High Frequency AC Research Articles

Pelatihan Perancangan dan Pengaplikasian Alat INTENSOR

Technological developments have a role in the competition for metal processing in the home industry, namely the development of metal heating devices. However, the home industry needs to consider environmentally friendly metal heaters. One of the environmentally friendly metal heaters is an induction heater. Induction heater has a metal heating technique by utilizing electromagnetic induction which is more efficient than using a conventional metal heating furnace. Induction heaters have advantages in terms of easier use, efficient in terms of energy, time and temperature regulation. Induction heating is a metal heating technique by utilizing electromagnetic induction from high frequency AC waves, which is more efficient than using conventional metal heating furnaces. This problem is the basis for holding training on the design and application of the INTENSOR tool. This community service activity has had quite a good impact in: 1) increasing the knowledge and skills of metal processing business actors in designing INTENSOR tools; 2) increase the knowledge of metal processing business actors in making and applying INTENSOR tools. Community service activities are carried out for 6 months and are intended for metal processing business actors.

Computational study on the discharge dynamics of atmospheric pressure He plasma driven by high frequency AC voltage

A two dimensional self-consistent fluid model has been established to investigate the discharge dynamics of double-ring electrode He atmospheric pressure plasma jet (APPJ) driven by high frequency AC voltage. The difference of the internal stream and external jet and the influence of the change of applied voltage polarity on plasma discharge characteristics has been discussed. It has been discovered that the capacitive breakdown characteristic of the double ring electrode significantly enhances the intensity of the APPJ. The discharge intensity of the external jet is stronger than that of the internal stream and the propagation speed of the external jet is faster than that of the internal stream due to the ionization and Penning ionization of N2 and O2. Therefore, the density of reactive species in the external jet is greater than that in the internal stream. When the negative voltage is applied to the downstream electrode, the propagation direction of the internal stream changes to the downstream electrode. The ionization of the external jet is also concentrated near the downstream electrode and in the streamer head. The radial propagation distance of the external jet on the dielectric surface continues to increase and the peak value of the radial electric field is concentrated at the streamer head. When the applied voltage changes from negative to positive, the propagation direction of the internal stream turns to the upstream electrode and the upstream jet is formed above the electrode. At the beginning of the positive cycle, the radial propagation distance of the external jet is shortened due to the effects of the electron attachment of O2 and the radial electric field. With the increase of applied voltage, the ionization in the streamer head gradually increases, which promoted the radial propagation of external jet.

CAPACITANCE AND IMPEDANCE OF IRIDIUM ELECTRODE IN MOLTEN ALKALI CHLORIDES

Сapacitance of the iridium electrode was studied by the electrochemical impedance spectroscopy with variation of the main physical and chemical parameters: electrical potential, temperature, radius of the alkali cation. The influence of the signal frequency used in AC electrochemical methods on the capacitance value and the shape of the curve was also checked. Capacitance of the iridium electrode was obtained in molten sodium, potassium and cesium chlorides in the temperature range 1093–1123 K and the frequency range of the AC signal 3 · 100–3 · 104 Hz in the entire accessible range of electrical polarization. The obtained capacitance curves have two main minima with a maximum between them. One of these minima (cathodic one) was identified as the classical potential of minimum capacitance. A decrease in the signal frequency and the temperature of experiment, as well as an increase in the cation radius in the NaCl–KCl–CsCl order, leads to the appearance of one or two additional minima in the potential region between the main minima. The depth of these intermediate minima increases and their potential shifts in the positive direction with an increase in the radius of the alkali metal cation of the salt electrolyte. The calculated values of the capacitance of the electrical double layer and the adsorption capacitance were obtained by the method of equivalent electrical circuits. One of the additional minima obtained by direct measurement of the dependence of the electrode capacitance on the potential at a high AC frequency corresponds to the calculated capacitance of the double layer. The other additional minimum obtained at a low AC frequency corresponds to the calculated adsorption capacitance.

