With the widespread use of wearable terminals, machine to machine (M2M) and internet of things (IoT) equipment, electrostatic discharge (ESD: Electrostatic Discharge) due to electrification of humans and objects can cause electromagnetic interference (EMI) inside these devices, which is called intra-EMC (Electromagnetic compatibility). This type of the EMI issue would be often derived from a steep transient electric near field generated by less than 1 kV spark discharges between micro-gaps. To clarify the characteristics of such electric near field, therefore, an optical electric field probe, which does not disturb any electromagnetic fields to be measured, has been used to measure the transient electric field caused by a micro-gap spark when charged metal spheres collide, while it is not fully understood whether or not the probe output precisely responds to the transient electric field in the vicinity of the discharge point. In this study, the measured waveforms of the above-mentioned electric field are verified by comparison with the electrostatic field theoretically derived from image charges and the transient electric field calculated from an image dipole charge model combining a spark resistance law. The result reveals that at a distance near the discharge point the optical field probe does not properly work due to the presence of the electrostatic field, whereas the transient electric field at a distance away from more than twice the diameter of metal spheres from the discharge point can be correctly measured because of sufficient attenuation of the electrostatic field component.

In designing motors, the magnetic properties of electrical steel sheets in the actual conditions must be grasped. In particular, the stress dependence of iron loss is important. This paper describes a newly developed apparatus to measure 2-D magnetic properties (properties under the arbitrary alternating and rotating flux conditions) of an electrical steel sheet in applying compressive stress normal to its surface. This apparatus has the flux density sensor with a thin needle probe composed of sputtered copper foils on the electrical steel sheet. The magnetic properties can be measured under the uniform stress condition throughout the evaluation area.

Epoxy resins are widely used as insulating material in electrical apparatus. Recently, X-ray phase imaging has attracted a lot of attention as a method to observe tree shape and propagation. However, observation of trees in filled epoxy is challenging because silica particles absorb X-rays and disturb the acquisition of a clear image of treeing. In this study, image subtraction was applied to overcome this issue and time evolution of treeing was observed. The visibility of electrical trees in a filled sample was evaluated through the noise analysis in spatial frequency domain. Since the noise generated by silica particles was much reduced, electrical trees in epoxy resins with 1.5 µm and 5 µm silica fillers were successfully observed.

Eddy current testing (ECT) system for the spring steel materials that is able to estimate crack shape was developed. Inspection signal of spring steel material is affected by the permeability distribution about its surface. Then the magnetizer that reduce variability of permeability and the pancake probe that grasps regional states of spring steel material were introduced to the system. It was confirmed thereby that this probe is able to detect depth 50 µm crack with a sufficient S/N ratio. Exciting coil that generates two-way direction eddy current was developed and average depth and outline of cross-sectional shape were estimated by its inspection signals. Then the method of estimating crack shape was developed, which has feature that integrates two results by different direction eddy current. In addition, the validity of the method was confirmed by evaluating relationship between crack shapes and calculated inspection results with finite element method (FEM) analysis.

Sintered Fe nanopaste with Fe nano-polycrystalline has ferromagnetism. Sintered Fe nanopaste with Fe nano-polycrystalline will be applicable to magnetic materials, especially to core inductors. Magnetization curve of the reduced Fe nanoparticles and the sintered Fe nano-polycrystalline were measured. Next, we researched the resistance of sintered Fe nanopaste when a power source with a high frequency was connected. It has been clarified that the resistivity of Fe nano-polycrystalline decreased by cancelling the skin effect due to the negative permittivity of Fe particles. In addition, a singular radical vanishing of the resistivity of the Fe nano-polycrystalline and negative resistance at low current around the high magnetic resonance frequencies were observed. These properties occur only in metal nano-polycrystalline. The measured resistivities were also compared with the calculated ones evaluated by a theoretical analysis. The calculation method includes magnetic field, electric field, and negative permittivity of the Fe particles in the Fe nano-polycrystalline. They have good consistence with the experimental ones.

Breakdown factors of XLPE cables are studied, using model cables and block XLPE samples. The influences of defects and peroxide decomposition products on breakdown strength and tree inception stress are evaluated. The breakdown strength of XLPE cables is greatly affected by the existence of defects. In addition, AC breakdown strength is increased by the effect of peroxide decomposition products, especially in cases where the size of the defects is small. The effect is caused by the concentration of decomposition products around defects due to dielectrophoresis, because decomposition products have high permittivity and low resistivity. Stress relaxation and an apparent increase of tip radius occurs. These effects are weakened at high temperature.

In this paper, seven kinds of lead acid batteries were assembled using Pb plates as imitated negative electrodes, and electrolyte resistances and charge transfer resistances in cases with and without additive agents were measured by AC impedance in the frequency range of 10 mHz - 20 kHz. Cyclic voltammetry (CV) was used to measure electrochemical reactions in 500 cycles, and the surface condition and element mapping of the Pb electrodes after the 500-cycle test were observed using field emission scanning electron microscope (FE-SEM) and energy dispersive X-ray spectroscopy (EDX). From the results, it was clarified that two types of additive agents showed high electro-conductivities and low quantities of sulfur and oxygen deposition on the surface of the Pb electrodes.