摘要 :
Optical metasurfaces, planar subwavelength nanoantenna arrays with the singular ability to sculpt wavefront in almost arbitrary manners, are poised to become a powerful tool enabling compact and high-performance optics with novel ...
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Optical metasurfaces, planar subwavelength nanoantenna arrays with the singular ability to sculpt wavefront in almost arbitrary manners, are poised to become a powerful tool enabling compact and high-performance optics with novel functionalities. A particularly intriguing research direction within this field is active metasurfaces, whose optical response can be dynamically tuned postfabrication, thus allowing a plurality of applications unattainable with traditional bulk optics. Designing reconfigurable optics based on active metasurfaces is, however, presented with a unique challenge, since the optical quality of the devices must be optimized at multiple optical states. In this article, we provide a critical review on the active meta-optics design principles and algorithms that are applied across structural hierarchies ranging from single meta-atoms to full meta-optical devices. The discussed approaches are illustrated by specific examples of reconfigurable metasurfaces based on optical phase-change materials.
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摘要 :
In this paper, an ultra-wideband tightly couple antenna array based on a low-loss phase-modulated frequency selective surface and a microstrip-based feeding structure is reported. The proposed antenna array, which employs tightly ...
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In this paper, an ultra-wideband tightly couple antenna array based on a low-loss phase-modulated frequency selective surface and a microstrip-based feeding structure is reported. The proposed antenna array, which employs tightly coupled bow-tie elements, features a very low profile (1.08 λhigh\lambda _{high} ). Specifically, a microstrip-to-parallel strip transition serves as an impedance transformer and a wideband balun to enable the array element to be excited with a 50 Ω\Omega unbalanced feeding scheme. Additionally, one shorting sheet is employed to expand the bandwidth by shifting the common-mode to a higher frequency band. The presented design achieves a bandwidth of 13.66:1 (0.52 GHz – 7.10 GHz) with VSWR < 2.49 and simulated radiation efficiency greater than 96% across the whole band. To validate the design concepts, an 8×88\times8 array prototype is fabricated and characterized experimentally. The measured results match well with the numerical analysis.
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摘要 :
Metasurfaces have shown promising potentials in shaping optical wavefronts while remaining compact compared to bulky geometric optics devices. The design of meta-atoms, the fundamental building blocks of metasurfaces, typically re...
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Metasurfaces have shown promising potentials in shaping optical wavefronts while remaining compact compared to bulky geometric optics devices. The design of meta-atoms, the fundamental building blocks of metasurfaces, typically relies on trial and error to achieve target electromagnetic responses. This process includes the characterization of an enormous amount of meta-atom designs with varying physical and geometric parameters, which demands huge computational resources. In this paper, a deep learning-based metasurface/meta-atom modeling approach is introduced to significantly reduce the characterization time while maintaining accuracy. Based on a convolutional neural network (CNN) structure, the proposed deep learning network is able to model meta-atoms with nearly freeform 2D patterns and different lattice sizes, material refractive indices and thicknesses. Moreover, the presented approach features the capability of predicting a meta-atom’s wide spectrum response in the timescale of milliseconds, attractive for applications necessitating fast on-demand design and optimization of a meta-atom/metasurface.
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摘要 :
In this letter, a low-profile flexible dual-band quasi-isotropic antenna based on half-wavelength crossed dipoles is developed for unmanned aerial vehicle (UAV) applications. Specifically, to decrease the antenna profile, a coaxia...
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In this letter, a low-profile flexible dual-band quasi-isotropic antenna based on half-wavelength crossed dipoles is developed for unmanned aerial vehicle (UAV) applications. Specifically, to decrease the antenna profile, a coaxial structure is used to feed the antenna and no external balun is applied. Theoretical and numerical analyses of the designed antenna were conducted. To validate the design concept, an antenna prototype was fabricated and characterized. Good agreements have been observed between simulations and measurements. The measured radiation patterns show that the gain deviations across the whole spherical radiation surface are less than 7.5 dBi at 2.4 GHz and less than 8.7 dBi at 4.6 GHz. For the purpose of system demonstration, a 2 × 2 multiple-input–multiple-output (MIMO) system employing the proposed antenna was assembled. The resulting dual-band MIMO system was deployed on a UAV for ground test, validating its potential for performance improvement of UAV communications.
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摘要 :
Filtering light by coherence by metasurfaces would enable compact, integrable coherence filters. A recent such proposal centered on a metasurface of zigzags. Here, we show that spatial coherence filtering can be achieved at normal...
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Filtering light by coherence by metasurfaces would enable compact, integrable coherence filters. A recent such proposal centered on a metasurface of zigzags. Here, we show that spatial coherence filtering can be achieved at normal incidence with a similar zigzag metasurface and can be traced to the band structure of the leaky modes of the thin film structure. We fabricate a metasurface of zigzags etched through a gold film deposited on a GaAs substrate and measure the transmittance of long wave infrared radiation. Selectivity matches predictions based on the band structure of fully coherent radiation. Furthermore, the degree of coherence filtering is shown to be controlled by the Q-factor of leaky modes.
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摘要 :
This paper presents a deep learning
approach for the inverse-design of metal-insulator-metal
metasurfaces for hyperspectral imaging applications.
Deep neural networks are able to compensate for the
complex interactions between...
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This paper presents a deep learning
approach for the inverse-design of metal-insulator-metal
metasurfaces for hyperspectral imaging applications.
Deep neural networks are able to compensate for the
complex interactions between electromagnetic waves and
metastructures to efficiently produce design solutions
that would be difficult to obtain using other methods.
Since electromagnetic spectra are sequential in nature,
recurrent neural networks are especially suited for
relating such spectra to structural parameters.
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摘要 :
Optical metasurface is a recently emerged paradigm
for controlling light propagation, which enables implementation
of ultra-compact optical devices with extended functionalities.
Nowadays the main challenge in the field is to r...
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Optical metasurface is a recently emerged paradigm
for controlling light propagation, which enables implementation
of ultra-compact optical devices with extended functionalities.
Nowadays the main challenge in the field is to realize active
metasurfaces with high quality, high efficiency, and large tuning
range. Here we present a design approach for constructing a twostate
reconfigurable metalens made of low-loss optical phasechange
material (O-PCM). The metalens design is capable to
produce diffraction limited focusing, large change in focal length
(from 1.5 mm to 2mm), and decent focusing efficiency of about
20% in both states. The proposed design methodology is generic
and can be easily extended towards constructing metasurfaces,
which can switch between two or more arbitrary phase maps.
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