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Hydrogen production technology is becoming increasingly important with the rapid development of hydrogen energy. Among existing hydrogen production technologies, alkaline water electrolysis (AWE) is drawing wide attention due to its advantages such as high maturity and low cost, and its performance analysis and optimization are important for applications. However, the AWE system contains processes with different physical and mathematical properties such as electrochemical reaction and heat transport processes, bringing difficulties to the system modeling. Moreover, the electrical and thermal processes have different characteristic time scales, and the system shows a sophisticated dynamic behavior, which has not been well studied yet. Here, a homomorphic dynamic model of the AWE system in the form of electrical circuit is built to describe the thermal and electrochemical processes uniformly, where the two parts are integrated via the energy conservation seamlessly. The model is verified by comparing with the experimental data and shows a high accuracy. The dynamic simulation analysis is conducted to investigate the dynamic response characteristics of the system under current step changes and fluctuations. The temperature overshoot and oscillation phenomena caused by delays in heat transport processes are studied. Results show that the time delay yields a maximum temperature overshoot of 10 °C, which would reduce the lifespan of the stack. This also highlights the importance of dynamic system analysis. [ABSTRACT FROM AUTHOR]

A circular ring structure monopolar printed antenna for Doppler and automotive radar systems (24 GHz) is designed with a size of 1.4λ0 × 1.4λ0 × 0.095λ0 mm3 observing |S11|> −20 dB, B.W. of 1.8 GHz and a peak gain of 5.1 dBi. This antenna upgraded initially into 2 × 1 and finally 4 × 1 array, having resonant frequencies at 24 GHz and 28 GHz, respectively. A peak gain of 7.12 and 7.16 dBi through 2 × 1 and 9 and 8.65 dBi through 4 × 1 array is observed at respective operating frequencies. Finally, the 4 × 1 array antenna with the tapered feed of size 4.4λ0 × 2.2λ0 × 0.095λ0 mm3 having |S11|≤ 40 dB at ISM-III (24 GHz) and |S11|≤ −30 dB at 5G (28 GHz) with B.W. of 0.77 GHz and 5.1 GHz, respectively, is proposed, qualifying the obtained measured results. Isolation between each antenna element for the 4 × 1 array is ≤ −20 dB with a maximum value of −65 dB. The ECC observed between antenna elements is less than 0.045 and DG is 10. An equivalent circuit is also evaluated for the proposed antenna. The quantification results present that the developed array antenna has excellent performance over the dual band. [ABSTRACT FROM AUTHOR]

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Pulsed electrochemical machining (PECM) has significant advantages for processing difficult-to-cut metal materials. Since the charge and discharge behavior of the electric double layer (EDL) in PECM greatly influences machining characteristics, an easy-to-use and time-saving method to simulate the ECM phenomenon with equivalent circuit and identify the circuit parameters (such as EDL capacitance and Faradaic resistance) is helpful for understanding the material removal rate and machining accuracy. However, identification of circuit parameters usually requires specialized equipment (such as an electrochemical workstation) to perform impedance measurements, which are cost and time consuming. In this study, an equivalent circuit model of ECM was established, and a simple method was adopted to identify the circuit parameters by analyzing time variation of the voltage and current waveforms between the workpiece and tool. The obtained circuit parameters were applied to the equivalent circuit model in the circuit simulation software, and the simulated current waveforms were compared with the experimentally obtained waveforms to verify the reliability of parameter identification. Furthermore, the established model was applied to ECM with a diode, which was usually inserted to the circuit to suppress the reverse current and reduce the tool wear in PECM. The Faradaic current and capacitive current of the workpiece anode were discussed in the simulated model, which helped understanding the material removal rate and machining accuracy in PECM. [ABSTRACT FROM AUTHOR]

In this work, we present a comprehensive study of the commutativity of fractional-order linear time-varying systems (LTVSs). Commutativity is a fundamental property in the analysis and control of dynamic systems and is often used to simplify the design of controllers. Fractional-order systems, which are characterized by a noninteger-order derivative, have been widely studied in recent years due to their ability to model a wide range of phenomena. However, the commutativity of fractional-order LTVSs has not been widely explored. In this work, we present a comprehensive study of the commutativity of fractional-order LTVSs. We first provide a mathematical definition of commutativity for these systems and demonstrate that it is equivalent to the commutativity of their transfer functions. We then propose a method for verifying the general condition for commutativity of fractional-order LTVSs under zero initial conditions (ICs) and prove it mathematically. Based on our findings, we realized that the commutative requirements, properties, theories, and conditions are general for fractional-order LTVSs, please observed that some fractional-order LTVSs are commutative, some are not commutative, while some are commutative under certain conditions. Based on this fact, we can say that not all fractional-order LTVSs are commutative.We apply explicit commutative results to several examples of fractional-order LTVSs. Our theoretical and simulation results show a good agreement and prove that our fractional-order LTVSs are commutative under certain conditions, moreover, the commutativity property holds for certain conditions and classes of fractional-order LTVSs, but not for others. Because of the application of fraction commutativity in various fields of science and engineering, we find it necessary to come up with explicit results for the first time. [ABSTRACT FROM AUTHOR]

The power and transportation sectors contribute to more than 66% of global carbon emissions. Decarbonizing these sectors is critical for achieving a zero-carbon economy by mid-century and mitigating the most severe impacts of climate change. Battery packs, which enable energy storage in electric vehicles, are a key component of electrified transport systems. The production of these batteries has significantly increased in recent years to meet rising demand, and this trend is expected to continue. However, current traction batteries exhibit lower energy density compared to fossil fuels. As a result, accurate battery models that balance computational complexity and precision are essential for designing high-performance energy storage systems. This paper provides a comprehensive review of the most used electrical models for lithium-ion batteries in traction applications, as reported in the technical literature. By exploring the strengths and limitations of different modeling approaches, this paper aims to offer valuable insights into their practical applicability for the electrification of transportation systems. Additionally, this paper discusses the primary methods employed to derive the values of the electrical components within these models. Finally, it examines the key parameters—such as temperature, state of charge, and aging—that significantly influence the component values. Ultimately, it guides researchers and practitioners in selecting the most suitable modeling approach for their specific needs. [ABSTRACT FROM AUTHOR]

