Negative Half Period Research Articles

A Flexible Printed Circuit Board Based Microelectromechanical Field Mill with a Vertical Movement Shutter Driven by an Electrostatic Actuator.

Micromachined electric field mills have received much interest for the measurement of DC fields; however, conventional designs with lateral moving shutters could have shutter lifting in the presence of strong fields, which affects their performance. This paper presents a MEMS electric field mill utilizing a vertical movement shutter to address this issue. The sensor is designed and fabricated based on a flexible PCB substrate and is released using a laser-cutting process. The movement of the shutter is driven by an electrostatic actuator. When the driving signal is a sine wave, the shutter moves in the same direction during both the positive and negative half-periods. This facilitates the application of a lock-in amplifier to synchronize with the signal at twice the frequency of the driving signal. In experimental testing, when the vertical shutter is driven at a resonance of 840 Hz, the highest sensitivity of the sensor is achieved and is measured to be 5.1 V/kVm-1. The sensor also demonstrates a good linearity of 1.1% for measuring DC electric fields in the range of 1.25 kV/m to 25 kV/m.

Current pulses and their influences on ozone production in oxygen-fed dielectric barrier discharge

The aim of this study is to investigate the current pulses and their effects on ozone generation during the process of ozone production in oxygen-fed dielectric barrier discharge. The experimental results show that there are large numbers of current pulses in the positive half-period of the current waveform but no obvious in the negative half-period. Moreover, the number of the current pulses in an AC cycle increases roughly linearly from 200 to 882 when applied voltage increases from 5 kV to 9 kV at 5 kHz. The number of these current pulses is almost independent of frequency. And these substantial current pulses occurring can be attributed to strong partial discharges generated in discharge gap may mainly resulting from the rough dielectric surface. Besides, these current pulses play an important role in the discharge characteristics and they are not in favor of ozone generation. The discharge power within current pulses is 1.47–1.76 times higher than the discharge power without current pulses and the ozone yield within current pulses is much lower than the ozone yield without current pulses. The decrease of ozone yield within current pulses is slightly more remarkable than the one without current pulses, because the discharge power within current pulses enhances more quickly.

Experimental and simulated investigation of microdischarge characteristics in a pin-to-pin dielectric barrier discharge (DBD) reactor

Both experimental and simulated studies of microdischarge (MD) are carried out in a dielectric barrier discharge with a pin-to-pin gap of 3.5 mm, ignited by a sinusoidal voltage with a peak voltage of 10 kV and a driving frequency of 5 kHz. Statistical results have shown that the probability of the single current pulse in the positive half-period (HP) reaches 73.6% under these conditions. Experimental results show that great luminous intensity is concentrated on the dielectric surface and the tip of the metal electrode. A 1D plasma fluid model is implemented by coupling the species continuity equations, electron energy density equations, Poisson equation, and Helmholtz equations to analyze the MD dynamics on the microscale. The simulated results are in good qualitative agreement with the experimental results. The simulated results show that the MD dynamics can be divided into three phases: the Townsend phase, the streamer propagation phase, and the discharge decay phase. During the streamer propagation phase, the electric field and electron density increase with the streamer propagation from the anode to the cathode, and their maximal values reach 625.48 Td and 2.31 × 1019 m−3, as well as 790.13 Td and 3.58 × 1019 m−3 in the positive and negative HP, respectively. Furthermore, a transient glow-like discharge is detected around the anode during the same period of streamer propagation. The formation of transient glow-like discharge is attributed to electrons drifting back to the anode, which is driven by the residual voltage in the air gap.

