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Metasurfaces have gained a considerable amount of interest in the past decade for their capabilities to manipulate electromagnetic (EM) waves in different manners. They have offered multiple functionalities in terms of wave control depending on the given application. In terms of wave control, particularly EM beam splitting, it can be challenging compared to the given literature review, to achieve a wide number of beam-splitting reflections and coverage for multiple incident angles simultaneously. In this paper, we focus on the design of a metasurface based on the methodology of high periodicity supercell design (5.76 λ) and impedance modulation to achieve a various number of beam-splitting angles, while maintaining the same coverage at multiple incident angles for millimeter-wave (mm-Wave) frequencies. Following the generalized phase law of reflection alongside proper optimization of the surface impedance, the proposed reflective anomalous beam splitter (RABS) metasurface is designed to be polarization independent, and high reflection efficiency is achieved with a wave beam split into 11 different directions while operating for multiple incident angles simultaneously, making it a promising candidate to overcome challenges for various mm-Wave communication applications, especially in expanding 5G coverage in non-line of sight regions at a 28 GHz frequency band. The performance of the RABS metasurface is evaluated using both full-wave simulations and experimental measurements, which demonstrate its effectiveness in achieving 11 efficient reflective anomalous beams with a reflection efficiency of up to 96.65% and 97.36% in TE and TM modes at 28 GHz. [ABSTRACT FROM AUTHOR]

Electromagnetic (EM) RF (radio frequency) energy harvesting in dynamic ambient environments is a challenge for conventional energy harvesting systems such as rectennas. The main challenges are the low efficiency of the collector and low ambient power levels, which makes it hard to consider in industrial applications. Several research works have focused on the design of high-efficiency antennas to achieve an efficient and maximum possible level of RF EM energy harvesting. Their main objective is to improve the EM energy harvesting system by overcoming the low efficiency of the collector, which is the main part of the rectenna system. In this work, we propose and investigate a methodology in terms of EM energy harvesting based on the concentration and focusing of EM energy in a small zone where it can be easily collected and transferred indirectly to the rectenna system. It consists of a focusing device and a methodology to associate the latter with existing RF energy harvesting systems. We demonstrate a focusing metasurface design implemented alongside an off-the-shelf rectenna device at 900 MHz, where an enhanced energy harvested power level up to a linear gain of 8 is achieved compared to the case when only the rectenna is used. Numerical results as well as measurements results in an anechoic chamber are shown. Experimental power received levels are given both in the focusing plane and in time for the validation of the concept. [ABSTRACT FROM AUTHOR]

In this paper, a cascaded retrodirective metasurface is designed and demonstrated to operate simultaneously at a wide range of incident angles from − 30 ° to − 10 ° and 10 ° to 30 °. It is based on the design of several retrodirective super-cells following the generalized Snell's law of reflection, where each super-cell is designed to redirect an incoming wave back in the same direction with high efficiency. This metasurface is a very good candidate as a retroreflector for radar cross-section (RCS) enhancement of targets with poor backscattering. Retrodirective topologies have been a subject of interest, and several engineered topologies exist, such as the corner dihedral. Despite their good performances at a range of incident angles, their 3-dimensional bulky structure makes them hard to implement for different applications and they do not address extreme incident angles. The metasurface proposed can be a complementary solution to existing topologies for addressing extreme oblique incident angles while being more compact due to its two-dimensional subwavelength structure design. The monostatic radar cross-section (RCS) performance of the designed metasurface of dimensions 8.163 × 56.23 cm 2 has been compared to that of a conventional corner dihedral of dimensions 8 × 15.5 × 7.75 cm 3 , and a gain of up to 50 dB of monostatic radar cross section (RCS) in the ranges − 30 ° to − 20 ° and 20 ° to 30 ° was obtained. Comparable performances are observed in the ranges − 20 ° to − 10 ° and 10 ° to 20 ° between the designed metasurface and the corner dihedral. Experimental results are shown to be in good agreement with simulation results. [ABSTRACT FROM AUTHOR]

