Showing papers by "David R. Smith published in 2010"
TL;DR: It is demonstrated how powerful emerging techniques in the field of transformation optics can be used to harness the flexibility of gradient index materials for imaging applications to achieve a new class of optical devices.
Abstract: One of the more promising uses of metamaterials is in imaging, where the capability to control the propagation of light could lead to new applications. In particular, the realization of a broadband metamaterial lens that has an almost complete hemispherical field of view that is focused on a flat plane represents a significant step towards such new uses.
613 citations
TL;DR: Simulations using a three-dimensional finite element model and measurements from single NPs confirm that the gaps formed by this process, between the NP and the gold film, are highly reproducible transducers of surface-enhanced resonant Raman scattering.
Abstract: The strongly enhanced and localized optical fields that occur within the gaps between metallic nanostructures can be leveraged for a wide range of functionality in nanophotonic and optical metamaterial applications. Here, we introduce a means of precise control over these nanoscale gaps through the application of a molecular spacer layer that is self-assembled onto a gold film, upon which gold nanoparticles (NPs) are deposited electrostatically. Simulations using a three-dimensional finite element model and measurements from single NPs confirm that the gaps formed by this process, between the NP and the gold film, are highly reproducible transducers of surface-enhanced resonant Raman scattering. With a spacer layer of roughly 1.6 nm, all NPs exhibit a strong Raman signal that decays rapidly as the spacer layer is increased.
152 citations
TL;DR: It is concluded that the design of metamaterials with tailored simultaneous electric and magnetic response-such as negative index materials-will generally be complicated by potentially unwanted magnetoelectric coupling.
Abstract: Electromagnetic metamaterials are artificially structured media typically composed of arrays of resonant electromagnetic circuits, the dimension and spacing of which are considerably smaller than the free-space wavelengths of operation. The constitutive parameters for metamaterials, which can be obtained using full-wave simulations in conjunction with numerical retrieval algorithms, exhibit artifacts related to the finite size of the metamaterial cell relative to the wavelength. Liu [R. Liu, T. J. Cui, D. Huang, B. Zhao, and D. R. Smith, Phys. Rev. E 76, 026606 (2007)] showed that the complicated, frequency-dependent forms of the constitutive parameters can be described by a set of relatively simple analytical expressions. These expressions provide useful insight and can serve as the basis for more intelligent interpolation or optimization schemes. Here, we show that the same analytical expressions can be obtained using a transfer-matrix formalism applied to a one-dimensional periodic array of thin, resonant, dielectric, or magnetic sheets. The transfer-matrix formalism breaks down, however, when both electric and magnetic responses are present in the same unit cell, as it neglects the magnetoelectric coupling between unit cells [C. R. Simovski, Metamaterials 1, 62 (2007)]. We show that an alternative analytical approach based on the same physical model must be applied for such structures. Furthermore, in addition to the intercell coupling, electric and magnetic resonators within a unit cell may also exhibit magnetoelectric coupling. For such cells, we find an analytical expression for the effective index, which displays markedly characteristic dispersion features that depend on the strength of the coupling coefficient. We illustrate the applicability of the derived expressions by comparing to full-wave simulations on magnetoelectric unit cells. We conclude that the design of metamaterials with tailored simultaneous electric and magnetic response-such as negative index materials-will generally be complicated by potentially unwanted magnetoelectric coupling.
101 citations
TL;DR: The generalized quasiconformal TO (QCTO) approach enables the design of media that can, in principle, be broadband and low loss, while controlling the propagation of waves with arbitrary angles of incidence and polarization.
Abstract: We introduce an approach to the design of three-dimensional transformation optical (TO) media based on a generalized quasiconformal mapping approach. The generalized quasiconformal TO (QCTO) approach enables the design of media that can, in principle, be broadband and low loss, while controlling the propagation of waves with arbitrary angles of incidence and polarization. We illustrate the method in the design of a three-dimensional carpet ground plane cloak and of a flattened Luneburg lens. Ray-trace studies provide a confirmation of the performance of the QCTO media, while also revealing the limited performance of index-only versions of these devices.
98 citations
TL;DR: In this paper, the authors derived the expressions for the effective nonlinear susceptibilities of a metacrystal formed from resonant elements that couple strongly to the magnetic field and experimentally illustrate the accuracy and validity of their theoretical framework.
