Equivalent Circuit Model Research Articles

A Triple-Tunable Dual-Band Metamaterial Absorber Based on Dirac Semimetal and InSb

The dynamically triple-tunable dual-band metamaterial absorber that can be electrically, thermally, and magnetically controlled is proposed in this paper. The absorber is composed of bulk Dirac Semimetal (BDS), SiO2, and InSb layers. The physical absorption mechanism can be analyzed theoretically by the equivalent circuit model (ECM) and electric field intensity distributions at absorption peaks. In the absence of applied magnetic field, based on the bright–bright coupling effect, the average absorption rate of dual-band absorber can reach 99.4% when the Fermi energy of the BDS is 0.13 eV and the temperature of the InSb is 475 K. When the applied magnetic field is along the X axis, the absorption frequencies and rates of dual-band absorber can be electrically tuned by adjusting the BDS Fermi energy and thermally and magnetically controlled by adjusting the InSb temperature and magnetic field. Furthermore, the impacts of parameters in dual-band absorbers and the application prospects of the dual-band absorber model as a refractive index sensor are further discussed. This work provides a theoretical basis for the designs of triple-tunable absorbers and sensors.

Chemi-Impeditive Sensing Platform Based on Single-Walled Carbon Nanotubes.

Chemical sensing methodology based on electrochemical impedance spectroscopy (EIS) targeting analytes in aqueous samples on functionalized single-walled carbon nanotube (SWCNT) is reported. The SWCNT in contact with electrolyte shows unique impedance spectra that cannot be analyzed with classical equivalent circuit models. Inspired by the charge transport property of mixed ionic-electronic conductors, we propose an equivalent circuit based on transmission line model (TLM), by which the impedance of the CNT-electrolyte system can be analyzed to track down all the equivalent circuit parameters. By combining multiple pieces of information, which are technically immeasurable with conventional chemiresistive or chemicapacitive techniques, several analyte species responding to the sensor can be differentiated from each other. We demonstrate the "chemi-impeditive" concept on chemically modified SWCNTs for detecting perfluoroalkyl substances (PFAS) in aqueous solutions. The EIS coupled with a fluorination chemistry on SWCNT surface provides unique changes in equivalent circuit components for each PFAS, i.e., changes in CNT and solution resistances, as well as interfacial CNT-solution capacitance, through which perfluorooctanesulfonic acid, perfluorooctanoic acid, hexafluoropropylene oxide dimer acid, and perfluorobutanesulfonic acid are detected in a discriminative manner. The new impedimetric method opens up new vistas in chemical sensing in that the EIS analysis provides an additional dimension of information beyond the single resistance or capacitance typically measured by many conventional types of sensors.

Interpretation of the degradation and trends in the performance of heterojunction silicon solar cells at low temperature

A compact model that combines numerical simulations using AFORS-HET and accurate equivalent circuit modelling is proposed and used to interpret the origins of the degradation and anomality's in the performance of the a-Si:H/c-Si heterojunction solar cells and its parameters at low temperature. The interpretations are applied to several trends reported on real cells. It is shown that as T decreases the a-Si:H(i) layer is depleted gradually from holes and that the cell operation fails once the layer is totally depleted and becoming intrinsic. The failure is caused by a substantial and sharp increase in the cell series resistance causing the collapse of the fill factor and of the cell current. It is found that at low temperature the open circuit voltage is significantly affected and its temperature dependence strongly distorted by hole depletion in the a-Si:H(i) spacer especially when the TCO work function is not appropriate. It is aslo shown that the S-shape in the cell I-V characteristics under illumination is closely linked to the TCO barrier reverse saturation current which explains its higher probability of appearnce at low temperature. Finally, it is concluded that the HJT cell would perform optimally down to the low 200 K range when the a-Si:H(p) is heavily doped and the front contact is ideally ohmic. Failing to satisfy such conditions the temperature range in which the HJT cell is useful is very limited.

