Introduction General historical perspective The concept of metamaterials Modeling the material response Phase velocity and group velocity Metamaterials and homogenization procedure Metamaterials and Homogenization of Composites The homogenization hypothesis Limitations and consistency conditions Forward problem Inverse problems: retrieval and constitutive parameters Homogenization from averaging the internal fields Generalization to anisotropic and bianisotropic media Designing Metamaterials with Negative Material Parameters Negative dielectric materials Metamaterials with negative magnetic permeability Metamaterials with negative refractive index Chiral metamaterials Bianisotropic metamaterials Active and nonlinear metamaterials Negative Refraction and Photonic Bandgap Materials Photonic crystals and bandgap materials Band diagrams and iso-frequency contours Negative refraction and flat lenses with photonic crystals Negative refraction versus collimation or streaming Media with e < 0 and < 0: Theory and Properties Origins of negative refraction Choice of the wave-vector and its consequences Anisotropic and chiral media Energy and Momentum in Negative Refractive Index Materials Causality and energy density in frequency dispersive media Electromagnetic energy in left-handed media Momentum density, momentum flow, and transfer in media with negative material parameters Limit of plane waves and small losses Traversal of pulses in materials with negative material parameters Plasmonics of Media with Negative Material Parameters Surface electromagnetic modes in negative refractive materials Waveguides made of negative index materials Negative refraction of surface plasmons Plasmonic properties of structured metallic surfaces Surface waves at the interfaces of nonlinear media Veselago's Lens Is a Perfect Lens Near-field information and diffraction limit Mathematical demonstration of the perfect lens Limitations due to real materials and imperfect NRMs Issues with numerical simulations and time evolution Negative stream of energy with a perfect lens configuration Effects of spatial dispersion Designing Super Lenses Overcoming the limitations of real materials Generalized perfect lens theorem The perfect lens in other geometries Brief Report on Electromagnetic Invisibility Concept of electromagnetic invisibility Excluding electromagnetic fields Cloaking with localized resonances Appendix A: The Fresnel Coefficients for Reflection and Refraction Appendix B: The Dispersion and Fresnel Coefficients for a Bianisotropic Medium Appendix C: The Reflection and Refraction of Light across a Material Slab References Index

Physics and Applications of Negative Refractive Index Materials

Metamaterials have been deployed for a wide range of fields including invisible cloak, superlens, electromagnetic wave absorption and magnetic resonance imaging, owing to their peculiar electromagnetic properties. However, few investigations on metamaterials were focused on wireless power transfer (WPT). WPT is the transmission of electrical energy from a power source to an electrical load without conductors like wires or cables. Metamaterials can enhance the transfer efficiency and enlarge the transfer distance due to their ability of focusing magnetic flux, which opens up a novel approach to promoting the development and application of WPT. This review paper aims to provide an overview of the fabrications, exotic properties, and their applications especially in the WPT field. Meanwhile, the perspective and future challenges of metamaterials and WPT are proposed.

An overview of metamaterials and their achievements in wireless power transfer

We investigate the effects of disorder on metamaterial samples composed of split ring resonators with randomly introduced variation in their geometrical dimensions. We demonstrate that disorder broadens the negative permeability band and introduces effective losses into the system. Transmission measurements on samples with varying degrees of disorder are found to be in excellent agreement with predictions based on standard homogenization theories.

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Characterizing the effects of disorder in metamaterial structures

The properties of planar, single-layer metamaterials, or metafilms, are studied by varying the structural components of the split-ring resonators used to comprise the overall medium. Measurements and simulations reveal how minor design variations in split-ring resonator structures can result in significant changes in the macroscopic properties of the metafilm. A transmission-line/circuit model is also used to clarify some of the behavior and design limitations of the metafilms. Though our results are illustrated in the terahertz frequency range, the work has broader implications, particularly with respect to filtering, modulation, and switching devices.

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ResearchArticle Effects of Microstructure Variations on Macroscopic Terahertz Metafilm Properties

Electromagnetic metamaterials are artificial materials composed of subwavelength structures to provide unusual effective macroscopic behavior not found in nature. These materials are characterized by constitutive relations which contain a maximum of 36 complex constitutive parameters. With different combinations of positive and negative parameters in the constitutive tensors, striking phenomena and novel applications were discovered. In this Feature Article, I briefly review the experimental progress in the metamaterial, focusing on their constitutive parameters and material performance, e.g. the bandwidth, the loss, and the electrical size with respect to the operating wavelength, etc. The two fabrication approaches: the structure approach that is widely used to construct periodic metamaterial structures, and the chemical approach that is very promising in constructing nano-scaled metamaterial with randomized patterns, are discussed. The practical potential of this field and the possible challenging future work are pointed out in the conclusion.

Metamaterials: constitutive parameters, performance, and chemical methods for realization

Artificial metamaterials made to date are all periodic in structure. Here we show that by randomizing contour patterns deposited lithographically on circuit board materials, a metamaterial characterized by a constitutive relation with negative constitutive parameters is produced in solid-state form. We clearly demonstrate the phenomenon of negative refraction to show that it is not produced by periodicity. This underlines the importance of using constitutive relations for media characterization in electromagnetic theory and suggests that metamaterials could be realized with composite materials or fabricated with various techniques by using versatile hosting materials.

Q. Jiang

Papers

Metamaterial with randomized patterns for negative refraction of electromagnetic waves