Abstract: We derive the expressions for the effective nonlinear susceptibilities of a metacrystal formed from resonant elements that couple strongly to the magnetic field. We experimentally illustrate the accuracy and validity of our theoretical framework.
98 citations
TL;DR: Through collective interpretation of individual particle Rayleigh spectra and spectral simulations, the geometric basis for small observed variations in the wavelength and intensity of plasmon resonant scattering from individual antenna on the three surfaces is explained.
Abstract: Surface plasmons supported by metal nanoparticles are perturbed by coupling to a surface that is polarizable. Coupling results in enhancement of near fields and may increase the scattering efficiency of radiative modes. In this study, we investigate the Rayleigh and Raman scattering properties of gold nanoparticles functionalized with cyanine deposited on silicon and quartz wafers and on gold thin films. Dark-field scattering images display red shifting of the gold nanoparticle plasmon resonance and doughnut-shaped scattering patterns when particles are deposited on silicon or on a gold film. The imaged radiation patterns and individual particle spectra reveal that the polarizable substrates control both the orientation and brightness of the radiative modes. Comparison with simulation indicates that, in a particle−surface system with a fixed junction width, plasmon band shifts are controlled quantitatively by the permittivity of the wafer or the film. Surface-enhanced resonance Raman scattering (SERRS) sp...
91 citations
TL;DR: In this article, a doubly uniaxial (magnetic and electric) anisotropic layer was proposed to achieve a wide angle impedance matching (WAIM) of waveguide-fed phased-array antennas.
Abstract: This work investigates the gains realisable through the use of artificially structured materials, otherwise known as metamaterials, in the wide angle impedance matching (WAIM) of waveguide-fed phased-array antennas. The authors propose that the anisotropic properties of a metamaterial layer, when designed appropriately, can be employed to achieve impedance matching at a wide contiguous range of phased-array antenna transmission angles. Simulation and numerical results show that an optimised impedance match over a broad angular range can be readily achieved using a doubly uniaxial (magnetic and electric) anisotropic layer, an outcome not found accomplishable when an optimised isotropic dielectric layer is used. The authors propose the possibility of using metamaterials to achieve anisotropic WAIM layer configurations, and the authors show, using two simple uniaxial designs, that a metamaterial layer over the phased-array gives performance characteristics similar to its homogeneous anisotropic effective medium counterpart.
84 citations
TL;DR: In this paper, an analysis of the nonlinear, power-dependent resonance frequency shift for two metamaterial mediums consisting of arrays of varactor-loaded split ring resonators (VLSRRs) is presented.
Abstract: We present an analysis of the nonlinear, power-dependent resonance frequency shift for two metamaterial mediums consisting of arrays of varactor-loaded split ring resonators (VLSRRs). We confirm that, over a limited range of power, a VLSRR medium can be described by its second and third order nonlinear susceptibilities, making it a useful analog medium for the quantitative investigation of other nonlinear phenomena that might be achieved using inherently nonlinear materials integrated into metamaterials. Experimental measurements of the resonance frequency shift with power from fabricated VLSRR samples are found to be in excellent agreement with the analytical model.
68 citations
TL;DR: A coordinate transformation is applied to flatten a Maxwell fish-eye lens, forming a near-perfect relay lens, and also flatten the focal surface associated with a conventional refractive lens, such that the system exhibits an ultra-wide field-of-view with reduced aberration.
Abstract: We apply the transformation optical technique to modify or improve conventional refractive and gradient index optical imaging devices. In particular, when it is known that a detector will terminate the paths of rays over some surface, more freedom is available in the transformation approach, since the wave behavior over a large portion of the domain becomes unimportant. For the analyzed configurations, quasi-conformal and conformal coordinate transformations can be used, leading to simplified constitutive parameter distributions that, in some cases, can be realized with isotropic index; index-only media can be low-loss and have broad bandwidth. We apply a coordinate transformation to flatten a Maxwell fish-eye lens, forming a near-perfect relay lens; and also flatten the focal surface associated with a conventional refractive lens, such that the system exhibits an ultra-wide field-of-view with reduced aberration.
68 citations
TL;DR: In this paper, a cylindrically symmetric metamaterial cloak was designed to operate at a frequency of 10 GHz and to reduce the scattering cross-section (SCS) of a cylinder 50mm in diameter.
