Scalar Impedance Research Articles

Simultaneously Transmitting and Reflecting (STAR)-RISs: Are They Applicable to Dual-Sided Incidence?

A hardware model and a signal model are proposed for dual-sided simultaneously transmitting and reflecting reconfigurable intelligent surfaces (STAR-RISs), where the signal simultaneously incident on both sides of the surface. Based on the proposed hardware model, signal models for dual-sided STAR-RISs are developed. For elements with scalar surface impedance, it is proved that their transmission and reflection coefficients on both sides are identical. Based on the obtained symmetrical dual-sided STAR model, a STAR-RIS-aided two-user uplink communication system is investigated for both non-orthogonal multiple access (NOMA) and orthogonal multiple access (OMA) schemes. Analytical results for the outage probabilities for users are derived in the high transmit signal-to-noise ratio (SNR) regime. Numerical results demonstrate the performance gain of NOMA over OMA and reveal that the outage probability error floor can be lowered by adjusting the ratio between the amplitudes of transmission and reflection signals.

Generation of Circularly Polarized Quasi-Non-Diffractive Vortex Wave via a Microwave Holographic Metasurface Integrated with a Monopole

In this paper, a novel method for generating a circularly polarized (CP) quasi-non-diffractive vortex wave carrying orbital angular momentum (OAM), based on the microwave holographic metasurface integrated with a monopole, is proposed. This method is the combination of the non-diffraction theory and the principle of waveguide-fed-based holography and is equivalent to a superposition of two scalar impedance modulation surfaces. To verify the proposed method, a holographic metasurface generating a left-handed circularly polarized (LHCP) quasi-non-diffractive vortex wave carrying −1 mode OAM at the normal direction, was simulated and analyzed. The metasurface consisted of inhomogeneous slot units on a grounded substrate and a monopole excitation. Moreover, the location distribution of slots was determined by a computed interferogram between the reference wave and the object wave with the non-diffractive feature. Compared with an ordinary vortex wave, the quasi-non-diffractive wave obtained by our proposed method possessed a smaller divergence radius and a stronger electric field strength in the 9 times wavelength range. It paved a new path for manipulating the non-diffractive vortex wave in medium distance without using an external feeding source, which holds great potential for the miniaturization devices applied in medium-distance high-capacity secure communication, high-resolution imaging and intelligent detection.

Perfect Conversion of a TM Surface Wave Into a TM Leaky Wave by an Isotropic Periodic Metasurface Printed on a Grounded Dielectric Slab

This article presents an exact solution for a perfect conversion of a TM-polarized surface wave (SW) into a TM-polarized leaky wave (LW) using a reciprocal and lossless penetrable metasurface (MTS) characterized by a scalar sheet impedance, located on a grounded slab. On contrary to the known realizations of LW antennas, the optimal surface reactance modulation which is found here ensures the absence of evanescent higher-order modes of the field Floquet-wave expansion near the radiating surface. Thus, all the energy carried by the SW is used for launching the single inhomogeneous plane wave into space without accumulation of reactive energy in the higher-order modes. It is shown that the resulting penetrable MTS exhibits variation from an inductive to a capacitive reactance passing through a resonance. The present formulation complements a previous article of the authors, in which a perfect conversion from TM-polarized SW to TE-polarized LW was found for impenetrable boundary conditions. Here, the solution takes into account the grounded slab dispersion, and it is convenient for practical implementation.

Modelling and analysis of equivalent SISO d-q impedance of grid-connected converters

Small-signal stability of three-phase grid-connected converters can be analysed by using the impedance-based method in d-q frame. Based on this approach, the d-q impedance models of both source and load subsystems are represented with 2-by-2 matrices, and their ratio (known as the return ratio matrix) is used for stability assessment. This, however, requires to apply the generalized Nyquist criterion (GNC), due to the intrinsic multi-input multi-output (MIMO) property of the d-q system. During the process, some complexities are inevitably caused because of the need to calculate the ratio of the impedance matrices, and to obtain the eigenvalues of the return ratio matrix. In this context, this paper presents an equivalent single-input single-output (SISO) model for the d-q impedance of three-phase grid-connected converters, which leads to two scalar impedance ratios of d- and q-axis, instead of the conventional 2-by-2 return ratio matrix. Consequently, the stability of the two SISO systems can be analysed by using the classic Nyquist stability criterion (NC), resulting in a much simpler and more intuitive analysis process than GNC. The equivalence between the original MIMO d-q impedance model and the proposed SISO model in stability assessment is verified by comparing their stability conditions. As an example of applying this approach, the effects of PLL, grid impedance, and power control on a grid-connected converter are investigated. The performed analysis is finally validated by Matlab/Simulink simulations.

