High EMF Research Articles

Analysis and design for constant current/constant voltage multi‐coil wireless power transfer system with high EMF reduction

The investigation on the constant current (CC)/constant voltage (CV) charging for the electric vehicle wireless power transfer (WPT) system has been widely conducted. However, the CC/CV performance under misalignment cases has been scarcely studied especially for the multi-coil WPT system. The resonant tank compensation methodology for the exciter-quadrature-repeaters (EQR) transmitter-based multi-coil WPT system is studied to achieve high power factor CC/CV charging with low leakage flux over ±150 mm lateral misalignment range. The EQR transmitter consists of one small exciter coil powered by a single full bridge inverter and two larger decoupled quadrature repeater coils which are magnetically coupled to the exciter coil. A variable switched capacitor is applied on the exciter side to maintain a high power factor in the CV mode. A 3-kW experimental setup with a 200 mm nominal vertical distance was built and a three-coil WPT system with a single large repeater coil is chosen as a comparison. Experimental results show that the EQR transmitter-based WPT system achieves 92% coil-to-coil efficiency and reduces the leakage flux density by 70% compared with the existing three-coil system in the CV mode at 150-mm lateral misalignment.

Refined Analysis of the Correlation Between the Accepted Maximum Permissible Levels of Radio Frequency Electromagnetic Fields for the Population and the Lethality Rate of Covid-19

In this paper, the results of a refined analysis of the correlation, previously discovered by the author, between the accepted maximum permissible levels (MPL) of radio frequency electromagnetic fields (RF EMF) for population and the mortality rate of COVID-19, carried out using the data samples from the World Health Organization (WHO), taken monthly from May 2020 to July 2021, are presented. To explain the results obtained, correlation between the accepted MPL for RF EMF, the level of vaccination of population against COVID-19, and the level of gross domestic product per capita in different countries were analyzed additionally. Analysis results confirm the presence of a noticeable correlation between the RF EMF MPLs and the COVID-19 mortality rate, especially in the first months of the analyzed period. The subsequent decrease in correlation between them by the end of analyzed period is a result of significantly larger efforts in struggle against COVID-19 in those countries where high RF EMF MPLs are adopted taking into account only the danger of thermal effects in human body, in comparison with countries where more stringent standards that take into account the danger of non-thermal bioeffects, are used. The first of these countries, having on average a higher level of economic development, ensured mass COVID-19 testing of population, imposition of tougher and longer restrictions (quarantines, lockdowns, etc.), as well as significantly higher rates of vaccination of the population. The presence of a confirmed correlation between these characteristics does not necessarily mean the existence of an unambiguous causal relationship between them. In countries of the first group with passive regulation of population protection from environmental factors, this principle is used not only in relation to RF EMF, but also in relation to the other factors. This determines the relevance of a deeper system analysis of the impact of the adopted legal systems for protecting the population from the entire set of anthropogenic factors on its health and collective immunity.

Efficient production of 5-ethoxymethylfurfural from 5-hydroxymethylfurfural and carbohydrates over lewis/brønsted hybrid magnetic dendritic fibrous silica core-shell catalyst

In the present work, a series of Brønsted and Lewis hybrid, magnetic, dendritic fibrous silica microsphere core shell particles with an open and easily accessible mesopore channels as the catalyst supports (Fe3O4@SiO2@KCC-1) were prepared, impregnated with aluminum (10 wt%) followed by encapsulation of different loadings of tungstophosphoric acid (PTA) from 10 to 40 wt% into mesoporous channels of fibrous silica shell (Fe3O4@SiO2@KCC-1/Al10/PTAx). They are utilised for the efficient and clean production of biomass-derived liquid fuel 5-ethoxymethylfurfural (EMF) through direct etherification of hydroxymethylfurfural (HMF) and one-pot conversion of fructose and other carbohydrates. High EMF yields of 93.1%, 62.2%, 23.9%, and 21.4% were obtained, when HMF, fructose, sorbose, and sucrose were subjected as substrate, respectively. These catalysts were characterised by XRD, py-FTIR, TGA, N2-physisorption, SEM and TEM-EDX mapping. Importantly, the catalyst could be reused at least four times almost without a significant loss of activity.