This study presents an analysis of magnetoelectric nanoparticles (MENPs) through the development of equivalent circuits to predict the frequency-dependent magnetoelectric coefficient, with a focus on the widely utilized CoFe2O4@BaTiO3 core–shell configuration. This approach involves –derivation of phenomenological expressions that capture the dynamic behavior of MENPs under varying magnetic and electric fields. By integrating piezoelectric and magnetostrictive constitutive equations, along with consideration of dynamic effects and bio-load conjugation, a magneto-elasto-electric effect equivalent circuit has been constructed. This circuit model not only facilitates the investigation of longitudinal data in cube-shaped MENPs but also offers insights into fundamental biological processes. The versatility of this model is shown through translation to other core–shell nanoparticles, composite structures, and multiferroic nanostructures. This analysis provides quantitative predictions of the magnetoelectric coefficients, enhancing general understanding of MENP characteristics across a broad frequency range. Furthermore, the study highlights the framework for future refinement to incorporate intrinsic composition-specific resonances, such as ferromagnetic and ferroelectric resonances, to further significantly improve the nanoparticles' performance. Overall, this work lays the groundwork for future technology to intelligently and wirelessly control biological processes using MENPs, thus paving a way for innovative biomedical applications. This quantitative approach may facilitate further interdisciplinary research and contribute to advancement of magnetoelectric materials and their applications. [ABSTRACT FROM AUTHOR]

Understanding the internal reactions in Li‐ion batteries is crucial to analyze them more accurately and improve their efficiency since they are involved in almost every aspect of everyday life. Electrochemical impedance spectroscopy is a valuable research technique to investigate such batteries, as it reveals sensitive properties and essential information about cell reaction mechanisms and kinetics. Physical understanding of the electrochemical process and system of a battery can be analyzed using equivalent electric circuits (EECs) with rational selection of electric circuit elements and their combination. However, impedance analysis of a battery is often conducted using oversimplified EEC models in practice due to the complexity and difficulty of the physics and mathematics of the modeling. This study proposes and verifies an EEC model that represents a three‐stage mechanism for intercalation‐type materials. For the systematic model study and verifications, we investigated cathode half cells using four different layered structured cathode materials, namely, LiCoO2, LiNi1/3Mn1/3Co1/3O2, LiNi0.9Mn0.05Co0.05O2, and Ni0.815Co0.15Al0.035O2. Parametric analysis of the impedance fittings for the four different cathode materials showed similar behavior depending on the states of charge. We also provided the complete set of parameters of the four systems: charge transfer resistance, double‐layer capacitance, and solid‐electrolyte interphase (SEI) resistance and capacitance. Lastly, we explain how different electrochemical processes, such as intercalation and alloying, can be analyzed and modeled in EEC models. [ABSTRACT FROM AUTHOR]

In order to provide a convenient and fast calculation method, the equivalent circuit of a novel stacked piezoelectric cymbal vibrator is studied. The equivalent circuit model of the piezoelectric stack is derived by combining the equivalent circuit models of the thin piezoelectric disk and electrode. The equivalent circuit of the cymbal structure is then derived. The equivalent circuit model of the stacked piezoelectric cymbal vibrator is further proposed. The output axial displacements and output forces of the cymbal vibrator under different excitation voltages are investigated using the equivalent circuit model. The effectiveness of the equivalent circuit has been verified by comparing it with the finite element method. Furthermore, the equivalent circuit method has a much faster calculation speed than the finite element method. [ABSTRACT FROM AUTHOR]

The article discusses the methods of substitution of a compound motor load as a consumer of higher harmonics. Two substitution schemes were used. The calculation of the complex resistance against them was compared with the results of simulation modeling. The simulation was carried out in the MATLAB Simulink environment, with the use of the Specialized Power Systems library, in which a simulation model with motors and a source of harmonic distortion was developed. Five asynchronous motors with a squirrel-cage rotor of the AIR brand with powers varying from 0.75 to 5.50 kW were selected for the study. The simulation was carried out at different motor loads. The shaft torque varied with values of 50; 70; 90 and 100 % of the nominal values of each motor. A six-pulse diode rectifier was used as a source of harmonic currents in the network, generating harmonics with numbers 5, 7, ..., 25, corresponding to a pulse rate equal to six. Oscillograms of currents and voltages were recorded at the point of common connection of asynchronous motors and the rectifier, which were subsequently used to calculate the complex resistance. Based on the results of the work, amplitude-frequency and phase-frequency characteristics of the impedance of a composite motor load were obtained, the analysis of which revealed the incongruence of calculation methods with simulation modeling. Conclusions have been drawn on the need to continue research in this direction, since there are qualitative discrepancies in the functional dependence of the complex resistance on the harmonic number with the experimental data obtained for a single asynchronous motor. The results of the work can be used in calculating the voltage distortion factor and modeling modes associated with higher harmonics both at existing enterprises and during their design, which will increase the reliability and efficiency of electrical networks.

To address the increasing demand for high microwave‐absorbing performance, new polarization‐response wave‐absorbing metamaterials are developed herein inspired by the microstructure of locust compound eyes by employing bionics and optimization principles. The materials overcome a common limitation of wave‐absorbing metamaterials, wherein the performance substantially decreases with changes in the polarization mode, enabling the broadband absorption for x and y polarizations. The designed bioinspired materials have various shapes of structural units, triggering a multifrequency point response mechanism that effectively improves the wave‐absorbing performance. Experimental and simulation results show that the designed materials can form different equivalent circuits based on structural and polarization differences, influencing the overall wave‐absorbing performance. They exhibit an effective absorption bandwidth of ≈12 GHz (reflection loss < −10 dB) for x or y polarizations at a thickness of 2 mm. This study provides a typical example for future research on wave‐absorbing metamaterials with polarization‐response characteristics. [ABSTRACT FROM AUTHOR]

The degaussing process is crucial for ensuring magnetic protection in ships. It involves the application of oscillating and attenuating magnetic fields to eliminate residual magnetism in the ship's structure. However, this process can lead to the generation of distorted magnetic fields within the ship's cabin, posing a potential threat to electronic equipment performance. Therefore, it is essential to have a comprehensive understanding of the dynamic magnetic field response in ship structures to develop effective degaussing systems. To address this need, this paper proposes an eddy current model for analyzing the dynamic magnetic field response in ferromagnetic metal structures. This model focuses on the role of eddy currents in shaping the magnetic field response and provides valuable insights into the underlying mechanisms. Using the proposed eddy current model, the effects of key system parameters such as thickness, conductivity, and the length-scale of the ship structure can be analytically investigated. This analysis helps in understanding how these parameters influence the dynamic magnetic field response and aids in the design and optimization of degaussing systems. The effectiveness and applicability of the proposed eddy current model are demonstrated through comprehensive investigations involving two simulation cases of varying complexity. The model accurately predicts the changing trends of the dynamic magnetic field response, as confirmed through finite element simulations. This validation highlights the model's ability to reproduce simulation results accurately and its potential as a powerful tool for analyzing and optimizing dynamic magnetic field responses. In summary, the proposed eddy current model represents a significant advancement in the field. It provides a valuable theoretical framework for understanding and analyzing the dynamic magnetic field response in ferromagnetic metal structures. By offering insights into the underlying mechanisms and the influence of key parameters, this research contributes to the development of improved degaussing systems and enhances the overall magnetic protection capabilities of ships. [ABSTRACT FROM AUTHOR]

