Surface Impedance Model Research Articles

Analysis of 3D plasmonic circuits by using surface impedance models.

Novel and accurate global and local surface impedance models have been developed to analyze plasmonic circuits fast and efficiently. In the analysis procedure, first the metal strip in the plasmonic circuit is modeled by a surface impedance. Then, the calculated surface impedance is employed in the surface integral equation to analyze the plasmonic circuit such as a through line and line coupler. Accuracy of the numerical results is shown in comparison with a commercial simulation software. The number of unknowns as well as the computational time are also compared with the volume integral equation, and it is obvious that, using our proposed surface impedance models, the analysis will be much faster and more efficient. This could have been evident from the beginning because usage of the surface impedance model helps bring the unknowns to the boundary of the structure, which reduces the number of unknowns.

The impact of coronal mass ejection on the horizontal geomagnetic fields and the induced geoelectric fields

This work investigates the influence of coronal mass ejection (CME) on the time derivatives of horizontal geomagnetic and geoelectric fields, proxy parameters for identifying GICs. 16 events were identified for the year 2003 from the CORONAS-PHOTON spacecraft. Five of the events (May 29, June 9, October 28, October 29, and November 4) were extensively discussed over four magnetic observatories, were analyzed using the time derivatives of the horizontal geomagnetic (dH/dt) and geoelectric (EH) fields obtained from data of the INTERMAGNET network. It was observed that energy distributions of the wavelet power spectrum of the horizontal geoelectric field are noticed at the nighttime on both 29 May and 9 June 2003 across the stations. Daytime and nighttime intensification of energy distribution of the wavelet power spectrum of the horizontal geoelectric field are observed on both 28 and 29 October 2003 due to strong westward electrojet. The 4 November 2003 event depicts daytime amplification of energy distributions of the wavelet power spectrum across the stations. The highest correlation magnitude is obtained in the event of 4 November 2003 between dH/dt and EH relationships during the intense solar flare of class X 17.4. We observed that the correlation magnitude between dH/dt and EH increases with increase in CME activity. We concluded that the response of the surface impedance model for different stations plays a key role in determining the surface electric field strength, due to large electric field changes at different stations.

Acoustic metasurfaces for scattering-free anomalous reflection and refraction

Manipulation of acoustic wavefronts by thin and planar devices, known as metasurfaces, has been extensively studied, in view of many important applications. Reflective and refractive metasurfaces are designed using the generalized reflection and Snell's laws, which tell that local phase shifts at the metasurface supply extra momentum to the wave, presumably allowing arbitrary control of reflected or transmitted waves. However, as it has been recently shown for the electromagnetic counterpart, conventional metasurfaces based on the generalized laws of reflection and refraction have important drawbacks in terms of power efficiency. This work presents a new synthesis method of acoustic metasurfaces for anomalous reflection and transmission that overcomes the fundamental limitations of conventional designs, allowing full control of acoustic energy flow. The results show that different mechanisms are necessary in the reflection and transmission scenarios for ensuring perfect performance. Metasurfaces for anomalous reflection require non-local response, which allows energy channeling along the metasurface. On other hand, for perfect manipulation of anomalously transmitted waves, local and non-symmetric response is required. These conclusions are interpreted through appropriate surface impedance models which are used to find possible physical implementations of perfect metasurfaces in each scenario. We hope that this advance in the design of acoustic metasurfaces opens new avenues not only for perfect anomalous reflection and transmission but also for realizing more complex functionalities, such as focusing, self-bending or vortex generation.

Left-handed propagation characteristics of a dielectric and metal-loaded periodic circular waveguide

In this paper, a periodic dielectric/metallic rod is located in a circular waveguide to obtain left-handed operation. Two geometries of the dielectric/metallic rod are proposed and examined. The dispersion characteristics of the investigated waveguides are obtained using a surface impedance model. Moreover, equivalent circuit models are proposed allowing for calculation of the dispersion characteristics and scattering parameters of the considered waveguide structures. The numerical results are compared with those obtained from commercial software and from experiment. The obtained results prove the left-handed properties of the investigated structures.

