Compact-sized and broadband carpet cloak and free-space cloak.
TL;DR: The first experimental demonstration of broadband and low-loss directive free-space cloak and compact-sized carpet cloak realized using non-resonant metamaterials in the microwave frequency represents a major step towards the real applications of invisibility cloaks.
Abstract: Recently, invisible cloaks have attracted much attention due to their exciting property of invisibility, which are based on a solid theory of transformation optics and quasi-conformal mapping. Two kinds of cloaks have been proposed: free-space cloaks, which can render objects in free space invisible to incident radiation, and carpet cloaks (or ground-plane cloaks), which can hide objects under the conducting ground. The first free-space and carpet cloaks were realized in the microwave frequencies using metamaterials. The free-space cloak was composed of resonant metamaterials, and hence had restriction of narrow bandwidth and high loss; the carpet cloak was made of non-resonant metamaterials, which have broad bandwidth and low loss. However, the carpet cloak has a severe restriction of large size compared to the cloaked object. The above restrictions become the bottlenecks to the real applications of free-space and carpet cloaks. Here we report the first experimental demonstration of broadband and low-loss directive free-space cloak and compact-sized carpet cloak based on a recent theoretical study. Both cloaks are realized using non-resonant metamaterials in the microwave frequency, and good invisibility properties have been observed in experiments. This approach represents a major step towards the real applications of invisibility cloaks.
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TL;DR: The first practical implementation of a fully 3D broadband and low-loss ground-plane cloak at microwave frequencies is realized, realized by drilling inhomogeneous holes in multi-layered dielectric plates.
Abstract: Optical cloaking has already been demonstrated in two dimensions, and also in three dimensions for a limited range of angles. Now, Ma and Cui present a metamaterial-based cloaking device that can shield an object lying on the ground plane from all viewing angles at microwave frequencies.
510Â citations
TL;DR: The design, realization and measurement of a three-dimensional approximate transformation-optics lens in the microwave frequency band is shown, made of non-resonant metamaterials, which are fabricated with multilayered dielectric plates by drilling inhomogeneous holes.
Abstract: Lenses with superior performance with respect to conventional uniform materials are desirable. The authors show a three-dimensional lens, made of multilayered metamaterials and based on approximate transformation optics, which works in different polarizations at broad viewing angles and with wide bandwidth.
417Â citations
TL;DR: Transformation optics is a modern application of Maxwell's equations offering unprecedented control over the flow of light that exploits spatially customized optical properties and mathematical techniques applied to space-time curvature as discussed by the authors.
Abstract: Transformation optics is a modern application of Maxwell's equations offering unprecedented control over the flow of light that exploits spatially customized optical properties and mathematical techniques applied to space-time curvature.
236Â citations
99Â citations
TL;DR: In this article, an X-band half Maxwell fish-eye lens antenna is designed based on the effective medium theory and metamaterials technology, where non-resonant I-shaped metammaterials have been chosen to realize the lens antenna due to the broadband and low-loss features.
Abstract: An X-band half Maxwell fish-eye lens antenna is designed based on the effective medium theory and metamaterials technology. The non-resonant I-shaped metamaterials have been chosen to realize the lens antenna due to the broadband and low-loss features. The laboratory prototype has been fabricated and measured using a two-dimensional near-field microwave scanning apparatus, where the experimental results agree with full-wave numerical simulations.
81Â citations
References
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TL;DR: In this paper, it was shown that microstructures built from nonmagnetic conducting sheets exhibit an effective magnetic permeability /spl mu/sub eff/, which can be tuned to values not accessible in naturally occurring materials.
Abstract: We show that microstructures built from nonmagnetic conducting sheets exhibit an effective magnetic permeability /spl mu//sub eff/, which can be tuned to values not accessible in naturally occurring materials, including large imaginary components of /spl mu//sub eff/. The microstructure is on a scale much less than the wavelength of radiation, is not resolved by incident microwaves, and uses a very low density of metal so that structures can be extremely lightweight. Most of the structures are resonant due to internal capacitance and inductance, and resonant enhancement combined with compression of electrical energy into a very small volume greatly enhances the energy density at critical locations in the structure, easily by factors of a million and possibly by much more. Weakly nonlinear materials placed at these critical locations will show greatly enhanced effects raising the possibility of manufacturing active structures whose properties can be switched at will between many states.
8,135Â citations
TL;DR: This work shows how electromagnetic fields can be redirected at will and proposes a design strategy that has relevance to exotic lens design and to the cloaking of objects from electromagnetic fields.
Abstract: 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.
7,811Â citations
TL;DR: This work describes here the first practical realization of a cloak of invisibility, constructed with the use of artificially structured metamaterials, designed for operation over a band of microwave frequencies.
Abstract: 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.
6,830Â citations
TL;DR: A general recipe for the design of media that create perfect invisibility within the accuracy of geometrical optics is developed, which can be applied to escape detection by other electromagnetic waves or sound.
Abstract: An invisibility device should guide light around an object as if nothing were there, regardless of where the light comes from. Ideal invisibility devices are impossible, owing to the wave nature of light. This study develops a general recipe for the design of media that create perfect invisibility within the accuracy of geometrical optics. The imperfections of invisibility can be made arbitrarily small to hide objects that are much larger than the wavelength. With the use of modern metamaterials, practical demonstrations of such devices may be possible. The method developed here can also be applied to escape detection by other electromagnetic waves or sound.
3,850Â citations
TL;DR: A new type of cloak is discussed: one that gives all cloaked objects the appearance of a flat conducting sheet that has the advantage that none of the parameters of the cloak is singular and can in fact be made isotropic.
Abstract: A new type of cloak is discussed: one that gives all cloaked objects the appearance of a flat conducting sheet. It has the advantage that none of the parameters of the cloak is singular and can in fact be made isotropic. It makes broadband cloaking in the optical frequencies one step closer.
1,419Â citations