The Experts below are selected from a list of 2772 Experts worldwide ranked by ideXlab platform
Martin Wegener - One of the best experts on this subject based on the ideXlab platform.
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uncloaking diffusive light Invisibility Cloaks by speckle analysis
Optics Letters, 2017Co-Authors: Andreas Niemeyer, Frederik Mayer, A Naber, Milan Koirala, Alexey Yamilov, Martin WegenerAbstract:Within the range of validity of the stationary diffusion equation, an ideal diffusive-light Invisibility cloak can make an arbitrary macroscopic object hidden inside of the cloak indistinguishable from the surroundings for all colors, polarizations, and directions of incident visible light. However, the diffusion equation for light is an approximation which becomes exact only in the limit of small coherence length. Thus, one expects that the cloak can be revealed by illumination with coherent light. The experiments presented here show that the Cloaks are robust in the limit of large coherence length but can be revealed by analysis of the speckle patterns under illumination with partially coherent light. Experiments on cylindrical core-shell Cloaks and corresponding theory are in good agreement.
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Invisibility Cloaks in relativistic motion
Physical Review A, 2016Co-Authors: Jad C. Halimeh, Robert T. Thompson, Martin WegenerAbstract:We consider an ideal Invisibility cloak which is illuminated by monochromatic light and which moves in vacuum at constant relativistic velocity with respect to the common inertial frame of light source and observer. We show that, in general, the moving cloak becomes detectable by image distortions and by generating a broad frequency spectrum of the scattered light. However, for many special combinations of incident light frequency, wave vector of light, and cloak velocity, ideal cloaking remains possible. It becomes nonreciprocal though. This means that light rays emitted by the light source arrive at the observer as though they have traveled through vacuum, but they take completely different paths after being retroreflected at the observer position.
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transient behavior of Invisibility Cloaks for diffusive light propagation
Optica, 2015Co-Authors: Robert Schittny, Muamer Kadic, Tiemo Bückmann, Andreas Niemeyer, A Naber, Martin WegenerAbstract:An ideal Invisibility cloak makes any object within itself indistinguishable from its surrounding—for all colors, directions, and polarizations of light. Nearly ideal Cloaks have recently been realized for turbid light-scattering media under continuous-wave illumination. Here, we ask whether these Cloaks also work under pulsed illumination. Our time-resolved imaging experiments on simple core–shell Cloaks show that they do not: they appear bright with respect to their surrounding at early times and dark at later times, leading to vanishing image contrast for time-averaged detection. Furthermore, we show that the same holds true for more complex cloaking architectures designed by spatial coordinate transformations. We discuss implications for diffuse optical tomography and possible applications in terms of high-end security features.
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Invisibility cloaking in a diffusive light scattering medium
Science, 2014Co-Authors: Robert Schittny, Muamer Kadic, Tiemo Bückmann, Martin WegenerAbstract:In vacuum, air, and other surroundings that support ballistic light propagation according to Maxwell’s equations, Invisibility Cloaks that are macroscopic, three-dimensional, broadband, passive, and that work for all directions and polarizations of light are not consistent with the laws of physics. We show that the situation is different for surroundings leading to multiple light scattering, according to Fick’s diffusion equation. We have fabricated cylindrical and spherical Invisibility Cloaks made of thin shells of polydimethylsiloxane doped with melamine-resin microparticles. The shells surround a diffusively reflecting hollow core, in which arbitrary objects can be hidden. We find good cloaking performance in a water-based diffusive surrounding throughout the entire visible spectrum and for all illumination conditions and incident polarizations of light.
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3D Optical Invisibility Cloak in the Diffusive-Light Limit
CLEO: 2014, 2014Co-Authors: Robert Schittny, Muamer Kadic, Martin WegenerAbstract:We design, fabricate, and characterize three-dimensional macroscopic free-space omnidirectional polarization-independent visible-wavelength broad-bandwidth Invisibility Cloaks in the diffusive limit of light propagation. The simple core-shell geometries are inspired by near-field optics.
Baile Zhang - One of the best experts on this subject based on the ideXlab platform.
