Distributed Circuit Model Research Articles

Multi-Layered Metamaterial Absorber: Electromagnetic and Thermal Characterization

Metamaterials, recognized as advanced artificial materials endowed with distinctive properties, have found diverse applications in everyday life, military endeavors, and scientific research. Starting from monolayer metamaterials, multilayer ones are increasingly researched, especially in the field of electromagnetic wave absorption. In this article, we propose a multilayer metamaterial-absorber (MA) structure comprising two resonant layers crafted with copper and FR-4 dielectric. The presented multilayer MA structure exhibited an absorption greater than 90% in a frequency range from 4.84 to 5.02 GHz, with two maximum absorption peaks at 4.89 and 4.97 GHz. The bandwidth of the multilayer MA surpassed that of the individual single-layer MAs, with extension fractions reaching 360% and 257%, respectively. Through the simulation and calculation, the field distribution and equivalent circuit model elucidated that both individual magnetic resonances and their interplay contribute significantly to the absorption behavior of the multilayer MA. The absorption of the proposed multilayer MA structure was also investigated for the oblique incidence in the transverse electric (TE) and transverse magnetic (TM) modes. In the TE mode, the absorption intensity of two maximum peaks was maintained at over 93% up to an incident angle of 40 degrees and dropped to below 80% at an incident angle of 60 degrees. In the TM mode, the absorption was more stable and not significantly affected by the incident angle, ranging from 0 to 60 degrees. An absorption greater than 97% was observed when the incident angle increased from 0 to 60 degrees in the TM mode. Additionally, the approach in our work was further demonstrated by adding more resonant layers, making 3- and 4-layer structures. The results indicated that the absorption bandwidths of the 3- and 4-layer structures increased by 16% and 33%, respectively, compared to the bilayer structure. Furthermore, we analyzed the thermal distribution within the MA to understand the dissipation of absorbed electromagnetic energy. This research offers valuable insight into the augmented MA through a multilayer structure, presenting the implications for microwave applications like electromagnetic shielding, as well as in the design of MAs for terahertz devices and technologies, including emission and thermal imaging. These findings contribute to the advancement of knowledge in enhancing the absorption capabilities across various frequency ranges, expanding the potential applications of metamaterials.

A transparent broadband flexible metamaterial absorber for radar infrared-compatible stealth

The iterative upgrading of the means of warfare has promoted the development of detection technology, and military activities are increasingly demanding target stealth. In this paper, a multifunctional metamaterial absorber is recommended, which simultaneously realizes the integrated stealth functions of ultra-wideband radar wave absorption, low infrared emission, and optically transparent. The structure is composed of an infrared shield, a radar-absorbing layer, and a reflective layer. Simulation results indicate that the absorption bandwidth in the radar band (1.81–20.4 GHz) is more than 90%, and the infrared emissivity is as low as 0.271 in the IR band (3–14 μm). Moreover, it has the features of flexibility, angle stability (0–45°), polarization insensitivity (0–90°), and so on. Furthermore, the electric field current distribution and equivalent circuit model of the structure are analyzed, and a 180 mm*180 mm sample is built and tested; the results show that the simulated and actual measurements are in agreement, and it is expected that such absorbers will be used in areas such as aircraft.

Interconnected square splits ring resonator based single negative metamaterial for 5G (N258, N257, N260 and N259) band sensor/EMI shielding/and antenna applications

This article proposed a new triple-band transmission block metamaterial (MTM) for 5G mm-wave applications. The peak transmission-blocking attributes are achieved at 27.09 GHz, 38.71 GHz, and 41.81 GHz frequency by interconnected square split ring resonators (ISSRR). A thin Rogers RT5880 substrate material of thickness 0.79 mm is employed to design the MTM structure, and the unit cell dimension is 5 × 5 mm2. The designed metamaterial shows a −10 dB transmission coefficient (S21) from 24.60 to 28.47 GHz, 36.50–39.65 GHz and 40.77–44 GHz frequency bands. The design evolution, metamaterial properties, surface current distribution, electric field, magnetic field, and equivalent circuit model are investigated to understand the transmission-blocking property of the MTM. The simulated results of the MTM are validated by measurement of the fabricated prototype, and both results agree well. The transmission-blocking attributes lead the proposed MTM as a potential candidate for different fields like EMI shielding, sensing, and antenna performance enhancement. The dielectric sensor performance of the MTM structure is investigated for different dielectric materials. Besides, MIMO antenna performances are also investigated, and gains of 1–3 dBi, isolations of 5–10 dB, and the radiation pattern deflection angle of 45˚ are enhanced by the proposed MTM. These significant features and applications of the proposed MTM make it a special candidate for 5G mm-wave applications.