Abstract: We present experimental quantitative scattering cross-section (SCS) measurements for a metamaterial cloak. The cloak is nearly identical to that reported in 2006; however, quantitative experimental measurements have not yet been reported for such a structure. This cylindrically symmetric cloak is designed to operate at a frequency of 10 GHz and to reduce the SCS of a cylinder 50 mm in diameter. Despite being only a crude approximation of the ideal transformation optical design, the fabricated metamaterial cloak is shown to reduce the SCS of the cylinder over the frequency range from 9.91 to 10.14 GHz, a span of 230 MHz or a 2.3% bandwidth. The maximum reduction in the SCS is 24%. This result provides a useful experimental, quantitative benchmark that can form the basis for comparison of the performances of future improved cloaking structures.
63 citations
TL;DR: In this article, the authors proposed a general methodology and a set of practical recipes for the construction of ultra-broadband acoustic cloaks, which can render themselves and a concealed object undetectable by means of acoustic scattering.
Abstract: We propose a general methodology and a set of practical recipes for the construction of ultra-broadband acoustic cloaks—structures that can render themselves and a concealed object undetectable by means of acoustic scattering. The acoustic cloaks presented here are designed and function analogously to electromagnetic cloaks. However, acoustic cloaks in a fluid medium do not suffer the bandwidth limitations imposed on their electromagnetic counterparts by the finite speed of light in vacuum. In the absence of specific metamaterials having arbitrary combinations of quasi-static speed of sound and mass density, we explore the flexibility of continuum transformations that produce approximate cloaking solutions. We show that an imperfect, eikonal acoustic cloak (that is, one which is not impedance matched but is valid in the geometrical optics regime) with negligible dispersion can be designed using a simple layered geometry. Since a practical cloaking device will probably be composed of combinations of solid materials rather than fluids, it is necessary to consider the full elastic properties of such media, which support shear waves in addition to the compression waves associated with the acoustic regime. We perform a systematic theoretical and numerical investigation of the role of shear waves in elastic cloaking devices. We find that for elastic metamaterials with Poisson's ratio > 0.49, shear waves do not alter the cloaking effect. Such metamaterials can be built from nearly incompressible rubbers (with 0.499) and fluids. We expect this finding to have applications in other acoustic devices based on the form-invariance of the scalar acoustic wave equation.
TL;DR: PC cloaks and other TO devices operating at visible wavelengths can be constructed from optically transparent substances such as glasses, whose attenuation coefficient can be as small as 10 dB/km, suggesting the TO design methodology can be applied to the development of optical devices not limited by the losses inherent to metal-based, passive metamaterials.
Abstract: We introduce a class of optical media based on adiabatically modulated, dielectric-only, and potentially extremely low-loss, photonic crystals (PC). The media we describe represent a generalization of the eikonal limit of transformation optics (TO). The basis of the concept is the possibility to fit some equal frequency surfaces of certain PCs with elliptic surfaces, allowing them to mimic the dispersion relation of light in anisotropic effective media. PC cloaks and other TO devices operating at visible wavelengths can be constructed from optically transparent substances such as glasses, whose attenuation coefficient can be as small as 10 dB/km, suggesting the TO design methodology can be applied to the development of optical devices not limited by the losses inherent to metal-based, passive metamaterials.
Patent•
15 Jan 2010TL;DR: In this paper, a broadband interface structure is arranged to provide electromagnetic energy characteristic of an apparent profile of the back surface region substantially different than an actual profile for electromagnetic energy received at the front surface region.
Abstract: Broadband metamateriai apparatus, methods, systems, and computer readable media are disclosed, as well as exemplary embodiments that provide cloaking, beam steering, and beam focusing. In one exemplary implementation, a broadband interface structure has a front surface region and a back surface region. The broadband interface structure is arranged to provide electromagnetic energy characteristic of an apparent profile of the back surface region substantially different than an actual profile of the back surface region for electromagnetic energy received at the front surface region.
01 Jan 2010
TL;DR: In this article, the authors discuss the important issues for the development and future of metamaterials, including the optical transformation, effective medium theory for periodic structures, broadband and low-loss metammaterials, and potential applications.
