Search Results (174)

External steep-front transient overvoltages may introduce high-frequency electromagnetic disturbances into modular multilevel converter-based high-voltage direct current (MMC-HVDC) systems, resulting in additional transient voltage stresses on converter valves and their sub-modules. This paper investigates the propagation, coupling, and transient voltage distribution characteristics of external high-frequency disturbances in MMC converter valves using a multi-scale wideband equivalent model covering the “sub-module–converter valve–converter station” hierarchy. A wideband equivalent model of a 4.5 kV/3 kA press-pack insulated gate bipolar transistor (IGBT)-based sub-module is developed and integrated with the distributed parasitic parameters of the valve tower and the high-frequency characteristics of converter-station components. To investigate the converter-valve response under different transient conditions, a representative lightning impulse is considered as an engineering transient condition, while a controlled fast-front impulse is employed to investigate the intrinsic high-frequency propagation and resonance characteristics of the distributed converter-valve network. Simulation results demonstrate that external transient disturbances can propagate into MMC converter valves through grounding parasitic capacitances and distributed coupling paths, resulting in additional differential-mode transient voltage stresses at sub-module terminals. Sub-modules closer to the disturbance source experience higher transient voltage peaks and larger dv/dt values. Moreover, multiple local resonance bands are identified within the valve tower, with high-frequency oscillatory components above 10 MHz being strongly influenced by the distributed parasitic network. Parameter analysis further indicates that the sub-module stray inductance has an important influence on the magnitude and oscillatory characteristics of the induced transient voltage. The proposed multi-scale modeling approach provides a practical method for evaluating high-frequency transient voltage stresses in MMC-HVDC converter valves and provides theoretical support for insulation coordination, converter-valve structural optimization, and transient reliability design of HVDC transmission systems. Full article

We review recent calculations and numerical simulations showing the formation of coherent states of protons in hydrogen-loaded metals with a cubic crystal lattice. The characteristic frequencies discussed here are the local proton frequency, the plasma frequency, and the resonant confined electromagnetic frequency; depending on the adopted parameters, they are of order ${10}^{13}$–${10}^{14}\mathrm{Hz}$. They are far from the much higher frequency corresponding to the full electron-capture energy transfer. In these states protons oscillate coherently and in a fixed phase relation with a strong high-frequency electric field which is trapped in the material, especially if the material is made of micro-powders. The energy gap of the coherent ground state is estimated to be well above thermal energies, of the order of a fraction of an eV per particle, and therefore large enough to make the state robust against thermal fluctuations. The analytical calculations address the realistic case of a large number of protons, in the rotating-wave approximation. The numerical calculations are presently limited to a small number of protons but go beyond the rotating-wave approximation and allow one to take into account a dissipation term associated with the strong oscillating electric field. The next task of this theoretical model is to compute the excited states of the coherent system. A simplified interacting-qubit model gives evidence of collective transition energies larger than the single-oscillator spacing. It does not yet establish whether a realistic external pump can populate such collective excited states with appreciable probability, nor the overall pump-to-capture conversion efficiency in a realistic proton lattice. If suitable states can be populated, their de-excitation could make some electron-capture processes energetically possible, with generation of slow neutrons. This dynamical mechanism offers an alternative to the Widom–Larsen hypothesis of “heavy electrons”, and is closer to current models in mainstream physics. The consequences, in terms of nuclear transmutations, of neutron generation via electron capture would be similar to those already known in the literature. Full article

High penetrations of converter-interfaced wind and photovoltaic (PV) generation erode synchronous inertia and make plant-level frequency support increasingly dependent on time-varying active-power headroom. Here we propose a risk-credibility-recovery primary frequency regulation (RCR-PFR) strategy for wind–PV renewable energy stations. The controller maps frequency excursion and negative rate of change of frequency (RoCoF) to a bounded frequency-drop risk index, converts reserve margin, resource volatility, downward trend, ramp-rate feasibility, and saturation margin into an executable-reserve credibility index, and dispatches wind and PV support under capacity and ramp-rate constraints. A recovery-debt term retards premature support withdrawal, while a battery energy storage system (BESS) compensates only the residual demand that remains infeasible after wind–PV projection. In the standard load-step case, RCR-PFR raises the frequency nadir to 49.788 Hz, 0.132 Hz higher than the no-renewable-PFR case, and reduces the secondary frequency dip by 73.4% relative to fixed-ratio allocation. In a constrained-reserve stress case, H = 3.0 s denotes a low-equivalent-inertia condition and the 0.105 p.u. disturbance corresponds to a 105 MW load increase on a 1000 MVA base. Under this condition, residual BESS compensation raises the nadir from 49.595 Hz to 49.813 Hz, limits the maximum frequency excursion to 0.187 Hz, eliminates the 4.24 s low-frequency interval below 49.8 Hz, and reduces unmet support energy from 1.2324 MWh to 0.0114 MWh. These single-area simulations indicate that RCR-PFR can improve frequency-security margins, executable-reserve utilization, and withdrawal-stage stability, although multi-machine, electromagnetic-transient, hardware-in-the-loop, and field validation remain necessary before plant-level deployment. Full article

