Preparations for a special issue, trends in research and development in 2003, have been initiated at committee level of the Fundamentals and Material Society (FMS). Each technical committee summarized the latest topics and future technical trends. FMS covers a number of technical fields, but particularly those related to electrical engineering applications, such as electric power and energy, electronics, information and education. It is clear that great advances in research and technology are being made in each of these fields. At the same time, there are several seeds that could potentially develop into new technologies having fundamental industrial applications. It is expected that this special issue will assist member's activities as they undertake future research and development. Finally, we would like to express our thanks to each technical committee and also to Prof. Yasuhiro Tanaka (secretary of Editing Planning Committee of FMS) for their planning around this issue.

View full abstract

A virtual cathode oscillator with a stainless-steel mesh anode of various transparencies and wire diameters was studied experimentally for improvement of microwave power and its repetitive operations. The maximum microwave power was observed to be about 20 MW at 12 GHz for the diode voltage of 250 kV and the electron beam current of 39 kA using the anode mesh with the wire diameter of 0.22 mm and the transparency of 67 %. The microwave emission enhanced with decreasing the wire diameter as the mean beam scattering angle decreased with the smaller wire diameter. Also the increased transparency of fine mesh caused an enhancement of microwave emission. Use of mesh anode allowed us a few repetitive operations.

View full abstract

A new method of repetitive operation of a virtual cathode oscillator was performed using a carbon plate anode with a hole in the center, a knife-edged annular cathode and an external axial magnetic field. Repetitive microwave radiations more than 450 were observed. Almost all microwave frequency of each operation was contained in 11.8 to 12.8 GHz, while the microwave emission was varied widely. The maximum microwave peak power and pulse duration were 14 MW and 16 ns, respectively, for the diode voltage of 460 kV, the electron beam current of 12.8 kA at the upstream. The dominant radiation pattern of microwave was found to be TE₀₁ mode.

View full abstract

A multi-channel system Optical Frequency Domain Reflectometry(OFDR) based on serrodyne modulation has been developed. OFDR that uses a stepped optical-frequency sweep utilizes heterodyne interference, so the developed system uses serrodyne modulation produced by vibration of an optical path with a saw-tooth waveform. The degree of serrodyne phase modulation is expressed in terms of the serrodyne coefficient K(br)-derived from the ratio (br) of the beat frequency to the serrodyne frequency. It is shown that even if the amount of serrodyne phase modulation is not 2π, there is no effect on the spectral distribution (which expresses the optical reflection position), but there is on spectral level. The effect on the spectral level can then be compensated according to the serrodyne coefficient. This paper describes the effect of this frequency ratio on position finding as well as the reflective position measurement (performed by multi-channel digital-signal-processing equipment) corresponding to each polarization direction.

View full abstract

A feasibility study has been conducted to determine whether Hollow Cathode Arc (HCA) can be used for a welding heat source in space. The HCA method enables an arc discharge to ignite and maintain under low pressure conditions, where it is extremely difficult for the conventional Gas Tungsten Arc (GTA) method to form an arc discharge. In the previous paper, it has been demonstrated that the melting process by HCA under the condition that the gas flow rate is high (1.7ml/s) is significantly dominated by the diffuse anode and is characterized by shallow penetration, and that the electron temperature is about 1200018000K in arc space. In the present paper, the volt-ampere characteristics and the plasma property of HCA under the condition that the gas flow rate is low (0.17ml/s) have been made clear, and the melting phenomenon have been discussed. The results are summarized as follows, (1) The HCA under the condition that the gas flow rate is low is characterized by high voltage and high electron temperature, and the arc column is concentrated under the cathode.(2) The electron temperature is above 60000K near the arc axis.(3) The electrons with high temperature, that is high energy, contribute to the deep/huge penetration under the condition that the gas flowrate is low.