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seamless integration of global dirichlet to neumann boundary condition and spectral elements for transformation electromagnetics
Computer Methods in Applied Mechanics and Engineering, 2016Co-Authors: Zhiguo Yang, Lilian Wang, Zhijian Rong, Bo Wang, Baile ZhangAbstract:Abstract In this paper, we present an efficient spectral-element method (SEM) for solving general two-dimensional Helmholtz equations in anisotropic media, with particular applications in accurate simulation of polygonal Invisibility Cloaks, concentrators and circular rotators arisen from the field of transformation electromagnetics (TE). In practice, we adopt a transparent boundary condition (TBC) characterised by the Dirichlet-to-Neumann (DtN) map to reduce wave propagation in an unbounded domain to a bounded domain. We then introduce a semi-analytic technique to integrate the global TBC with local curvilinear elements seamlessly, which is accomplished by using a novel elemental mapping and analytic formulas for evaluating global Fourier coefficients on spectral-element grids exactly. From the perspective of TE, an Invisibility cloak is devised by a singular coordinate transformation of Maxwell’s equations that leads to anisotropic materials coating the cloaked region to render any object inside invisible to observers outside. An important issue resides in the imposition of appropriate conditions at the outer boundary of the cloaked region, i.e., cloaking boundary conditions (CBCs), in order to achieve perfect Invisibility. Following the spirit of Yang and Wang (2015), we propose new CBCs for polygonal Invisibility Cloaks from the essential “pole” conditions related to singular transformations. This allows for the decoupling of the governing equations of inside and outside the cloaked regions. With this efficient spectral-element solver at our disposal, we can study the interesting phenomena when some defects and lossy or dispersive media are placed in the cloaking layer of an ideal polygonal cloak.
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Transformation Cloaks for surface electromagnetic waves
2015 IEEE 4th Asia-Pacific Conference on Antennas and Propagation (APCAP), 2015Co-Authors: Hongyi Xu, Baile Zhang, Xu Su, Hongsheng ChenAbstract:Aiming at suppressing the scattering of surface electromagnetic wave propagating on rough surface, we present the theoretical design and experimental realization of Invisibility Cloaks for surface wave using the nonmagnetic transformation optics method. Near-unitary broadband transmission of surface electromagnetic wave on rough surface have been experimentally realized in microwave regime.
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Design, implementation, and extension of thermal Invisibility Cloaks
AIP Advances, 2015Co-Authors: Youming Zhang, Baile ZhangAbstract:A thermal Invisibility cloak, as inspired by optical Invisibility Cloaks, is a device which can steer the conductive heat flux around an isolated object without changing the ambient temperature distribution so that the object can be “invisible” to external thermal environment. While designs of thermal Invisibility Cloaks inherit previous theories from optical Cloaks, the uniqueness of heat diffusion leads to more achievable implementations. Thermal Invisibility Cloaks, as well as the variations including thermal concentrator, rotator, and illusion devices, have potentials to be applied in thermal management, sensing and imaging applications. Here, we review the current knowledge of thermal Invisibility Cloaks in terms of their design and implementation in cloaking studies, and their extension as other functional devices.
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Electromagnetic Invisibility Cloaks based on inverse design method
Proceedings of 2014 3rd Asia-Pacific Conference on Antennas and Propagation, 2014Co-Authors: Su Xu, Yuyu Jiang, Xiangxiang Cheng, Hongsheng Chen, Faxin Yu, Hua Chen, Baile ZhangAbstract:Inspired from the thoughts of forward-design cloaking techniques, Invisibility Cloaks with inverse designs have experience a period of remarkably fast development in the past few years. In this paper, we report an inverse design method of Invisibility Cloaks based on the Mie scattering theory with the adoption of the genetic algorithm. With the inverse design, an invisible dipole antenna is demonstrated experimentally and an omnidirectional spherical Invisibility cloak design is proposed.
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Towards omnidirectional, large scale, full polarization, and broadband practical Invisibility Cloaks: challenges and progress
EPJ Applied Metamaterials, 2014Co-Authors: Yihao Yang, Baile Zhang, Hongsheng ChenAbstract:Invisibility Cloaks have experienced a tremendous development in the past few years, but the current technologies to convert the Cloaks into practical applications are still facing numerous bottlenecks. In this paper, we provide the review of the challenges and recent progress in the Invisibility Cloaks from a practical perspective. In particular, the following key challenges such as non-extreme parameters, homogeneity, omnidirectivity, full polarization, large scale and broad band are addressed. We analyze the physical mechanisms behind the challenges and consequently evaluate the merits and defects of the recent solutions. We anticipate some compromises on the ideal Cloaks are required in order to achieve practical Invisibility Cloaks in the future.
David R Smith - One of the best experts on this subject based on the ideXlab platform.