An analysis about the enhancement of backscattering radar cross section from an equivalent human body cylinder using a specific type of coating is presented. The types of coatings considered for the human body are taken to inductive meta surface (MS), inductive MS followed by a dielectric layer and an epsilon negative (ENG) metamaterial. An eigenfunction expansion method has been used to derive analytical expressions for the scattered electric and magnetic fields. It is investigated that inductive MS and inductive MS followed by a dielectric layer type of coatings cannot be used to enhance the backscattering radar cross section from the human body. It is found that an ENG metamaterial coating having specific permittivity and coating thickness can be used to significantly enhance the back‐scattering radar cross section from the human body under oblique incidence. Therefore, an ENG metamaterial coating is selected for the proposed model and finally, the modelling of the proposed design is suggested. [ABSTRACT FROM AUTHOR]

Electromagnetic metamaterials are generally defined and classified in terms of their effective parameters. They are evaluated in the far-field which limits the evaluation of its near field interaction in some applications such as metamaterial inspired design. An alternative approach proposed in this paper is based on the modal stored energy of metamaterial inclusion. This approach is based on the surface current distribution which would address the challenge of metamaterial near-field application. This paper describes a method for quantifying the modal stored energy of arbitrary-shaped metamaterial inclusions based on the theory of characteristic modes. The theory of characteristic modes is independent of excitation, gives good physical insight into the behaviour of an inclusion and would be helpful for near-field application of metamaterials. The modal stored energy approach is also compared with the common effective parameter approach. It shows similarity in terms of the physical and qualitative analysis when far-field assumptions are accounted for. The broadside-coupled split-ring resonator and the S-shaped inclusion are considered. The physical and qualitative analysis based on the modal stored energy approach shows a good agreement with the effective parameter approach. [ABSTRACT FROM AUTHOR]

A novel compact coplanar waveguide (CPW)-fed planar monopole antenna with triple-band operation is presented for simultaneously satisfying the LTE 2600, WiMAX, WLAN and X-band applications. It is printed on a single-layered FR4 substrate. In this paper, the proposed antenna, which occupies a small volume of 3 0 × 2 8 × 0. 8 mm3 including the ground plane, is simply composed of a CPW-fed monopole with U-, L- and T-shaped slots. By carefully selecting the lengths and positions of both L-shaped and U-shaped slots, a good dual notched band characteristic at center-rejected frequencies of 3.10 GHz and 4.50 GHz can be achieved, respectively. The T-shaped slot is etched on the radiating element to excite a resonant frequency in the 7 GHz band. Then, to prove the validation of the typical design, a prototype model is fabricated and measured. The experimental result shows that the three frequency bands of 2.31–2.80 GHz (490 MHz), 3.37–3.84 GHz (470 MHz) and 5.04–7.94 GHz (2900 MHz) can successfully cover the desired bandwidths of LTE2600/WiMAX (3.50/5.50 GHz)/WLAN (5.20/5.80 GHz) and the X-band communication systems (7.1-GHz operation). The principal applications of the X-band are radar, aircraft, spacecraft and mobile or satellite communication system. Nearly omnidirectional and bidirectional radiation patterns of the triband antenna are observed in both H- and E-planes, respectively. In addition, a reasonable gain over the operating bands has been obtained. Indeed, the good agreements between simulation and measurement results have validated the proposed structure, confirming its potential for multiband wireless communication services. [ABSTRACT FROM AUTHOR]

We present a numerical study of resonant negative refractive index (NRI) metamaterials in which their effective parameters are calculated. For a periodic media consisting of split-ring resonators and metallic wires the effective refractive index is compared by means of two different methods. The first one is an inversion procedure in which the effective refractive index is calculated from the reflection and transmission coefficients of a finite structure and the second one consists its calculation from the phase velocity issued from the dispersion diagram. A significant difference between the two cases is highlighted in the frequency interval of interest (NRI regime) and for the finite media, counterintuitive observations are made. These anomalous features are observed in a frequency range in which there is a non-negligible contribution of the higher-order modes to propagation inside the periodic metamaterial. Hence in this particular frequency interval, the media cannot be described by an effective refractive index in a Fresnel sense. In other frequency regions, both methods converge and it will be shown that the metamaterial exhibits a negative refractive index. [ABSTRACT FROM AUTHOR]

