Circuit Model Research Articles

CO2 sensing via periodic Array of graphene disks

This work aims to introduce a gas detection structure based on stacked layers of graphene-spacer-metal. The presented structure consists of three stacked layers. The first layer is the periodic arrays of graphene disks on top of a typical dielectric such as TOPAS or KAPTON with a known refractive index. Then the second layer provides an air gap opening room for a sample environment. Finally, the third layer includes the dielectric and a continuous graphene sheet. All the exploited elements are modeled by circuit element while the equivalent impedance of the whole structure is calculated. The impedance matching concept is also exploited to obtain absorption power based on the calculated impedance. Additionally, full-wave simulation is performed to investigate the circuit modeling accuracy. Achieving a perfect match for absorption versus frequency verifies the developed method's robustness. Furthermore, comprehensive and ample simulation results are reported to highlight the sensitivity and reliability of the proposed gas detector.

Infrared\radar stealthy metasurface design method based on equivalent circuit model

Infrared\radar stealthy metasurface design method based on equivalent circuit model

Using the Single-Term Haar Wavelet to Solve the State Variable Models of nth-Order Circuits

This study is dedicated to investigating the utilization of the single-term Haar wavelet approach for solving a state variable model of nth-order circuits. We provide the matrix calculations in a simplified manner to facilitate comprehension. Furthermore, a numerical mathematical illustration is presented, demonstrating the application of this technique to solving two first-order differential equations with both constant and variable coefficients. The study’s findings unequivocally demonstrate that the suggested approach surpasses previous methods, providing greater levels of accuracy and precision. Moreover, the single-term Haar wavelet approach is exceptionally user-friendly and efficient, necessitating only a minimal amount of processing resources.

Magnetic and dielectric properties of low‐loss MnZn ferrites with wide temperature stability

AbstractTo meet the needs for higher energy efficiency and a wide operating temperature range of electric vehicles, the low‐loss MnZn ferrites in a wide temperature range have been developed by optimizing the Fe content and the oxygen partial pressure (PO2) during the sintering process in this work. For the optimal sample, power loss at 300 kHz/100mT is 204 kW/m3 at 25°C and remains below 290 kW/m3 in the wide temperature range from ‐10 to 120°C. The loss separation method was employed to clarify the effects of the Fe content and PO2 on power loss. The equivalent circuit model has been employed to fit the complex impedance and it is found that the increase of PO2 enhances both the grain resistance Rg and the grain boundary resistance Rgb. The enhancement of Rgb is mainly responsible for the reduction of eddy current loss and consequently power loss. Dielectric permittivity is as large as about 15000 in this series of samples due to the electric polarization at the rich grain boundaries. Dielectric loss is very low between ‐50 and 150°C and has little contribution to the energy loss.

Utilizing quantum processor for the analysis of strongly correlated materials

This study introduces a systematic approach for analyzing strongly correlated systems by adapting the conventional quantum cluster method to a quantum circuit model. We have developed a more concise formula for calculating the cluster’s Green’s function, requiring only real-number computations on the quantum circuit instead of complex ones. This approach is inherently more suited to quantum circuits, which primarily yield statistical probabilities. As an illustrative example, we explored the Hubbard model on a 2D lattice. The ground state was determined utilizing Xiaohong, a superconducting quantum processor equipped with 66 qubits, supplied by QuantumCTek Co., Ltd. Subsequently, we employed the circuit model with controllable noise to compute the real-time retarded Green’s function for the cluster, which is then used to determine the lattice Green’s function. We conducted an examination of the band structure in the insulator phase of the lattice system. This preliminary investigation lays the groundwork for exploring a wealth of innovative physics within the field of condensed matter physics.

