High Transmission Coefficient Research Articles

Theoretical design and implementation of equal and unequal split ultra-wide band Wilkinson power divider with Chebyshev impedance transform

Abstract In this study, we designed multi-section UWB Wilkinson power dividers for both equal and unequal power divider. The key innovation is successfully matching these power dividers using the Chebyshev method. The proposed method achieves very low insertion losses and high transmission coefficients across the ports. For the three-section equal power divider, Chebyshev polynomials were used to model the reflection coefficient, and the characteristic impedance for each section was calculated symmetrically. The design achieved a fractional bandwidth of 106% for a 20 dB return loss, with an insertion loss of 0.3 dB. For unequal multi-section dividers, power division ratios of 1.5:1 and 2:1 were chosen. Theoretical microwave calculations were used to determine the input and output transmission line impedances. Chebyshev approximation was then applied to design the three-section unequal power dividers. The return losses for these unequal dividers were measured at 17 dB and 15 dB, with fractional bandwidths of 120% and 126%. Both circuits had insertion losses of 0.25 dB. The consistent results from analytical calculations, simulations, and measurements confirm the effectiveness of the Chebyshev method for both equal and unequal power division.

Reconfigurable multi-band electromagnetically induced transparency metamaterial based on graphene

By utilizing the monolayer graphene, we propose a reconfigurable multiband EIT 3D structure in the THz region, which exhibits eight consecutive transparency windows spanning from 1.16 to 2.80 THz, and the according transmission intensities were in the range of 0.75–1.0. Furthermore, with the help of graphene and VO2, the transmission curves can be modulated efficiently. The research results demonstrate that the structure proposed can generate high-intensity slow light effects at multiple frequency points within the terahertz range. Compared to existing research on EIT metamaterials, this structure offers advantages such as operation in multiple frequency bands, high transmission coefficients, and flexible modulation capabilities. Therefore, this study helps design novel tunable THz devices.

Enhancing 5G propagation into vehicles and buildings using optically transparent and polarisation insensitive metasurfaces over wide-incidence angles

This article introduces two transmissive metasurfaces applied to normal windows, aiming to improve the 5G outdoor-to-indoor (O2I) coverage. These windows can be utilized in various settings, such as vehicles or buildings. The proposed unit cells, designed to be wide-incident angle and polarization insensitive, are implemented in both single-glazing and double-glazing glasses, arranged in a periodic structure to form the transmission surfaces. Both metasurfaces maintain optical transparency by incorporating Indium Tin Oxide (ITO) as the conductive element in each unit cell. These engineered transmission surfaces enhance the 5G signal indoor coverage at the 3.5 GHz band across a broad range of incident angles. While multi-layer structures typically exhibit heightened sensitivity to the angle of incidence, the proposed two-layered transmissive surfaces demonstrate substantial angular stability, reaching up to 65 and 75 degrees for double- and single-glazed glass, respectively. To achieve this wide and stable angular response, evolutionary optimization techniques were employed to fine-tune the proposed unit cells. Both designs exhibit a high transmission coefficient across the operating frequency for a variety of incident angles, surpassing those reported in the existing literature. Experimental evaluations of the fabricated prototypes indicate that both metasurfaces hold significant potential for enhancing signal propagation into buildings and vehicles.

Analytical Modeling of [001] Orientation in Silicon Trigate Rectangular Nanowire Using a Tight-Binding Model