Abstract: There have been increasing interests in metamaterials in the past 10 years in the scientific communities. However, metamaterials are sometimes regarded as left-handed materials or negative refractive index materials by a lot of people including researchers. In fact, the rapid development in this exciting area has shown that metamaterials are far beyond left-handed materials. In this chapter, we will clarify what metamaterial is and report the recent progress on metamaterials. We also summarize the important issues for the development and future of metamaterials, including the optical transformation, effective medium theory for periodic structures, broadband and low-loss metamaterials, rapid design of metamaterials, and potential applications. The impact of computational electromagnetics on metamaterials is briefly discussed.
TL;DR: In this article, a transfer matrix approach was proposed to determine the effective nonlinear susceptibilities of a simple nonlinear metamaterial by applying a retrieval method applied to full-wave numerical simulations of a single layer of the structure.
TL;DR: A generalized nonlinear susceptibility retrieval method for metamaterials based on transfer matrices and valid in the nondepleted pump approximation is presented and quantitative agreement with an analytical effective medium theory model is found.
Abstract: We present a generalized nonlinear susceptibility retrieval method for metamaterials based on transfer matrices and valid in the nondepleted pump approximation. We construct a general formalism to describe the transfer matrix method for nonlinear media and apply it to the processes of three- and four-wave mixing. The accuracy of this approach is verified via finite element simulations. The method is then reversed to give a set of equations for retrieving the nonlinear susceptibility. Finally, we apply the proposed retrieval operation to a three-wave mixing transmission experiment performed on a varactor loaded split ring resonator metamaterial sample and find quantitative agreement with an analytical effective medium theory model.
TL;DR: In this article, a bis-maleimide tetrafuran (2MEP4F) was synthesized by mixing two monomers, furan and maleimide, at elevated temperatures, and the polymer viscosity as a function of time and temperature was quantified in order to optimize the fabrication of the composite material and to guarantee a uniform flow of the resin through the reinforcement.
Abstract: Carbon fiber reinforced polymer (CFRP) laminates with remendable cross-linked polymeric matrices were fabricated using a modified resin transfer mold (RTM) technique. The healable composite resin, bis-maleimide tetrafuran (2MEP4F), was synthesized by mixing two monomers, furan (4F) and maleimide (2MEP), at elevated temperatures. The fast kinetic rate of the reaction of polymer constituents requires a fast injection of the healable resin into the carbon fiber preform. The polymer viscosity as a function of time and temperature was experimentally quantified in order to optimize the fabrication of the composite material and to guarantee a uniform flow of the resin through the reinforcement. The method was validated by characterizing the thermo-mechanical properties of the polymerized 2MEP4F. Additionally, the thermo-mechanical properties of the remendable CFRP material were studied.
TL;DR: The acoustic emission technique is used to characterize the initiation of microfailures within laminated composites with integrated electronics.
Abstract: The low-cost, widespread availability and robust nature of current electronic devices suggest the feasibility of creating a composite structure with integrated networked sensors to monitor in real time the life of civil and aerospace structures while in service conditions. For structures that need to survive to high number of life cycles under varying load-environmental conditions, it is of crucial importance that the strength, stiffness, endurance, and general load-bearing capabilities of the composite not to be severely degraded by the integrated networked components. Therefore, design tools must be developed to achieve optimized, safe, and reliable structures. High values of stress concentrations due to the presence of a rigid device within a highly anisotropic material can trigger the initiation of microcracks in the resin matrix. To quantify these effects, the acoustic emission technique is used to characterize the initiation of microfailures within laminated composites with integrated electronics.
TL;DR: In this paper, the authors describe the strain-dependent behavior of an electric-LC (ELC) resonator unit cell, commonly used in metamaterial designs, and leverage analytic expression to understand the way strain manifests itself in a change in electromagnetic (EM) response.
Abstract: In this paper, we describe the strain-dependent behavior of an electric-LC (ELC) resonator unit cell, commonly used in metamaterial designs. We leverage analytic expression to understand the way strain manifests itself in a change in electromagnetic (EM) response. We verify the simplified physical models using full-wave simulations and generalize the trends to accommodate the strain profile for any arbitrary plane-stress loading scenario.