Finding the Optimal Size of Permanent Magnets for a Transverse Magnetic Flux Generator with a Disk Rotor

Based on the analysis of the transverse flux machine designs, they were found to have a relative design simplicity and a high-power density. The purpose of this work is to determine the optimal height of a permanent magnet and to define its effect on the induced EMF value in the stator coils and the cogging torque, as well as to define the picture of the magnetic flux leakage between the stator poles. To achieve these goals, the 3D model of a low speed generator was studied. The electromagnetic analysis was carried out using a modern software, which allows us to determine the magnetic field distribution in the 3D, as well as the induced EMF value and the rotor cogging torque. The criterion for the optimal calculation is the highest EMF value at the minimum value of the rotor cogging torque. The parameters of the permanent magnets, such as the width and length, remained unchanged, whereas, the height varied from 1 to 8 mm at a 1-mm step. The corresponding dependencies are obtained for each height. The most significant result of the work is the conclusion that the height of the permanent magnet should not exceed the 3-mm value. The significance of the obtained results is that the used methodology allowed finding the optimal height of the permanent magnet, since a further increase in its height leads to no growth in the EMF value, but rather significantly enhances the negative effect from the rotor cogging torque. In addition, the simulation results were supported experimentally.

Radiofrequency Electromagnetic Field Levels at Workplaces of Technical Specialists of Cellular Communication

Introduction: One of the main professional groups of workers in cellular radiotelephone communication includes technical specialists who serve and ensure trouble-free operation of radio transmitters of cellular base stations (BS). Transmitting antennas and BS equipment are powerful sources of radiofrequency electromagnetic fields (RF EMFs) and one of the main adverse physical factors of the working environment for technicians. RF EMFs affect the functional state of various systems of the human body including the nervous, cardiovascular, and immune systems. The objective of our study was to assess the exposure to RF EMFs of cellular communication technical specialists and to establish occupations with the highest exposure levels. Materials and methods: Instrumental testing of energy flux density of the electromagnetic wave generated by BS receiving and transmitting equipment was carried out at service sites of cellular communication facilities by technical specialists of the industry. The time spent by technicians at workplaces with high EMF levels during the average work shift was measured. Results: The analysis of collected data showed that 28 % of energy flux density values measured at workplaces exceeded the maximum permissible level for the personnel serving radio transmitters and spending from 12 to 61 % of the work shift in the specified conditions. We established that network construction engineers, network operation engineers, power engineers, technical audit specialists, network development engineers, and mechanics were exposed to increased RF EMF levels. Conclusion: Our findings indicate the necessity to monitor and reduce occupational exposures of technical specialists of cellular communication in order to improve their working conditions and prevent, inter alia, RF EMS-related diseases.

Exciter–Quadrature–Repeater Transmitter for Wireless Electric Vehicle Charging With High Lateral Misalignment Tolerance and Low EMF Emission

In this article, an exciter–quadrature–repeater transmitter pad is proposed in order to achieve high lateral misalignment tolerance and low leakage flux emission in electric vehicle wireless charging applications. In the proposed WPT system, a single half-bridge inverter unit is needed to energize the exciter coil, which is magnetically coupled to two larger quadrature repeater coils. The currents in the two repeater coils naturally adjust based on the lateral misalignment of the receiver pad to reduce the leakage flux density around the charging zone. The system can maintain zero phase shift between excitation voltage and current and achieve constant current charging conditions with fixed compensation capacitors in the ±150-mm lateral misalignment range. In order to verify the attributes of the proposed wireless power transfer (WPT) system, a 3-kW experiment setup with a 200-mm vertical gap was built and compared to a three-coil WPT system, which consists of a small transmitter coil, a single large repeater coil, and a receiver coil. According to the experiment results, even under extreme 150-mm lateral misalignment, the proposed WPT system has 90.7% coil-to-coil transmission efficiency. Furthermore, it achieves a 30% reduction of leakage flux density compared to the three-coil system in the 150-mm lateral misalignment case.

