共查询到20条相似文献,搜索用时 15 毫秒
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Utilizing a microwave setup, we experimentally verify our recently developed theory of energy squeezing and tunneling [Phys. Rev. Lett. 97, 157403 (2006)10.1103/PhysRevLett.97.157403] through an ultranarrow waveguide channel that mimics zero-permittivity properties. Exploiting the infinite phase velocity supported by a waveguide transition section at cutoff, we test our theory of tunneling in this zero-permittivity region without use of resonant inclusions. This "supercoupling" is shown to have unique anomalous properties: an almost uniform phase along the narrow channel and weak dependence over its geometry. 相似文献
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Aaron F. Matthews 《Optics Communications》2009,282(9):1789-1271
I studied experimentally beam self-collimation and splitting in two-dimensional microwave photonic crystals. Using a microwave photonic crystal fabricated from alumina rods, I present an experimental proof of principle for an earlier theoretical proposal [A.F. Matthews, S.K. Morrison, Yu.S. Kivshar, Opt. Commun. 279 (2007) 313] of a photonic crystal beam splitter based on the self-collimation effect. 相似文献
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Alessio Monti Filiberto Bilotti Alessandro Toscano Lucio Vegni 《Optics Communications》2012,285(16):3412-3418
Metamaterials (MTMs) exhibiting a near-zero real part of the permittivity function in a given frequency range have been demonstrated to be useful in several application fields, including field localization and focusing. So far, however, the realistic implementations of such materials working at optical frequencies and exhibiting a reasonable level of losses are rare. In this work, we propose a possible implementation of optical epsilon-near-zero (ENZ) MTMs based on the employment of an array of core-shell nano-spheres embedded in a dielectric medium. The core of the nano-spheres and the host medium are both made of silica, while the shell is formed by a plasmonic material (i.e. silver). Using classical homogenization formulas, we show that it is possible to design the array in such a way to exhibit near-zero values of the effective real permittivity with relatively low losses at optical frequencies. These results are supported and confirmed by proper full-wave simulations and design examples. 相似文献
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We present the design, simulation and fabrication of a dual-band metamaterial absorber. The designed structure consists of periodic composite metallic holes array and dielectric layer. The availability of absorption enhancement is verified by our measured results. Cavity and electrical resonances lead to these two absorption peaks at and . Effects of structural parameters on absorption and resonant wavelengths have been experimentally surveyed. The average absorption can be increased by optimizing the structural parameters of the designed metamaterial absorber. 相似文献
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In this Letter, we demonstrate theoretically that electromagnetic waves can be "squeezed" and tunneled through very narrow channels filled with epsilon-near-zero (ENZ) materials. We show that the incoming planar wave front is replicated at the output interface, independently of the specific geometry of the channel. A closed analytical formula is derived for the scattering parameters of a particular class of geometries. It is discussed that in some cases the isotropy of the ENZ material may not be an issue. A metamaterial realization of an anisotropic ENZ material is suggested and numerically studied. 相似文献
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We design and analyze a novel multiband left-handed metamaterial based on a fishnet-like structure at terahertz (THz) frequencies.The metamaterial exhibits simultaneous negative refractions around the frequencies of 0.48,1.05,and 1.19 THz for the electromagnetic (EM) wave normal incidence,and around the frequencies of 0.20,0.79,and 1.13 THz for parallel incidence.The simulated results verify the left-handed properties.A particularly important observation is the capability of the proposed metamaterial with a single geometrical structure to display multifrequency operations in a unit cell.The compact metamaterial is a major step toward the miniaturization of THz materials and devices suitable for multifrequencies. 相似文献
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We construct a barrier with anisotropic metamaterial to explore the complete tunneling conditions of light through it. And then we take a semiconductor metamaterial as an example to discuss the dispersive properties of the barrier and show a possible application as a flat-top filter. 相似文献
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We introduce a metamaterial design composed of square plasmonic loops loaded by Kerr nonlinearities that combines enhanced nonlinear response with strong artificial magnetism, ensuring a negative refractive index with bistable and self-tunable response. We verify with full-wave simulations that positive-to-negative switching of refractive index may be obtained with moderate loss. The design of a finite-size metamaterial prism is also presented, supporting at the same frequency, and for the same light intensity, positive or inverted Snell refraction as a function of its previous excitation history. 相似文献