Influence of Rotor Eccentricity On Electromagnetic Performance of 2-pole/3-slot PM Motors

This paper investigates the influence of static and dynamic rotor eccentricities on electromagnetic performance, including air-gap flux density, back electromotive force (EMF), electromagnetic torque, cogging torque, and unbalanced magnetic force (UMF), of a 2-pole/3-slot permanent magnet (PM) motor considering eccentricity ratio, eccentricity angle, and rotor initial angle. Both finite element analyses and experiments show that in a 2-pole/3-slot PM motor, the static rotor eccentricity leads to unbalanced magnitudes and phase angles of fundamental back-EMFs of three phases but does not change the harmonic contents, while the dynamic rotor eccentricity will not cause unbalance in three phase back-EMFs but affects the harmonic contents of back-EMFs and their phase angles, which causes asymmetric positive and negative half-periods and corresponding even harmonics of phase back-EMF waveform. In addition, both static and dynamic rotor eccentricities have negligible influence on the average torque, but result in large torque ripple, cogging torque, and UMF.

Two-stage digital differential atomic spin precession detection method

We propose and experimentally demonstrate a two-stage digital differential method for atomic spin precession detection. The first differential operation is carried out with a polarimeter module and subsequent digital differential. The second differential operation is achieved by orthogonally modulating the polarization direction of a linearly polarized probe light with a LiNbO3 electro-optic modulation module and by digitally demodulating the difference in the outputs corresponding to the positive and negative half periods of the modulation square-waves. This method is insensitive to the error of modulator and double sensitivity coefficient was obtained. The built detection system with the digital circuit was applied to a spin-exchange relaxation-free magnetometer, and the sensitivity coefficient, sensitivity, and bias instability were tested and compared with two other typical detection methods. The highest sensitivity and minimum bias instability and noise were achieved with the proposed method.

Analysis of Influence of Stator and Rotor Pole Shape on Electromagnetic Performance of Flux Switching Motor With Segmental Rotor

According to the relationship between the stator and rotor structure and magnetic flux density of the traditional flux switching motor with segmental rotor (SFSM), the mathematical model of the SFSM was established. It was found that the height of the stator pole shoe has a great influence on the no-load electromagnetic characteristics of the motor. After the flux barrier was added on the segmental rotor, it can effectively solve the problem that the positive and negative half period of the no-load electromotive force (EMF) waveform of the motor with low pole shoe height. Using the method of finite element (FEM) parametric simulation, the optimal size of the flux barrier was obtained. Compared with the traditional SFSM, the even harmonics in the phase winding EMF waveform were greatly reduced, and the inductance waveform tends to be sinusoidal. Finally, a prototype was made, and the correctness of the new segmental rotor structure was verified by experiments.

Time and space-resolved imaging of an AC air discharge in contact with water

Numerous physical and chemical phenomena are involved in liquid plasmas. These phenomena are highly sensitive to the plasma source and to experimental conditions. In this study, we investigate the temporal dynamics of an AC-sustained plasma produced in air by a discharge between a pin electrode and water. Depending on the gap distance (d), a discharge transition is observed at d = 4.5 mm. At d < 4.5 mm, voltage drop is observed during both positive and negative half-periods (i.e. when water is cathode and anode, respectively). Meanwhile, at d > 4.5 mm, voltage drop is observed only during the negative half-period (i.e. when water is anode). Before transition and when water is cathode, the plasma emission in the gap space consists of two components: a conical-like emission at the water surface and a cylindrical-like emission in the gap. When water is anode, strong emission is observed at the electrode pin, along with a disc-like emission at the water surface. Increasing d beyond 4.5 mm (i.e. after transition) modifies the emission structure at the water surface, forming an inner homogeneous spot at the center of an outer ring. The temporal evolution of the emission in the gap and at the water surface is also discussed, and its relationship with the injected power is assessed.