An inverted F-shaped slotted broadband metasurface-based circularly polarized patch antenna for 5G application

This paper presents an inverted F-shaped slotted broadband metasurface (MS)-based circularly polarized (CP) microstrip patch antenna. The host antenna comprises a truncated corner square patch with an inverted F-shaped slot, positioned on a 1.6 mm thick FR-4 substrate backed by ground plane. Concurrently, the MS layer is composed of a 4 × 4 square ring array, constructed on a separate 1.6 mm thick FR-4 substrate with net compact dimensions 0.54λo × 0.54λo × 0.027λo at 5.13 GHz, serving as a superstrate layer. The proposed antenna exhibits impressive performance, including a −10-dB impedance bandwidth from 4.40 GHz to 7.38 GHz as well as a 3-dB axial ratio (AR) bandwidth from 4.74 GHz to 5.52 GHz. Furthermore, at 5.13 GHz, it achieves a notable maximum radiation efficiency and realized gain of 85 % and 6.95 dBic respectively. Moreover, polarization of the antenna is observed as left-handed circularly polarized (LHCP). To validate the impedance response, the antenna’s equivalent circuit model has been sequentially developed, followed by the fabrication of a prototype. The measured results closely resemble with the simulated responses, indicating strong consistency between theory and experimental results. With its overall compact dimension of 0.65λo × 0.65λo × 0.027λo at 5.13 GHz, the proposed CP antenna is well-suited for 5G application.

Electrical and piezoresistive properties of ultra-high toughness cementitious composite incorporating multi-walled carbon nanotubes: Testing, analyzing, and phenomenological modeling

This study explores the electrical and piezoresistive properties of ultra-high toughness cementitious composites (UHTCC) enhanced with multi-walled carbon nanotubes (MWCNTs) ranging from 0 to 1 wt% of cementitious binders. The observed polarization behavior is found to be analogous to the charging process of a capacitor. The polarization process and resistivity drift over time in the piezoresistive response are explained using an existing equivalent electrical circuit model incorporating a capacitor. The average results of electrical conductivity initially decrease and subsequently increase with higher MWCNTs concentrations, a phenomenon attributed to increased porosity and reduced matrix conductivity. The percolation threshold is identified at a volume fraction of 0.00387. Notably, even in the absence of MWCNTs, UHTCC materials exhibit piezoresistive properties due to the presence of metal impurities and ionic compounds. The insufficient polarization process results in an increasing trend in fractional change in resistance (FCR). The highest FCR sensitivity to external load occurs within the percolation threshold. Additionally, three equations are proposed to calculate electrical conductivity, incorporating the effects of interfaces, porosity, and matrix conductivity reduction, which align well with the experimental findings. These insights contribute to a deeper understanding of the electrical properties of UHTCC-MWCNTs composites, enabling more precise conductivity measurements and improved sensor sensitivity.

An efficient and miniaturized ultra-thin tunable UWB graphene metasurface absorber for terahertz gap regime

This work introduces an ultra-thin tunable ultra-wideband (UWB) metasurface absorber (MSA) for the terahertz (THz) gap. The polarization-insensitive MSA provides an absorptivity (A(f)) ≥ 90% from 0.1 to 11.5 THz, corresponding to 196.6% fractional bandwidth. The usage of resonant slots engraved on top patterned graphene sheet (Gpat) and strong plasmonic coupling in the Fabry-Perot cavity formed between top Gpat and bottom continuous graphene (Gcont) in bilayer stack configuration ensures absorptivity over a UWB THz spectrum. An equivalent circuit model (ECM) closely follows the A(f) response of the proposed MSA. The proposed DC-biasing mechanism can regulate the chemical potential (μc) of the connected Gcont efficiently. A DC bias voltage of 0 to 6.1 V is adequate to vary μc of Gcont from 0 to 0.6 eV for achieving tunable A(f). The structure maintains its ultra-thin nature and has a thickness of only λ0/1500, where λ0 is the free space wavelength calculated at 0.1 THz. In addition, the periodicity is only λ0/300. The MSA also provides stable absorption response from 0.1 to 11.5 THz with A(f) ≥ 80% for incidence angle (θ) up to 60∘ under both transverse magnetic (TM) and transverse electric (TE) polarization.

