D.H. Werner

Pennsylvania State University, University Park, Maryland, United States

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Publications (437)509.04 Total impact

  • Zhi Hao Jiang, Douglas H. Werner
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    ABSTRACT: Low-profile and light-weight coatings that offer comprehensive manipulation of the electromagnetic scattering for finite-length objects are highly desirable, but not yet achieved, for applications including camouflaging, deceptive sensing, radar cognition control, and defense security. Here, for the first time, the theory, practical design, and experimental demonstration of quasi-three-dimensional and angle-tolerant electromagnetic illusion coatings are presented which have been enabled by ultrathin single-layer functional metasurfaces. By controlling the multiple Mie scattering coefficients using the tangential and non-vanishing radial electromagnetic responses of the metasurface, the quasi-two-dimensional coating transforms the electromagnetic perception of one object to mimic that of another which has been pre-selected by the designer. The illusion coating, which is homogeneous but anisotropic, is realized using hundreds of composite electric and magnetic sub-wavelength unit cells operating at frequencies away from their resonance. Two different prototypes of the metasurface illusion coatings were fabricated and characterized, demonstrating very good camouflaging performance for finite-length dielectric as well as conducting objects within a field-of-view up to ±10° off normal. This work paves the way for practical artificially engineered material coatings with exotic and versatile scattering control capabilities that would enable a wide range of applications throughout the entire electromagnetic spectrum.
    Advanced Functional Materials 10/2014; · 10.44 Impact Factor
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    ABSTRACT: A high-gain reduced-profile antenna is designed by combining the effects of a near-zero-index volumetric metamaterial lens and an artificial magnetic conducting (AMC) ground plane. The AMC/metalens antenna design presented here has 20% reduced height over an equivalent metalens antenna with conventional metallic ground plane at the cost of reduced peak directivity and pattern bandwidth. Both the metamaterial unit cells and the mushroom-type AMC structure are designed independently and retuned in the presence of the other for optimal performance. The lens collimates the electromagnetic radiation of a dipole feed by refraction as well as via a Fabry-Perot cavity effect, with resulting gain and patterns that are better than either mechanism can achieve individually. Full wave simulations of the entire metamaterial and AMC structure with a feed dipole agree well with measurements of the fabricated design.
    IEEE Transactions on Antennas and Propagation 03/2014; 62(4). · 2.33 Impact Factor
  • Farhad A. Namin, Douglas H. Werner
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    ABSTRACT: A rigorous approach for the analysis of diffraction from quasicrystalline gratings is presented. Previous methods for determining the diffraction properties of quasicrystalline gratings have relied on periodic supercell approximations. Our method exploits the cut-and-project method, which constructs quasicrystals as irrational slices of higher-dimensional periodic structures onto the physical space. The periodicity in the higher-dimensional space allows for the application of Floquet’s theorem. The solutions can then be obtained by solving Maxwell’s equations in the higher-dimensional space and projecting the results to the lower dimensional physical space. As an example, the method is applied to a one-dimensional aperiodic grating based on a Fibonacci quasicrystal (QC) where the results that were generated are shown to be in near-perfect agreement with those obtained using the supercell approximations.
    ACS Photonics. 02/2014; 1(3):212–220.
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    ABSTRACT: In this paper, we demonstrate an ultra-thin, low-loss optical metamaterial filter with high transmission and near constant group delay across a broad pass-band from 3.0 to 3.5μ m. Deep-subwavelength air hole inclusions positioned at the corners of a conventional metallodiectric fishnet were used engineer the dispersive properties of the structure to have an impedance match to free space over the pass-band. The optical properties of the metamaterial filter were verified by experimentally fabricating and characterizing the optimized free-standing nano-notched fishnet. The measured experimental results agreed well with the simulated response, showing a high transmission band over the targeted wavelength band.
    02/2014;