Remote testing for defects in service high-voltage insalators

On the basis of the two-channel remote measurement method previously developed at the Department of PES KGEU, a set of characteristics of the PD with the simultaneous use of electromagnetic and acoustic sensors, which allows you to remotely measure and evaluate the technical condition of high-voltage insulators (HVI). The article presents the results of developments in the development of the previously proposed method, which allowed to determine not only the type and location of the defect, but also its size and the degree of influence on the working condition of the VI. Particular attention is paid to the evolution of defects under the influence of overvoltage and other electrophysical processes in operating conditions. In particular, the generation of ultra-large PDs that can create erosion of the dielectric surfaces of defects was recently discovered, and the technical condition of highvoltage polymer insulators was examined. All measurements were performed on an experimental bench by non-contact receiving pulse signals of the PD by an electromagnetic tunable receiver in the range of 50-600 MHz. Their indication and computer processing were carried out in order to determine in each of the discrete intervals of the phase voltage the average values of the number and intensity of PD pulses, which either do not exceed the allowable threshold for the occurrence of defects and their development, in comparison with the reference HVI, or exceed it. Based on the results of preliminary bench tests on model specimens and real HVIs under operating conditions, and the obtained set of PD parameters, diagnostic signs were established that made it possible to determine the type, location of the most dangerous defects and the degree of their influence on the HVI working capacity. At the same time, the presence of the most dangerous defects is determined by the expansion of the phase intervals of PD radiation, a sharp increase in PD in negative half-periods of high voltage compared with positive half-periods, and also by a significant difference in the width and shape of single PD pulses.

The Effect of Phase Shift on the Plasma Driven by an AC Voltage and a Pulsed DC Voltage

One of the most important features of atmospheric-pressure nonequilibrium plasmas (APNPs) is its capability of generating high concentration of reactive species while keeping low gas temperature. To generate such plasma, alternative current (ac) voltage and pulsed dc voltage have been used separately. In this paper, the combination of ac voltage and pulsed dc voltage is used to generate APNPs for the first time. The plasma characteristics, including the power deposited to the plasma, the gas temperature, the emission spectra, and the O atom concentration of the plasma for different phase shifts of the two power supplies, are investigated. It is found that when the pulsed dc voltage is added on the negative ac half period at the phase shift of about 90°, the average power deposited to the plasma, the gas temperature, and the optical emission spectrum of O atom all reach their maxima. On the other hand, the ground state O atom concentration has two peaks; one of the peaks also appears when the phase shift is about 90°. When the pulsed dc voltage is applied on the positive half period at the phase shift of 270°, the O concentration reaches another peak and the peak value is higher than that when the ac or the pulsed dc power supply works alone. Furthermore, at the phase shift of 270°, the gas temperature of the plasma and the total power deposited to the plasma are all lower than the case when the ac or the pulsed dc power supply works independently. Thus, it is more energy efficient to adjust the phase shift to 270° for applications such as plasma medicine where the gas temperature of the plasma at or close to room temperature is strictly required.

Statistical behavior of a single microdischarge in atmospheric-pressure air dielectric barrier discharges

This work investigates the statistical behavior including the dimensions and electrical properties of a single microdischarge (MD) generated in a planar atmospheric-pressure air dielectric barrier discharge reactor using a kHz sinusoidal power source with a gap of 1.4 mm. The MD diameters and surface wave (SW) dimensions are captured by an intensified charge-coupled device camera with currents and charge transferred being recorded. The average currents measured in positive and negative half periods (HPs) are 58.9 and 50.5 mA, respectively. The average diameters measured are 256 and 258 μm in positive and negative HPs, respectively. Therefore, the average current densities calculated in positive and negative HPs are 1.14 × 106 and 9.66 × 105 A m−2, respectively. The high current density leads to the high density of surface charge reaching up to 51.5 nC cm−2 in the positive HP at the anode, which is one order of magnitude higher than those observed in filamentary discharges using He/N2 mixtures. The gap dimension is adjusted to 2.0 mm to investigate the effect of the gap dimension on MD properties. Larger MD diameters, currents, SW dimensions, and the charge transferred are measured in the gap of 2.0 mm although the average current densities evaluated in positive and negative HPs are lower than those of gap 1.4 mm as 9.39 × 105 and 8.15 × 105 A m−2, respectively. The average density of surface charge evaluated in the positive HP at the anode of gap 2.0 mm is 51.7 nC cm−2, which is almost identical to that evaluated in the gap of 1.4 mm.

