Xiande Wang

Pennsylvania State University, University Park, Maryland, United States

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Publications (45)58.15 Total impact

  • Xiande Wang · D.H. Werner · J.P. Turpin
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    ABSTRACT: An efficient methodology is introduced for rapid analysis and design of three-dimensional (3-D) doubly periodic structures over a wide frequency range based on hybrid finite element boundary integral (FEBI) methods. The 3-D doubly periodic structures can be represented as nonorthogonal lattices composed of general inhomogeneous bianisotropic media with arbitrarily-shaped metallic patches. Based on Floquet theory and periodic boundary conditions, the original stated problem that involves infinite periodic structures can be converted into a single unit cell. Using the equivalence principle, the derived BI equation formulation is applied to the top and bottom surfaces of the unit cell, which results in a perfectly reflectionless boundary condition for the FE-based approach. Then, the unit cell was meshed using triangular prismatic volume elements, which provide a great deal of flexibility in modeling complex planar geometries with arbitrary shapes in the transverse direction. The adaptive integral method (AIM) was employed to accelerate the calculation of the matrix-vector product for the BI portion within the iterative solver. Furthermore, a model-based parameter estimation (MBPE) technique was proposed for the wide-band interpolation of the required impedance matrix elements in the BI part for near field components that were used in the AIM procedure. The accuracy and efficiency of the proposed hybrid algorithms are demonstrated by the presented numerical results (e.g., in comparison with analytical solutions). Several simulation results are presented to illustrate the flexibility of the proposed methods for analysis of frequency selective surfaces with arbitrarily-shaped metallic patches, bianisotropic materials, and nonorthogonal lattice configurations.
    No preview · Article · Aug 2014 · IEEE Transactions on Antennas and Propagation
  • Xiande Wang · Douglas H. Werner
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    ABSTRACT: The body of revolution finite-difference time-domain (BOR-FDTD) method is accelerated using graphics processing units (GPUs). The developed BOR-FDTD algorithm can be employed to efficiently characterize an axisymmetric gradient-index (GRIN) lens embedded in a planar multilayered medium when illuminated by an oblique incidence plane wave. The BOR- method is carried out by using the open computing language (OpenCL) programming that can be executed across heterogeneous platforms consisting of CPUs and GPUs. The accuracy and efficiency of the developed parallel techniques are demonstrated by the presented numerical results.
    No preview · Conference Paper · Jul 2014
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    ABSTRACT: A sub-entire domain (SED) basis function method, which was first introduced for modeling large-scale finite periodic PEC structures in free space, has been extended for fast characterization of electromagnetic scattering from an electrically large planar finite periodic microstrip patch array. The microstrip array may have a nonrectangular layout and non-orthogonal lattice configurations (e.g., hexagons or quadrangles). Based on the mixed potential integral equation, and utilizing the proposed SED basis function algorithm, the original large-scale finite periodic array of microstrip patches can be efficiently simulated by decomposing it into two problems with matrix equations of small dimensions. The first is to construct the SED basis functions for the corresponding microstrip arrays with orthogonal/non-orthogonal lattices. Three kinds of the SED basis functions are constructed, including those related to the edge patch elements, the interior patch elements, and the corner patch elements. The second is to solve the system equation with significantly reduced problem dimension as compared to the original larger problem. Based on the obtained SED basis functions, the reduced matrix equation of small size can be generated by the Galerkin procedure, and solved by use of the LU (lower-upper) decomposition-based direct solver, which results in a fast solution. The accuracy and efficiency of the developed algorithms are demonstrated by numerical tests that include the scattering from several large-scale finite periodic arrays of microstrip patches with rectangular, non-orthogonal lattices.
    No preview · Article · May 2014 · IEEE Transactions on Antennas and Propagation