AbstractIn the realm of electronics, the performance of Silicon Trigate Rectangular Nanowires (Si-TRNW) and the structural characteristics of <001> orientation using tight-binding models have been analyzed. The fast algorithm based on the tight-binding model for Trigate Silicon nanowires yielded a remarkable ION/IOFF ratio of 1.49 × 1010 and leakage current (ILeak or IOFF) of 3.7 × 10−17μA. Furthermore, a maximum conduction band energy level (Ecmax) of −0.003 eV and a Subthreshold Slope (SS) of 120 mV has been obtained for a channel length of 15 nm. At an energy level of 3 eV, a high Transmission coefficient, T(ε), of 4 has been attained using the E-k dispersion method. This analysis also involved the calculation of three ∆ valleys pertinent to the channel’s effectiveness in <001> orientation, with proximity nearer to 1 m0. The Schrodinger-Poisson equation has been analyzed with the Ballistic transport along the [001] z-direction in channel potential. A comparative assessment has been also performed between the lateral dimensions of rectangular nanowires with equal energy levels, utilizing both the tight-binding model and Density Functional Theory (DFT) techniques. In some high-frequency applications, a high transmission coefficient is beneficial to maximize the amount of energy or information that gets transmitted. Reducing leakage current would offer a technological pathway for performance improvement of high-frequency applications. The high ON-current (ION) has been obtained through the DFT approach between source and drain terminals is particularly desirable for applications demanding for fast switching speeds and high-performance computing. The strengths of both methods in hybrid approaches is a common strategy to achieve simulations that are both accurate and efficient. Notably, the nanowires subjected to hydrostatic strain, exhibiting enhanced mobility and exceptional electrostatic integrity, emerged as pivotal components for forthcoming technology nodes. This research augments the potential feasibility of strain-based Si nanowires, even at the 3 nm scale, in subsequent technological advancements.

Designing van der Waals magnetic tunnel junctions with high tunnel magnetoresistance via Brillouin zone filtering.

Magnetic tunnel junctions (MTJs) consisting of two-dimensional (2D) van der Waals heterostructures have no inter-layer chemical bonds; therefore, their spin tunneling is determined solely by the Brillouin zone (BZ) filtering effect. To obtain high tunnel magnetoresistance (TMR), they should possess transversal momentum-resolved conduction channels for the electrodes and transmission channels for the barriers. Here, we investigate 2D magnets as electrodes whose Curie temperatures approach room temperature and also hexagonal 2D insulators as the barrier. Iron-based compounds such as FexGeTe2 (x = 3 and 4) are calculated to have high transmission coefficients over the entire in-plane BZ for the majority spin channel, while this should only happen around Γ for the minority spin channel. Correspondingly, various 2H-type transition metal dichalcogenides (TMDs) are found to function effectively as spin barriers, where electrons are only allowed to tunnel through them around the K and M points. BZ spin filtering is confirmed to be the major mechanism of the TMR effect by the MTJ transport calculation using the non-equilibrium Green function method. Furthermore, the TMR is calculated to be nearly independent of the barrier layer thickness as the BZ filtering is an interfacial effect. This work sheds light on material selection procedures and designing ultra-thin and robust van der Waals MTJs.

Development method of splitting the radio-reflective large-sized reflector surface into cutting patterns made of mesh with coarse cells

An important design component of space antenna reflectors is a reflecting surface. At present, metallic knitted mesh fabric is most often used as a reflective surface; it fully meets the requirements for such surfaces in terms of physical and mechanical properties. Particularly important characteristics for large-sized reflectors are low specific gravity and high light transmission coefficient, which a mesh with coarse cells provides. However, the structural features of this mesh fabric impose additional requirements on its use as a reflective surface for large-sized transformable reflectors. The article deals with a special approach to designing patterns for a reflective surface made of mesh with coarse cells. The developed pattern cutting option allows to obtain a reflective surface with the least distortion (error), in accordance formulated criteria. The authors have suggested the option of obtaining cutting patterns of metallic mesh fabric, described the advantages of the proposed option over the classical one. The cutting pattern of the parabolic surface for the offset reflector was obtained. The proposed cutting pattern option was analyzed. Furthermore, optimization was carried out, which made it possible to maintain the integrity of the cellular structure of patterns along one loop row. The compared results show that the developed cutting pattern option completely complies with the requirements and it can be used to form a reflective surface from the metallic knitted mesh with coarse cells.

