Suboptimal Coding Metasurfaces for Terahertz Diffuse Scattering

Moccia, Massimo; Koral, Can; Papari, Gian Paolo; Liu, Shuo; Zhang, Lei; Wu, Rui Yuan; Castaldi, G.; Cui, Tie Jun; Galdi, Vincenzo; Andreone, A.

doi:10.1038/s41598-018-30375-z

Cited by 43 publications

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References 37 publications

(61 reference statements)

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“…The concept of digital coding and programmable metasurfaces was originally proposed by Cui et al in 2014, and has been rapidly developed and implemented in many applications . Such metasurfaces are composed of a limited numbers of meta‐atoms and can control EM waves in a discretized manner, which offers the inherent advantage of greatly simplifying the design and optimization procedures.…”

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confidence: 99%

“…The digital representation of coding metasurfaces is remarkably suitable for integrating active devices (e.g., diodes), which can be independently controlled by a field‐ programmable gate array (FPGA), thereby leading to programmable metasurfaces. These concepts have been widely explored in several applications including holograms, imaging, vortex beams, reflect and transmit arrays, diffuse scattering, information processing, and new architectures of wireless communication systems . More recently, a general theory of space‐time‐coding digital metasurfaces has been proposed to enable simultaneous manipulations of EM waves in both the space and frequency domains, such as harmonic beam steering.…”

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confidence: 99%

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Breaking Reciprocity with Space‐Time‐Coding Digital Metasurfaces

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which can manipulate electromagnetic (EM) waves in unconventional ways, and have enabled many exotic physical phenomena and effects, also inspiring novel devices and engineering applications. [1] Their 2D versions, commonly referred to as metasurfaces, are experiencing a strong surge of interest owing to a number of attractive features, including ultrathin thickness, low loss, easy fabrication, and potential conformability. In the wake of the pioneering work by Yu et al. [2] on generalized Snell's laws enabled by imparting an abrupt phase shift, metasurfaces have demonstrated unprecedented capabilities in wavefront engineering, amplitude modulation, and polarization conversion, just to mention a few. [2][3][4][5][6] However, metasurfaces that only impart space-gradient phase discontinuities are inherently constrained by Lorentz reciprocity. This implies, for instance, that the time-reversed version of a reflected wave propagates along the same direction as the original incident wave at the same frequency.The quest for breaking reciprocity is of longstanding interest in EM engineering, and is currently eliciting renewed attention in view of its pivotal role in lifting some fundamental limitations in communication systems as well as energy harvesting and heat management. [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] For instance, in wireless communication systems, a nonreciprocal antenna could radiate a very directive beam without being bound to receiving its reflected echo. [20] A common way to attain nonreciprocal effects, especially at microwave frequencies, is to break the time-reversal symmetry by means of biased magnetic materials (e.g., ferrites). These, however, are typically bulky, costly, and difficult to integrate and scale up to optical wavelengths, [10] which motivates the strong interest in magnetless approaches. Some of these are based on nonlinear materials, which are not bound by the reciprocity theorem, but are power-dependent and require sufficiently high signal intensity. [11,12] Other magnetless approaches rely on transistor-based devices [13] and moving media, [14,15] but are limited in terms of operating frequency, and are difficult to extend to the optical regime. Timevarying approaches have emerged as attractive alternatives based on time-modulated devices, [16][17][18][19][20][21][22][23][24] which have smaller size, lower cost, and better integrability. In 2015, Shaltout et al. [19] Metasurfaces are artificially engineered ultrathin structures that can finely tailor and control electromagnetic wavefronts. There is currently a strong interest in exploring their capability to lift some fundamental limitations dictated by Lorentz reciprocity, which have strong implications in communication, heat management, and energy harvesting. Time-varying approaches have emerged as attractive alternatives to conventional schemes relying on magnetic or nonlinear materials, but experimental evidence is currently limited to devices such as circulators and antennas. Here, the recently...