Behavioral state and stimulus strength regulate the role of somatostatin interneurons in stabilizing network activity.

Inhibition stabilization enables cortical circuits to encode sensory signals across diverse contexts. Somatostatin-expressing (SST) interneurons are well-suited for this role through their strong recurrent connectivity with excitatory pyramidal cells. We developed a cortical circuit model predicting that SST cells become increasingly important for stabilization as sensory input strengthens. We tested this prediction in mouse primary visual cortex by manipulating excitatory input to SST cells, a key parameter for inhibition stabilization, with a novel cell-type specific pharmacological method to selectively block glutamatergic receptors on SST cells. Consistent with our model predictions, we find antagonizing glutamatergic receptors drives a paradoxical facilitation of SST cells with increasing stimulus contrast. In addition, we find even stronger engagement of SST-dependent stabilization when the mice are aroused. Thus, we reveal that the role of SST cells in cortical processing gradually switches as a function of both input strength and behavioral state.

A Quantum Particle Swarm Optimization Extended Kalman Quantum Particle Filter approach on state of charge estimation for lithium-ion battery

The accurate estimation of battery state of charge serves as the foundation for estimating state of health, remaining useful life, and safety, making it an indispensable part of battery management system. Based on the lithium-ion battery parameter identification using quantum particle swarm optimization, this paper presents a state of charge estimation method utilizing the Extended Kalman Quantum Particle Filter. A Quantum Particle Swarm Optimization algorithm is used for second-order equivalent circuit model parameter identification. By combining Extended Kalman Filter with Particle Filter and employing Grover search algorithm for resampling of quantized particles, the Extended Kalman Quantum Particle Filter is designed for estimation. Validation is conducted under standard operating conditions, and the Quantum Particle Swarm Optimization Extended Kalman Quantum Particle Filter algorithm demonstrates better accuracy and adaptability compared to Extended Kalman Filter, Extended Kalman Particle Filter and other popular algorithms under FUDS, UDDS and DST working conditions by two types of battery. Both theoretical and experimental results indicate good performance of Quantum Particle Swarm Optimization Extended Kalman Quantum Particle Filter in state of charge estimation.

Signal Components and Impedance Spectroscopy of Potential p‐Si/n‐CdS/ALD‐ZnO Solar Cells: EIS and SCAPS‐1D Treatments

AbstractA silicon heterojunction (SHJ) solar cell with the attractive and widely used atomic layer deposited (ALD)‐ZnO/n‐CdS/p‐Si configuration is examined in this work to learn more about its electrical properties. Using EIS and SCAPS‐1D, a comprehensive model of the device is created and then simulated. Theoretical aspects of the cell are examined through the use of similar electrical circuit models, focusing on the transmittance spectrum made possible by the ALD‐ZnO layer's low reflectance and high visible transmittance. In this study, the C–V tool is used to study the trap states in the silicon absorber layer under different lighting conditions and wavelengths. The doping concentration and built‐in potential are determined using the Mott–Schottky technique. In addition, the cell's properties are investigated by measuring its G–V, G–F, C–T, and C–F in different real‐world scenarios. As a means of visualizing the electrochemical impedance data, Nyquist plots—sometimes called Cole–Cole plots—are utilized. By utilizing absolute impedance and phase shifts, Bode plots are employed to examine the system's frequency response. Last, the results of the SHJ cell's spectral response measurements are given, which confirm the results of the Nyquist plots.

Drifting plasmons in two-dimensional electron channels: circuit analogy.