InP- and GaAs-Based Photonic Power Converters Under O-Band Laser Illumination: Performance Analysis and Comparison

Photonic power converters (PPCs), which convert narrow-band light to electricity, are essential components in power-by-light systems. When designed for telecommunications wavelengths such as the O-band, near 1310 nm, the devices are well-suited to power-over-fiber applications. Despite the potential for very high power conversion efficiencies ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {&gt;50\%}$</tex-math></inline-formula> ), PPCs can be adversely affected by high-intensity nonuniform illumination conditions. In this work, we characterized two O-band PPC designs based on: high-quality InGaAsP absorber material lattice-matched to an InP substrate, and metamorphic InGaAs absorber material lattice-mismatched to a GaAs substrate, a more cost-effective and scalable alternative. We measured each device under O-band laser illumination with five beam profiles having peak-to-average ratios ranging from 2 to 11. Both devices were insensitive to the beam uniformity for input illumination with average irradiance below 2 W/cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {^{2}}$</tex-math></inline-formula> over their 5.4-mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {^{2}}$</tex-math></inline-formula> active areas, but exhibited better open-circuit voltages under larger, more uniform illumination profiles at higher incident powers. Measured efficiencies reached 52.8% and 48.7% for the lattice-matched and mismatched devices, respectively. Distributed circuit modeling results suggested that both lateral conduction losses and localized heating effects were responsible for the measured dependence on beam-size. Our work demonstrates the potential for O-band PPCs, presenting two highly efficient designs suitable for powering devices requiring <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {\lesssim 250}$</tex-math></inline-formula> mW, with an appropriate illumination profile.

A 3D distributed circuit-electrochemical model for the inner inhomogeneity of lithium-ion battery

Performance degradation and operational safety are vital issues for lithium-ion batteries. After summarizing each battery failure accident, it is found that local defects caused by the inconsistency within the battery are one of the critical reasons for battery failure. To study the influence of the internal inconsistency of the battery on its safety performance, a 3D distributed circuit and electrochemical coupling model that can reflect the internal structure of the battery are established. Moreover, the model’s solid-phase potential and liquid-phase lithium ion concentration are corrected to improve the simulation accuracy. The RMSE of the model is less than 10 mV under 1.0 C constant current charging condition and dynamic discharge condition. Based on the proposed distributed model, this paper investigates the influence of the cell size, tab position, and other structural parameters on the internal inconsistency of the cell. And the phenomenon of “current reversal” and the possible local lithium deposition away from the tab position is discovered. The model’s correctness and efficacy in simulating internal inconsistencies are further illustrated by reproducing the local lithium deposition of a homemade LFP cell and a commercial NCM cell by controlling the charging current.

High-sensitivity metamaterial sensor based on electromagnetically induced transparency (EIT) effect

We propose a metamaterial sensor based on electromagnetically induced transparency (EIT) effect, which is composed of two elliptical structures with splits. Based on the coupling of bright and dark modes, a low-loss transparent window is realized at 1.88 THz. Surface current distribution and equivalent circuit model are used to analyze the physical mechanism of the EIT effect. In addition, the sensitivity of the sensor is investigated for different thickness and refractive index for analyte. The simulation results show that when the analyte thickness is 15 μm and the refractive index is between 1 and 1.5, the sensitivity of the sensor is as high as 450.7 GHz/RIU, and the figure of merit (FOM) value is 7.7. And when the refractive index of analyte is 1.5 and its thickness is between 0 and 5 μm, the sensor can also be used for thickness sensing with a sensitivity of 40.8 GHz μm−1. In addition, the proposed metamaterial sensor can be used to simulate the detection of sodium chloride solution, and the sensitivity is 66.2 GHz/. These above features indicate that the proposed structure paves the way for designing high-sensitivity EIT sensors in the terahertz region, which plays important roles in promoting terahertz sensing and detection technology.