Design of tunable notch filter based on plasmonic and InGaAsP waveguide

A highly efficient compact tunable optical notch filter is proposed and analyzed using the 2D Finite Element Method (FEM). The proposed structure consists of a slanted stub plasmonic resonator, Metal–Insulator–Metal (MIM) waveguide, and InGaAsP as a third-order non-linear optical material. By altering the pumping state of the InGaAsP, the filtered wavelengths may be easily controlled continuously over 200 nm a range. The suggested notch filter can remove four narrow bands of wavelengths, each around 50 nm wide, and a transmission of about − 17 dB. The proposed filter’s key advantages are its high transmission coefficient and fabrication simplicity with compact size. For future integrated plasmonic devices such as outdoor visible light communications and optical imaging, the proposed filter can be manufactured using an oblique angle shadow evaporation technique.

Multiple Fano Resonances in Dynamic Resonant Tunneling Processes

The existence of Fano resonances in dynamic resonant tunneling (RT) systems has been investigated. Fano resonances are characterized by the appearance of a 100% reflection coefficient in proximity to a high transmission coefficient. For a Fano resonance to appear, a bound state must exist. On the other hand, a resonant tunneling process is characterized by a high transmission and the existence of a quasi-bound state (QBS) instead of a bound one. It has been shown that, by narrowing the width of the barrier, the resonance energy of the QBS gradually decreases and eventually turns into a bound state. Consequently, in a dynamic RT process, there are two scenarios: either a bound state exists, in which case, Fano resonances exist for any barrier width, or a QBS exists, and the barrier should be narrow enough for the Fano resonance to appear. In both cases, the incoming particle’s frequency must be lower than the oscillating well’s frequency. In this work, these resonances are investigated in detail, and both exactly numerically and approximated analytical expressions are derived for both the weak and strong oscillating amplitude regimes. One of the conclusions is that, when the oscillating frequency is low enough, multiple Fano resonances can appear by varying the barrier’s width. Since these resonances are very sharp and zero transmission can easily be detected, this property can be used as a very accurate method for measuring the barrier’s width, even when the particle’s de-Broglie wavelength is much larger than the barrier’s width.

Freestanding narrowband terahertz filters based on aluminum foil.

Terahertz (THz) filters with high transmission coefficient (T) in the passband and frequency selectivity are critical in numerous applications such as astronomical detection and next-generation wireless communication. Freestanding bandpass filters eliminate the Fabry-Pérot effect of substrate, thus providing a promising choice for cascaded THz metasurfaces. However, the freestanding bandpass filters (BPFs) using the traditional fabrication process are costly and fragile. Here, we demonstrate a methodology to fabricate THz BPFs using aluminum (Al) foils. We designed a series of filters with center frequencies below 2 THz and manufacture them on 2-inch Al foils with various thicknesses. By optimizing the geometry, T of the filter at the center frequency is over 92%, and the relative full-width half maxima (FWHM) is as narrow as 9%. The responses of BPFs show that "cross-shaped" structures are insensitive to the polarization direction. The simple and low-cost fabrication process of the freestanding BPFs promise their widespread applications in THz systems.

High Performance Multiple Passband Substrate Integrated Plasmonic Filters

We proposed a new variety of substrate integrated plasmonic filters (SIPFs) with multiple passband characteristics based on the concept of spoof surface plasmon polaritons (SSPPs). By etching a periodic interdigital structure array on the top metal layer of substrate integrated waveguide (SIW), we can achieve high-efficiency microwave SSPP transmission with an insertion loss of 1 dB in the passband of 7.4-12.5 GHz, and a high rejection level of 27 dB in the rejection bands. By introducing antisymmetric C-ring resonators (ASCRs) in the filter structure, the passband number and bandwidth of the filter can be flexibly manipulated. To validate the proposed design, four SSPP filters prototypes are fabricated and tested, showing good filtering performances with a high transmission coefficient ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{S}21\mathbf {&gt;}-$ </tex-math></inline-formula> 1 dB) and low reflection coefficient ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{S}11\,\,\mathbf { &lt; } - $ </tex-math></inline-formula> 12 dB) in their passbands, and a high rejection level over 15 dB between them. By changing the geometric parameters of ASCR, the number of passbands can be increased from 1 to 3, and the passband center frequency and bandwidth can be engineered accordingly. The proposed SSPP filters with good multiple passband characteristics may have great potential applications in microwave wireless integrated plasmonic circuits and communication systems.

