- 标题
- 摘要
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Geometrical optics and geodesics in thin layers
摘要： The propagation of a light ray in a thin layer (film) within geometrical optics is considered. It is assumed that the ray is captured inside the layer due to reflecting walls or total internal reflection (in the case of a dielectric layer). It has been found that for a very thin film (the length scale is imposed by the curvature of the surface at a given point) the equations describing the trajectory of the light beam are reduced to the equation of a geodesic on the limiting curved surface. There have also been found corrections to the trajectory equation resulting from the finite thickness of the film. Numerical calculations performed for a couple of exemplary curved layers (cone, sphere, torus, and catenoid) confirm that for thin layers the light ray which is repeatedly reflected propagates along the curve close to the geodesic but as the layer thickness increases, these trajectories move away from each other. Because the trajectory equations are complicated nonlinear differential equations, their solutions show some chaotic features. Small changes in the initial conditions result in remarkably different trajectories. These chaotic properties become less significant the thinner the layer under consideration.
关键词： thin layers,geometrical optics,light propagation,geodesics,curved surfaces
更新于2025-09-04 15:30:14
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Building two-dimensional metal–organic networks with tin
摘要： We show that Sn atoms combined with organic ligands can be used to build 2D coordination networks on Au(111) surfaces. The use of metal–organic bonding has been recognized as a powerful strategy for the generation, directly on solid surfaces, of 2D modular functional materials with potential application in catalysis, organic electronics, and magnetism. This has lead to the important progress observed in recent years in the engineering of a great variety of surface-supported 2D metal–organic networks (MONs). In this Communication, we report the first example of a surface-confined Sn-based MON. With only a few studies of surface-supported MONs based on p-block metals reported in the literature, the possibilities of building modular 2D MONs based on this group of metals remains almost unexplored to date. Tin, with formal oxidation states 2 and 4, forms a large diversity of metal–organic compounds (organotin compounds) which have a wide range of applications ranging from all sorts of biological activity to industrial catalytic processes. Organotin compounds have also attracted the attention of the condense-matter community, especially since stanene-cyanide was proposed as a candidate topological-insulator material. We thus investigated the synthesis, directly on Cu(100) and Au(111) surfaces, of Sn-based MONs using 7,7,8,8-tetracyanoquinodimethane (TCNQ) molecules as ligands.
关键词： Au(111) surfaces,TCNQ molecules,2D coordination networks,Sn-based MON,metal–organic bonding
更新于2025-09-04 15:30:14
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Phase diagram of Bi2Sr2CaCu2O8+δ revisited
摘要： In cuprate superconductors, the doping of carriers into the parent Mott insulator induces superconductivity and various other phases whose characteristic temperatures are typically plotted versus the doping level p. In most materials, p cannot be determined from the chemical composition, but it is derived from the superconducting transition temperature, Tc, using the assumption that the Tc dependence on doping is universal. Here, we present angle-resolved photoemission studies of Bi2Sr2CaCu2O8+δ, cleaved and annealed in vacuum or in ozone to reduce or increase the doping from the initial value corresponding to Tc = 91 K. We show that p can be determined from the underlying Fermi surfaces and that in-situ annealing allows mapping of a wide doping regime, covering the superconducting dome and the non-superconducting phase on the overdoped side. Our results show a surprisingly smooth dependence of the inferred Fermi surface with doping. In the highly overdoped regime, the superconducting gap approaches the value of 2Δ0 = (4 ± 1)kBTc.
关键词： cuprate superconductors,Fermi surfaces,superconducting gap,doping,angle-resolved photoemission spectroscopy
更新于2025-09-04 15:30:14
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[Institution of Engineering and Technology 12th European Conference on Antennas and Propagation (EuCAP 2018) - London, UK (9-13 April 2018)] 12th European Conference on Antennas and Propagation (EuCAP 2018) - Wireless Detection of Moving Chipless Tags made of Metamaterial Resonators
摘要： An innovative reading procedure based on the Inverse Synthetic Aperture Radar technique aimed at improving the reliability of chipless RFID tags wireless detection is presented. More in detail, the considered scenario comprises a moving tagged item travelling along a known path. The detection scheme relies on the integration of multiple received signals and benefits from the information on the background echo, which is intrinsic to the procedure. This technique greatly enhances the detection probability in complex scenarios subject to a high level of clutter. An equivalent model for the detection procedure of chipless tags in a noisy environment is presented. Successful experimental tests of tag readings with low Signal to Noise Ratio (SNR) are illustrated.
关键词： Artificial Impedance Surface (AIS),Chipless RFID,Inverse Synthetic Aperture Radar (ISAR),Frequency Selective Surfaces (FSS)
更新于2025-09-04 15:30:14
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[Institution of Engineering and Technology 12th European Conference on Antennas and Propagation (EuCAP 2018) - London, UK (9-13 April 2018)] 12th European Conference on Antennas and Propagation (EuCAP 2018) - Circuit-model approach for polarizing surfaces based on stacked meander-line gratings
摘要： This manuscript reports the design of polarizers consisting of stacks of several meander-line gratings for axial-ratio enhancement. Analysis and design are carried out with analytical equivalent circuits that fully characterize periodic meander-line architectures. The advantage of using the analytical equivalent-circuit approach lies on its accuracy as well as in the better physical insight of the structure’s behavior provided by this approach. Extension to the case of oblique incidence is also carried out. Comparisons between results obtained by a commercial software and by the circuit model will evidence the good accuracy of the proposed approach.