A frequency domain finite element solver for acoustic simulations of 3D rooms with microperforated panel absorbers

Microperforated panel (MPP) absorbers, which provide broadband sound absorption without the use of fibrous materials, have favorable material properties that support recyclability, flexibility of design, hygiene demands, and cleaning. Many earlier studies have specifically examined the development of absorbers themselves. However, to use the absorption performance of MPP absorbers sufficiently in room acoustic applications, it is beneficial to develop accurate prediction methods of sound fields in rooms with MPP absorbers. Such methods are expected to be useful for room acoustics design and absorber design tools. This study constructs a frequency domain finite element (FE) solver for acoustic simulations of a practical sized room with MPP absorbers. Then the accuracy and effectiveness are evaluated. In the FE solver, spatial domains are discretized by fourth-order accurate FEs in terms of dispersion error, and MPP absorbers are modeled using first-order hexahedral limp MPP elements that can deal with sound propagation in the backing structure of absorbers. First, the accuracy of present FE solver is demonstrated using impedance tube problems in comparison with conventional second-order accurate FEs. Results show higher convergence of solutions for the present FE solver. Then, exploration of an iterative solver for efficient multi-frequency analyses reveals that the recently developed CSQMOR is a faster and more stable solver. Finally, comparison with a conventional surface impedance model based on a locally reacting assumption confirms the effectiveness of present FE solver by presenting the importance of dealing with the incident angle dependence of reactance of a rigid-backed air cavity in the modeling of single-leaf MPP absorbers.

Differential global surface impedance (DGSI): a rigorous model for analyzing periodic structures

A new and efficient differential global surface impedance (DGSI) model has been developed for the analysis of periodic structures. The proposed rigorous model makes use of the equivalence principle to relate the surface electric current and the tangential electric field on the boundary of the object made of a general medium. This approach not only enables one to limit the discretization to the surface of the object located in one unit cell of the periodic structure but also eliminates the need for equivalent surface magnetic current in applying the equivalence principle. These advantages result in a great reduction in the need for computational resources and time. The use of an efficient periodic Green’s function by employing the complex images technique combined with the proposed DGSI model has increased the numerical efficiency of the proposed method. A number of dielectric periodic structures made of an array of cylinders with circular or square cross sections have been analyzed by this method. Accuracy of the proposed method as well as its numerical efficiency have been demonstrated by comparing its results with other methods in the literature employing surface and volume integral equations.

Mutual coupling reduction in planar antenna by graphene metasurface for THz application

This paper presents an effective approach to mitigate mutual coupling between two densely packed planar antenna operating at the lower THz frequency band by incorporating a graphene-based metasurface. The graphene metasurface has been designed using Electric inductive capacitive (ELC) resonator on the both sides of a silicon substrate. The metasurface is designed to provide band stop functionality in the operating bandwidth of the antenna. Here, surface impedance model of the graphene is used for analysing the metasurface layer. Throughout the operating band of the antenna, coupling suppression of 8–12 dB is obtained with element separation of less than . Thus, this proposed approach can be utilized to mitigate mutual coupling between antennas in THz application.

Absorption performance optimization of perforated plate using multiple-sized holes and a porous separating partition

This research proposes a new type of sound absorptive perforated plate with multiple-sized holes and a porous separating partition in an attempt to extend the sound absorption bandwidth. Separating different sized holes with a porous partition instead of a conventional rigid partition is an unprecedented idea. However, existence of a porous separating partition makes it hard to use theoretical surface impedance models to predict absorption performance. So we introduce appropriate finite element simulation method using the effective density of hole. To consider the end correction effects for hole length and viscosity length of a perforated plate, the effective density of the Johnson-Champoux-Allard model is modified and the end correction lengths of the modified effective density are corrected again in connection with finite element simulation. Material property of a porous separating partition is modeled by the Delany-Bazley material model. After constructing the finite element model, we analyzed the absorption coefficient graphs of perforated plates with two-sized holes and four-sized holes according to the separating partition types: no partition, rigid partition and porous partition. To enhance the wide-band absorption performance, flow resistivity value and thickness of a porous separating partition as well as hole sizes are optimized. From the analysis and design examples, we confirmed that the perforated plate using multiple-sized holes and a porous separating partition can make a continuous frequency range of high absorption coefficient compared to the perforated plate with a conventional rigid partition.