TL;DR: In this article, the stationary long-range plasmons that exist for self-focusing and self-defocusing Kerr-type nonlinearities are investigated and the solutions are similar to the well-known case of infinitely wide nonlinear waveguides -they are strongly power-dependent and can experience symmetry-breaking bifurcations under appropriate conditions.
Abstract: We report on plasmonic waveguides made of a thin metal stripe surrounded on one or both sides by a Kerr nonlinear medium. Using an iterative numerical method, we investigate the stationary long-range plasmons that exist for self-focusing and self-defocusing Kerr-type nonlinearities. The solutions are similar to the well-known case of infinitely wide nonlinear waveguides - they are strongly power-dependent and can experience symmetry-breaking bifurcations under appropriate conditions.
TL;DR: A beam emission spectroscopy system has been installed on the National Spherical Torus Experiment (NSTX) to study ion gyroscale fluctuations and Alfvén/energetic particle modes on NSTX.
Abstract: A beam emission spectroscopy (BES) system has been installed on the National Spherical Torus Experiment (NSTX) to study ion gyroscale fluctuations. The BES system measures Dα emission from a deuterium neutral heating beam. The system includes two optical views centered at r/a≈0.45 and 0.85 and aligned to magnetic field pitch angles at the neutral beam. f/1.5 collection optics produce 2–3 cm spot sizes at the neutral beam. The initial channel layout includes radial arrays, poloidal arrays, and two-dimensional grids. Radial arrays provide coverage from r/a≈0.1 to beyond the last-closed flux surface. Photodetectors and digital filters provide high-sensitivity, low-noise measurements at frequencies of up to 1 MHz. The BES system will be a valuable tool for investigating ion gyroscale turbulence and Alfven/energetic particle modes on NSTX.
TL;DR: In this paper, the second harmonic generated by a slab of varactor loaded split ring resonator metamaterial and the retrieval of the effective quadratic nonlinear magnetic susceptibility χm(2) using an approach based on transfer matrices was presented.
Abstract: This letter presents a quantitative measurement of the second harmonic generated by a slab of varactor loaded split ring resonator metamaterial and the retrieval of the effective quadratic nonlinear magnetic susceptibility χm(2) using an approach based on transfer matrices. The retrieved value of χm(2) is in excellent agreement with that predicted by an analytical effective medium theory model.
TL;DR: In this paper, the authors perform numerical simulations demonstrating parametric generation and oscillation processes in a single-layer metamaterial composed of split ring resonators (SRRs), where a parametric resonance is achieved by introducing a time-modulation of one of the energy-storing parameters of a resonant system.
21 Jul 2010
TL;DR: The paper provides the possible solutions for the challenges at hand and insight into the modelling work which will help the microwave engineering community to understand the behaviour of the microwave antennas in coupling media.
Abstract: This paper surveys the development of microwave medical imaging and the fundamental challenges associated with microwave antennas design for medical imaging applications. Different microwave antennas used in medical imaging applications such as monopoles, bow-tie, vivaldi and pyramidal horn antennas are discussed. The challenges faced when the latter used in medical imaging environment are detailed. The paper provides the possible solutions for the challenges at hand and also provides insight into the modelling work which will help the microwave engineering community to understand the behaviour of the microwave antennas in coupling media.
Patent•
06 Oct 2010TL;DR: In this article, a gradient index lens with no aberrations and related methods for making such lenses are described, which can be a substantially spherically-shaped lens that has at least one side that is flattened such that a locus of focal points resides on a plane.
Abstract: Gradient index lenses with no aberrations and related methods for making such lenses are described. In one aspect, a gradient index lens can be a substantially spherically-shaped lens that has at least one side that is flattened such that a locus of focal points resides on a plane. A method for making a gradient index lens can include forming material layers, each of the material layers defining an effective refractive index, and laminating the material layers together to form a substantially spherically-shaped lens having at least one side that is flattened to a substantially planar surface. The material layers can have a gradient refractive index distribution such that a locus of focal points resides on the substantially planar surface.
TL;DR: A new beam emission spectroscopy (BES) diagnostic is under development that includes a next-generation preamplifier and upgraded optical coupling system and notable features of the design are surface-mount components, minimized stray capacitance, a wide angular acceptance photodiode, a differential output line driver, and reduced input capacitance.
