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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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

Tasmanian devil optimization (TDO) algorithm represents one of the most recent optimization algorithms that were introduced based on the nature behavior of Tasmanian devil behavior. However, as a recent optimizer, its performance may provide inadequate balance among the exploitation and exploration abilities, especially when dealing with the multimodal and high-dimensional natures of optimization tasks. To overcome this shortage, a novel variant of the TDO, called improved Tasmanian devil optimization (ITDO), is introduced in this paper. In ITDO, two competitive strategies are embedded into TDO to enrich the scope of the searching capability with the aim of improving the diversification and identification of the algorithm. The effectiveness of the ITDO algorithm is examined by validating its performance on CEC 2020 benchmark functions with different landscape natures. The recorded results proved that the ITDO is very competitive with other counterparts. After ITDO exhibited a sufficient performance, then, it was applied to estimate the parameters of the 1 kVA, 230/230 V, single-phase transformer. Some assessment metrics along with convergence analysis are conducted to affirm the performance of the proposed algorithm. The recorded results confirm the competitive performance of the proposed method in comparison with the other optimization methods for the benchmark functions and can identify the accurate parameters for the single-phase transformer as the estimated parameters by ITDO are highly coincident with the experimental parameters. [ABSTRACT FROM AUTHOR]

Existing calculations of leakage energy in the Litz wire winding region of high-frequency transformers usually ignore the influence of Litz wire stranded structures. Therefore, a new approach is established in this paper to accurately calculate Litz wire leakage energy through the segmented equivalent circuit approach and the two-dimensional finite element method. That is, a single Litz wire in a complete stranded pitch is segmented and equated to the linear structure of multiple inductance cells. First, the two-dimensional finite element method calculates the impedance of each strand of Litz wire. Then the strand current vector is solved according to the system equation. Finally, the current vector is substituted back into the 2D Litz wire transverse-sectional model to calculate the leakage magnetic field energy under the skin effect and internal proximity effect, which is combined with the analytical expression of the external leakage magnetic field to calculate the total magnetic leakage energy of the Litz wire winding. Calculation results indicate that the new approach has an average relative deviation of less than 2.154% and a maximum relative deviation of no more than 4.953%. [ABSTRACT FROM AUTHOR]

The development of a computational model of an induction motor with ring windings (IMRWs) for processing of nuclear waste is considered. At the first stage of the work, the overload capacity of the computational model of an IMRW was analyzed using the finite element method, the calculation being carried out in stages, taking into account the production and physical features of the IMRW prototype design. The IMRW model takes into account the influence of the oxide film on stator core sheets, technological gaps, eddy currents, and temperature conditions of the stator and rotor windings on the overload capacity of the IMRW. At the second stage, the mechanical characteristics of the IMRW were analytically calculated in the Ansys program using the parameters of the equivalent circuit determined by analyzing the design model of the motor. The calculated mechanical characteristics of an IMRW obtained by the finite element method and analytical calculation are compared with the results of testing the prototype. [ABSTRACT FROM AUTHOR]

Fe2O3 and SmFeO3 were synthesized using a sol–gel method based on Pechini's technique. At ambient temperature, an X-ray powder diffraction indicated that these compounds crystallize in the monoclinic system with Pnma, hexagonal system, and R-3c space group for Fe2O3 and SmFeO3, respectively. As a result, the current study looked into the shape and electrical properties of Fe2O3 and SmFeO3 samples. Moreover, scanning electron microscopy was used to show both substances' morphologies and average particle size. The complex impedance diagram displayed a single semicircle, showing that the response originates with the grains. Thus, an equivalent circuit has been presented to explain the impedance data. Jonscher's power law of frequency was used to study AC conductivity. Then, as a function of inverse temperature, the σdc variation supports the presence of two phases for both compounds, where a distinct conduction mechanism ensures conductivity. On the other hand, the dielectric investigation verifies the transformation of the Fe2O3 compound at T = 565 K and the start of the ferroelectric transition for the SmFeO3 compound. [ABSTRACT FROM AUTHOR]

A simulation technique for the RF signal propagation in a traveling wave accelerating structure by the method of equivalent circuits is described. Calculations have been carried out for the propagation of a signal with a frequency of 2856 MHz in an accelerating structure with a constant gradient consisting of 102 cells. The possibility of changing the energy of an accelerated beam through rotation of the signal phase within a long pulse is shown. [ABSTRACT FROM AUTHOR]

