Polarization-Engineered Noninterleaved Metasurface for Integer and Fractional Orbital Angular Momentum Multiplexing

Traditional methods of generating vortex beams based on metasurfaces consist mainly in modulating propagation phase or geometric phase. Here, by introducing detour phase, we propose the construction of dual-polarized vortex beam generators in the form of metasurface and metagrating (MG). The phase is modulated through moving the position of meta-atoms instead of varying the geometrical parameters or rotating the unit cells. To use detour phase, two kinds of unit cells are designed to achieve specific diffraction order. Each unit can arbitrarily and independently adjust the operation frequency and diffraction angle of transverse electric (TE) and transverse magnetic (TM) polarizations. Two vortex beam generators are designed and fabricated with different topological charges carried by orthogonal polarizations. To demonstrate the ability to independently manipulate, two polarizations of the generator based on MG are designed in different frequency bands. Both the simulation and experimental results validate the proposed method, showing great potential for polarization division multiplexing in orbital angular momentum (OAM) communication systems. 

Generating Dual-Polarized Vortex Beam by Detour Phase: From Phase Gradient Metasurfaces to Metagratings

Symmetric spin–orbit interaction (SOI)‐based approaches apply a practical limit on helicity multiplexed metaoptics, i.e., center symmetric information encoding. Contrarily, asymmetric SOI's based on the combination of geometric and propagation phase‐delay approaches can effectively address such limitations for multifunctional multiplexed metaoptics on the cost of design complexities. In this paper, a simple asymmetric SOI‐based technique is realized for multifunctional metaoptics, employing only a single unit cell, breaking the conventional tradeoff between design complexity and efficient asymmetric transmission efficiency. The design approach depends on geometric phase alone, which eases the fabrication challenges and decreases the computational cost associated with previous asymmetric SOI‐based metaoptics. Furthermore, this study utilizes a new, low‐cost CMOS‐compatible material to optimize the proposed single unit cell for low loss and high transmission efficiency over the complete visible domain. On‐axis and off‐axis holographic metasurfaces are designed and integrated with pressure‐sensitive liquid crystal cells to demonstrate actively tunable metaholography with no limitation of center symmetric information encoding. The simple design technique, cost‐effective fabrication, and finger touch‐enabled holographic output switching make this integrated setup a potential candidate for many applications such as smart safety labeling, motion or touch recognition, and interactive displays for impact monitoring of precious artworks and products.

Novel Spin‐Decoupling Strategy in Liquid Crystal‐Integrated Metasurfaces for Interactive Metadisplays

Resonant metasurface (MTS) antennas (RMAs) are antennas leveraging unusual standing-wave modes of truncated MTS. By introducing resonant exciters, such as wire (electric currents), aperture (magnetic currents), or both, the antenna bandwidth can be improved. However, the contributing modes of apertures are not well recognized. A systematic framework is formulated for the characteristic mode analysis (CMA) and design of RMAs involving resonant apertures, by designing a low-profile wideband dual-polarized RMAs fed by slot arrays at 5 GHz Wi-Fi bands. Unlike regular microstrip patches, the aperture-backed MTS supports two fundamental TM03 modes of different symmetries. Even and odd symmetries are also observed for the aperture modes. By calculating the radiating power of individual mode, quantitative evidence is provided to clarify the operating principle of RMAs with resonant apertures that the bandwidth improvement and high-isolations are due to the modes from both the MTS and the aperture, rather than from individual. The overall size of the proposed antenna is $\lambda _{\mathrm {L}} \times \lambda _{\mathrm {L}} \times 0.058\lambda _{\mathrm {L}}$ ( $\lambda _{\mathrm {L}}$ is the free-space wavelength at 4.8 GHz). The measured bandwidth is 25% (4.8–6.2 GHz) with $\vert S_{11}\vert dB, $\vert S_{21}\vert dB, boresight gain of 8–10 dBi and cross-polarization level better than −28 dB.