Power Factor Corrector with Bridgeless Flyback Converter for DC Loads Applications

Since power systems with a DC distribution method has many advantages, such as conversion efficiency increase of about 5–10%, cost reducing by about 15–20% and so on, the AC distribution power system will be replaced by a DC distribution one. This paper presents a DC load power system for a DC distribution application. The proposed power system includes two converters: DC/DC converter with battery source and power factor corrector (PFC) with a line source to increase the reliability of the power system when renewable energy or energy storage equipment are adopted. The proposed PFC adopts a bridgeless flyback converter to achieve power factor correction for supplying power to DC loads. When the bridgeless flyback converter is used to achieve PFC, it needs two transformers to process positive and negative half periods, respectively. In order to increase conversion efficiency, the flyback one can add two sets of the active clamp circuit to recover energies stored in leakage inductances of transformers in the converter. Therefore, the proposed bridgeless flyback converter can not only integrate two transformers into a single transformer, but also share a clamp capacitor to achieve energy recovery of leakage inductances and to operate switches with zero-voltage switching (ZVS) at the turn-on transition. With this approach, the proposed converter can increase conversion efficiency and decrease component counts, where it results in a higher conversion efficiency, lower cost, easier design and so on. Finally, a prototype with a universal input voltage source (AC 90–265 V) under output voltage of 48 V and maximum output power of 300 W has been implemented to verify the feasibility of the proposed bridgeless flyback converter. Furthermore, the proposed power system can be operated at different cases among load power PL, output power PDC1 of DC/DC converter and output power PDC2 of the proposed PFC for supplying power to DC loads.

Electric field in Ns pulse and AC electric discharges in a hydrogen diffusion flame

Time-resolved electric field is measured in ns pulse and AC sine wave dielectric barrier discharges sustained in an atmospheric pressure hydrogen diffusion flame, using picosecond second harmonic generation. Individual electric field vector components are isolated by measuring the second harmonic signals with different polarizations. Electric field measurements in a ns pulse discharge are self-calibrating, since the field follows the applied voltage until breakdown. Electric field is measured in a ns pulse discharge sustained both in the hydrogen flow below the flame and in the reaction zone of the flame. Peak electric field in the reaction zone is lower compared to that in the near-room temperature hydrogen flow, due to a significantly lower number density. In hydrogen, most of the energy is coupled to the plasma at the reduced electric field of E/N ≈ 50–100 Td. In both cases, the electric field decreases to near zero after breakdown, due to plasma self-shielding. The time scale for the electric field reduction in the plasma is relatively long, several tens of ns, indicating that it may be controlled by a relatively slow propagation of the ionization wave over the dielectric surfaces. In the AC discharge, the electric field is put on the absolute scale by measuring a Laplacian electric field between two parallel cylinder electrodes. The measurement results demonstrate that a strong electric field in the plasma-enhanced flame is produced during the entire AC voltage period, without correlation with the random micro-discharges detected in the plasma images. The measurement results indicate consistently higher peak electric field during the negative AC half-period, as well as a significant electric field offset. Both the asymmetry and the offset of the electric field are likely responsible for the ion wind resulting in the flame distortion. The results suggest that at the present conditions the ion wind is dominated by the transport of negative ions generated in the ambient air plasma near the flame. The results demonstrate a significant potential of ps second harmonic generation diagnostics for non-intrusive measurements of the electric field in atmospheric pressure flames enhanced by electric discharge plasmas.

Damage effects and mechanism of the silicon NPN monolithic composite transistor induced by high-power microwaves

A two-dimensional model of the silicon NPN monolithic composite transistor is established for the first time by utilizing the semiconductor device simulator, Sentaurus-TCAD. By analyzing the internal distributions of electric field, current density, and temperature of the device, a detailed investigation on the damage process and mechanism induced by high-power microwaves (HPM) is performed. The results indicate that the temperature elevation occurs in the negative half-period and the temperature drop process is in the positive half-period under the HPM injection from the output port. The damage point is located near the edge of the base–emitter junction of T2, while with the input injection it exists between the base and the emitter of T2. Comparing these two kinds of injection, the input injection is more likely to damage the device than the output injection. The dependences of the damage energy threshold and the damage power threshold causing the device failure on the pulse-width are obtained, and the formulas obtained have the same form as the experimental equations, which demonstrates that more power is required to destroy the device if the pulse-width is shorter. Furthermore, the simulation result in this paper has a good coincidence with the experimental result.

