Circuit Model Research Articles

Analytical model for helical particle array assessment for EMI shielding applications

This paper introduces an analytical method for studying power transmission through an infinite array of helical-shaped metal particles in a lossy dielectric medium. While the assessment of composite slabs’ transmitted power has been extensively researched in the electromagnetic interference (EMI) shielding field, many studies lack an adequate problem description. The primary inadequacy of these studies is the need for an analytical framework. This study, besides presenting a new approach to designing a concrete composite that leverages the magnetoelectric properties of the particles, making it suitable for EMI shielding, also employs a theoretical method to analyze the composite. A circuit model of the array is introduced using a modal field decomposition, which justifies the impact of helix transmission modes and the transverse magnetic field component on the shielding properties of the array. It is also shown that the resonances of the array can be tuned by engineering the helix properties. Furthermore, to broaden the applicable bandwidth of the composite, a multi-layer structure is proposed. The computational load of the proposed method demonstrates exceptional speed due to its circuit model foundation. The model yields valuable results compared to experimental measurement, making it ideal for optimizing various shielding composite structures for EMI shielding applications.

Design of Four-Plate Parallel Dynamic Capacitive Wireless Power Transfer Coupler for Mobile Robot Wireless-Charging Applications

A detailed theoretical design of an electric resonance-based coupler for dynamic wireless power transfer (DWPT) at the mobile robot level is presented. The scattering matrix of the coupler was derived by transforming and multiplying transmission matrices for each circuit network in a practical equivalent circuit that accounted for loss resistance. This theoretical approach was validated through equivalent circuit models, yielding results consistent with 3D full-wave simulations and showing an error rate of less than 1%. Additionally, a null-power point characteristic, where efficiency sharply decreases when the receiver moves outside the transmitter’s range, was observed. The detailed theoretical design of the practical equivalent circuit for electric resonance-based dynamic WPT couplers is expected to contribute to the design of couplers for various specifications in future applications.

Enhancing fine-tuning efficiency and design optimization of an eight-channel 3T transmit array via equivalent circuit modeling and Eigenmode analysis.

Radiofrequency (RF) transmit arrays play a crucial role in various MRI applications, offering enhanced field control and improved imaging capabilities. Designing and optimizing these arrays, particularly in high-field MRI settings, poses challenges related to coupling, resonance, and construction imperfections. Numerical electromagnetic simulation methods effectively aid in the initial design, but discrepancies between simulated and fabricated arrays often necessitate fine-tuning. Fine-tuning involves iteratively adjusting the array's lumped elements, a complex and time-consuming process that demands expertise and substantial experience. This process is particularly required for high-Q-factor arrays or those with decoupling circuitries, where the impact of construction variations and coupling between elements is more pronounced. In this context, our study introduces and validates an accelerated fine-tuning approach custom RF transmit arrays, leveraging the arrays equivalent circuit modeling and eigenmode analysis of the scattering (S) parameters. This study aims to streamline the fine-tuning process of lab-fabricated RF transmit arrays, specifically targeting an eight-channel degenerate birdcage coil designed for 3T MRI. The objective is to minimize the array's modal reflected power values and address challenges related to coupling and resonance. An eight-channel 3T transmit array is designed and simulated, optimizing capacitor values via the co-simulation strategy and eigenmode analysis. The resulting values are used in constructing a prototype. Experimental measurements of the fabricated coil's S-parameters and fitting them into an equivalent circuit model, enabling estimation of self/mutual-inductances and self/mutual-resistances of the fabricated coil. Capacitor adjustments in the equivalent circuit model minimize mismatches between experimental and simulated results. The simulated eight-channel array, optimized for minimal normalized reflected power, exhibits excellent tuning and matching and an acceptable level of decoupling (|Snn|≤-23dB and |Smn|≤-11dB). However, the fabricated array displays deviations, including resonances at different frequencies and increased reflections. The proposed fine-tuning approach yields an updated set of capacitor values, improving resonance frequencies and reducing reflections. The fine-tuned array demonstrates comparable performance to the simulation (|Snn|≤-15dB and |Smn|≤-9dB), mitigating disparities caused by construction imperfections. The maximum error between the calculated and measured S-parameters is -7dB. This accelerated fine-tuning approach, integrating equivalent circuit modeling and eigenmode analysis, effectively optimizes the performance of fabricated transmit arrays. Demonstrated through the design and refinement of an eight-channel array, the method addresses construction-related disparities, showcasing its potential to enhance overall array performance. The approach holds promise for streamlining the design and optimization of complex RF coil systems, particularly for high Q-factor arrays and/or arrays with decoupling circuitry.

