Showing papers by "David R. Smith published in 2008"
TL;DR: This work fabricate, characterize, and analyze a MM absorber with a slightly lower predicted A(omega) of 96%.
Abstract: 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.
5,550 citations
TL;DR: In this article, a square electromagnetic cloak and an omni-directional electromagnetic field concentrator are described and the functionality of the devices is numerically confirmed by two-dimensional finite element simulations.
Abstract: The technique of applying form-invariant, spatial coordinate transformations of Maxwell’s equations can facilitate the design of structures with unique electromagnetic or optical functionality. Here, we illustrate the transformation-optical approach in the designs of a square electromagnetic cloak and an omni-directional electromagnetic field concentrator. The transformation equations are described and the functionality of the devices is numerically confirmed by two-dimensional finite element simulations. The two devices presented demonstrate that the transformation optic approach leads to the specification of complex, anisotropic and inhomogeneous materials with well directed and distinct electromagnetic behavior.
770 citations
TL;DR: It is reported that the metal film induces a polarization to the single nanoparticle light scattering, resulting in a doughnut-shaped point spread function when imaged in the far-field.
Abstract: We present an experimental analysis of the plasmonic scattering properties of gold nanoparticles controllably placed nanometers away from a gold metal film. We show that the spectral response of this system results from the interplay between the localized plasmon resonance of the nanoparticle and the surface plasmon polaritons of the gold film, as previously predicted by theoretical studies. In addition, we report that the metal film induces a polarization to the single nanoparticle light scattering, resulting in a doughnut-shaped point spread function when imaged in the far-field. Both the spectral response and the polarization effects are highly sensitive to the nanoparticle−film separation distance. Such a system shows promise in potential biometrology and diagnostic devices.
498 citations
TL;DR: This work applies finite, embedded coordinate transformations 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.
Abstract: 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.
496 citations
TL;DR: Through acoustic scattering theory, the mass density and bulk modulus of a spherical shell that can eliminate scattering from an arbitrary object in the interior of the shell are derived--in other words, a 3D acoustic cloaking shell.
Abstract: Through acoustic scattering theory we derive the mass density and bulk modulus of a spherical shell that can eliminate scattering from an arbitrary object in the interior of the shell—in other words, a 3D acoustic cloaking shell. Calculations confirm that the pressure and velocity fields are smoothly bent and excluded from the central region as for previously reported electromagnetic cloaking shells. The shell requires an anisotropic mass density with principal axes in the spherical coordinate directions and a radially dependent bulk modulus. The existence of this 3D cloaking shell indicates that such reflectionless solutions may also exist for other wave systems that are not isomorphic with electromagnetics.
460 citations
TL;DR: An experimental demonstration of microwave tunneling between two planar waveguides separated by a thin ENZ channel is presented, in agreement with theory and numerical simulations.
Abstract: Silveirinha and Engheta have recently proposed that electromagnetic waves can tunnel through a material with an electric permittivity ($ϵ$) near zero (ENZ). An ENZ material of arbitrary geometry can thus serve as a perfect coupler between incoming and outgoing waveguides with identical cross-sectional area, so long as one dimension of the ENZ is electrically small. In this Letter we present an experimental demonstration of microwave tunneling between two planar waveguides separated by a thin ENZ channel. The ENZ channel consists of a planar waveguide in which complementary split ring resonators are patterned on the lower surface. A tunneling passband is found in transmission measurements, while a two-dimensional spatial map of the electric field distribution reveals a uniform phase variation across the channel---both measurements in agreement with theory and numerical simulations.
428 citations
TL;DR: In this paper, a hybrid-metamaterial architecture is proposed for tuning a far-infrared resonance frequency with vanadium dioxide (VO2), a material whose optical properties can be strongly and quickly changed via external stimulus.
Abstract: We demonstrate a metamaterial device whose far-infrared resonance frequency can be dynamically tuned. Dynamic tuning should alleviate many bandwidth-related roadblocks to metamaterial application by granting a wide matrix of selectable electromagnetic properties. This tuning effect is achieved via a hybrid-metamaterial architecture; intertwining split ring resonator metamaterial elements with vanadium dioxide (VO2)-a material whose optical properties can be strongly and quickly changed via external stimulus. This hybrid structure concept opens a fresh dimension in both exploring and exploiting the intriguing electromagnetic behavior of metamaterials.