CALCULATION METHOD OF IMPEDANCE MODULE FOR CORROSION MONITORING OF SURFACE STATE OF CHROMONICKEL STEELS

In discussed issue the additional criterion for chromium-nickel steels surface state assessment is proposed. It is used in periodic potentiostatic regime of stainless steels surface state monitoring under the condition of pitting corrosion origin. Electrochemical investigations were carried out with pitting corrosion resistant austenitic (12Х18Н10Т) and austenitic-ferritic chromium-nickel steels 10Х17Н13М2Т in chloride solutions of 0.1 mol/L NaCl and 0.5 mol/l NaCl with the additional oxidant K2Cr2O7. Polarization curves were recorded under potentiostatic mode of polarization in the electrochemical three-electrode cell using the ZIVE SP2 workstation and a personal computer. The fast Fourier transformation method was used for conducting the spectral analysis, as this method is more effective in terms of the algorithmic complexity when processing a large amount of the initial data. It is established that scalar impedance angular coefficient shows the current oscillation frequencies change concerned with the pitting occurrence and passivation process. The scalar impedance angular coefficient allows to estimate the pitting corrosion evaluation processes boundaries: passivity; metal dissolution due to the development of metastable pittings; the metastable nucleation and passivation processes concurred with the stable pitting development. The algorithm based on the statistical method of spectral analyses for scalar impedance angular coefficient calculation is developed. It is established that the decrease in passive film total resistance corresponds to the breakdown process and first metastable, and then stable local surface destructions that reflect on the higher the scalar impedance angular coefficient value. The boundary values of an additional criterion for surface state assessment were proposed, on the basis of which an interval scale was constructed to determine the current state of the surface of chromium-nickel steels. It is shown that the boundary values of the scalar impedance angular coefficient correspond to the metallographic studies of investigated steels.

Analytical study of surface wave multiple refraction in boundary of a scalar impedance surface with a tensor impedance surface

In this paper, the multiple refraction phenomenon is investigated on the boundary of a scalar impedance surface (SIS) and a tensor impedance surface (TIS). When a surface wave (SW) propagates on the SIS and radiates to the boundary of the TIS, the propagation direction of it is changed and the refraction phenomenon is accrued. The method that is proposed in this paper can predict the multiple refraction for the SW. Moreover, another analytical method is introduced for designing the proposed structure which the double refraction (DR) occurs at arbitrary angles on it. Using it, a sample of the structure is designed by printed circuits in 15.2GHz and the results are verified by the full-wave simulation and measurement. The results are shown that in the structure, DR is occurred in 2° and 22° as predicted. The proposed method can provide many applications such as design of SW power dividers based on the TISs, impedance surface based waveguides, holographic antennas, and feeding of array antennas.

RF Impedance Sensor for Antenna-Tuning Front Ends

A method for complex RF impedance sensing is proposed. The method is based on using a scalar impedance meter and an impedance tuning network for sensing the complex load impedance. The scalar measurements are conducted three times for different settings of the digitally controlled tuning network after which the load impedance is evaluated based on the scalar outputs from the reflectometer. The measurements of the prototype device are demonstrated. The target application for the presented system and method is the antenna-tuning front end of the multiantenna cellular handheld devices.

Design Method of Passive Lossless Metasurfaces With Auxiliary Waves for Beam Control

The use of cross-polarized auxiliary waves in the design procedure of the passive lossless metasurface has been reported as an effective approach to improve its performance. However, the design with only one auxiliary wave leads to low efficiency of an impenetrable metasurface in general when the incident and reflected waves interact with each other. This communication presents two auxiliary waves to design high-efficiency metasurfaces for arbitrary beam control. Besides the cross-polarized auxiliary wave, the copolarized auxiliary wave is proposed to design metasurfaces with a scalar impedance for beam control. Moreover, auxiliary waves are expanded into Fourier series in the procedure and their coefficients can be effectively determined with a numerical optimization method. Some instances are provided and the numerical results show that the designed metasurfaces effectively can control beams. The comparison between the designed metasurface and the conventional phase-gradient one is also provided.

Analytical Study and Experimental Verification of the Refraction Angle as a Function of Frequency Due to Surface Waves Incident Onto a Tensor Impedance Sheet

In this paper, using the theory of tensor impedance boundary conditions, a surface structure with new applications is presented. The proposed structure includes a tensor impedance sheet (TIS) alongside a scalar impedance sheet (SIS) which is designed by arrays of cells containing subwavelength patterned metallic cladding over a grounded dielectric substrate. In this structure, a method is presented to study the electromagnetic surface wave (SW) passing through a boundary between an isotropic and anisotropic impedance surface. If an SW with a specified frequency is excited on a SIS and orthogonally propagates onto the boundary of a TIS, due to the refraction of the SW, the propagation direction of the SW on the TIS will change. Therefore, the SW will enter the TIS with a specified angle, which is called the refraction angle. In this paper, the frequency variations of the refraction angle are studied in the proposed structure. Finally using the presented method, a sample structure is designed and simulated in 15.1-15.75 GHz frequency. In addition, the structure is fabricated and the results of the proposed model are verified with simulation and measurement. Moreover, an equation with an analytical solution is presented in order to model tensor impedance boundary conditions using printed circuits. This can make TIS design quick and accurate.