Episodic and associative memory from spatial scaffolds in the hippocampus.

Hippocampal circuits in the brain enable two distinct cognitive functions: the construction of spatial maps for navigation, and the storage of sequential episodic memories1-5. Although there have been advances in modelling spatial representations in the hippocampus6-10, we lack good models of its role in episodic memory. Here we present a neocortical-entorhinal-hippocampal network model that implements a high-capacity general associative memory, spatial memory and episodic memory. By factoring content storage from the dynamics of generating error-correcting stable states, the circuit (which we call vector hippocampal scaffolded heteroassociative memory (Vector-HaSH)) avoids the memory cliff of prior memory models11,12, and instead exhibits a graceful trade-off between number of stored items and recall detail. A pre-structured internal scaffold based on grid cell states is essential for constructing even non-spatial episodic memory: it enables high-capacity sequence memorization by abstracting the chaining problem into one of learning low-dimensional transitions. Vector-HaSH reproduces several hippocampal experiments on spatial mapping and context-based representations, and provides a circuit model of the 'memory palaces' used by memory athletes13. Thus, this work provides a unified understanding of the spatial mapping and associative and episodic memory roles of the hippocampus.

Investigation of networked SSHI configurations for plate-based piezoelectric energy harvesters

Piezo-patch energy harvesters attached to plate-like structures can be used to extract multimodal vibrational energy. For each piezo-patch, SSHI circuits can boost the harvested power compared to standard rectifier circuits. However, the effect of using different configurations of the SSHI network for multiple piezo-patches on plate structures has not yet been understood. This study aims to assess the performance of the networked SSHI configurations compared to networked rectifier configurations and investigate the optimum configurations for energy harvesting purposes. For this, three piezo-patches are bonded to an aluminum plate and connected to single and/or multiple circuits. The equivalent circuit model (ECM) of the electromechanical system is developed from the experimentally validated analytical model and utilized in simulation software LTspice. The performances of considered configurations are evaluated regarding peak power outputs, and the optimal load resistances are obtained. Based on the experimental findings, the best configuration is determined and verified by simulations. The results show that by using respective SSHIs, the power output can be improved by preventing charge cancellation despite the cost of increased diode loss. This study contributes to our understanding of optimal energy harvesting techniques by investigating the effectiveness of networked SSHI configurations for multiple piezo-patches on plate structures.

Transport dynamics of photo-induced carriers in GaN quantum well infrared photodetectors influenced by triangular potentials

The intrinsic spontaneous and piezoelectric polarizations of GaN lead to the formation of triangular wells and barriers, resulting in the manifestation of chaotic transport models in GaN quantum well intersubband transition (ISBT) infrared detectors and giving rise to various adverse effects. The APSYS software was utilized to construct a novel GaN quantum well ISBT infrared detector in this study. By endeavoring to modify the quantum well structure, our objective was to precisely adjust the energy level of the first excited state (E1) to align with the apex of the triangular barrier. The objective is to reduce the transport barrier for photo-induced carriers and simultaneously investigate the mechanisms through which the triangular potentials influence the transport modes of ISBT infrared detectors. The construction of a GaN/AlGaN quantum well device reveals that the inclusion of 10 periods of 1.7/2.0 nm GaN/Al0.8Ga0.2N in the device structure results in an ISBT absorption wavelength of approximately 1550 nm. In comparison to the deep well structure featuring 2.0/2.0 nm GaN/AlN, the polarization field strengths of both wells and barriers in the quantum well region exhibit a reduction of 23% and 36%, respectively, while the depth of the well decreases by 0.35 eV. The E1 energy level penetrates the region of a triangular barrier, resulting in an approximate 18.5-fold enhancement of the absorption coefficient. By employing innovative transient spectroscopy techniques in conjunction with AC impedance spectroscopy, we have conducted an in-depth analysis of the transport dynamics of photo-induced carriers. The results reveal that the time constant for carrier transport within the E1 energy level, situated in the region of a triangular barrier, amounts to 318.9 ps, thereby indicating a remarkable enhancement in the overall transport process. Furthermore, based on impedance spectroscopy data, this work has successfully derived equivalent circuit models for various quantum well structures and distinct carrier transport pathways, thus providing valuable theoretical insights to optimize photo-induced carrier transportation.