Titanium matrix composites (TMCs) are commonly used in aerospace applications and can be effectively processed using electrochemical machining (ECM). This study aims to investigate the impact of reinforced particles on the electrochemical corrosion behavior of these composites. Three alloys with varying particle contents were subjected to electrochemical characterization and dissolution experiments, revealing a mechanism of passive film fragmentation through pore corrosion. The results indicate that while the content of reinforced particles does not affect the rate of passive film formation, it does increase defects in the film, making electrochemical reactions more likely. Additionally, this study introduces a new method for measuring passive film removal time using constant potential discrete time analysis, which highlights limitations in current waveform observation methods. Finally, a model was developed to simulate TMC dissolution in NaCl solution. [ABSTRACT FROM AUTHOR]

The paper presents the results of a theoretical study of the influence of wave impedances of a shorted slot and open microstrip quarter-wave stubs on the broadband response of the transition between perpendicularly located microstrip and slot transmission lines. A formula for the transfer coefficient of such transition has been obtained that considers the electromagnetic coupling coefficient between the microstrip and slot transmission lines. It has been shown that a decrease in the coupling coefficient narrows the frequency band for a given transfer coefficient. Based on the studies performed, recommendations are provided for selecting optimal wave impedances of stubs that ensure the maximization of the operating frequency band of microstrip-slot transition. [ABSTRACT FROM AUTHOR]

When fault occurs on cross-coupling autotransformer (AT) power supply traction network, the up-line and down-line feeder circuit breakers in the traction substation trip at the same time without selectivity, which leads to an extended power failure. Based on equivalent circuit and Kirchhoff's current law, the feeder current characteristic in the substation, AT station and sectioning post when T-R fault, F-R fault, and T-F fault occur are analyzed and their expressions are obtained. When the traction power supply system is equipped with wide-area protection measurement and control system, the feeder protection device in each station collects the feeder currents in other two stations through the wide-area protection channel and a wide-area current differential protection scheme based on the feeder current characteristic is proposed. When a short-circuit fault occurs in the power supply arm, all the feeder protection devices in each station receive the feeder currents with time stamp in other two stations. After data synchronous processing and logic judgment, the fault line of the power supply arm can be identified and isolated quickly. The simulation result based on MATLAB/Simulink shows that the power supply arm protection scheme based on wide-area current differential has good fault discrimination ability under different fault positions, transition resistances, and fault types. The verification of measured data shows that the novel protection scheme will not be affected by the special working conditions of the electrical multiple unit (EMU), and reliability, selectivity, and rapidity of relay protection are all improved. [ABSTRACT FROM AUTHOR]

Matching the pumping generator (power supply) with the load (laser tube) is the determining criterion for efficient pumping of metal vapor lasers (MVLs). The challenge of achieving the energy potential of the MVL emerges when thyratrons are used as switches, which have a limited stable zone of operation with a maximum limit for most thyratrons ~ 6 kV. Matching the pumping generator with the load under these conditions is carried out providing an aperiodic discharge process of the peaking capacitor C0. Therefore, the pumping processes in the active medium significantly depend on the electrode locations in the gas discharge tube (GDT). In this work is shown, in the structure of GDT, where electrodes are located in the active medium (hot zone of the discharge channel), the pumping is occurred in the discharge process of the storage capacitor C, where C0 is a matching element. While the pumping is executed in the discharge process of C0 and the capacitance component of the GDT (CGDT) in GDT with electrodes located out of active medium where buffer gas (cold buffer zones). In this structure of GDT, the efficient pumping is realized using controlled switch, which prevents energy input going into GDT from C after charging C0 and the CGDT. [ABSTRACT FROM AUTHOR]

Controlled-source audio magnetotellurics, which is a common technology in geophysical surveys, typically uses the multichannel mode of data acquisition. Often, a capacitive coupling effect occurs among the multiple receiving wires and receiving electrodes and the earth. This effect causes the distortion of the observed apparent resistivity and phase curves. The capacitive coupling of the observation mode is simulated using an equivalent circuit model, and the characteristics of the influence of the length of the receiving wire and grounding resistance of the electrode on capacitive coupling are investigated via the forward simulation of several typical models. The capacitive decoupling of a device for controlled-source audio geomagnetic observation is studied and applied to process the measured data from the Hongtoushan mining area in Liaoning Province, China. This approach effectively weakens the capacitance coupling effect and improves observation quality, and the inversion results match well with known geological information. This study examines the capacitive decoupling technique and offers a scientific foundation for the standardization of the controlled-source audio geomagnetic data gathering technology. [ABSTRACT FROM AUTHOR]

