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posted to cloaking
by norris
to the group Norris1
on 2013-03-28 03:47:11
Abstract
This Letter presents the design, fabrication, and experimental characterization of a directional three-dimensional acoustic cloak for airborne sound. The cloak consists of 60 concentric acoustically rigid tori surrounding the cloaked object, a sphere of radius 4 cm. The major radii and positions of the tori along the symmetry axis are determined using the condition of complete cancellation of the acoustic field scattered from the sphere. They are obtained through an optimization technique that combines genetic algorithm and simulated annealing. The scattering cross ...
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posted to cloaking
by norris
to the group Norris1
on 2013-03-27 23:41:09
Abstract
We combine a transformational acoustic (TA) conformal map with a scattering cancellation (SC) layer to produce a hybrid design that reduces the scattering cross-section of an object in an aqueous environment. Our method is an inertial design that does not rely on negative-valued media. Using multiple scattering theory for cylindrical shells, our calculations demonstrate that the hybrid design outperforms both a discretized transformational acoustic superlattice and a scattering cancellation layer over a broad frequency bandwidth. The hybrid method can be utilized ...
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posted to cloaking
by norris
to the group Norris1
on 2013-02-27 17:04:43
along with 1 person
mvanwol
Abstract
The existing knowledge on the electrodynamics of invisibility cloaking based on transformation optics is reviewed from an integrated science and engineering perspective. Several significant electromagnetic problems that have resulted in intense discussions in the past few years are summarized in terms of propagation, scattering, radiation and fabrication. Finally, the road ahead toward invisibility cloaking and transformation optics is discussed from the viewpoint of the author. ...
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(9 Nov 2012)
posted to cloaking
by norris
to the group Norris1
on 2013-02-01 18:58:30
Abstract
Invisibility cloaking in acoustic scattering via the approach of transformation optics is considered. The near-cloaks of both passive medium and active/radiating object are investigated. From a practical viewpoint, we are especially interested in the cloaking of an arbitrary (but regular) content. It is shown that one cannot achieve the near-cloak unless some special mechanism is introduced into the construction. A general lossy layer is incorporated into the construction of our near-cloaking devices. We derive very accurate estimates of the scattering amplitude in terms of the regularization parameter and the ...
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posted to cloaking
by norris
to the group Norris1
on 2013-02-01 18:47:26
Abstract
We consider approximate cloaking from a regularization viewpoint introduced in Kohn et al (2008 Inverse Problems 24 015016) for EIT and further investigated in Kohn et al (2010 Commun. Pure Appl. Math. 63 0973–1016) and Liu (2009 Inverse Problems 25 045006) for the Helmholtz equation. The cloaking schemes given by Kohn et al and Liu are shown to be (optimally) within |ln ρ| −1 ...
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(16 Jan 2013)
posted to cloaking metamaterial
by norris
to the group Norris1
on 2013-01-23 14:41:48
Abstract
The creation of wave-dynamic illusion functionality is of great interests to various scientific communities, which can potentially transform an actual perception into the pre-controlled perception, thus empowering unprecedented applications in the advanced-material science, camouflage, cloaking, optical and/or microwave cognition, and defense security, etc. By using the space transformation theory and engineering capability of metamaterials, we propose and realize a functional ghost illusion device, which is capable of creating wave-dynamic virtual ghost images off the original object's position under the illumination of electromagnetic waves. The scattering signature of the object is ...
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posted to cloaking
by norris
to the group Norris1
on 2013-01-22 16:02:40
Abstract
A two-dimensional acoustic cloak is realized to generate virtual image in air. The cloak is designed to make the backscattering characteristics of a quadrangular prism the same as that of a plate based on transformation acoustics. The required anisotropic parameters of the cloak shell are obtained by acoustic metamaterial made of perforated plates, which are easy to fabricate and unitize. The measurements of the backward and near-backward scattering fields confirm the validity of the proposed cloak. Experimental results show the possibility ...