Extensible Approach to Nonlinear Circuit Simulation of Terahertz Radiation Phenomena from Stacked Josephson Junctions

Abstract This paper proposes an enhanced numerical simulation of a high-Tc cuprate terahertz source using the LTspice® electric circuit simulator. By implementing a nonlinear circuit model proposed in our previous work utilizing behavioral sources in LTspice, we accurately reproduce current-voltage-radiation power characteristics of the device measured by the authors over the entire bias points. We also identify that high-frequency losses significantly increase the damping of the oscillation in the gauge-invariant phase differences of stacked Josephson junctions. This model enables quantitative analysis of maximum radiation intensity through structural optimization, paving the way for a systematic approach to efficient device design.

Measurement of resistivity of biofluids in the presence of an electrical double layer

Abstract Detecting alterations in the electrical response of human biofluids can provide valuable information in the early stages on pathological conditions in a patient. Developing techniques for obtaining rapid information on the electrical resistivity of common ionic biofluids by non-invasive techniques can improve medicare through a rapid and more precise diagnosis. In this work, we analyze the use of an electrical device consisting of a cell formed of flat parallel steel plates to measure the resistivity of these substances. When the electrical cell is filled with a biofluid an electrical double layer (EDL) is formed on the electrodes/biofluid interface. Then, we measure the electrical response and examine the general conditions under which the EDL does not interfere with the assesment of the biofluid’s resistivity. The electrical response is analyzed in terms of an equivalent circuit model. Also, a simplified theoretical model of a suspension of biological cells considering spherical particles with a membrane is discussed to validate measurements and theoretically exhibit the contribution of the cell’s membrane to the effective resistivity. We present measurements of the resistance of the electrical cell filled with electrolyte solutions, blood plasma, and diluted suspensions of erythrocytes in a hypotonic solution. Results show that the resistance of the electrical cell is sensitive to the volume density of biological cells suspended between the parallel plate electrodes, producing a signal with a high signal to noise ratio. From the measured resistance of a suspension of erythrocytes in a isotoinc solution and the simplified theoretical model, we estimate the value of the conductivity of the interior of the erythrocytes. The results show that measured resistance varies with blood samples and hemolysis progression. The device's sensitivity to the number of erythrocytes passing between the electrodes makes it useful for measuring sedimentation kinetics.

Absolute number of three populations of interneurons and all GABAergic synapses in the human hippocampus.

