Showing papers by "David R. Smith published in 2006"
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.
7,811 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.
6,830 citations
TL;DR: Full electromagnetic simulations of the cylindrical version of this cloaking structure are reported, using ideal and nonideal electromagnetic parameters that show that the low-reflection and power-flow bending properties of the electromagnetic cloaky structure are not especially sensitive to modest permittivity and permeability variations.
Abstract: Pendry et al. have reported electromagnetically anisotropic and inhomogeneous shells that, in theory, completely shield an interior structure of arbitrary size from electromagnetic fields without perturbing the external fields. Neither the coordinate transformation-based analytical formulation nor the supporting ray-tracing simulation indicate how material perturbations and full-wave effects might affect the solution. We report fully electromagnetic simulations of the cylindrical version of this cloaking structure using ideal and nonideal (but physically realizable) electromagnetic parameters that show that the low-reflection and power-flow bending properties of the electromagnetic cloaking structure are not especially sensitive to modest permittivity and permeability variations. The cloaking performance degrades smoothly with increasing loss, and effective low-reflection shielding can be achieved with a cylindrical shell composed of an eight- (homogeneous) layer approximation of the ideal continuous medium. An imperfect but simpler version of the cloaking material is derived and is shown to reproduce the ray bending of the ideal material in a manner that may be easier to experimentally realize.
796 citations
TL;DR: In this article, a lithographically patterned inductive-capacitive resonator is described that has a strong electric response and can be used to construct metamaterials with desired positive or negative permittivity.
Abstract: A lithographically patterned inductive-capacitive resonator is described that has a strong electric response. This resonator can be used to construct metamaterials with desired positive or negative permittivity. Such materials provide an alternative to wire media, and have the benefit of not requiring continuous current paths between unit cells. A planar medium composed of these resonators was simulated, fabricated, and measured in the microwave frequency range.
756 citations
TL;DR: The calculation of material properties for coordinate transformations that describe spaces with spherical or cylindrical holes in them can then implement invisibility cloaks in flat space and a method is described for performing geometric ray tracing in these materials.
Abstract: 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
741 citations
TL;DR: In this paper, the authors present a homogenization technique in which macroscopic fields are determined via averaging the local fields obtained from a full-wave electromagnetic simulation or analytical calculation.
Abstract: Over the past several years, metamaterials have been introduced and rapidly been adopted as a means of achieving unique electromagnetic material response. In metamaterials, artificially structured—often periodically positioned—inclusions replace the atoms and molecules of conventional materials. The scale of these inclusions is smaller than that of the electromagnetic wavelength of interest, so that a homogenized description applies. We present a homogenization technique in which macroscopic fields are determined via averaging the local fields obtained from a full-wave electromagnetic simulation or analytical calculation. The field-averaging method can be applied to homogenize any periodic structure with unit cells having inclusions of arbitrary geometry and material. By analyzing the dispersion diagrams and retrieved parameters found by field averaging, we review the properties of several basic metamaterial structures. © 2006 Optical Society of America OCIS codes: 160.0160, 160.1190, 260.2110, 350.5500.
581 citations
TL;DR: In this article, a negative refractive index property is found in metamaterials that exhibit exotic and unique electromagnetic properties not inherent in the individual constituent components. But, the negative index is not found in any known naturally occurring material.
363 citations
TL;DR: In this paper, a radial gradient-index lens with an index of refraction ranging from −2.67 (edge) to −0.97 (center) was presented.
Abstract: Metamaterial structures designed to have simultaneously negative permittivity and permeability are known as left-handed materials. Their complexity and our understanding of their properties have advanced rapidly to the point where direct applications are now viable. We present a radial gradient-index lens with an index of refraction ranging from −2.67 (edge) to −0.97 (center). Experimentally, we find that the lens can produce field intensities at the focus that are greater than that of the incident plane wave. These results are obtained at 10.3GHz and in excellent agreement with full-wave simulations. We also demonstrate an advanced fabrication technique using conventional printed circuit board technology which offers significant design, mechanical, and cost advantages over other microwave lens constructions.