A new optimization strategy, the influence of hollow electrode chamfers on the development of helium atmospheric pressure plasma jets

This work suggests applying chamfering treatment to the plasma generator of the empty electrode structure. Enhancing the electrodes’ physical structure can significantly improve plasma characteristics without requiring intricate control systems. Experiments have shown that changes in the electrode’s shape can lead to changes in the formation of the atmospheric pressure plasma jet. Specifically, our observations indicate that an increase in the chamfer radius leads to an increase in the ignition voltage and a greater density of reactive species inside the jet. We developed a multi-channel equivalent circuit model to describe the discharge process of a plasma jet. Then, using the mixed layer theory, we investigated the effect of the chamfer radius on the plasma jet. Our findings suggest that chamfering increases the effective discharge area, resulting in more discharge channels in the model. This leads to a higher density of reactive species. Additionally, chamfering improves the mixing of helium and air, increasing the concentration of N2 and O2. This consumes some of the avalanche electrons and raises the ignition voltages, ultimately enhancing the chemical reactivity of the plasma jet. This work provides new ideas for the optimization strategy of atmospheric pressure plasma radiation devices.

Unravelling the Electrochemical Impedance Spectroscopy of Hydrogenated Amorphous Silicon Cells for Photovoltaics

Abstract This research reveals the application of electrochemical impedance spectroscopy (EIS) in analyzing and improving the performance of hydrogenated amorphous silicon (a-Si: H) based photovoltaic cells. As a non-destructive technique, EIS provides deep insight into the electrochemical characteristics of photovoltaic cells, including series resistance, layer capacitance, recombination mechanisms, and charge transport. The impedance data is obtained and analyzed using small AC potential signals at various frequencies via Nyquist diagrams and Bode plots. This analysis allows the identification of resistive and capacitive elements as well as the evaluation of the quality of the interface between the active layer and the electrode. The results show that EIS can identify internal barriers that reduce the efficiency of a-Si: H solar cells, such as dominant recombination mechanisms and inefficient charge transport. Using equivalent circuit models, electrochemical parameters are extracted to reveal cell behavior and performance. In addition, these results also confirm that EIS is an important tool in design optimization and performance improvement of a-Si: H photovoltaic cells, providing a solid scientific basis for the development of more efficient and sustainable solar cell technology. These findings contribute to efforts to increase solar energy efficiency, supporting broader and more effective use of photovoltaic technology in meeting global sustainable energy needs.

Applicability assessment of equivalent circuit-thermal coupling models on LiFePO4 batteries operated under wide-temperature and high-rate pulse discharge conditions

In military scenario, high-power lithium iron phosphate (LFP) batteries are frequently used under wide-temperature and high-rate pulse discharge conditions. An accurate electro-thermal coupling model (ETCM) is crucial for the safe operations. Equivalent circuit-thermal coupling model (ECTCM), which combines equivalent circuit model (ECM) and lumped thermal model, is the most widely used type of ETCM in applications. However, the applicability of ECTCM under wide-temperature and high-rate pulse discharge conditions is not clear. To assess the applicability of ECTCM under these special conditions, this study establishes six typical ECTCMs and accurately identify their corresponding model parameters. Then, these models are tested under high-rate pulse discharge conditions from -40oC to 50oC. The results indicate that ECTCMs are effective for pulse discharge at ambient and high temperatures, but not suitable for low-temperature conditions below 0oC. When the temperature is below 0oC, the pulse discharge voltage of the batteries can not be accurately simulated by ECTCMs. This work provides guidance for electro-thermal coupling modeling under high-rate pulse discharge conditions, and also points out the direction for the development of high-precision ETCM capable of handling wide-temperature and high-rate pulse discharge in the future.

Electrical Doping Regulation of Carrier Recombination Enhances the Perovskite Solar Cell Efficiency beyond 28.