Phase-modulated dual-homodyne interferometer without periodic nonlinearity

A novel dual-homodyne interferometer, in which one interferometer acts as the reference interferometer and the other as the measurement one, is proposed to eliminate periodic nonlinearity for nanometer displacement measurement. By using one electro-optic phase modulator to modulate the common reference arm of the two interferometers, the DC interference signals of homodyne interferometers are modulated to AC signals. The measured displacement is carried on the phase difference change of the two AC interference signals. To address the influence of unequal fluctuations of the DC offsets of interference signals on the zero-crossing phase detection, a new phase difference detection method is proposed by counting the sample numbers in positive and negative half periods of interference signals. The merits of this interferometer are not only eliminating the nonlinear errors inherent to heterodyne and homodyne interferometers but also having the abilities of strong anti-interference, insensitivity to laser power drift and the unequal gain of detectors, as well as not demanding quadrature signals. An experiment of nanometer displacement measurement was performed to verify the feasibility of the interferometer, and the results show that sub-nanometer accuracy can be realized without periodic nonlinearity. The large displacement experiment shows that the results obtained with the proposed interferometer are in good accordance with those obtained from a comparison interferometer. These results show that the proposed interferometer can realize large displacement measurement with nanometer accuracy.

Torque Density Improvement of Doubly Salient Electromagnetic Machine With Asymmetric Current Control

Due to the introduction of field winding, the doubly salient electromagnetic (DSEM) machine is featured with good torque production capability. However, this capability is limited by the problems of the phase current reversal and excessive back- electromotive force with traditional control methods. In this paper, a new control method, namely asymmetric current control (ASCC), is proposed to further improve the output torque. Two control angles α and γ are introduced to implement the current-angle control. Simultaneously, the pulse width modulation control is utilized to shape the waveform of phase current. Consequently, the torque is increased drastically because of more effective phase current waveforms, which presents the asymmetry of positive and negative half period. Furthermore, the reluctance torque resulting from the interaction between self-inductance and asymmetric phase current exerts favorable effects on the torque output. By field-circuit-coupled analysis, the ASCC method for a 1.3 kW prototype is analyzed and compared with other traditional control methods. Laboratory testing of the 1.3 kW DSEM machine driven by the new control method confirms the validity of theoretical analysis and simulation improvement of torque. The simulation and experimental results show that the torque and power density can be improved to 1.5 times by the proposed control method.

An atmospheric‐pressure microplasma array produced by using graphite coating electrodes

In this work, a novel non‐thermal atmospheric‐pressure microplasma array (APMPA) has been characterized. The APMPA employs 16 parallel capillaries with an inner diameter of 200 µm and arranged in a square configuration. Our measurements show that the stable plasma plumes can be generated by the APMPA and then spread along the dielectric surface. Both the power in the plasma source region and the one transferred onto the dielectric surface are calculated by plotting Lissajous figures. The power strongly depends on the applied voltage, frequency, and the distance between the nozzles and the dielectric surface. In addition, the temperature of N2 molecules in APMPA plasmas is calculated by using optical emission spectroscopy. The temporally resolved images of the APMPA plasmas show that the total emission intensities for the case of positive half‐period is much higher than that of negative half‐period. In order to describe the performance of the APMPA, the optical emission of the APMPA is compared with a single tube plasma jet with the same configuration and cross section area, and the result illustrates the APMPA can provide a higher density plasma and larger treatment area which may have a beneficial effect on various applications.