Single Phase High Frequency AC Link DC/AC Converter for Photovoltaic Systems

In this article, an isolated high-frequency AC link bidirectional AC/DC Push-Pull converter is proposed for photovoltaic systems. Conventional DC/AC converters, such as back-to-back converters, are multi-stages converter with a common DC link. These converters due to their huge DC link capacitor, despite the simplicity of control, have some drawbacks such as high size and volume, low reliability and short life span, and fault ride-through (FRT) problems. In this article, a DC/AC converter with high-frequency AC link and transformer is proposed for the integration of photovoltaic (PV) arrays to a single-phase AC grid or load. The presented converter, beside the reduced number of active switches and cost, due to the lack of intermediate bulky energy storage element, has none of the conventional converter disadvantages. Modulation and commutation techniques of the proposed converter are also presented. The performance of the proposed system is proved using simulation in the MATLAB/SIMULINK environment and using a laboratory setup.

Control Strategy for Resonant Inverter in High Frequency AC Power Distribution System with Harmonic Suppression and Transient Performance Improvement

In high frequency AC (HFAC) distribution system, the resonant inverter is used to improve power quality and keep the stability of the output AC voltage. Aiming at the problems of poor output power quality and slow transient performance caused by unreasonable filter parameter design and load change during inverter operation, a single-phase H-bridge LCLC resonant inverter based on analog circuit controller implement is introduced in this paper for HFAC power distribution system (PDS). In this study, to design harmonic compensator and analyze the responsiveness of the inverter, it is necessary to analyze the output voltage total harmonic distortion (THD) of LCLC resonant inverter and the performance of the open loop system in detail. On the one hand, a proportional-integral-resonant (PIR) controller is designed to maintain the zero static error of the voltage output and suppress the output voltage THD of LCLC resonant inverter. On the other hand, an integral controller combines with phase-shift modulation (PSM) method is presented to effectively improve the transient performance of resonant inverter and provide the fixed frequency of the output voltage. On the basis of the above, the experimental prototype is implemented with the output AC voltage root mean square of 28 V, and the output voltage frequency for resonant inverter is equal to switching frequency. A rated output power of 130 W experimental platform is built to verify the effectiveness of the theoretical analysis, control strategy, and modulation method.

Dynamic Capacitance Measurement of SF6 Circuit Breaker During Opening Operation

In order to mine the state information of SF6 circuit breakers (CBs) interruption chamber and evaluate the contacts state, a method of measuring and calculating the dynamic capacitance between contacts in CBs opening process was proposed. The test CB is connected in series with a high frequency AC power supply, and the voltage and current of the circuit breaker are measured during the opening process. The fundamental frequency components of the voltage and current are extracted by the short-time Fourier transform, and the dynamic capacitance curve as a function of time is calculated. The results show that due to the variation of capacitance, there are a large number of harmonics with frequencies close to the fundamental frequency in terminal voltage and current. During the first two cycles after contacts separation, the capacitance drops sharply to 33.25 pF, then with the increase of the contact distance, the capacitance decreases much more slowly and tends to be constant, and the capacitance is 20.70pF after the completion of the opening.

The Physical Mechanism of Frequency-Induced Inflection Point for Oil–Paper Insulation Under High-Frequency Square-Wave Voltage

High-frequency (HF) oil-immersed transformers with small size and light weight have been paid wide attention by researchers. Its oil–paper insulation frequently withstands HF over-voltages at frequencies of several kilohertz and above, resulting in the too early failure of oil–paper insulation. In order to investigate the effect of HF on oil–paper insulation, this article investigates the partial discharge (PD) characteristics of oil–paper insulation under HF stress. The experimental results show that a frequency-induced inflection point is existed near 10 kHz and the PD parameters of HF voltages is much higher than that ac voltages. Besides, the theoretical mechanism is expounded to interpret and understand the formation process of frequency-induced inflection points more easily. It can be found that the change in frequency causes the change in the charge decay time constant and the residual charge on the insulating surface, resulting in the formation of the frequency-induced inflection point at HF. These results might contribute to determine the characteristics of PDs between HF voltages and ac voltages. It can provide references for the research and production of HF transformers.