With the power conversion efficiency (PCE) of perovskite solar cells (PSCs) exceeding 26.7%, achieving further enhancements in device performance has become a key research focus. Here, we investigate the impact of electrical doping in the perovskite layer using the drift-diffusion equation-based device physics model, coupled with a self-developed equivalent circuit model. Our results demonstrate that electrical doping can increase the PCE from 24.78% to >28%. In-depth theoretical analysis reveals that these improvements in performance are driven by the modulation of carrier recombination processes through doping, leading to significant increases in the open-circuit voltage and fill factor. Additionally, we explore the influence of physical parameters on device performance. Our study identifies an optimal doping concentration range from 1.0 × 1017 to 1.0 × 1019 cm-3 and a transport layer mobility of >0.01 cm2 V-1 s-1. This work provides a theoretical foundation for the development of ultra-high-performance PSCs through targeted electrical doping strategies.

Negative Resistor-Based Equivalent Circuit Model of Lithium-Ion Battery Energy Storage System for Grid Inertia Support

Negative Resistor-Based Equivalent Circuit Model of Lithium-Ion Battery Energy Storage System for Grid Inertia Support

Spatial distribution of corrosion products from a bridge pier

AbstractThis paper studies the spatial distribution of corrosion by-products by a bridge pier within a conductive medium. An electrochemical impedance spectroscopy (EIS) technique was used to investigate an uncoated metallic bridge pier submerged in static distilled water. An equivalent circuit model, derived from EIS results, served as the foundation for the study. Further, the role of diffusion was analysed, considering its significance in characterising the transfer of particles from the pier into the surrounding water. This exploration revealed the complex interaction between the diffusion processes of various corrosion by-products as a function of distance. In addition, by evaluating the spatial distribution of iron (II) corrosion by-products and modelling nanoparticle diffusion, the research examined the impact of diffusion and concentration on corrosion particle transmission. The findings, analysed via Nyquist and Bode plots, demonstrate significant differences between theoretical and empirical diffusion coefficients. Results indicated that under natural corrosion conditions, the primary product of the corrosion reaction, iron (II), disperses into the medium when oxidation occurs. The elevated resistivity due to the presence of iron (II) underscores the diffusion effect, leading to corrosion product precipitation and reaching saturation level. Additionally, the results demonstrated ideal values for the diffusion coefficient, which are crucial for advanced corrosion modelling. The results emphasised the need for empirical data to improve corrosion prediction models and informed maintenance strategies for submerged structures.

Partial Discharge Method for State-of-Health Estimation Validated by Real-Time Simulation

Accurate estimation of the state of health (SOH) of batteries for automotive applications, particularly in electric vehicle battery management systems (EV-BMS), remains a critical study area to ensure battery system availability. This paper proposes a comprehensive SOH estimation method that transcends traditional approaches based on estimating the available capacity using the integral of the battery current or estimating the increase in internal resistance. The SOH estimator employs a partial discharge method (PDM) and a linear state-of-charge (SOC) observer based on an equivalent electrical circuit model (ECM), utilizing readily available manufacturer data and designed for real-time applications. The proposed method was tested and validated using three different automotive battery technologies and a real-time simulation on the OPAL-RT platform. The simulations involved voltage and current measurements of pulsed-discharge current profiles under temperature-controlled conditions and an electric vehicle driving profile. The results showed a high accuracy in SOH estimation, with a maximum standard deviation of approximately 0.03497 V for lithium-ion batteries, representing about 7.124% of the mean value of the SOH estimator output. For other technologies, the standard deviations were even lower, all below 0.61% of their respective mean values. These outcomes demonstrate the reliability and accuracy of our method, making it suitable for real-time SOH estimation in EV-BMSs.

A hybrid equivalent circuit model and plane wave spectrum method for decoupling surface designs in multi‐band shared‐aperture antenna arrays