This study introduces a rheological equivalent circuit model inspired by electrochemical impedance spectroscopy (EIS) to analyze complex viscosity data. By exploiting the similarity between the Cole–Cole plot in rheology and the Nyquist plot in EIS, the study adopts circuit fitting methodologies to interpret rheological behavior of various polymers. The model employs redefined electrochemical elements, including dashpots, springs, rheological constant phase elements, and Warburg elements, to capture both linear and non‐linear responses. This approach offers both analytical and predictive capabilities, providing new insights into material composition. [ABSTRACT FROM AUTHOR]

Lithium Aluminosilicate glass-ceramics with striae (LAS-WS) and without striae (LAS-WoS) were processed using melt casting technique. LAS-WS and LAS-WoS samples were characterized and found stress birefringence >10 nm/cm and <10 nm/cm, respectively. LAS-WS and LAS-WoS samples were subjected to structural, microstructural, high temperature dielectric and electrical characterization. The presence of striation did not significantly affected the formation of β-spondumene structure during crystallization heat treatment. TEM image confirms the formation of nanocrystals in the glass matrix of lithium aluminosilicate glass-ceramics. The homogeneous distribution of LAS nanocrystals of average size of 3–6 nm is evident from TEM results. Stress birefringence distribution in lithium aluminosilicate glass-ceramic clearly shows the striae formation. Shadowgraphy images confirmed the striae free and striae containing regions in the glass-ceramic. The effect of striae on dielectric properties and AC conductivity was analysed using impedance spectroscopy and it was found that the value of the relative permittivity decreased from 415 (1.2 Hz) to 9.76 (1.2 MHz) for LAS-WoS and from 401 (1.2 Hz) to 10.3 (1.2 MHz) for LAS-WS, respectively. It was found that striae in LAS glass-ceramics influence the electrical impedance and AC conductivity relaxation process rather than relative permittivity. The effect of striae on crystallization and morphology are presented. Both the samples have shown crystallinity of more than 75 %. The electrical conductivity of σ = 2.0 × 10−3 S/cm for LAS-WoS and 2.7 × 10−3 S/cm for LAS-WS at 300 °C as well as σ = 4.6 × 10−3 S/cm for LAS-WoS and 6.9 × 10−3 S/cm for LAS-WS at 700 °C are found to be in good agreement due to increase in the electrical conductivity with temperature. The ionic conductivity of the material due to Li-ion mobility with respect to temperature and electric field and possible mechanism of AC conductivity are discussed. The results presented indicates the potential application of this material that demands high temperature operation of lithium aluminosilicate glass-ceramics. [ABSTRACT FROM AUTHOR]

In this study, we introduce a novel tunable infrared filter design aimed at stress sensor applications such as health monitoring, advanced robotics and industrial automation. The design utilizes a double-layer plasmonic frequency-selective surface (FSS) of indium tin oxide (ITO) with an aerogel inter-space region. The unique feature of this design is its ability to control the transmission pattern based on the stress exerted, which alters the distance between the two filter layers. Our approach employs both numerical simulations and a simplified model grounded in equivalent circuit theory and the transfer matrix method for accurate transmission pattern estimation where the sensor achieved a sensitivity of 20nm/MPa for average stress of 14MPa and spectrum range ( λ > 800 n m ). The work provides an in-depth analysis of how layer dimensions and inter-layer distance influence both transmission and force, taking into account the elastic properties of the inter-space material. [ABSTRACT FROM AUTHOR]

This study presents an innovative approach to attitude control in microsatellites by utilizing a spherical magnetohydrodynamic attitude control device (MHD-SACD) for three-axis attitude adjustments. A novel method is developed to quantify the output torque generated by this device, analyzing the relationship between torque, voltage, and average fluid velocity. Utilizing the energy conservation principle, an equivalent coupling circuit for the MHD-SACD is derived to assess its power dynamics. This leads to the formulation of the electromagnetic torque equation. Additionally, simulations are conducted to calculate friction torque and resultant output torque. The findings provide a qualitative assessment of the device's torque characteristics, serving as a reference for future design optimization and setting the stage for subsequent experimental investigations. This study introduces a groundbreaking perspective to the domain of microsatellite attitude control. [ABSTRACT FROM AUTHOR]

A perfect metamaterial absorber (MMA) using a SiO2 substrate has been designed. The suggested absorber model was created by implementing graphene as a metallic layer for the structured patch and copper in the ground plane of the design. The geometry of the prescribed absorber was finalized by cutting the rectangular and circular slots and loading the open-ended dual rings on the structure. Furthermore, the approach based on equivalent circuit modeling (ECM) with mathematical analysis for the proposed MMA is thoroughly discussed. The simulation outcome (S11) obtained with the help of CST software has been compared with the ECM analysis result. The proposed absorber shows a perfect absorbance of 99.97% at the operating frequency of 6.15 THz. The absorption characteristics of the suggested structure have been parametrically investigated as a function of oblique incidence and polarization angles. Furthermore, the designed structure has been analyzed by using various substrates and conducting materials to achieve the optimal value of the absorption peak as a percentage. Overall, the compact, ultra-thin, simple geometry of the prescribed MMA with a high absorption peak and polarization-insensitive nature makes it a suitable choice for utilization in sensing, imaging, and detection in the terahertz regime. [ABSTRACT FROM AUTHOR]

In this study, homogeneous NiO particles on ZnO heterojunction were incorporated with the objective of scrutinizing its probable applications in antifungal processes. Advanced instruments were engrossed to determine the phase identification, elemental composition, and particle discrepancy of the synthesized material. The electrochemical impedance response was pondered using Nyquist diagrams to accredit an equivalent circuit and extract fundamental circuit parameters. The Z″ versus Z′ plot plugged a semicircular shape, broaching the presence of heterogeneous or broad relaxation processes. The antifungal efficacy of the homogeneous NiO on ZnO heterojunction was appraised against various fungi species, including Aspergillus Niger, Aspergillus flavus, Rhizopus microspores, and Pencillium sp., at a concentration of 20 µl. These results accentuated the versatile applicability of the studied material. [ABSTRACT FROM AUTHOR]

