4,669 research outputs found
Accurate metasurface synthesis incorporating near-field coupling effects
One of the most promising metasurface architectures for the microwave and
terahertz frequency ranges consists of three patterned metallic layers
separated by dielectrics. Such metasurfaces are well suited to planar
fabrication techniques and their synthesis is facilitated by modelling them as
impedance sheets separated by transmission lines. We show that this model can
be significantly inaccurate in some cases, due to near-field coupling between
metallic layers. This problem is particularly severe for higher frequency
designs, where fabrication tolerances prevent the patterns from being
highly-subwavelength in size. Since the near-field coupling is difficult to
describe analytically, correcting for it in a design typically requires
numerical optimization. We propose an extension of the widely used
equivalent-circuit model to incorporate near-field coupling and show that the
extended model can predict the scattering parameters of a metasurface
accurately. Based on our extended model, we introduce an improved metasurface
synthesis algorithm that gives physical insight to the problem and efficiently
compensates for the perturbations induced by near-field coupling. Using the
proposed algorithm, a Huygens metasurface for beam refraction is synthesized
showing a performance close to the theoretical efficiency limit despite the
presence of strong near-field coupling
The Casimir zero-point radiation pressure
We analyze some consequences of the Casimir-type zero-point radiation
pressure. These include macroscopic "vacuum" forces on a metallic layer
in-between a dielectric medium and an inert () one. Ways
to control the sign of these forces, based on dielectric properties of the
media, are thus suggested. Finally, the large positive Casimir pressure, due to
surface plasmons on thin metallic layers, is evaluated and discussed.Comment: 4 2-column pages, LATE
Interaction of radially polarized focused light with a prolate spheroidal nanoparticle
The interaction of a nanoparticle with light is affected by nanoparticle geometry and composition, as well as by focused beam parameters, such as the polarization and numerical aperture of the beam. The interaction of a radially focused beam with a prolate spheroidal nanoparticle is particularly important because it has the potential to produce strong near-field electromagnetic radiation. Strong and tightly localized longitudinal components of a radially polarized focused beam can excite strong plasmon modes on elongated nanoparticles such as prolate spheroids. In this study, near field radiation from a prolate spheriodal nanoparticle is investigated when it is illuminated with a radially polarized focused beam of light. Near-field radiation from the nanoparticle is investigated in the absence and presence of metallic layers. It is shown that the interaction of a radially polarized focused beam with a prolate spheroidal nanoparticle can be enhanced by creating images of monopole charges using metallic layers. In addition, it is also observed that the presence of a metallic layer shifts the resonance of the prolate spheroid toward longer wavelengths. Dipole, quadruple, and off resonance field distributions for particles with different sizes and aspect ratios are presented when they are illuminated with a radially focused beam of light
Hydrophobic/icephobic coatings based on thermal sprayed metallic layers with subsequent surface functionalization
Hydrophobic/icephobic coatings have been fabricated using a combination of thermal sprayed metallic MCrAlY (M = Ni, Co) coatings with a subsequent deposition process using 1H,1H,2H,2H-perfluorooctyltriethoxysilane (POTS). The MCrAlY coatings provide the desirable surface roughness feature for hydrophobicity, and water contact angle of 135° was directly obtained after aged in the atmosphere for 1 week. However, it was found that the hydrophobicity of MCrAlY was not stable under water impinging due to unstable hydrocarbon absorption. Better hydrophobicity with water contact angle of 154° and improved durability have been achieved by further modification using POTS vapour on the rough MCrAlY coatings. X-ray photoelectron spectroscopy results revealed that replacement of absorption of hydrocarbon by functional C-F groups played important role in the improvement of hydrophobicity and durability. The ice adhesion test confirmed that lower ice adhesion strength of MCrAlY based coatings have been obtained compared with the threshold for icephobicity which is desirable to be applied as icephobic coatings for aircraft. The electro-thermal heating de-icing test showed an energy saving of 28.6% for de-icing with the two-step MCrAlY based coatings. The combination of strong metallic MCrAlY rough layers and the subsequent functionalization enables a new approach for the fabrication of durable hydrophobic/icephobic coatings
Magnon Mediated Electric Current Drag Across a Ferromagnetic Insulator Layer
In a semiconductor hererostructure, the Coulomb interaction is responsible
for the electric current drag between two 2D electron gases across an electron
impenetrable insulator. For two metallic layers separated by a ferromagnetic
insulator (FI) layer, the electric current drag can be mediated by a
nonequilibrium magnon current of the FI. We determine the drag current by using
the semiclassical Boltzmann approach with proper boundary conditions of
electrons and magnons at the metal-FI interface.Comment: 13 pages, 2 figures: to appear in PR
Optimal T of cuprates: role of screening and reservoir layers
We explore the role of charge reservoir layers (CRLs) on the superconducting
transition temperature of cuprate superconductors. Specifically, we study the
effect of CRLs with efficient short distance dielectric screening coupled
capacitively to copper oxide metallic layers. We argue that dielectric
screening at short distances and at frequencies of the order of the
superconducting gap, but small compared to the Fermi energy can significantly
enhance T, the transition temperature of an unconventional superconductor.
We discuss the relevance of our qualitative arguments to a broader class of
unconventional superconductors.Comment: 8 Pages, 4 figure
Plasmon resonances of a prolate spheroid nanoparticle illuminated by a focused beam
The interaction of a radially focused beam with a prolate spheroidal nanoparticle is particularly important because it has the potential to produce strong nearfield electromagnetic radiation. Strong and tightly localized longitudinal components of a radially polarized focused beam can excite strong plasmon modes on elongated nanoparticles such as prolate spheroids. In this study, near field radiation from a prolate spheriodal nanoparticle is investigated when it is illuminated with a radially polarized focused beam of light. Nearfield
radiation from the nanoparticle is investigated in the absence and presence of metallic layers
New constraints for non-Newtonian gravity in nanometer range from the improved precision measurement of the Casimir force
We obtain constraints on non-Newtonian gravity following from the improved
precision measurement of the Casimir force by means of atomic force microscope.
The hypothetical force is calculated in experimental configuration (a sphere
above a disk both covered by two metallic layers). The strengthenings of
constraints up to 4 times comparing the previous experiment and up to 560 times
comparing the Casimir force measurements between dielectrics are obtained in
the interaction range 5.9 nmnm. Recent speculations about
the presence of some unexplained attractive force in the considered experiment
are shown to be unjustified.Comment: 5 pages, 1 figur
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