123 citations
TL;DR: From the measured mappings of the electric field, the interplay between the microstructure of the metamaterial lattice and the macroscopic averaged response is revealed and the mapped phase fronts within a meetingamaterial having a negative refractive index are consistent with a Macroscopic phase-in accordance with the effective medium predictions.
Abstract: We perform an experimental study of the phase and amplitude of microwaves interacting with and scattered by two-dimensional negative index metamaterials. The measurements are performed in a parallel plate waveguide apparatus at X-band frequencies (8–12 GHz), thus constraining the electromagnetic fields to two dimensions. A detection antenna is fixed to one of the plates, while a second plate with a fixed source antenna or waveguide is translated relative to the first plate. The detection antenna is inserted into, but not protruding below, the stationary plate so that fields internal to the metamaterial samples can be mapped. From the measured mappings of the electric field, the interplay between the microstructure of the metamaterial lattice and the macroscopic averaged response is revealed. For example, the mapped phase fronts within a metamaterial having a negative refractive index are consistent with a macroscopic phase—in accordance with the effective medium predictions—which travels in a direction opposite to the direction of propagation. The field maps are in excellent agreement with finite element numerical simulations performed assuming homogeneous metamaterial structures.
116 citations
TL;DR: In this paper, a method of directly calculating the magnetoelectric coupling terms using averages over the fields computed from full-wave finite-element based numerical simulations is presented, and the predicted bianisotropy of a fabricated SRR medium is confirmed by measuring the cross polarization of a microwave beam transmitted through the sample.
Abstract: A medium that exhibits artificial magnetism can be formed by assembling an array of split ring resonators SRRs—planar conducting elements that exhibit a resonant response to electromagnetic radiation. The SRR exhibits a large magnetic dipole moment when excited by a magnetic field directed along its axis. However, the SRR also exhibits an electric response that can be quite large depending on the symmetry of the SRR and the orientation of the SRR with respect to the electric component of the field. So, while the SRR medium can be considered as having a predominantly magnetic response for certain orientations with respect to the incident wave, it is generally the case that the SRR exhibits magnetoelectric coupling, and hence a medium of SRRs arranged so as to break mirror symmetry about one of the axes will exhibit bianisotropy. We present here a method of directly calculating the magnetoelectric coupling terms using averages over the fields computed from full-wave finite-element based numerical simulations. We confirm the predicted bianisotropy of a fabricated SRR medium by measuring the cross polarization of a microwave beam transmitted through the sample. We also demonstrate that the magnetoelectric coupling that gives rise to the bianisotropic response is suppressed by symmetrizing the SRR composite structure and provide measurements comparing the cross polarization of the symmetric and asymmetric structures. © 2006 American Institute of Physics. DOI: 10.1063/1.2218033
98 citations
TL;DR: The development of a superlens that would allow imaging of details finer than the wavelength of light used, which constrains the performance of all positive-index optical elements, is explored.
Abstract: This article explores the development of a superlens that would allow imaging of details finer than the wavelength of light used. Materials made out of carefully fashioned microscopic structures can have electromagnetic properties including a negative index of refraction, which means they refract light in a totally new way. A slab of negative-index material could act as a superlens, able to outperform today's lenses, which have a positive index. Such a superlens could create images that include detail finer than that allowed by the diffraction limit, which constrains the performance of all positive-index optical elements. Although most experiments with metamaterials are performed with microwaves, they might use shorter infrared and optical wavelengths in the future.
TL;DR: This work's computational method is based on analyzing the eigenfrequencies corresponding to the wave equation subject to a mixture of periodic, electric and magnetic boundary conditions and demonstrates the accuracy of this approach through comparisons with previously reported simulations based on the semi-analytical method-of-lines.
