Xiande Wang

Pennsylvania State University, University Park, Maryland, United States

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Publications (38)51.61 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Infrared (IR) absorbers have been previously studied for use in narrow-band and multi-band applications. Here, we investigate a novel absorber structure based on an electromagnetic band-gap (EBG) metasurface with a curvilinear metallic screen. CMA-ES was employed to determine the coefficients used in the screen generation in order to successfully design an absorber for the near-IR.
    2013 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting; 07/2013
  • Xiande Wang, D.H. Werner, J.P. Turpin
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    ABSTRACT: This paper presents a hybrid approach for efficient analysis of electromagnetic (EM) scattering from large-scale aperiodic structures (e.g., aperiodic Penrose and Danzer tilings), which integrates the characteristic basis function method (CBFM) and the adaptive integral method (AIM). By performing a domain decomposition, a series of characteristic basis functions (CBFs) that are defined on a macro block and comprised of a relatively large number of sub-domain basis functions facilitate a substantial reduction in the method of moments (MoM) matrix size, enabling the use of a direct solver for large problems. The AIM is applied to accelerate the calculation of CBFM-reduced MoM matrices, significantly decreasing the CPU time and memory required for solving large-scale problems. As the size of one block becomes electrically large, the original CBFM combined with the AIM is employed to generate the initial CBFs by solving a large problem with multiple excitations, which results in efficiently constructing the final CBFs afforded by the singular value decomposition (SVD) procedure. This methodology produces a two-level “CBFM + AIM” hybrid algorithm for efficiently characterizing large-scale objects. The numerical results presented demonstrate the accuracy and efficiency of the proposed hybrid algorithm. Then, the developed solver is applied to investigate EM scattering properties of large-scale aperiodic tilings. The numerical results show that Penrose/Danzer tilings exhibit significantly improved grating lobe suppression as compared to their periodic counterparts.
    IEEE Transactions on Antennas and Propagation 06/2013; 61(6):3149-3160. · 2.33 Impact Factor
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    ABSTRACT: [1] A body of revolution, finite-difference time-domain (BOR-FDTD) method is developed for rigorous analysis of axisymmetric transformation optics (TO) lens devices. For normal incidence, a one dimensional (1-D) FDTD method based on the total-field scattered-field (TFSF) technique was proposed to model the propagation of a plane wave launched from the top of a layered medium in cylindrical coordinates. The 1-D FDTD solutions were employed to efficiently inject normally incident plane waves into the BOR-FDTD method. For oblique incidence, analytical formulations were derived and presented by expanding the plane wave into a series of cylindrical modes via Fourier series expansion of the ϕ-dependent variables, which were then used to introduce obliquely incident plane waves into the TFSF formulas associated with the BOR-FDTD method. These procedures allowed for accurate simulations of BOR TO lenses embedded in layered media illuminated by obliquely incident waves. The accuracy and efficiency of the proposed method were verified by comparing numerical results with either analytical solutions or a commercial software (COMSOL) package. Thereafter, the developed BOR-FDTD code was utilized to study the imaging properties of (a) radial gradient-index (GRIN) lenses with a parabolic index profile, (b) a flat TO GRIN lens, (c) a spherical Luneburg lens, and (d) a cylindrical TO Luneburg lens both in free space and on top of a substrate. Here the TO GRIN lenses were designed by using the quasi-conformal transformation optics (QCTO) technique. It was found that the flat TO lens was able to provide identical focusing properties as a cemented doublet in both free space and over a dielectric substrate. Moreover, the numerical results demonstrated that the flattened TO Luneburg lens possessed the desired imaging properties under different illuminations for both polarizations.
    Radio Science. 05/2013; 48(3).
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    ABSTRACT: Generalized Mie theory is employed to study the reflection and transmission properties of finite-sized spherical arrays of nanoparticles based on aperiodic geometries. To simulate realistic experimental conditions, a circular aperture is used to create an incident field with a finite beamwidth. The diffracted fields from the circular aperture are expanded in terms of vector spherical wave harmonics, which are then employed to derive the scattered fields using the generalized Mie theory. Expansion of diffracted fields in terms of spherical harmonics also led to new analytical expressions for two important integrals involving Bessel, associated Legendre, and trigonometric functions, which arise in electromagnetic diffraction problems. Subsequently, generalized scattering parameters were defined in terms of far-field specular energy fluxes. To verify the results, the method was applied to a truncated periodic array of spherical gold nanoparticles for which the generalized scattering parameters were compared and found to agree with the scattering parameters obtained for an infinite planar structure subject to periodic boundary conditions. The method was then applied to an aperiodic array of gold nanoparticles based on a Penrose geometry, and the lowest-order photonic resonances were observed in the predicted regions. Furthermore, it was shown that by proper scaling, the photonic resonances can be strategically placed in the plasmonic region of the gold, where they are enhanced due to strong coupling between the plasmonic and photonic modes.
