High Frequency Currents Research Articles

Chemical reactions at high-speed HFC-boriding

Strengthening of parts and units of machines, increased reliability and longer service life is an important task of modern industry. As an promising materials for protective-strengthening coatings, offered matrix composites based on the ternary system Fe-B-FenB. The article is proposed the complex heating of steel being borated and imbued medium by high frequency currents (HFC), and to combine the diffusion boriding from liquid and solid media and the transition of the diffusion boriding to chemical interaction between the elements of Fe and B. We determined the main components of the reaction-boronizing system, as well as their roles and possible processes that lead to the implementation of topochemical boriding initiated by HFC-heating. Confirmed the course of the reaction leading to the occurrence of reducing agents Ca, Si and active boron in the boronizing mixture.

The Formation of Composite Coatings with High Hardness with High-Speed Heating

The article dwells on the developed method of induction cladding of refractory compounds based on carbide-boride products (Ti,Cr)B2+W2B5+B4 and TiC+W2B5+FeV using a special charge material in the condition of high-speed heating by high frequency current. It has been established that during induction heating the cladding layers are formed as per the scheme where the refractory component is partially diluted in the bonding molten metal, it does not dissociate and forms strong matrix-reinforced structures with high resistance to wear. The article describes the efficiency of their use in case of abrasive wear.

High-Frequency Injection-Based Sensorless Control for a General Five-Phase BLDC Motor Incorporating System Delay and Phase Resistance

This paper investigates the sensorless control of a general Five-phase permanent magnet brushless DC (5Φ-BLDC) motor working at the low speeds. High frequency (HF) injection-based sensorless control is most popular, however, the system delay and stator resistance could deteriorate the sensorless control performance. In this paper, an HF model of 5Φ BLDCs at frequency-domain is primarily established as a replacement over the conventional static model, and an interpretation from the sinusoidal internal model is carried out to direct the sensorless control implementation. Accordingly, the measured d-axis HF current, which is typically neglected in the conventional method, is reused to demodulate the position angular information from the measured q-axis HF current. The proposed sensorless control is performed on a 5Φ BLDC drive, and experimental results confirm the effectiveness of this method while comparing its performance with the conventional method.

Research on Series Arc Fault Detection Based on Higher-Order Cumulants

At present, the detection methods on series arc faults are mainly based on the current of the main circuit, which probably results in misjudgment because of the singularity of the normal working current in a nonlinear load. What’s worse, is the arc fault characteristic in the small power branch is easily ignored in the current of the main circuit, which leads to missed judgment. To solve these problems, a detection method based on coupling signal acquisition and higher-order cumulant identification is presented, through the electromagnetic coupling mechanism of high frequency current. By analyzing the coupling signal of the high-frequency current and using the higher-order cumulant algorithm during arcing process, the kurtosis of the coupling signal is calculated. In this paper, the unified threshold value on the kurtosis in various conditions is obtained. The results show that the novel method can be effectively used to detect and identify the series arc faults.

A Mathematical Model for the Action of High-Frequency Currents on Biological Tissues

An analysis of the actions of high-frequency currents on biological tissues is presented and an applied mathematical model of electrosurgical actions is proposed for studying coagulation by correlation with the parameters of the high-frequency generator at the moment of tissue coagulation.

A Novel Approach for Partial Discharge Measurements on GIS Using HFCT Sensors.

This paper presents a novel measuring system for partial discharge (PD) measurements in Gas Insulated Systems (GIS) using high frequency current transformers (HFCT). The system is based on the measurement of the induced PD currents in the GIS enclosure. In opposition to the existing antenna technologies that measure the radiated energy in the very high frequency/ultra-high frequency (VHF/UHF) range, the proposed system measures the PD conducted currents in the high frequency (HF) range and below. The foundation of the measurements together with a detailed explanation of the sensor installed conveniently at the bolts of the GIS spacer are presented. An experimental study on the current distribution in the GIS enclosure is described to evaluate the impact of the sensor on the measurements. Laboratory experiments have been performed that show the suitability of this method to properly measure particle discharges caused by corona, surface and free moving particle discharges in SF6. Discharges in the range of 1 to 4 pC have been properly measured. An analysis to evaluate the performance of the method is shown, in comparison to VHF/UHF antenna measurements. The potential benefits of this novel technique rely on the small attenuation of PD signals in the GIS components in the HF range and sample rate reductions. Finally, a discussion on the potential applicability of present cluster and charge calculation techniques to the proposed PD GIS measurement using HFCT is presented.