Microscopic mechanism for nanoparticle-laden droplet–droplet electrocoalescence: A molecular dynamics study

Electrocoalescence is an energy-efficient and environmentally friendly process for separating water-in-oil emulsions. In this study, nanoparticle-laden droplet–droplet electrocoalescence behaviors under external electric fields were numerically investigated using molecular dynamics (MD) methods. Good agreement was obtained between numerical results and experimental validation work. The influences of electric field strength, droplet diameter, nanoparticle (NP) concentration, NP size, and electric frequency were systematically examined, analyzed, and discussed from the perspective of intermolecular interactions. The NPs migrated to the liquid bridge to form nanoparticle shell under electric fields, and the NP brown motion increased the breakup probabilities, leading to partial electrocoalescence, which is undesirable in oil–water separation process. As to unequal droplets (droplet pairs of 6&4 nm, 6&6 nm, and 6&8 nm), the daughter droplets were always ejected from the apex of the small droplet. The NP concentrations influence not only the film coalescence process but also the droplet approach process, and high concentrations (0.15, 0.22 and 0.29 mol L−1) resulted in partial coalescence. The NP size also played significant roles during electrocoalescence. At large NP sizes (0.86 & 1.16 nm), the electrostatic repulsion between NPs played the dominant roles in the overall system, accounting for the PC mode with increasing NP size. In addition, applying high frequency (10 & 40 GHz) AC electric fields was found to be a time-saving and high-efficiency method. The results of this work will be potentially useful for optimizing the design of compact and efficient oil–water separators.

Electrical Machines Winding Technology: Latest Advancements for Transportation Electrification

The ever-increasing demand for higher-power dense electrical machines has resulted in different electrical, mechanical, and thermal stresses, which can eventually cause machine failure. For this reason, the management of stresses and losses must be thoughtfully investigated to have a highly reliable electrical machine. The literature agrees that winding losses are the dominant loss mechanism in many electrical machines. However, statements vary on how to mitigate these losses along with the aforementioned stresses. To avoid winding failure, a study of the various winding topologies would allow for a better consideration of the challenges and limitations in the performance of different electrical machines. To this aim, this paper introduces a comprehensive review for different winding topologies. Many reported cases in the literature are summarized and compared. Moreover, the utilization of additive manufacturing (AM) in the production of the machine windings is presented, showing a high level of maturity of this emerging technology. Finally, different challenges facing the design of machine windings are introduced including the AC high frequency losses, thermal management, mechanical and acoustic problems, insulation aging, automated production, and winding manufacturability.

Sensorineural damage in chronic suppurative otitis media with and without cholesteatoma: a comparative study.