Resonant Metasurface Antennas With Resonant Apertures: Characteristic Mode Analysis and Dual-Polarized Broadband Low-Profile Design

Modern humanity wades daily through various radiations, resulting in frequent exposure and causing potentially important biological effects. Among them, the brain is the organ most sensitive to electromagnetic radiation (EMR) exposure. Despite numerous correlated studies, critical unknowns surround the different parameters used, including operational frequency, power density (i.e., energy dose), and irradiation time that could permit reproducibility and comparability between analyses. Furthermore, the interactions of EMR with biological systems and its precise mechanisms remain poorly characterized. In this review, recent approaches examining the effects of microwave radiations on the brain, specifically learning and memory capabilities, as well as the mechanisms of brain dysfunction with exposure as reported in the literature, are analyzed and interpreted to provide prospective views for future research directed at this important and novel medical technology for developing preventive and therapeutic strategies on brain degeneration caused by microwave radiation. Additionally, the interactions of microwaves with biological systems and possible mechanisms are presented in this review. Treatment with natural products and safe techniques to reduce harm to organs have become essential components of daily life, and some promising techniques to treat cancers and their radioprotective effects are summarized as well. This review can serve as a platform for researchers to understand the mechanism and interactions of microwave radiation with biological systems, the present scenario, and prospects for future studies on the effect of microwaves on the brain.

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Microwave Radiation and the Brain: Mechanisms, Current Status, and Future Prospects

Vortex beams have witnessed tremendous development in the past
decade by exhibiting profound implications for both fundamental physics
and a multitude of novel engineering applications. In this work, broadband
high-efficiency multiple vortex beams with independent topological modes
and inclination angles are generated leveraging an interleaved
geometric-phase multifunctional metasurface operating in a very broadband
frequency range. A set of meta-atoms are elaborately engineered to offer
broadband high-efficiency complete phase control covering the entire
2π range. Multiple geometric-phase sub-arrays implemented by the
designed meta-atoms are synthesized into one metasurface via a
shared-aperture interleaved manner, in which each sub-array can be
individually manipulated and serves as an independent channel for
launching a vortex beam. According to the established design methodology,
two vortex beams with topological modes of −1 and +2 and
distinct inclination angles are generated by one metasurface. Experimental
results are provided to corroborate the proposed mechanism for multiple
vortex beams generation, which exhibit broadband and high-efficiency
features. The presented multifunctional metasurface paves the way for the
generation of broadband high-efficiency multiple vortex beams in the
microwave, millimeter-wave and terahertz regions. This work is of
significance for high-capacity wireless communication applications,
high-efficiency manipulation of electromagnetic waves, and novel design of
radar and imaging systems.

Broadband high-efficiency multiple vortex beams generated by an interleaved geometric-phase multifunctional metasurface

As a rapidly developing novel electromagnetic imaging technique, microwave-induced thermoacoustic tomography (MITAT) has found many applications and attracted tremendous research interest. Using sparse data to reconstruct images is very challenging for MITAT. This work proposes a novel deep-learning-enabled MITAT (DL-MITAT) modality to address the sparse data reconstruction problem and applies it in breast cancer detection. The applied network is a domain transform network called feature projection network (FPNet) + ResU-Net. Detailed structure and implementation method of the network is described. We conduct both simulation and ex vivo experiments with breast phantoms to test the validity of the DL-MITAT approach. The obtained images given by the trained network exhibit much better quality and have much less artifacts than those obtained by a traditional imaging algorithm. We show that only 15 measurements can still reliably recover an image of the breast tumor for both full-view and limited-view configurations in ex vivo experiments. We also provide detailed discussions on the capability and limitations of the proposed scheme. This work presents a new paradigm for MITAT based on sparse data and can be applied in all related applications of MITAT, including biomedical imaging, nondestructive testing, and therapy guidance.

Deep-Learning-Enabled Microwave-Induced Thermoacoustic Tomography Based on Sparse Data for Breast Cancer Detection

Metasurfaces have provided new opportunities to control electromagnetic waves, which may find applications in areas such as wireless communications, imaging, energy harvesting, and invisible cloaks. Among all of the applications, Bessel beams and orbital angular momentum (OAM) beams have been investigated extensively. The combination of Bessel beam and OAM can engender some interesting phenomenon. In this work, we report a topological transformation of mode in the transmission of OAM using millimeter wave metasurface. Unit cell of the metasurface is designed to adjust phase of the transmitted wave. Two kinds of Bessel beams carrying OAM are encoded simultaneously with a crossed arrangement. Simulation results show that with the propagation of the beam, the mode number of OAM transformed from one to four and the energy delivered to all four modes. This work may be helpful in the transportation exploring of OAM and can be used in multifunction wireless communication.

Jiale Zhang

Papers

Broadband high-efficiency multiple vortex beams generated by an interleaved geometric-phase multifunctional metasurface

Deep-Learning-Enabled Microwave-Induced Thermoacoustic Tomography Based on Sparse Data for Breast Cancer Detection

Topological Transformation OAM Based on Metasurface Generated Bessel Beam