Casting glass coated microwires of alloys based on silver and nickel

This work presents the results of studying the features of the casting process of glass-coated microwires of alloys based on silver, which has a near-zero TCR, and nickel, which has a high thermo emf.

Analysis of the Fractional Pole-Pair Linear PM Vernier Machine for Force Ripple Reduction

Linear permanent magnet Vernier machine (LPMVM) is attracting more and more attentions recently due to its simple structure, high efficiency, and high thrust density at low speed. In this article, a novel fractional pole-pair linear permanent magnet Vernier machine (FP-LPMVM) is proposed, which gives more freedom in the design of the LPMVM to reduce the force ripple of the machine. The operation and force ripple reduction principles of the FP-LPMVM are also given in this article with the help of analytical equations. It is found that some of the proposed FP-LPMVM exhibit inherent good performances such as high EMF symmetry and low thrust ripple due to the combining of the flux modulation effect and the FP-LPMVM. In order to verify the theoretical analysis in this article, two LPMVM prototypes (i.e., 12 slots 20 poles integer pole-pair LPMVM and 18 slots 29 poles fractional pole-pair LPMVM) are manufactured, tested, and compared with each other. The experimental results are consistent with the FEA results, and the validity of the analysis and the superiorities of the proposed FP-LPMVM are verified.

Electromagnetic Performance Comparison Between 12-Phase Switched Flux and Surface-Mounted PM Machines for Direct-Drive Wind Power Generation

In this article, the 12-phase switched flux permanent magnet (PM) (SFPM) machine and three surface-mounted PM (SPM) machines designed for direct-drive wind power generation are comparatively analyzed. First, feasible stator-slot/rotor-pole combinations for symmetrical 12-phase winding layout are investigated for both machine topologies. Second, the key design parameters of the PM generators including the split ratio and stator teeth width ratio are optimized by finite element analysis to achieve a high phase fundamental EMF per turn and a low cogging torque, both of which are desired by the direct-drive wind power generator. Third, electromagnetic performances including air-gap field, cogging torque, static torque, inductance, output voltage and its regulation factor, output power, and efficiency of the generators are compared. A 10-kW 24-slot/22-pole SFPM prototype is built and tested to validate the FE predicted results.

Assessment of thermodynamic data for CuCrO2 delafossite from calorimetric measurements

A detailed investigation of the thermodynamic properties of delafossite CuCrO2 was carried out by experimental methods on synthetic CuCrO2 delafossite samples (differential scanning calorimetry from ambient to 871 K and drop calorimetry from 823 to 1123 K) and theoretical methods (density functional theory). Based on these data and available literature (low temperature heat capacity measurements and calculations, high temperature emf data), we propose, for the first time, a full set of thermodynamic data for the phase CuCrO2. Our selection comes to: ΔfH°298(CuCrO2) = −670.8 ± 1.3 kJ mol−1, S°298(CuCrO2) = 88.9 J K−1, and cp°(T)=1.02564.102-2.87159.107 T-3-1.28542.105 T-1.5 (298 < T < 1300 K).

Mapping the Electromagnetic Field in Front of a Microwave Oven

There is limited evidence that EMF may have negative health effects on human beings with extended exposure. This study measured the power density and strength of EMF at different distances and directions in front of a microwave oven. Our results showed that the EMF levels are high (≥ 100 mG) at “one arm’s length” distance (61 cm) in all directions, although the power density drops to a range of 0.01 – 0.10 mW/cm2. To achieve a power density of 0.05 mW/cm2 or less and an EMF level of 25 mG or less, the distance should be at least 91 cm and 122 cm, respectively, away from the microwave oven, especially in the left and front directions. Based on the measurement data, we created exposure maps using precautionary thresholds of 0.05 mW/cm2 and 25 mG for power density and EMF, respectively. The measurement results help to understand the EMF distribution in front of the microwave oven. The results suggest that one should avoid staying less than 122 cm away from the microwave oven during operation , and that the “one arm’s length” distance (61 cm) may not be sufficient due to the high EMF levels. This study helps to promote awareness of the potential health risks associated with microwave ovens.