AbstractShared‐aperture antenna arrays are attractive for 5G base stations, owing to their compact size and multi‐band frequency coverage. Decoupling surfaces are effective for suppressing crossband mutual coupling. However, their designs typically rely on full‐wave simulations of scattering parameters, which may not ensure a good radiation performance and is time‐consuming. A systematic methodology based on the hybrid equivalent circuit model and plane wave spectrum method is proposed for decoupling surface designs. The decoupling surface is represented by its equivalent circuit and the spectral expression converts the electromagnetic field into a circuit problem. Both the scattering parameter and radiation pattern can be solved with the circuit, offering an efficient design method that ensures consistent radiation patterns between the model and full‐wave simulations. A double‐layer decoupling surface with wide stopbands, high transmission property, and sharp roll‐off transition was realised. Furthermore, to reduce the overall profile height, the reflection phase of the decoupling surface was tuned. A triple‐band shared‐aperture base station antenna array was developed. Simulated and measured results demonstrate the array works properly in the 0.69–0.96 GHz, 1.7–2.7 GHz, and 3.3–3.8 GHz frequency bands with stable radiation patterns, and crossband mutual coupling is well suppressed, validating the effectiveness of the proposed methodology.

Low-profile, wideband RCS-reduction antenna array based on a metal–ink hybrid metasurface

In this study, a highly flexible metal–ink hybrid metasurface that can be integrated with planar structures is proposed. The metasurface achieves wideband absorption performance while maintaining an efficient transmission window. Based on equivalent circuit model analysis, an aperture-coupled antenna array was integrated with the metasurface, enabling simultaneous wideband radar cross-section (RCS) reduction and high-performance radiation. The integration of the metasurface and antenna array allowed the overall structure to maintain a low profile. Simulation results show that the proposed array achieves a 10 dB RCS reduction against a metal plate of the same size over the [2.03, 8.11] GHz range, with a fractional bandwidth of 119.9% under x-polarized wave incidence. Under y-polarized wave incidence, a 10 dB RCS reduction is achieved at both [2.12, 5.1] GHz and [6.1, 8.06] GHz, with fractional bandwidths of 82.5% and 27.6%, respectively. Moreover, the array maintains a peak gain of 26.3 dBi and sidelobe levels less than -18 dB. The experimental results align well with the simulated results. The proposed low-RCS antenna array offers potential advancements in planar antenna technology, enhancing stealth capabilities.

Estimation of Lithium-Ion Battery SOC Based on IFFRLS-IMMUKF

The state of charge (SOC) is a characteristic parameter that indicates the remaining capacity of electric vehicle batteries. It plays a significant role in determining driving range, ensuring operational safety, and extending the service life of battery energy storage systems. Accurate SOC estimation can ensure the safety and reliability of vehicles. To tackle the challenge of precise SOC estimation in complex environments, this study introduces an improved forgetting factor recursive least squares (IFFRLS) method, which integrates the Golden Jackal optimization (GJO) algorithm with the traditional FFRLS method. This integration is grounded in the formulation of a lithium battery state equation derived from a second-order RC equivalent circuit model. Additionally, the research utilizes the interactive multiple model unscented Kalman filter (IMMUKF) algorithm for SOC estimation, with experimental validation conducted under various conditions, including hybrid pulse power characterization (HPPC), urban dynamometer driving schedule (UDDS), and real underwater scenarios. The experimental results demonstrate that the SOC estimation method of lithium batteries based on IFFRLS-IMMUKF exhibits high accuracy and a favorable temperature applicability range.

Temperature tunable broadband filter based on hybridized vanadium dioxide (VO2) metasurface

Abstract In this paper, a novel temperature tunable terahertz (THz) broadband filter based on hybridized vanadium dioxide (VO2) metasurface (MS) was proposed. The designed MS is composed of subwavelength metallic square-grid structure situated between two layers of metallic square-patch structure integrated with VO2 film pad spaced with two layers of dielectric substrate. Utilizing the insulator-metal phase transition characterizations of VO2 in the THz regime, the operation mode of the proposed MS filter accomplishes the broadband transmission-to-reflection transition. Simulation results show that when VO2 is in the insulating state with a lower external temperature, the proposed MS behaves like a broadband filter with transparent window and a transmittance of above 80% over the frequency range of 0.66–1.12 THz. However, when VO2 undergoes the metallic state with a higher external temperature, the MS becomes a broadband filter with low-transmission shielding and exhibiting a transmittance of below 10% across the frequency spectrum from 0.56 THz to 1.4 THz. The physical mechanism of the proposed MS based tunable broadband filter is illustrated by introducing impedance matching theory, equivalent circuit model and field analysis. In addition, the proposed MS structure offers exceptional angular stability and polarization insensitivity, opening up new opportunities for the utilization of energy selective surface in THz applications.