Extreme Anisotropic Dispersion and One-Dimensional Confined Electrons in 2-D SiP₂ FETs With High Transmission Coefficients

2-D semiconductors are promising Si alternatives for channels in next-generation electronic devices. Considering the 2-D SiP2 with unique dispersion at the band edge and intrinsic P–P chains with 1-D confined electrons, we provide a comprehensive investigation on the electronic and ballistic transport properties of SiP2. Based on first-principle and ballistic quantum transport simulations, the 2-D SiP2 exhibits a strong anisotropy in both geometric structures and electronic properties, playing a critical role in the anisotropy of transmission path and device performance for SiP2 field-effect transistors (FETs). Considering the ultrahigh saturation current ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}_{\text {sat}}$ </tex-math></inline-formula> ) of SiP2 FETs in along-chain direction, the transfer characteristic with different gate lengths (3–12 nm) is calculated to thoroughly evaluate the performance. As a result, 5–12 nm SiP2 n-FETs with underlap (UL) configuration can fulfill the International Technology Roadmap for Semiconductors (ITRS) and International Roadmap for Devices and Systems (IRDS) goals, showing an ultrahigh ON-state current of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3420 ~{\mu } \text{A}/ {\mu } \text{m}$ </tex-math></inline-formula> with 10 nm gate length. In addition, the figures of merits, such as delay time and power dissipation, are comprehensively assessed, proving the fast-switching and low-energy consumption ability of SiP2 FETs. Hence, our study demonstrates the great potential of 2-D SiP2 for future competitive electronic devices.

An ultra-narrow-band optical filter based on zero refractive index metamaterial

Owing to the photonic band gap effect and defect state effect, photonic metamaterials have received much attention in the design of narrow bandpass filters, which are the key devices of optical communication equipment such as wavelength division multiplexing devices. In this work, based on zero-index metamaterial (ZIM), a compact filter with both high peak transmission coefficient and ultra-narrow bandwidth is proposed. The photonic metamaterial with conical dispersion and Dirac-like point is achieved by optimizing the structure and material component parameters of dielectric rods with square lattice in air. It is demonstrated that a triply degenerate state can be realized at the Dirac-like point, which relates this metamaterial to a zero-index medium with effective permittivity and permeability equal to zero simultaneously. Electromagnetic (EM) wave can propagate without any phase delay at this frequency, and strong dispersion occurs in the adjacent frequency cone, leading to dramatic changes in optical properties. We introduce a ZIM into photonic metamaterial defect filter to compress the bandwidth to the realization of ultra-narrow bandpass filter. The ZIM is embedded into the resonant cavity of line defect filter, which is also composed of dielectric rods with square lattice in air. In order to increase the sensitivity of the phase change with frequency, the Dirac-like frequency is adjusted to match the resonant frequency of the filter. We study the transmission spectrum of the structure through the COMSOL Multiphysics simulation software, and find that the peak width at half-maximum of the filter decreases as the thickness of ZIM increases, and the peak transmittance is still high when bandwidth is greatly compressed. The zero phase delay inside the slab can be observed. Through field distribution analysis, the zero-phase delay and strong coupling characteristics of electromagnetic field are observed at peak frequency. The comparison with conventional photonic metamaterials filter is discussed. We believe that this work is helpful in investigating the realization of ultra-narrow bandpass filters.

Investigation of Waveguide Propagation of Terahertz Signal with Different Polarization Angle and Twisting Rate for Terabit DSL Application

