The in-plane spatial resolution of time domain terahertz imaging using broadband pulsed terahertz waves (0.1-1.6THz) was evaluated using the edge of a metal plate. The spatial resolution of 0.8mm could be improved to 0.4mm by limiting the frequency region of the broadband terahertz wave to 1.0-1.5THz. Experiments using a resolution target showed that the method is effective for improving the spatial resolution and the constrast ratio.

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In this study, ion-migration (IM) endurance of the electroless plating to the electrodes was evaluated by the water drop test (WDT) method. The characteristics of the top layer metal affected the durability of IM when different types of metals were laminated in the plating process. After WDT, dendrites were found on the printed wiring board (PWB) with the electroless plating of Ag, but they were absent with electroless plating of Au, Pd or Ni of the top layer of an electrode. From the result, it is clear that the plating process of Au, Pd and Ni at the top layer of an electrode can improve the IM endurance. Moreover, the risk of metal elution increases with the electrical field concentration at electrode edge. Therefore, even if the surface of electrode was covered with excellent IM endurance metal, the IM endurance may decrease greatly if inferior IM tolerance metal was slightly exposed at the electrode edge.

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The well-developed thundercloud causes local downpours and tornadoes accompanied with lightning discharges. The remote sensing for lightning discharges from space is useful for the short-term forecast of weather disasters over vast areas, the understanding of global electrical circuit, and so forth. The broadband digital interferometer (DITF) has been already used to study on the lightning activities as ground-based equipment. The DITF makes it possible to visualize lightning channels by VHF radio observations. The goal of the study, in future, is to realize the space borne DITF and to monitor the thunderstorm activities constantly. In 2012, global lightning and sprite measurements (GLIMS) mission is started its observations on exposed facility of Japanese experiment module (JEM-EF) of the international space station (ISS). The very high frequency (VHF) broadband digital interferometer (VITF) attached on JEM-EF is designed to estimate the direction of arrival with about 10 km resolution. This paper discusses the propagation characteristics through the ionosphere of the VHF radio waves with Lightning Discharges. The numerical simulation based on the ray-tracing method in consideration of the electron density in the ionosphere is performed. The electron density in the nighttime ionosphere has an insignificant effect on the propagation path of the VHF waves, while the electron density in the daytime ionosphere causes the distance error between the radiation source and the estimated radiation source using the VITF is greater than several tens of kilometers when the incident angle for the VITF antenna is greater than 60 degrees.

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Electron acceleration in magnetic reconnection event has been experimentally investigated using the plasma merging technique in the University of Tokyo Spherical Tokamak (UTST) device. Intense emission of He II line (468.58nm) was observed only in the vicinity of the X-point by using a multi-channel spectroscopic measurement system. This localized emission indicates the generation of energetic electrons inside the current sheet region, possibly due to the electron acceleration by the strong toroidal electric field induced by magnetic reconnection in the presence of a guide field.

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Recently, a method for estimating permittivity distributions was reported. The method combined a numerical technique (Finite Element Method) with Genetic Algorithm (GA). However, methods for estimating the distribution of permittivity have not yet been established. The purpose of this study is to obtain experimental data in order to improve the estimation method. We measured capacitance and electrical potential of plural points when an acrylic rod is placed in various positions within a measurement system.

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The educational program by learn-by-doing engineering has been conducted by the grand in aid of MEXT of Japan. The skills and educational factors lie in the practical R&D driven in the company researches. We have attempted to adopt the before-graduation students to the research collaborations among the company engineers.

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This paper described PD phenomena in SF₆ gas with the spatial-resolved spectroscopic measurement system. The results allow us to understand where and how PDs were generated and propagated near the tip of the needle electrode and also how difference the PD light emission properties were, among the test gases. We also discussed effects of N₂ addition to SF₆ gas on the PD phenomena to improve the detection of light emission information.