Modeling and Simulation of Wide-Frequency Characteristics of Electromagnetic Standard Voltage Transformer

To achieve the broadband applicability of standard voltage transformers in “dual high” power systems, an equivalent circuit model of the standard voltage transformer is first established. Using the complex magnetic permeability method and utilizing existing core parameters, the excitation impedance values are obtained. Next, based on the equivalent circuit model, the no-load error function of the standard voltage transformer is analyzed, and through simulation, the no-load error response curve of the standard voltage transformer in the frequency range of 20 Hz to 3000 Hz is derived. The simulation results indicate that within the 20 Hz to 700 Hz range, both the no-load ratio error and the no-load angular error meet the accuracy requirements, with the ratio error within ±0.05% and the angular error within 2′. Additionally, the derivation of the error transfer function demonstrates the correlation between the no-load error values and the number of turns and cross-sectional area of the standard voltage transformer. Simulation results, obtained by increasing and decreasing the number of turns and cross-sectional area by 10%, provide valuable insights for the error compensation and structural design of standard voltage transformers.

Design of Band Stop Filter Using Epsilon-Negative Frequency Selective Surface

This paper focuses on designing a band stop filter based on epsilon-negative frequency-selective surface (FSS). The unit cell has an electrical length of 0.104λ0 × 0.104λ0 which offers a bandwidth of 2.53 GHz from 1.24 GHz to 3.77 GHz. It has a center frequency of 2.44 GHz and the obtained fractional bandwidth is above 100%. Additionally, the behavior of the presented FSS is explained by the equivalent circuit model and surface current distribution. Within the entire bandwidth, it offers a negative permittivity. The refractive index of BSF is almost zero for 2.45−3.98 GHz range of frequency. The proposed FSS structure exhibits polarization-independent properties and offers a stable frequency response for normal and oblique angles under both TE and TM polarization. Good agreement between the simulated and measured results is obtained for the designed prototype.

Super Low Profile 5G mmWave Highly Isolated MIMO Antenna with 360∘ Pattern Diversity for Smart City IoT and Vehicular Communication

This study introduces a planar folded super low profile 5G mmWave monopole antenna for small IoT devices with superior efficiency and gain. Low-loss Rogers RT-5880 substrate material has been utilized to achieve higher efficiency, gain, and diversity performance in a relatively compact size. The unit element planar monopole antenna has been designed within 6.15×5.13×0.8mm3 with a partial ground. Four unit element antenna was orthogonally arranged on alternating sides of the substrate plane with narrow inter-component spacing in the multiple input multiple output (MIMO) system. The integration of the double negative (DNG) metamaterial array on the antenna led to a cumulative improvement in the overall performance of the antenna, which includes gain, efficiency, and isolation. The minimum isolation of the antenna increased by 11 dB with substrate-loaded metamaterial. The proposed MIMO antenna model with substrate-loaded metamaterial demonstrates 8 GHz instantaneous bandwidth (33.1 GHz - 41.1 GHz), 0.001 envelope correlation coefficient (ECC), diversity gain (DG) greater than 9.99 dB, channel capacity loss (CCL) less than 0.2bits/s/Hz, and a total active reflection coefficient (TARC) of 25 dB, which suggests that the diversity characteristics of the MIMO antenna system is impressive. Moreover, a densely packed 12-element antenna model has been introduced in this study with 360∘ pattern diversity, capable of receiving signals from any direction. Three 4-element MIMO systems have been arranged in an architecture to develop the 12-element MIMO system, and the size of the 12-element MIMO architecture is 15×15×15mm3. Despite having this compact size and dense packing, the 12-element MIMO antenna model shows similar diversity performance as the 4-element antenna model. Analog equivalent circuit models or resistor-inductor-capacitor (RLC) equivalent systems for the antenna models were created. A concept of a 128-element massive MIMO antenna has been presented to support the end devices, creating an application scenario of an IoT-interconnected smart city.

