux utilization and miniaturization of the sensor can be expected. Therefore, after verifying the validity of the analytical solution through experiments, the speed characteristics are calculated for a case in which the parameters relating to the moving conductor-slab are varied and that in which the coil system aspect ratio is varied. The configuration of the proposed eddy current speed meter is shown in Fig. 1. The eddy current speed meter consists of a rectangular excitation coil arranged horizontally on a moving conductor slab and two rectangular detection coils arranged horizontally and bilaterally symmetrical to the excitation coil. The detection coil is considered for differential connection so as to counteract the magnetic field from the excitation coil. Both the excitation coil and detection coil adopt a rectangular coil system. As a result, an improvement in the sensitivity of the electromotive force and an expansion of the linear characteristic range is expected when compared to the existing differential coil method. In order to investigate the effect of the conductor slab speed, the conductor speed and excitation coil alternating current frequency were set as parameters. The conductor slab is moved only in the у-direction. The analysis results were calculated using the Gauss–Legendre method and by adjusting the integration range. The electromotive force frequency characteristics when the speed is set to v = 2.5 m/s, 6.4 m/s, and 9.6 m/s are shown in Fig. 2 (a). The maximum electromotive force is close to f = 80 Hz. Beyond this, the electromotive force decreases as the excitation frequency increases. The electromotive force speed characteristics when the excitation frequency was set to f = 40 Hz, 80 Hz, and 150 Hz are shown in Fig. 2 (b). Hardly any electromotive force is generated when the conductor is stationary at v = 0 m/s. Electromotive force is generated when the conductor moves and increases as the speed of the conductor increases. At f = 80 Hz and 150 Hz the electromotive force changes linearly within the range v = 0−10 m/s; however, at f = 40 Hz the linearity is lost at more than 4 m/s. In the past, eddy current speed meter has mainly been analyzed in terms of circular coils. This study proposes a new eddy current testing method using a rectangular coil system and clarifies the speed characteristics of this method. Further, the study also demonstrates the superiority of a rectangular coil speedometer over a circular coil speedometer from the perspective of miniaturization and improvements to the coil system aspect ratio and flux utilization. The results obtained are as follows. (1 ) It is possible to measure speed within a range of 0 m/s to 10 m/s for a moving non-magnetic conductor-slab. In this case, the thickness and conductivity of the slab are known quantities. (2 ) The optimum excitation frequency for favorable sensitivity and linearity exists due to the thickness and conductivity of the conductor used. (3 ) Sensitivity improved when a vertical rectangular coil system is used in which the long side of the rectangle is in the direction of conductor movement. Consequently, it is possible to select the optimum aspect ratio for the coil system in accordance with the installation conditions. (4 ) By varying the aspect ratio, one can achieve a rectangular coil having higher flux utilization and smaller size than those of a circular coil. Fig. 1. Proposed eddy current speed meter (a) (b)

Relationship between Remaining Antioxidant Content and Radiation-Thermal Degradation in Crosslinked Polyethylene

Abstract: To clarify the deterioration mechanism of cables installed in nuclear power plants, three kinds of XLPE sheets with various antioxidant contents were aged by 100 Gy/h γ-ray irradiation at room temperature, 60, and 100°C. The remaining antioxidant content estimated from an oxidation induction time of a differential calorimetric thermogram as well as the elongation at break decreases faster as the initial antioxidant content decreases. On the other hand, an evaluation parameter called oxidation degree, which is the absorbance ratio of the carbonyl group to the methylene group obtained by infrared spectroscopy, increases with aging time. The oxidation degree increases with an increase in the elongation at break, and the relationship of these two parameters can be plotted around a sigmoid curve. Furthermore, the elongation at break and oxidation degree show reasonably stable transitions until the antioxidant content decreases to a certain value. After such a period, the elongation at break starts to change drastically and becomes sufficiently low value. It is clarified from these experimental results that there exists a certain antioxidant content that effectively inhibits oxidation.