View full abstract

New control method of a pulsed volume discharge in CO₂ laser gas of 13.3 kPa pressure is studied using a pair of hollow electrodes that acts as a plasma cathode.The pulsed operation of the hollow cathode plasma of 0.75 mm² ×0.7 mm in volume initiates a stable volume discharge of 0.75 mm² ×100 mm in volume.The hollow plasma-cathode improves the stability of volume discharge, so that the repetitive and long pulsed operation is possible up to 1 kHz and 100 µsec, respectively.The current owing path through the hollow and the volume discharge changes according to the current values of the both discharges.The measured small signal gain with 10 cm discharge shows the apparent ampli cation of a CO₂ laser beam.

View full abstract

A glow-to-arc transition of rarefied plasma that controls the ultimate performance of a vacuum interrupter depends on the state of remaining plasma in the contact gap after current zero. In this study, the electron temperature and the ion density of residual plasma of a magnetically stabilized high-current vacuum arc were measured by the electrostatic (Langumuir) probe method. As a result of measurements, electron temperature was of the order of 3eV with a uniform space distribution and was independent of the arc current. The space distribution of the ion density was diffusion-controlled mode, contrary to the confined mode in the steady state condition. The ion density was independent of peak arc current and increased linearly with current zero gradients. The density of the copper ions decayed with a time constant of about 2 µs.

View full abstract

This paper clarifies an important fact that the time parameters evaluated from the mean curve obtained after applying moving average are identical to the ones deduced from the original lightning impulse voltage. Digital recording device is always associated with random thermal noise caused by semi-conductor components used in the pre-amplifier in the recorder. The fact makes it possible for us to get rid of random noise superposed on the measured impulse wave form by means of moving average method. Also using the finding, even jittery noisy records can be averaged to a smooth curve from which one can easily distil identical time parameters.

View full abstract

Space charge accumulation for various glass materials under DC stress was studied by using a pulse electro-acoustic (PEA) method. We should make an acoustic matching between the sample and electrode of high voltage side when the hetero-space charge distribution in glass materials is measured. Because the acoustic pressure waves generated from the induced charge at high voltage side is cancelled by the reflected one generated from hetero-charge in accumulated in sample. The big hetero-charge are observed in the glass materials contained MgO and CaO compound to compare to the quartz glass contained no-compound.

View full abstract

The laser induced pressure pulse (LIPP) method has the advantage of higher resolution in the depth direction than other methods. However, in this method, it is demerits that induction noise in laser system is large and measurement signal is low reliability. Therefore, we have developed a new LIPP measurement system using pulse laser of low-density energy, shield technique and deconvolution processing. This system can observe the space charge profile with high reliability. Furthermore, we introduce the new LIPP system, which has sub-micron resolution of 0.6 microns.

View full abstract

This paper addresses the critical exponent of dielectric breakdown strength of composites made with carbon black and polyethylene below the percolation threshold for the first time. At first place, the percolation threshold p_c is determined based on the critical exponents of resistivity and relative permittivity of the composites. Dielectric breakdown strength E_B of the composites below p_c is measured by using an impulse voltage in the range of 10 kV to 40 kV in order to avoid the effect of joule heating. Although the observed data of E_B seem to be well fitted to the straight line with the slope of 0.9 on a double logarithm of (p_c -p) and E_B, a method of least squares gives the slopes of 0.72 ± 0.12 and 0.96 ± 0.05 for the composites made with BP2000 and Asahi-Thermal, respectively. It has been found that finite carbon black clusters play an important role in the dielectric breakdown of the composites.

View full abstract

The effect of sulfur on the magnetic properties of non-oriented electrical steel sheets was studied. In an ultra low sulfur steel with annealing temperatures ranging from 850°C to 975°C, hysteresis loss is lower than that of a high sulfur steel. However, the hysteresis loss in the ultra low S steel increases with an increase in the final annealing temperature ranging from 975°C to 1050°C. This phenomenon is associated with the precipitation of AlN near the surface of the steel. The nitride forming reaction is accelerated with a decrease in S content. In the ultra low S non-oriented electrical steel sheets, the low core loss was obtained by the reduction of the surface nitriding and the high magnetic flux density was obtained by a reduction of Si and Al content. This steel shows; 1)low hysteresis loss, 2)high magnetic flux density, 3)excellent punching properties and 4)low production cost.

View full abstract