When the demand for higher data rates grows, various telecommunications technologies are proposed; for these cases, the terabit DSL is investigated. Terabit DSLs provides solutions to the inevitable bottleneck that future wireless systems encounter. However, the propagation loss in twisted pairs becomes a massive concern in terabit DSL. Besides the attenuation, propagation characteristics at terahertz frequencies in twisted pair are not much explored by the researcher. Therefore, terahertz signal propagation characteristics in a waveguide based on surface plasmonic are investigatedin this project by using simulation software CST MICROWAVE STUDIO. A circular waveguide with radius of 0.25 mm and length of 20 mm respectively has been simulated in between 360 GHz to 380 GHz. The reflection coefficient and transmission coefficient analysis of the circular waveguide are investigated in terms of the polarization angles and twisting rate. Based on the simulated results, it is discovered that the polarization angle influences the reflection coefficient and transmission coefficient of the circular waveguide. When the polarization angle difference is 90 degrees, it has the worst reflection. The circular waveguide with a polarization angle difference of 0 degrees and 180 degrees, it has the best transmission coefficient. The transmission coefficient of the circular waveguide, on the other hand, is unaffected by the twisting rate. Even though the highest twisting rate that has the highest transmission coefficient, it is still lower than 3 dB. Besides, the higher the twisting rate the lesser the number of resonances for the circular waveguide.

Nano optical temperature sensor based on fiber Bragg grating using graphene

In this paper, a novel Graphene-Assisted Microfiber based temperature sensor is proposed that changing the surrounding temperature has a severe effect on the refractive index of the graphene, so these changes result in the transmission power of microfiber. In the proposed structure, the position of the graphene sheet affects the interaction of light and graphene, effectively. Simply, by examining the change in transmission power, the temperature sensitivity of 0.1038 dBC in the heating process and 0.1072 dBC in the high-resolution cooling process of 0.0098 ℃ is obtained, which is 16 times more than bare fiber. Moreover, in this paper, both MgF2 layer and the graphene ribbon affect fiber refractive index so a high sensitivity, compact size, low cost, linear operation and suitable transmission coefficient temperature sensor is achieved. This sensor has great potential in the field of measurement, especially surrounding temperature measurement. Also, a comprehensive and detailed study of the properties of surface conductivity, electric dispersion, refractive index and permittivity for graphene with sensitivity simulation is accomplished.

Locating Transition Zone in Phase Space.

Understanding the reaction mechanism is required for better control of chemical reactions and is usually achieved by locating transition states (TSs) along a proper one-dimensional coordinate called reaction coordinate (RC). The identification of RC can be very difficult for high-dimensional realistic systems. A number of methods have been proposed to tackle this problem. A machine learning method is developed here to incorporate the influence of velocity on the reaction process. The method is also free of the unbalanced label problem resulting from the rather low fraction of configurations near the TS and can be easily extended to large systems. It locates the transition zone in the phase space and defines the dividing surface with a high transmission coefficient. Moreover, considering that the reaction environment can not only change the reaction path but also activate the reactive mode through energy transfer, we devise two measures to quantify the influence of these two factors on the reaction process and find that solvents can assist the reaction by directly doing work along the reactive mode. Not surprisingly, there is a positive correlation between the efficiency of energy transfer into the reactive mode and the reaction rate.

Electrical and Optical Properties of CaTi1−yFeyO3−δ Perovskite Films as Interlayers for Optoelectronic Applications

CaTi1−yFey O3−δ perovskite oxide films are promising candidate materials for p-type interlayers of third generation solar cells or light-emitting devices. The impact of atomic Ti substitutions by Fe on electrical and optical properties of CaTi0.5Fe0.5O3−δ perovskite films have been studied. The best compromise between a high transmission coefficient and the suitable electrical conductivity is obtained for a specific atomic composition of Ca (1) Ti (0.5) Fe (0.5) O (3−δ) perovskite films. This paper shows that CaTi1−yFeyO3−δ perovskite oxides can be integrated as p-type interfacial layers of optoelectronic devices through their work functions, electrical, and optical properties.

New Reconfigurable Transmitarray Unit Cell Design at Ku-Band Using PIN Diodes

Beam reconfigurable Transmitarray antennas require the unit cell phase variation capability. This paper presents a new reconfigurable Transmitarray unit cell design using PIN diodes at the Ku-band. The unit cell is comprised of three layers having four PIN diodes used in every unit cell layer. This results in phase controlling by switching the PIN diodes on every layer individually. The unit cell s-parametric analysis shows a high transmission coefficient magnitude (&gt; -3.6dB) at a design frequency of 12.5GHz and maximum wide impedance bandwidth (17.5%). Four different switching states configurations are used, which result in phase variations over the range of 150.5 degrees. The transmission coefficient magnitude remains high for all four switching states. The proposed reconfigurable unit cell can be used in designing beam switched Transmitarray antennas for satellite communications and beam steering applications.