Novel Surface Impedance Modeling for Broadband Parameter Extraction of 3-D Interconnects

A novel boundary integral equation based method for modeling 3-D interconnects is proposed to compute the equivalent surface impedance in this letter. Differing from the traditional algorithm to discretize the conductor cross section, the proposed method only discretizes the contour of the conductor cross section, thus reducing the CPU time and memory cost. The loss characteristics of conductors describing the skin effect are taken into account through Green’s function. The equivalent surface impedance model can be used to simplify electromagnetic simulation only using electric field integral equation. Numerical results show that the proposed method is both efficient and accurate in a broadband frequency, which is suited for modeling of 3-D interconnects and integrated passive structures.

Surface Impedance Modeling of Plasmonic Circuits at Optical Communication Wavelengths

A novel surface impedance model is developed to analyze plasmonic circuits supporting long range surface plasmon polaritons (LR-SPP). The analysis is carried out in two steps. First, a higher order approximation of the surface impedance is obtained for the metal strip through a 2-D analysis of the waveguide cross section. Second, the developed surface impedance boundary condition is incorporated in the mixed potential integral equation formulation of the problem, and the method of moments is employed to find the unknown surface current distributions on the strips carrying LR-SPP. In other words, in this method, the volumetric currents flowing inside the metal are substituted by a surface current model flowing on an infinitely thin strip characterized by the developed surface impedance model. This procedure reduces the number of unknowns significantly, in this way increasing the speed of simulation. Validity and accuracy of the proposed model are demonstrated by analyzing three popular LR-SPP circuits.

Leaky and bound modes in terahertz metasurfaces made of transmission-line metamaterials

Prism coupling and reflection spectroscopy are used to characterize bound modes within composite right/left handed terahertz metamaterial waveguides. The cavity antenna model is used to understand the polarization dependence of the radiative coupling to TM00 and TM01 waveguide modes. Furthermore, the cavity model along with transmission-line theory is used to derive a surface impedance model for a waveguide array metasurface. Qualitative agreement with the experiment is observed, including a mode splitting for p-polarized surface waves at the light line and the existence of s-polarized magnetic spoof surface plasmons.

Collective behavior of impedance matched plasmonic nanocavities

Nanometer sized cavities arranged as a subwavelength metallic grating can provide omni-directional and complete absorption of light. We present an explanation of this extraordinary phenomenon as a collective resonant response of a system based on a surface impedance model. This model gives a straightforward way to design systems for optimum light trapping performance and as well gives fundamental insights into the interaction of light with metals at the nanoscale.

Wideband Modeling of Conductor Loss in General Large-Scale Problems

Wideband modeling of conductor loss is of critical importance in millimeter-wave applications. This letter presents a conformal three-dimensional (3-D) surface impedance model based on fully automated mesh generation suitable for large-scale problems with arbitrary problem geometry. The method is described in the context of a parallelized time-domain finite-difference algorithm. The approach is validated using rectangular, cylindrical, and spherical cavity resonators against analytical reference data. The wideband performance of the method is validated at 1-MHz to 1-THz frequency band.

Surface-impedance quasi-transverse electromagnetic approach for the efficient calculation of conductor losses in multilayer single and coupled microstrip lines

In this study the authors present a new surface-impedance model for the accurate computation of the effect of metal losses on the parameters of printed microstrip lines. The novelty of the authors' approach lies in the fast and direct calculation of the tangential magnetic fields above and below the strip conductors, which allows us to develop a very efficient quasi-transverse electromagnetic (TEM) solution for the conductor losses of multilayer single or coupled microstrip lines. The overall computational effort of the authors' method is much less than that required by purely numerical approaches. The accuracy of the method has been verified by comparison with other techniques, including a general-purpose full-wave finite elements method. It is also shown that the proposed method provides better results than other previously surface-impedance approaches.

Surface impedance model for extraordinary transmission in 1D metallic and dielectric screens

Extraordinary Optical Transmission of TM waves impinging at oblique incidence on metallic or high permittivity dielectric screens with a periodic distribution of 1D slits or any other kind of 1D defects is analyzed. Generalized waveguide theory altogether with the surface impedance concept are used for modeling such phenomena. A numerical analysis based on the mode matching technique proves to be an efficient tool for the characterization of these structures for any angle of incidence and slit or defect apertures.

