Browsing by Author "Urzhumov, Y"

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Open Access
Acoustic cloaking transformations from attainable material properties
(New Journal of Physics, 2010-07-12) Urzhumov, Y; Ghezzo, F; Hunt, J; Smith, DR
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 v > 0.49, shear waves do not alter the cloaking effect. Such metamaterials can be built from nearly incompressible rubbers (with v ≈ 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. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
Open Access
Active negative-index metamaterial powered by an electron beam
(Physical Review B - Condensed Matter and Materials Physics, 2012-08-21) Shapiro, MA; Trendafilov, S; Urzhumov, Y; Alù, A; Temkin, RJ; Shvets, G
An active negative index metamaterial that derives its gain from an electron beam is introduced. The metamaterial consists of a stack of equidistant parallel metal plates perforated by a periodic array of holes shaped as complementary split-ring resonators. It is shown that this structure supports a negative-index transverse magnetic electromagnetic mode that can resonantly interact with a relativistic electron beam. Such a metamaterial can be used as a coherent radiation source or a particle accelerator. © 2012 American Physical Society.
Open Access
Characterization of high order modes of plasmonic antenna formed by nanoparticle/thin film hybrid structures
(Proceedings of SPIE - The International Society for Optical Engineering, 2012-05-04) Chen, SY; Urzhumov, Y; Smith, DR; Lazarides, AA
The plasmonic modes of a nano-antenna formed by a nanoparticle/thin film hybrid system are investigated. Plasmonic nano-antennas are well-known for their capabilities to concentrate electromagnetic wave into extreme small region and couple the emission from active materials in proximity to the antennas into far-field region. Previously, we have shown through direct measurement of emission profile images that the nano-antennas not only enhance Raman emission but also systematically direct inelastic emission to the far-field through the dipole mode. We also showed that high order modes of the hybrid structure can be detected. Here, the higher order plasmonic modes are characterized through imaging, variable angle linearly polarized excitation, and simulation. Through spectral simulation with improved resolution, two distinct modes are found to contribute to the broad band high order mode. One has dipole-like behavior and the other has quadrupole-like behavior. The modes are characterized both through near-field distribution and farfield scattering profiles. The quadrupole-like mode can be excited by both p- and s-polarized light whereas the dipolelike mode is only excited by p-polarized light. These high order modes are not as bright as the dipole mode in the farfield spectrum but have substantial near field enhancement which can be utilized for surface-enhancing spectroscopy and sensing. In addition, characterization of high order modes may serve to clarify the interaction between nano-antenna and active materials and will lead to design rules for applications of active plasmonic structures in integrated optical circuits. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE). Photonic and Phononic Properties of Engineered Nanostructures II;82691M.
Open Access
Construction of invisibility cloaks of arbitrary shape and size using planar layers of metamaterials
(Journal of Applied Physics, 2012-06-15) Paul, O; Urzhumov, Y; Elsen, C; Smith, D; Rahm, M
Transformation optics (TO) is a powerful tool for the design of electromagnetic and optical devices with novel functionality derived from the unusual properties of the transformation media. In general, the fabrication of TO media is challenging, requiring spatially varying material properties with both anisotropic electric and magnetic responses. Though metamaterials have been proposed as a path for achieving such complex media, the required properties arising from the most general transformations remain elusive, and cannot implemented by state-of-the-art fabrication techniques. Here, we propose faceted approximations of TO media of arbitrary shape in which the volume of the TO device is divided into flat metamaterial layers. These layers can be readily implemented by standard fabrication and stacking techniques. We illustrate our approximation approach for the specific example of a two-dimensional, omnidirectional "invisibility cloak", and quantify its performance using the total scattering cross section as a practical figure of merit. © 2012 American Institute of Physics.
Open Access
Electronically reconfigurable metal-on-silicon metamaterial
(Physical Review B - Condensed Matter and Materials Physics, 2012-08-08) Urzhumov, Y; Lee, JS; Tyler, T; Dhar, S; Nguyen, V; Jokerst, NM; Schmalenberg, P; Smith, DR
Reconfigurable metamaterial-based apertures can play a unique role in both imaging and in beam-forming applications, where current technology relies mostly on the fabrication and integration of large detector or antenna arrays. Here, we report the experimental demonstration of a voltage-controlled, silicon-based electromagnetic metamaterial operating in the W-band (75-110 GHz). In this composite semiconductor metamaterial, patterned gold metamaterial elements serve both to manage electromagnetic wave propagation while simultaneously acting as electrical Schottky contacts that control the local conductivity of the semiconductor substrate. The active device layers consist of a patterned metal on a 2-μm-thick n-doped silicon layer, adhesively bonded to a transparent Pyrex wafer. The transmittance of the composite metamaterial can be modulated over a given frequency band as a function of bias voltage. We demonstrate a quantitative understanding of the composite device through the application of numerical approaches that simultaneously treat the semiconductor junction physics as well as wave propagation. © 2012 American Physical Society.
Open Access
Isotropic-medium three-dimensional cloaks for acoustic and electromagnetic waves
(Journal of Applied Physics, 2012-03-01) Urzhumov, Y; Landy, N; Smith, DR
We propose a generalization of the two-dimensional eikonal-limit cloak derived from a conformal transformation to three dimensions. The proposed cloak is a spherical shell composed of only isotropic media; it operates in the transmission mode and requires no mirror or ground plane. Unlike the well-known omnidirectional spherical cloaks, it may reduce visibility of an arbitrary object only for a very limited range of observation angles. In the short-wavelength limit, this cloaking structure restores not only the trajectories of incident rays, but also their phase, which is a necessary ingredient to complete invisibility. Both scalar-wave (acoustic) and transverse vector-wave (electromagnetic) versions are presented. © 2012 American Institute of Physics.