Fast Current Distribution Simulation Method for No-Insulation HTS Coil With Defects

This paper presents a numerical method for fast simulation of current distribution in a no-insulation (NI) high temperature superconductor (HTS) coil with defects. A refined distributed-circuit model based on the partial element equivalent circuit (PEEC) approach is adopted to calculate the transient current distribution due to screening current. To reduce the time required for the simulation, a nonuniform axial segmentation method is presented in which the outer axially-subdivided azimuthal element is narrower than the inner element. In order to verify the simulation method, three NI HTS single-pancake coils are considered with the following characteristics: 1) the coil without any defects; 2) with one defect; 3) with two defects. The simulation results of current distribution due to screening current, total azimuthal current, radial current, and central magnetic field are presented. Moreover, it is proved that the time required for the simulation can be reduced by the nonuniform axial segmentation method without significant discrepancies in results.

Electronic transport in doped and dielectric inserted MLGNR interconnects: Crosstalk induced delay and stability analyses at sub-threshold regime

A simplified equivalent distributed temperature-dependent RLC circuit model of coupled multilayer graphene nanoribbon (MLGNR) interconnects has been discussed by considering the relaxation time induced mean free path (MFP), and its impact on line resistance (R) has been examined in detail. Further, the performance of copper, undoped, doped and dielectric inserted MLGNRs has been compared in terms of crosstalk induced delay and frequency response at sub-threshold operating conditions. It is revealed that the various scattering mechanisms (acoustic scatterings, edge roughness etc.) control the overall MFP in undoped and doped MLGNRs, however, the electron MFP in dielectric inserted MLGNRs depends on surrounding dielectric environment. Out of the five different cases of dielectric inserted MLGNRs, the insertion of hafnium oxide (HfO2) between GNR layers, along with silicon dioxide (SiO2) provides the best performance characteristics. To obtain minimum crosstalk delay at the subthreshold operating mode, copper, undoped, doped, and dielectric inserted MLGNRs have been optimized for thicknesses of 36, 38.25, 41.4, and 43.65 nm.

Simulation of Electro-Thermal Runaway and Thermal Limits of a Loaded HVDC Cable

This paper presents simultaneous simulation of interdependent electric and thermal fields inside a dc cable under loaded conditions using analogous distributed circuit models for thermal and electrical phenomena. Certain nonlinearities are integrated in such circuit models, leading to simulation of electro-thermal runaway, for the first time, in a dc cable. Using the suggested, nonlinear circuit models, complete dynamics of the temperature profile and electric field inside the cable dielectric can also be obtained under various test and operating conditions until electro-thermal runaway limits in time domain. The results are useful for design and development of dc cables with safety factors, apart from understanding the electro-thermal limits. The models are validated with experimental results, found to be in excellent agreement.

A Novel Design of a Compact Frequency-Selective Surface With High Selectivity and Angular Stability

A novel bandpass frequency-selective surface (FSS) with high selectivity and angular stability is presented. In the skirts of the narrow passband, two transmission zeros (TZs) are generated, leading to the steep roll-offs at both left and right skirts. The realization of two TZs using a single piece of a printed circuit board facilitates the fabrication. The current distribution and equivalent circuit model are given to illustrate the generation mechanism of the TZs. The proposed FSS can achieve good stabilities of polarization and angle. The size of this FSS is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.15\lambda $ </tex-math></inline-formula> . The prototypes of the proposed FSS are fabricated, and good performance is obtained.

Defect‐induced current coupling in multi‐junction solar cells revealed by absolute electroluminescence imaging

AbstractAn electroluminescence (EL) anomaly singular spot was observed in an industry‐standard InGaP/GaAs multi‐junction solar cell (MJSC). Affected by this singular spot, the spatially resolved subcell current distributions were found to exhibit unique opposite characteristics, which we call “defect‐induced current coupling.” Herein, we conducted systematic investigations to reveal the defect‐induced current coupling phenomenon, for the first time, through the absolute EL imaging technique. Specifically, a modified carrier‐balance model was first proposed to describe the subcell optoelectronic distribution around the singular spot. Then, optical and electrical properties including subcell non‐radiative recombination distributions, J–V characteristics, essential photovoltaic parameters, and energy losses were quantitatively extracted for characterizing the performance inhomogeneity caused by the defect‐induced coupling. Moreover, a three‐dimensional distributed circuit model was established to numerically simulate the absolute EL emissions and extract local electrical parameters around the singular spot. Simulation results revealed that the defect‐induced current coupling phenomenon is attributed to the deterioration of weak‐diode and shunt parameters at the GaAs bottom cell, and the efficiency of the MJSC was estimated to be reduced by 0.408% compared with the defect‐free MJSC model.