318 citations
TL;DR: The design of adaptive beam bends and beam splitters with arbitrary bend and split angles by use of finite embedded coordinate transformations are described and it is observed that a pure transformation-optical design cannot result in a reflectionless beam expander/compressor.
Abstract: We describe the design of adaptive beam bends and beam splitters with arbitrary bend and split angles by use of finite embedded coordinate transformations. The devices do not exhibit reflection at the entrance or exit surfaces. It is shown that moderate and practically achievable values of the relative permittivity and permeability can be obtained for beam bends and splitters with both small and large bend radius. The devices are also discussed in the context of reconfigurable metamaterials, in which the bend and split angles can be dynamically tuned. The performance of adaptive beam bends and splitters is demonstrated in full wave simulations based on a finite-element method. Furthermore, the design of an adaptively adjustable transformation-optical beam expander/compressor is presented. It is observed that a pure transformation-optical design cannot result in a reflectionless beam expander/compressor.
289 citations
TL;DR: In this paper, the design of arbitrarily shaped electromagnetic (EM) concentrators and their potential applications are studied. But the design is restricted to the case of a rectangular concentrator, which is much more efficient and easier than the existing techniques.
Abstract: We study the design of arbitrarily shaped electromagnetic (EM) concentrators and their potential applications. To obtain closed-form formulas of EM parameters for an arbitrarily shaped concentrator, we employ nonuniform rational B-spline (NURBS) to represent the geometrical boundary. Using the conformally optical transformation of NURBS surfaces, we propose the analytical design of arbitrarily shaped concentrators, which are composed of anisotropic and inhomogeneous metamaterials with closed-form constitutive tensors. The designed concentrators are numerically validated by full-wave simulations, which show perfectly directed EM behaviors. As one of the potential applications, we demonstrate a way to amplify plane waves using a rectangular concentrator, which is much more efficient and easier than the existing techniques. Using NURBS expands the generality of the transformation optics and could lead toward making a very general tool that would interface with commercial softwares such as 3D STUDIOMAX and MAYA.
174 citations
TL;DR: In this article, the authors describe the use of finite embedded coordinate transformations to design a medium that can be incorporated into a waveguide bend or corner, rendering the structure reflectionless.
Abstract: Transformation optics is a recently appreciated approach for designing complex electromagnetic media. Here, we describe the extension of transformation optical techniques to include waveguide boundary conditions. We illustrate the use of finite embedded coordinate transformations to design a medium that can be incorporated into a waveguide bend or corner, rendering the structure reflectionless. The expected behavior of the waveguide bends is confirmed with numerical simulations.
142 citations
TL;DR: In this paper, the authors demonstrate fast electrical modulation of freely propagating terahertz waves at room temperature using hybrid metamaterial devices fabricated on doped semiconductor epitaxial layers.
Abstract: We demonstrate fast electrical modulation of freely propagating terahertz waves at room temperature using hybrid metamaterial devices. The devices are planar metamaterials fabricated on doped semiconductor epitaxial layers, which form hybrid metamaterial—Schottky diode structures. With an applied ac voltage bias, we show modulation of terahertz radiation at inferred frequencies over 2MHz. The modulation speed is limited by the device depletion capacitance which may be reduced for even faster operation.
TL;DR: A strong correspondence between measured and simulated difference spectra validates the structural models that link the observed plasmon modulation with DNA nanostructure reconfiguration.
Abstract: Molecular control of plasmon coupling is investigated in sub-100 nm assemblies composed of 13 nm gold “satellite” particles tethered by reconfigurable DNA nanostructures to a 50 nm gold “core” particle. Reconfiguration of the DNA nanostructures from a compact to an extended state results in blue shifting of the assembly plasmon resonance, indicating reduced interparticle coupling and lengthening of the core−satellite tether. Scattering spectra of the core−satellite assemblies before and after reconfiguration are compared with spectra calculated using a structural model that incorporates the core/satellite ratio determined by TEM imaging and estimates of tether length based upon prior measurements of interparticle separation in DNA linked nanoparticle networks. A strong correspondence between measured and simulated difference spectra validates the structural models that link the observed plasmon modulation with DNA nanostructure reconfiguration.
TL;DR: In this paper, an elliptical invisible cloak is proposed using a coordinate transformation in the elliptical-cylindrical coordinate system, which crushes the cloaked object to a line segment instead of a point.