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Abstract
The design rules of transformation optics generally lead to spatially inhomogeneous and anisotropic impedance-matched magneto-dielectric material distributions for, e.g., free-space invisibility cloaks. Recently, simplified anisotropic non-magnetic free-space cloaks made of a locally uniaxial dielectric material (calcite) have been realized experimentally. In a two-dimensional setting and for in-plane polarized light propagating in this plane, the cloaking performance can still be perfect for light rays. However, for general views in three dimensions, various imperfections are expected. In this paper, we study two different ...
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(13 Nov 2012)
posted to cloaking
by norris
to the group Norris1
on 2012-12-27 15:37:03
Abstract
The approximate cloaking is investigated for time-harmonic Maxwell's equations via the approach of transformation optics. The problem is reduced to certain boundary effect estimates due to an inhomogeneous electromagnetic inclusion with an asymptotically small support but an arbitrary content enclosed by a thin high-conducting layer. Sharp estimates are established in terms of the asymptotic parameter, which are independent of the material tensors of the small electromagnetic inclusion. The result implies that the `blow-up-a-small-region' construction via the transformation optics approach yields a near-cloak for the electromagnetic waves. A novelty lies ...
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(22 Dec 2012)
posted to cloaking
by norris
to the group Norris1
on 2012-12-27 15:30:44
Abstract
In this paper, we consider near cloaking for the full Maxwell equations. We extend the recent results, where the quasi-static limit case and the Helmholtz equation are considered, to electromagnetic scattering problems. We construct very effective near cloaking structures for the electromagnetic scattering problem at a fixed frequency. These new structures are, before using the transformation optics, layered structures and are designed so that their first scattering coefficients vanish. Inside the cloaking region, any target has near-zero scattering cross section for a band of frequencies. We analytically show that ...
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posted to cloaking
by norris
to the group Norris1
on 2012-12-27 15:28:59
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(20 Apr 2011)
posted to cloaking
by norris
to the group Norris1
on 2012-12-27 15:22:24
Abstract
The aim of this paper is to provide an original method of constructing very effective near-cloaking structures for the conductivity problem. These new structures are such that their first Generalized Polarization Tensors vanish. We show that this in particular significantly enhances the cloaking effect. We then present some numerical examples of Generalized Polarization Tensors vanishing structures. ...
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Abstract
In this Letter, we aim at making nanoparticles embedded in a host semiconductor with a size comparable to electronic wavelengths “invisible” to the electron transport. Inspired by the recent progress made in optics and working within the framework of the expansion of partial waves, we demonstrate that the opposite effects imposed by potential barriers and wells of a core-shell nanoparticle on the phase shifts associated with the scattered electron wave could make the scattering cross section of the first two partial ...
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Abstract
The possibility of making an optically large (many wavelengths in diameter) object appear invisible has been a subject of many recent studies. Exact invisibility scenarios for large (relative to the wavelength) objects involve (meta)materials with superluminal phase velocity [refractive index (RI) less than unity] and/or magnetic response. We introduce a new approximation applicable to certain device geometries in the eikonal limit: piecewise-uniform scaling of the RI. This transformation preserves the ray trajectories but leads to a uniform phase delay. We show ...
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Abstract
The method of transformation optics (TO) has recently been applied to the problem of manipulating the flow of surface plasmon polaritons (SPPs) along metal–dielectric interfaces. Although it allows one to theoretically control the flow in any manner desired, it usually leads to material properties not found in nature, thus making the realization of theoretical potentialities impractical. Therefore, artificial materials (called metamaterials), with both inhomogeneous and anisotropic electromagnetic response, are normally required to create the optical space designed with the TO method. ...
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Abstract
A multidimensional transformation design method that allows us to design a cloaking shell of multivariables for matter waves is proposed. As applications, cloaking shells for an elliptical invisible region, a region specified by the radial and angular variables, and an invisible region specified by the polar angle for the Coulomb scattering wave have been designed. It is shown that the mass parameters required for a perfect cloaking of a matter wave in the elliptical coordinate system are constant. ...