An explicit analysis of the retrodirective mechanism of a flattened dihedral using periodic arrays is proposed. Once flattened, a corner dihedral requires a phasing mechanism to restore its retrodirective behaviour. This can be achieved by equipping each of the panels with passive phase-shifting cells that obey a global retrodirective phase law. The challenge is to have a trade-off between two steering mechanisms on each side such that this global phase law is achieved. In this work, an analytical study of the reflection phenomenon between the two panels is presented and sufficient information are provided to predict the retrodirective performance affected by the dihedral geometrical configuration itself. The analytical formulation of the global phase law is thus defined along with other complementary formulations to provide a better understanding of the reflection phenomenon involved. Based on these analysis and comprehension, guidelines are suggested in terms of the cell design and the dihedral geometrical configuration so that to efficiently engineer the retrodirective profile of the dihedral. A simple method utilizing these guidelines is proposed to enhance the flattened dihedral performances. And an experimental validation of this design is finally proposed at 24 GHz. [ABSTRACT FROM AUTHOR]

To incorporate two different communication standards in a single device, a miniaturized dual-band planar monopole antenna is presented in this paper. The proposed antenna is formed by a CPW feed line and a rectangular ring monopole with a vertical strip. The designed antenna has a small overall size of 19 mm  36 mm  1.6 mm. A prototype of the proposed antenna which was fabricated and measured to validate the design shows a good agreement between the simulation and the experiment. The measured results indicate that the antenna has the impedance bandwidths of 650 MHz (2.30-2.95 GHz) and 2460 MHz (3.40-5.86 GHz) at the first and second bands, respectively with a reflection coefficient less than - 10 dB covering all the WLAN bands (2.4/5.2/5.8 GHz) and WiMAX bands (2.6/3.5/5.5 GHz). In addition, the nearly omni-directional and bi-directional radiation patterns are also achieved in both H- and E-planes, respectively. It is also noticeable that a good antenna gain over both operating bands has been obtained. Therefore, this simple compact planar monopole antenna with multi-band characteristics is well suitable for WLAN and WiMAX wireless communication applications. Details of the proposed antenna design and both simulated and experimental results are analyzed and discussed. [ABSTRACT FROM AUTHOR]

Evaluating the $Q$ factor of antennas using metamaterial substrates is a challenge and requires new analysis techniques. This challenge is even more important for arbitrary-shaped antennas. In this paper, we address the problem of analysis and evaluation of metamaterial-based antennas through the use of characteristic modes. We propose a new expression for the total $Q$ factor, which is independent of the excitation and based on the eigenvalues of the structure. The proposed expression is used to compute the $Q$ factor of an arbitrary-shaped resonant antenna and shows excellent agreement with other expressions in the literature such as the ones proposed by Yaghjian, Best, and Gustafsson. The approach is then used to analyze small patch antennas over metamaterial and magnetodielectric substrates. It is shown using the defined $Q$ factor expression that a magnetic substrate offers a significant bandwidth enlargement for the first active modes, and a dielectric substrate presents the opposite effect. This agrees with other works based on analytical approaches. Furthermore, we demonstrate that a reactive impedance metamaterial substrate presents identical modal significances that are identical to a conventional magnetodielectric substrate when associated with a patch antenna. This analysis is suitable for structures presenting noncanonical geometries and arbitrary shapes such as metamaterial inclusions. [ABSTRACT FROM AUTHOR]

In this letter, new metrics are proposed to provide physical insight into the behavior of metamaterial-based structures by means of the theory of characteristic modes. A relationship between the first eigenmode and an expression of the polarizability is proposed for a split-ring resonator. It thus allows us to describe a link between the artificial magnetic response of a split-ring resonator and modal characteristics. Using the new metrics proposed, a reactive impedance substrate based on metal-dielectric metamaterial excited by a parallel magnetic field is shown to exhibit artificial magnetism. These metrics are shown to propose good agreement with other analytical and numerical methods. This analysis should be useful when such metal-dielectric metamaterial structures are associated to radiating elements like antennas since it could be performed in the near-field region, unlike common approaches based on plane wave and far-field assumptions. [ABSTRACT FROM PUBLISHER]