Lessons From Tesla for Plasma Medicine

It can be argued that plasma medicine originated with Nikola Tesla in the late 19th century when he showed that one could pass large quantities of high frequency currents through a human body with no apparent damage. Tesla's work inspired much more extensive investigations over a period of several decades by numerous other researchers, on both the physics and biomedical effects of these currents. These early pioneers had a surprisingly modern view of some aspects of the therapeutic mechanisms of high frequency currents that clearly overlap with recent results. The perspective of this community was that the most important physiological effects are associated with the high frequency currents rather than the gas phase plasma per se. Some early work, such as the analgesic effects of dielectric barrier air plasma on tissue, is not well known today. The range of afflictions that early practitioners treated successfully is remarkable. This body of work, in some cases almost 130 years old, might have important lessons for current investigations into plasma medicine. Observations from Tesla and other early practitioners suggests that high frequency currents are potentially important and plasma medicine researchers should probably pay more attention to them.

Efficiency of hybrid equipment combining operations of surface hardening by high frequency currents and abrasive grinding

The methods of different processing steps concentration on the same equipment have been gaining wider application at the current stage of cutting machining development. It allows improving performance and reducing energy costs in the processing of machine components. The paper considers the finishing stage of the manufacturing process of a machine critical part. In comparison with the standard technology, the integrated treatment applied at the finishing stage of the manufacturing process is proved to improve the performance by the factor 3.5 for the main processing time and reduce energy consumption by the factor 5.7.

Increase in wear resistance of nickel plasma coatings under traditional and combined treatment conditions

The paper reports the prospective approaches to the increase in wear resistance of nickel plasma coatings. We considered the features of the two methods: combined high-energy heating by high frequency currents and spraying of composite cermet coatings of powder mixtures. The research provides the results of comparative wear resistance tests of the investigated nickel coatings under the conditions of sliding friction. The obtained fused and cermet coatings have a higher wear resistance compared to the original ones. The samples with composite coatings showed a significant decrease in the volumetric wear, averaging 56% along the entire length of the friction path due to the introduction of ceramic particles with high hardness (12150…15840 MPa) into the powder mixture. We present the results of the chemical composition research of nickel-ceramic powder mixture components and the sprayed cermet coating. The composite coating is established to have an increase in oxygen content owing to the intensive oxidation in the process of plasma spraying. There is a decrease in the percentage of the basic elements of the powder mixture, namely of aluminum and nickel. There is also an insignificant change in the share of the remaining chemical elements.

Methods for Determining the Quality of Galvanic Chromium Coating

The surface and microsections of the cross-section of the chromium coating samples were studied. The microhardness of the coating and the base material was tested, their metallographic studies were conducted. The analysis of the microstructure showed that the base metal of 45 and 38XA steel of all samples is in the normalized state. The analysis of the microstructure of the samples subjected to surface HFC hardening (high frequency currents) showed that the temperature of heating during quenching is insufficient, and it leads to a lower strength and hardness of the layer. The sample with a lower hardness of the chromium coating has a higher coating viscosity and resistance to wear. The sample with the highest microhardness of the coating is characterized by increased brittleness. The hardness of the metal substrate and its structure does not affect the properties of the chromium coating layer.

Sensorless Control of IPMSM Drives Using a Pseudo-Random Phase-Switching Fixed-Frequency Signal Injection Scheme

The conventional high-frequency (HF) voltage injection method can accurately extract rotor position for interior permanent magnet synchronous motor (IPMSM) drives at low and zero speed ranges. However, the fixed injection frequency will produce a loud audible noise. To solve this problem, a pseudo-random phase-switching fixed-frequency (PRPSFF) signal injection method is proposed in this paper. Based on the principle of phase selection for the PRPSFF injection scheme, the dc bias problem in the induced HF current can be diminished by setting a limitation in the injected voltage. Then a corresponding signal processing method is investigated to deal with the signal delay in the HF current extraction. Besides, the current power spectra density (PSD) for PRPSFF injection is analyzed, and a comparison between PRPSFF and the pseudo-random frequency-switching fixed-phase (PRFSFP) injection schemes is also introduced. The results show that the discrete harmonic spectrum in current PSD can be offset, and the continuous spectrum is smoother than that of PRFSFP injection. Finally, the effectiveness of the sensorless control method is verified by experiments on a 2.2-kW IPMSM drive platform.