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posted to cloaking
by norris
to the group Norris1
on 2012-11-13 08:01:36
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(20 Oct 2012)
posted to cloaking
by norris
to the group Norris1
on 2012-10-30 19:28:35
Abstract
We developed a completely new method of earthquake-proof engineering to create an artificial seismic shadow zone using acoustic metamaterials. Helmholtz resonators intercept acoustic waves according to their resonance frequency, which creates a negative modulus or stop-band of the wave. By designing huge empty boxes with a few side-holes corresponding to the resonance frequencies of seismic waves and burying them around the buildings that we want to protect, the velocity of the seismic wave becomes imaginary. The meta-barrier composed of many meta-boxes attenuates the seismic waves, which reduces the amplitude ...
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(25 Oct 2012)
posted to cloaking
by norris
to the group Norris1
on 2012-10-29 15:49:03
Abstract
In this work a transformation acoustics scheme for generic elastic media is developed. Our approach starts form the decomposition of the elasticity tensor in terms of its eigentensors, an idea previously used by Norris. While Norris' transformation acoustics is restricted to the special class of so-called pentamode materials, we show that a similar scheme can be defined for the most general elasticity tensor. As in case of Norris' model (and in sharp contrast to transformation optics), the compatibility equations of the transformation medium are not purely algebraic and ...
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posted to angular beam cloaking momentum optics physics
by pak
to the group ukplasmeta
on 2012-10-22 13:09:14
Abstract
We propose a scheme to controllably convert the wave front of an arbitrary incident beam into a helical one by compact transformation slabs, thus enabling the output beam to carry a desirable orbital angular momentum (OAM). First, based on transformation optics, a three-dimensional (3D) phase transformation between any two wave fronts by flat transformation media is established and then used to mold the wave front of a Gaussian beam into a helical one. Second, 3D finite-difference time-domain simulations are performed to ...
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(14 Oct 2011)
posted to cloaking
by norris
to the group Norris1
on 2012-10-16 12:34:27
Abstract
As invisibility cloaking has recently become experimental reality, it is interesting to explore ways to reveal remaining imperfections. In essence, the idea of most invisibility cloaks is to recover the optical path lengths without an object (to be made invisible) by a suitable arrangement around that object. Optical path length is proportional to the time of flight of a light ray or to the optical phase accumulated by a light wave. Thus, time-of-flight images provide a direct and intuitive tool for probing imperfections. Indeed, recent phase-sensitive experiments on ...
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(2 Oct 2012)
posted to cloaking
by norris
to the group Norris1
on 2012-10-16 12:31:30
Abstract
The design rules of transformation optics generally lead to spatially inhomogeneous and anisotropic impedance-matched magneto-dielectric material distributions for, e.g., free-space invisibility cloaks. Recently, simplified anisotropic non-magnetic free-space cloaks made of a locally uniaxial dielectric material (calcite) have been realized experimentally. In a two-dimensional setting and for in-plane polarized light propagating in this plane, the cloaking performance can still be perfect for light rays. However, for general views in three dimensions, various imperfections are expected. In this paper, we study two different purely dielectric uniaxial cylindrical free-space cloaks. For one, the ...
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posted to cloaking
by norris
to the group Norris1
on 2012-09-20 12:39:09
Abstract
This paper describes the operation and the interaction of cloaking devices when they are periodically arranged. The main focus is on analyzing the dispersion relation of structures, which should mimic that of the vacuum in the ideal scenario. We distinguish between two cloaking mechanisms: cloaks designed within the framework of transformation optics and cloaks designed on the basis of the scattering cancellation technique. The difference between the two approaches is that the first operates independently of the frequency by assuming nondispersive ...
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Abstract
We cloak a region from a known incident wave by surrounding the region with three or more devices that cancel out the field in the cloaked region without significantly radiating waves. Since very little waves reach scatterers within the cloaked region, the scattered field is small and the scatterers are for all practical purposes undetectable. The devices are multipolar point sources that can be determined from Green's formula and an addition theorem for Hankel functions. The cloaking devices are exterior to ...