    Journal of the Optical Society of America B 04/2013; 30(4):1008-. · 2.21 Impact Factor
  • IEEE Transactions on Antennas and Propagation 03/2013; 61(3):1089-1098. · 2.33 Impact Factor
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    ABSTRACT: A body-of-revolution finite-difference time-domain (BOR-FDTD) method was developed and employed to rigorously analyze axisymmetric transformation optics (TO) lenses. The novelty of the proposed BOR-FDTD technique is that analytical expressions were derived and presented to introduce obliquely incident plane waves into the total-field/scattered-field formulation, allowing for accurate simulation of BOR objects in layered media illuminated by obliquely incident waves. The accuracy of the proposed method was verified by comparing numerical results with analytical solutions. The developed code was further utilized to study the imaging properties of a cylindrical TO Luneburg lens on a substrate, demonstrating the desired focusing of light onto a flat plane.
    Optics Letters 01/2013; 38(1):67-9. · 3.39 Impact Factor
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    ABSTRACT: Metamaterial surfaces (metasurfaces) with a low effective index of refraction have been recently proposed for application in the design of hybrid-mode horn antennas, such as soft and hard horns. Here we explore designs of several metasurfaces and their use as liners for coating the interior walls of horn antennas. The design process combines the genetic algorithm optimization technique with a full-wave electromagnetic solver to create dispersion-engineered metamaterials that possess customized surface impedance properties. A metamaterial parameter extraction technique is developed and employed in the optimization process, which is based on the surface impedance expressions for a homogeneous slab backed by a perfectly conducting ground plane illuminated at near grazing incidence. The optimized metasurface is found to be equivalent to a low index metamaterial with a dispersion that can improve the performance of conventional horn antennas over the entire Ku -band while introducing negligible losses. We conclude with a numerical study of a conical horn antenna whose interior is lined with a low index metasurface. The far-field radiation patterns and aperture field distributions confirm hybrid-mode operation over a wide bandwidth, validating the proposed metasurface design methodology.
    IEEE Transactions on Antennas and Propagation 08/2012; 60(8):3594-3604. · 2.33 Impact Factor
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    ABSTRACT: A novel methodology is introduced for the design synthesis of thin planar realizations of volumetric high-impedance or artificial magnetic conducting surfaces (AMC). The design synthesis involves optimization of two different metallic frequency selective surface (FSS) type structures printed on each side of a thin dielectric substrate material. This technique eliminates the need for a complete metallic backplane common in conventional AMC designs, making use of the same dielectric substrate for two high-impedance surfaces; one on each side. Optimization of the FSS unit cell geometries is carried out with a robust genetic algorithm (GA) technique that is combined with a full-wave periodic finite element boundary integral (PFEBI) electromagnetic simulation code for fast and accurate optimization of desired AMC performance at a single frequency or over multiple frequency bands. Several examples of thin AMC ground planes are optimized for use in the X-band. Additional design examples that provide AMC behavior on one side and absorber behavior on the other are also provided. Lastly, an example illustrating the utility of the double-sided AMC separator structure is shown for a design targeting the standard Wi-Fi frequencies of 2.4 GHz and 5.2 GHz.
    IEEE Transactions on Antennas and Propagation 06/2012; 60(6):2770-2780. · 2.33 Impact Factor
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    ABSTRACT: A parallelized real-valued clonal selection algorithm (CLONALG) is successfully implemented in this paper utilizing message passing interface (MPI) to reduce the computational burden of a large clone pool. CLONALG is one of the many branches of Artificial Immune System (AIS) algorithms with unique inherent properties that make it a very efficient optimization techniques for multimodal problems such as the ones commonly encountered in computational electromagnetic design. As a demonstration of its effectiveness, a numerical study is carried out with known benchmark functions along with the optimization of multi-layered frequency selective surface (FSS) filters in the X-band. Our results show that the CLONALG can consistently outperform a standard GA implementation particularly in multi-modal optimization problems.