The impedance cardiography technique in medical diagnosis

Background: Thoracic Electrical Bioimpedance (TEB) Technology sometimes called the Impedance Cardiography (ICG). In 1940, the Impedance Cardiography emerged; the studies of this technique are realized to the cardiovascular diseases detection which used hemodynamic parameters measurements based on the skin electrodes contact by injecting a low amplitude alternating signal. The objective of this article is to review the various studies based on this signal type and to present the multiple methods used for the treatment and to have a correct analysis.
 Methods: This ICG technique consists for applying an electric field longitudinally across a segment of the thorax with amplitude in mean, high frequency and low amplitude current. To analyze the ICG signal, the signal denoising is necessary that’s why a multiple filters are proposed, and the Discrete Wavelet Transform (DWT) denoising is also used.
 Results: The ICG is considered advantageous compared to other invasive conventional techniques; it gives a good correlation, and solves the Doppler ultrasound and Thermodilution problems. According to the studies, the Daubechies wavelet family (db8) is the best DWT to eliminate the noises. There are several algorithms for the signal characteristic point’s detection.
 Conclusion: For the purpose of cardiovascular disease diagnosis and monitoring, the non-invasive ICG technique comes to solve the complexity problem for measurement and analyzing heart disease based on the thoracic electrical impedance change assessment that is due to blood velocity and resistivity changes (blood volume changes) in order to estimate several hemodynamic parameters.
 Keywords: ICG, cardiovascular disease, hemodynamic parameters, diagnosis and monitoring, correct analysis.

Удосконалення механізму інноваційного розвитку суб’єктів аграрного виробництва в Україні.

Стаття присвячена оцінці сучасного стану функціонування підприємств тваринництва в Україні та обґрунтуванню стратегічних напрямів реноваційного розвитку. Ідентифіковано, що нестабільність соціально-економічної ситуації в Україні, низький рівень концентрації капіталу в аграрній сфері, диспаритет цін між сільськогосподарською продукцією і продукцією промисловості та його наслідки зумовили хронічні проблеми у сфері тваринництва. Обґрунтована необхідність формування стратегії реновацій виробничо-господарської діяльності підприємств тваринництва на основі моделі інноваційного розвитку. Визначена необхідність створення нових харчових технологій, які повинні максимально повно використовувати рослинну й тваринну сировину на основі мембранної й екструзійної техніки, струмів високої частоти й вакууму, сублімації й інших нових методів. Зазначено, що саме освоєння інноваційних технологій – конкретний шлях переходу від витратного до ресурсозберігаючого типу відтворення.

Investigations on the Characteristics of Thermally Sprayed NiCrBSi Coatings Fused by Flame and Inductive Processing

Ni-based materials are some of the most used hardfacing alloys to improve wear and corrosion resistance for parts functioning under severe conditions. For the current study, a NiCrBSi self-fluxing alloy powder with particle size in range of 45-106 μm was employed as feedstock material and deposited onto a steel substrate material using the oxyacetylene thermal spraying process. The as-sprayed components have been subsequently subjected to thermal post-processing in order to increase the adhesion to the substrate and to reduce the inherent porosity of the coatings. Consequently, two types of heating sources were chosen. One of them was the neutral oxyacetylene flame and the second one was based on high frequency currents. The aim of this work was to study the influence of the heat source type of the post treatment on the final characteristics of the coatings. Evaluation of the morphology and microstructure of the developed coatings was performed after the remelting process by means of scanning electron microscopy. Hardness tests were carried out in cross-section complying with the ASTM E384 standard. In both cases, after fusing, the microstructure was refined, with a drastic decrease in porosity. Evaluation of the hardness distribution along the coating cross-section revealed similar values of microhardness.

