1,304 research outputs found
Method for Extracting the Equivalent Admittance from Time-Varying Metasurfaces and Its Application to Self-Tuned Spatiotemporal Wave Manipulation
With their self-tuned time-varying responses, waveform-selective metasurfaces
embedded with nonlinear electronics have shown fascinating applications,
including distinguishing different electromagnetic waves depending on the pulse
width. However, thus far they have only been realized with a spatially
homogeneous scattering profile. Here, by modeling a metasurface as time-varying
admittance sheets, we provide an analytical calculation method to predict the
metasurface time-domain responses. This allows derivation of design
specifications in the form of equivalent sheet admittance, which is useful in
synthesizing a metasurface with spatiotemporal control, such as to realize a
metasurface with prescribed time-dependent diffraction characteristics. As an
example, based on the proposed equivalent admittance sheet modeling, we
synthesize a waveform-selective Fresnel zone plate with variable focal length
depending on the incoming pulse width. The proposed synthesis method of
pulse-width-dependent metasurfaces may be extended to designing metasurfaces
with more complex spatiotemporal wave manipulation, benefiting applications
such as sensing, wireless communications and signal processing
Tunable plasmon-enhanced birefringence in ribbon array of anisotropic 2D materials
We explore the far-field scattering properties of anisotropic 2D materials in
ribbon array configuration. Our study reveals the plasmon-enhanced linear
birefringence in these ultrathin metasurfaces, where linearly polarized
incident light can be scattered into its orthogonal polarization or be
converted into circular polarized light. We found wide modulation in both
amplitude and phase of the scattered light via tuning the operating frequency
or material's anisotropy and develop models to explain the observed scattering
behavior
Analytical Equivalent Circuits for Three-dimensional Metamaterials and Metagratings
In recent times, three-dimensional (3D) metamaterials have undergone a
revolution driven mainly by the popularization of 3D-printing techniques, which
has enabled the implementation of modern microwave and photonic devices with
advanced functionalities. However, the analysis of 3D metamaterials is complex
and computationally costly in comparison to their 1D and 2D counterparts due to
the intricate geometries involved. In this paper, we present a fully-analytical
framework based on Floquet-Bloch modal expansions of the electromagnetic fields
and integral-equation methods for the analysis of 3D metamaterials and
metagratings. Concretely, we focus on 3D configurations formed by periodic
arrangements of rectangular waveguides with longitudinal slot insertions. The
analytical framework is computationally efficient compared to full-wave
solutions and also works under oblique incidence conditions. Furthermore, it
comes associated with an equivalent circuit that allows to gain physical
insight into the scattering and diffraction phenomena. The analytical
equivalent circuit is tested against full-wave simulations in commercial
software CST. Simulation results show that the proposed 3D structures provide
independent polarization control of the two orthogonal polarizations states.
This key property is of potential interest for the production of full-metal
polarizers, such as the one illustrated
Compact Metamaterials Induced Circuits and Functional Devices
In recent years, we have witnessed a rapid expansion of using metamaterials to manipulate light or electromagnetic (EM) wave in a subwavelength scale. Specially, metamaterials have a strict limitation on element dimension from effective medium theory with respect to photonic crystals and other planar structures such as frequency selective surface (FSS). In this chapter, we review our effort in exploring physics and working mechanisms for element miniaturization along with the resulting effects on element EM response. Based on these results, we afford some guidelines on how to design and employ these compact meta-atoms in engineering functional devices with high performances. We found that some specific types of planar fractal or meandered structures are particularly suitable to achieve element miniaturization. In what follows, we review our effort in Section 1 to explore novel theory and hybrid method in designing broadband and dual band planar devices. By using single or double such compact composite right-/left-handed (CRLH) atom, we show that many microwave/RF circuits, i.e., balun, rat-race coupler, power divider and diplexer, can be further reduced while without inducing much transmission loss from two perspectives of lumped and distributed CRLH TLs. In Section 2, we show that a more compact LH atom can be engineered by combining a fractal ring and a meandered thin line. Numerical and experimental results demonstrate that a subwavelength focusing is achieved in terms of smooth outgoing field and higher imaging resolution. Section 3 is devoted to a clocking device from the new concept of superscatterer illusions. To realize the required material parameters, we propose a new mechanism by combining both electric and magnetic particles in a composite meta-atom. Such deep subwavelength particles enable exact manipulation of material parameters and thus facilitate desirable illusion performances of a proof-of-concept sample constructed by 6408 gradually varying meta-atoms. Finally, we summarize our results in the last section
Printed circuit metasurfaces for millimeter wave applications
Metasurfaces are artificial composite materials with subwavelength inclusions which have been shown to enable very versatile manipulation of electromagnetic waves. Especially at microwave frequencies, the concept is widely explored and the scope of previous methods of wavefront manipulation such as frequency selective surfaces and leaky-wave antennas has been largely extended. Emerging applications like next generation wireless communication and radar sensing could benefit from novel metasurface-based antennas which have been recently proposed. Although most of these emerging applications use frequencies of operation in the millimeter wave (mm-wave) band, research on metasurfaces in this band is still scarce. Many secondary effects known in the microwave community such as fabrication constraints and material losses are more severe using mm-waves and they significantly hamper the development of efficient devices. The aim of this thesis is to explore design and characterization methods for mm-wave metasurfaces. In particular, this thesis concentrates on planar metasurface architectures that are compatible with established printed circuit board fabrication, which is a requirement for many consumer applications. Causes for significant performance degradation in printed circuit metasurfaces for mm-waves are identified and synthesis techniques with which they can be minimized are proposed. The effectiveness of the proposed synthesis techniques is verified by comprehensive experimental works. Building on these synthesis approaches, two kinds of antenna systems are experimentally demonstrated, based on transmissive metasurfaces and on leaky-wave antennas
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