    IEEE Transactions on Antennas and Propagation 04/2012; 60(4):1831-1843. · 2.33 Impact Factor
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    ABSTRACT: A novel methodology is presented for the design synthesis of matched impedance thin planar composite magneto-dielectric metasurfaces. The design synthesis involves optimizing thin, metallo-dielectric metasurfaces comprised of a periodic array of electrically small and rotationally symmetric metallic unit cells which are sandwiched between two thin dielectric layers and backed by a perfectly conducting ground plane. Optimization of the structures is carried out with a genetic algorithm (GA) to obtain a design with electromagnetic properties that are equivalent to a desired matched-impedance homogeneous medium of the same thickness. Optimized design results demonstrate the effectiveness of this new technique in synthesizing thin planar composite matched-impedance magneto-dielectric metasurfaces (MIMDM). To validate the approach, full-wave simulations of the actual metamaterial structure were compared with results obtained by employing an equivalent homogeneous effective medium and found to be in excellent agreement. Several designs are optimized with targeted applications such as substrates for miniaturized patch antennas and electromagnetic absorbing materials.
    IEEE Transactions on Antennas and Propagation 01/2012; 60(4):1910-1920. · 2.33 Impact Factor
  • Xiande Wang, Qi Wu, D.H. Werner
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    ABSTRACT: The body-of-revolution, finite-difference time-domain (BOR-FDTD) method is presented for solving electromagnetic scattering from inhomogeneous dielectric BOR objects embedded in multilayered media. To efficiently truncate the infinite spatial domain for computations, a generalized unsplit perfectly matched layer (UPML) absorbing boundary condition technique in cylindrical coordinates is incorporated into the BOR-FDTD solver. The total-field scattered-field (TFSF) method is utilized to introduce the incident plane waves into the BOR-FDTD simulations. In the presence of the layered media, a 1-D auxiliary grid is created to generate a normal plane-wave injector by performing 1-D FDTD calculations along the direction of wave propagation with the help of a 1-D TFSF technique. The numerical results presented here demonstrate the accuracy and efficiency of the proposed method. Finally, the code is employed to investigate the influence of substrates on the characteristics of flat transformation optics (TO) BOR lenses.
    Antennas and Propagation Society International Symposium (APSURSI), 2012 IEEE; 01/2012
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    ABSTRACT: This paper illustrates the use of quasi-conformal (QC) transformation optics (TO) techniques to design flat gradient-index (GRIN) lenses as replacements for conventional optical lenses. Three flat TO lenses are considered to demonstrate the flexibility of the new design approach. Two dimensional (2D) Finite-Difference Time Domain (FDTD) simulations show equivalent performance between the original lenses and the flat TO lenses. Furthermore, a body of revolution (BOR) FDTD method was developed and employed to characterize the imaging properties of the three dimensional (3D) cylindrical lenses, validating the predictions of 2D simulations. These designs only require spatially-varying dielectric materials with no magnetic properties, facilitating low-loss, broadband operation in both the microwave and optical regimes.
    Antennas and Propagation (EUCAP), 2012 6th European Conference on; 01/2012
  • Xiande Wang, D.H. Werner
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    ABSTRACT: This paper presents a hybrid method for fast analysis of electromagnetic (EM) scattering from large-scale aperiodic structures (e.g., Penrose and Danzer tilings), which integrates the characteristic basis function method (CBFM) and the adaptive integral method (AIM). The CBFs defined on the macro block facilitate a substantial reduction in the method of moments (MoM) matrix size, enabling the use of direct solvers for large problems. The initial CBFs are constructed by illuminating one block with θ- and φ-polarization plane waves for multiple incident angles. Thereafter, the singular value decomposition (SVD) method and threshold are used to extract the independent basis from the initial solution space, ultimately leading to the final CBFs. The AIM is applied to accelerate the calculation of CBFM reduced MoM matrices, significantly decreasing the CPU time and memory required for solving large-scale problems. As the size of one block becomes electrically large, the original CBFM combined with AIM is employed to generate the initial CBFs by solving a problem with multiple excitations, which results in efficiently constructing the final CBFs afforded by the SVD procedure. After validating the developed code, the subsequent solver is applied to investigate EM scattering from large-scale aperiodic tilings in order to demonstrate the efficiency of the proposed method. Further, the numerical results show that Penrose and Danzer tilings exhibit improved grating lobe suppression as compared to their periodic counterparts.
    Antennas and Propagation Society International Symposium (APSURSI), 2012 IEEE; 01/2012
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    ABSTRACT: We present a detailed comparison of surface-enhanced Raman spectroscopy (SERS) signals from metallic nanoparticle arrays and their complementary hole arrays. Using an analytical model for local field enhancement, we show that the SERS enhancements of the hole arrays are closely related to their transmission spectra. This trend is experimentally confirmed and characterized by a cos(4 )θ dependence of the SERS signal on the excitation polarization angle θ. The particle arrays, on the other hand, exhibit quite different behavior because of the existence of considerable evanescent modes in the near field. Their maximal local field gains appear at wavelengths generally much larger than their localized surface plasmonic resonant wavelengths.
