Metamaterials最新文献

We theoretically demonstrate that there is an angle of incidence and frequency at which a p-polarized electromagnetic wave can be perfectly absorbed without reflection by a half-space of lossy indefinite anisotropic medium. We show that this perfect absorption occurs when the Zenneck wave guided by a surface of indefinite medium transits to a homogenous plane wave. This angular and frequency selectivity of the absorption can find a use for photovoltaic systems.

We present experimental results of the transmission coefficient of a metamaterial slab and the effect of the metamaterial on the radiation pattern of an antenna placed near the slab in the frequency range close to the plasma frequency of the slab. The metamaterial focuses the radiation from the patch antenna within a narrow cone close to the slab's normal. We give a new simple explanation of the focusing effect based on the index of refraction of the metamaterial being less than one and the attenuation of electromagnetic waves within the metamaterial slab.

This paper shows, using both a ray optics approach and in the framework of the generalized Lorenz–Mie theory (GLMT), what happens to the optical forces exerted on a lossless spherical particle with an arbitrary (positive or negative) relative refractive index, allowing the external medium also to be metamaterial. It is shown that the anti-parallelism between the linear momentum p of each photon and the Poynting vector S associated with the propagating wave, observed in negative refractive index media, leads to shifts in the direction of the optical force of a single ray and, consequently, to the total optical force exerted by an arbitrary-shaped laser beam. This extends the possible realizable traps and reveals how arbitrary-shaped laser beams can be used to trap particles with arbitrary refractive indices.

We develop general results for nonlinear metamaterials based on simple circuit models that reflect the elementary nonlinear behavior of the medium. In particular, we consider both active and passive nonlinearities which can lead to gain, harmonic generation and a variety of nonlinear waves depending on circuit parameters and signal amplitude. We show that the medium can exhibit a phase transition to a synchronized state and derive conditions for the transformation based on a widely used multiple time scale approach that leads to the well-known Complex Ginzburg–Landau equation. Further, we examine the variety of nonlinear waves that can exist in such systems, and we present numerical results for both active and passive metamaterial cases.

In this Letter to the Editor, I review briefly a historical background of the research on backward waves carried out in the XX century. I also provide a brief introduction to the isofrequency method of analysis for metamaterials and discuss a few unusual examples of wave phenomena at the interfaces.

Analytical, simulation and experiment based technique has been reported in this paper to determine the plasma frequency of artificial media formed by arrays of parallel conducting wires called wire media. A generalized analytical approach based on quasi-static analysis has been done and compared with previously reported results to determine the plasma frequency of wire media. An eigenmode solver based simulation method has been used for plasma frequency extraction of infinite wire array using a commercial finite element method (FEM) based electromagnetic solver. The limitations of scattering-parameter based technique has been discussed and a new loss-factor method has been proposed. On the basis of simulated data, wire array has been fabricated and experiments has been carried out at X-band (8.2–12.4 GHz). Loss-factor method has been validated using the experimental data. Finally, the results of different techniques are compared to establish the efficacy of the loss-factor method supported by experimental results.

Microwave properties of the 3D-nanocomposite media based on opal matrix with the metallic cobalt nanoparticles embedded have been investigated. Magnetic antiresonance is observed at frequencies of millimeter waveband along with the ferromagnetic resonance. The experimental magnetic field dependence of transmission coefficient is compared to the theoretically calculated one. The magnetic field dependence of the refraction coefficient is restored and it is shown that the refraction index is close to zero in weak magnetic fields.

Multi-element inductive coil systems are used to measure locally resolved conductivity profile. Usually such sensors rely on the separate interrogation of each coil. In addition, the coils must generally be magnetically decoupled for accurate signal processing. Here we demonstrate a metamaterial conductivity sensor that uses broadband interrogation of a line of coupled resonators. No decoupling is needed, which allows a transmission measurement to be carried out. The resonant elements of the metamaterial are coupled with each other and their neighbourhood which affects their quality factor. We derive analytically an algorithm to extract the local perturbation in each element from the modal measurement. We investigate numerically the performance of the sensor and derive an optimal configuration in terms of nearest neighbour coupling and the initial non-uniformity. Finally we implement a four-element magneto inductive conductivity sensor and show that a conductive perturbation along the line can be accurately reconstructed. Generalisation to higher number of elements is also discussed.

Controllable phase shifting of magneto-inductive waves is demonstrated by ferrite loading of magneto-inductive waveguides, which consist of simple linear arrangements of magnetically coupled L–C resonators. It is shown that ferrite loading reduces the resonant frequency in isolated resonators and lowers the pass-band in waveguides. Simple theory is presented to estimate the dependence of the phase shift on the perturbed waveguide parameters and wavelength, and confirmation is provided using experiments carried out using thin film L–C resonators and thin-film magneto-inductive cable operating near 100 MHz frequency. Phase shifts are converted into amplitude changes by interference of magneto-inductive waves in Mach–Zehnder interferometer structures analogous to those used in guided wave optics, using conventional RF components for beam splitting and recombination. Modulation and space switching are both demonstrated, and in each case the variation of output power with phase shift follows the conventional sinusoidal characteristic.

In this paper we present a macroscopic model of a metasurface—optically dense grids of resonant scatterers located on a refracting interface. Similar models were previously built for the case when the scatterers are non-resonant electric dipoles and for the case when there is no substrate. In the present case scatterers are resonant, can have magnetic response, and for substrates with large refraction index acquire also substrate-induced bianisotropic properties. Representing the homogenized response of a metasurface to incident electric and magnetic fields through surface susceptibilities we derive the reflection and transmission formulas for semi-infinite and finite-thickness substrates. We develop a robust algorithm of the retrieval of the characteristic surface parameters from the reflection and transmission coefficients measured or exactly calculated for three different incidence angles. With numerical examples we show that the retrieved susceptibilities of metasurfaces are independent on the incidence angle and can be really called characteristic parameters.