BackgroundChronic suppurative otitis media (CSOM) is a common otolaryngology disease, and cholesteatoma is the most aggressive type of CSOM. CSOM with and without cholesteatoma both result in a certain level of sensorineural damage, which can be categorized as air conduction (AC), bone conduction (BC), or air-bone gap (ABG), and AC, BC, and ABG are affected by many factors. Further analyses and comparisons of factors affecting sensorineural damage in CSOM with and without cholesteatoma were conducted in this study.MethodsA comparative study was conducted of 79 patients with CSOM (39 with cholesteatoma and 40 without cholesteatoma) whose diagnoses were mainly based on chronic middle ear infections and hearing loss (HL), typical computed tomography (CT) and surgical findings. Audiological evaluation included AC, BC and ABG, and sensorineural damage was defined as mixed and sensorineural HL (SNHL).ResultsIn relation to the types of HL, there were no significant differences between both groups. The CSOM with cholesteatoma group had significantly greater AC (P=0.000) and a significantly greater ABG (P>0.05) than the CSOM without cholesteatoma group, but BC did not differ significantly between both groups (P>0.05). The average AC-middle frequency (MF), AC-high frequency (HF), ABG-MF and ABG-HF of CSOM without cholesteatoma were smaller than these of CSOM with cholesteatoma (P<0.05). The degree of HL differed significantly between both groups (P=0.000). The CSOM with cholesteatoma group showed a higher level of HL than the CSOM without cholesteatoma group. The presence of cholesteatoma was presented a protective factor associated with sensorineural damage (P<0.05), while higher degrees of hearing and aging were risk factors (P<0.05), respectively.ConclusionsOur direct comparisons showed that HL progressed more rapidly in the CSOM with cholesteatoma group, which had higher frequencies in relation to AC, the ABG, and severity. However, in relation to BC, there were no significant differences between both groups, which was in line with the similar proportions of the types of HL in both groups. The logistic regression showed that the presence of cholesteatoma was a protective factor, and the degree of hearing and aging were risk factors associated with sensorineural damage.

Impedance Modeling and Stability-Oriented Parameter Optimization of Isolated Dual Active Bridge-Based Two-Stage AC-DC-DC Converter

The isolated dual active bridge (DAB)-based two-stage AC-DC-DC converters have been widely applied in grid-connected power electronics systems. However, the impedance interactions between the DAB converter and the AC-DC rectifier can cause instability problems to the two-stage converter systems. The accurate terminal impedance characteristics of the DAB converters are still not clear due to the high frequency ac conversion stage. This makes it difficult to assess the impacts of the DAB circuit parameters on the stability of the two-stage converters. To address these issues, the impedance models of the DAB converters are originally derived in this paper. Based on the developed impedance models, the stability of the DAB-based two-stage AC-DC-DC converters is analyzed. The impacts of the DAB converter circuit parameters on the stability of the two-stage AC-DC-DC converters are comprehensively revealed by the Bode and Nyquist plots. The analysis results offer instructive implications to finetune the design rules of the DAB converters. The conclusions are validated by comprehensive simulation and experimental results.

Thermal Characteristics Investigation of Lithium-Ion Battery Under High-Frequency AC Excitation in Low-Temperature Environment

At low operating temperatures, the power capability and charging/discharging capacity of lithium-ion (Li-ion) batteries can decay rapidly. Therefore, it is essential to preheat the Li-ion batteries in advance of the normal operations of a battery electric vehicle. High-frequency ac preheating methods are advantageous to achieve a miniaturized and lightweight design. In this article, a self-heating circuit topology is used for studying the characteristics of Li-ion batteries at low temperatures and under high-frequency ac excitation. The thermal behaviors of Li-ion batteries under high-frequency ac excitations are comprehensively analyzed with an improved heat generation model. Experimental results exhibit that heat generation due to electrochemical reactions has a significant influence on self-heating rates under the high-frequency ac excitation, and the heating rate is positively correlated with the current frequency and root-mean-square (rms) value. Specifically, when the current frequency is 90 kHz and the rms value is 3.51 A or 1.17 C, validated by experiment and numerical simulation, a 2.9-Ah 18650 Li-ion cell can be heated up from −20 °C to 5 °C in 7.33 min with an average electrochemical heat generation of 2.962 W.

Experimental study on the performance of an electric field enhanced separator for crude oil production fluid