Study of the transport properties of cobalt atomic contact under mechanical strain in a nitrogen atmosphere

Achieving an efficient spin-filter effect and large magneto-resistance in molecular junctions is very important in spintronics. By employing the non-equilibrium Green's function formalism combined with the density functional theory, this study investigated the atomic structures and spin-resolved transport properties of molecular junctions consisting of nitrogen (N2) sandwiched between two cobalt (Co) electrodes with different crystal lattices as a function of stretching distance. In the case of face-centred cubic Co electrodes, our calculations showed that the transport properties depend strongly on the stretching process, which changes the contact between the N2 and Co electrodes. Specifically, the maximum spin polarization is due to the configuration of N2 molecules sitting in parallel with the protruding Co atoms. Furthermore, the Co dxz,yz orbitals interact with the N px,y orbitals, which contribute to the high transmission coefficient at the Fermi level for spin-down electrons. Meanwhile, the Co s-dz2 hybridization orbitals, which interact weakly with the N p orbitals, contribute to the small transmission coefficient at the Fermi level. This can also be verified by the molecular junction model adopting simple monatomic Co chain electrodes, which also show a perfect spin-filter effect and achieve an ideal magnetoresistance. In contrast, in the case of hexagonal Co electrodes, the spin-filter effect disappears. However, the effect appears again by adding one more Co atom to the central point contact. Our findings show that the spin-resolved electronic transport of molecular junctions depends on the stretching process and the nature of the electrodes, which can help in the future design of molecular devices based on the spin degree of freedom.

Edge spin wave transmission through a vertex domain wall in triangular dots

Spin waves (SWs), being usually reflected by domain walls (DWs), could also be channeled along them. Edge SWs yield the interesting, and potentially applicable to real devices property of broadband spin wave confinement to the edges of the structure. Here, we investigate through numerical simulations the propagation of quasi one-dimensional spin waves in triangle-shaped amorphous YIG (Y3Fe5O12) micron sized ferromagnets as a function of the angle aperture. The edge spin waves (ESWs) have been propagated over the corner in triangles of 2 microns side with a fixed thickness of 85 nm. Parameters such as superior vertex angle (in the range of 40^circ –75^circ ) and applied magnetic field have been optimized in order to obtain a higher transmission coefficient of the ESWs over the triangle vertex. We observed that for a certain aperture angle for which dominated ESW frequency coincides with one of the localized DW modes, the transmission is maximized near one and the phase shift drops to pi /2 indicating resonant transmission of ESWs through the upper corner. We compare the obtained results with existing theoretical models. These results could contribute to the development of novel basic elements for spin wave computing.

Transmissive type dual band polarization converter integrated microstrip patch antenna in THz regime

This article proposes the generation of both LHCP and RHCP waves simultaneously –at two distinct frequencies by using a single-layered compact polarization converter (PC). The proposed PC has been designed with a gold pattern inscribed on a polyimide substrate. A modified I-shaped structure with semi-circular curved ends provides a quadrature phase shift between the orthogonal components of the incident electric field with a high transmission coefficient and low insertion loss across the two THz frequency bands. Two equivalent circuit models have been proposed for TE and TM modes separately. As a proof of concept of the proper functioning of the proposed PC, one dual-band linearly polarized antenna is designed and integrated with the PC. The linearly polarized radiated waves from the dual-band antenna across 1.55 THz and 4.05 THz have been successfully converted into both the RHCP and LHCP waves simultaneously. The integration of a simple profile PC with a dual-band THz antenna to produce dual CP radiated waves simultaneously are the key achievements of this proposed work. Moreover, the results of equivalent circuit models for both TE and TM modes are justified after proper validation with the full-wave EM simulation results. The proposed dual-band PC, dual-band THz antenna, and the integrated structures are systematically investigated using FEM-based CST Microwave studio.