Metamaterials最新文献

Abstract

The characteristic impedance of magnetoinductive waveguides is complex and frequency-dependent, whereas the input impedance of standard RF and microwave devices is real and constant. Transducers capable of coupling magnetoinductive waveguides to other devices are, therefore, required for high-performance magnetoinductive systems. The author designed and experimentally realised a resonant coupling transducer capable of minimising reflections from magnetoinductive waveguides over the whole pass band.

For a magnetoinductive cable with the resonant frequency of 95 MHz and the pass band between 73 and 174 MHz, the experimental value of |S₁₁ | was as low as −25 dB at the resonant frequency and about −20 dB over more than 90% of the pass band, the most broadband performance achieved up to date. Yet, the transducer has simple design and comprises only three resonant circuits, which makes it a promising candidate for wide-band applications.

Electromagnetic smart screen (ESS) containing conductive patch array loaded with pin diodes was investigated experimentally and numerically. Reflectivity of smart screen was measured with free space method and calculated through finite element simulation. The reflectivity of ESS with thickness about 2.3 mm can be as low as −40 dB and the absorption peak can be tuned from 3 GHz to 4 GHz. The relative absorption bandwidth (less than −7.5 dB) can be as large as 40% which is much wider than non-tunable metamaterials.

We present a comprehensive analysis of natural modes of a planar metamaterial layer (metalayer) formed by arrayed pairs of metallic dogbone-shaped conductors separated by a thin dielectric layer. The in-plane modes are classified based on the symmetric and anti-symmetric current distributions in the pairs. Of particular interest are the anti-symmetric modes, since the anti-symmetric current is associated with the magnetic resonance in metamaterial particles made of tightly coupled pairs. It is shown that the modal spectrum includes both TE and TM bound (proper real) and leaky (proper complex and improper complex) modes. An interesting observation is that a peculiar dominant TM improper leaky wave with a low attenuation constant, for the anti-symmetric current distribution, occurs at low frequencies, with a potential application in periodic leaky-wave antennas.

Temporal fluctuations of the speckle pattern formed upon backscattering of a laser beam from an interface between gold and nonlinear polymer film have been observed as a function of optical power. The instability can be explained by coupling of laser light to surface plasmons and other guided modes, which experience multiple scattering while propagating in the film along the interface. The speckle pattern produced in this process is extremely sensitive to fluctuations of the scattering potential near the interface.

We investigate the scattering formalism of the Green's theorem including a discontinuity in the magnetic permeability μ (isotropic and homogeneous). For this purpose we make use of the continuity or saltus conditions for the EM field across the interface between media having different ɛ and μ. Numerical analysis has been made for linearly polarized light and randomly rough media with negative μ on the phenomenon of backscattering enhancement. We obtain enhanced backscattering peaks for both polarizations (s and p) in the case of rough surfaces with large correlation length. On the other hand, in the case of subwavelength roughness, enhanced backscattering is also observed, but mediated by s-polarized surface-plasmon polaritons (negative μ) similar to that mediated by p-polarized surface-plasmon polaritons for conventional metallic media (negative ɛ).

We propose wedge-shaped composite metamaterials consisting of alternate metal and dielectric layers capable of light control. We simulated the energy-stream distributions of the silver/alumina composites with different pairs of the alternate layers and different ways of arrangement. The simulation results show that the composite structure can control the directions of light and the transmitted light can carry sub-wavelength information. Such a controller has potential applications in sub-wavelength focusing and imaging, optical communication and tailoring.

We spectroscopically investigate the scaling properties of a metamaterial consisting of a square array of gold cylindrical dots. The electromagnetic response of the gold-dot array is found to scale in relation to the ratio of the incident wavelength over the array spacing, in agreement with general predictions of metamaterial theory. The appropriateness of an effective medium description of the array is analyzed in terms of the resonant polarizability of the array components, and the onset of van der Hulst backscattering at higher frequencies.

Magneto-inductive (MI) waveguides are periodic structures that operate by magnetic coupling between a set of lumped-element L-C resonators. The effect of waveguide bending on the propagation of MI waves is investigated, and it is shown that discontinuities in axis curvature will typically generate reflections. Changes in the equivalent circuit parameters of two types of MI waveguides (formed from discrete elements and continuous cable, respectively) at abrupt bends are identified, and simple formulae are developed for the reflection and transmission coefficients in each case. It is shown that thin-film MI cable can outperform MI waveguides formed using separate elements, due to the inherent stability of the mutual inductance, and can tolerate extremely tight bends. The theory is confirmed using experiments carried out using thin-film cable operating at ca. 100 MHz frequency.

We study theoretically the negative refraction of a surface plasmon polariton. The system we consider consists of a vacuum that is in a contact with two metals that each fill a quarter space with a periodic boundary between them. The interface of each of the metals with the vacuum supports a surface plasmon polariton. When a surface plasmon polariton passes through the periodic boundary between the metals it transforms partly into the Bragg beams of the refracted and reflected surface plasmon polaritons and partly into volume waves in the vacuum. A suitable choice of the period can ensure that the only propagating Bragg beams of the refracted surface plasmon polariton are the specular beam and the (−1)-order beam, which is negatively refracted. With a suitable choice for the form of the profile function and its amplitude the specular beam can be made to vanish.