Lossless Scalar Metasurfaces for Anomalous Reflection Based on Efficient Surface Field Optimization

For polarization-preserving anomalous plane-wave reflections by impenetrable surfaces, an efficient numerical field optimization technique is presented for designing lossless metasurfaces. Auxiliary surface waves copolarized with the incident and reflected plane waves are introduced and optimized such that the scalar surface impedance characterizing the reflecting surface approach a purely reactive profile. The resulting inhomogeneous scalar reactance can be discretized for realization as a periodic metasurface. Full-wave simulation of a physical design that is directly translated from the optimized reactance profile shows near-perfect anomalous reflection.

On a possibility of usage of the scalar impedances for solving the inverse MTS problem for three-dimensional models

A review of the results of calculating of seeming specific resistance for a set of elementary models by scalar impedance method, in particular, by impedance parameter z has been given in the article. The values of electromagnetic field parameters of the models have been calculated by the Mackie 1994 program. According to this method of calculation the field is excited by flat low-frequency homogeneous electromagnetic wave. Calculation of electromagnetic field parameters for each model object was accomplished for a set of values of T periods. Specific resistances calculated by scalar impedance z, are presented as a graphs rz(x) and isolines fields across the observations area. The results obtained for the given class of models have shown a possibility to restore the conducting characteristics of lower half-space without determining the impedance tensor Ž and predetermined a possibility of further development of this method not only for visualization of data but also for obtaining numerical solutions of the inverse MTS problem.

Design of a UWB Reflectarray as an Impedance Surface Using Bessel Filters

This paper develops a framework for designing wideband reflectarray antennas. The proposed reflectarray is implemented as a scalar impedance surface composed of subwavelength elements, whose response is designed to realize a Bessel filter response. The underlying unit cells therefore have maximum group delay bandwidth with no group delay ripples in the passband. It is shown that the reflectarrays designed using this Bessel filter approach exhibit wide bandwidth only limited by the order of the filter used to realize the Bessel filter. Simulated and measured antenna characteristics of the proposed reflectarray are presented for a $C$ -/ $X$ -band reflectarray design. It is shown to have good beam characteristics and ultra-low temporal dispersion from 5 to 10 GHz, two attractive qualities accomplished simultaneously by the proposed reflectarray.

Polarized Beams Using Scalar Metasurfaces

This paper deals with the design of scalar metasurface antennas capable of radiating a well-polarized beam in the far-field or near-field zones. The equivalent electric current over the metasurface is used to derive design equations to generate the desired field pattern based on the scalar impedance condition. In particular, it is shown that scalar metasurfaces can be used to generate linear and circular polarizations for a fixed pointing direction in the far field by properly changing locally the scalar impedance boundary condition. In addition, they can also be used to generate normal polarized Bessel beams in the near-field region. Several solutions are presented at 20 GHz, with different polarizations and feeders developed in the framework of a two-year research project financed by the French space agency (Centre National d’Etudes Spatiales). Measurements and full-wave results validate the proposed approach.

Design of Scalar Impedance Holographic Metasurfaces for Antenna Beam Formation With Desired Polarization

This paper presents the design of a novel planar scalar impedance holographic metasurface, which is capable of beam forming with a desired electric field polarization and high gain. It is demonstrated that the surface can be constructed with patches of simple geometry and design. A detailed analysis of the mechanism of scalar impedance holographic metasurfaces is discussed. The scalar impedance holographic metasurface is designed at a dominant TM surface wave mode frequency. It is observed that the TM surface wave mode has an impurity of TE polarized electric fields of small magnitude. The presence of this impurity is exploited to design a holographic metasurface for beam forming with a desired polarization. This modified-HAIS is capable of forming a beam at a nonphase crossover frequency, unlike the conventional HAIS. The design procedure of the surface, with simulation and measurement results, is presented.

Vizualizing of MTS data by the method of scalar impedances for numerical models of elementary conducting structures

The work is devoted to the analysis of a possibility and traits of use of the method of scalar impedances for the purpose of visualizing the results of MTS. It is made by the example of a number of elementary structures, for which the values of anomalously electromagnetic field was calculated by the program of 3D modeling. Graphic equivalents of modules of scalar parameters of impedance type | % | and Z , designed for the given models are resulted, their characteristic features for various types of conducting structures are considered.

