A new-type microwave plasma source has been developed for materials processing. The plasma reactor employed a launcher of azimuthally symmetric surface waves at a frequency of 2.45 GHz and also magnetic multicusp fields around the reactor chamber walls. This configuration yielded high-density (Ne_??_1011cm-3) plasmas sustained by surface waves even at low gas pressures below 10m Torr, following easy plasma ignition by electron cyclotron resonance (ECR) discharges. Electrical and optical diagnostics were made to obtain the plasma properties in Ar. It was shown that a transition from ECR excited to surface-wave excited plasmas occurs under conditions where the plasma electron density exceeds a critical value of Ne-1×10"cm-3.

View full abstract

Using epoxy resin with the various quantities and diameters of alumina, dielectric breakdown characteristics from room temperature to 180°C were studied. Moreover, the relationship between changing temperature of breakdown voltage and thermal deformation temperature which was measured by a apparatus for thermomechanical analysis was investigated.
The results are as follows:
(1) Dielectric breakdown voltage of epoxy resin filled alumina with 40 filler parts is higher than that with 5 and 100 filter parts at any temperature.
(2) When heating the epoxy resin filled filler parts, dielectric breakdown voltage begins to decrease from the glass transition temperature, and as the filler parts increase the temperature that begins to decrease shifts to higher one.
(3) The heat transformation temperature becomes high with increasing in filler parts.

View full abstract

This paper describes a new method for estimating nanometer order density distribution of polyethylene with an energy-filtering transmission electron microscope. Mass thickness distribution can be measured by a zeroloss electron micrograph and an unfiltered electron micrograph or other combinations of electron micrographs with different energy loss electron. Density distribution can be estimated through mass thickness distribution and geometrical thickness distribution. This paper proposes a method to estimate the geometrical thickness distribution using known lamellar crystalline density of polyethylene and finally estimates nanometer order density distribution. Experimental result shows the estimated density distribution seems to be reasonable in terms of average density.

View full abstract

The amorphous melt-spun ribbons of Nd-Fe-Co-Cu-Nb-B system alloys were prepared by single roller rapid-quenching method. The effects of composition, wheel velocity and heat-treatment on the magnetic properties were investigated. The amorphous Nd9Fe75.5Co8Cu0.5Nb1B6 ribbon prepared at a wheel velocity of 15.0m/s were crystallized by heat-treatment, and the optimum heat-treatment condition was found to be at 700°C for 5min, then the value of (BH)max was 114.8kJ/m3. The temperature coefficients of Jγ and HCJ for the ribbons crystallized from the amorphous Nd9Fe75.5Co8Cu0.5Nb1B6 alloy were α(Jγ)=-0.064%/°C (reversible) and β(HCJ)=-0.426%/°C (irreversible), respectively. The value of (BH)max for the compression molding Nd9Fe75.5Co8Cu0.5Nb1B6 isotropic bonded magnet prepared by using the ribbons annealed at 700°C for 5 min is 78.66kJ/m3 and the density is 6.23Mg/m3

View full abstract

After the discovery of ceramic superconductors, research works for realizing high temperature superconducting devices have been advanced, where liquid nitrogen has high possibility to be used as a part of electrical insulation as well as the refrigerant. It is -very important from a point of superconducting device protection to elucidate surface breakdown characteristics along the spacer in gaseous condition.
We measured breakdown voltage of gaseous nitrogen under various condition along the cylindrical small gap spacer sandwiched by parallel plane electrodes. When the spacer has good contact with electrodes, flashover seldom occurred along the spacer surface. In this case, flashover voltage follows Paschen's law and depends only on the product of gas density and gap distance, even though there existed the spacer between electrodes However, when the contact between the spacer and the electrodes is perturbed by a small gap, the flashover voltage decreases and depends on the small gap area directly connected to the spacer edge rather than the total small gap area.

View full abstract

Enhancements of the localized specific absorption rate (SAR) caused by metal-framed spectacles are analyzed numerically for 1.5GHz hand-held mobile telephones. The finite-difference time-domain (FDTD) method and an anatomically based human head model are employed in the analysis. Enhancements up to 1.2 times for the ten-gram-averaged spatial peak SAR in the head and up to 2.75 times for the onegram-averaged SAR in the eye are found, whereas there is no significant variation on the absorbed power or averaged SAR in the whole head. The mechanism of localized SAR enhancement is clarified to be due to an induced current on the metal frame.