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    ABSTRACT: Nanostructured optical coatings with tailored spectral absorption properties are of interest for a wide range of applications such as spectroscopy, emissivity control, and solar energy harvesting. Optical metamaterial absorbers have been demonstrated with a variety of customized single band, multiple band, polarization, and angular configurations. However, metamaterials that provide near unity ab-sorptivity with super-octave bandwidth over a specified optical wavelength range have not yet been demonstrated experimentally. Here, we show a broadband, polarization-insensitive metamaterial with greater than 98% measured average absorptivity that is maintained over a wide ±45º field-of-view for mid-infrared wavelengths between 1.77 and 4.81 µm. The nearly ideal absorption is realized by using a genetic algorithm to identify the geometry of a single-layer metal nanostructure array that excites multiple overlapping electric resonances with high optical loss across greater than an octave band-width. The response is optimized by substituting palladium for gold to increase the infrared metallic loss and by introducing a dielectric superstrate to suppress reflection over the entire band. This demonstration advances the state-of-the-art in high-performance broadband metamaterial absorbers that can be reliably fabricated using a single patterned layer of metal nanostructures.
    ACS Nano 01/2014; · 12.03 Impact Factor
  • X. Wang, D.H. Werner, J.P. Turpin
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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.
    IEEE Transactions on Antennas and Propagation 01/2014; 62(5):2543-2552. · 2.33 Impact Factor
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    ABSTRACT: We propose a compact conformal wearable antenna that operates in the 2.36–2.4 GHz medical body-area network band. The antenna is enabled by placing a highly truncated metasurface, consisting of only a two by two array of I-shaped elements, underneath a planar monopole. In contrast to previously reported artificial magnetic conducting ground plane backed antenna designs, here the metasurface acts not only as a ground plane for isolation, but also as the main radiator. An antenna prototype was fabricated and tested, showing a strong agreement between simulation and measurement. Comparing to previously proposed wearable antennas, the demonstrated antenna has a compact form factor of $0.5 lambda _{0} times 0.3 lambda _{0} times 0.028 lambda _{0}$, all while achieving a 5.5% impedance bandwidth, a gain of 6.2 dBi, and a front-to-back ratio higher than 23 dB. Further numerical and experimental investigations reveal that the performance of the antenna is extraordinarily robust to both structural deformation and human body loading, far superior to both planar monopoles and microstrip patch antennas. Additionally, the introduced metal backed metasurface enables a 95.3% reduction in the specific absorption rate, making such an antenna a prime candidate for incorporation into various wearable devices.
    IEEE Transactions on Antennas and Propagation 01/2014; 62(8):4021-4030. · 2.33 Impact Factor
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    ABSTRACT: A low-profile high-gain unidirectional antenna is proposed and demonstrated using both metamaterial (MM) and substrate-integrated waveguide (SIW) technologies. First, the leaky modes supported by a grounded anisotropic slab are studied. These investigations reveal that a grounded slab consisting of an anisotropic zero/low index material can provide an extremely low value for the real part of the propagation constant of the leaky mode, thereby facilitating stable unidirectional broadside radiation over a wide frequency range. The truncation effect of the slab is then investigated through full-wave simulations, which is found to be beneficial for a practical implementation of dispersive metamaterials. Finally, to validate the proposed concept, a subwavelength end-loaded dipole array is designed to realize the required anisotropic zero-index property and is applied to a SIW fed longitudinal slot antenna for the 5.8 GHz wireless local area network (WLAN) band. Measurements of the fabricated antenna prototype are shown to be in strong agreement with simulation results, thus confirming the proposed antenna design. The resulting antenna is only $0.12 lambda $ thick, all while accomplishing a broadside gain of more than 10 dBi and a front-to-back ratio larger than 26 dB, which is $sim {hbox{7 dB}}$ and $sim {hbox{10 dB}}$ higher than that of the SIW fed slot alone, respectively. The $-{hbox{10 dB}}$ impedance bandwidth is more than 9% both with and without the presence of the MM coating. The proposed technique offers a means for realizing low-cost and low-profile unidirectional antennas with moderate bandwidth.
    IEEE Transactions on Antennas and Propagation 01/2014; 62(3):1173-1184. · 2.33 Impact Factor
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    ABSTRACT: The use of inhomogeneous metamaterial lenses is proposed to enable suitable radiation properties for arbitrary-shape antenna arrays. Towards this end, the Quasi-Conformal Transformation Optics (QCTO) methodology is generalized to allow an arbitrary physical arrangement coated with a suitable lens to exhibit the same radiating features of an arbitrary reference virtual array in free space. A representative numerical example, concerned with a two-dimensional layout, is presented to assess the effectiveness of the proposed method as well as the enhanced features of the resulting metamaterial-coated arrays with respect to standard conformal arrangements.
    IEEE Transactions on Antennas and Propagation 01/2014; 62(8):4089-4095. · 2.33 Impact Factor
  • X. 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.
    IEEE Transactions on Antennas and Propagation 01/2014; 62(8):4067-4080. · 2.33 Impact Factor
