We present experimental scattering data at microwave frequencies on a structured metamaterial that exhibits a frequency band where the effective index of refraction (n) is negative. The material consists of a two-dimensional array of repeated unit cells of copper strips and split ring resonators on interlocking strips of standard circuit board material. By measuring the scattering angle of the transmitted beam through a prism fabricated from this material, we determine the effective n, appropriate to Snell's law. These experiments directly confirm the predictions of Maxwell's equations that n is given by the negative square root of epsilon.mu for the frequencies where both the permittivity (epsilon) and the permeability (mu) are negative. Configurations of geometrical optical designs are now possible that could not be realized by positive index materials.

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Experimental Verification of a Negative Index of Refraction

Using the freedom of design that metamaterials provide, we show how electromagnetic fields can be redirected at will and propose a design strategy. The conserved fields-electric displacement field D, magnetic induction field B, and Poynting vector B-are all displaced in a consistent manner. A simple illustration is given of the cloaking of a proscribed volume of space to exclude completely all electromagnetic fields. Our work has relevance to exotic lens design and to the cloaking of objects from electromagnetic fields.

/pdf/controlling-electromagnetic-fields-3ryxkryf1t.pdf

Controlling Electromagnetic Fields

We present the design for an absorbing metamaterial (MM) with near unity absorbance A(omega). Our structure consists of two MM resonators that couple separately to electric and magnetic fields so as to absorb all incident radiation within a single unit cell layer. We fabricate, characterize, and analyze a MM absorber with a slightly lower predicted A(omega) of 96%. Unlike conventional absorbers, our MM consists solely of metallic elements. The substrate can therefore be optimized for other parameters of interest. We experimentally demonstrate a peak A(omega) greater than 88% at 11.5 GHz.

Perfect metamaterial absorber.

Recently, artificially constructed metamaterials have become of considerable interest, because these materials can exhibit electromagnetic characteristics unlike those of any conventional materials. Artificial magnetism and negative refractive index are two specific types of behavior that have been demonstrated over the past few years, illustrating the new physics and new applications possible when we expand our view as to what constitutes a material. In this review, we describe recent advances in metamaterials research and discuss the potential that these materials may hold for realizing new and seemingly exotic electromagnetic phenomena.

/pdf/metamaterials-and-negative-refractive-index-5ehczes1hu.pdf

Metamaterials and negative refractive index.

Artificially engineered metamaterials are now demonstrating unprecedented electromagnetic properties that cannot be obtained with naturally occurring materials. In particular, they provide a route to creating materials that possess a negative refractive index and offer exciting new prospects for manipulating light. This review describes the recent progress made in creating nanostructured metamaterials with a negative index at optical wavelengths, and discusses some of the devices that could result from these new materials.

/pdf/optical-negative-index-metamaterials-2q5qafgl3m.pdf

Optical negative-index metamaterials

We demonstrate a composite medium, based on a periodic array of interspaced conducting nonmagnetic split ring resonators and continuous wires, that exhibits a frequency region in the microwave regime with

/pdf/composite-medium-with-simultaneously-negative-permeability-16lgrquuw2.pdf

Composite Medium with Simultaneously Negative Permeability and Permittivity

We present experimental data, numerical simulations, and analytical transfer-matrix calculations for a two-dimensionally isotropic, left-handed metamaterial (LHM) at X-band microwave frequencies. A LHM is one that has a frequency band with simultaneously negative eeff(ω) and μeff(ω), thereby having real values of index of refraction and wave vectors, and exhibiting extended wave propagation over that band. Our physical demonstration of a two-dimensional isotropic LHM will now permit experiments to verify some of the explicit predictions of reversed electromagnetic-wave properties including negative index of refraction as analyzed by Veselago [Usp. Fiz. Nauk 92, 517 (1964), Sov. Phys. Usp. 10, 509 (1968)].

/pdf/microwave-transmission-through-a-two-dimensional-isotropic-3pb2y87qwo.pdf

Microwave transmission through a two-dimensional, isotropic, left-handed metamaterial

We present numerical simulations and microwave measurements on a loop-wire structure that acts as an effective medium exhibiting a well-defined bulk plasma frequency in the microwave regime, with an effective negative dielectric function below this plasma frequency. The dependence of this plasmonic response on the self-inductance of the constituent wire elements is made explicit. A finite structure, approximately spherical, composed of this inductive medium is studied, and reveals subwavelength surface plasmon resonances below the bulk plasma frequency.

/pdf/loop-wire-medium-for-investigating-plasmons-at-microwave-5f9l9uq0mi.pdf

Loop-wire medium for investigating plasmons at microwave frequencies

Porosity (or void ratio) is one of the most important index measures of granular materials. It alone is not, however, enough for a reasonably complete description of the basic properties of materials of this kind. The fabric ellipsoid appears to be a good second index measure. It is closely related to the probability density function e(alpha, beta) which defines the angular distribution of the contact normals. Based on experimental evidence the following is concluded. The fabric ellipsoid is closely related to the stress ellipsoid and characterizes a second-order tensor with a clear physical meaning; the principal axes of the fabric ellipsoid seem to tend toward those of the stress ellipsoid and this appears to hold whether the principal stress axes rotate gradually or discontinuously during a course of deformation; and there seems to exist a quantitative relation between the fabric ellipsoid and the overall applied stresses, especially in the post-failure states. It appears that the function e(alpha, beta) continuously changes in a manner so as to increase the ability of the material to withstand the increased applied stresses. The changes of the fabric, characterized by the changes of e(alpha, beta) result in the hardening (or softening) of the granular materials in a given deformation course. (Author/TRRL)

Some experimentally based fundamental results on the mechanical behaviour of granular materials

A system for identifying a driver comprises an image capturing device, a processor, and a memory The image is captured during vehicle operation and of an expected driver location The processor is configured to detect a face of a driver in the image, determine a set of face data from the image, and identify the driver based at least in part on the set of face data The memory is coupled to the processor and configured to provide the processor with instructions

Syrus C. Nemat-Nasser

Papers

Composite Medium with Simultaneously Negative Permeability and Permittivity

Microwave transmission through a two-dimensional, isotropic, left-handed metamaterial

Loop-wire medium for investigating plasmons at microwave frequencies

Some experimentally based fundamental results on the mechanical behaviour of granular materials

Driver identification based on face data