Supercapacitors have emerged as a potential technology in the search for energy storage solutions, delivering astounding performance, environmental sustainability, safety, and economic feasibility. Biomass‐derived activated carbon electrodes have received much interest in this area because of their inherent mechanical stability and eco‐friendliness. While Wells‐Dawson POMs exhibit excellent redox properties for electrochemical performance, however, their solubility nature leads to poor conductivity. Biomass‐derived activated carbon was employed as a solid support material to address this issue, which offers high surface area and cost‐effectiveness. This work explores the synthesis of new nanofabricated electrodes by adding vanadium‐substituted Wells‐Dawson polyoxometalates (P2VW17) to activated carbon derived from lignin (LDAC). In depth, we investigated these novel nanohybrid material's structural properties and electrochemical performance. Furthermore, electrochemical testing was performed for 20 wt % LDAC‐P2VW17 in a 0.25 M H2SO4 electrolyte. The 20 wt % LDAC‐P2VW17 supercapacitor cell has an excellent specific capacitance of 216.48 F g−1, with great energy and power densities of 30.06 Wh kg−1 and 1999.98 W kg−1. Additionally, it has an excellent capacitance retention of 94.4 % over 4000 cycles with 82.6 % columbic efficiency. A test for practical application has been conducted on 20 wt % LDAC‐P2VW17. The first series of LEDs were connected to the workstation and took hold of 30 seconds to discharge. A piezoelectric buzzer was subjected to a trial as part of our testing procedure. Upon integration with our system, the buzzer produced an audible tone that persisted for 140 seconds. [ABSTRACT FROM AUTHOR]

The paper deals with the dynamics of a resistance spot welding system. At the core of this system is a transformer, which is powered on the primary side by a pulse-width modulated inverter and has a full-wave output rectifier on the secondary side that provides a direct welding current. The entire system is nonlinear, due to magnetic hysteresis and electronics. The electronics prevent the current from flowing in all parts of the welding transformer at separate time intervals during the voltage supply period; therefore, not all the parameters affect the dynamic of currents and voltages all the time so the system is also time-variant. To design a high-performance welding system and to predict the maximum possible welding current at a specific load, it is necessary to know the welding and primary currents. The leakage inductances of the system can reduce the maximum welding current significantly at higher frequencies and the same load. There are several methods to determine these currents, each with its drawbacks. Measurements are time-consuming, using professional software is expensive and requires time to learn and free open-source software has many limitations and does not guarantee the correctness of the results. The article presents a new, fourth option—a theoretical derivation of analytical expressions that facilitate straightforward and rapid calculation of the welding and primary currents of the resistance spot welding system with symmetrical secondary branches. The derivation of the mathematical expressions is based on the equivalent circuits that describe the system in different operating states. The results of the numerical simulations confirmed the derived expressions completely. [ABSTRACT FROM AUTHOR]

High‐level voltage and extremely low current are the main characteristics of Triboelectric Nanogenerators (TENGs). Despite TENGs, their Integrated Energy Storage (IES) units like supercapacitors and battery units require low‐level voltage and a high amount of current for self‐charging power applications. Using proper materials with higher triboelectric charge density is the most common approach to enhance the output current of TENGs. However, this approach alone does not satisfy the requirement of the integrated energy storage units, in which a relatively low voltage along with a sufficiently high current is needed. Consequently, alternative approaches such as employing a power management circuitry have been proposed. This paper introduces a technique based on the texture of multiple TENGs with identical small surface areas to adapt the TENGs to their IESs, specifically tailored for wearable electronics. Some experiments are conducted to evaluate the merits and limitations of the proposed approach. The experimental and analytical results are thoroughly analyzed to show the capabilities and restrictions of the method. [ABSTRACT FROM AUTHOR]

When a long cable is included in power conversion systems, it causes adverse effects, such as voltage spikes and ringing at load terminals. These nonideal voltages can break the insulation of electric machines, such as transformers and motors, and reduce their lifespan. To estimate such voltage characteristics, cable impedance should be modeled on the basis of the cable length. In this paper, two cable impedance models, a multiphysics model and an equivalent circuit model, are introduced. The multiphysics model using Ansys Q3D Extractor is suggested in consideration of the structure, material, and length of a practical cable. Meanwhile, the equivalent circuit model can be quickly utilized to examine voltage spikes and frequency. The accuracy of the proposed models is verified through simulation and the experimental results based on a motor drive system equipped with 30 and 100-m cables. [ABSTRACT FROM AUTHOR]

The magnetoelectric (ME) antennas rely on the mechanical movement of magnetic dipoles, making it possible to break the constraints on physical dimensions decided by the wavelength of the electromagnetic wavelength. The ME antennas achieve super-low frequency (SLF) communications with a smaller size to provide a novel solution for long-range, underwater, and underground communications; navigation over the horizon; and geological exploring. As a result, further theoretical research and optimization of ME antennas have been an open challenge for decades. Here, we report on minitype arrays of acoustically actuated ME antenna and their more rigorous equivalent circuits. These arrays of ME antenna adjust amplitude-frequency response through the mechanical regulation method. The mechanical parameters of ME antennas in the arrays result in regulating amplitude-frequency response, such as working frequency, fractional bandwidth, and intensity of magnetic induction. Our work provides a more accurate theoretical model and diverse array form over state-of-the-art ME antenna arrays. The frequency, fractional bandwidth, and magnetic induction strength of the ME antenna arrays were achieved to be adjustable in the ranges of 84 to 181 Hz, 3.9% to 8.3%, and two to four times, respectively. In addition, we have calculated the attenuation characteristics of ME antennas and their minitype arrays in seawater. The results show that the ME antenna array described in this manuscript is able to enhance the radiation intensity and information-loading capability, which has a positive potential for application in SLF communication systems. [ABSTRACT FROM AUTHOR]

In recent years, with a large number of distributed energy sources connected to the grid, the distribution network has shown a clear trend towards the use of power electronics. As a power conversion interface, the stability of the converter's interaction with the grid has received considerable attention. Adequate admittance (impedance) modeling of the three‐phase grid‐connected converter is a prerequisite for analyzing the stability and resonance characteristics of the grid‐connected system. Understanding the internal mechanisms and proposing effective solutions are crucial to enable power systems to effectively cope with the impact of power electronics. Therefore, by studying the admittance equivalence relationship and equivalent circuit of three‐phase AC systems in various coordinate systems, this paper focuses on solving the non‐uniqueness problem of impedance admittance modeling of three‐phase converter system. It is proposed that the input admittance of the three‐phase asymmetrical system in the dq and fb rotating coordinate systems is a 2‐order matrix and equivalent. The input admittance of the three‐phase unbalanced system in the αβ and “12” static coordinate systems is a 4‐order matrix and equivalent. From both theoretical analysis and simulation verification, it is shown that the number of eigenvalues of the three‐phase asymmetrical system in the stationary coordinate system is twice that in the rotating coordinate system, and the overall damping of the system is improved. The control strategy based on the stationary coordinate system will make the system more stable. The second contribution of this paper is to establish the equivalent circuit of the three‐phase symmetric converter system by the node admittance matrix and extend it to the multi‐machine system to explain the system instability mechanism by the circuit resonance mechanism. Finally, the frequency coupling phenomenon is studied for the three‐phase asymmetrical converter system, and it is explained that it cannot establish an equivalent circuit similar to the three‐phase symmetrical converter system. [ABSTRACT FROM AUTHOR]