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posted to cloaking cui multilayer
by kadisake
on 2012-07-27 22:41:10
Abstract
We present a nonmagnetic electromagnetic transparent wall (EMTW) using the principle of total transmission and phase compensation. The device consists of two or more nonmagnetic stacked anisotropic slabs. With proper design of the constitutive tensors and relative thicknesses of each slab, EMTW is achieved which is independent of the incident angle of striking EM waves. The realization of the anisotropic slabs and furthermore EMTW in the optical range is mimicked using a metal-dielectric nano-structured system with alternating Na3AlF6-Ag layers. Compared to ...
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In Proceedings of the 2nd International Workshop on Adversarial Information Retrieval on the Web (AIRWeb) (August 2006), pp. 17-24
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posted to cloaking direction em optics physics propagation
by pak
to the group ukplasmeta
on 2012-07-05 15:02:57
Abstract
The method of optical conformal mapping is used to design two isotropic devices through which light travels in a unidirectional manner. The first device is a directional emitter. By setting a line current source in a properly tuned refractive index profile, fields can be radiated in only one direction or its opposite without using any reflector or metallic structure. The second proposal is a dual-functional device. It works not only as a directional emitter for an embedded source but also as ...
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(20 Jun 2012)
Abstract
Electromagnetic cloaking refers to the ability to prevent an object from scattering an incident electromagnetic field. This has been accomplished in recent works by routing the incident field around the object or by changing the scattering properties of the object itself through specially designed materials, surfaces or guiding structures. In this letter, we introduce a new way of cancelling the electromagnetic scattering of an object by using an array of sources. We show that by superimposing magnetic and electric surface current densities at the boundary of an object, ...
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(31 May 2012)
Abstract
Most of us will have at some time thrown a pebble into water, and watched the ripples spread outwards and fade away. But now there is a way to reverse the process, and make those ripples turn around and reconverge again, ... and again, and again. To do this we have designed the Maxwell's Fishpond, a water wave or "Tranformation Aquatics" version of the Maxwell's Fisheye lens [Tyc et al. 2011, Luneberg 1964] that is now well-known from transformation optics. These are transformation devices where wave propagation ...
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(5 Jun 2012)
Abstract
Natural Sciences are largely devoted to study conservation laws, such as charge, energy, linear momentum or angular momentum, because they give us information about the symmetries of our Universe. Here, we propose to add the relation between electromagnetic duality and helicity of light fields to the toolkit. This relationship is proven to hold both in free space and, under certain conditions, in the presence of material systems, independently of the geometry of the problem. It then provides a powerful and simple tool for the study of light-matter interactions ...
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posted to cloaking em physics scattering
by pak
to the group ukplasmeta
on 2012-05-11 13:48:46
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(9 Mar 2012)
Abstract
We show that cloaking of isolated objects is subject to a diameter-bandwidth product limitation: as the size of the object increases, the bandwidth of good (small cross-section) cloaking decreases inversely with the diameter, as a consequence of causality constraints even for perfect fabrication and materials with negligible absorption. This generalizes a previous result that perfect cloaking of isolated objects over a nonzero bandwidth violates causality. Furthermore, we demonstrate broader causality-based scaling limitations on any bandwidth-averaged cloaking cross-section, using complex analysis and the optical theorem to transform the frequency-averaged problem ...
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Abstract
The technique of transformation optics (TO) is an elegant method for the design of electromagnetic media with tailored optical properties. In this paper, we focus on the formal structure of TO theory. By using a complete covariant formalism, we present a general transformation law that holds for arbitrary materials including bianisotropic, magneto-optical, nonlinear and moving media. Due to the principle of general covariance, the formalism is applicable to arbitrary space-time coordinate transformations and automatically accounts for magneto-electric coupling terms. The formalism ...