Plasmons in two-dimensional electron channels have potential applications in the terahertz frequency range. Equivalent circuit models provide a convenient framework for analysing the plasmons. This article introduces a circuit model for plasmons in the presence of a dc current that flows in a gated channel. It is shown that drifting plasmons can be described by an LC-transmission line with distributed dependent sources. A circuit analogue of the Dyakonov-Shur instability is demonstrated. Then, a lumped-element transmission line with dependent sources is analysed, and non-reciprocity is demonstrated for examples of a right- and a left-handed transmission line. Effects of ohmic loss are discussed. The results could be used for the design of non-reciprocal transmission line devices. This article is part of the theme issue 'Celebrating the 15th anniversary of the Royal Society Newton International Fellowship'.

Pre-cooling systems in modern hydrogen liquefaction

The research work presents recommendations for choosing a circuit design for low-capacity hydrogen liquefaction plants with a production rate up to 20 kg/h or 0,48 tpd (ton per day). Main design criteria considered are specific energy cost, as well as capital costs and overall characteristics of the system. A review of theoretical and real hydrogen liquefaction cycles is presented. Mathematical models of different circuits are built up considering real parameters of the typical equipment. The advantages and disadvantages of certain solutions are identified, efficiency trends in terms of hydrogen liquefaction plants are analysed. According to the obtained results of the research main of the circuits for low-capacity hydrogen liquefaction plants are selected.

Markovian to non-Markovian phase transition in the operator dynamics of a mobile impurity

We study a random unitary circuit model of an impurity moving through a chaotic medium. The exchange of information between the medium and impurity is controlled by varying the velocity of the impurity, v_dvd, relative to the speed of information propagation within the medium, v_BvB. Above supersonic velocities, v_d> v_Bvd>vB, information cannot flow back to the impurity after it has moved into the medium, and the resulting dynamics are Markovian. Below supersonic velocities, v_d< v_Bvd<vB, the dynamics of the impurity and medium are non-Markovian, and information is able to flow back onto the impurity. We show the two regimes are separated by a continuous phase transition with exponents directly related to the diffusive spreading of operators in the medium. This is demonstrated by monitoring an out-of-time-order correlator (OTOC) in a scenario where the impurity is substituted at an intermediate time. During the Markovian phase, information from the medium cannot transfer onto the replaced impurity, manifesting in no significant operator development. Conversely, in the non-Markovian phase, we observe that operators acquire support on the newly introduced impurity. We also characterize the dynamics using the coherent information and provide two decoders which can efficiently probe the transition between Markovian and non-Markovian information flow. Our work demonstrates that Markovian and non-Markovian dynamics can be separated by a phase transition, and we propose an efficient protocol for observing this transition.

Optimal Fast-charging Strategy for Cylindrical Li-ion Cells

This paper presents an innovative approach to optimize the fast-charging strategy for cylindrical Li-ion NMC 3Ah cells, with a focus on enhancing both charging efficiency and thermal safety. Leveraging the power of Model Predictive Control (MPC), we introduce a cost function that approximates the thermal safety boundary of Li-ion batteries, revealing a relationship between temperature gradient and state of charge. Our proposed approach formulates the fast and safe charging problem as an optimal output regulator problem, incorporating thermal safety margin constraints. To solve the optimization problem, we develop an MPC algorithm. Our charge control structure incorporates an equivalent circuit model coupled with a thermal equation for battery state of charge and temperature estimation. Through numerical validation with real experimental data obtained from testing an NMC 3Ah cylindrical cell, we demonstrate that our approach respects the battery’s electrical and thermal constraints throughout the charging process.

Rheological Equivalent Circuit Model Using Electrochemical Impedance Analysis

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

Design of a 10.8 to 34.6 GHz Ultra‐Wideband Transparent Metamaterial Absorber Using an Equivalent Circuit Model