Electric-field measurement in emerging power systems requires compatibility with multiple frequency bands, high field strengths, and complex electromagnetic environments. This study proposes a low-frequency AC electric-field amplitude reconstructed method based on the nitrogen-vacancy (NV) center in diamond. A Hahn–echo sequence converts the electric-field-induced quantum phase accumulation into NV fluorescence variations, and the field amplitude is retrieved through time-domain fitting and frequency-domain feature extraction. A parallel-plate electric-field generator was first calibrated using a standard electro-optic probe, followed by measurements at 2500 Hz. With the electro-optic probe result as the reference, the reconstructed electric-field amplitudes showed good quantitative agreement in the moderate-field range, with a best single-point absolute deviation of 0.0219 kV/m, while larger deviations were observed at the lower and higher ends of the tested amplitude range. By adjusting the Hahn–echo sequence to match different field periods, amplitudes at 1500 Hz and 2000 Hz were also successfully retrieved. The results demonstrate that the method is applicable to narrowband AC electric fields at known frequencies within a certain range, supporting an experimental basis for applying quantum sensing technology to power-equipment condition monitoring and measurements in complex electromagnetic environments. Full article

Light Fidelity (LiFi) has emerged as a promising wireless communication technology for enabling indoor networks in future sixth-generation (6G) systems. It can offer very high data rates, low electromagnetic interference, elevated spatial reuse and inherent physical layer security advantages. In LiFi-based indoor deployments, however, the characteristically small coverage footprint of each AP can produce frequent handovers when users move across the indoor environment. Conventional key management approaches adopt static key lifetime policies that expire session keys after a fixed duration regardless of user movement conditions. This creates a fundamental inefficiency where static policies can generate key refresh operations that are not required. Further, an additional signaling overhead can happen when users are stationary or leave session keys active for comparatively long periods under high mobility conditions. This paper proposes a lightweight mobility-aware adaptive session key lifetime control mechanism that dynamically adjusts session key validity duration. The mechanism introduces a three-component mobility metric that aggregates user speed, handover frequency and AP residence time which is used to compute a normalized mobility risk score. The mobility score drives an adaptive lifetime formula that contracts or extends key validity according to mobility-associated exposure conditions. The proposed mechanism operates entirely within the post-authentication session phase and does not introduce new cryptographic primitives, authentication protocols or key generation algorithms. Compared with fixed session key lifetime policies of 120 s, 300 s and 600 s, the Adaptive Key Lifetime Control Engine (AKLCE) dynamically adapts the session key lifetime according to user mobility, reducing refresh operations and signaling overhead under low mobility while progressively shortening the scheduled key lifetime under higher mobility to limit key exposure. This adaptive behavior enables AKLCE to provide mobility-dependent adaptation of session key lifetime that enables a flexible trade-off between key exposure duration and signaling overhead. Full article