View full abstract

Thermally stimulated current (TSC) of unirradiated and electron beam irradiated polyetheretherketone (PEEK) was investigated. PEEK films were irradiated in air for three kinds of doses: 50, 75MGy and 100MGy. When the biasing voltage Vb is not applied, spontaneous current starts to increase above 180°C, and the temperature at which this current increases rapidly shifts to a higher one with increasing the dose. Next, when Vb is applied at 100°C, 140°C and 180°C, peaks of TSC appear at about 120°C, 160°C and 180°C, respectively, and the peak temperature shifts to a higher one with increasing the dose. On the other hand, in the case of Tb=100°C, the peak value is very small, and hardly changes with increasing the dose. In the case of Tb=140°C, the peak value decreases a little with increasing the dose. However, in the case of Tb=180°C, the peak value shows the maximum at 50MGy, and its tendency is different from the others. From the results, it was considered that the molecular crosslinking in amorphous regions were advanced with increasing the dose, while dipoles and ions were increased by the collapse of molecules.

View full abstract

Dc conduction through dielectric insulating materials has been the subject of intensive theoretical and experimental investigations in the study of dielectric material. It has been reported that the conduction current of multilayer ceramic capacitors at elevated temperature could be correlated to a thermally activated ionic transition process. In this paper, the conduction processes in BaTiO3 based multilayer ceramic capacitors (MLC) at room and elevated temperature were discussed from the dc conduction measurements. It was found that the dc conduction processes were different at these two temperatures.
At the elevated temperature, the conduction current could be caused by a thermally activated ionic transition process described. The hopping distance of dielectric material was calculated to be 60.3A, the carrier mobility of the electrical conduction was computed to be the order of 10-12cm2/V.s. It was estimated that the effective onset voltage of ionic conduction was higher than 6.9×104V.cm-1.
The conduction process at room temperature was also detail discussed. It was found that dc conduction currents in MLC at room temperature were consistent with the values predicted by a theory based on the conventional thermally activated electronic injection process. It was obtained that the Ohmic field of MLC was lower than 55kV/cm. The resistivity of MLC was calculated to be 1.8×10-13Ω.cm when subtracted the Ohmic current from the total measured current. It was estimated that the effective Schottky field was higher than 1.1×105V.cm-1. From these results, it is concluded that electronic conduction based on the Schottky mechanism may dominate the conduction current of MLC at room temperature.
It was presumed that the migration ion density in the bulk of dielectric material which changed with the temperature, was responsible for the different conduction processes.

View full abstract

Study on the correlation between the tracking resistances of outdoor polymer insulating materials and environmental stresses regarding the ambient outdoor conditions has been progressing. In this study, the tracking resistance variation of a cycloaliphatic epoxy resin filled with high concentration of silica powder due to thermal ageing and water absorption is investigated. Experimental works show that the tracking resistance of this epoxy system is considerably decreased by thermal ageing and water absorption. The decrease due to water absorption is found to be an apparent phenomenon because the completely drying treatment makes the tracking resistance recover to the initial. Furthermore, it is found that the multiple effect of thermal ageing and water absorption makes the tracking resistance decrease more considerably than the case that each stress works. In addition, the tracking resistance of the thermally aged epoxy system after water absorption-drying treatment can not recover to the initial one before water absorption. Mechanisms of the tracking resistance variations of this epoxy system resulting from thermal ageing and water absorption are discussed in this paper.

View full abstract

This research is carried out to analyze the treeing degradation phenomena with a needle shape void by a discharge magnitude and a discharge luminous quantity at each phase angle of an applied voltage. Discharge pulses and discharge luminous images are measured by original measurement system for measuring the discharge magnitude and the discharge luminous image according to several phase angle area of the applied voltage. Each phase angle area is named Φ1-Φ20 in order from the negative peak point to the next negative peak point of the applied voltage. The luminous image is digitized to the luminous quantity with a computer after experiment. In this study, we focused on the product of instantaneous value and dv/dt at the applied voltage. The resuks obtalned are as follows. The discharge magnitude and the luminous quantity are the maximum at phase angle areas of Φ7 and Φ17. We deflne an effective instantaneous value that includes a voltage of residual electrical charge. The discharge magnitude closely correlates the effective instantaneous value × dv/dt. It is important to measure the discharge quantities at each phase angle area for analyzing the treeing degradation phenomena.

View full abstract

This paper describes a computer simulation study for estimating the multiple sources in the brain based on a three dimensional measurement of magnetoencephalogram (MEG). An estimation algorithm with search method proposed here is used three components of magnetic field measured by vector gradiometer. In the calculation of estimating multiple sources existing in the brain, magnetic distributions perpendicular to the scalp is not helpful owing to the lack of a dipole pattern. However, the magnetic distribution tangential to the scalp can provide information on constraint conditions for estimation of multiple sources. This method using three components of magnetic field can estimate two and three sources models.