The Effect of Ferulic Acid and D`Arsonwal's High Frequency Currents Activity over the Number of Exanthema among Adult Women

The Effect of Ferulic Acid and D`Arsonwal's High Frequency Currents Activity over the Number of Exanthema among Adult Women

Improved Initial Rotor Position Estimation for PMSM Drives Based on HF Pulsating Voltage Signal Injection

In a permanent magnet synchronous motor (PMSM) drive system, high-frequency (HF) pulsating voltage signal injection has demonstrated high accuracy to estimate the initial rotor position. However, a conventional signal demodulation method may face the problems of long convergence time and limited system stability, owing to the low-pass filter (LPF) used in signal demodulation process. Thus, a direct signal demodulation method is proposed, in which, the LPF is removed to improve system stability and dynamic property. A direct demodulation collection is generated to extract the position deviation signal from estimated q-axis HF current. Recursive discrete Fourier transform is employed to calculate the amplitude of estimated d-axis HF current, thus an amplitude normalized technique is implemented to reduce the effects of HF signal and PMSM. Meanwhile, the stability and dynamic property are compared between the conventional and proposed method, with the aid of D-partition technique and amplitude-frequency characteristics diagram. Furthermore, a novel magnetic polarity detection method is put forward based on the magnetic saturation, which has a high signal-to-noise ratio. Finally, the experimental results on three PMSM drive systems prove that the proposed method is practicable and effective.

Predicting the hardening depth of a sprocket by finite element analysis and its experimental validation for an induction hardening process

Case hardening, or surface hardening, is the process of hardening of a metal object at its outer surface while allowing its core to remain relatively soft, thereby forming a thin layer of harder metal at the surface. Currently, induction heating using high frequency current is applied to carry out this hardening process. We modeled this hardening process using the powerful Abaqus finite element tool and validated the results of the numerical analysis by comparing them with experimental results. Our model accurately predicted the hardened area at the outer surface of the metal for a steel sprocket. Future research will optimize the coil geometry and other parameters.

Magnetoresistor with Planar Magnetic Concentrator as Wideband Contactless Current Sensor for Power Electronics Applications

High-frequency power electronic converters require lossless, accurate, and isolated current measurement. High-frequency currents through a printed circuit board (PCB) trace generate nonuniform magnetic field around the trace. The nonuniform magnetic fields can be normalized by means of magnetic field concentrators (MCONs) using conductive materials. In this study, a novel technique for high-frequency contactless current sensing using magnetoresistor (MR) sensors with planar magnetic concentrators (MCON) utilizing conductive materials has been proposed. The effect of different MCONs on the performance of anisotropic MR (AMR) sensors for high-frequency contactless current detection has been investigated. The performance of the AMR sensor equipped with different MCONs is demonstrated experimentally with respect to a fast rise step current. A detailed frequency analysis is performed on the sensor response with different MCONs to determine the effect on the detection bandwidth of the current sensors.

Formation of Hardening Coatings for Working Elements of Agricultural Machines When Combining the High-Frequency Heating and High-Temperature Synthesis of the Materials

A method of surfacing of a wide range of cast, hard, wear-resistant materials on a steel base was created based on the performed investigations. The surfacing was carried out in the conditions of heating with high-frequency currents (HFCs). The exothermic thermite mixtures were used, including the mixtures of metal oxides, aluminum, or silicon. In the course of synthesis, the coatings with the weld pad of 100–900 μm were obtained. The surfacing process was carried out in two main synthesis modes—high and low-temperature using the exothermic thermite mixtures—and allowed extending significantly the raw material base of the surfacing materials, including refusing the use of the traditional surfacing eutectic alloys and charge mixtures with the boron carbide for deep borating. It is shown that the synthesis of the coating of the exothermic thermite mixture FeO/B2O3/Si is identical to the diffusion saturation of the surface layer with the classical mode of borating during the HFC-heating.

Principle and Stability Analysis of an Improved Self-Sensing Control Strategy for Surface-Mounted PMSM Drives Using Second-Order Generalized Integrators

For the purpose of avoiding the drawbacks of large volume, heavy weight, complex wiring, and low reliability caused by the mechanical position sensors in aeronautic power drives, the self-sensing control of permanent magnet synchronous machines (PMSMs) has been getting increasing attention. High-frequency (HF) pulsating current injection is an efficient method to obtain the rotor position at low speeds. However, in this method, the rotor position is extracted from the command voltage instead of the actual measurement due to the lack of voltage sensors, and the control performance of the HF current is nonideal because of the proportional-integral controller (PI) current regulators. Both these shortcomings give rise to position estimation error. To avoid the aforementioned problems, a novel current regulator consisting of the PI and second-order generalized integrator (SOGI) is presented. The different combinations of the PI and SOGI in the d–q axes current regulators are studied. The system stabilities of the proposed and existing HF pulsating current injection-based self-sensing control strategies are comparatively analyzed considering the current control error and some other aspects. The experimental results demonstrate the feasibility of the proposed strategy by a surface-mounted PMSM vector controlled system.