The study of the induction periods of hydration and structure formation of cement stone is one of the most urgent problems of modern building materials science. Water and aqueous solutions of inorganic salts are the most widespread forms of mixing liquids for cement systems. The properties of distilled water and aqueous solutions of sodium chloride with different concentrations have been investigated by dielectrometry. It is proposed to consider the structural organization of water and aqueous solutions as a combination of strongly and weakly bound water. The strongly bound water is the result of manifestation of hydrogen bond forces; this type of water specifies the ordered state of the system. Weakly bound water causes fragmentation of the initial water continuum into smaller structural units. The change in the impedance and admittance spectra of cement paste during hardening has been analyzed. Spectra were measured in the frequency range from 20 Hz to 2 MHz using a capacitor measurement cell. Investigations have been performed to find the optimal equivalent electric circuits describing the transformation of the electrical properties of cement paste and the interface phenomena occurring in the near-electrode layer of the measurement cell in dependence of the hardening time. It is found that the equivalent circuit parameters are sensitive to different stages of cement paste hardening. A relationship between the spectra of electrical parameters and the processes of cement stone hardening is demonstrated. [ABSTRACT FROM AUTHOR]

Supercapacitors (SCs) have been successfully used in electric vehicles or military equipment systems for their high power density. However, the mechanical impacts from vehicle crashes and missile penetration probably cause performance fluctuations or failure of SCs, which may threaten the safety of systems using SCs. In this paper, a generalized circuit model to analyze the transient process of SCs under mechanical loads is proposed. The circuit model simultaneously takes capacitance change, internal short-circuit and resistance change into account, and an extra resistor-capacitor circuit (RCC) is added to simulate the nonlinear behavior during charging and discharging. Subsequently, the relationships between pressure and fundamental circuit parameters are determined by static methods. By taking the static test data into the circuit model, the transient response of different types of SCs under particular mechanical loading conditions is predicted. Finally, the influences of some crucial parameters on the voltage responses of SCs are revealed based on the simulations, which provide references for designing and optimizing mechanical load-resistant or self-sensing SCs in specific application scenarios. [ABSTRACT FROM AUTHOR]

In order to design wideband absorption, especially at the low-frequency band, a magnetic layer was used in the absorbing structure based on two different resistance layers. The two resistance layers were a Jerusalem cross and a ring shape made of conductive carbon black, while the magnetic layer was filled with FeSi and silicone rubber, with polymethylacrylamide and a low dielectric epoxy plate as the medium layer. The simulation results show that the absorption bandwidth below −10 dB is 3.1–18 GHz (bandwidth ratio 141.2%), the total thickness is 7.2 mm, the absorption peak appears at 4.3 GHz, and the reflection loss (RL) is lower than −40 dB. The wave-absorbing characteristics were analyzed using the equivalent circuit model, which indicated the absorbing structure maintained a good impedance match with the free space. The effects of parameters including the impedance layer resistance, magnetic coating thickness and dielectric layer thickness on the absorbing performance were analyzed. Increasing the resistance of the first impedance layer makes the absorption peak decrease, increasing the magnetic coating thickness makes the absorption peak move to the low frequency, and increasing the dielectric layer thickness makes the absorption peak increase first and then decrease. The experimental results show that the absorptive structure has an absorptive performance below −10 dB in 3.45–18 GHz, indicating that the absorber has good potential application in the field of microwave absorption. [ABSTRACT FROM AUTHOR]

This article provides a comprehensive analysis of low-profile, frequency-reconfigurable graphene dipole antennas for THz applications. The antenna consists of two graphene patches to form the bow-tie dipole and the wideband artificial magnetic conductor (AMC). Frequency tuning has been introduced by changing the chemical potential of graphene. The AMC has been designed to operate from 2 to 3.4 THz with a ± 90° reflection phase bandwidth of 50.39%. Using AMC surface, the total profile of the antenna has been achieved up to 0.09λ0 (where λ0 is free space wavelength) at the 0° operating frequency of 2.5 THz. In another approach, a hybrid surface combination of AMC and PEC has been used instead of AMC surface to enhance the radiation performance by reducing unwanted current distribution. The input impedance of the proposed antennas is almost stable and well-matched to the impedance of the THz source. [ABSTRACT FROM AUTHOR]

The structures of devices based on both an insulated-gate field-effect transistor and a bipolar transistor are proposed and theoretically investigated. The main design feature of the devices is that the drain and collector electrodes are made in the form of MOS capacitors. The manufacturing of devices does not require changes in the standard technological routes. Distributed equivalent circuits of devices are constructed, taking into account their design and technological features. SPICE-models of devices are developed and the parameters of these models are identified on numerical examples. The considered devices are elementary high-pass filters and have wide-ranging prospects for application in analog electronics. [ABSTRACT FROM AUTHOR]