View full abstract

Surface dielectric breakdown phenomenon of printed wiring board needs to be studied from the viewpoint of the reliability and safety of device. It is generally believed that the contribution of environmental parameters is very pronounced in printed wiring board. In this paper, surface dielectric breakdown phenomenon of contaminated printed wiring board was investigated in the range of 10kPa to 100kPa. The study revealed that dielectric breakdown time increases with lowering pressure, and the capacitance between electrodes decrease with lowering pressure. Discharge current characteristics under different pressure, applied voltage and electrode distance conditions were discussed by using power spectral and wavelet analysis of discharge current waveforms. The results show that as the pressure decreases the frequency of discharge current change to low, and discharge energy increases with lowering pressure. As the applied voltage increases the discharge energy increases with electrode distance of 0.20mm, and as the electrode distance increases the discharge energy decreases under 10kPa pressure condition.

View full abstract

The principles of both PIPWP and PEA methods for measuring the space charge distributions in solid dielectrics are comparatively analyzed. The relationship between the charge distribution in a specimen and the current signal of PIPWP method or the voltage signal of PEA method are expressed in the time domain and frequency domain. Furthermore, the calibration method of amount of accumulated charge density, using mathematical deconvolution technique, was described for both methods. To compare the two methods, the charge profiles in the electron irradiated PMMA samples were observed. The results of both methods show the exactly same charge profile signal for charge accumulated test sample with the position resolution of 20μm. Furthermore it is discussed on the electric field distribution and electric potential distribution in the sample which were obtained from the measured charge profiles.

View full abstract

In order to clarify the propagation mechanisms of the laser induced discharge, we measured the electric field due to a leader channel in a long air gap by using an optical electric field sensor based on the Pockels effect. We also calculated the electric field by simulating the leader with a line charge and applying the charge simulation method. The propagation velocity of the leader ranges from 2×105m/s to 1×106m/s for plasma channel produced by a high power carbon dioxide laser. The velocity depends on the number density of the plasmas produced by the laser. The velocity is about 10 times larger for a dense channel with plasmas more than 50per meter than without the plasma channel.

View full abstract

Measurement of electron transmission ratio is carried out experimentally using eccentric electrodes in nitrogen. Electron current is measured with varing applied voltages between the electrodes under constant gas pressures. These curves are compiled in current-V/po plots. Here, V/po is the ratio of the applied voltage between the electrodes to the gas pressure reduced to 273K.
The current-V/po plots are unified as a curve which depends only on V/po. The ratio of these currents to the photoelectron current in the vacuum is defined as the electron transmission ratio in nitrogen. It is found that the electron transmission ratio in nonuniform field is proportional to the electron drift velocity in nitrogen. The electron transmission ratio in uniform field is also proportional to the electron drift velocity as reported by us previously. This fact means that the electrons are transported through nitrogen with an electron energy distribution almost same as that in the uniform field.
In this paper, we report the results of an experiment and the discussions on the transmission process of photoelectron avoiding the back scatterings near the cathode.

View full abstract

Measurements of photoionization current have been carried out in N2/NO mixtures for the first step to make clear the mechanism of photoionization processes of air. For the purpose of the study, a deuterium. discharge lamp with MgF2 window is used for the vacuum ultraviolet source. CaF2, BaF2 and quartz filters are prepared to change short side wavelengths of the vacuum ultraviolet. The photoionization current produced by the vacuum ultraviolet absorption is detected by eccentric cylinder electrodes in the gas cell. With the wavelength shorter than 134nm, the observed currents are proportional to the partial pressure of NO clearly. Consequently, it is confirmed that the NO is ionized by the vacuum ultraviolet. Furthermore, the photoelectron current emitted from the surface of electrode by the ultraviolet, is observed simultaneously. We also find the decreases of photoelectron current with an increase in the partial pressure of NO. It is proved that the decrease of these currents are caused by the reduction in ultraviolet which can release photoelectrons from the electrode surface. In this case, ultraviolet will be absorbed by NO in the optical path and the gap space.

View full abstract

This paper analyses quantitatively approximation error of RC distributed line by discrete elements. It is to be clarified that with a normal RC ladder approximation, error evaluated in the response time becomes as large as a few per cents even when a RC distributed line is replaced with as many as 50 small discrete RC elements. In the paper, more efficient approximation, which makes the error small enough to be neglected using some ten discrete elements only, is to be introduced. The proposed approximation is applied to the unit step response analysis of the potential divider for the switching impulse voltage and its effectiveness is confirmed in comparison to the measured waveform.

View full abstract