The human hippocampus, essential for learning and memory, is implicated in numerous neurological and psychiatric disorders, each linked to specific neuronal subpopulations. Advancing our understanding of hippocampal function requires computational models grounded in precise quantitative neuronal data. While extensive data exist on the neuronal composition and synaptic architecture of the rodent hippocampus, analogous quantitative data for the human hippocampus remain very limited. Given the critical role of local GABAergic interneurons in modulating hippocampal functions, we employed unbiased stereological techniques to estimate the density and total number of three major GABAergic cell types in the male and female human hippocampus: parvalbumin (PV)-expressing, somatostatin (SOM)-positive, and calretinin (CR)-positive interneurons. Our findings reveal an estimated 49,400 PV-positive, 141,500 SOM-positive, and 250,600 CR-positive interneurons per hippocampal hemisphere. Notably, CR-positive interneurons, which are primarily interneuron-selective in rodents, were present in humans at a higher proportion. Additionally, using 3-dimensional electron microscopy, we estimated approximately 25 billion GABAergic synapses per hippocampal hemisphere, with PV-positive boutons comprising around 3.5 billion synapses, or 14% of the total GABAergic synapses. These findings contribute crucial quantitative insights for modeling human hippocampal circuits and understanding its complex regulatory dynamics.Significance Statement Understanding the operating principles of cortical networks is a major goal in neuroscience, requiring a detailed description of cortical neurons, including their proportions, densities, and, most critically, their absolute numbers. Such precise quantification is essential for constructing predictive computational models of neuronal circuits. In this study, we present the density and total number of three major, non-overlapping GABAergic cell groups across each layer of the human hippocampus. Additionally, we quantify the total number of all GABAergic boutons and synapses, as well as separately quantifying those originating from parvalbumin (PV)-positive cells within each of the 15 hippocampal layers. This dataset provides a foundational framework for accurately modeling hippocampal inhibition at the cellular level.

Identification of Parameters for Solar Photovoltaic Systems Using a Human Optimization Algorithm

By increasing the global demand for electricity, there is a heightened need for power generation. The rising costs of natural gas and regulatory pressures to limit greenhouse gas emissions have escalated the expenses associated with electricity production from fossil fuels. Consequently, there is a growing inclination to utilize alternative energy sources for electricity generation, particularly solar power through photovoltaic systems. Evolutionary algorithms are among the most favored methods for identifying and optimally estimating the parameters of photovoltaic systems, and this article examines their functionality. A critical issue in these systems is the appropriate selection of photovoltaic system parameters. This paper presents a new method for optimal parameters identification of the photovoltaic (PV) systems using a newly modified version of a metaheuristic algorithm. The propose algorithm is based on adapting the performance of the Human Evolutionary Optimizer and is called AHEO algorithm. Simulation results indicate that the estimation of the photovoltaic cell's circuit model parameters has been effectively accomplished, with the mean square error (MSE) associated with the AHEO demonstrating a high level of accuracy and robustness in parameters identification of the PV system.

Analysis and Applications of Magnetically Coupled Resonant Circuits

Magnetically coupled resonant circuits have been utilized in radio engineering for many years. Recently, these circuits have found new applications, particularly in supplying low- and medium-power devices through medium-range wireless power transmission technology based on magnetic resonance coupling. There is also a growing need to analyze magnetically coupled resonant circuits in the design of metamaterials, which exhibit specific electromagnetic properties within certain frequency bands. This paper provides a coherent and concise overview of the phenomena associated with magnetically coupled resonant circuits. The results encompass numerous established relations as well as new ones. They can be helpful in the design phase of magnetically coupled resonant circuits. The outcomes include equations for determining the coupling resonant frequencies and some parameters of resonance curves. These analytical results are accompanied by 3D and cross-sectional (contour) graphs for better visualization. Moreover, a lumped-element circuit model that includes magnetically coupled resonant circuits is proposed for the resonators used in metamaterials. Formulas for resonant frequencies are derived in the specific case of exciting such resonators. To validate the accuracy of the derived equations, the analytical results are compared with simulations from SPICE (IsSPICE4 ver. 8.1) and COMSOL 5.4 software, which are widely used tools for circuit analysis and electromagnetic simulations. The results of these comparative analyses indicate that the assumptions employed in the analytical solutions introduce only tiny errors.