Abstract: An elliptical invisible cloak is proposed using a coordinate transformation in the elliptical-cylindrical coordinate system, which crushes the cloaked object to a line segment instead of a point. The elliptical cloak is reduced to a nearly circular cloak if the elliptical focus becomes very small. The advantage of the proposed invisibility cloak is that none of the parameters is singular and the changing range of all parameters is relatively small.
TL;DR: In this article, an elliptical invisible cloak is proposed using a coordinate transformation in the elliptical-cylindrical coordinate system, which crushes the cloaked object to a line segment instead of a point.
Abstract: An elliptical invisible cloak is proposed using a coordinate transformation in the elliptical-cylindrical coordinate system, which crushes the cloaked object to a line segment instead of a point. The elliptical cloak is reduced to a nearly-circular cloak if the elliptical focus becomes very small. The advantage of the proposed invisibility cloak is that none of the parameters is singular and the changing range of all parameters is relatively small.
TL;DR: The design, fabrication, and measurement of a dual-band planar metamaterial with two distinct electric resonances at 1.0 and 1.2 THz is presented, as a step towards the development of frequency agile or broadband THz materials and devices.
Abstract: We present the design, fabrication, and measurement of a dual-band planar metamaterial with two distinct electric resonances at 1.0 and 1.2 THz, as a step towards the development of frequency agile or broadband THz materials and devices. A method of defining the effective thickness of the metamaterial layer is introduced to simplify the material design and characterization. Good agreement between the simulated and measured transmission is obtained for the fabricated sample by treating the sample as multi-layer system, i. e. the effective metamaterial layer plus the rest of the substrate, as well as properly modeling the loss of the substrate. The methods introduced in this paper can be extended to planar metamaterial structures operating in infrared and optical frequency ranges.
TL;DR: In this article, angle-resolved free-space transmission and reflection measurements of a surface composed of complementary electric inductive-capacitive (CELC) resonators are presented.
Abstract: We present angle-resolved free-space transmission and reflection measurements of a surface composed of complementary electric inductive-capacitive (CELC) resonators. By measuring the reflection and transmission coefficients of a CELC surface with different polarizations and particle orientations, we show that the CELC only responds to in-plane magnetic fields. This confirms the Babinet particle duality between the CELC and its complement, the electric field coupled LC resonator. Characterization of the CELC structure serves to expand the current library of resonant elements metamaterial designers can draw upon to make unique materials and surfaces.
TL;DR: Experimental observations and agreement with numerical results from a linear gyrokinetic stability code support the conjecture that the observed turbulence is driven by the electron-temperature gradient.
Abstract: Measurements with coherent scattering of electromagnetic waves in plasmas of the National Spherical Torus Experiment indicate the existence of turbulent fluctuations in the range of wave numbers ${k}_{\ensuremath{\perp}}{\ensuremath{\rho}}_{e}=0.1--0.4$, corresponding to a turbulence scale length nearly equal to the collisionless skin depth. Experimental observations and agreement with numerical results from a linear gyrokinetic stability code support the conjecture that the observed turbulence is driven by the electron-temperature gradient.
TL;DR: The technique of source transformations are proposed as a powerful approach for antenna design, especially in relation to conformal antennas, using finite-element full-wave simulations.
Abstract: Transformation optics is a recently appreciated methodology for the design of complex media that control the propagation of electromagnetic and other types of waves. The transformation optical technique involves the use of coordinate transformations applied to some region of space, providing a conceptual means to redirect the flow of waves. Successfully designed devices to date have made use of transformations acting on passive space only; however, the technique can also be applied when source distributions (e.g., current and charge) are included within the space being transformed. In this paper we present examples of source transformations that illustrate the potential of these expanded transformation optical methods. In particular, using finite-element full-wave simulations, we confirm the restoration of dipole radiation patterns from both a distorted ‘pin-wheel’ antenna and a bent dipole partially occluded by a cylindrical scatterer. We propose the technique of source transformations as a powerful approach for antenna design, especially in relation to conformal antennas.
TL;DR: A collective scattering system has been installed on the National Spherical Torus Experiment (NSTX) to measure electron gyroscale fluctuations in NSTX plasmas, and initial measurements indicate rich turbulent dynamics on the electron Gyroscale.