Open Access
Magnetic levitation of metamaterial bodies enhanced with magnetostatic surface resonances
(Physical Review B - Condensed Matter and Materials Physics, 2012-02-27) Urzhumov, Y; Chen, W; Bingham, C; Padilla, W; Smith, DR
We propose that macroscopic objects built from negative-permeability metamaterials may experience resonantly enhanced magnetic force in low-frequency magnetic fields. Resonant enhancement of the time-averaged force originates from magnetostatic surface resonances (MSRs), which are analogous to the electrostatic resonances of negative-permittivity particles, well known as surface plasmon resonances in optics. We generalize the classical problem of the MSR of a homogeneous object to include anisotropic metamaterials and consider the most extreme case of anisotropy, where the permeability is negative in one direction but positive in the others. It is shown that deeply subwavelength objects made of such indefinite (hyperbolic) media exhibit a pronounced magnetic dipole resonance that couples strongly to uniform or weakly inhomogeneous magnetic field and provides strong enhancement of the magnetic force, enabling applications such as enhanced magnetic levitation. © 2012 American Physical Society.
Open Access
Magnetic superlens-enhanced inductive coupling for wireless power transfer
(Journal of Applied Physics, 2012-03-15) Huang, D; Urzhumov, Y; Smith, DR; Hoo Teo, K; Zhang, J
We investigate numerically the use of a negative-permeability perfect lens for enhancing wireless power transfer between two current carrying coils. The negative permeability slab serves to focus the flux generated in the source coil to the receiver coil, thereby increasing the mutual inductive coupling between the coils. The numerical model is compared with an analytical theory that treats the coils as point dipoles separated by an infinite planar layer of magnetic material Urzhumov, Phys. Rev. B 19, 8312 (2011). In the limit of vanishingly small radius of the coils, and large width of the metamaterial slab, the numerical simulations are in excellent agreement with the analytical model. Both the idealized analytical and realistic numerical models predict similar trends with respect to metamaterial loss and anisotropy. Applying the numerical models, we further analyze the impact of finite coil size and finite width of the slab. We find that, even for these less idealized geometries, the presence of the magnetic slab greatly enhances the coupling between the two coils, including cases where significant loss is present in the slab. We therefore conclude that the integration of a metamaterial slab into a wireless power transfer system holds promise for increasing the overall system performance. © 2012 American Institute of Physics.
Open Access
Metamaterial-enhanced coupling between magnetic dipoles for efficient wireless power transfer
(Physical Review B - Condensed Matter and Materials Physics, 2011-05-18) Urzhumov, Y; Smith, DR
Nonradiative coupling between conductive coils is a candidate mechanism for wireless energy transfer applications. In this paper we propose a power relay system based on a near-field metamaterial superlens and present a thorough theoretical analysis of this system. We use time-harmonic circuit formalism to describe all interactions between two coils attached to external circuits and a slab of anisotropic medium with homogeneous permittivity and permeability. The fields of the coils are found in the point-dipole approximation using Sommerfeld integrals which are reduced to standard special functions in the long-wavelength limit. We show that, even with a realistic magnetic loss tangent of order 0.1, the power transfer efficiency with the slab can be an order of magnitude greater than free-space efficiency when the load resistance exceeds a certain threshold value. We also find that the volume occupied by the metamaterial between the coils can be greatly compressed by employing magnetic permeability with a large anisotropy ratio. © 2011 American Physical Society.
Open Access
Nonlinear oscillator metamaterial model: numerical and experimental verification.
(Opt Express, 2011-04-25) Poutrina, E; Huang, D; Urzhumov, Y; Smith, DR
We verify numerically and experimentally the accuracy of an analytical model used to derive the effective nonlinear susceptibilities of a varactor-loaded split ring resonator (VLSRR) magnetic medium. For the numerical validation, a nonlinear oscillator model for the effective magnetization of the metamaterial is applied in conjunction with Maxwell equations and the two sets of equations solved numerically in the time-domain. The computed second harmonic generation (SHG) from a slab of a nonlinear material is then compared with the analytical model. The computed SHG is in excellent agreement with that predicted by the analytical model, both in terms of magnitude and spectral characteristics. Moreover, experimental measurements of the power transmitted through a fabricated VLSRR metamaterial at several power levels are also in agreement with the model, illustrating that the effective medium techniques associated with metamaterials can accurately be transitioned to nonlinear systems.
Open Access
Probing the ultimate limits of plasmonic enhancement.
(Science, 2012-08-31) Ciracì, C; Hill, RT; Mock, JJ; Urzhumov, Y; Fernández-Domínguez, AI; Maier, SA; Pendry, JB; Chilkoti, A; Smith, DR
Metals support surface plasmons at optical wavelengths and have the ability to localize light to subwavelength regions. The field enhancements that occur in these regions set the ultimate limitations on a wide range of nonlinear and quantum optical phenomena. We found that the dominant limiting factor is not the resistive loss of the metal, but rather the intrinsic nonlocality of its dielectric response. A semiclassical model of the electronic response of a metal places strict bounds on the ultimate field enhancement. To demonstrate the accuracy of this model, we studied optical scattering from gold nanoparticles spaced a few angstroms from a gold film. The bounds derived from the models and experiments impose limitations on all nanophotonic systems.