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flat face approximations of Invisibility Cloaks with planar metamaterial layers
arXiv: Optics, 2011Co-Authors: Oliver Paul, David R Smith, Yaroslav A Urzhumov, Christoffer Elsen, Marco RahmAbstract:Transformation optics (TO) is a powerful tool for the design of artiffcial materials with unprecedented optical properties. Here, we propose the approximation of TO structures of arbitrary shape by faceting, in which curved surfaces are approximated by at metamaterial layers that can be implemented by standard fabrication and stacking techniques. We illustrate the approximation approach for the specific example of a cylindrical Invisibility cloak. First, we introduce a numerical method for the design of Cloaks with arbitrary boundary shapes, and apply it to faceted shapes. Subsequently, we reduce the complexity of the metamaterials needed to implement the perfect faceted cloak by introducing several approximations, whose validity is quantified by an investigation of the scattering cross section.
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optical design of reflectionless complex media by finite embedded coordinate transformations
Physical Review Letters, 2008Co-Authors: Marco Rahm, Steven A Cummer, David Schurig, J B Pendry, David R SmithAbstract:Transformation optics offers an unconventional approach to the control of electromagnetic fields. The transformation optical structures proposed to date, such as electromagnetic ``Invisibility'' Cloaks and concentrators, are inherently reflectionless and leave the transmitted wave undisturbed. Here, we expand the class of transformation optical structures by introducing finite, embedded coordinate transformations, which allow the electromagnetic waves to be steered or focused. We apply the method to the design of several devices, including a parallel beam shifter and a beam splitter, both of which are reflectionless and exhibit unusual electromagnetic behavior as confirmed by 2D full-wave simulations.
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calculation of material properties and ray tracing in transformation media
Optics Express, 2006Co-Authors: David Schurig, J B Pendry, David R SmithAbstract:Complex and interesting electromagnetic behavior can be found in spaces with non-flat topology. When considering the properties of an electromagnetic medium under an arbitrary coordinate transformation an alternative interpretation presents itself. The transformed material property tensors may be interpreted as a different set of material properties in a flat, Cartesian space. We describe the calculation of these material properties for coordinate transformations that describe spaces with spherical or cylindrical holes in them. The resulting material properties can then implement Invisibility Cloaks in flat space. We also describe a method for performing geometric ray tracing in these materials which are both inhomogeneous and anisotropic in their electric permittivity and magnetic permeability.
Min Qiu - One of the best experts on this subject based on the ideXlab platform.
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Design of Invisibility Cloaks with an open tunnel.
Optics Express, 2010Co-Authors: Thomas Ako, Min Yan, Min QiuAbstract:In this paper we apply the methodology of transformation optics for design of a novel Invisibility cloak which can possess an open tunnel. Such a cloak facilitates the insertion (retrieval) of matter into (from) the cloak’s interior without significantly affecting the cloak’s performance, overcoming the matter exchange bottleneck inherent to most previously proposed cloak designs. We achieve this by applying a transformation which expands a point at the origin in electromagnetic space to a finite area in physical space in a highly anisotropic manner. The Invisibility performance of the proposed cloak is verified by using full-wave finite-element simulations.
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Invisibility Cloaking by Coordinate Transformation
Progress in Optics, 2009Co-Authors: Min Yan, Wei Yan, Min QiuAbstract:Abstract Recently, the covariance property of the Maxwell equations under a coordinate transformation has been exploited for controlling the flow of electromagnetic waves in an unprecedented manner. Together with the development of electromagnetic metamaterial technologies, realization of perfect Invisibility Cloaks is no longer an intangible dream. Here we review both theoretical and experimental efforts to realize such Invisibility Cloaks. Their perspectives and limitations are also discussed.
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Transformation optics and Invisibility Cloaks
Optoelectronic Materials and Devices III, 2008Co-Authors: Min Qiu, Min Yan, Wei YanAbstract:In this paper, we briefly summarize the theory of transformation optics and introduce its application in achieving perfect Invisibility cloaking. In particular, we theoretically show how the task of realizing cylindrical Invisibility Cloaks can be eased by using either structural approximation or material simplification. The corresponding Invisibility performances of the approximate or simplified cylindrical Cloaks are presented in detail.
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Coordinate transformations make perfect Invisibility Cloaks with arbitrary shape
New Journal of Physics, 2008Co-Authors: Wei Yan, Min Yan, Zhichao Ruan, Min QiuAbstract:By investigating wave properties at cloak boundaries, Invisibility Cloaks with arbitrary shape constructed by general coordinate transformations are confirmed to be perfectly invisible to the exter ...