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    ABSTRACT: A method is presented that allows for the efficient design of capacitively loaded finite-size electromagnetic bandgap (EBG) structures, which can target a wide range of design objectives. The design flexibility is achieved by adding arbitrary nonuniform capacitive loading to an underlying periodic EBG structure. This system can be interpreted as having an effective aperiodic structure, which allows more design flexibility in terms of bandgap engineering. To choose the proper capacitances, a powerful global optimization technique known as the covariance matrix adaptation evolutionary strategy is employed that is aided by a fast port-reduction strategy. This approach avoids the need to carry out multiple computationally expensive full-wave simulations during the course of the optimization process by requiring only a single full-wave simulation be performed prior to initiating the optimization. To demonstrate the utility of this method, the capacitive loading of a mushroom-type EBG structure in a parallel-plate waveguide is optimized to reduce transmission from 2.4 to 7 GHz. This design was fabricated and the measured response was found to be in good agreement with the simulations. Using the same initial full-wave simulation, another structure was designed to improve isolation at the 2.4-, 3.6-, and 5-GHz WLAN bands to below $-{hbox{22}}$ dB. An additional set of structures are also designed using capacitively loaded mushroom-type EBG surfaces without placing them inside of a parallel-plate waveguide.
    IEEE Transactions on Microwave Theory and Techniques 01/2014; 62(9):1962-1972. · 2.23 Impact Factor
  • P.J. Gorman, M.D. Gregory, D.H. Werner
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    ABSTRACT: Recently, the covariance matrix adaption evolutionary strategy (CMA-ES) has received attention for outperforming conventional global optimization techniques such as the genetic algorithm (GA) or particle swarm optimization (PSO), often used in electromagnetic designs. Here, CMA-ES is first applied to the design of ultra-wideband aperiodic arrays using realistic spiral radiating elements. To improve the axial ratio of the array, optimization was extended to incorporate a mechanical rotation of each spiral element. This novel strategy of optimizing both the location and rotation of each element provides noticeable improvement in both the axial ratio and sidelobe level performance.
    IEEE Transactions on Antennas and Propagation 01/2014; 62(4):1663-1672. · 2.33 Impact Factor
  • Zhi Hao Jiang, Lan Lin, Jeremy A Bossard, Douglas H Werner
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    ABSTRACT: In this work, we present the design, numerical experiments, and analysis of a plasmonic metamaterial thin film based on subwavelength nano-notch loaded modified fishnet structures. The resulting device offers a simultaneous bandpass filtering functionality with a broad enhanced optical transmission window and a gapless negative-zero-positive index transition to enable polarization-independent passive beam-steering. This unique characteristic is made possible by the introduced subwavelength nano-notches, which provide fine tuning and hybridization of the external and internal surface plasmon polariton modes. This allows tailoring of the dispersive properties of the plasmonic metamaterial for broadband operation. Specifically, a multilayer nanostructured modified fishnet with feature sizes accessible by modern nanofabrication techniques is presented, exhibiting a broad passband at the mid-infrared wavelengths from 3.0 to 3.7 µm and stopbands elsewhere in the 2.5 ~4.5 µm window. The transmittance normalized to area is around 3 dB within the broad 20% bandwidth of the passband. Additionally, the effective index undergoes a smooth transition from negative unity through zero to positive unity with low loss within the passband. The physical mechanism and the angular dispersion of the metamaterial are analyzed in detail. Finally, full-wave simulations of a prism formed from this metamaterial are performed to demonstrate that the proposed structure achieves simultaneous polarization-insensitive passive beam-steering and filtering functionalities.
    Optics Express 12/2013; 21(25):31492-505. · 3.55 Impact Factor
  • Zhi Hao Jiang, Douglas H. Werner
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    ABSTRACT: In this paper, we report an approach for achieving near-perfect low-profile electromagnetic cloaking beyond the quasi-static limit. In contrast to previous works on metasurface cloaks where only the Leontovich surface impedance boundary condition has been considered, we employ a second-order surface impedance boundary condition to account for the radial response of the proposed anisotropic metasurfaces. This radial surface polarizability tensor parameter can be tailored to eliminate the higher order scattering modes. It is shown from analytical expressions that for a moderate-sized perfect electric conducting or dielectric cylinder (∼0.4λ0 in width), near-perfect scattering reduction, i.e. >98%, can be achieved by a single anisotropic metasurface with non-vanishing radial response, which is far superior to the conventional scalar impedance surface. A practical design of the metasurface is also presented and further validated by full-wave simulations. The physical mechanism of the metasurface cloaks is investigated in detail, revealing that the radiation cancellation of the induced surface currents is responsible for the scattering reduction. Importantly, it is shown that in addition to a ‘low-visibility coating’, the metasurface also functions to provide induced current enhancement which would be beneficial for the operation of a ‘cloaked sensor’. These findings will broaden the usage of metasurfaces to applications ranging from scattering reduction to noninvasive probing for objects beyond the quasi-static limit.