Design of Periodic End-Coupled Leaky-Wave Antenna With Asymmetrically Loading Unit

In this letter, a periodic end-coupled leaky-wave antenna is designed based on an asymmetrically loading unit. A simple balancing condition in the equivalent distributed circuit model is developed for the open stopband suppression by introducing a complex effective resonant frequency. The proposed balancing condition naturally satisfies both the frequency-balancing condition and Q-balancing condition in the lumped circuit model. Based on the derived formula, the physical parameters could be quantitatively determined. Subsequently, two typical periodic end-coupled leaky-wave antennas are designed, implemented, and verified experimentally. The measured reflection coefficient and the radiation results show that the open stopband at the broadside frequency is successfully suppressed.

Compact transition enabled broadband propagation of spoof surface plasmon polaritons based on the equivalent circuit model

In this paper, a strategy to develop a compact transition of the spoof surface plasmon polariton (SSPP) transmission line (TL) is proposed. First, an equivalent distributed circuit model is employed for the theoretical analysis and optimization design of the SSPP unit. The mapping relation between the unit performance and the geometric parameters is deduced from the transmission matrix. The calculated results are compared with the numerical ones from the three-dimensional (3D) simulations for validation. Then, a compact transition (only 0.26λ g) is built with only two matching units and a tapered strip through optimizations. The optimizations are implemented with the circuit simulations based on the equivalent model, which can remarkably save time in comparison with the 3D simulations. The transition principle is also explained by quantitatively extracting the dispersion properties and impedance characteristics. Finally, a prototype of the proposed SSPP TL is fabricated and measured for demonstration. The measured operating band (0–7.7 GHz) is almost up to the cut-off frequency (about 8 GHz), which remains the inherent broadband low-pass transmission characteristics. Meanwhile, the measured in-band return loss is almost higher than 10 dB, which verifies the high-efficiency propagation. This work can pave the way for building up a new SSPP-based framework of microwave circuits.

A quantitative approach for trap analysis between Al0.25Ga0.75N and GaN in high electron mobility transistors

The characteristics of traps between the Al0.25Ga0.75N barrier and the GaN channel layer in a high-electron-mobility-transistors (HEMTs) were investigated. The interface traps at the Al0.25Ga0.75N/GaN interface as well as the border traps were experimentally analyzed because the Al0.25Ga0.75N barrier layer functions as a dielectric owing to its high dielectric constant. The interface trap density Dit and border trap density Nbt were extracted from a long-channel field-effect transistor (FET), conventionally known as a FATFET structure, via frequency-dependent capacitance–voltage (C–V) and conductance–voltage (G–V) measurements. The minimum Dit value extracted by the conventional conductance method was 2.5 × 1012 cm−2·eV−1, which agreed well with the actual transistor subthreshold swing of around 142 mV·dec−1. The border trap density Nbt was also extracted from the frequency-dependent C–V characteristics using the distributed circuit model, and the extracted value was 1.5 × 1019 cm−3·eV−1. Low-frequency (1/f) noise measurement provided a clearer picture of the trapping–detrapping phenomena in the Al0.25Ga0.75N layer. The value of the border trap density extracted using the carrier-number-fluctuation (CNF) model was 1.3 × 1019 cm−3·eV−1, which is of a similar level to the extracted value from the distributed circuit model.

Time-resolved investigation of plasmon mode along interface channels in integer and fractional quantum Hall regimes

The authors investigate here the fundamental charge dynamics of interface quantum Hall (QH) channels, formed at the interface of two QH regions, by using a time-resolved scheme. The measured plasmon mode is delayed and broadened due to the influence of charge puddles formed around the channel. The transport behavior can be understood with a distributed circuit model, which reveals the importance of gate-puddle capacitive coupling on plasmon dissipation. By reducing the puddle capacitance, a high-quality fractional interface channel can be realized.