High‐Performance Droplet‐Based Triboelectric Nanogenerators: A Comparison of Device Configuration and Operating Parameters

AbstractDroplet‐based electricity generators (DEGs) harness liquid‐solid electrification to convert water droplets impacts into electrical energy. This study systematically examines how droplet height, droplet volume, flow rate, and substrate tilt angle influence DEG performance using polytetrafluoroethylene (PTFE) as a triboelectric layer and deionized water. Three electrode designs (double, top, bottom) are evaluated, revealing that the double‐electrode configuration delivers the highest output. This enhanced performance arises from synergistic droplet motion, electrical double‐layer formation, and charge discharge, as validated by an equivalent circuit model. By varying droplet heights from 1–20 cm, volumes of 7.7–50 µL, flow rates of 50–300 drops/min, and tilt angles of 0–90°, an optimized setup yields −70 V and 22 mA, translating to a power density of 0.28 µW cm−2. High‐speed imaging correlates these outputs with droplet impact dynamics and the resulting charge transfer. Additionally, the optimized DEG can power small electronic devices, charge capacitors, and monitor artificial acid rain in real‐time, displaying distinct electrical signals compared to typical rainwater. These findings underscore the potential of DEGs as renewable energy harvesters and smart environmental sensors, paving the way for advanced on‐demand power generation in diverse settings.

Small‐Signal Modelling of Bidirectional CLLC Converters for Onboard Charging Application in Electric Vehicles

ABSTRACTA two‐stage onboard battery charger with an CLLC resonant converter is a widely adopted configuration in the automotive industry. The ZVS and ZCS capability of the switching devices with high operating frequency of the CLLC converters encourages its application in various EV platforms to improve efficiency. In the literature, various authors proposed many methods to control the CLLC converters efficiently, but up to now, no simple and accurate small‐signal equivalent circuit modelling is available. As dynamic networks are load‐dependent, closed‐loop voltage and current controllers provide more stable operations in these converters. In this paper, a detailed mathematical modelling of the CLLC converters with time domain analysis has been presented. The proposed mathematical model accurately predicts the small‐signal behaviors seen in pulse‐frequency‐modulated (PFM) CLLC resonant converters whether the switching frequency is below, near to, or above the resonant frequency. Stable closed‐loop controllers for both current and voltage loops in battery charging applications are designed and detailed. A prototype hardware is been built and the experimental results with the load variations with the designed controllers are tested and the results are been discussed in the paper.

State of Charge Estimation for Lithium Battery in Shipboard DC Power Grid Based on Differential Evolutionary Algorithm

More and more attention has been paid to ships with a DC power grid. State-of-charge (SOC) estimation is a pivotal and challenging assignment for lithium-ion batteries in such ships. However, the precision of SOC estimation is strongly connected with the system parameters. To better identify these parameters in lithium-ion batteries, a differential evolution (DE) algorithm was introduced into this paper as the optimizer. Initially, a first-order RC equivalent circuit model (ECM) was created to characterize the battery’s dynamic behavior. Following this, to estimate open-circuit voltage (OCV) throughout the entire dynamic process, a math model of optimization was established to minimize inaccuracies between the real and estimated terminal voltages. Moreover, estimated SOC values were obtained through OCV-SOC mappings and were contrasted against the true SOC values. The findings manifested the efficacy of the presented structure and technique in comparison with various frequently-cited DE variants.

Development and Validation of a Capacitor–Current Circuit Model for Evaporation-Induced Electricity

Evaporation-induced electricity is a promising approach for sustainable energy generation which is particularly suited for off-grid and Internet-of-Things (IoT) applications. Despite significant progress, the mechanism of electricity generation remains debated due to complex factors. In this study, we introduce a simplified capacitor–current circuit model to describe the behavior of evaporation-induced electricity. The primary objective of this work is to provide a framework for understanding the transient and steady-state behavior of this phenomenon. We validated this model using experimental data from wood-based nanogenerators with citric acid modified microchannels. The fitting results revealed a steady-state current of approximately 9.832 μA and an initial peak current of 16.168 μA with a time constant of 621.395 s. These findings were explained by a hybrid model incorporating a capacitor and current source components, and subsequent discharge through internal resistance. This simplified model paves the way for better understanding and optimization of evaporation-induced electricity, highlighting potential improvements in device design for enhanced performance. While improving device performance is beyond the scope of this study, the insights gained from this model offer a foundation for future optimization and the enhanced performance of evaporation-induced electricity generation devices.