Abstract: We present simulations of plasmonic transmission lines consisting of planar metal strips embedded in isotropic dielectric media, with a particular emphasis on the long-range surface plasmon polariton (SPP) modes that can be supported in such structures. Our computational method is based on analyzing the eigenfrequencies corresponding to the wave equation subject to a mixture of periodic, electric and magnetic boundary conditions. We demonstrate the accuracy of our approach through comparisons with previously reported simulations based on the semi-analytical method-of-lines. We apply our method to study a variety of aspects of long-range SPPs, including tradeoffs between mode confinement and propagation distance, the modeling of bent waveguides and the effect of disorder and periodicity on the long-ranging modes.
TL;DR: In this article, the authors review both the theoretical electromagnetic response and the spectroscopic measurements of metamaterials and discuss the complexity of extracting the optical constants from experimental observables.
Abstract: We review both the theoretical electromagnetic response and the spectroscopic measurements of metamaterials. To critically examine published results for metamaterial structures operating in the range from terahertz to optical frequencies, we focus on protocols allowing one to extract the optical constants from experimental observables. We discuss the complexity of this task when applied to metamaterials exhibiting electric, magnetic, and magneto-optical response. The general theory of the electromagnetic response of such systems is presented and methods are described. Finally, we briefly overview possible solutions for implementing metamaterials with tunable resonant behavior. © 2006 Optical Society of America OCIS codes: 160.3820, 300.6270, 120.2130, 160.4760.
TL;DR: In this article, a radial gradient-index (GRIN) lens with an index-of-refraction ranging from -2.67 to -0.97 was presented.
Abstract: Metamaterial structures designed to have simultaneously negative permittivity and permeability are known as left-handed materials. Their complexity and our understanding of their properties have advanced rapidly to the point where direct applications are now viable. We present a radial gradient-index (GRIN) lens with an index-of-refraction ranging from -2.67(edge) to -0.97(center). Experimentally, we find the lens can produce field intensities at the focus that are greater than that of the incident plane wave. These results are obtained at 10.45 GHz and in excellent agreement with full-wave simulations. This lens is a demonstrate an newly pioneered advanced fabrication technique using conventional printed circuit board (PCB) technology which offers significant design, mechanical, and cost advantages over other microwave lens constructions.
TL;DR: The National Spherical Torus Experiment (NSTX) has explored the effects of shaping on plasma performance as determined by many diverse topics including the stability of global magnetohydrodynamic (MHD) modes (e.g., ideal external kinks and resistive wall modes), edge localized modes (ELMs), bootstrap current drive, divertor flux expansion, and heat transport.
Abstract: The National Spherical Torus Experiment (NSTX) has explored the effects of shaping on plasma performance as determined by many diverse topics including the stability of global magnetohydrodynamic (MHD) modes (e.g., ideal external kinks and resistive wall modes), edge localized modes (ELMs), bootstrap current drive, divertor flux expansion, and heat transport. Improved shaping capability has been crucial to achieving βt∼40%. Precise plasma shape control has been achieved on NSTX using real-time equilibrium reconstruction. NSTX has simultaneously achieved elongation κ∼2.8 and triangularity δ∼0.8. Ideal MHD theory predicts increased stability at high values of shaping factor S≡q95Ip∕(aBt), which has been observed at large values of the S∼37[MA∕(m∙T)] on NSTX. The behavior of ELMs is observed to depend on plasma shape. A description of the ELM regimes attained as shape is varied will be presented. Increased shaping is predicted to increase the bootstrap fraction at fixed Ip. The achievement of strong shaping ...
TL;DR: The results show that the recent use of reflectance measurements to characterize planar split ring resonator samples can reveal the presence of circulating currents in a sample--the precursor to artificial magnetism--but are insufficient to provide quantitative results unless the symmetry of the underlying metamaterial elements is carefully specified.