Dual acidic titania carbocatalyst for cascade reaction of sugar to etherified fuel additives

An inexpensive carbocatalyst containing Brønsted acidic sulfonic acid group and Lewis acidic Ti4+ is found to be effective for cascade conversion of C6 sugar to 5-ethoxymethylfurfural (EMF) via sequential dehydration, and etherification reactions. HMF and fructose conversions at mild conditions achieved 91% and 64% EMF yields, respectively. The results indicate that the two acid sites interplay synergistically for high EMF yield and minimal ring-opened product ethyl levulinate (EL), another promising biofuel additive. Etherification of 2,5-bis(hydroxymethyl)furan (BHMF) with alcohols of varying carbon lengths formed alkoxymethylfurans (AMF) with high yields. The catalyst retained good activity upon recycling. The nature and strength of the acid sites are elucidated.

Enhanced mixed potential NOx gas response performance of surface modified and NiO nanoparticles infiltrated solid-state electrochemical-based NiO-YSZ composite sensing electrodes

We have designed the solid-state electrochemical mixed potential type NiO and yttrium-stabilized zirconia (YSZ) composite based sensing electrode for selective detection of NOx at elevated temperatures. The planner NiO-YSZ composite sensing electrode could detect NOx even at 400 °C, with acceptable response/recovery rates. The change in emf values of the sensor varied linearly with NOx concentrations on a logarithmic scale in the range of 5–100 ppm. The response characteristic of the sensor was improved by modifying the surface with different vol% of pore former. As a result, obtained porous electrodes showed better response characteristics concerning speed and response owing to higher porosity. To improve response kinetics of porous NiO-YSZ electrode, NiO nanoparticles are infiltrated into an optimized NiO-YSZ sensing electrode surface by controlled urea/cation infiltration method. The experimental results demonstrated that NiO nanoparticles infiltrated NiO-YSZ sensor electrode reveal remarkably high emf response to NOx compared that of planar electrode, suggesting that NiO nanoparticles introduction can significantly enhance catalytic activity and electrochemical performance of NiO-YSZ electrode. Finally, the porosity effect of electrode subtracts (YSZ) with NOx gases response and recovery kinetics was examined under the optimum operating temperature at 400 °C. The sensing mechanism based on the mixed potential for the surface modified NiO-YSZ composite sensing electrode was discussed based on the obtained result of sensing characterizations.

Development of Technology of Nicrosil and Nisil Thermocouple Materials Using Extrusion of Metal Powders

Nicrosil-nisil (NiCrSi-NiSi) thermocouples (Type N) have a high thermal EMF stability, radiation resistance, resistance to oxidation of the thermocouple wires and can be used as a universal means of measuring temperatures up to 1300 °C. However, when the traditional metallurgical method is used for the production of rod and wire materials of nicrosil and nisil from ingots of metals, it is difficult to ensure the homogeneity of the ingots and materials of the thermocouple. It is known that powder metallurgy methods can provide a greater homogeneity of the material compared to casting technology. The aim of this work was to study the possibility of using powder technology for the fabrication of rods of nicrosil and nisil thermocouple materials by extrusion and sintering of powders of source metals. Reduction in size and mixing of the raw powder components in a planetary ball mill was investigated. The regularities of pressing the prepared mixtures and microstructure of materials sintered from them were determined. Samples of nicrosil and nisil thermocouple materials in the form of cylindrical rods with a diameter of about 5 mm and a length of 200 mm with an uniform microstructure were also fabricated by extrusion of prepared mixtures followed by sintering. Experimentally determined specific differential thermal EMF of the thermocouple made from the sintered rods coincided with the theoretical value.