This paper presents a procedure to implement the concept of surface impedance boundary condition (SIBC) for lossy dielectrics in time domain. The SIBC formulation, validation, and results are obtained with a time domain numerical method, namely the transmission-line matrix (TLM). The formulation of surface impedance in frequency domain is converted to the time domain using a rational approximation followed by a bilinear transform with a canonical representation in the state-space. This surface impedance formulation has been implemented in TLM. Simulations show that the proposed model is valid for interfaces between air and a lossy dielectric, and arbitrary conductivity $\sigma$. An application that concerns mode propagation in a rectangular tunnel with lossy dielectric walls is shown. A comparison with an approximate method proposed by Marcatilli is presented. It confirms that the propagation in electrically large guided structures, such as tunnels with lossy dielectric walls, can be efficiently modeled by this approach. [ABSTRACT FROM PUBLISHER]

The in-phase radiation from a conformal metamaterial surface is numerically and experimentally reported. The LC-resonant metasurface is composed of a simultaneously capacitive and an inductive grid constituted by copper strips printed on both sides of a dielectric board. The metasurface is designed to fit a curved surface by modifying its local phase. The latter phase-compensated metasurface is used as a reflector in a conformal Fabry-Pérot resonant cavity designed to operate at microwave frequencies. Far-field measurements performed on a fabricated prototype allow showing the good performances of such a phase-compensated metasurface in restoring in-phase emissions from the conformal surface and producing a directive emission in the desired direction. [ABSTRACT FROM AUTHOR]

A general methodology for obtaining the reflection and transmission dyads from a general bianisotropic metasurface under oblique incidence have been developed. In this case, it is assumed that the normal electric and magnetic surface polarization currents are negligible. The proposed theory is then used for a metasurface composed of chiral spheres under normal illumination. It is shown that due to an additional parameter of chirality, one can control the reflection, transmission and absorption properties of a metasurface. It is also studied that a metasurface composed of chiral spheres may be used as almost perfect reflector, perfect anti-reflector and good absorber having some specific geometrical and electromagnetic parameters. For completeness, the analytic expressions for electric, magnetic, electromagnetic and magnetoelectric polarizibilities of a chiral sphere have also been derived using Mie theory. [ABSTRACT FROM AUTHOR]

Abstract: Nowadays, a wide variety of terminals are proposed to nomadic users. Generally these terminals provide wireless communication operating at frequencies between one and a few GHz. For technical reasons, including multiple access to the communication channel and battery autonomy, these terminals transmit only during very short periods i.e. transmission bursts. For a direct observation of certain characteristics of the transmitted signals radiated by such terminals, only a few measurement setups exist. This article proposes such a novel real-time 3D electromagnetic field measurement instrument with direct visualization. The prototype used for validation is based on an array of probes regularly attached on a non-conductive rigid loop which is put into fast rotation around the terminal under test. To cite this article: J. Rioult et al., C. R. Physique 10 (2009). [Copyright &y& Elsevier]

An analysis of the scattering characteristics of a chiral sphere covered with a metasurface is presented. The electromagnetic fields inside and outside of a metasurface covered chiral sphere are expanded in terms of spherical vector wave functions. The influences of chirality and surface impedance of a metasurface upon the scattering cross section are investigated. It is seen that a specific type of metasurface can be used to significantly enhance and diminish the back scattering cross section from a chiral sphere having a fixed value of chirality but different radii. It is also observed that a chiral sphere having chirality close to unity apparently cannot be cloaked using a lossless metasurface as compared to a dielectric sphere, both having the same electromagnetic and geometrical parameters. A comparative study of the scattering characteristics of metasurface covered realistic chiral and low-loss Teflon dielectric spheres is developed. It is found that a metasurface covered realistic chiral sphere can be used to significantly reduce the scattering as compared to scattering from a metasurface covered Teflon sphere at a specific angle, provided that both spheres have the same radii and surface reactance.