Abstract: We explore the electromagnetic characterization of a planar artificial magnetic metamaterial. Because the composite structure is two- rather than three-dimensional, it does not form a medium with assignable bulk properties, such as the electric permittivity and magnetic permeability. However, we find that it is possible to characterize the expected bulk response of a structure composed of repeated layers of metamaterial planes, from a reflectance measurement of a single metamaterial surface made at an oblique angle. We present an analytical theory that relates the reflectance of a single plane to the expected bulk permeability and permeability of the composite, as well as supporting experiments and numerical simulations. Our results show that the recent use of reflectance measurements to characterize planar split ring resonator samples can reveal the presence of circulating currents in a sample--the precursor to artificial magnetism--but are insufficient to provide quantitative results unless the symmetry of the underlying metamaterial elements is carefully specified.
TL;DR: In this paper, the authors described the irradiation of 95 electron multiplication charge coupled devices (EMCCDs) at the Paul Scherrer Institut (PSI) in Switzerland, to investigate the effects of proton irradiation on the operational characteristics of CCDs featuring electron multiplication technology for space use.
Abstract: This paper describes the irradiation of 95 electron multiplication charge coupled devices (EMCCDs) at the Paul Scherrer Institut (PSI) in Switzerland, to investigate the effects of proton irradiation on the operational characteristics of CCDs featuring electron multiplication technology for space use. This work was carried out in support of the CCD development for the radial velocity spectrometer (RVS) instrument of the European Space Agency's cornerstone Gaia mission. Previous proton irradiations of EMCCDs, have shown the technology to be radiation hard to /spl sim/10/spl times/ the required six-year Gaia lifetime proton fluence, with no device failures or unexpected operational changes. The purpose of the study described in this paper was to further investigate the statistical probability of device failure as a result of radiation damage, the large number of devices and high proton fluence used, making the study equivalent to testing /spl sim/50 complete RVS CCD focal planes to the expected end of life proton dose. An outline of the earlier EMCCD proton irradiations is given, followed by a detailed description of the proton irradiation and characterization of the 95 devices used in this latest study.
01 Sep 2006
TL;DR: A novel microwave imaging approach for early stage breast cancer detection that involves the use of an Indirect Microwave Holographic technique employing a patented synthetic reference wave and results using a simulated phantom are described.
Abstract: A novel microwave imaging approach for early stage breast cancer detection is described. The proposed technique involves the use of an Indirect Microwave Holographic technique employing a patented synthetic reference wave. This approach offers benefits in terms of simplicity, expense, comfort and safety when compared to current mammography techniques. Experimental results using a simulated phantom are included to demonstrate the validity of this technique.
Princeton Plasma Physics Laboratory1, Columbia University2, University of California, San Diego3, Oak Ridge National Laboratory4, KAIST5, University of California, Los Angeles6, Johns Hopkins University7, General Atomics8, European Atomic Energy Community9, CompX International Inc.10, University of California, Irvine11, University of Washington12, University of California, Davis13, Princeton University14, University of Colorado Boulder15, Hiroshima University16, Massachusetts Institute of Technology17, Lawrence Livermore National Laboratory18, University of Tokyo19, University of Rochester20
TL;DR: In this article, the authors showed that a discharge with a plasma current of 1 MA has been sustained for 1 s (0.8 s current flat top) in a spherical torus.
Abstract: In order to reduce recirculating power fraction to acceptable levels, the spherical torus concept relies on the simultaneous achievement of high toroidal β and high bootstrap fraction in steady state. In the last year, as a result of plasma control system improvements, the achievable plasma elongation on NSTX has been raised from K ∼ 2.1 to K ∼ 2.6-approximately a 25% increase. This increase in elongation has led to a substantial increase in the toroidal β for long pulse discharges. The increase in β is associated with an increase in plasma current at nearly fixed poloidal β, which enables higher β t with nearly constant bootstrap fraction. As a result, for the first time in a spherical torus, a discharge with a plasma current of 1 MA has been sustained for 1 s (0.8 s current flat-top). Data are presented from NSTX correlating the increase in performance with increased plasma shaping capability. In addition to improved shaping, H-modes induced during the current ramp phase of the plasma discharge have been used to reduce flux consumption and to delay the onset of MHD instabilities. Based on these results, a modelled integrated scenario, which has 100% non-inductive current drive with very high toroidal β, will also be discussed. The NSTX poloidal field coils are currently being modified to produce the plasma shape which is required for this scenario, which requires high triangularity (δ ∼ 0.8) at elevated elongation (K ∼ 2.5). The other main requirement of steady state on NSTX is the ability to drive a fraction of the total plasma current with RF waves. The results of high harmonic fast wave heating and current drive studies as well as electron Bernstein wave emission studies will be presented.