Abstract: A collective scattering system has been installed on the National Spherical Torus Experiment (NSTX) to measure electron gyroscale fluctuations in NSTX plasmas Up to five distinct wavenumbers are measured simultaneously, and the large toroidal curvature of NSTX plasmas provides enhanced spatial localization Steerable optics can position the scattering volume throughout the plasma from the magnetic axis to the outboard edge Initial measurements indicate rich turbulent dynamics on the electron gyroscale The system will be a valuable tool for investigating the connection between electron temperature gradient turbulence and electron thermal transport in NSTX plasmas
TL;DR: In this paper, a thin Au stripe embedded in a transparent polymer film was used to characterize long-range surface plasmon waveguide bends at telecom wavelengths (λ=1550 nm).
Abstract: We report on the characterization of long-range surface plasmon waveguide bends at telecom wavelengths (lambda=1550 nm). The structures consist of a thin Au stripe embedded in a transparent polymer film. When the polymer thickness is larger than the lateral extension of the plasmon, the stripe sustains a conventional long-range mode; in the opposite case, the mode is hybrid because its field distribution is confined by total internal reflection in the dielectric cladding. This hybridization increases the damping by absorption but dramatically reduces the radiation loss that occurs for curved geometries, such as bends. Our results are supported quantitatively by full-wave finite-element simulations.
Patent•
06 Feb 2008
TL;DR: In this article, the authors define an electromagnetic distance between first and second locations substantially greater than a physical distance between the first and the second locations, and the first two locations may be occupied by antennas having an inter-structure coupling (such as a near-field coupling) that is a function of the electromagnetic distance.
Abstract: Apparatus, methods, and systems provide electromagnetic compression. In some approaches the electromagnetic compression is achieved with metamaterials. In some approaches the electromagnetic compression defines an electromagnetic distance between first and second locations substantially greater than a physical distance between the first and second locations, and the first and second locations may be occupied by first and second structures (such as antennas) having an inter-structure coupling (such as a near-field coupling) that is a function of the electromagnetic distance. In some approaches the electromagnetic compression reduces the spatial extent of an antenna near field.
Patent•
22 Sep 2008
TL;DR: In this article, a wide angle impedance match (WAIM) layer of material disposed over the plurality of aperture antenna elements formed in the sheet of conductive material is used to minimize return loss and optimize an impedance match between the phased array antenna system and free space to permit scanning of the antenna system up to a predetermined angle in elevation.
Abstract: A phased array antenna system may include a sheet of conductive material with a plurality of aperture antenna elements formed in the sheet of conductive material. Each of the plurality of aperture antenna elements is capable of sending and receiving electromagnetic energy. The phased array antenna system may also include a wide angle impedance match (WAIM) layer of material disposed over the plurality of aperture antenna elements formed in the sheet of conductive material. The WAIM layer of material includes a plurality of metamaterial particles. The plurality of metamaterial particles are selected and arranged to minimize return loss and to optimize an impedance match between the phased array antenna system and free space to permit scanning of the phased array antenna system up to a predetermined angle in elevation.
Patent•
21 Oct 2008
TL;DR: In this paper, the authors provide an overview of methods and systems for both emitting and negatively-refractive focusing of electromagnetic energy, where the transformation medium may include an artificially-structured material such as a metamaterial.
Abstract: Apparatus, methods, and systems provide emitting and negatively-refractive focusing of electromagnetic energy. In some approaches the negatively-refractive focusing includes negatively-refractive focusing from an interior field region with an axial magnification substantially less than one. In some approaches the negatively-refractive focusing includes negatively-refractive focusing with a transformation medium, where the transformation medium may include an artificially-structured material such as a metamaterial.
TL;DR: In this paper, a two-dimensional partial focusing within a planar waveguide using complementary indefinite metamaterials was realized using complementary electric resonator (CELC) structures.
Abstract: We have experimentally realized a two-dimensional partial focusing within a planar waveguide using complementary indefinite metamaterials. When the electric fields emitted from the dipole are TE polarized, the focusing condition requires negative magnetic response in the propagation direction of the waveguide, which can be achieved by the complementary electric resonator (CELC) structures. We have carefully designed the experimental configurations and the dimensions for the CELC structures. The experimental result is consistent with the theoretical prediction, which validates the partial focusing phenomenon.
Patent•
30 Jul 2008
TL;DR: In this article, the authors provide a focus adjustment approach using a transformation medium, where the transformation medium may include an artificially-structured material, such as a metamaterial.
Abstract: Apparatus, methods, and systems provide focusing, focus-adjusting, and sensing. In some approaches the focus-adjusting includes providing an extended depth of focus greater than a nominal depth of focus. In some approaches the focus-adjusting includes focus-adjusting with a transformation medium, where the transformation medium may include an artificially-structured material such as a metamaterial.