AbstractIn this paper, an ultra‐wideband metamaterial absorber (UWMA) is proposed and demonstrated by using a transparent and flexible sandwich structure, which consists of a top patterned double‐square loop (DSL) of conductive film, the polymer interlayer, the bottom conductive film. The work presents the UWMA's equivalent circuit model for a macroscopic analysis of its physical mechanism. Further, optimizing UWMA's structural parameters using this equivalent circuit model can greatly enhance its efficiency. The absorption coefficient of the designed structure achieves over 90% within the wide frequency range from 10.82 to 34.59 GHz due to the overlapping of three absorption bands. The experimental results indicate that the absorption coefficient of the fabricated structure exceeds 60% in the frequency range of 10.45–35.28 GHz, and reaches 90% in the majority of frequency range of 10.71–28.51 GHz, while its averaged optical transparency in the visible spectrum exceeds 75%. The UWMA achieves high transparency due to a small ratio of the surface area occupied by the ITO pattern to the total area and realizes multiple‐resonance ultra‐wideband absorption with conformality while maintaining a thickness of only 2.2 mm, which has diverse applications in the field of electromagnetics, including aircraft stealth, transparent chambers, and flexible electronic screens.

Optimized array for powering sensors: Thermal and electromagnetic energy harvesting and fusion

Environmental energy harvesting technology has achieved great success in remote sensor power supply applications. However, existing technologies in the power grid neglect the potential of weak energy sources. This study aims to optimize the most reasonable array configurations and create hybrid energy fusion schemes for different weak energy environments. Taking thermal and electromagnetic energy harvesting from cable surfaces and currents in coaxial cables as an example, this paper introduces a genetic algorithm-based optimization method of harvester array configuration under multiple constraints and a dual-source energy fusion system. First, a vector impedance parameter identification method based on the equivalent circuit model of current transformer (CT) is proposed. Later, an optimization model for harvester array is established. Then, a genetic algorithm is used to optimize array combinations. And, a dual-source energy fusion system is proposed. Finally, thermal and electromagnetic energy harvesting and fusion are performed using 3 × 1 TEGs array and 6 × 1CT array. Under the specified conditions of a hot end temperature of 50 ℃ and an effective current value of 2 A, the power supply for the Zigbee wireless sensing system is realized to monitor the temperature of the cable core.

Radiation Impedance of Rectangular CMUTs.

Recently, capacitive micromachined ultrasound transducers (CMUTs) with long rectangular membranes have demonstrated performance advantages over conventional piezoelectric transducers; however, modeling these CMUT geometries has been limited to computationally burdensome numerical methods. Improved fast modeling methods, such as equivalent circuit models, could help achieve designs with even better performance. The primary obstacle in developing such methods is the lack of tractable methods for computing the radiation impedance of clamped rectangular radiators. This paper presents a method that approximates the velocity profile using a polynomial shape model to rapidly and accurately estimate radiation impedance. The validity of the approximate velocity profile and corresponding radiation impedance calculation was assessed using finite element simulations for a variety of membrane aspect ratios and bias voltages. Our method was evaluated for rectangular radiators with width:length ratios from 1:1 up to 1:25. At all aspect ratios, the radiation resistance was closely modeled. However, when calculating the radiation reactance, our initial approach was only accurate for low aspect ratios. This motivated us to consider an alternative shape model for high aspect ratios, which was more accurate when compared with FEM. To facilitate the development of future rectangular CMUTs, we provide a MATLAB script that quickly calculates radiation impedance using both methods.

Observation of Young’s double-slit phenomenon in anti-PT-symmetric electrical circuits

Abstract In the last few decades, interference has been extensively studied in both the quantum and classical fields, which reveals light volatility and is widely used for high-precision measurements. We have put forward the phenomenon in which the discrete diffraction and interference phenomena, presented by the time-varying voltage of a Su-Schrieffer-Heeger (SSH) circuit model with an anti-PT (APT) symmetry. To demonstrate Young’s double-slit phenomenon in an APT circuit, we initially explore the coupled mode theory (CMT) of voltage in the broken phase, observe discrete diffraction under single excitation and interference under double excitations. Furthermore, we design a phase-shifting circuit to observe the effects of phase difference and distance on discrete interference. Our work combines the effects in optics with condensed matter physics, show the Young’s double-slit phenomenon in electrical circuits theoretically and experimentally.