Abstract: A new beam emission spectroscopy (BES) diagnostic is under development Photon-noise limited measurements of neutral beam emissions are achieved using photoconductive photodiodes with a novel frequency-compensated broadband preamplifier The new BES system includes a next-generation preamplifier and upgraded optical coupling system Notable features of the design are surface-mount components, minimized stray capacitance, a wide angular acceptance photodiode, a differential output line driver, reduced input capacitance, doubling of the frequency range, net reduced electronic noise, and elimination of the need for a cryogenic cooling system The irreducible photon noise dominates the noise up to 800 kHz for a typical input power of 60 nW This new assembly is being integrated into an upgraded multichannel optical detector assembly for a new BES system on the NSTX experiment
TL;DR: In this article, a synthetic diagnostic for high-k scattering measurements has been developed, which predicts the propagation of the beam in an anisotropic, inhomogeneous plasma and accounts for the spatial variation of the instrumental transfer function.
Abstract: Comparison between spectra of short-scale density fluctuations measured with coherent electromagnetic scattering experiments and those extracted from space-resolved numerical simulations is affected by a number of systematic errors. These include the locality of scattering measurements, the different domain covered (space-resolved simulations versus wavenumber resolved measurements), and the stationarity of simulated nonlinear spectra. To bridge the gap between theory-simulations and experiments, a synthetic diagnostic for high-k scattering measurements has been developed. This synthetic scattering predicts the propagation of the beam in an anisotropic, inhomogeneous plasma and accounts for the spatial variation of the instrumental transfer function. The latter, in particular, is proven to provide an important calibration factor not only for the simulated spectra, but also for the measured ones, allowing the use of the synthetic diagnostic in predictive mode. Results from a case study for National Spherical Torus Experiment plasmas using high-k tangential scattering system [Smith et al., Rev. Sci. Instrum. 75, 3840 (2004)] and the gyrokinetic tokamak simulation code [Wang et al., Phys. Plasmas 13, 092505 (2006)] are presented.
01 Sep 2010
TL;DR: In this paper, the 3D deposited energy profile of MeV energy electrons in CdS quantum-dot-doped silica glass have been studied by Monte Carlo simulation using the CASINO and PENELOPE codes.
Abstract: We are currently developing 2D dosimeters with optical readout based on CdS or CdS/CdSe core-shell quantum-dots using commercially available materials. In order to understand the limitations on the measurement of a 2D radiation profile the 3D deposited energy profile of MeV energy electrons in CdS quantum-dot-doped silica glass have been studied by Monte Carlo simulation using the CASINO and PENELOPE codes. Profiles for silica glass and CdS quantum-dot-doped silica glass were then compared.
TL;DR: In this article, an artificial dielectric material designed to operate at W-band millimeter-wave frequencies was presented, which is suitable for use in planar gradient index (GRIN) microwave lenses and other quasi-optical devices.
Abstract: We present an artificial dielectric material designed to operate at W-band millimeter-wave frequencies. The artificial dielectric exhibits a wide range of variation in its effective refractive index, making it suitable for use in planar gradient index (GRIN) microwave lenses and other quasi-optical devices. These devices include those designed using recently developed transformation optics techniques. Because the artificial materials are designed to be nonresonant, their effective refractive indices display very low dispersion with frequency; simulation and measurement results for a number of test samples are presented that confirm the expected broad bandwidth properties. A comparison between the expected and experimentally determined indices-of-refraction for these samples further reveals close, quantitative agreement.
TL;DR: A dual-channel high-efficiency, high-throughput custom spectroscopic system has been designed and implemented at DIII-D to measure localized ion thermal fluctuations associated with drift wave turbulence.
Abstract: A dual-channel high-efficiency, high-throughput custom spectroscopic system has been designed and implemented at DIII-D to measure localized ion thermal fluctuations associated with drift wave turbulence. A large-area prism-coupled transmission grating and high-throughput collection optics are employed to observe C VI emission centered near λ=529 nm. The diagnostic achieves 0.25 nm resolution over a 2.0 nm spectral band via eight discrete spectral channels. A turbulence-relevant time resolution of 1 μs is achieved using cooled high-speed avalanche photodiodes and ultralow-noise preamplifiers. The system sensitivity is designed to provide measurements of normalized ion temperature fluctuations on the order of δTi/Ti≤1%.