STAKEHOLDERS READINESS TO IMPLEMENT NEW LEGISLATION ON OCCUPATIONAL EXPOSURE TO THE ELECTROMAGNETIC FIELDS

– European companies are expected to check their compliance with a new legislation about occupational exposure to the electromagnetic fields . Corresponding EU directive was issued in 2013 and was to be implemented into the national legislation of member states by 2016. The current study was launched with the aim to determine the readiness of the companies and other stakeholders affected by this new legislation. The target groups investigated by this study include workers, working environment specialists, occupational health doctors and labour inspectors. A questionnaire was developed to determine the level of knowledge and other issues introduced by the new legislation. Altogether 67 responses was received from Estonia. Significant shortcomings were reported in regard to the training of workers at high EMF workplaces/companies - score 0,15 out of 1. EMF safety arrangements, as described in the new directive, were reported to be sufficiently fulfilled only in 11 per cent of the high EMF companies. Also the workers' knowledge about the EMFs propagation and health effects was low, averaging at only 0,15 out of 1. The results indicate that at present little attention is paid on training the workers that may be affected by high levels of EMFs. Shortcomings are characteristic to all sizes of companies but are less evident in large companies. Considering the requirements of the new EMF legislation, immediate planning of appropriate schooling programs is necessary for all parties involved.

Lipophilic Redox Buffers for Polymeric Solid-Contact Electrodes

A calibration-free measurement with an ion-selective membrane requires that only the phase boundary potential at the sample/sensing membrane interface is variable, i.e., either dependent on the activity of the target ion in the sample, as in a potentiometric experiment, or determined by an applied potential, as in a voltammetric experiment. All the other phase boundary potentials in the electrochemical cell are constant. Unfortunately, one of the biggest challenges in the fabrication of devices comprising solid-contact membranes has been to establish a reproducible phase boundary potential at the interface of the hydrophobic ion-selective membrane and the underlying electron conductor. This talk will address our use of ion-selective membranes doped with lipophilic redox buffers, both in view of potentiometry and voltammetry. Solid contact ion-selective electrodes (ISEs) typically have an intermediate layer between the ion-selective membrane and the underlying solid electron conductor that reduces the irreproducibility and instability of the measured electromotive force (emf). Nevertheless, the electrode-to-electrode reproducibility of the emf of current solid-contact electrodes in a zero-current measurement is widely considered to be unsatisfactory. To address this problem, we reported on lipophilic redox buffers consisting of the Co(III) and Co(II) complexes with hydrophobic ligands such as 1,10-phenanthroline (e.g., [Co(phen)3]3+/2+) paired with tetrakis(pentafluorophenyl)borate as counterion [1,2]. The resulting electrodes exhibit zero-current emf values with an electrode-to-electrode standard deviation as low as 1.7 mV after conditioning of freshly prepared electrodes for 1 h. While many prior examples of solid contact ISEs also used intermediate layers that contained redox-active species, the importance of selecting a balanced ratio of the reduced and oxidized species has typically been difficult and was often ignored, contributing to emf irreproducibility. The ease of the control of the [Co(phen)3]3+ / [Co(phen)3]2+ ratio explains the high emf reproducibility, as confirmed by the emf decrease of 58 mV per tenfold increase in the ratio of the reduced and oxidized redox buffer species. The result is an electrode-to-electrode standard deviation of Eº of 0.7 mV after 1 week of exposure to KCl solution. The use of this redox buffer in combination with colloid-imprinted mesoporous carbon [3,4] will also be discussed. [1] Zou, X. U.; Cheong, J. H.; Taitt, B. J.; Bühlmann, P., Anal. Chem. 2013, 85, 9350–9355. [2] Zou, X. U.; Zhen, X. V.; Cheong, J. H.; Bühlmann, P. Anal. Chem., 2014, 86, 8687–8692. [3] Hu, J.; Ho, K. T.; Zou, X. U.; Smyrl, W. H.; Stein, A.; Bühlmann, P. Anal. Chem., 2015, 87, 2981–2987 [4] Hu, J.; Stein, A.; Bühlmann, P. Angew. Chem. Int. Ed., in press (DOI: 10.1002/anie.201603017).