30 Sep 2008
TL;DR: In this article, a modification of the synthetic-plane-wave-based holographic technique for determining radiation patterns and aperture fields of medium-gain horn antennas is proposed, based on using both the sum and difference of the near field and reference signals to form the hologram via simple low-cost amplitude-only near field measurements.
Abstract: A modification of the synthetic-plane-wave-based holographic technique for determining radiation patterns and aperture fields of medium-gain horn antennas is proposed. The modification is based on using both the sum and difference of the near field and reference signals to form the hologram via simple low-cost amplitude-only near field measurements. This approach when compared to the previous version, where only the sum signal is used, allows increased sample spacing, and also provides an improvement in quality of the final results. The effectiveness of the modified technique is confirmed by both calculated and measured results obtained for pyramidal and conical horn antennas at 10 GHz frequency.
Patent•
05 Sep 2008
TL;DR: In this article, the authors provide an extended depth of field greater than a nominal depth of fields, where the transformation medium may include an artificially-structured material such as a metamaterial.
Abstract: Apparatus, methods, and systems provide emitting, field-adjusting, and focusing of electromagnetic energy. In some approaches the field-adjusting includes providing an extended depth of field greater than a nominal depth of field. In some approaches the field-adjusting includes field-adjusting with a transformation medium, where the transformation medium may include an artificially-structured material such as a metamaterial.
TL;DR: In this paper, the authors focus on cloaking and transformation optics for the full dielectric electromagnetic cloak and metal-dielectric planar hyperlens for cloaking with canonical spiral inclusions, and the potentials of multi-layered plasmonic covers for multi-frequency cloaking.
Abstract: 'Any sufficiently advanced technology is indistinguishable from magic', as the late Arthur C Clarke wrote So what does it take to do magic by technology? Transformation optics has developed some tantalizing ideas and the first practical demonstrations of 'pure and applied magic' Transformation optics gathers an unusual mix of scientists, ranging from practically-minded engineers to imaginative theoretical physicists and mathematicians or hybrids of all three The engineers have been developing new materials with extraordinary electromagnetic properties, from materials for microwaves, to be used in radar or wireless technology, to materials for terahertz radiation and visible light These materials typically are composites—they consist of artificial structures much smaller than the wavelength that act like man-made atoms, apart being much larger in size The properties of these artificial atoms depend on their shapes and sizes and so they are tunable, in contrast to most real atoms or molecules This degree of control is what makes these materials—called metamaterials—so interesting Such new-won freedom invites the other side of the spectrum of scientists, the theorists, to dream Just imagine there are no practical limits on electromagnetic materials—what could we do with them? One exciting application of metamaterials has been Veselago's idea of negative refraction, dating back to the 1960s Metamaterials have breathed life into Veselago's idea, culminating in recent optical demonstrations (see for example [1,2]) Another application is cloaking, developing ideas and first experimental demonstrations for invisibility devices [3] It turns out that both negative refraction and cloaking are examples where materials seem to transform the geometry of space Any optical material appears to change light's perception of space, as countless optical illusions prove, but the materials of transformation optics act in more specific ways: they appear to perform coordinate transformations If the coordinates they conjure up run backwards one gets negative refraction, if they exclude some region of space one makes anything inside invisible [4] In physics, general relativity has honed the theoretical tools for understanding curved space and curved-coordinate transformations In transformation optics, general relativity has become a theoretical tool for solving practical engineering problems [4] What an unorthodox connection! This focus issue represents a snapshot of this rapidly developing research area It is not restricted to optics or electromagnetism, though Metamaterials for acoustics also exist and can be applied in ways similar to optical metamaterials So transformation optics not only attracts an unusual mix of scientists, but also spans a range of applications in optics and beyond Transformation optics has the potential to transform optics, for example by visualizing invisibility and making materials beyond materials—metamaterials But before we transgress the boundaries to the hermeneutics of transformation optics [5], let the papers speak for themselves References [1] Yao J, Liu Z, Liu Y, Wang Y, Sun C, Bartal G, Stacy A M and Zhang X 2008 