Resonant dynamics of arbitrarily shaped meta-atoms

Meta-atoms, nanoantennas, plasmonic particles, and other small scatterers are commonly modeled in terms of their modes. However these modal solutions are seldom determined explicitly, due to the conceptual and numerical difficulties in solving eigenvalue problems for open systems with strong radiative losses. Here these modes are directly calculated from Maxwell's equations expressed in integral operator form, by finding the complex frequencies which yield a homogeneous solution. This gives a clear physical interpretation of the modes, and enables their conduction or polarization current distribution to be calculated numerically for particles of arbitrary shape. By combining the modal current distribution with a scalar impedance function, simple yet accurate models of scatterers are constructed which describe their response to an arbitrary incident field over a broad bandwidth. These models generalize both equivalent-dipole and and equivalent-circuit models to finite-sized structures with multiple modes. They are applied here to explain the frequency-splitting for a pair of coupled split rings, and the accompanying change in radiative losses. The approach presented in this paper is made available in an open-source code.

Exploiting metasurface anisotropy for achieving near-perfect low-profile cloaks beyond the quasi-static limit

In this paper, we report an approach for achieving near-perfect low-profile electromagnetic cloaking beyond the quasi-static limit. In contrast to previous works on metasurface cloaks where only the Leontovich surface impedance boundary condition has been considered, we employ a second-order surface impedance boundary condition to account for the radial response of the proposed anisotropic metasurfaces. This radial surface polarizability tensor parameter can be tailored to eliminate the higher order scattering modes. It is shown from analytical expressions that for a moderate-sized perfect electric conducting or dielectric cylinder (∼0.4λ0 in width), near-perfect scattering reduction, i.e. >98%, can be achieved by a single anisotropic metasurface with non-vanishing radial response, which is far superior to the conventional scalar impedance surface. A practical design of the metasurface is also presented and further validated by full-wave simulations. The physical mechanism of the metasurface cloaks is investigated in detail, revealing that the radiation cancellation of the induced surface currents is responsible for the scattering reduction. Importantly, it is shown that in addition to a ‘low-visibility coating’, the metasurface also functions to provide induced current enhancement which would be beneficial for the operation of a ‘cloaked sensor’. These findings will broaden the usage of metasurfaces to applications ranging from scattering reduction to noninvasive probing for objects beyond the quasi-static limit.

Artificial Tensor Impedance Surface Waveguides

A surface waveguide structure is studied using a theoretical model and simulated using Ansoft HFSS. A tensor impedance surface is surrounded by two lower impedance surfaces on a plane. Surface waves are guided losslessly within the inner region as long as it has higher impedance than the outer region. A theoretical model is proposed which predicts the dispersion relation of the waveguide using a ray optics method. Our tensor impedance surface theory can also predict the dispersion of scalar impedance surfaces. The theory and simulation show agreement for scalar and tensor impedance surfaces. Two applications of tensor impedance surface waveguides are presented.

Effective Surface Impedance of a Printed-Circuit Tensor Impedance Surface (PCTIS)

The surface impedance and dispersion equation of a printed-circuit tensor impedance surface (PCTIS) are derived using a modified transverse resonance technique. A PCTIS consists of a subwavelength-patterned metallic cladding over a grounded dielectric substrate. The metallic cladding is analytically modeled as a tensor impedance sheet. An explicit expression is derived for the effective surface impedance of the PCTIS using a transmission-line approach. First, the surface-impedance expression is found for a printed-circuit scalar impedance surface using the transverse resonance technique. Next, a modified transverse resonance technique is applied to an idealized tensor impedance boundary condition (TIBC) to find its dispersion equation. Finally, the analysis of the printed-circuit scalar impedance is combined with that of the idealized TIBC to find the tensor surface impedance and dispersion equation of a PCTIS. A discussion of the principal axes and the propagation of TM and TE waves is provided. The special case of electrically thin PCTISs is also analyzed and discussed.

Love waves in a coated vertically periodic substrate

We study the dispersion spectrum of Love shear horizontal (SH) waves in coated vertically periodic substrates. The analysis is based on the properties of the scalar SH impedances of substrate and coating layer. The dispersion branches, which lie in the Floquet stopbands, are proved to be monotonic. They may have the form of broken segments truncated at the stopband edges and connected by non-monotonic dispersion curves of ’non-physical’ waves (increasing into depth). In contrast to the SH surface waves in a free periodic substrate, there may be more than one Love wave per stopband due to coating. Their number is related to the number of resonances of the coating layer. The criterion for existence of the fundamental Love branch is derived. Examples are provided where coating of periodically layered or functionally graded substrates drastically enriches their SH spectrum.