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posted to cloaking
by norris
to the group Norris1
on 2012-03-27 14:32:38
along with 1 person
Demeter
Abstract
Invisibility to electromagnetic fields has become an exciting theoretical possibility. However, the experimental realization of electromagnetic cloaks has only been achieved starting from simplified approaches (for instance, based on ray approximation, canceling only some terms of the scattering fields, or hiding a bulge in a plane instead of an object in free space). Here, we demonstrate, directly from Maxwell equations, that a specially designed cylindrical superconductor-ferromagnetic bilayer can exactly cloak uniform static magnetic fields, and we experimentally confirmed this effect in ...
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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. ...
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posted to cloaking em optics physics waveguide
by pak
to the group ukplasmeta
on 2012-03-09 17:22:59
Abstract
We investigate the potential of transformation optics for the design of novel electromagnetic cavities. First, we determine the dispersion relation of bound modes in a device performing an arbitrary radial coordinate transformation and we discuss a number of such cavity structures. Subsequently, we generalize our study to media that implement azimuthal transformations, and show that such transformations can manipulate the azimuthal mode number. Finally, we discuss how the combination of radial and azimuthal coordinate transformations allows for perfect confinement of subwavelength ...
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(20 Feb 2012)
posted to cloaking laplace optics physics transform
by pak
to the group ukplasmeta
on 2012-03-09 13:15:01
Abstract
Recently, researchers have proposed several carpet cloaking designs that are able to hide a real object under a bump in a way that it is perceived as a flat ground plane. Here, we present a method to design two-dimensional isotropic carpet cloaking devices using Laplace transformation. We show that each functional form of a Laplace transformation corresponds to a different carpet cloaking design. Therefore, our approach allows us to systematically design a rich variety of cloaking devices. Our analysis includes several examples containing different bump geometries that illustrate ...
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(10 Sep 2010)
Abstract
We cloak a region from a known incident wave by surrounding the region with three or more devices that cancel out the field in the cloaked region without significantly radiating waves. Since very little waves reach scatterers within the cloaked region, the scattered field is small and the scatterers are for all practical purposes undetectable. The devices are multipolar point sources that can be determined from Green's formula and an addition theorem for Hankel functions. The cloaking devices are exterior to the cloaked region. ...
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posted to acoustic cloaking physics water wave
by pak
to the group metacoustics
on 2012-03-09 11:25:12
Abstract
Here we show that floating objects in stratified fluids can be cloaked against broadband incident waves by properly architecting the bottom corrugations. The presented invisibility cloaking of gravity waves is achieved utilizing a nonlinear resonance concept that occurs between surface and internal waves mediated by the bottom topography. Our cloak bends wave rays from the surface into the body of the fluid. Wave rays then pass underneath the floating object and may be recovered back to the free surface at the ...
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posted to cloaking
by norris
to the group Norris1
on 2012-02-14 22:57:27
along with 1 person
dploss
Abstract
Following a theoretical proposal [ M. Farhat et al. Phys. Rev. Lett. 103 024301 (2009)], we design, fabricate, and characterize a cloaking structure for elastic waves in 1 mm thin structured polymer plates. The cloak consists of 20 concentric rings of 16 different metamaterials, each being a tailored composite of polyvinyl chloride and polydimethylsiloxane. By using stroboscopic imaging with a camera from the direction normal to the plate, we record movies of the elastic waves for monochromatic plane-wave excitation. We observe ...
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posted to cloaking
by norris
to the group Norris1
on 2012-02-14 22:53:50
Abstract
Transformation acoustics opens a new avenue towards the design of acoustic metamaterials, which are materials engineered at the subwavelength scale in order to mimic the parameters in wave equations. The design of the acoustic cloaking is based on the property of equations being invariant under a coordinate transformation, i.e. a specific spatial compression is equivalent to a variation of the material parameters in the original space. In this paper, the sound invisibility performance is discussed for spherical cloaks. The original domain ...
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Abstract
Invisibility devices based on coordinate transformation have opened up a new field of considerable interest. We present here the first practical realization of a low-loss and broadband acoustic cloak for underwater ultrasound. This metamaterial cloak is constructed with a network of acoustic circuit elements, namely, serial inductors and shunt capacitors. Our experiment clearly shows that the acoustic cloak can effectively bend the ultrasound waves around the hidden object, with reduced scattering and shadow. Because of the nonresonant nature of the building ...