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We report the theoretical design and experimental demonstration of a three-dimensional(3D)omnidirectional and broadband metamaterial-based concentrator for airborne sound.The proposed mechanism uses a homogeneous anisotropic acoustic metamaterial with an ellipsoidal equifrequency contour to efficiently redirect the acoustic energy impinging on its outer surface into the central region,regardless of the incident direction.A design of the metamaterial unit cell is proposed as a practical implementation of our strategy,which is simply realized by perforating a solid spherical shell with a linearly shrinking cross section in the radial direction.We analytically and numerically prove that the non-resonant anisotropic effective acoustic parameters required for building the concentrator are produced with such a design.Good agreement is observed between the theoretical predictions and experimental measurements.An effective concentration of the incident acoustic energy is observed within a broadband that ranges 1000-1600 Hz.The experimental realization of this 3D acoustic concentrator with a simple design,low energy loss,replaceable constituent material,and omnidirectional and broadband functionality offers new possibilities for acoustic manipulations and may have important applications in a plethora of scenarios ranging from energy harvesting to noise mitigation. 相似文献
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Utilizing terahertz time domain spectroscopy, we have characterized the electromagnetic response of a planar array of split ring resonators (SRRs) fabricated upon a high resistivity GaAs substrate. The measured frequency dependent magnetic and electric resonances are in excellent agreement with theory and simulation. For two polarizations, the SRRs yield a negative electric response (epsilon < 0). We demonstrate, for the first time, dynamical control of the electrical response of the SRRs through photoexcitation of free carriers in the substrate. An excited carrier density of approximately 4 x 10(16) cm(-3) is sufficient to short the gap of the SRRs, thereby turning off the electric resonance, demonstrating the potential of such structures as terahertz switches. Because of the universality of metamaterial response over many decades of frequency, these results have implications for other regions of the electromagnetic spectrum. 相似文献
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Equivalent electromagnetic parameters for microwave metamaterial absorber using a new symmetry model
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《中国物理 B》2019,(5)
Transmission line theory uses the complex nature of permeability and permittivity of a conventional magnetic absorber to evaluate its absorption properties and mechanism. However, because there is no method to obtain the electromagnetic parameters of a metamaterial-absorber integrated layer(composed of a medium layer and a periodic metal array), this theory is seldom used to study the absorption properties of the metamaterial absorber. We propose a symmetry model to achieve an equivalent complex permittivity and permeability model for the integrated layer, which can be combined with the transmission line theory to calculate metamaterial absorption properties. The calculation results derived from both the transmission line theory and the high-frequency structure simulator are in good agreement. This method will be beneficial in practical investigations of the absorption mechanism of a metamaterial absorber. 相似文献
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Summary Intrinsic absorptive bistability and hysteresis cycles in a steady-state regime are obtained at microwave frequencies. A theory
is presented which takes into account the Gaussian shape of the fundamental mode excited into the resonator and is compared
with the experimental results.
Riassunto Sono state osservate la bistabilità assorbitiva intrinseca e l’isteresi nel caso stazionario, operando alle frequenze delle microonde. Si presenta una teoria che tiene conto della forma gaussiana del modo fondamentale eccitato nel risuonatore e che è confrontata con i risultati sperimentali.
Резюме На микроволновых пастотах наблюдаются внутренняя абсорбционная бистабильность и гистерезисные циклы в стационарном режиме. Предлагается теория, которая учитывает гауссову форму основной моды, возбужденноц в резонаторе, и которая сравнивается с экспериментальными резулстатами.相似文献
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Instrumental requirements for pulsed NMR studies of hyperfine splittings in rate-earth metals and compounds are considered,
with particular attention to factors affecting the design of the specimen cavity. A spin-echo spectrometer for hyperfine studies
in the 2 to 8 GHz frequency range is described. 相似文献
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G. T. Adamashvili N. G. Gapishvili R. R. Koplatadze N. M. Zviadadze 《Radiophysics and Quantum Electronics》1992,35(5):310-313
The process of nonlinear-wave formation in a waveguide at microwave frequencies is studied theoretically. It is shown that a nonlinear wave in the form of a pulsating soliton is formed under conditions of uniform spectrum-line broadening. The possibility of experimental observation of the phenomenon is considered.Tbilisi State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 35, No. 5, pp. 475–480, May, 1992. 相似文献
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Tunable electromagnetically induced transparency at terahertz frequencies in coupled graphene metamaterial
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《中国物理 B》2015,(11)
A graphene-based metamaterial with tunable electromagnetically induced transparency(EIT)-like transmission is numerically studied in this paper. The proposed structure consists of a graphene layer composed of coupled cut-wire pairs printed on a substrate. The simulation confirms that an EIT-like transparency window can be observed due to indirect coupling in a terahertz frequency range. More importantly, the peak frequency of the transmission window can be dynamically controlled over a broad frequency range by varying the Fermi energy levels of the graphene layer through controlling the electrostatic gating. The proposed metamaterial structure offers an additional opportunity to design novel applications such as switches or modulators. 相似文献
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L.A.A. Read 《Optics Communications》1975,15(3):429-431
3 cm microwave are being used to investigate the beam shifts which occur for external reflection from a planar dielectric interface. The adaptation of a planar wave theory to the microwave case has proved successful in predicting the magnitudes and direction of such shifts. 相似文献