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Breaking Reciprocity with Space‐Time‐Coding Digital Metasurfaces

et al. 2019

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“…The controllable distribution of the nonlinearity can be directly demonstrated by diverse scattering performances of the metasurface illuminated by plane waves, such as beam deflections, vortex beams, diffused scatterings, and holograms, which have been rigorously investigated in previous literatures. Assuming that the reflection magnitudes of the particles are unity, and their reflection phases are ϕ mn , where m and n indicate the position of the particle on the metasurface, the anomalous scattering far‐field patterns of the metasurface are calculated as

\begin{matrix} left \\ F (θ, φ) = f_{normale} (θ, φ) \sum_{m = 1}^{N} \sum_{n = 1}^{N} \exp false{- i false{φ_{m n} \\ + k D \sin θ ([], (m - 1 / 2) \cos φ + (n - 1 / 2) \sin φ) false} false} \end{matrix}

where f e (θ,ϕ) is the field function of a certain particle, D is period of the particles, k = 2π/λ is wave number in free space, and θ and ϕ are the elevation and azimuthal angles, respectively.…”

Section: Resultsmentioning

confidence: 99%

“…In the recent decades, 2D metasurfaces arise with the advantages of negligible profiles, lower loss, and high degrees of integration, becoming more of interest in the manipulations of waves . Since the proposal of the generalized Snell's laws of reflection and refraction based on the abrupt phase shift caused by a metasurface, a variety of interesting applications were put forward . Specifically, to extend exotic and attractive properties of the metasurfaces, integrations with tuning substances or elements, including graphene, vanadium dioxide, liquid crystal in optics, and MEMS switches, PIN diodes, varactors in the microwave domain, giving the metasurfaces with dynamic tunabilities.…”

Section: Introductionmentioning

confidence: 99%

Intensity‐Dependent Metasurface with Digitally Reconfigurable Distribution of Nonlinearity

Luo

Wang

Zhang

et al. 2019

Advanced Optical Materials

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Nonlinear metamaterials are of continuing interest by manipulating electromagnetic (EM) waves depending on incident intensity. Most of the existing nonlinear metamaterials rely on the interactions between superconcentrated EM fields and nonlinear substances within the resonant composites, which cannot be easily adjusted dynamically. Here, an intensity‐dependent metasurface is proposed, whose nonlinearity distribution is digitally reconfigurable. Different from previous works, an active microwave detecting circuit is integrated into each particle of the metasurface as the nonlinear module, endowing reflection phase of the particle with strong dependence on microwave intensities. By controlling the circuit using a digital bit, the particle can be switched to be linear with a fixed phase, which provides a digital way to reconfigure the arrangement of nonlinear and linear particles on the metasurface. Therefore, the phase profile on the surface is determined by the incoming intensity and digital controlling signals, opening up new possibilities in nonlinear EM wave manipulations. The concept is demonstrated by the digitally defined nonlinear scattering measurements at microwave frequencies. As a new metamaterial with the digitally reconfigurable nonlinearity and negligible thickness, this proposal may find potential applications including power protection, EM compatibility, nonlinear beam scanning, and so on.

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“…Initially, coding metasurfaces [85] are aimed at digitalizing EM information of the metasurface by programming the amplitudes and phases of sub-wavelength resonators to control EM waves. After nearly a decade of development, this concept has been extended from microwave to terahertz frequencies [86], from isotropic to anisotropic, from reflection-type to transmission-type [87], from single-band to multi-band, and from spatial coding to time coding [88]. Initially, our group mainly focuses on the resonator optimization through genetic algorithm combined with some kinds of intelligent algorithm.…”

Section: Coding Metasurface For Rcs Reductionmentioning

confidence: 99%

Recent developments of metamaterials/metasurfaces for RCS reduction

Yang

Wang

et al. 2019

EPJ Appl. Metamat.

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In this paper, recent developments of metamaterials and metasurfaces for RCS reduction are reviewed, including basic theory, working principle, design formula, and experimental verification. Super-thin cloaks mediated by metasurfaces can cloak objects with minor impacts on the original electromagnetic field distribution. RCS reduction can be achieved by reconfiguring scattering patterns using coding metasurfaces. Novel radar absorbing materials can be devised based on field enhancements of metamaterials. When combined with conventional radar absorbing materials, metamaterials can expand the bandwidth, enlarge the angular range, or reduce the weight. Future tendency and major challenges are also summarized.

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Suboptimal Coding Metasurfaces for Terahertz Diffuse Scattering

Cited by 43 publications

References 37 publications

Breaking Reciprocity with Space‐Time‐Coding Digital Metasurfaces

Breaking Reciprocity with Space‐Time‐Coding Digital Metasurfaces

Intensity‐Dependent Metasurface with Digitally Reconfigurable Distribution of Nonlinearity

Recent developments of metamaterials/metasurfaces for RCS reduction

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