关键词： meander-line gratings,Circuit model,periodic surfaces,polarizers
更新于2025-09-04 15:30:14
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ANALYSIS OF POWER FLOW BY POYNTING VECTORS FOR ELECTROMAGNETIC WAVE ABSORBERS USING FREQUENCY SELECTIVE SURFACES
摘要： The power ?ow for electromagnetic wave absorbers consisting of pattern conductor layers acting as frequency selective surfaces, absorption layers, and short circuit layers was investigated by Poynting vectors. A method was developed to evaluate the ?ow of electromagnetic wave power by an electromagnetic wave absorber upon irradiation with electromagnetic waves. The results indicate that the electromagnetic wave absorption phenomenon involves generation of real power, a real part of the time averaged Poynting vector, which moves horizontally along the pattern surface after the incident wave has irradiated the pattern conductor from the vertical direction, and the direction of power ?ow changes to enter the polymer layer from the pattern interval, causing an accumulation of power inside the polymer layer, followed by absorption, which is converted into heat due to the loss factor.
关键词： Electromagnetic wave absorbers,Absorption layers,Power flow,Frequency selective surfaces,Poynting vectors
更新于2025-09-04 15:30:14
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Detecting Ocean Glint on Exoplanets Using Multiphase Mapping
摘要： Rotational mapping and specular reflection (glint) are two proposed methods to directly detect liquid water on the surface of habitable exoplanets. However, false positives for both methods may prevent the unambiguous detection of exoplanet oceans. We use simulations of Earth as an exoplanet to introduce a combination of multiwavelength, multiphase, time-series direct-imaging observations and accompanying analyses that may improve the robustness of exoplanet ocean detection by spatially mapping the ocean glint signal. As the planet rotates, the glint spot appears to “blink” as Lambertian scattering continents interrupt the specular reflection from the ocean. This manifests itself as a strong source of periodic variability in crescent-phase disk-integrated reflected light curves. We invert these light curves to constrain the longitudinal slice maps and apparent albedo of multiple surfaces at both quadrature and crescent phase. At crescent phase, the retrieved apparent albedo of ocean-bearing longitudinal slices is increased by a factor of 5, compared to the albedo at quadrature phase, due to the contribution from glint. The land-bearing slices exhibit no significant change in apparent albedo with phase. The presence of forward-scattering clouds in our simulated observation increases the overall reflectivity toward crescent, but we find that clouds do not correlate with any specific surfaces, thereby allowing for the phase-dependent glint effect to be interpreted as distinct from cloud scattering. Retrieving the same longitudinal map at quadrature and crescent phases may be used to tie changes in the apparent albedo with phase back to specific geographic surfaces (or longstanding atmospheric features), although this requires ideal geometries. We estimate that crescent-phase time-dependent glint measurements are feasible for between 1 and 10 habitable zone exoplanets orbiting the nearest G, K, and M dwarfs using a space-based, high-contrast, direct-imaging telescope with a diameter between 6 and 15 m.
关键词： planets and satellites: oceans,astrobiology,planetary systems,planets and satellites: terrestrial planets,planets and satellites: surfaces
更新于2025-09-04 15:30:14
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Controlling shedding characteristics of condensate drops using electrowetting
摘要： We show here that ac electrowetting (ac-EW) with structured electrodes can be used to control the gravity-driven shedding of drops condensing onto ?at hydrophobic surfaces. Under ac-EW with straight interdigitated electrodes, the condensate drops shed with relatively small radii due to the ac-EW-induced reduction of contact angle hysteresis. The smaller shedding radius, coupled with the enhanced growth due to coalescence under EW, results in an increased shedding rate. We also show that the condensate droplet pattern under EW can be controlled, and the coalescence can be further enhanced, using interdigitated electrodes with zigzag edges. Such enhanced coalescence in conjunction with the electrically induced trapping effect due to the electrode geometry results in a larger shedding radius, but a lower shedding rate. However, the shedding characteristics can be further optimized by applying the electrical voltage intermittently. We ?nally provide an estimate of the condensate volume removed per unit time in order to highlight how it is enhanced using ac-EW-controlled dropwise condensation.
关键词： condensate drops,coalescence,shedding characteristics,hydrophobic surfaces,electrowetting
更新于2025-09-04 15:30:14
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Continuous-range tunable multilayer frequency-selective surfaces using origami and inkjet printing
摘要： The tremendous increase in the number of components in typical electrical and communication modules requires low-cost, flexible and multifunctional sensing, energy harvesting, and communication modules that can readily reconfigure, depending on changes in their environment. Current subtractive manufacturing-based reconfigurable systems offer limited flexibility (limited finite number of discrete reconfiguration states) and have high fabrication cost and time requirements. Thus, this paper introduces an approach to solve the problem by combining additive manufacturing and origami principles to realize tunable electrical components that can be reconfigured over continuous-state ranges from folded (compact) to unfolded (large surface) configurations. Special 'bridge-like' structures are introduced along the traces that increase their flexibility, thereby avoiding breakage during folding. These techniques allow creating truly flexible conductive traces that can maintain high conductivity even for large bending angles, further enhancing the states of reconfigurability. To demonstrate the idea, a Miura-Ori pattern is used to fabricate spatial filters—frequency-selective surfaces (FSSs) with dipole resonant elements placed along the fold lines. The electrical length of the dipole elements in these structures changes when the Miura-Ori is folded, which facilitates tunable frequency response for the proposed shape-reconfigurable FSS structure. Higher-order spatial filters are realized by creating multilayer Miura-FSS configurations, which further increase the overall bandwidth of the structure. Such multilayer Miura-FSS structures feature the unprecedented capability of on-the-fly reconfigurability to different specifications (multiple bands, broadband/narrowband bandwidth, wide angle of incidence rejection), requiring neither specialized substrates nor highly complex electronics, holding frames, or fabrication processes.
关键词： origami,tunable electromagnetic structures,deployable structures,frequency-selective surfaces,reconfigurable spatial filters
更新于2025-09-04 15:30:14