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influence of geometrical perturbation at inner boundaries of Invisibility Cloaks
Journal of The Optical Society of America A-optics Image Science and Vision, 2008Co-Authors: Wei Yan, Min Yan, Zhichao Ruan, Min QiuAbstract:The influence of a geometrical perturbation delta at the inner boundaries of both cylindrical and spherical Invisibility Cloaks on Invisibility performance is presented. The analytic solutions for such influence in the case of the general coordinate transformation are given. We show that the cylindrical cloak is more sensitive than a spherical cloak to such a perturbation. The difference results from the different asymptotic properties of eigenfunctions for the cylindrical and spherical wave equations. In particular, the zeroth-order scattering coefficient for a cylindrical cloak determined by -1/ln(delta) converges to zero very slowly. The noticeable scattering induced by the slow convergence speed can be decreased by choosing appropriate coordinate transformation functions. More interestingly, the slow convergence can be overcome dramatically by putting a PEC (PMC) layer at the interior boundary of the cloak shell for TM (TE) wave.
Hongsheng Chen - One of the best experts on this subject based on the ideXlab platform.
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Experimental study on Invisibility Cloaks
2016 IEEE International Workshop on Electromagnetics: Applications and Student Innovation Competition (iWEM), 2016Co-Authors: Liqiao Jing, Bin Zheng, Lian Shen, Hongsheng ChenAbstract:In the past few years, Invisibility cloaking has experienced a tremendous development in both design methodologies and experimental implementations. However, serious bottlenecks still exist, such as the superluminal propagation in the cloak, the extreme parameters for an omnidirectional cloak and so on. To overcome the bottlenecks, plenty of works have been done. In this paper, some progresses of our group on the Invisibility Cloaks are reviewed, such as cylindrical cloak based on a new inverse design by combining the scattering cancellation method and transformation optics, large scale far-infrared Invisibility cloak using inversed quasi-conformal mapping approach, broadband surface-wave transformation cloak and broadband polygonal Invisibility cloak for visible light. We anticipate that the Invisibility cloaking technology will be more useful in the future.
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Transformation Cloaks for surface electromagnetic waves
2015 IEEE 4th Asia-Pacific Conference on Antennas and Propagation (APCAP), 2015Co-Authors: Hongyi Xu, Baile Zhang, Xu Su, Hongsheng ChenAbstract:Aiming at suppressing the scattering of surface electromagnetic wave propagating on rough surface, we present the theoretical design and experimental realization of Invisibility Cloaks for surface wave using the nonmagnetic transformation optics method. Near-unitary broadband transmission of surface electromagnetic wave on rough surface have been experimentally realized in microwave regime.
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Electromagnetic Invisibility Cloaks based on inverse design method
Proceedings of 2014 3rd Asia-Pacific Conference on Antennas and Propagation, 2014Co-Authors: Su Xu, Yuyu Jiang, Xiangxiang Cheng, Hongsheng Chen, Faxin Yu, Hua Chen, Baile ZhangAbstract:Inspired from the thoughts of forward-design cloaking techniques, Invisibility Cloaks with inverse designs have experience a period of remarkably fast development in the past few years. In this paper, we report an inverse design method of Invisibility Cloaks based on the Mie scattering theory with the adoption of the genetic algorithm. With the inverse design, an invisible dipole antenna is demonstrated experimentally and an omnidirectional spherical Invisibility cloak design is proposed.
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Towards omnidirectional, large scale, full polarization, and broadband practical Invisibility Cloaks: challenges and progress
EPJ Applied Metamaterials, 2014Co-Authors: Yihao Yang, Baile Zhang, Hongsheng ChenAbstract:Invisibility Cloaks have experienced a tremendous development in the past few years, but the current technologies to convert the Cloaks into practical applications are still facing numerous bottlenecks. In this paper, we provide the review of the challenges and recent progress in the Invisibility Cloaks from a practical perspective. In particular, the following key challenges such as non-extreme parameters, homogeneity, omnidirectivity, full polarization, large scale and broad band are addressed. We analyze the physical mechanisms behind the challenges and consequently evaluate the merits and defects of the recent solutions. We anticipate some compromises on the ideal Cloaks are required in order to achieve practical Invisibility Cloaks in the future.
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A Simple Unidirectional Optical Invisibility Cloak Made of Water
Progress In Electromagnetics Research, 2014Co-Authors: Bin Zheng, Lian Shen, Zuozhu Liu, Huaping Wang, Xianmin Zhang, Hongsheng ChenAbstract:Previous Invisibility Cloaks were based on metamaterials, which are di-cult for practical realization in visible light spectrum. Here we demonstrate a unidirectional Invisibility cloak in visible light spectrum. By using water as the efiective material and separated into several regions by glass sheets, a simplest and cheapest invisible device is realized. This device can hide macroscopic objects with large scale and is polarization insensitive. Owing to simple fabrication and easily acquisitive materials, our work can be widely applied in our daily life.