A Novel Power Failure Compensation Control Method for Active Magnetic Bearings Used in High-Speed Permanent Magnet Motor

Active magnetic bearings (AMBs) have been proved superior to conventional bearings in many ways. However, the AMB system will lose magnetic force if the power fails which may cause fatal damage to the rotor and the backup bearings. In order to improve the reliability of the AMB system, a power failure compensation control (PFCC) method is proposed in this paper. A novel hardware composition of PFCC is designed to cooperate with the motor drives using either pulse-width modulation (PWM) or pulse-amplitude modulation techniques. Once the power fails, the motor works as a generator and the back electromotive force (back EMF) is rectified by the antiparallel diodes of the inverter. Meanwhile, a buck converter is utilized to convert the voltage from dc-link of the inverter to the supply voltage for the AMB system. When the motor speed is too low to supply high back EMF for the buck converter, the switches of the inverter are used to boost the dc-link voltage with the motor windings. Furthermore, a hybrid controller combining sliding mode control with PID algorithm is introduced to improve the transient response of the buck converter. Several experimental results confirm the feasibility and effectiveness of the proposed method.

Efficient catalytic conversion of carbohydrates into 5-ethoxymethylfurfural over MIL-101-based sulfated porous coordination polymers

In this work, a series of MIL-101-SO3H(x) polymeric materials were prepared and further used for the first time as efficient heterogeneous catalysts for the conversion of fructose-based carbohydrates into 5-ethoxymethylfurfural (EMF) in a renewable mixed solvent system consisting of ethanol and tetrahydrofuran (THF). The influence of –SO3H content on the acidity as well as on the catalytic activity of the porous coordination polymers in EMF production was also studied. High EMF yields of 67.7% and 54.2% could be successively obtained from fructose and inulin in the presence of MIL-101-SO3H (100) at 130°C for 15h. The catalyst could be reused for five times without significant loss of its activity and the recovery process was facile and simple. This work provides a new platform by application of porous coordination polymers (PCPs) for the production of the potential liquid fuel molecule EMF from biomass in a sustainable solvent system.

FPGA Based Speed Control of SRM with Optimized Switching Angles by Self Tuning

The electromagnetic torque and speed in Switched Reluctance Motor (SRM) greatly depend on the excitation parametersi.e. turn-on angle, turn-off angle, dwell angle and magnitude of the phase currents of its phases. At lower speeds, a change in the current contributes the torque requirement which can be achieved either by voltage control (pulse width modulation) or instantaneous current control techniques. At high speeds, due to high back EMF, the regulation of current is crucial and achieved with the control of switching angles of phases. This type of control is referred as average torque control, where the torque is averaged over one stroke (2π/Nr). With constant dwell angle, advancing the phase angle influences the current into the phase winding at minimum inductance position. It has more time to get the current out of the phase winding before the rotor reaches the negative inductance slope. To maintain the speed of the motor at different load conditions, the turn-on and turn-off angles are adaptively varied. The change in dwell angle may be required where the turn-on and turn-off angle may not be sufficient to reach the required speed. In this paper, a new algorithm is proposed for self tuning of switching parameters of SRM. The proposed algorithm is simulated in MATLAB-Simulink and experimentally validated with Field Programmable Gated Array (FPGA) using MATLAB- system generator environment.

유한요소법을 이용한 서비스 로봇관절용 외전형 BLDC 모터설계에 관한 연구

This s paper presents characteristics Analysis of Outer Rotor type BLDC Motor. To reduce the cogging torque and to make the high back EMF constant of the motor, Not only magnetization directions of a permanent magnet are investigated, but also a tooth chamfer of a stator is optimized. The design and analysis results are verified with experimental results.