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Inactivation mechanism was investigated using biological method in an atmospheric pressure plasma jet with a plane-to-plane DBD structure. This plasma jet, fed by helium/oxygen gas, was operated by a sub-microsecond pulsed voltage with a repetition rate of 1-10kHz range. The electrical property of the discharge was studied by means of a classical DBD model. The optical property was analyzed by spectroscopy. Escherichia coli K-12 strains, MG1655, BW25113 and CSH26 with their mutants, totally 8 kinds of bacteria, were employed to separate various bactericidal plasma agents. Results showed that oxidative stress and charged species are playing the most significant roles in inactivation process, which was also verified by the indirect inactivation experiments with mesh insertion. Rather than the superoxide O₂^-, neutral reactive oxygen species like O₃ and metastable state O₂^* were identified as dominant sources for oxidative stress.

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This study details the effects of a streamer-like discharge under water on undesired micro-organisms in water such as algae. Algae are water organisms classified separately from plants. They are known to cause hazards to humans and the environment. Many face difficulties with the removal of algae. The present investigation shows algae treatment effects by pulse power discharges in water. Algae were treated by high voltage pulsed discharges using a copper pin electrode. Plasma discharge effects such as shock wave, hydroxyl radical, electric field and ultraviolet light on algae were investigated. The efficacy of the electric discharge phenomena in the inactivation of algae in water is shown.

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Application of polymeric materials for electric power apparatus is spreading worldwide. However, the aged deterioration is anxious because of dry band arc discharges generated on the surface of the polymer materials. In this paper, we carried out composite pollution tests and measured the discharge ignition time of silicone rubber. The results showed that there was no large difference in the discharge ignition times obtained between ac and dc voltage applications. Additionally, it was shown that the difference of the discharge ignition was influenced by hygroscopic property of the pollution material.

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Effect of discharge inside bubble in water on growth rate of a vegetable was investigated experimentally for application on vegetable cultivation system. Brassica rapa var. perviridis was used as a specimen and was cultivated in pots filled with artificial soil. The water was circulated from a water pool to the cultivation pots. The discharge was produced out of the water in the pool during 30 minutes by one day. The growth rate of the Brassica rapa var. perviridis was improved drastically with discharge inside bubble in water. The growth rate increased with increasing duration of the Brassica rapa var. perviridis and was also improved by adding HNO₃ ions into the circulation water. An inactivation of bacteria in the water was also confirmed with discharge inside bubble in water.

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In this study, we conducted a detailed investigation of iron loss distribution using a thermographic camera system. Such measurements are important because the stator in an electric motor consists of electrical steel sheets and reducing their iron loss is an important factor in efficiency. Because iron loss is ultimately converted into heat, it can be estimated by measuring the amount of heat generated. However, there was no study yet investigating accuracy of iron loss measurements using thermography. We examined the errors of iron loss measurements using thermographic system and confirmed effectiveness of this approach through experiments.

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Epoxy that used as insulating material in electronic and electrical devices plays an important role in system reliability. Addition of nanoparticles can improve the insulating properties of epoxy compared with undoped material. However, due to the change of the material structure, trap characteristics and charge behaviors are altered as a consequence. This possibly leads to the distortion of electric field that initiates discharge which results in the degradation of the insulation. From the viewpoint of safety, it is necessary to investigate the charge behavior of epoxy nanocomposites. This paper presents study aimed at clarifying the effect of nano-filler concentration on the surface charge accumulation and the decay behaviors of epoxy/Al₂O₃ nanocomposites. Samples were prepared by dispersing nano-scale Al₂O₃ into epoxy. Corona charging tests were performed at room temperature with a relative humidity of less than 40%. The charge distribution was measured by means of an electrostatic voltmeter. Obtained results show the dependence of the charge density as well as the charge decay rate upon the concentration of Al₂O₃, varying as a function of the charge polarity, charging time and charging voltage. It is suggested that the charge dynamics is dependent upon the characteristics of localized surface states that are altered by the nanoparticles.

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Embryonic chick assay was introduced as a biological method for an experiment to apply a nanosecond pulse electric field on a tumor. Embryonic chick assay allowed many in vivo tests. Pulsed electric fields were applied on a solid tumor of the mouse breast adenocarcinoma cell, EMT6/KU, which was formed on the chorioallantoic membrane. We found that average weight of solid tumors applied pulsed electric fields was significantly smaller than that of controls.

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