Arbitrary Wave Transformations With Huygens’ Metasurfaces Through Surface-Wave Optimization

Ataloglou, Vasileios G.

doi:10.1109/lawp.2021.3095469

Cited by 42 publications

(20 citation statements)

References 20 publications

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“…Specifically, losses are estimated to be around 7.4% (3.3% Ohmic losses in the wires and the ground plane and 4.1% in the dielectric). This constitutes a promising result, as multi-layer transmissive metasurfaces using auxiliary surface waves for similar functionality exhibit significantly higher losses [44]. In addition, the frequency variation of directivity is plotted in Fig.…”

Section: A Chebyshev Array Patternmentioning

confidence: 92%

Extreme Beam-Forming With Impedance Metasurfaces Featuring Embedded Sources and Auxiliary Surface Wave Optimization

Ataloglou

Hum

et al. 2022

IEEE Access

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We present the end-to-end design of compact passive and lossless metasurface antennas with integrated feeds. The complete low-profile system consists of a single-layered reactive impedance metasurface on top of a grounded dielectric substrate, and is fed by sources which are embedded inside the substrate. The top impedance layer is implemented with an array of printed metallic wires, each of which is periodically loaded with subwavelength reactive elements (e.g. printed capacitors). An accurate and efficient volumesurface integral equation-based model of the device is developed, and used as the basis for the rapid optimization of the wire impedances, with the goal of producing the desired radiation characteristics. It is found that the optimized designs leverage tailored surface waves to facilitate the realization of extreme field transformations. In particular, we present surfaces capable of wide-angle beamforming up to 60 • offbroadside with nearly 100% aperture efficiency. We also demonstrate a multi-input, multi-output, antenna with two embedded sources emitting independent beams at ±20 • . The output beams each exhibits an aperture efficiency of around 90%, despite sharing the same physical aperture. Our design framework is supplemented by several feasibility-related constraints, which can significantly enhance the power efficiency as well as the bandwidth of the metasurface antennas when they are implemented in practice. Utilizing these constraints, a Chebyshev pattern antenna with a side lobe level of −20 dB is designed with realistic loaded wires and validated with full-wave simulations. The obtained radiation pattern confirms the ability of the developed framework for arbitrary beam-shaping. The realized power efficiency (limited by copper and dielectric losses) is over 93% and the 3-dB directivity bandwidth slightly over 6%.

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Section: A Chebyshev Array Patternmentioning

confidence: 92%

Extreme Beam-Forming With Impedance Metasurfaces Featuring Embedded Sources and Auxiliary Surface Wave Optimization

Ataloglou

Hum

et al. 2022

IEEE Access

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“…This implies that the RIS needs to introduce local power amplifications (a negative resistance is equivalent to an amplification) or local power losses along the surface S, depending on the desired angle of reflection for a given angle of incidence. By assuming, e.g., normal incidence (i.e., θ i (r Tx ) = 0), we evince that a unit amplitude reflection coefficient corresponds to an engineered surface S with a positive surface impedance, which implies that no power amplifiers or other sophisticated methods for creating virtual power amplifications through the use of, e.g., surface waves [27], [62], [63], are needed to realize the RIS. The design constraints to be imposed on Z(r Rx , y, r Tx )) for ensuring that the RIS has a high power efficiency for any pair (θ i (r Tx ), θ r (r Rx )) are discussed in the next sub-sections.…”

Section: A Electromagnetically Consistent Modeling Of Rissmentioning

confidence: 99%

“…The power amplification can be virtual, e.g., by using surface waves, or can be realized through actual power amplifiers [27]. The corresponding power flow in (63) is oscillatory in [−L y , L y ] as well.…”

Section: B Power Efficiency and Reradiated Power Fluxmentioning

confidence: 99%

Communication Models for Reconfigurable Intelligent Surfaces: From Surface Electromagnetics to Wireless Networks Optimization

Renzo¹,

Danufane²,

Tretyakov³

2021

Preprint

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A reconfigurable intelligent surface (RIS) is a planar structure that is engineered to dynamically control the electromagnetic waves. In wireless communications, RISs have recently emerged as a promising technology for realizing programmable and reconfigurable wireless propagation environments through nearly passive signal transformations. With the aid of RISs, a wireless environment becomes part of the network design parameters that are subject to optimization.In this tutorial paper, we focus our attention on communication models for RISs. First, we review the communication models that are most often employed in wireless communications and networks for analyzing and optimizing RISs, and elaborate on their advantages and limitations. Then, we concentrate on models for RISs that are based on inhomogeneous sheets of surface impedance, and offer a step-by-step tutorial on formulating electromagnetically-consistent analytical models for optimizing the surface impedance. The differences between local and global designs are discussed and analytically formulated in terms of surface power efficiency and reradiated power flux through the Poynting vector. Finally, with the aid of numerical results, we discuss how approximate global designs can be realized by using locally passive RISs with zero electrical resistance (i.e., inhomogeneous reactance boundaries with no local power amplification), even for large angles of reflection and at high power efficiency.

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“…The surface waves supported by beamforming metasurfaces reshape the local power density by redistributing power transversally along the metasurface from places where local loss is needed to places where local gain is needed, a concept first introduced in [9]. For example, the metasurfaces in [3]- [5], [8]- [23] use surface waves to control either the near or far-fields in a passive and lossless manner.…”

Section: Introductionmentioning

confidence: 99%

“…The effects of not modeling spatial dispersion are explained in [6], where the authors employed conducting baffles to separate unit cells thereby eliminating non-local responses. The baffle approach was also adopted in [2], [3], [20], [24], to achieve agreement between the homogenized models and the realized metasurfaces. The solution presented in this paper is to use integral equations to model the metasurfaces.…”

Section: Introductionmentioning

confidence: 99%

Design of Planar and Conformal, Passive, Lossless Metasurfaces That Beamform

2022

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A general technique for synthesizing both planar and conformal beamforming metasurfaces is presented that utilizes full-wave modeling techniques and rapid optimization methods. The synthesized metasurfaces consist of a patterned metallic cladding supported by a finite-size grounded dielectric substrate. The metasurfaces are modeled using integral equations which accurately account for mutual coupling and the metasurface's finite dimensions. The synthesis technique consists of three phases: a direct solve phase to obtain an initial metasurface design with complex-valued impedances satisfying the desired far-field beam specifications, a subsequent optimization phase that converts the complex-valued impedances to purely reactive ones, and a final patterning phase to realize the purely reactive impedances as a patterned metallic cladding. The optimization phase introduces surface waves which facilitate passivity. The metasurface is optimized using gradient descent with a semi-analytic gradient obtained using the adjoint variable method. Three examples are presented: a low-profile directly-fed metasurface antenna with near perfect aperture efficiency, a scanned-beam reflectarray design with controlled sidelobes, and a conformal metasurface reflectarray. The far-field and near-field performance of the metasurfaces are verified and the bandwidth and loss tolerance of the metasurfaces are investigated. Metasurface, beamforming, conformal, adjoint variable method. INDEX TERMS

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Arbitrary Wave Transformations With Huygens’ Metasurfaces Through Surface-Wave Optimization

Cited by 42 publications

References 20 publications

Extreme Beam-Forming With Impedance Metasurfaces Featuring Embedded Sources and Auxiliary Surface Wave Optimization

Extreme Beam-Forming With Impedance Metasurfaces Featuring Embedded Sources and Auxiliary Surface Wave Optimization

Communication Models for Reconfigurable Intelligent Surfaces: From Surface Electromagnetics to Wireless Networks Optimization

Design of Planar and Conformal, Passive, Lossless Metasurfaces That Beamform

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