    Journal of Physics D Applied Physics 12/2013; 46(50):5306-. · 2.53 Impact Factor
  • IEEE Antennas and Propagation Magazine 10/2013; 61(10):4947-4956. · 1.18 Impact Factor
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    ABSTRACT: We report a thin nanostructured dielectric optical coating with a nearly ideal polarization insensitive reflectance at a wavelength of 3.46 μm. A genetic algorithm was used to optimize the doubly periodic amorphous silicon subwavelength nanostructure to satisfy a metamaterial-enabled reflecting condition at this resonance wavelength. Optical measurements of the nanofabricated dielectric coating had a peak reflectance of 99.76% at 3.46 μm, showing strong agreement with simulation. The average reflectance measured at nine positions on a 2.54 cm × 2.54 cm coating demonstrated a high optical uniformity of 99.5% ± 0.1% across the large-area component. These results outline a route to design and manufacture low-loss metamaterial-enabled dielectric optical coatings.
    Applied Physics Letters 05/2013; 102(17). · 3.79 Impact Factor
  • Source
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    ABSTRACT: A new type of nature-inspired global optimization methodology based on atmospheric motion is introduced. The proposed Wind Driven Optimization (WDO) technique is a population based iterative heuristic global optimization algorithm for multi-dimensional and multi-modal problems with the potential to implement constraints on the search domain. At its core, a population of infinitesimally small air parcels navigates over an N-dimensional search space following Newton's second law of motion, which is also used to describe the motion of air parcels within the earth's atmosphere. Compared to similar particle based algorithms, WDO employs additional terms in the velocity update equation (e.g., gravitation and Coriolis forces), providing robustness and extra degrees of freedom to fine tune. Along with the theory and terminology of WDO, a numerical study for tuning the WDO parameters is presented. WDO is further applied to three electromagnetics optimization problems, including the synthesis of a linear antenna array, a double-sided artificial magnetic conductor for WiFi applications, and an E-shaped microstrip patch antenna. These examples suggest that WDO can, in some cases, out-perform other well-known techniques such as Particle Swarm Optimization (PSO), Genetic Algorithm (GA) or Differential Evolution (DE) and that WDO is well-suited for problems with both discrete and continuous-valued parameters.
    IEEE Transactions on Antennas and Propagation 05/2013; 61(5):2745-2757. · 2.33 Impact Factor
  • Xiande Wang, Qi Wu, Jeremiah P. Turpin, Douglas H. Werner
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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).
  • 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.
    Journal of the Optical Society of America B 04/2013; 30(4):1008-. · 2.21 Impact Factor
  • Source
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    ABSTRACT: Metamaterials have the potential to create optical devices with new and diverse functionalities based on novel wave phenomena. Most practical optical systems require that the device properties be tightly controlled over a broad wavelength range. However, optical metamaterials are inherently dispersive, which limits operational bandwidths and leads to high absorption losses. Here, we show that deep-subwavelength inclusions can controllably tailor the dispersive properties of an established metamaterial structure thereby producing a broadband low-loss optical device with a desired response. We experimentally verify this by optimizing an array of nano-notch inclusions, which perturb the mode patterns and strength of the primary and secondary fishnet nanostructure resonances and give an optically thin mid-wave-infrared filter with a broad transmissive pass-band and near-constant group delay. This work outlines a powerful new strategy for realizing a wide range of broadband optical devices that exploit the unique properties of metamaterials.
    Scientific Reports 03/2013; 3:1571. · 5.08 Impact Factor

Publication Stats

3k Citations
509.04 Total Impact Points

Institutions

  • 1993–2014
    • Pennsylvania State University
      • • Department of Electrical Engineering
      • • Applied Research Laboratory
      • • College of Engineering
      University Park, Maryland, United States
  • 2011
    • Northrop Grumman
      Falls Church, Virginia, United States
  • 2004–2010
    • University of Granada
      • Departamento de Electromagnetismo y Física de la Materia
      Granada, Andalusia, Spain
  • 2003–2010
    • University of Massachusetts Amherst
      • Department of Electrical and Computer Engineering
      Amherst Center, MA, United States
    • Università di Pisa
      Pisa, Tuscany, Italy
  • 2007
    • Urmia University
      Rezâiyye, Āz̄ārbāyjān-e Gharbī, Iran
  • 2006
    • York College of PA
      State College, Pennsylvania, United States
  • 2003–2006
    • University of Massachusetts Lowell
      • Department of Electrical & Computer Engineering
      Lowell, MA, United States