As one of the most important electrical equipment in power system, the stable operation of transformer is the key factor to ensure the safety of power grid system. Winding deformation is the most common fault of transformer, which will seriously affect the reliable operation of the whole power system. Therefore, the detection of transformer winding deformation is of great significance to prevent transformer accidents. In order to further improve the reliability of transformer winding deformation detection, this paper proposes a transformer winding deformation detection method based on oscillation wave method. Firstly, the equivalent circuit model of transformer winding is established, and the transformer winding fault is simulated by changing the inductance and capacitance parameters in the model, and the law between the change of oscillation wave curve and the change of related performance indexes and equivalent parameters is obtained. Finally, the field test verification is carried out on a 10 kV transformer in the laboratory. The results show that the oscillation wave method can diagnose the transformer winding deformation and can be used for the actual transformer winding deformation detection. [ABSTRACT FROM AUTHOR]

Terahertz generation through a photoconductive antenna is quite popular, mainly due to the advancement of nanotechnology and material research. Based on numerical modelling, a thorough study of the interdigitated photoconductive antenna (IPCA) in the terahertz (THz) frequency region has been conducted. To comprehend the capacitive behaviour of the gap between the interdigitated electrodes, an equivalent circuit model for IPCA based on its electrical perspective with matching expressions has been solved. This work explores the performance of IPCA with variations in structural parameters of their interdigitated electrode geometry in the active region. The interdigitated elemental periodicity, width and length of the IPCA are varied by keeping the interdigitated gap constant between the elements. The temporal behavior of the generated electric field and its corresponding spectral response of the IPCAs with variations in the interdigitated electrode geometry have been compared. Moreover, the coupling behavior of the elements has been observed in the generated radiation. Finally, the results prove that the THz amplitude, frequency and efficiency can be enhanced by optimizing the structural parameters of the interdigitated electrode elements in the active region. This analysis is very useful when doing practical experiments in spectroscopy, imaging and communication applications. [ABSTRACT FROM AUTHOR]

his study proposes a novel approach to designing reconfigurable multiple input multiple output (MIMO) antennas operating at 26 GHz. The design process begins with determining the dimensions of polygonal patches using a transmission line model, followed by the implementation of quarter-wavelength transformers for the microstrip feed lines. The antennas are constructed on FR4 substrate, chosen for its accessibility and cost-effectiveness, with specific electromagnetic properties. A 2 x 1 MIMO antenna configuration is suggested by combining traditional polygon-type patch radiation antennas on a 50 mm x 30 mm ground plane. To address impedance mismatch issues when connecting reconfigurable antennas to a common feed line, an equivalent circuit model is employed. This model incorporates lumped elements such as capacitances, resistors, and inductors to simulate the antenna's behavior accurately. Adjustments to these components are made to achieve desired S11 and S22 characteristics. The proposed design is evaluated through simulations using HFSS and AWR, demonstrating its effectiveness in achieving the desired performance metrics. Overall, this research presents a comprehensive approach to designing reconfigurable MIMO antennas, offering insights into practical implementation and performance optimization in wireless communication systems. [ABSTRACT FROM AUTHOR]

A zero-dimensionl model is developed to study the chemical kinetics of a volumetric dielectric barrier discharge (DBD) reactor operating with humid air at atmospheric pressure. This work focuses on the relation between molecular vibrational excitation, the plasma reactor input power and the number densities of several species that are known to play an important role in biomedical applications (e.g. O 3 , NO, NO 2 ,...). A preliminary study is carried out to observe the influence of water molecules on the electron energy distribution function for different values of water concentration and reduced electric field. A simplified approach is then adopted to quantify the contribution of vibrationally-excited O 2 molecules to NO formation. The results obtained using our detailed model suggest that for the physical conditions considered in this work O 2 vibrational kinetics can be neglected without compromising the overall accuracy of the simulation. Finally, a reaction set is coupled with an equivalent circuit model to simulate the E-I characteristic of a typical DBD reactor. Different simulations were carried out considering different values of the average plasma input power densities. A particular focus was given to the influence of the Zeldovich mechanism on O 3 and NO X production performing simulations where this reaction is not considered. The obtained results are shown and the role of vibrationally excited N 2 molecules is discussed. The simulation results indicate also that N 2 vibrational excitation, and more precisely the Zeldovich mechanism, has a larger effect on O 3 and NO X production at intermediate input power levels. [ABSTRACT FROM AUTHOR]

Abstract Understanding the internal reactions in Li‐ion batteries is crucial to analyze them more accurately and improve their efficiency since they are involved in almost every aspect of everyday life. Electrochemical impedance spectroscopy is a valuable research technique to investigate such batteries, as it reveals sensitive properties and essential information about cell reaction mechanisms and kinetics. Physical understanding of the electrochemical process and system of a battery can be analyzed using equivalent electric circuits (EECs) with rational selection of electric circuit elements and their combination. However, impedance analysis of a battery is often conducted using oversimplified EEC models in practice due to the complexity and difficulty of the physics and mathematics of the modeling. This study proposes and verifies an EEC model that represents a three‐stage mechanism for intercalation‐type materials. For the systematic model study and verifications, we investigated cathode half cells using four different layered structured cathode materials, namely, LiCoO2, LiNi1/3Mn1/3Co1/3O2, LiNi0.9Mn0.05Co0.05O2, and Ni0.815Co0.15Al0.035O2. Parametric analysis of the impedance fittings for the four different cathode materials showed similar behavior depending on the states of charge. We also provided the complete set of parameters of the four systems: charge transfer resistance, double‐layer capacitance, and solid‐electrolyte interphase (SEI) resistance and capacitance. Lastly, we explain how different electrochemical processes, such as intercalation and alloying, can be analyzed and modeled in EEC models.

In this paper, a new design method of E-plane waveguide bandpass filter (BPF) using high-order modes of spoof surface plasmon polaritons (SSPPs) is proposed. The high-order modes of the double-layer SSPP (DL-SSPP) unit cell can be effectively manipulated by adjusting the dimensions of grounded metallic patterns in SSPP array, which mainly determines the filtering characteristics of E-plane waveguide BPFs. For improving the out-of-band rejection, two extra transmission zeros (TZs) are designed at the upper and lower stopbands of E-plane waveguide BPF, and then the operating mechanism of TZs is clearly investigated. Moreover, the filtering characteristics of the E-plane waveguide BPF with different transition parts are discussed to demonstrate the generalization of proposed design method. To verify the design feasibility, two examples of E-plane waveguide BPF are fabricated and measured. Good agreement between measurements and simulations shows that the proposed design method possesses good potential for the applications of high-performance E-plane waveguide BPF design.