Factors Determining the Partial Discharge Resistance of Polymers

Abstract: The practical lifetime of a polymeric insulating material is determined in most cases by its partial discharge resistance at an operating temperature. Therefore, in this research, the partial discharge resistance was examined for eight kinds of polymer samples. An ac 500-Hz voltage with a designated value was applied to a sample sheet sandwiched between a pair of IEC (b) electrodes at 353K and 30% relative humidity for a designated period. The sheet surface degraded by partial discharges was then observed by a mechanical surface profilometer to measure the shape, from which the whole eroded volume was estimated. As a result, it has been clarified that polymers can exhibit superior partial discharge resistance when their melting point, molecular weight of chain repeating unit, density, weight ratio of benzene rings, and crystallinity are high.

Stimulation and Inhibition of Arabidopsis Seed Germination with Repetitive Barrier Discharges Produced by Polarity-Reversed Voltage Pulses

Abstract: SUMMARY This paper presents an experimental study of control of the germination of Arabidopsis seed with a barrier discharge produced by polarity-reversed voltage pulses. 100 ns-width polarity-reversed pulses were applied to the seeds between plane electrodes covered by glass barriers. The electrode configuration allowed barrier discharge propagation along the seed surface at a relatively low voltage. After the discharge treatment, the seeds were incubated for 2 or 3 days to measure the germination rate. The relationships between the cumulative input energy density into the plasma and the germination rate were investigated. The germination rate was significantly reduced at 20 J/cm3. However, it increased at cumulative energy densities up to 50 J/cm3 and then decreased again on further energy input. These results suggest a superposition of two effects, stimulation and inhibition, of the discharge treatment on the germination of Arabidopsis seed. The results of Evans Blue dyeing of the discharge-exposed seeds indicate that necrosis of the seed coat is caused by the discharge treatment.

Internal Defect Position Evaluation of Ground Coil by Detecting Electromagnetic Waves from Partial Discharge

Abstract: As a huge number of ground coils will be used outdoors for a long time in the superconducting magnetically levitated transportation (Maglev) system, a reduction in ground coil cost with high reliability will be required. Especially the propulsion coil needs the high insulation stability as the high-voltage equipment. On the other hand, as it is assumable that the ground coil has the resin molded winding coil with coreless construction, the ground coil must be exposed to the severe environment where it receives electromagnetic force directly. Therefore, there is a possibility that minute defects that are latent in the mold construction of the ground coil may expand, become apparent and cause of deterioration of the insulation stability. In this paper, we examined the insulation diagnostic measures to assess the existence/nonexistence of the inside defect and locate the defect position by setting a simulated defect artificially inside the mold construction of the ground coil and detecting the electromagnetic waves effectively that are generated from the discharge at the defect point.

DC Dielectric Breakdown Characteristic of Mesoporous-Alumina/Epoxy Composite

Abstract: This paper presents an attempt to derive the dc dielectric breakdown characteristics of polymer composite filled with the metal oxide particle which has mesoporous structure. Mesoporous-alumina/epoxy composite was fabricated by compounding epoxy resin and mesoporous-alumina particles which had the micrometric particle-diameter and the nanometric pore-size. Measurement of the specific gravity of mesoporous-alumina/epoxy composites indicated that the porosity of mesoporous-alumina particle in the epoxy matrix was higher than that of nonporous-alumina particle. From the breakdown test with using McKeown electrode, DC breakdown strength of mesoporous-alumina/epoxy composites was obtained, which was compared with DC breakdown strength of the nonporous-alumina/epoxy composites. These results suggested that the nanometric pore with wormhole structure inside mesoporous particle could not be critical defect for DC dielectric breakdown characteristics in low filler concentration.

Development of a One Dimensional Fluxgate Array and its Application to Magnetocardiogram Measurements

Abstract: SUMMARY We have designed an excitation part of the driving circuit of the fundamental mode orthogonal fluxgate (FG) to avoid an interference problem between fluxgates that may occur when individually operating fluxgates are placed closely. In this new design, three sensor heads are driven by a common excitation current while their outputs are processed separately to yield their own outputs. With magnetometers of this design, we have built a 6-channel FG array of a linear arrangement with the spacing of 3 cm, as a step to a 6 × 6 fluxgate array. The excitation frequency was shared by two excitation circuits, each of which provides a set of three sensor heads with the excitation current. A magnetocardiogram (MCG) was measured with the 6-channel FG array by repeatedly sliding the top plate of a bed carrying a healthy volunteer by 3 cm. The distribution of the QRS complex observed on a 5 × 6 of array measurement points resembles with that observed by a SQUID MCG measurement system.