211 research outputs found
Plane-wave scattering by self-complementary metasurfaces in terms of electromagnetic duality and Babinet's principle
We investigate theoretically electromagnetic plane-wave scattering by
self-complementary metasurfaces. By using Babinet's principle extended to
metasurfaces with resistive elements, we show that the frequency-independent
transmission and reflection are realized for normal incidence of a circularly
polarized plane wave onto a self-complementary metasurface, even if there is
diffraction. Next, we consider two special classes of self-complementary
metasurfaces. We show that self-complementary metasurfaces with rotational
symmetry can act as coherent perfect absorbers, and those with translational
symmetry compatible with their self-complementarity can split the incident
power equally, even for oblique incidences
Frequency-Independent Response of Self-Complementary Checkerboard Screens
This research resolves a long-standing problem on the electromagnetic
response of self-complementary metallic screens with checkerboardlike geometry.
Although Babinet's principle implies that they show a frequency-independent
response, this unusual characteristic has not been observed yet due to the
singularities of the metallic point contacts in the checkerboard geometry. We
overcome this difficulty by replacing the point contacts with resistive sheets.
The proposed structure is prepared and characterized by terahertz time-domain
spectroscopy. It is experimentally confirmed that the resistive checkerboard
structures exhibit a flat transmission spectrum over 0.1--1.1 THz. It is also
demonstrated that self-complementarity can eliminate even the
frequency-dependent transmission characteristics of resonant metamaterials.Comment: 6 pages, 5 figures + Supplemental Material (6 pages, 7 figures
Broadband and energy-concentrating terahertz coherent perfect absorber based on a self-complementary metasurface
We demonstrate that a self-complementary checkerboard-like metasurface works
as a broadband coherent perfect absorber (CPA) when symmetrically illuminated
by two counter-propagating incident waves. A theoretical analysis based on wave
interference and results of numerical simulations of the proposed metasurface
are provided. In addition, we experimentally demonstrate the proposed CPA in
the terahertz regime by using a time-domain spectroscopy technique. We observe
that the metasurface can work as a CPA below its lowest diffraction frequency.
The size of the absorptive areas of the proposed CPA can be much smaller than
the incident wavelength. Unlike conventional CPAs, the presented one
simultaneously achieves the broadband operation and energy concentration of
electromagnetic waves at the deep-subwavelength scale.Comment: 5 pages, 4 figure
Highly porous melamine-formaldehyde monoliths with controlled hierarchical porosity toward application as a metal scavenger
We report a new synthetic strategy for melamine-formaldehyde (MF) monoliths with controlled hierarchical porosity toward metal-ion scavengers. The obtained MF monoliths possessed micro-, meso- and macroporosity, which allowed efficient adsorption performance of precious metal ions in water. Applications such as recovery/removal of metal ions are expected
Sol–gel based structural designs of macropores and material shapes of metal–organic framework gels
We have developed a general synthetic strategy to control macroporous structures and material shapes of metal–organic framework (MOF) gels via a sol–gel based structural control process. A series of 1, 3, 5-benzene tricarboxylic acid (BTC) based MOF gels, Cr-BTC and Zr-BTC, have been chosen as a proof of concept
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