Due to the development of electric transport and the growth of “green” energy, electric energy storage systems (ESS) are increasingly being used in the world. The growth of the battery market in the last decade has been 20-30%. One of the ways to increase the efficiency of an electric power storage device is its hybridization, i.e. the use of heterogeneous battery units. The paper examines the features of passive coupling of lead-acid and lithium-ion batteries in a hybrid storage device. A model is presented for calculating the electrical characteristics of these units during operation. The possibility of choosing a hybrid drive structure that provides a comparable operating voltage range of the units (operation without voltage converters) is demonstrated. The modes of operation of a hybrid energy storage system are modeled both for simple parallel connection and for switching blocks according to a threshold algorithm. It is demonstrated that in order to equalize the discharge rate of the main and additional units, it is necessary to coordinate the capacity of the ESS, the degree of hybridization, the type of load and the electrical parameters of the batteries, which is impossible without modeling the system. When the threshold switching of the blocks takes place, additional control parameters, making it possible to change the discharge rate of the additional block and increase the economic efficiency of the hybrid ESS. Estimates of the economic efficiency of hybrid ESSs have been made for different values of the threshold switching voltage of the lithium-ion unit, as well as for three characteristic loads: an electric forklift truck, a 30-apartment apartment building and a 300-apartment residential complex. The results demonstrate the features and technical and economic potential of passive hybridization, can be used for the design of hybrid ESSs for small power systems with solar and wind power plants, in the calculation and design of generator – storage – consumer systems.

The work presents monitoring of the corrosion rate for pure magnesium and the binary magnesium alloy Mg72Zn28. Alloying elements with a purity of 99.9% were used. The melting was performed under the protection of inert gas - argon in an induction furnace. The liquid alloy was poured into a copper mold. In order to make amorphous ribbons, the obtained samples in the form of rods were re-melted on a melt spinner machine. The next step was to perform corrosion tests in Ringer's solution. Corrosion tests were carried out at a temperature of 37°C and pH 7.2. The purpose of using Ringer's solution was to recreate the conditions for the body fluids of the human body. The use of the following research methods, such as: OCP (open circuit potential), LSV (linear sweep voltammetry) and EIS (electrochemical impedance spectroscopy), was aimed at determining the corrosion resistance of the tested materials. Tests carried out in Ringer's solution showed that pure magnesium has significantly worse corrosion resistance than the binary Mg72Zn28 alloy. The conducted research also confirmed that the cathodic reaction takes place faster on the surface of amorphous ribbons. It was also confirmed that for both crystalline materials there is diffusion of chloride ions through the corrosion product layer. SEM-EDS tests were performed on the surface of an amorphous ribbon of the Mg72Zn28 alloy after corrosion in Ringer's solution.

The application of virtual synchronous generators (VSGs) in power systems is gradually increasing to address the low inertia issue caused by the high penetration of renewable energy sources. Besides, the stability of microgrids (MGs) is threatened by constant power loads (CPLs) consisting of power electronic converters with closed‐loop controllers. To investigate the stability of the MG composed of VSG and CPL, this paper analyzes the operational principles of VSG and CPL, revealing that only the bipolar switch logic function is suitable for establishing a closed‐loop model if the output of the inner‐loop controller is considered as the duty cycle of the PWM signal. Furthermore, the closed‐loop impedance models of VSG and CPL were established in the dq frame. Impedance‐based analysis results show that the MG is prone to oscillation in the mid‐band. Therefore, the active power loop parameters of the VSG have a small impact on the stability of the MG, while the LC filter and inner loop controllers have a greater impact on the stability. Based on the oscillation mechanism and passivity theory, the impedance reshaping strategy for VSG and CPL is proposed. It is verified that the proposed control strategy can significantly improve the stability of the MG through the comparison of simulation results and theoretical analysis. [ABSTRACT FROM AUTHOR]

Period-permanent-magnet (PPM) electromagnetic acoustic transducer (EMAT) has been widely used in shear horizontal (SH) ultrasonic guided wave testing owing to its advantages, such as non-contact coupling, and convenient to excite SH waves. However, its poor transduction efficiency leads to weak signals and limits the lift-off performance. This article investigates how to improve the signal amplitude by adjusting the number of turns of the racetrack coil. The inductive coupling process of the PPM-EMAT receiver is first studied using the equivalent circuit method, and the corresponding equivalent model is obtained. Aiming at the effects of coil configurations, the equivalent impedance parameters of multilayer racetrack coils are analyzed by calculations and measurements. The proposed model can be used to predict the receiving frequency response of PPM-EMAT receivers with different coil structures, and it has been verified experimentally. It can be obtained that by choosing an appropriate coil configuration and matching resistance, the SH wave signal amplitude can be increased by 3 times. [ABSTRACT FROM AUTHOR]

In this paper, a novel dual-band circular polarization was proposed, which converts the incident linear polarization electromagnetic waves into left-handed and right-handed circularly polarized waves at 22. 1 ~ 24. 2 and 30. 1 ~ 33. 2 GHz, respectively. These two channels precisely cover the two observation channels of (23. 8 ± 0. 2) and (31. 4 ± 0. 1) GHz in atmospheric remote sensing. The insertion loss in the remote sensing observation channel is less than 1 dB, and the axial ratio is better than 1. 26. It fully meets the detection requirements of the existing atmospheric remote sensing in two observation channels of (23. 8 ±0. 2) and (31. 4 ±0. 1) GHz. For designing this circular polarizer, the circuit resonance theory was used to construct the passband, and preliminary analysis was conducted through equivalent circuits. It is optimized by the electromagnetic simulation software to complete the design. [ABSTRACT FROM AUTHOR]

Understanding the dynamics of electric-double-layer (EDL) charging in porous media is essential for advancements in next-generation energy storage devices. Due to the high computational demands of direct numerical simulations and a lack of interfacial boundary conditions for reduced-order models, the current understanding of EDL charging is limited to simple geometries. Here, we present a network model to predict EDL charging in arbitrary networks of long pores in the Debye-Hückel limit without restrictions on EDL thickness and pore radii. We demonstrate that electrolyte transport is described by Kirchhoff's laws in terms of the electrochemical potential of charge (the valence-weighted average of the ion electrochemical potentials) instead of the electric potential. By employing the equivalent circuit representation suggested by these modified Kirchhoff's laws, our methodology accurately captures the spatial and temporal dependencies of charge density and electric potential, matching results obtained from computationally intensive direct numerical simulations. Our network model provides results up to six orders of magnitude faster, enabling the efficient simulation of a triangular lattice of five thousand pores in 6 min. We employ the framework to study the impact of pore connectivity and polydispersity on electrode charging dynamics for pore networks and discuss how these factors affect the time scale, energy density, and power density of capacitive charging. The scalability and versatility of our methodology make it a rational tool for designing 3D-printed electrodes and for interpreting geometric effects on electrode impedance spectroscopy measurements. [ABSTRACT FROM AUTHOR]