As most of the oil fields gradually come to the middle and late exploitation period, the crude oil production becomes more complex, stable and water cut is also very high. This has brought challenges to oil–water separation in onshore and offshore production trains especially for the demulsification and dehydration of crude oil. In particularly, the pre-separation efficiency of conventional three-phase separators installed at the front position of the crude oil processing systems are severely affected. In this paper, we explored the demulsification performance of W/O emulsion in an electric field-enhanced separator with insulated electrode assembly inside by static demulsification experiment and dynamic demulsification experiment separately. Focused beam reflectance measurement (FBRM) was used to make real-time online measurements of water droplet sizes in the emulsion. The average water droplet diameters, distribution of droplets within certain size and water content in oil outlet of the separator are set as indicators for evaluating the dehydration performance. The effect of electric voltage, frequency, water content and inlet flowrate on the demulsification performance were both investigated. Experimental results showed that the high frequency AC electric field with insulated electrode can promote the growth of small water droplets and thus contribute to the demulsification. The dehydration performance is deteriorated drastically with the increase of inlet water content or flowrate. The electrical field parameters such as electrical voltage and frequency both have obvious effect on the diameter distribution of dispersed water droplets and water contents at oil outlet of the separator. For certain inlet water content 20% and inlet flowrate 0.3 m3/h, the optimal electrical voltage is 5 kV and frequency is 3 kHz. The research results can provide guidance for the optimization and performance improvement of the electric field-enhanced separator.

Promotion of ferrofluid microchannel flows by gradient magnetic fields

• Ferrofluid Couette-Poiseuille flows subject to gradient magnetic field are analyzed. • Steady gradient magnetic fields promote the ferrofluid Couette-Poiseuille flows. • The backflow is completely suppressed and the flow separation disappears. • The gradient magnetic field enhances the effect of magnetization relaxation. • The gradient magnetic field increases magnetic stress and reduces shear stress. Inspired from the wide engineering applications of ferrofluids, we investigated the ferrofluid microchannel flows subject to a gradient magnetic field applied perpendicular to the channel walls. The ferrohydrodynamic problem encompassing the Fokker-Planck magnetization equation in a Couette-Poiseuille configuration is solved numerically. The velocity and spin profiles, vorticity, magnetization, flow rate, and stresses acting on the moving plate are examined for favorable and unfavorable field gradients, as well as the adding of different pressure gradients. We show that the steady gradient magnetic fields promote the flow of both pure Couette and Couette-Poiseuille flows in the microchannel geometry. The increment of the velocity attains 35% and the resulting volumetric flow rate increases by about 24% at the most. This phenomenon was only observed in ferrofluid flows subject to high frequency AC magnetic fields or temperature gradient field in the past. The backflow occurs in normal Couette-Poiseuille flows can be completely suppressed by the gradient fields and the flow separation disappears correspondingly. The gradient magnetic fields are able to enhance the effect of magnetization relaxation and dramatically increase the magnetic stress and reduce the shear stress by comparison with the cases subject to uniform magnetic fields, yet the tradeoff between them leads to a rise in the total tangential stress acting on the moving plate.

High-Frequency ac Susceptibility of Iron-Based Superconductors.

A microwave technique suitable for investigating the AC magnetic susceptibility of small samples in the GHz frequency range is presented. The method—which is based on the use of a coplanar waveguide resonator, within the resonator perturbation approach—allows one to obtain the absolute value of the complex susceptibility, from which the penetration depth and the superfluid density can be determined. We report on the characterization of several iron-based superconducting systems, belonging to the 11, 122, 1144, and 12442 families. In particular, we show the effect of different kinds of doping for the 122 family, and the effect of proton irradiation in a 122 compound. Finally, the paradigmatic case of the magnetic superconductor EuP-122 is discussed, since it shows the emergence of both superconducting and ferromagnetic transitions, marked by clear features in both the real and imaginary parts of the AC susceptibility.

Enhanced luminescence, electric-field and actinic-light modulation of emission in nematic-CdSeS gradient nanocrystal composites by polymer confinement

We demonstrate that dispersing a small amount of CdSeS gradient quantum dots (QDs) in a nematic liquid crystal and geometrically confining the nanocomposite in a polymer network leads to their ordered linear assembly, as observed through electron microscopy. Such an orientational order not only enhances the base photoluminescence (PL), but brings in significant anisotropy in the emission magnitude, a feature barely seen for the system without the polymer network. A high frequency (∼kHz) AC field adds the attractive dimension of on-demand and spatially addressable PL modulation. Using a photoisomerizable azobenzene derivative and a carefully selected excitation wavelength, it is shown that an actinic-light driven modulation of PL is also possible, which is furtherenhanced by the presence of the polymer network.