Carbon-Nanotube Loaded Antenna-Based Ammonia Gas Sensor

Carbon nanotubes (CNTs) have been researched extensively for gas-sensing applications due to their unique electrical, chemical, and structural properties. Single-walled carbon nanotubes (SWNTs) have been predominantly used due to their superior electrical conductivity and higher sensitivity relative to multiwalled CNTs. This paper presents the design and characterization of a novel planar sensor fabricated on paper substrate to detect small concentrations of ammonia gas, using the shift in resonance frequency of a patch antenna as the discriminator. We have investigated three main design issues in depth. First, functionalization of the SWNTs with a polymer is studied in order to enhance the gas detection sensitivity. Second, a thin film of the functionalized SWNT is characterized to create a surface impedance model for the explanation and prediction of the resonance shift due to different gas concentrations. Finally, as a proof of concept, functionalized SWNTs are integrated into a patch antenna design and the return loss is measured in a closed-system environment to show high sensitivity for low concentrations of ammonia gas. The proposed antenna-based wireless gas sensor can be utilized in several applications, given its small form factor, light weight, and little to no power requirements.

Features of technology of high-temperature superconductor films for microwave filters

The characteristics of fourth-order bandpass microwave filters based on high-temperature super-conductor (HTS) films have been numerically simulated and experimentally measured for the devices based on YBCO films purchased from Theva GmbH (Munich) and manufactured at the Institute for Physics of Microstructures (Nizhni Novgorod). Experimental data were used to determine the parameters of the surface impedance model for the HTS films. The results show that HTS-based filters with high performance characteristics can be obtained using HTS films manufactured by different technologies.

Surface impedance models for high impedance surfaces

Different analytical and numerical methods for calculating the surface impedance of a high impedance surface (HIS) structure have been studied and compared. In this article, two new approaches are proposed for calculating the surface impedance for general 2D-spatial periodic HIS structures, which include both the symmetric and asymmetric planar structures. Different comparisons are made, among analytical, numerical and experimental results, to validate our numerical calculation.

STUDY OF FRACTAL-SHAPED STRUCTURES WITH PIN DIODES USING THE MULTI-SCALE METHOD COMBINED TO THE GENERALIZED EQUIVALENT CIRCUIT MODELING

A multi-scale (MS) approach combined to the generalized equivalent circuit (GEC) modeling is applied to compute the input impedance of pre-fractal structures with incorporated PIN diodes. Instead of treating the whole complex problem at once, the MS method splits the complex structure into a set of scale levels to be studied separately. The computation is done gradually from the lowest level. Each scale level is artiflcially excited by N modal sources to compute its input impedance matrix. The MS method is based on converting this input impedance matrix into an impedance operator to achieve the transition toward the subsequent level. The PIN diodes were easily integrated in the MS approach thanks to their surface impedance model. The main advantage of the MS-GEC method is the signiflcant reduction of the problem's high aspect ratio since flne details are studied separately of the larger structure. Consequently, the manipulated matrices are well conditioned. Moreover, the reduced size of matrices manipulated at each level leads to less memory requirement and faster processing than the MoM. Values obtained with the MS- GEC approach converge to those given by the MoM method when a su-cient number of modal sources are used at each scale level. For frequencies between 1GHz and 6.8GHz, the agreement between the two methods is conspicuous.

Performance Analysis of Resonance-Based Transducers in Terahertz Bio-Chips Using Equivalent Surface Impedance Model

The concept of equivalent surface impedance is applied for electromagnetic modeling of thin-film samples, e.g., nano-layers of deoxyribonucleic acid, placed on a metallic surface. For the first time, it is shown that by using such a concept, the performance of resonance-based terahertz bio-chips can be easily evaluated in terms of analytic sensitivity and selectivity. Numerical results are presented for the performance of a planar resonator as an example when used as a transducer in a bio-chip sensor. The proposed model is general and can be applied to any resonant transducer with metallic surface for receiving thin-film samples.