The XY model is a simplified insulation model for transformers that aims to connect the frequency spectrum of major insulation, insulation paper, and oil. It enables the calculation of the paper's frequency spectrum, facilitating a quantitative evaluation of the transformer's insulation status. Given the scarcity of research addressing the accuracy of the XY model and its corresponding equivalent circuit, this paper investigates the accuracy of the XY model and conducts an in‐depth analysis of the error associated with its equivalent circuit. Firstly, the frequency spectrum of oil‐paper insulations based on the XY model with varying moisture content and structure configurations were measured, followed by the simulation of both the corresponding 2D‐coaxial and XY models. By comparing the results obtained from these simulations with experimental data on oil‐paper insulation, the accuracy of XY model is verified. Subsequently, two variants of the equivalent circuit of the XY model are derived by combining the oil, spacer, and paper differently, which denoted as Type I and II circuits. Finally, we analyzed and explained the errors present in these equivalent circuits compared with the XY model. Our findings show that the width‐thickness ratio of oil‐paper insulation is the most critical influencing factor, while moisture content and insulation structure have a less decisive impact. Notably, for general transformers, as the width‐thickness ratio is between 30 and 70, the relative error of the Type I circuit remains consistently below 0.3% across different frequencies. Consequently, the Type I circuit proves to be a more suitable representation of the equivalent circuit for the XY model in the context of general transformers. © 2024 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

This paper reports an equivalent circuit model of self‐assembled electret (SAE) micro‐electro‐mechanical systems (MEMS) vibrational energy harvesters (VEHs). For the first time, a detailed equivalent circuit model of the SAE‐MEMS VEH has been implemented on a circuit simulator, considering the device energy diagram. The implemented equivalent circuit model allows analysis of the relationship between output current and SAE properties, device structures, and electrode materials. The validity of the model is confirmed by comparing the measurement and simulation results. Thus, the proposed model would be useful for the design of SAE‐MEMS VEHs. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

This research paper presents a compact dual-band polyester-based wearable bandpass microstrip filter using stepped impedance resonator. In the proposed wearable filter, pass band of 1.85 GHz to 2.66 GHz is useful for ISM band and 3.74 GHz to 7.42 GHz is appropriate to Wi-Fi, WLAN and Wi-Max frequency band applications respectively. In this filter, insertion loss of 0.147 dB and return loss of 32.6 dB at 2.38 GHz insertion loss of 0.469 dB and return loss of 32.3 dB at 4.54 GHz with fractional bandwidth of 34% and 81% is respectively achieved. The proposed wearable filter is fabricated using polyester cloth substrate and selfadhesive copper tape. The Agilent vector network analyzer is used to test the fabricated polyester filter. Good agreement is obtained between the simulated as well as measured insertion loss and return loss of the proposed wearable filter. Equivalent circuit and SAR analysis of this filter is also presented in this paper. Novelty of this research paper is fabrication of high bandwidth dual band wearable filter that can be integrated with wearable antenna to be a wearable Filtenna. Modified equivalent circuit of SIR is prepared and validated. Simulated and measured results are found to be in good agreement. [ABSTRACT FROM AUTHOR]

We measured the S-parameters of six different types of liquid samples, such as aqueous alcohol solutions, NaCl ionic solutions, alcoholic beverages, and fruit juices in the 1 to 100 MHz frequency range, and calculated their impedance and admittance. Equivalent circuits of the liquid samples were synthesized by curve fitting on a Smith chart and Cartesian coordinates. The relationship between the impedance, admittance, and circuit element values of the synthesized equivalent circuit and the ethanol C2H5OH, polar water molecule H2O, and cation (K+ ion) that constitute the liquid sample was analyzed. Distilled alcoholic beverages showed a high impedance, but the impedance decreased after aging. Nondistilled alcoholic beverages showed a significant decrease in impedance due to cation (K+ ion). The impedance of the dehydrated reduced concentrated beverage increased significantly due to the reduction of cation (K+ ion). [ABSTRACT FROM AUTHOR]

The thickness of a metal grid represents a significant factor in electromagnetic interference shielding effectiveness (SE), and the skin depth of the uniform metal surface does not represent the critical thickness of the metal grid. In this study, the influence of Cu grid thickness on the electromagnetic interference SE and critical thickness was assessed using a theoretical model, followed by simulation analysis. According to the equivalent circuit model theory, the skin depth in the equivalent resistance was replaced by the actual thickness of the grid, and the equivalent reactance was corrected by changing the coefficient. A physical field model was established, considering the effects of different grid structures on the SE, using the finite element method. The Cu grids were fabricated in line with the simulation results, and we found that the tested electromagnetic interference SE values of the Cu grids with different thicknesses were generally consistent with the equivalent circuit model when the thickness was less than the critical thickness. The simulation demonstrated that the critical thickness of the Cu grid was constant for different periods and line widths, and the critical thickness of the Cu grid was approximately 170 nm at 1–12 GHz. When the thickness of the Cu grid was 170 nm, the average electromagnetic interference SE was 24.8 dB at 1–12 GHz. In engineering applications, grid thickness greater than the critical thickness should be preferentially designed, and the period or line width should be optimized to further improve the electromagnetic interference SE of the target frequency band. In addition, the electromagnetic interference SE of a metal grid can be quickly estimated by the equivalent circuit model, thus guiding future design work. [ABSTRACT FROM AUTHOR]

The work presents monitoring of the corrosion rate for pure magnesium and the binary magnesium alloy Mg72Zn28. Alloying elements with a purity of 99.9% were used. The melting was performed under the protection of inert gas - argon in an induction furnace. The liquid alloy was poured into a copper mold. In order to make amorphous ribbons, the obtained samples in the form of rods were re-melted on a melt spinner machine. The next step was to perform corrosion tests in Ringer's solution. Corrosion tests were carried out at a temperature of 37°C and pH 7.2. The purpose of using Ringer's solution was to recreate the conditions for the body fluids of the human body. The use of the following research methods, such as: OCP (open circuit potential), LSV (linear sweep voltammetry) and EIS (electrochemical impedance spectroscopy), was aimed at determining the corrosion resistance of the tested materials. Tests carried out in Ringer's solution showed that pure magnesium has significantly worse corrosion resistance than the binary Mg72Zn28 alloy. The conducted research also confirmed that the cathodic reaction takes place faster on the surface of amorphous ribbons. It was also confirmed that for both crystalline materials there is diffusion of chloride ions through the corrosion product layer. SEM-EDS tests were performed on the surface of an amorphous ribbon of the Mg72Zn28 alloy after corrosion in Ringer's solution. [ABSTRACT FROM AUTHOR]