A nanostructured sensor for the detection of hydrogen peroxide vapors has been manufactured. A gas sensitive film based on ZnO metal oxide doped with 2 at % La was obtained by high-frequency magnetron sputtering. In the temperature range from room temperature to 200°C, the impedance and current-voltage characteristics of the ZnO❬La❭ sensor were studied both before and after exposure to hydrogen peroxide vapors. Based on the analysis of the frequency characteristics of the complex impedance, an equivalent electrical circuit for the studied sensor structure was proposed, the parameters of its elements were estimated, and the approximating curves were calculated. It has been shown that the main contribution to the sensitivity of the manufactured sensor comes from the processes occurring on the surface of the semiconductor film. The effect of gas concentration changing on the sensitivity of the ZnO❬La❭ sensor has been studied. [ABSTRACT FROM AUTHOR]

Based on the topology of a heterostructure with quantum wells, its equivalent circuit is proposed in the form of a series connection of parallel RC-circuits describing the electrophysical properties of barrier layers and quantum wells. The scheme takes into account the properties of the process of delivery of carriers to the wells, the capture of charge carriers by them, their radiative recombination, and also the through current through the heterostructure. Expressions are obtained for finding the capacitance and resistance of a serial RC equivalent circuit, as well as expressions for calculating the active and reactive elements of the equivalent circuit. [ABSTRACT FROM AUTHOR]

A comparison is made of the characteristics of bandpass filters consisting of two interacting resonators, which are either half-wave or quarter-wave segments of microstrip transmission lines with the same widths of strip conductors. Plates with a thickness of 0.5 mm made of TBNS high-frequency ceramics with a relative permittivity ε = 80 were used as substrates for microstrip structures. The structures having a maximum coupling region of the resonators and the maximum value of their coupling to external ports with a wave impedance of 50 Ω were studied. The filters were tuned by selecting the gap between the strip conductors so that the maximum reflection level in the passband was equal to –20 dB. Electromagnetic simulation of 3D models showed that the fractional bandwidth of filters based on quarter-wave resonators is almost 2 times wider than the bandwidth of filters based on half-wave resonators, and this fact is confirmed by the measurement results. The discovered effect is explained by twice the characteristic impedance of a quarter-wave resonator relative to a half-wave one. [ABSTRACT FROM AUTHOR]

Terahertz generation through photoconductive antenna (PCA) is quite popular mainly due to the advancement of nanotechnology and material research. An extensive investigation of the interdigitated photoconductive antenna (IPCA) in the terahertz (THz) frequency band has been carried out based on numerical modeling. An equivalent circuit model for IPCA based on its electrical perspective with corresponding expressions has been solved to understand the capacitive behavior of the gap between the interdigitated electrodes. This work explores the performance of IPCA with variation 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 generated electric field and its corresponding spectral response of the IPCAs with variation in the interdigitated electrode geometry has 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 while doing the practical experiments in spectroscopy, imaging and communication applications. [ABSTRACT FROM AUTHOR]

Impedance spectroscopy is used for the characterization of electrochemical systems as well as for the monitoring of bioprocesses. However, the data obtained using this technique allow multiple interpretations, depending on the methodology implemented. Hence, it is necessary to establish a robust methodology to reliably follow-up biomass in fermentations. In the present work, two methodological approaches, mainly used for the characterization of electrochemical systems, were employed to characterize and determine a frequency that allows the monitoring of biomass in Bacillus thuringiensis fermentations by impedance spectroscopy. The first approach, based on a conventional analysis, revealed a single distribution with a characteristic frequency of around 2 kHz. In contrast, the second approach, based on the distribution of relaxation times, gave three distributions (A, B, and C). The C distribution, found near 9 kHz, was more related to the microbial biomass than the distribution at 2 kHz using the equivalent circuits. The time course of the B. thuringiensis fermentation was followed; bacilli, spores, glucose, and acid and base consumption for pH were determined out of line; and capacitance at 9 kHz was monitored. The correlation between the time course data and the capacitance profile indicated that the monitoring of B. thuringiensis at 9 kHz mainly corresponds to extracellular activity and, in a second instance, to the cellular concentration. These results show that it is necessary to establish a robust and reliable methodology to monitor fermentation processes by impedance spectroscopy, and the distribution of relaxation times was more appropriate. Key points: • Application of impedance spectroscopy for bioprocess monitoring • Low-frequency monitoring of biomass in fermentations • Analysis of impedance data by two methodological approaches [ABSTRACT FROM AUTHOR]