A novel ultra-wideband rasorber based on triple lossy layers

Abstract By surpassing the limitations of transmission efficiency found in traditional double-lossy-layers rasorbers, a novel rasorber with three distinct lossy absorption layers is presented, offering low insertion loss and ultra-wideband bandwidth. Compared to conventional rasorbers which have non-negligible insertion loss and large thickness, our design extends the bandwidth in the higher frequency band without increasing thickness, while maintaining high transmission efficiency. To further broaden the absorption band, an additional lossy layer resonating at lower frequency band, with high transmission above the resonance frequency was incorporated into the previous design. The composite structure is developed by the equivalent circuit model (ECM) whose results are in accord well with the simulation results. The simulated results demonstrate that an insertion loss of 0.37 dB at 10 GHz, and a 159.5% 10 dB reflection reduction bandwidth from 2.04 to 18.05 GHz are attained under normal incidence. A manufactured specimen of the proposed structure is measured to validate our design.

Advanced parameter estimation for lithium-ion battery model using the information sharing group teaching optimization algorithm

Accurate battery modeling is crucial for optimizing the performance and safety of Lithium-ion batteries (LiBs), particularly in applications such as electric vehicles and smart grids. This paper introduces the Information Sharing Group Teaching Optimization Algorithm (ISGTOA), a novel human-based metaheuristic algorithm designed to estimate the 21 parameters of third-order Equivalent Circuit Model (ECM) for LiBs. Unlike existing methods, ISGTOA effectively manages the increased complexity of a model through advanced group teaching strategies and sophisticated information-sharing mechanisms inspired by classroom dynamics. We validated the effectiveness of ISGTOA using two distinct datasets—High Dynamic Profile (HDP) and Urban Dynamometer Driving Schedule (UDDS)—across various LiB chemistries (NCA and NMC) and temperature conditions (−5 °C, 25 °C and 45 °C). The results demonstrate that ISGTOA achieves superior parameter estimation accuracy and convergence speed compared to established and recent optimization methods such as TLBO, TLSBO, AISA, MTBO, and DTBO. Specifically, ISGTOA attained a minimum RMSE of 8.357 mV with rapid convergence and high stability in the HDP dataset and minimized RMSE to 10 mV within ten iterations at both 25 °C and 45 °C in the UDDS dataset. Additionally, ISGTOA exhibited high efficiency (up to 97.75 %) under varying thermal environments. This work not only introduces a novel algorithm for complex battery modeling but also sets the stage for future advancements in real-time battery management systems, emphasizing the importance of robust, versatile, and efficient parameter estimation techniques.

Influence of Substrate on Sb2Se3/CdS Heterojunction Thin Film Solar Cells and Evaluation of Their Performance by Dark J‐V Analysis

ABSTRACTA simple binary antimony selenide (Sb2Se3) absorber is evolving as an alternative photovoltaic material in thin film solar cells because of its unique properties and easy processing. Sb2Se3 thin films having good crystalline quality are grown via versatile thermal evaporation from pre‐synthesized near stoichiometric compound material on molybdenum‐coated soda lime glass (SLG) and borosilicate glass (BG) substrates. Following the systematic characterizations on the absorber films, substrate configured Sb2Se3/CdS heterojunction devices were fabricated and their photovoltaic characteristics have been studied using current density vs. voltage (J‐V), dark J‐V modeling, external quantum efficiency and capacitance vs. voltage measurements. The power conservation efficiency values of 4.88% and 5.04% were achieved for the devices fabricated on SLG and BG substrates, respectively with deficit in open circuit voltage. The obtained values are higher in comparison to the reported device efficiencies in substrate configured Sb2Se3 solar cells, in which the absorber is prepared through thermal evaporation. To understand the loss in open circuit voltage, a compact equivalent circuit model was considered and identified the contribution of different shunt leakage paths in the devices. In addition to that, the device fabricated on the SLG was stable with minimal changes in its photovoltaic performance for a period spanning over 200 days. The results obtained are encouraging with scope for improving the device performance through interface engineering and back surface passivation strategies.