    ACS Nano 06/2011; 5(7):5472-7. · 12.03 Impact Factor
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    ABSTRACT: In this paper, we present a method to retrieve the effective electromagnetic parameters of a slab of anisotropic metamaterial from reflection and transmission coefficients (or scattering parameters). In this retrieval method, calculated or measured scattering parameters are employed for plane waves incident obliquely on a metamaterial slab at different angles. Useful analytical expressions are derived for extracting the homogeneous anisotropic medium parameters of a metamaterial. To validate the method, the effective permittivity and permeability tensor parameters for a composite split-ring resonator-wire array are retrieved and shown to be consistent with observations previously reported in the literature. This retrieval method is further incorporated into a genetic algorithm (GA) to synthesize an infrared zero-index-metamaterial with a wide field-of-view, demonstrating the utility of the new design approach. The anisotropic parameter retrieval algorithm, when combined with a robust optimizer such as GA, can provide a powerful design tool for exploiting the anisotropic properties in metamaterials to achieve specific angle dependant or independent responses.
    Journal of Applied Physics 01/2011; 109(1):013515-013515-11. · 2.21 Impact Factor
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    ABSTRACT: An efficient technique is developed to fabricate optically thin metallic films with subwavelength patterns and their complements simultaneously. By comparing the spectra of the complementary films, we show that Babinet's principle nearly holds in the optical domain. A discrete-dipole approximation can qualitatively describe their spectral dependence on the illuminating polarization. Using pyridine as probe molecules, we studied surface-enhanced Raman scattering (SERS) from the complementary structures. Although the complementary structures possess closely related linear spectra, they have quite different near-field behaviors. For hole arrays, their averaged local field gains as well as the SERS enhancements are strongly correlated to their transmission spectra. We therefore can use cos 4 �� to approximately describe the dependence of the Raman intensity on the excitation polarization angle �� , while the complementary particle arrays present maximal local field gains at wavelengths generally much larger than their localized surface plasmonic resonant wavelengths.
    01/2011;
  • Xiande Wang, Douglas H. Werner
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    ABSTRACT: We present an efficient method for modeling 3-D doubly periodic structures over a wide frequency range based on hybrid finite element/boundary integral (FEBI) methods. The 3-D periodic structures can be represented as non-orthogonal lattices composed of inhomogeneous bianisotropic media with arbitrary metallic patches. Triangular prismatic volume elements were utilized to mesh the unit cell, which provided a great deal of flexibility in modeling complex planar geometries of arbitrary shape. The adaptive integral method (AIM) was applied to speed up the calculation of the matrix-vector product for the BI part within the iterative solver. Furthermore, a model-based parameter estimation (MBPE) technique was proposed for the wide-band interpolation of sparse impedance matrix elements in the BI portion for near field components that were used in the AIM. The accuracy and efficiency of the proposed algorithm is demonstrated by the presented numerical results. To demonstrate the flexibility of the proposed method in modeling arbitrarily shaped elements of frequency selective surfaces (FSS), we included simulation results for an FSS with a non-orthogonal lattice and two elliptical shaped patches embedded in bianisotropic media.
    01/2011;
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    ABSTRACT: An efficient technique is developed to fabricate optically thin metallic films with subwavelength patterns and their complements simultaneously. By comparing the spectra of the complementary films, we show that Babinet’s principle nearly holds for these structures in the optical domain. Rigorous full-wave simulations are employed to verify the experimental observations. It is further demonstrated that a discrete-dipole approximation can qualitatively describe the spectral dependence of the metallic membranes on the geometry of the constituent particles as well as the illuminating polarization.
    Applied Physics Letters 11/2010; 97(19):193101-193101-3. · 3.52 Impact Factor
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    ABSTRACT: A flexible polarization-insensitive metamaterial absorber design with a wide field of view was proposed for mid-infrared applications. Both single-band and dual-band designs based on bilayer metallo-dielectric stacks were presented. According to the simulated results, the proposed metamaterial absorbers optimized using a GA (genetic algorithm) could provide absorptivity greater than 0.94 at the target frequency bands for both polarizations over a wide range of incident angles. Efforts are currently underway to fabricate and measure a prototype for confirmation of the numerically predicted absorber performance.
    Antennas and Propagation Society International Symposium (APSURSI), 2010 IEEE; 08/2010
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    ABSTRACT: In this paper, the authors present an impedance-matched low loss infrared zero index metamaterials (ZIM) with a wide field-of-view. The ZIM structure is optimized by a genetic algorithm combined with a generalized inversion method capable of retrieving the effective anisotropic constitutive parameters of the metamaterial with its angular response considered.
    Antennas and Propagation Society International Symposium (APSURSI), 2010 IEEE; 08/2010