Autonomous robotic systems designed for extraterrestrial in situ resource utilization (ISRU) will play a central role in enabling a sustained human presence on the Moon and Mars. These robots are expected to perform tasks such as regolith excavation, water extraction, oxygen production, and propellant generation under extremely harsh environmental conditions, including large temperature variations, abrasive dust, high radiation levels, and significant communication delays with Earth. Consequently, their onboard electrical systems must operate with high reliability, autonomy, and fault tolerance. A critical enabling technology for these systems is the isolated power conversion architecture, which distributes energy from primary power sources to multiple robotic subsystems, including mobility actuators, drilling systems, sensors, computing units, and thermal management modules. Future lunar and Martian missions are expected to rely on a combination of alternative energy sources, including solar photovoltaic arrays with energy storage, fuel cells, radioisotope power systems, and nuclear surface power reactors, which can provide continuous and high-density energy independent of sunlight availability. These diverse power sources require flexible and highly efficient isolated DC–DC power conversion architectures capable of managing wide input voltage ranges while ensuring electrical isolation, safety, and system stability across distributed robotic platforms. This literature review surveys recent developments in autonomous isolated power conversion architectures suitable for lunar and Martian resource extraction robots. The review examines advanced converter topologies such as resonant converters, phase-shifted full-bridge converters, dual-active bridge converters, and modular multiport power converters designed for high efficiency, high power density, and scalable power distribution. Emphasis is placed on converter architectures capable of interfacing with nuclear-powered systems and other high-energy-density sources while supporting distributed loads in robotic mining and processing systems. In addition, the paper reviews emerging autonomous control strategies, including adaptive digital control, intelligent power management, fault detection and self-recovery mechanisms, and distributed power architectures capable of maintaining stable operation under dynamic load conditions. The role of wide-bandgap semiconductor technologies, including silicon carbide (SiC) and gallium nitride (GaN), is also examined, highlighting their potential to enable higher switching frequencies, improved efficiency, reduced system mass, and enhanced thermal performance in vacuum environments. Finally, system-level considerations for integrating isolated power conversion within robotic ISRU platforms are discussed, including redundancy strategies, power bus architectures, electromagnetic compatibility, thermal management, and long-duration reliability requirements. By consolidating advances across power electronics, autonomous control, and space power systems, this review identifies key research gaps and outlines design directions for next-generation autonomous power conversion systems capable of supporting scalable lunar and Martian resource extraction infrastructures powered by both renewable and nuclear energy sources. Full article

High-frequency induction (HFI) tube welding is an energy-intensive process in which the impeder plays a critical role in power utilization. Conventional ferrite cores often operate near magnetic saturation in small-diameter applications, which can limit efficiency and process stability, particularly under high production rates. Soft magnetic composites (SMCs) offer higher saturation potential, but their internal behavior under welding conditions is difficult to assess experimentally. To address this challenge, this study proposes a methodology for evaluating impeder performance without relying on industrial-scale trials. The approach combines a three-dimensional electromagnetic–thermal model of the welding process with a reduced two-dimensional model for detailed analysis. The predictive capability of the 3D model was assessed through comparison with experimental measurements, providing an initial experimental validation under the investigated operating conditions. Based on this reference, a 2D model is derived by removing the tube and introducing an equivalent correction factor, obtained through comparison with the 3D results, to account for its influence. The reduced model is then used to investigate the internal thermal behavior of a representative SMC (Fluxtrol 50) impeder. The results reveal a pronounced hotspot in the region corresponding to the inductor position, with significantly higher temperatures than in other areas, indicating a critical thermal limitation for operation. The proposed methodology provides a reliable and efficient framework for analyzing and designing impeder systems, offering a practical alternative to costly industrial testing. Full article

During train operation, railway traction-returning current generates a power-frequency magnetic field around the rail, offering a potential energy source for self-powered trackside monitoring nodes. The H-shaped-core magnetic field energy harvester (MFEH) is attractive because it can be installed beneath the rail without enclosing the conductor, yet its output is strongly affected by the coupled rail-core-coil system. To clarify these effects, a three-dimensional electromagnetic-circuit-coupled finite-element model of an experimentally validated laminated-silicon-steel H-shaped-core MFEH was established to examine core and coil parameters. Increasing the center-leg and side-leg lengths weakens demagnetization but intensifies eddy-current losses, causing output power to approach saturation. Under a 50 Hz, 300 A current in a 54E1 rail and series-tuned matching, output power approaches 5.1 W beyond a center-leg length of 1000 mm and 3.25 W beyond a side-leg length of 700 mm. Within the investigated ranges, center-leg and side-leg lengths of approximately 800 and 400 mm provide the best power–volume performance, respectively. Increasing side-leg height or width also improves output. A larger coil span improves output by reducing internal resistance, whereas more turns yield diminishing gains because of higher winding and eddy-current losses. These findings provide a quantitative basis for parametric design of H-shaped-core MFEHs in railway environments. Full article

We carried out a study on adjusting the voltage at the output terminals of a three-phase synchronous generator using the voltage encoder EMBSIN 121u. The purpose of this study was to increase the quantity and quality of the electrical energy produced by the generator. This paper is innovative as the author generates three models in MATLAB-Simulink to study voltage adjustment in a three-phase synchronous generator with electromagnetic excitation in two distinct cases: case 1, running the three-phase synchronous generator with a variable load and constant frequency, and case 2, running this generator with a constant load and variable frequency. In the first case, the voltage is adjusted through an automatic voltage adjustment system equipped with a proportional integrative (PI) controller (model 1) or through a fuzzy logic (FL) controller (model 2). The voltage is adjusted in the second case through an automatic voltage adjustment system equipped with a PI controller (model 3). In the case of the automatic voltage adjustment system with a fuzzy logic controller, the electrical energy supplied by the three-phase synchronous generator will be higher than in the case of the automatic voltage adjustment system equipped with a PI controller (at the moment, t = 6 s: $S_{gen\_PI}=158.2$ (VA) and $S_{gen\_FL}=230.7$ (VA)). Moreover, to implement the adjustment algorithm of the three-phase synchronous generator voltage through the voltage encoder EMBSIN 121u, the author has created a program in the programming environment Arduino IDE. The results of this study could also be used for three-phase synchronous generators with electromagnetic excitation used to construct wind power stations. Full article

