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All-angle wideband electromagnetic (EM) transparency for dual polarizations is desired for many practical applications. Conventionally, surface-mount anti-reflection materials or films are usually used to reduce the reflection and thus enhance transparency. In this paper, we propose to achieve wideband EM transparency under extreme angles for both TE- and TM-polarizations using embedded anti-reflection metasurface. The metasurface is composed of a pair of long and short metallic strips, which can introduce both plasma and lattice modes into the original half-wave wall. The plasma mode can create an angle-stable transmission peak at a lower frequency while the lattice mode renders a transmission peak under extreme angles at a higher frequency due to scattering cancellation between short strips and the substrate. By synergizing the plasma, half-wave, and lattice modes consecutively, wide-band transparency can be achieved under extreme angles for TE polarization. Due to the anisotropy of the metasurface, wideband transparency under TM-polarization is maintained. This finally enables us to obtain wideband EM transparency for dual polarizations under extreme angles. More importantly, the metasurface can also be customized to operate best under any given incident angle. Prototypes were designed, fabricated, and measured. Both the simulation and experiment results verify our method. This work provides an efficient route to wideband EM transparency under extreme angles and may find wide applications in communication, radar, and others. [ABSTRACT FROM AUTHOR]

In this article, we propose a design method of aperture-multiplexing metasurfaces using back-propagation neural network (BPNN), which can achieve independent wavefront modulation for orthogonally-polarized waves. To this end, we first propose a modified Jerusalem Cross (MJC) structure as the metasurface unit cell, which decouples orthogonal interactions by increasing the effective inductances of each of the two Jerusalem Cross (JC) branches. Due to the reduced orthogonal couplings, the MJC can achieve nearly independent control of orthogonally-polarized waves. Then, via BPNN, a dictionary mapping between reflection phase and structural parameters of MJC is established to facilitate metasurface design using MJCs. It is verified that the fitting degree of dataset exceeds 99.99% and that the prediction error of reflection phase is less than 0.01°. Using this design method, we demonstrated a focusing metasurface that can focus reflected waves for both $x$ - and $y$ -polarized waves simultaneously, with focus lengths of 150 and 300 mm, respectively. The simulated and measured results are well consistent, which prove the feasibility of this method. This work provides an efficient method of designing multiplexing and multifunctional metasurfaces, which may find applications in fields, such as satellite communication and base stations. [ABSTRACT FROM AUTHOR]

• Aerogel felt is employed as dielectric substrate for metasurface design. • A high-temperature resistant multi-spectrum compatible metasurface framework is proposed. • The flexible metasurface framework is fabricated. • Microwave polarization rotation and infrared low emissivity are realized simultaneously in the surface layer. Advanced electromagnetic functional materials are more and more inclined to integrated design, for instance the compatibility in different spectra as well as wide temperature ranges. Metasurface provides an effective solution for multi-spectrum compatible design owning to its extraordinary performance. In this work, we propose a high-temperature flexible metasurface framework, which can simultaneously realize microwave polarization rotation and low infrared emissivity. As verification, a high-temperature resistant multi-spectrum compatible flexible metasurface is fabricated and measured, which can availably work up to 300 °C. For microwaves, the metasurface achieves the orthogonal polarization rotation efficiency of more than 90% in 5.2–7.5 GHz. For infrared, the metallic filling ratio of 84.42% is constructed by designing the metasurface pattern, thus reducing the infrared emissivity to 0.22 in 3–14 µm. This work provides a flexible metasurface framework for implementing multi-spectrum compatibility at high temperatures, which can be easily attached to the surface of high-temperature components and extended to more functional integration. [ABSTRACT FROM AUTHOR]

[Display omitted] • The concept of active–passive compound metasurface (APCM) is proposed. • The possibility is explored of utilizing the single meta -atom to achieve flexible radiation and scattering manipulations at the same time. • The designed single layer meta -atom structure produces stable radiation direction across the entire X band from 8.0 GHz to 12.0 GHz. • The scattering and radiation patterns can be independently custom-tailored. • Wideband geometric phase with linear-polarization-preserving capacity is obtained. Metasurfaces, which are usually passive or non-radiating, have provided unprecedented degree of freedom especially for scattering manipulation. For the manipulating radiation, metasurfaces often serve as auxiliaries to radiators since they cannot radiate themselves. Thus, it is unfavorable for integration and miniaturization. In this work, we propose the concept of active–passive compound metasurface (APCM) and explore the possibility of utilizing meta -atoms as active radiators, so as to simultaneously achieve flexible radiation and scattering manipulations at the same time. To this end, a meta -atom structure with large reflection phase-span is delicately designed. In this way, the meta -atom can serve both as wideband radiator fed by a probe and reflection-phase modulator. Flexible scattering-pattern manipulation for one polarization state and high-efficiency radiation-pattern manipulation for the orthogonal polarization state can be simultaneously achieved within the same band from 8.0 to 12.0 GHz. As a proof of concept, two prototypes, one for scattering-cancellation and high-directive radiation while the other for deflected reflection and vortex-beam radiation, were designed, fabricated, and measured, respectively. Both the simulated and measured results verify the active–passive compound design. This work paves an alternative route to integrated multi-functional materials or interfaces and may find wide applications in next-generation communication, radar, smart skin, and others. [ABSTRACT FROM AUTHOR]

[Display omitted] • We propose the orthogonality-simplified machine learning framework to design vectorial-holography metasurface. • A structure with orthogonality is designed to independently control x- and y- polarized waves. • Resistors are embedded in meta -atoms to tailor amplitude. • The design of machine learning architecture is simplified based on the physical principle of orthogonality. • The vectorial-holography metasurface is designed by customizing the polarization. Metasurfaces can provide unprecedented degree of freedom in manipulating electromagnetic waves and have been introduced to holography. Aiming to explore the full capability for information presentation, vectorial metasurface holography is sprung up, which exhibits mesmerizing capability in carrying information compared with scalar counterpart. However, the more flexible modulation means the more complex design dimension, which hinders the development of vectorial metasurface holography. In this work, we propose an orthogonal I-shaped structure embedded with resistors to synthesize arbitrary polarization with less crosstalk. Benefiting from the independent control of phase and amplitude on orthogonal base, the orthogonality-simplified machine learning framework is employed to assist vectorial metasurface holography design. As a proof-of-concept, a vectorial metasurface holography carrying multi-polarization information was designed, simulated and measured. All the results exhibit a high degree of consistency, which fully demonstrates the effectiveness of our design. Encouragingly, our method paves a new route to simplify machine learning framework based on physical significance, which can be handily extended to more functional structures. [ABSTRACT FROM AUTHOR]