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    ABSTRACT: Transformation Optics (TO) has enabled new methodologies for the design and specification of gradient-index (GRIN) lenses for radio-frequency and optical applications by linking refractive index gradients to a mathematically equivalent change in geometry in another dimension. With the new mathematical design tools, there have been many interesting devices introduced in the literature, such as optical collimators and absorbers (optical “black holes”), GRIN couplers and bends for optical waveguides, and compressed or flattened collimating lenses for imaging and non-imaging applications. Many of the most interesting TO designs are not feasible for implementation, however, due to the complex anisotropic, inhomogeneous material parameters required by the full TO formulation. Instead, restricting the geometric transformations to be mathematically conformal or quasi-conformal (qTO) eliminates the anisotropic material requirements and allows implementation with an isotropic 2D or 3D GRIN profile, for which multiple fabrication methods exist in the RF and IR wavelength ranges and are under development for the complete optical spectrum. We present an overview of the usefulness of combining TO, qTO, and GRIN optics for energy concentration along with the associated design and analysis techniques. Moving away from traditional lenses to GRIN and TO optics for which, in general, no analytical geometric optics or full-wave solution exists, involves the development of new design strategies for individual lenses and systems of lenses. We demonstrate results obtained using advanced, multivariate optimizations that are tightly coupled to a fast, advanced inhomogeneous ray tracing engine for electrically-large lenses, and to an efficient body-of-revolution solver for electrically-small cylindrically-symmetric lenses.
    No preview · Conference Paper · Sep 2013
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    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.
    No preview · Conference Paper · Jul 2013
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    ABSTRACT: An implementation of the finite element boundary integral method with GPU accelerated code was developed to provide a significant improvement in computation time over the standard method.
    No preview · Conference Paper · Jul 2013
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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.
    No preview · Article · Jun 2013 · IEEE Transactions on Antennas and Propagation
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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.
    Preview · Article · May 2013
  • Frank A. Namin · Xiande Wang · Douglas H. Werner
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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.
    No preview · Article · Apr 2013 · Journal of the Optical Society of America B
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    ABSTRACT: Metamaterials with properly engineered surface properties have been recently proposed for application in the design of broadband hybrid-mode horn antennas, such as soft and hard horns. In this paper, we present the design, fabrication, and measured results of a square dual-polarization horn antenna with thin metasurfaces lining the four walls, demonstrating broadband, negligible-loss hybrid-mode operation. By employing a powerful genetic-algorithm (GA) design optimization technique, we have dispersion-engineered low-index metaliners whose surface impedances satisfy the balanced hybrid condition across the Ku-band. The optimized metaliners were synthesized based on conventional printed-circuit board technology, leading to a lightweight and low-cost construction. To improve the cross-polarization response, a simple dielectric plug was placed in the throat of the horn to perform effective mode conversion. Measurements showed that the fabricated horn antenna prototype provided low sidelobes, low cross-polarization levels, and radiation patterns that are approximately independent of polarization. Excellent agreement was found between measured and simulated results across the entire band of operation. Both the far-field radiation patterns and the aperture field distributions confirm the hybrid-mode operation of the horn, validating the balanced metasurface design. This metamaterial-enabled antenna represents a low-cost alternative to other types of soft feed horns, such as corrugated horns.
    No preview · Article · Mar 2013 · IEEE Transactions on Antennas and Propagation

  • No preview · Article · Mar 2013 · IEEE Transactions on Antennas and Propagation
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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.
    No preview · Article · Jan 2013 · Optics Letters
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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.
    No preview · Article · Aug 2012 · IEEE Transactions on Antennas and Propagation
  • Xiande Wang · Douglas 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.
    No preview · Conference Paper · Jul 2012
  • Xiande Wang · Qi Wu · Douglas 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.
    No preview · Conference Paper · Jul 2012
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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.
    No preview · Article · Jun 2012 · IEEE Transactions on Antennas and Propagation
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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.
    No preview · Article · Apr 2012 · IEEE Transactions on Antennas and Propagation
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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.
    No preview · Article · Apr 2012 · IEEE Transactions on Antennas and Propagation
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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.
    No preview · Conference Paper · Mar 2012
  • 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.
    No preview · Article · Jul 2011