In recent years, a problem of interfering by artificial noises from a electrical power transfer become large and deterioration of a sound quality of an AM radio is worried. In this paper, a noise suppression system using quadrature demodulation techniques is proposed to reduce the effect of the interfering. The proposed system utilizes a fact that the quadrature signal includes only the interference, while the in-phase signal from the demodulator includes both of AM signal and interference. To cancel the noise component in the in-phase signal, the noise component in the quadrature signal is adjusted by a tapped delay line because the sign of the both interference is different each other. Weight coefficients of the tapped delay line are determined based on power inversion (PI) algorithm. Thus, the interference in the in-phase signal can be canceled by the quadrature signal. Validity of the proposed system is shown through computer simulations.

View full abstract

A transition duration at the steady arc occurrence and termination caused by interrupting a current is measured. In consideration of the fast transients and high frequency discharge phenomena due to interrupting the current, a transmission line system was introduced. It consists of a coaxial switch, coaxial cables as transmission lines on the right and left sides of the switch, and termination resistors. The material of the inner conductor of the coaxial switch for interruption of the current is silver and copper. The resistors were designed to match the characteristic impedance of the cables. A semi-rigid cable as a coaxial cable and a coaxial attenuator (DC∼8.5GHz) as the termination resistor were used on the right side of the switch for measurement of transition duration. When the current is interrupted by the switch, the transient waveform of output of the attenuator is measured by an oscilloscope (DC∼4.5GHz). Regardless of the materials of the center conductor of the switch, the transition duration at the arc occurrence and termination caused by interrupting low current (0.5-1.0A) is 0.2∼0.4 ns and 1.28∼2.08 ns, respectively, and does not depend on the material of the inner conductor of the switch and current value. The transition duration at the arc occurrence is very rapid.

View full abstract

In electrostatic discharge (ESD) immunity tests specified by the international electrotechnical commission (IEC), it has been learned empirically that a contact discharge test sometimes provides a severe test result even under the same test level. This is said to be due to the existence of small air gaps between an ESD generator and equipment under test. To clarify the phenomena, we previously measured discharge currents through small air gaps from 30 µm to 1000 µm in contact discharges of an ESD generator to an IEC current calibration target, which revealed that multiple current peaks appear depending on the gap length and test voltage as well. It was also demonstrated that the contact discharge current with a small gap provides a faster rise time and larger current peak in comparison with normal contact discharge tests even at the same test voltage. In this study, to explain these findings quantitatively, we proposed a simplified circuit model combined with a spark-resistance formula which allows one to analyze the discharge currents through the above-mentioned air gaps in 8 kV contact discharge tests. As a result, we found that the calculated waveforms in contact discharges with/without a gap fairly agree with the measured results. It was also found that the proposed circuit provides roughly the same dependence of current peaks on a gap length as the measured results.

View full abstract

The intensity of unintended electromagnetic radiation caused by connector contact failure mainly depends on the increased inductance at the contact failure portion. Self-inductance caused from increased current path at the contact boundary surface has been considered the factor of increased inductance. However, investigation of mutual inductance due to the interaction among contact points is insufficient. In this paper, by using contact failure model, calculated current path length and increased inductance including mutual inductance are compared. The result shows that the more current path lengthens, the more mutual inductance increases. Mutual inductance should be considered when estimating contact failure.

View full abstract

In the electrostatic discharge (ESD) immunity testing specified by the IEC 61000-4-2, an ESD generator simulating a human ESD is normally used for contact discharges, while air discharge testing is also being accepted despite the fact that the testing is likely to provide inconsistent test results from the poor reproducibility of discharge current waveforms. To confirm to what extent air discharges affect the discharge currents with respect to charge voltages and approach speeds, we measured the discharge currents through a hand-held metal piece with fast and slow approaches from a male subject charged from 1000 V to 8000 V, which were calculated from two equivalent circuits. An equivalent circuit with an ideal switch in view of a spark was used to show the limit waveform of the discharge current through the inverse Fourier transform from the measured human impedance. The other equivalent circuit consisting of a time varying spark resistance and lumped circuit parameters derived from the human body impedance was used to estimate the discharge current based on a spark resistance formula. As a result, we found that the first equivalent circuit provides the maximum current peak and minimum rise time of discharge currents regardless of the charge voltages or approach speeds, while under an appropriate spark length according to the charge voltage the second equivalent circuit gives the discharge current waveform that approximately coincides with the measured result.