Polarization-Agile Circular Polarized Antenna Based on Proximity Feeding Technique

In this letter, the design and experimental validation of polarization-agile circular polarized antenna are presented. The antenna is comprised of a patch antenna with truncated slits and two proximity feedlines. The antenna produces a vertical linear polarized wave when it is fed by a proximity feedline. Horizontal linear polarized wave is then generated by applying a potential difference between two proximity feedlines. The quadrature phase difference between two orthogonal polarized waves is created by adding truncated slits into the patch antenna. By swapping the polarity of the proximity feedlines, polarization sense can be changed. The distributed circuit model is presented to describe the working mechanism of the antenna. Patch antenna with circular polarization agility is then validated through passive-type and active-type switching circuits. The measured axial ratio bandwidth is 4.085% (100 MHz), and the fractional impedance bandwidth is greater than 7% for the left-handed and right-handed circular polarized radiations.

Diagnosing breakdown mechanisms in monocrystalline silicon solar cells via electroluminescence imaging

The local breakdown behavior may be harmful to solar cells and could possibly permanently damage the cell. Therefore, understanding the breakdown mechanisms in commercially competitive photovoltaic devices such as monocrystalline silicon (Si) solar cells is of great importance. Here, by using the reverse-biased electroluminescence (ReBEL) imaging technique, we observed three types of breakdown phenomena in monocrystalline Si solar cells: defect-induced breakdown, avalanche breakdown, and early breakdown. We have applied a variety of methods to diagnose each breakdown mechanism. The positions of defect-induced breakdown were first determined by combining EL and ReBEL imaging. An innovation method, the distributed circuit modeling was further introduced to trace the formation of different defect-induced breakdown sites. It is firstly applied this approach in the analysis of the breakdown mechanism. Then, avalanche breakdown was demonstrated by the temperature coefficient. The origin of its emission spectra was analyzed by the Si energy band structure combined with Baraff theory. Moreover, the characteristic of early breakdown was found to be consistent with the Zener effect, which may be caused by the metal stains such as aluminum (Al) during the manufacturing process.

Electroluminescence imaging of laser induced defect formation in Cu(In, Ga)Se2 solar cell

The combination of lasers and solar cells has potential applications in many areas. Therefore, investigating the laser induced damage and defect formation in such cells is crucial. In this study, a Cu(In, Ga)Se2 solar cell was irradiated with a 532 nm continuous wave laser beam. The damage threshold power density with irradiation for 10 s was found to be approximately 5000 W/cm2 by analyzing the light current density–voltage curves and the variation of the solar cell efficiency after laser exposure. Further, absolute electroluminescence (EL) imaging with distributed circuit modeling was used to determine the laser induced defects. By simulating the measured injection current dependent EL intensities of the defect spots, the defects created by exposure to laser power densities less than 5000 W/cm2 could be mainly attributed to increased series resistance or increased transparent conductive oxide layer resistance, whereas those created by exposure to laser power densities greater than 5000 W/cm2 could be mainly attributed to decreased shunt resistance.

Dual-Beam Leaky-Wave Antenna (Lwa) Based on Microstrip

Second-order higher mode periodic leaky-wave antennas (LWAs) are proposed. The distributed circuit model is used to balance the impudence matching and open stop-band suppression. By loading the longitudinal slots in the unit cell, the leaky-wave antenna produces a dual symmetrical beam that scans from backward to forward. The LWA shows good radiation performance and gain in the scanning region of -500 (backward region) to +500 (forward region).

Upper Limit Estimation of Resistive Heating Made by No-Insulation HTS Magnet Having Defects

Seoul National University and Hanmi Techwin Inc. have launched a program for the development of a large bore, low field, and low-cost high temperature superconductor (HTS) magnet for industrial applications. HTS coils exhibit defect-irrelevant behaviors when wound using no-insulation (NI) technique, i.e., wound without turn-to-turn insulation. Incorporation of defect-irrelevant winding (DIW) technique would be favorable to constructions of HTS magnets as it may drive the cost of production down and curtail construction time if used appropriately. An HTS magnet having a center magnetic field of 2 T and cold bore size of 230 mm has been designed, and charging simulation was performed using a turn distributed circuit model. Defect-irrelevant behaviors are examined stochastically, considering random occurrences of defective turns. Using the turn distributed circuit model indicates that the magnitudes of defects have limited effects on resistive heatings in both steady state and transient operations. The upper bounds of excess heat contributed by defective turns are numerically formulated using characteristic resistances and operating currents.