Energy storage batteries are currently composed of a large number of low-voltage battery cells. The state of charge of the cells is different due to the characteristic differences between cells. This causes some of the cells to be over-charged during charging and some of the cells to be over-discharging during discharging. To improve this phenomenon, this paper proposes a battery charger with an equalizing function that works during the charging and discharging processes. A performance comparison among the proposed charger and other similar topologies is carried out. The operational principle of the proposed strategy is analyzed and a control strategy with only a single voltage loop is proposed, which can guarantee two-stage charging. Experimental results show that the proposed charger can simultaneously achieve a high efficiency and the requirement of voltage equalization between cells. [ABSTRACT FROM AUTHOR]

The ultrasonic transducer employing helical slots to generate longitudinal-torsional (L&T) ultrasonic vibration is popular in the field of hard and brittle material machining. However, the design approach for this type of L&T ultrasonic transducer is not well established. An improved design model combining equivalent circuit theory and material parameter equivalent method based on stiffness variation was proposed in this study. The structure parameters of the transducer can be obtained according to given resonance frequency and nodal position. The model can further predict electrical characteristics and mechanical responses under specific excitation. For the preliminary verification of this theoretical model and the optimization of the transducer, finite element analyses were carried out to investigate the influences of slot structure parameters on dynamic performances in terms of resonance frequency, frequency separation, and amplitude of L&T vibration. After that, a prototype was manufactured according to the design results, and the measurements of impedance curve and vibration amplitude were conducted. The experimental results indicate that this prototype resonates at 24,920 Hz with an effective electromechanical coupling coefficient of 0.19. Meanwhile, the vibration amplitude in longitudinal direction is 8.1 μm and that in tangential direction is 5.6 μm under 70-V sinusoidal voltage excitation, which are consistent with the theoretical design and simulation results. Furthermore, machining tests demonstrate that surface roughness reduction and surface quality improvement can be gained by adopting this L&T ultrasonic transducer, compared to using the longitudinal vibration transducer. The proposed design approach was validated and this study can provide guidelines for the design of L&T ultrasonic transducer for rotary ultrasonic machining (RUM). [ABSTRACT FROM AUTHOR]

Decomposition is an important tool that is used in many differential systems for solving real engineering problems and improving the stability of a system. It involves breaking down of high-order linear systems into lower-order commutative pairs. Commutativity plays an essential role in mathematics, and its applications are extended in physical science and engineering. This paper explicitly expresses all form of necessary and sufficient conditions for decomposition of any kind of fourth-order linear time-varying system as commutative pairs of two second-order systems. Regarding the nonzero initial conditions, additional requirements are derived in order to satisfy the decomposition process. In this paper, explicit method for reducing fourth-order linear time-varying systems (LTVS) into two second-order commutative pairs is derived and solved. The method points out the effect of disturbance and sensitivity on the systems and also highlights the necessary and sufficient conditions for commutativity of the decomposed systems. The results are illustrated by solving some examples. [ABSTRACT FROM AUTHOR]

In this research, treated metakaolinite (TMK) was introduced into the TiO2 photoelectrode to fabricated dye-sensitized solar cells (DSSCs). The photovoltaic cells have four main natural components, i.e., a photosensitizer (carotenoid bixin), photoelectrode (TiO2/kaolinite), electrolyte (glycerine carbonate derivative), and counter-electrode (carbon). Their stability, reusability, and equivalent circuit were studied. The presence of 5% of TMK in anatase TiO2 paste decreased the TiO2 band gap from 3.21 to 3.16 eV. The result showed that the presence of 5% of TMK in TiO2 paste was more favorable to obtain higher energy conversion efficiency. Under a light intensity of 200 W/m2, it produced an energy conversion yield of 0.086%. The combination of the electrolyte and the TMK demonstrated a synergistic effect to improve the electrical properties of the DSSC. The energy storage function worked well until the third day of analysis. The DSSC based on TiO2/TMK photoelectrode exhibited 16 times better stability than pure TiO2-based photoelectrode. The Faraday charge transfer processes showed that the TiO2/TMK photoelectrode is not in direct contact with the carbon counter-electrode. [ABSTRACT FROM AUTHOR]