Science 321 930 [2] Valentine J, Zhang S, Zentgraf T, Ulin-Avila E, Genov D A, Bartal G and Zhang X 2008 Nature 455 376 [3] Schurig D, Mock J J, Justice B J, Cummer S A, Pendry J B, Starr A F and Smith D R 2006 Science 314 977 [4] Leonhardt U and Philbin T G 2006 New J Phys 8 247 [5] Sokal A D 1996 Social Text 14(46/47) 217 Focus on Cloaking and Transformation Optics Contents Transformation optics for the full dielectric electromagnetic cloak and metal–dielectric planar hyperlens D P Gaillot, C Croenne, F Zhang and D Lippens Transmutation of singularities in optical instruments Tomas Tyc and Ulf Leonhardt Electromagnetic cloaking with canonical spiral inclusions K Guven, E Saenz, R Gonzalo, E Ozbay and S Tretyakov Theory and potentials of multi-layered plasmonic covers for multi-frequency cloaking Andrea Alu and Nader Engheta Electromagnetic cloaking devices for TE and TM polarizations Filiberto Bilotti, Simone Tricarico and Lucio Vegni An aberration-free lens with zero F-number D Schurig Transformational optics of plasmonic metamaterials I I Smolyaninov An acoustic metafluid: realizing a broadband acoustic cloak J B Pendry and Jensen Li On the possibility of metamaterial properties in spin plasmas G Brodin and M Marklund A homogenization route towards square cylindrical acoustic cloaks Mohamed Farhat, Sebastien Guenneau, Stefan Enoch, Alexander Movchan, Frederic Zolla and Andre Nicolet Transformation optics: approaching broadband electromagnetic cloaking A V Kildishev, W Cai, U K Chettiar and V M Shalaev Generalized field-transforming metamaterials Sergei A Tretyakov, Igor S Nefedov and Pekka Alitalo Electromagnetic beam modulation through transformation optical structures Xiaofei Xu, Yijun Feng and Tian Jiang Superantenna made of transformation media Ulf Leonhardt and Tomas Tyc Material parameters and vector scaling in transformation acoustics Steven A Cummer, Marco Rahm and David Schurig Isotropic transformation optics: approximate acoustic and quantum cloaking Allan Greenleaf, Yaroslav Kurylev, Matti Lassas and Gunther Uhlmann Transformation optical designs for wave collimators, flat lenses and right-angle bends Do-Hoon Kwon and Douglas H Werner Alternative derivation of electromagnetic cloaks and concentrators A D Yaghjian and S Maci Solutions in folded geometries, and associated cloaking due to anomalous resonance Graeme W Milton, Nicolae-Alexandru P Nicorovici, Ross C McPhedran, Kirill Cherednichenko and Zubin Jacob Finite wavelength cloaking by plasmonic resonance N-A P Nicorovici, R C McPhedran, S Enoch and G Tayeb
Patent•
29 Sep 2008
TL;DR: In this article, the authors present a system for negatively-refractive focusing and sensing of electromagnetic energy, which includes an interior focusing region with an axial magnification substantially greater than one.
Abstract: Apparatus, methods, and systems provide negatively-refractive focusing and sensing of electromagnetic energy. In some approaches the negatively-refractive focusing includes providing an interior focusing region with an axial magnification substantially greater than one. In some approaches the negatively-refractive focusing includes negatively-refractive focusing with a transformation medium, where the transformation medium may include an artificially-structured material such as a metamaterial.
TL;DR: A new real time trajectory generator that provides improved performance over previous implementations and provides not only the desired position over the interval, but also the velocity and acceleration, permitting their use in feedforward control to improve the tracking accuracy at all points on the path.
Abstract: For any telescope, a fundamental performance requirement is the acquisition and tracking of the source
While this depends on many factors, the system accuracy is fundamentally limited by the servo tracking performance
on the encoders This tracking performance must be balanced with the need for large slewing motions
to new sources While the classical rate loop and position loop model permits basic operation, there has been
increasing use through the years of gain scheduling or command pre-processors to improve telescope path planning
and enable better performance This is particularly important for telescopes that employ scanning or fast
switching motions
As telescope control systems have moved to fully digital systems running at high update rates, more sophisticated
approaches have become possible for telescope path planning Taking advantage of the speed of available
computation, we have developed a new real time trajectory generator that provides improved performance over
previous implementations Given a position command, the system generates a path to the desired end point
The resulting path is guaranteed to be continuous in position, velocity, and acceleration, as well as to respect
specified limits in velocity, acceleration, and jerk Significantly, the calculation provides not only the desired
position over the interval, but also the velocity and acceleration, permitting their use in feedforward control to
improve the tracking accuracy at all points on the path The algorithm is presented, as well as some results with
the system implemented on a real telescope