Ignition dynamics of dry-etched vertical cavity single-hole microdischarge reactors in ac regime operating in noble gases

Silicon-based multi-cavity microdischarge reactors allow the generation of large-area uniform glow discharges over a wide pressure range up to atmospheric pressure. These devices, fabricated using micro electro-mechanical system technology, have shown complex interactions between the individual cavities. To discriminate these interactions, devices with only one shallow vertical cavity are studied here. Operation characteristics are investigated using electrical and optical analysing techniques. The spatial and temporal dynamics of the discharge are investigated for positive and negative voltage polarity of the applied ac voltage ramp by phase-resolved imaging. Within each voltage half-period, emission from the single cavity shows repetitive pulsing features and distinct spatial distributions. In the positive half-period, ring-shaped structures develop, while the negative half-period is distinguished by a bell-shaped intensity distribution. Effects of pressure and operation frequency on the spatial and temporal intensity profiles are discussed.

Experimentally obtained values of electric field of an atmospheric pressure plasma jet impinging on a dielectric surface

We report on experimentally obtained values of the electric field magnitude on a dielectric surface induced by an impinging atmospheric pressure plasma jet. The plasma plume was striking the dielectric surface at an angle of 45°, at 5 mm from the surface measured at the axis of the jet. The results were obtained using Pockels technique on a BSO (Bi12SiO20) crystal. A coaxial configuration of the plasma jet was used, operating in a stable mode with one bullet per voltage period, at 30 kHz and amplitude of 2 kV. The electric field was shown to be a function of the gas flow (He, at 300, 500 and 700 SCCM) and the manner in which the discharge spreads over the dielectric surface. The maximum value of 11.6 × 105 V m−1 was obtained at the negative half-period of the discharge current measured at the grounded electrode, at the flow of 300 SCCM. The largest electric field averaged over the area of the spreading of the discharge (3.6 × 105 V m−1) was found in the same conditions.

Asymmetric properties and ozone production of surface dielectric barrier discharge with different electrode configurations

For two electrode configurations of surface dielectric barrier discharge we investigated the asymmetry of the electrical parameters for the positive and negative half-periods of the discharge voltage and the discharge ozone production. In both configurations the first electrode was a square on one side of the dielectric plate. A set of 9 or 14 interconnected parallel strips on the other side of this plate served as the second electrode. The asymmetry is caused by different micro-discharges activity, which is reflected by peaks in the discharge current waveforms. When the strip electrode is connected to the high voltage terminal of the power source the series of current peaks appears mainly during the positive voltage half-periods whereas only a few smaller current peaks are observed during the negative voltage half-periods. When the strip electrode is grounded the situation is reversed. For the electrode configuration with 14 strips the asymmetry in micro-discharges activity is decreased in comparison with the 9 strip electrode. Finally the discharge electrode system with 9 strips produces, for a particular power, higher ozone concentrations than the system with 14 strips and the concentration of ozone does not depend on which electrode is grounded.

Characterization of millimeter magnitude atmospheric pressure glow discharge in pin-to-plane dielectric barrier discharge

Discharge mode in pin-to-plane dielectric barrier discharge at atmospheric pressure was investigated by means of the electrical measurement, the photo-electricity and the fast macro photography. The discharge was operated in atmospheric air. Streamer and glow discharge were generated in the positive half-period and negative half-period of discharge respectively with a 10 kHz AC power supply when the applied voltage reached a high value. The subject of this paper is the study of the characterization of the glow discharge. It was found that the glow discharge have the hierarchical structure, although the discharge gap is small (only 0.9 mm). The positive column is shortened as the distance of discharge gap decreases, but the dimensions of other discharge area do not change. The discharge current waveform illustrates that the positive half-period discharge current is very short, which is streamer current waveform, and the negative half-period one is longer, which is glow discharge current waveform. The photo-electricity signal waveform corresponds with discharge current waveform. Two main glow discharge generating reasons are proposed in this paper. One is a sufficient number of space charge produced in the very uneven electric field around needle electrode; the other is the effective secondary electron emission process on the exposed needle electrode.