A device modeling and topology design method suitable for high-power-density and high-temperature applicationare important to develop with the development of devices. A novel multi-physics analysis model based on GaN high electron mobility transistor (HEMT) is proposed in this paper. The coupled electromagnetic and electrothermal model for GaN HEMT is beneficial to simulate a device's external characteristic waveform affected by different stray parameters in the surrounding. In addition, the proposed method can accurately reflect the switching loss and transient switching process of GaN HEMT. [ABSTRACT FROM AUTHOR]

In this paper, an equivalent circuit model of swastika-like structure metamaterial is investigated. Mutual inductance between adjacent swastikas ring arrays is taken into consideration in the proposed equivalent circuit model. The analytical expression for calculating the effective permeability of the windmill structure is derived. By the derived expressions, the physical mechanisms of the magnetic resonance frequency versus structural parameters are well explained. Based on the equivalent circuit model, some strategies for the fast and efficient optimization metamaterial structures can be used to achieve a better target performance in the future. [ABSTRACT FROM AUTHOR]

Analysis of cataloged data of crane asynchronous motors of the MT and MTK series is performed to verify the cataloged data reliability and compliance with the general laws of parameter variations depending on the nominal power of the motor. Analytical expressions for determining magnetic and mechanical losses as a share of total losses are obtained. These expressions are necessary to calculate the parameters of the equivalent circuit. The program developed in the Mathcad environment makes it possible to determine six unknown parameters, the resistances of the equivalent circuit, to maintain the balance of active and reactive powers. The results of calculations of the equivalent circuit parameters of all motors are given, which makes it possible to construct mechanical characteristics. [ABSTRACT FROM AUTHOR]

Many studies have been conducted on the use of nano field-effect transistor (nanoFET) sensors for the detection of biological species. However, the practical application of nanoFET-based biosensors is difficult because their operating principle has not been clarified. Most existing studies focused on ion concentration and pH level in a solution, the Debye length (the physical distance at which charged particles affect the electric field), and the surface potential of the gate electrode of the nanoFET device. In this study, we verified the operating principle of the nanoFET biosensor with an extended gate electrode and established an equivalent circuit. We experimented using a solution with different pH levels to demonstrate the operating principle of the sensor. Additionally, we analyzed the responses of the device based on the material of the extended gate electrode, the effects of the reference electrode, and the connection configuration of the electrodes. We derived an equivalent circuit to explain how the nanoFET sensor works. The analysis results show that the operating principle of measuring pH or biomolecules depends on the change of the polar capacitor in the liquid-electrode interface on the surface of the sensing electrode. The roles of the reference and extended gate electrodes were clearly explained in this paper. The results of this research will improve the understanding of the operating principle of nanoFET-based biosensors and accelerate the studies for practical biosensor applications of nanoFET devices. [ABSTRACT FROM AUTHOR]

Reconfigurable sensing antennas (RSA) play a significant role in modern internet-of-things (IOT) applications. The RSAs are capable of transmiting and receiving electromagnetic waves besides sensing different enviroment parameters. This paper introduces a reconfigurable sensing microstrip patch antenna desinged to sense high temperature variations in harsh environment. The indium antimonide (InSb) semiconductor material is a temperature sensitive material employed in RSA designs in the Terahertz (THz) frequency band. An investigation of the temperature dependency of the electrical properties of the InSb-material is introduced. The proposed sensing antenna introduces high sensitivity of 1.588 GHz shift in resonance frequency per unit change in temperature (Kelvin). The resonance frequency of the InSb sensor antenna is changed according to the surrounding environment temperature from 264 GHz to 502.2 GHz with a broadband tuning range of 90.2%. The InSb patch sensor have temperature sensing range of 150 K starting from 250 up-to 400 K. At 300 K the InSb sensor antenna proposes a peak gain of 6.4 dBi with impedance matching bandwidth of 9.57%. An equivalent circuit consists of five lumped elements is estimated for the InSb sensor antenna using particle swarm optimization (PSO) technique at different temperatures. At T = 250 K the maximum radiation efficiency is 2.5% and is increased up to 86.3% at T = 400 K. [ABSTRACT FROM AUTHOR]