View full abstract

The ESD robustness of the electric device becomes weak year by year because of the high frequency operation. For that reason, the development of a countermeasure technology is necessary. Especially, the countermeasure technology in the system level is important for the next generation electric devices. In this paper, the discharge current and the radiated electromagnetic wave caused by ESD from ESD countermeasure materials which are conductive composite resin with a carbon fiber, a carbon nano fiber and a carbon nano tube were investigated.

View full abstract

Cryptographic circuits were analyzed regarding their side-channel information leaking behavior based on internal current source. Cryptographic circuits were implemented in an FPGA with registers arranged to demonstrate three known side-channel information leaking behaviors; (1) leakage is reduced by making Hamming distance (HD) at registers constant, (2) leakage increases with signal-to-noise ratio of side-channel traces, and (3) unbalance of routing path from registers to load circuits produces leakage. The implemented circuits were measured in terms of voltage fluctuation in the power distribution network for FPGA core circuit where the circuits were implemented. The measured voltage fluctuations were converted into internal current sources that were exploited to analyze the information leaking behavior by applying a side-channel analysis, correlation power analysis (CPA). The analysis confirmed that internal current source clearly demonstrated the side-channel information leaking behaviors. This results suggests that internal current source would allow to understand what parts of encryption circuits largely contribute to leak information and how to develop an efficient and low-cost countermeasure against side-channel attacks.

View full abstract

Our previously developed velocimeter based on laser Doppler effects was used to measure spark lengths by moving a grounded metal-plate to an electrostatic discharge generator with charge voltages from 1000 V to 8000 V at three different approach speeds of 20 mm/s, 100 mm/s and 200 mm/s. Results show that with increasing the approach speed, spark time lags exponentially decrease, while the resultant reduction rates of spark lengths logarithmically increase. An empirical formula of spark length was also derived from the reduction rates of spark lengths.

View full abstract

Impulsive electromagnetic noise is caused by ESD. Especially, micro gap discharge of less than 1kV produces GHz band width electromagnetic noise. It is thought ESD noise has possibility that affects to various electrical systems. Then, we investigated whether the approach speed of spherical electrodes has an influence on the amplitude of electromagnetic radiation. As the result, we concluded that the approach speed of spherical electrode was one of the parameters which decide the size of the electromagnetic radiation from this experiment. Moreover, we considered that the amplitude change with the approach speed becomes logarithm.

View full abstract

We previously developed a measurement system of spark length in air discharges of electrostatic generator (ESD gun) using laser Doppler effects. The spark length can be obtained through time integration of the velocity data from spark occurrence time to collision time when moving the grounded plate to the ESD gun, while the measurement accuracy has not yet been validated. In this study, we compared the measured spark lengths using two methods that identify the collision time by detecting field emission and by detecting discharge of gun remaining charges, respectively.

View full abstract

The electric field strength in streamer discharges in dry air at atmospheric pressure was measured using the intensity ratio of spectral bands of molecular nitrogen. The streamer discharges were produced in the needle-plane electrode by applying the positive impulse voltage. It was shown that the reduced electric field strength of the primary streamer was ∼700 Td. It was clarified that the propagation velocity of the streamer was increased with increasing the applied voltage on the electrode, but the reduced electric field strength slightly decreased. The spatial distribution of the reduced electric field strength in the gap was discussed in terms of the secondary streamer near the needle electrode and the photoemission from the plane electrode.

View full abstract

In power modules, silicone gel is widely used for encapsulation. It is well known that partial discharges (PDs) such as surface discharge at the gel-substrate interface give rise to growth of cavities in gel. This paper reveals the relationship between the deformation behavior of cavity and PRPD (Phase-Resolved-Partial-Discharge) pattern in silicone gel. It turns out that a single trunk of tree tends to emit light with occurrence of single positive partial discharge pulse, while multiple trunks emit light with negative PD pulse. The results also show that PDs which have relatively large magnitude expand or shrink voids at the cavity tip.

View full abstract

Space charge accumulation in insulating material under a high electric field is said that it is closely related to the breakdown of the insulating material. Since a thin insulating film is used as a flexible printed circuit board, such high stress might be generated in the film. Therefore, it is required to measure the space charge distributions accumulated in such thinner insulating layers to evaluate the characteristics them. We tried to improve the positional resolution of the PEA system to measure the space charge distributions in such thin insulating films. It is found that the improvement enables us to measure the space charge distribution with a positional resolution of about 2.5µm.

View full abstract