TL;DR: In this article, the authors describe a qualification program for Electron-Multiplication Charge Coupled Devices (EMCCDs) for use in space applications, which was carried out in the context of CCD development for the Radial Velocity Spectrometer (RVS) instrument on the European Space Agency's cornerstone Gaia mission.
Abstract: This paper describes a qualification programme for Electron-Multiplication Charge Coupled Devices (EMCCDs) for use in space applications. While the presented results are generally applicable, the programme was carried out in the context of CCD development for the Radial Velocity Spectrometer (RVS) instrument on the European Space Agency's cornerstone Gaia mission. We discuss the issues of device radiation tolerance, charge transfer efficiency at low signal levels and life time effects on the electron-multiplication gain. The development of EMCCD technology to allow operation at longer wavelengths using high resistivity silicon, and the cryogenic characterisation of EMCCDs are also described.
01 Sep 2006
TL;DR: This work describes how the indirect holographic approach can be used to reconstruct 3D images of objects from a single scalar 2D holographic intensity pattern.
Abstract: The use of microwaves for imaging applications is currently of much research interest particularly in the areas of security imaging and medical imaging. Microwaves have been shown to be able to image objects concealed beneath clothing and recent research work has indicated that microwaves could offer a new low cost non-ionising technique for the detection and imaging of breast cancer tumours. Traditional intensity only measurements have only been able to provide 2D images of objects. This work will describe how our indirect holographic approach can be used to reconstruct 3D images of objects from a single scalar 2D holographic intensity pattern.
Journal Article•
TL;DR: In this paper, a radial gradient-index (GRIN) lens with an index-of-refraction ranging from -2.67 to -0.97 was presented.
Abstract: Metamaterial structures designed to have simultaneously negative permittivity and permeability are known as left-handed materials. Their complexity and our understanding of their properties have advanced rapidly to the point where direct applications are now viable. We present a radial gradient-index (GRIN) lens with an index-of-refraction ranging from -2.67(edge) to -0.97(center). Experimentally, we find the lens can produce field intensities at the focus that are greater than that of the incident plane wave. These results are obtained at 10.45 GHz and in excellent agreement with full-wave simulations. This lens is a demonstrate an newly pioneered advanced fabrication technique using conventional printed circuit board (PCB) technology which offers significant design, mechanical, and cost advantages over other microwave lens constructions.
01 Oct 2006
TL;DR: In this article, split ring resonator arrays have been fabricated to demonstrate magnetic resonance in the terahertz regime, and Spectroscopic transmission measurements as a function of oblique angle enable quantitative values of the permeability to be calculated.
Abstract: Split ring resonator arrays have been fabricated to demonstrate magnetic resonance in the terahertz regime. Spectroscopic transmission measurements as a function of oblique angle enable quantitative values of the permeability to be calculated
TL;DR: In this article, the authors describe the development, operation, and characterization of charge-coupled devices (CCDs) that feature an electrode structure that allows the transfer of charge both horizontally and vertically through the image area.