To satisfy the demands of 5G communication and reliable data connectivity for unmanned aerial vehicles (UAVs), a novel two-element dual-band MIMO antenna with an inherent self-decoupling property based on orthogonal linear polarization diversity is proposed. Distinct from conventional designs relying on extra decoupling components, the antenna realizes isolation enhancement via coupled currents between annular strips and S-shaped strips without additional decoupling structures, representing the core design novelty. Fabricated on a low-cost 1.6 mm thick FR4 substrate, the antenna features compact overall dimensions of 60 mm × 30 mm × 1.6 mm, covering the 2.40–2.73 GHz ISM band and 3.38–3.63 GHz 5G Sub-6 GHz band. Measured results demonstrate that the reflection coefficient remains below −10 dB across the entire operating bands, with port isolation exceeding 27 dB for the 2.4 GHz band and 20 dB for the 3.5 GHz 5G band. The measured realized gain is 0.7–1.5 dB in the lower band and 2.3–2.9 dB in the upper band. The radiation efficiency, which is obtained exclusively from ANSYS HFSS 2025 R1 simulation, is higher than 90% for the lower band and over 80% for the upper band. The calculated envelope correlation coefficient (ECC) is less than 0.15 throughout the working bandwidth, which effectively suppresses inter-channel electromagnetic interference and mitigates channel fading caused by varying UAV attitudes to improve system channel capacity. Further verifications via epoxy encapsulation and co-simulation on an eight-rotor UAV platform prove slight frequency drift after packaging and installation, whereas its bandwidth and isolation still meet practical engineering requirements. Benefiting from a compact layout and omnidirectional radiation performance, the proposed low-cost MIMO antenna is convenient for conformal integration into a UAV fuselage, improving the practicability of UAV-aided emergency communication, equipment inspection and 5G network coverage. Full article

With the expansion of electromagnetic wave communication frequency bands and the improvement of integrated circuit integration, electromagnetic waves emitted by on-chip antennas are easily scattered by electronic components, causing radiation pattern distortion, which limits the improvement of integration and communication stability. Traditional cloaks can reduce electromagnetic scattering, but they cannot achieve broadband and omnidirectional performance simultaneously, and are mostly designed for external sources, making it difficult to protect on-chip antenna radiation patterns. In this work, a broadband air-impedance-matched metamaterial (AIMM) with characteristic impedance matched to free space is proposed in 2–8 GHz, with geometry-tunable phase delay and transmittance higher than 93%. Based on AIMM, a broadband source-surrounded cloak (SSC) is designed, which can guide electromagnetic waves from the surrounded source to bypass obstacles in any direction and restore the original wavefront outside the cloak, so as to protect the radiation pattern from scattering distortion. Numerical simulations show that the SSC works well in the whole bandwidth and remains effective when the source is offset. This work has important potential for improving the integration of integrated circuits and the stability of communication systems. Full article

Underwater communication is essential for marine research, yet saline environments pose significant challenges as electromagnetic waves suffer from severe attenuation and optical systems face scattering. Consequently, acoustic transmission remains the most practical method for medium- to long-range communication. This study investigates the impact of salinity, transmission frequency, and propagation distance on signal integrity, specifically focusing on the feasibility of using a square-wave carrier with On-Off Keying (OOK) modulation as a simpler, low-cost alternative to traditional sinusoidal frequency-shift keying (FSK). Experiments were conducted in a custom glass tank and analyzed via MATLAB. The results reveal that increased salinity and higher frequencies led to greater signal distortion and attenuation, which complicates reliable binary recovery. However, despite these environmental hurdles, the study demonstrates that square-wave OOK allows for successful binary data recovery over short distances. The findings suggest that simplified modulation schemes could potentially be used for short-range underwater communication in controlled environments, particularly where minimizing system complexity is of concern. Ultimately, the work provides valuable insights into how environmental factors influence acoustic signal integrity, offering a preliminary basis for future development of accessible and efficient underwater communication platforms targeted to shallow water communication. Full article