Three types of nBn structures based on mercury cadmium telluride grown by molecular beam epitaxy have been fabricated. As barrier layers in nBn structures, Hg1–xCdxTe at x = 0.67 and 0.84 and the 18 period Hg0.20Cd0.80Te (9 nm) – HgTe (2 nm) superlattice were used. To study the properties of barrier layers based on nBn structures, MIS devices were created using dielectric Al2O3 films. The impedance of the created devices was investigated over wide ranges of voltages, frequencies, and temperatures. Equivalent circuits of MIS devices based on nBn structures in the accumulation mode are proposed. It is shown that measurements of the frequency dependences of the impedance make it possible to determine the values of the differential resistance of the barrier layer in a wide range of conditions. It was found that the values of the differential resistance are determined only by the bulk component of the dark current, and the surface leakage component does not affect the measured impedance of MIS devices. The dependences of the values of the equivalent circuit elements on the area of structures, voltage, and temperature are determined. It is shown that in the temperature range 210–300 K, the values of the differential resistance of the barrier layer based on Hg0.33Cd0.67Te are determined by the diffusion-limited flow of holes from the contact and absorbing layers, at the forward and reverse biases, respectively. The values of the product of the differential resistance and the area are determined for nBn structures with various parameters of the barrier layers. The possibilities of using the measurements of impedance of MIS devices based on nBn structures to study the homogeneity of properties of various layers are demonstrated.. [ABSTRACT FROM AUTHOR]

A new class of corrosion inhibitors, namely, pyridine-2,6-diamine (PD) , pyrimidin-2-amine (PA), 6-amino-3,4-dihydropyrimidine-2(1H)-thione (ADT) and ethyl (R)-6-(4-chlorophenyl)-2-mercapto-4-methyl-1,6-dihydropyrimidine-5-carboxylate (EMMD) has been used. The influence of these pyridine-pyrimidine on the dissolution of aluminum in molar HCl has been investigated using impedance spectroscopy as well as potentiodynamic polarization and molecular dynamics simulations. Impedance spectroscopy data show that values of constant phase elements, CPE are decreased. Polarization resistance and protection efficiency increase with increasing concentration of pyridine-pyrimidine derivatives as the electric double layer increased. Electronic equivalent circuit of the investigated system is suggested. Potentiodynamic polarization results showed that these derivatives are mixed-type inhibitors with mainly cathodic action. Molecular simulations are used to simulate the adsorption of pyridine-pyrimidine, on the aluminum oxide substrate. [ABSTRACT FROM AUTHOR]

Analytical equations for the voltammetric curve at the linear voltage sweep and for cyclic voltammograms for the system of connected in series resistance and capacitance were derived. The presence of the resistance results in an substantial distortion and curvature of the voltammogram, which distinguishes this system from the system with the parallel connection of the capacitance and resistance. The character of the voltammograms is determined by the ratio of the following parameters: resistance (R), capacitance (C), voltage sweep rate (v), and voltage (U). The system is capacitive in character at RC ≪ U/v, whereas the character of the system is resistive at RC ≫ U/v. [ABSTRACT FROM AUTHOR]

Brief information on the features of equivalent circuits of low-power high-frequency induction motors (HFIMs) powered by nonsinusoidal voltage from a transistor frequency converter (TFC) is presented. It is shown that the difference between active and inductive resistance in the magnetizing branch of the HFIM equivalent circuit for the fundamental harmonic of the voltage applied to the HFIM is less than in induction motors (IMs) powered by a 50 Hz voltage. Therefore, significant errors occur if the active resistance of the magnetizing branch is not taken into account when analyzing and calculating the TFC–HFIM system. [ABSTRACT FROM AUTHOR]

The experience of successful creation of samples of marine switched reluctance drives of small and medium power and the need for electric propulsion systems with a power from units to dozens of megawatts for next-generation ships has resulted in the implementation of design solutions for a switched reluctance motor (SRM). The SRM equivalent circuit is presented along with some assumptions simplifying the analysis of electric propulsion static modes. The adopted functional scheme is based on a variant with mutual loading of the test and load identical SRM. A variant of a nine-phase SRM of traditional magnetic design with the corresponding number of inverters and their capacity was chosen—the identity of the SRM and converters ensures the complete reversibility of the power circuit. The creation of a deliverable propulsion SRM for a sea tug and its subsequent no-load tests are considered, which show the motor's efficiency and compliance with vibration requirements. The main dimensions and winding parameters of this motor are presented. The specified performance characteristics are obtained due to the distinctive advantages of SRM-based electric propulsion. The idea of constructing a complete electric drive with a capacity of 1000 kW is proposed, and the distinguishing characteristics of a Schorch induction drive (ID) and a 1000-kW switched reluctance drive are presented. [ABSTRACT FROM AUTHOR]