Abstract: This paper describes the development, operation, and characterization of charge-coupled devices (CCDs) that feature an electrode structure that allows the transfer of charge both horizontally and vertically through the image area. Such devices have been termed two-dimensional (2-D) transfer CCDs (2DT CCDs), as opposed to the conventional devices, which might be called one-dimensional transfer CCDs, but in other respects are the same as conventional CCD devices. Batches of two different 2DT CCD test devices, featuring different electrode structures but with identical clocking operation in each case, were produced and tested. The methodology of 2-D charge transfer in each of the device types is described, followed by a presentation of test results from the new CCDs. The ability of both 2DT CCD transfer electrode schemes to successfully transfer charge in both horizontal and vertical directions in the image section of the devices has been proven, opening up potential new applications for 2DT CCD use
TL;DR: In this article, the azimuth track for the Large Millimeter-wave Telescope (LMT/GTM) is described, together with lessons learned during the installation, welding, and initial use of the track.
Abstract: In the design of high precision wheel-on-track systems for large telescopes, the azimuth track presents
a significant challenge. Generally, the track must be aligned very accurately to provide good pointing
performance and must have high hardness to withstand the contact stresses. It is also advantageous, in
terms of both performance and stress, to have a continuous rolling surface with no gaps. Such a surface can
be achieved by using a welded track, but it is challenging to maintain alignment and surface hardness during
the welding process. For future designs, it is useful to understand what practical limits have been reached
during previous installations. The azimuth track for the Large Millimeter-wave Telescope (LMT/GTM)
serves as an excellent example of this type of system. It is 39.6m diameter and has been installed, aligned,
and welded on site. As of early 2005, it has been supporting the weight of the alidade, and some initial
rotations of the structure have taken place. The achieved alignment accuracy and hardness performance are
presented, together with lessons learned during the installation, welding, and initial use of the track.
05 Oct 2006
TL;DR: The National Spherical Torus Experiment (NSTX) has made considerable progress in advancing the scientific understanding of high performance long-pulse plasmas needed for ITER and future low-aspect-ratio Spherical torus (ST) devices as mentioned in this paper.
Abstract: The National Spherical Torus Experiment (NSTX) has made considerable progress in advancing the scientific understanding of high performance long-pulse plasmas needed for ITER and future low-aspect-ratio Spherical Torus (ST) devices. Plasma durations up to 1.6s (5 current redistribution times) have been achieved at plasma currents of 0.7 MA with non-inductive current fractions above 65% while achieving {beta}{sub T} and {beta}{sub N} values of 16% and 5.7 (%mT/MA), respectively. Newly available Motional Stark Effect data has allowed systematic study and validation of current drive sources and improved the understanding of ''hybrid''-like scenarios. In MHD research, six mid-plane ex-vessel radial field coils have been utilized to infer and correct intrinsic error fields, provide rotation control, and actively stabilize the n=1 resistive wall mode at ITER-relevant low plasma rotation values. In transport and turbulence, the low aspect ratio and wide range of achievable {beta} in NSTX provide unique data for confinement scaling studies. A new high-k scattering diagnostic is investigating turbulent density fluctuations with wavenumbers extending from ion to electron gyro-scales. In the area of energetic particle research, cyclic neutron rate drops have been associated with the destabilization of multiple large Toroidal Alfven Eigenmodes (TAEs) similar to the ''sea-of-TAE'' modes predicted for ITER.more » Three wave coupling processes between energetic particle modes and TAEs have also been observed for the first time. In boundary physics, advanced shape control has been utilized to study the role of magnetic balance in H-mode access and ELM stability. Peak divertor heat flux has been reduced by a factor of 5 using an H-mode compatible radiative divertor, and Lithium conditioning has demonstrated particle pumping and improved thermal confinement. Finally, non-solenoidal plasma start-up research is particularly important for the ST, and Coaxial Helicity Injection has now produced 160kA plasma currents on closed magnetic flux surfaces.« less
TL;DR: In this article, the authors present simulations of plasmonic transmission lines consisting of metal strips embedded in dielectric media, based on calculating the eigenmodes using a finite-element method.
Abstract: We present simulations of plasmonic transmission lines consisting of metal strips embedded in dielectric media. Our numerical method is based on calculating the eigenmodes using a finite-element method as will be illustrated by several examples.