Wireless power transfer (WPT) systems for electric vehicles (EVs) are increasingly being studied in the MHz range to increase power density and reduce the size of passive components. However, operation at higher frequencies significantly changes electromagnetic interference (EMI) behaavior. Fast switching in SiC- and GaN-based inverters, high-Q resonant operation, and frequency-dependent parasitic capacitances create conductive, capacitive, and magnetic interference mechanisms that are less significant in conventional kHz-range systems. Although many existing studies focus on power-transfer efficiency and converter optimization, EMI mechanisms in MHz-range EV WPT systems remain insufficiently systematized from a system-level electromagnetic perspective. This paper presents a state-of-the-art review of EMI generation mechanisms and system-level effects in high-frequency WPT systems for electric vehicles. The review considers the main interference sources and coupling paths, including switching-induced common-mode currents, resonant amplification of current and voltage stress, capacitive coupling between the coupler and nearby conductive structures, and magnetic-field redistribution caused by coil misalignment. Special attention is given to the transition from lumped-element assumptions to more distributed electromagnetic behavior at higher frequencies. The review also discusses the possible impact of these mechanisms on vehicle electronic subsystems and highlights the need for frequency-aware electromagnetic design, integrated modeling, and more rigorous EMC assessment for reliable MHz-range wireless EV charging systems. Full article

This paper presents a comparative analysis of Flywheel Energy Storage Systems (FESS) employing Permanent Magnet Synchronous Machines (PMSMs) and AC Brushless DC (AC-BLDC) machines for fast and efficient frequency regulation. The study examines their electromechanical behavior during the key operational stages of charging, standby, and discharging, with a focus on mitigating inrush current and enhancing overall system efficiency. MATLAB/Simulink models were developed to evaluate machine dynamics, electromagnetic behavior, and harmonic distortion during their operation. The results show that electromagnetic effects, particularly inrush current, commutation harmonics, and inverter limitations, significantly influence torque smoothness, efficiency, and overall system performance. PMSMs demonstrate superior torque quality, lower Total Harmonic Distortion (THD), and more stable energy conversion under Field-oriented Control (FOC), making it well suited for high-performance FESS applications. In contrast, the AC-BLDC machine exhibits higher torque ripple and elevated THD due to six-step commutation but offers a simpler drive topology and cost advantages. The findings offer practical insights for selecting machines and controllers in high-speed FESS designs and emphasize the importance of mitigating transient electromagnetic effects to enhance efficiency and reliability in modern grid support applications. Improved modeling incorporating magnetic saturation, frequency-dependent iron losses, and inverter constraints is essential for accurate performance prediction. Future work includes Hardware-In-the-Loop (HIL), Power-HIL validation, and DlgSILENT PowerFactory co-simulation to confirm dynamic performance under grid-connected operation. Full article

A pressing challenge of modern wireless networks is ensuring stable radio coverage inside buildings, where radio signal propagation is significantly complicated by the influence of building structures. Reinforced concrete walls, floor slabs, internal partitions, and energy-efficient windows with metallized coatings create substantial obstacles to the propagation of electromagnetic waves, causing reflection, absorption, and scattering. As a result, areas with weakened coverage are formed inside buildings, leading to deterioration in mobile communication quality and reduced data transmission rates. This study presents an experimental investigation of the received signal strength of mobile operators inside a multi-storey residential complex. An analysis was conducted to evaluate the impact of building height, architectural features, and construction materials on radio signal propagation. In addition, the frequency bands used in 4G LTE and 5G networks by mobile operators were examined. It was found that LTE networks mainly operate in the 1.8–2.1 GHz frequency range, whereas 5G networks operate in the n77 band (3.6–3.7 GHz), which provides higher data throughput but is characterized by greater signal attenuation when propagating inside buildings. To address this issue, a Distributed Antenna System (DAS) based on GPON technology was implemented in the studied building. The placement of antenna equipment on the roof enabled the efficient reception of the signal from the base station and its subsequent distribution inside the building through an internal antenna network. The measurement results demonstrated that the deployment of a GPON-based DAS significantly improves the received signal level and ensures more uniform radio coverage inside indoor environments. The obtained results confirm that the use of distributed antenna systems is an effective solution for compensating signal losses caused by the shielding effect of building structures and can significantly improve the quality of mobile communications in dense urban environments. The results show that the RSRP level in indoor environments without DAS decreases to approximately −100 to −110 dBm, while after deployment of the GPON-based DAS, it improves to −45 to −75 dBm. This corresponds to a signal gain of up to 40–50 dB, ensuring stable connectivity and significantly improved data transmission performance. Full article