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The storage mechanisms of solid-solid supercapacitors based on graphene oxide (rGO/GO/rGO) were explored by Zhang Q et al. (Zhang et al., 2014) [1], using Density Functional Theory (DFT) and Impedance Spectroscopy (EIS) to elucidate the unusual capacitive behavior of GO sandwich films. Their study revealed alternating charged layers without diffusion zones. Analysis of complex impedance (Z*) data, ranging from 10−3 to 3.106 Hz, was conducted using an equivalent circuit, though this was limited to Nyquist plot data.To further investigate charge storage mechanisms, the current study delved deeper into complex impedance (Z*) and conductivity (σ*). A theoretical approach identified relaxation processes in the imaginary parts of (Z″) and (σ'') across frequencies. Extrapolation up to 3.10^9 Hz and deconvolution confirmed three distinct relaxation processes in Z* and σ*, similar to Cole-Cole relaxation, which describes Maxwell-Wagner-Sillars (MWS) relaxation. This reflects local electrical interactions between active sites on molecular chains and counterions, creating induced dipolar moments or diffusion processes.The identified relaxations at low, medium, and high frequencies correspond well with DFT results, attributed to specific regions: graphene oxide (GO), the (rGO/GO) interface, and reduced graphene (rGO). Key parameters extracted from each relaxation, such as relaxation time, ionic strength, and conductivity values at different frequencies, showed good correlation. This approach, based on deep conductivity (σ*) analysis, effectively highlighted the charge conduction and storage mechanisms in rGO/GO/rGO supercapacitor films.

Magnetoelectric dipoles have attracted global research attention due to its broadband, unidirectional, and high front-to-back ratio characteristics. This study implemented a co-simulation between a basic magnetoelectric dipole and its front feeding circuit through the step-by-step numerical extraction of its equivalent circuit model equipped with lumped and frequency-independent components. First, the series resonance subcircuit was derived from the series resonance point in the impedance of the magnetoelectric dipole. Second, the parallel resonance sub-circuit was achieved based on the parallel resonance point. By combining the series and parallel sub-circuits according to the sequence of their resonance frequency, the final form of the equivalent circuit for the basic magnetoelectric dipole was realized. Furthermore, to obtain the component values of the proposed circuit, a numerical fitting technique was adopted to accurately match the input impedance of the antenna and its equivalent circuit. A comparison of the circuit and antenna electromagnetic simulations showed that they agreed well with each other. Hence, the correctness and feasibility of the extraction process were verified. The overall results showed that the proposed circuit model can easily substitute for a basic magnetoelectric dipole in the implementation of antenna/circuit co-simulation in circuit simulators.

Objectives. A DC/DC converter based on SEPIC topology is a unipolar electronic device which converts an input positive voltage into a stabilized output voltage of the same polarity. It also has the ability to regulate polarity both below and above the input voltage. The aim of the paper is to analyze the DC/DC converter in its both operation phases, as well as to draw up equivalent circuits and obtain characterizing differential equations using Kirchhoff’s rules for each phase. Each system of differential equations is reduced to Cauchy equations, in order to be further transformed into a limiting continuous mathematical model. Each system of equations is converted into a matrix form and subsequently combined into a single matrix system.Methods. The construction of a limiting continuous mathematical model was accomplished using Kirchhoff’s rules. Multisim software was used for the computer simulation, thus enabling the calculated results of direct currents and voltages to be compared to those of the simulation.Results. Results show that the phase coordinates of the mathematical model tend towards the values of real currents and voltages of the converter at a switching frequency higher than 200 kHz. Fairly good agreement is established between the calculated values of currents and voltages and the values obtained by simulation (with varying fill factor and switching frequency).Conclusions. The resulting limiting continuous mathematical model of the DC/DC converter based on SEPIC topology allows for an estimation of the dependence of the currents flowing through the inductor windings and the voltages across the capacitors on a number of parameters. The limiting continuous mathematical model of the DC/DC converter based on SEPIC topology is the basis for its circuit design and physical-and-mathematical analysis.

Hybrid power supply systems (HPSSs) are considered as a good option for electric power supply of remotely located from the grid consumers due to significant fuel savings compared to diesel sets. Quick development and improvement of HPSSs may be achieved using specialized methodologies and programs. In the paper a schematic diagram is proposed and operation principles of a 400 V / 50 Hz HPSS were developed. The system’s main component is the master generating unit of the hydropower plant using a 250 kW induction generator (IG). The voltage of the system is controlled by the controller of the AC/DC power converter. The electrical frequency of the system is controlled by the speed controller of the hydropower turbine. A wind turbine, an energy storage system and a regulated dump load are connected to the IG through the AC/DC converter. Goal. The paper aims to develop a methodology for steady state performance analysis of the hydraulic turbine driven isolated IG operating in parallel through an AC/DC power converter with additional sources and consumers of active power. Methodology. The methodology for evaluation of performance characteristics of the IG operating in the proposed system has been developed. The methodology is based on the equivalent circuit of the system, equations of active and reactive power balance in the system and the superposition method. Results. The equations of frequency, voltage and power regulators of the system are given. The performance characteristics of the IG operating in the system supplying resistive and RL load in «constant voltage – constant frequency» mode are obtained. Novelty. The developed methodology is innovative in taking into account the control algorithms of the system. The comparative analysis of the IG’s performance operating in the stand-alone generating unit and in the generating unit connected to the proposed system is performed. Practical value. The developed methodology can be used for development and performance improvement of hybrid AC power systems.

This study introduces a coplanar waveguide MIMO antenna design that offers both frequency and pattern reconfigurability. The antenna is intended for applications in WiMAX, WLAN, and X-Band. It is constructed using an FR4 substrate with dimensions of 1.6mm thickness and 0.025 loss tangent. Based on the proposed design, MIMO antennas can operate at 3.5 & 3.9GHz (WiMAX), 5.5 & 5.8GHz (WLAN) and 10.5 & 12.5GHz (X-Band). To accomplish this, two open-circuited 3mm x 3mm quatre wavelength transformers are linked to each radiator through PIN diodes. The performance enhancement of the reconfigurable MIMO antenna was fine-tuned utilizing microwave solvers in both CST and ADS. The system’s performance was validated through practical measurements. Furthermore, the analysis of diversity conducted on the suggested antenna reveals that the antenna has a low correlation coefficient (