High frequency AC electric glow discharge visualization technology and application in big diameter hypersonic low-density wind tunnel

In order to visualize the rarefied flow field in a Φ1m hypersonic low-density wind tunnel, an electric glow discharge technique based on high frequency excited power has been developed. Firstly, finite element simulation analysis has been carried out, and it is concluded that the breakdown voltage can be reduced by using high frequency power supply; then an electric glow discharge apparatus has been fabricated, and the discharge images were compared with simulations; besides, a clear flow field around HB-1 standard model has been observed using this technology; finally, the influence of glow discharge on the flow field, as well as the differences between direct current and high frequency electric glow discharges is discussed at the end of this paper.

Capacitive Impedance for Following In-Situ Grafting Kinetics of Diazonium Salts.

A new method to follow in-situ grafting kinetics of diazonium compounds based on imposing small amplitude high frequency AC oscillations at grafting potential, is outlined. This enables the time-resolved measurements of capacitive impedance concomitantly with the growth of the organic layer at the working electrode. The impedance values were quantitatively correlated with the ex-situ (from voltammograms) and in-situ (from quartz crystal microbalance) measured surface coverages, providing a validation of the new methodology. The versatility of the developed approach was demonstrated on the grafting via reduction of 4-nitrobenzenediazonium on Au and glassy carbon (GC) substrates and via deposition of in-situ generated diazonium salts from 1-aminoanthraquinone and 4-ferrocenylaniline on GC. The capacitive impedance measurements are simple, fast, and non-destructive, making it an appealing methodology for an exploration of grafting kinetics of a wide range of diazonium salts.

Synergistic Photothermal-Chemotherapy Based on the Use of Biomimetic Magnetic Nanoparticles.

MamC-mediated biomimetic magnetic nanoparticles (BMNPs) have emerged as one of the most promising nanomaterials due to their magnetic features (superparamagnetic character and large magnetic moment per particle), their novel surface properties determined by MamC, their biocompatibility and their ability as magnetic hyperthermia agents. However, the current clinical application of magnetic hyperthermia is limited due to the fact that, in order to be able to reach an effective temperature at the target site, relatively high nanoparticle concentration, as well as high magnetic field strength and/or AC frequency are needed. In the present study, the potential of BMNPs to increase the temperature upon irradiation of a laser beam in the near infrared, at a wavelength at which tissues become partially transparent, is explored. Moreover, our results also demonstrate the synergy between photothermia and chemotherapy in terms of drug release and cytotoxicity, by using BMNPs functionalized with doxorubicin, and the effectiveness of this combination therapy against tumor cells in in vitro experiments. Therefore, the findings of the present study open the possibility of a novel, alternative approach to fight localized tumors.

Resonant BLDC Motor Drive System for Medical Applications

Aim: The work aims to implement a soft switched high frequency ac link universal power converter controlled BLDC motor for medical applications. The universal power converter is an ac link converter, with the parallel combination of an inductor and a capacitor which offers improved power factor, low power consumption and more efficiency. Materials and Methods: SVPWM technique is utilized as a control technique for the proposed converter. AC link converter controlled with PDM technique requires an additional control procedure or an algorithm for regulating the output power of the PDM converters. SVPWM technique was adopted to turn ON and OFF the input and output switches in sequence to get the regulated power at the output. Results and Conclusion: These types of inverters could be used in medical field as an alternate to conventional inverters during power shut downs. The inverter proposed in this work has both the capability to step up and step down the input voltage based on the load requirements. The soft switched AC link inverter may be incorporated in a variety of applications including medial applications, industrial needs, renewable energy resources, variable frequency drives and electric and hybrid vehicles.