Research on Water Flow Control Strategy for PEM Electrolyzer Considering the Anode Bubble Effect

At higher current densities, the bubble effect in the anode flow field of the PEM electrolyzer (PEM EL) worsens mass transfer losses and energy consumption. This study employs a moderate increase in the water flow rate to remove accumulated bubbles under fluctuating electrical input, thereby improving PEM EL system efficiency. An enhanced PEM EL equivalent circuit model incorporating bubble over-potential based on the oxygen volume fraction is developed. Considering the energy consumption of auxiliary equipment and the reduction in losses from mitigating the bubble effect, a numerical simulation evaluates the impact of flow rate variations on overall electrolysis energy consumption, leading to a comprehensive energy consumption model for the PEM EL system, incorporating electrical, chemical, and thermal energy conversions. The control objective is to maximize system efficiency by optimizing the water flow rate, with a performance-preset-based controller implemented in MATLAB/Simulink. The simulation results show that the controller can accurately track the target flow rate, and the dynamic regulation time improved by 1.5 s compared to the traditional performance constraint function, better matching the rate of change in electrical energy. Under the water flow control mode, hydrogen production increased by 6.6 L within 130 s of the simulation, available energy increased by 8.32 × 106 J, and the efficiency of the PEM EL system improved by 2.79%.

Design, construction and test of a 13 T no-insulation REBCO magnet: validation of an improved circuit model considering the screening current

Design, construction and test of a 13 T no-insulation REBCO magnet: validation of an improved circuit model considering the screening current

Dual circularly polarized dual-band antenna combining transmitarray and reflectarray for K/Ka-band uplink and downlink satellite communication

This paper presents a dual-band antenna system utilizing transmitarray (TA) and reflectarray (RA) having dual-circularly polarized (CP) characteristics for K/Ka-band satellite communication. The antenna consists of the TA and RA surfaces operating at 19.5 GHz and 29.7 GHz respectively. The RA is designed on a single substrate layer with element size of 0.30 λ × 0.30 λ (λ corresponding to 30 GHz), whereas the TA is designed on two substrate layers with element size of 0.33 λ × 0.33 λ (λ corresponding to 20 GHz). The equivalent circuit model (ECM) of the TA and RA elements is extracted to validate the working of the proposed elements. A small window of the size of a patch antenna is cut in both the RA and TA surfaces to accommodate the coaxially-fed illuminating sources. The antenna shows the peak gain of 17 dBiC at 19.5 and 29.7 GHz. The 3 dB axial ratio bandwidths range from 19.3–19.6 GHz (1.55 % ) and 29.5–29.9 GHz (1.35 % ) in the two frequency bands. The antenna radiates two orthogonally polarized CP waves at two frequency bands which makes the antenna suitable for satellite communication applications.

Bandwidth enhancement of resonating absorber using a lossy dielectric layer for RCS reduction in X-band

Abstract In this paper, a resonating absorber is proposed for radar cross section reduction in the X-band, with the inclusion of a high loss dielectric layer. The absorber consists of a pair of co-centered resonating Jerusalem cross printed on a FR4 substrate cascaded with a high-loss dielectric layer and a metallic back plane. The designed absorber offers 90 % absorption from 7.8–12 GHz with a fractional bandwidth of 42.42 %. The designed absorber is 0.106λ L thick with a compact square unit cell of size 0.076λ L (wavelength at the lowest frequency). An equivalent circuit model is developed to analyze the proposed absorber. The absorber is angularly stable for varying angle of incidences up to 40°–60° for TE and TM polarizations respectively. The planar as well as the conformal structure of the proposed absorber offer a minimum 10 dB radar cross section reduction in the X-band. The conventional approach which involves complex fabrication process of soldering thousands of lumped resistors to increase the bandwidth, whereas the proposed absorber is realized to offer wide absorption using simple PCB etching technique. To validate the design prototype is fabricated and the measurement is carried out.

Integrative Evaluation of Skin-Electrode Interface based on Graphical Analysis and Circuit Modeling of Electrochemical Impedance Spectra

Integrative Evaluation of Skin-Electrode Interface based on Graphical Analysis and Circuit Modeling of Electrochemical Impedance Spectra