Thermoelectric modeling is based on the profound physical analogy between heat conduction and current flow in various media. In developing the equivalent circuit, steady machining is assumed (constant spindle speed and cutter feed). That corresponds to a dc circuit. Since the current from a source is constant in any circuit conditions, a current source is used in the circuit, rather than an emf. The integral current source in the equivalent circuit corresponds to a set of thermal components. In this approach, the system consisting of the workpiece, the cutting insert, the tool holder, and the machine-tool housing may be regarded as an element in the block diagram of the thermodynamic control system for the turning of any material. [ABSTRACT FROM AUTHOR]

The cause of a methodological error in the calculations of short-circuit currents as exemplified in the power supply of a traction network with two-way supply has been shown. It is to be noted that, in an actual power supply circuit, two adjacent traction substations are connected along the 110 (220)-kV lines by mutual resistance, whereas there is no such connection in the designed arrangement. On the basis of the designed scheme, a new equivalent circuit is formed, in which the resulting traction power circuit remains unchanged. The transformation of the initial circuit has enabled removing the error and calculating the short-circuit voltages in the traction network explicitly. Replacement of a symmetric three-phase external power supply system and a traction transformer with an equivalent single-phase circuit when calculating two-phase short-circuit currents in the traction network is shown to be viable. The validity of replacement of a symmetrical three-phase network for a single-phase one has been proved both by transformation of the three-phase equivalent circuit and by means of the equivalent generator method. It is established that, despite the difference in phase resistances of substations with Y/Δ and Y/Y transformer connection circuits, equations for determination of two-phase short-circuit currents prove to be the same. [ABSTRACT FROM AUTHOR]

In order to make conductive woven fabrics with electromagnetic shielding effectiveness (EMSE) and flame retardance, polysufonamide (PSA)/stainless steel (SS) core yarn are used as the weft yarns and PSA yarns are used as the warp yarns. The conductive woven fabrics are denoted as SS-60, SS-80, SS-100, SS-120, and SS-140 according to the twist counts of the core yarn, and evaluated in terms of mechanical properties, flame retardance, surface resistivity. The test results show that the best twist of the core yarn is 120 turns/10 cm. SS-60 has the maximum burnt length, while SS-140 has the minimum burnt length. Moreover, the surface resistivity of the PSA/SS woven fabrics is proportional to the twist counts, and the surface resistivity along the warp direction is higher than that along the weft direction. Changing the fabric lamination angle can form a complete shielding network, and the EMSE is significantly increased. For SS-80, SS-100, and SS-120, when they are composed of 4–6 layers with lamination angles of 0°/45°/90°/-45°/0°/45° and 0°/90°/0°/90°/0°/90°, the EMSE is above 40 dB and the shielding effect is above 99.99 % against the incident waves at 2000–3000 MHz. Specifically, SS-120 has the maximum EMSE of 64 dB against incident waves at 2844 MHz. [ABSTRACT FROM AUTHOR]

We estimated different Van Dyke equivalent circuits for low and high power levels. The R, C, L model is compared and matched with AFC of the radial vibrations of a piezoelectric disk. The proposed conception of taking into account only constant (frequency-independent) values of dielectric, elastic, and piezoelectric loss tangents does not conflict with the analytical and experimental results. The additional loss resistor, under high power conditions, has less influence at the resonance than at the antiresonance and must be connected in series with clamped shunting capacity. [ABSTRACT FROM AUTHOR]

A photoelectrochemical method was proposed for DNA hydroxymethylation determination using black TiO2 (B-TiO2) nanosphere as photoactive material and ZnO as photoactivity inhibitor. After hydroxymethylated DNA (5hmC-DNA) was captured on the probe modified B-TiO2/ITO electrode surface through hybridization, a glycosyl can be then transferred from uridine diphosphoglucose to 5hmC-DNA and formed a covalent structure with –CH2OH in the presence of T4 β-glucosyltransferase (β-GT). Afterwards, based on a series of covalent reaction, amino functionalized ZnO nanoparticles are further immobilized to the surface of the electrode. Due to the capacity to expend the irradiation light and the photogenerated electron of electron donor, the modified ZnO nanoparticles can result in a decreased photocurrent. The developed method shows wide linear ranges from 0.05-200 nM for hydroxymethylated DNA and 1-220 unit·mL−1 for T4-β-glucosyltransferase. The corresponding determination limits were 0.013 nM and 0.24 unit·mL−1, respectively. The enzyme activity inhibited by 4-phenylimidazole was evaluated. This photoelectrochemical method shows high specificity for 5hmC-DNA (compared to 5fC, 5mC, m6A, control) and β-GT (compared to β-AGT, UGT2B7), and shows excellent stability for testing 5hmC (RSD = 2.75%). [ABSTRACT FROM AUTHOR]