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

A recently published theory has suggested that a cloak of invisibility is in principle possible, at least over a narrow frequency band. We describe here the first practical realization of such a cloak; in our demonstration, a copper cylinder was "hidden" inside a cloak constructed according to the previous theoretical prescription. The cloak was constructed with the use of artificially structured metamaterials, designed for operation over a band of microwave frequencies. The cloak decreased scattering from the hidden object while at the same time reducing its shadow, so that the cloak and object combined began to resemble empty space.

/pdf/metamaterial-electromagnetic-cloak-at-microwave-frequencies-1qj4zdgl8e.pdf

Metamaterial Electromagnetic Cloak at Microwave Frequencies

Conventional optical components rely on gradual phase shifts accumulated during light propagation to shape light beams. New degrees of freedom are attained by introducing abrupt phase changes over the scale of the wavelength. A two-dimensional array of optical resonators with spatially varying phase response and subwavelength separation can imprint such phase discontinuities on propagating light as it traverses the interface between two media. Anomalous reflection and refraction phenomena are observed in this regime in optically thin arrays of metallic antennas on silicon with a linear phase variation along the interface, which are in excellent agreement with generalized laws derived from Fermat’s principle. Phase discontinuities provide great flexibility in the design of light beams, as illustrated by the generation of optical vortices through use of planar designer metallic interfaces.

http://www.zenogaburro.it/papers/LightPropagation.pdf

Light Propagation with Phase Discontinuities: Generalized Laws of Reflection and Refraction

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.

Metamaterials are artificially fabricated materials that allow for the control of light and acoustic waves in a manner that is not possible in nature. This Review covers the recent developments in the study of so-called metasurfaces, which offer the possibility of controlling light with ultrathin, planar optical components. Conventional optical components such as lenses, waveplates and holograms rely on light propagation over distances much larger than the wavelength to shape wavefronts. In this way substantial changes of the amplitude, phase or polarization of light waves are gradually accumulated along the optical path. This Review focuses on recent developments on flat, ultrathin optical components dubbed 'metasurfaces' that produce abrupt changes over the scale of the free-space wavelength in the phase, amplitude and/or polarization of a light beam. Metasurfaces are generally created by assembling arrays of miniature, anisotropic light scatterers (that is, resonators such as optical antennas). The spacing between antennas and their dimensions are much smaller than the wavelength. As a result the metasurfaces, on account of Huygens principle, are able to mould optical wavefronts into arbitrary shapes with subwavelength resolution by introducing spatial variations in the optical response of the light scatterers. Such gradient metasurfaces go beyond the well-established technology of frequency selective surfaces made of periodic structures and are extending to new spectral regions the functionalities of conventional microwave and millimetre-wave transmit-arrays and reflect-arrays. Metasurfaces can also be created by using ultrathin films of materials with large optical losses. By using the controllable abrupt phase shifts associated with reflection or transmission of light waves at the interface between lossy materials, such metasurfaces operate like optically thin cavities that strongly modify the light spectrum. Technology opportunities in various spectral regions and their potential advantages in replacing existing optical components are discussed.

Flat Optics With Designer Metasurfaces

thegiveninitialconditions(e.g.,startofillumination,etc.).The better theQ factor the closer the system may come toan ideal behavior, in the present caseVto superlensing.As one can see, superlensing appears in a linearelectromagnetic problem and does not need any Btwopaths[ and Bsynchronization[ for signal amplification.Nonlinearity may limit the resolution, in addition to otherfactors mentioned above. Since this is a linear problem,thereisnodeteriorationofSNR;bothBsignal[andBnoise[at the source would be restored in the image, i.e., aBblinking[source wouldproduceaBblinking[replica withthe use of an ideal superlens.I hope this answers the questions raised in [1] andclarifies the behavior of theBsuperlenses.[ h

Comments on BConsensus and Cooperation in Networked Multi-Agent Systems(

The papers in this special cluster collectively represent a snapshot of many of the research directions currently underway in the metamaterials community and are illustrative of the potential that can be unlocked by simply taking a broader view of what constitutes a "material."

Guest Editorial: Special Cluster on Metamaterials

In this paper, we present an analytical approach to calculate the far-field radiation pattern of conformal arrays, consisting of arbitrarily oriented antennas. In particular, we focus on spherical arrays of microstrip patch antennas. This approach reduces the computational time and resource requirements as compared to a full-wave conventional EM solver. It should be mentioned that this method is not limited to spherical arrays only and can be applied to any other configurations as well. Also, this analytical approach makes it possible to run optimization processes faster, and to meet various design objectives.

Analytical far-field calculation of arbitrarily oriented antenna arrays

A novel design and fabrication technique for complex microwave waveguide components has been developed. Open cellular structures, characterized by effective medium theory, are used as a replacement for conventional highly-conductive materials. The fabrication is enabled by advancements in additive manufacturing and metal deposition techniques. Components that can be fabricated by vat polymerization followed by electroless deposition of copper, are specifically addressed. The open cellular structure allows fluid penetration to the internal surfaces, allowing for more uniform deposition of metal throughout the part. This makes it feasible to fabricate electrically conductive, complex, multi-function, monolithic parts, something which has proven to be difficult with conventional fabrication techniques, even with recent developments in additive manufacturing. Effective conductivity values are reported for cellular structures that can be practically fabricated. The characterization as a meta surface, not only allows for the easy adoption into existing design work flows, but also enables the exploration of new designs, since the properties of the material can be easily manipulated by changing the fine details of the cellular mesh. Because of the extra degrees of freedom offered in the new process, it is possible to improve performance of secondary properties such as: size, weight, and thermal management characteristics.

Additive-Manufactured, Highly-Conductive Metasurfaces, With Application Enabling Secondary Properties, for Microwave Waveguide Components

We present the first experimental realization of a terahertz (THz) waveguide that exhibits a negative effective index of refraction. To demonstrate this, we designed fabricated and characterized a linear array of three-dimensional structures that consist of split ring resonators and posts. THz radiation is launched and guided in the form of surface plasmon polaritons (SPPs) along the 3D metallic structures. Using THz time-domain spectroscopy, we measure the temporal evolution of the propagating THz SPP, which yields the evidence of a negative refractive index.

David Schurig

Papers

Comments on BConsensus and Cooperation in Networked Multi-Agent Systems(

Guest Editorial: Special Cluster on Metamaterials

Analytical far-field calculation of arbitrarily oriented antenna arrays

Additive-Manufactured, Highly-Conductive Metasurfaces, With Application Enabling Secondary Properties, for Microwave Waveguide Components

Terahertz waveguide with a negative effective index of refraction measured using time domain techniques