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Abstract
We report the experimental verification of metamaterial cloaking for a 3D object in free space. We apply the plasmonic cloaking technique, based on scattering cancellation, to suppress microwave scattering from a finite-length dielectric cylinder. We verify that scattering suppression is obtained all around the object in the near- and far-field and for different incidence angles, validating our measurements with analytical results and full-wave simulations. Our near-field and far-field measurements confirm that realistic and robust plasmonic metamaterial cloaks may be realized for ...
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(2 Dec 2011)
posted to cloaking em nonlocal optics physics
by pak
to the group ukplasmeta
on 2012-01-24 16:21:58
Abstract
We show that the powerful framework of transformation optics may be exploited for engineering the nonlocal response of artificial electromagnetic materials. Relying on the form-invariant properties of coordinate-transformed Maxwell's equations in the spectral domain, we derive the general constitutive "blueprints" of transformation media yielding prescribed nonlocal field-manipulation effects, and provide a physically-incisive and powerful geometrical interpretation in terms of deformation of the equi-frequency contours. In order to illustrate the potentials of our approach, we present an example of application to a wave-splitting refraction scenario, which may be implemented via a ...
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Proceedings of the Royal Society A: Mathematical, Physical and Engineering Science, Vol. 468, No. 2138. (08 February 2012), pp. 563-580, doi:10.1098/rspa.2011.0477
posted to cloaking
by norris
to the group Norris1
on 2012-01-24 14:53:39
along with 1 person
miccoli
Abstract
A theory is presented showing that cloaking of objects from antiplane elastic waves can be achieved by employing nonlinear elastic pre-stress in a neo-Hookean elastomeric material. This approach would appear to eliminate the requirement of metamaterials with inhomogeneous anisotropic shear moduli and density. Waves in the pre-stressed medium are bent around the cloaked (cavity) region by inducing inhomogeneous stress fields via pre-stress. The equation governing antiplane waves in the pre-stressed medium is equivalent to the antiplane equation in an unstressed medium ...
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posted to cloaking
by norris
to the group Norris1
on 2012-01-23 22:07:06
Abstract
Recently, it was demonstrated that active sources can be used to cloak any objects that lie outside the cloaking devices [ F. Guevara Vasquez, G. W. Milton and D. Onofrei Phys. Rev. Lett. 103 073901 (2009)]. Here, we propose that active sources can create illusion effects so that an object outside the cloaking device can be made to look like another object. Invisibility is a special case in which the concealed object is transformed to a volume of air. From ...
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(7 May 2012)
posted to cloaking
by norris
to the group Norris1
on 2012-01-04 20:36:11
Abstract
Following the ideas proposed in \citeOMV1 and \citeOMV2 on active exterior cloaking, we present here a systematic integral equation method to generate suitable quasistatic fields for cloaking, illusions and energy focusing (with given accuracy) in multiple regions of interests. In the quasistatic regime, the central issue is to design appropriate source functions for the Laplace equation so that the resulting solution will satisfy the required properties. We show the existence and non-uniqueness of solutions to the problem and study the physically relevant unique $L^2$-minimal energy solution. We also provide ...
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(16 Sep 2011)
posted to cloaking
by norris
to the group Norris1
on 2012-01-04 20:35:18
Abstract
We design a device that generates fields canceling out a known probing field inside a region to be cloaked while generating very small fields far away from the device. The fields we consider satisfy the Laplace equation, but the approach remains valid in the quasistatic regime in a homogeneous medium. We start by relating the problem of designing an exterior cloak in the quasistatic regime to the classic problem of approximating a harmonic function with harmonic polynomials. An explicit polynomial solution to the problem was given earlier in ...
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In Proceedings of the 2010 IEEE Second International Conference on Social Computing (2010), pp. 1093-1098
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