Do-Hoon Kwon

University of Massachusetts Amherst, Amherst Center, Massachusetts, United States

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Publications (44)70.43 Total impact

  • Do-Hoon Kwon, Caglar Dogu Emiroglu
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    ABSTRACT: Characteristics of two-dimensional metamaterials based on non-orthogonal grids of transmission lines are investigated. From periodic analysis on a unit cell, the dispersion function is derived and compared with the orthogonal grid case. Isomorphism between Kirchhoff's circuital laws and two-dimensional Maxwell's equations is utilized to characterize the effective medium parameters. It is shown that a non-orthogonal grid structure is effective in realizing two-dimensional full-tensor anisotropic medium parameters in a simple geometrical configuration. For verification, a design example is provided where a probe current radiates near a planar interface between two anisotropic media and the results are compared with the analytical solution.
    IEEE Transactions on Antennas and Propagation 09/2012; 60(9):4210-4218. · 2.33 Impact Factor
  • Do-Hoon Kwon, C.D. Emiroglu
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    ABSTRACT: Using a coordinate transformation on a folded geometry, appropriate transformation media can make an embedded antenna appear as if it is positioned at a virtual location. For the TE polarization in two dimensions, embedding media for an electric line source are designed in transmission-line and inclusion-based resonant metamaterial configurations. For a line source positioned inside a recess in a conducting ground plane, the metamaterials are specifically designed to form a virtual line source above the ground plane. Metamaterial design details and simulation results for predicted radiation patterns are presented.
    Antennas and Propagation (EUCAP), 2012 6th European Conference on; 01/2012
  • C.D. Emiroglu, Do-Hoon Kwon
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    ABSTRACT: Dichroic frequency selective surface having stable filtering characteristics over a wide range of incidence angle is designed. The resonator layer is first represented by a homogeneous material slab using effective medium parameters. An optimal quarter-wave superstrate layer is subsequently applied. Angularly stable filtering responses are confirmed with simulation results.
    Antennas and Propagation Society International Symposium (APSURSI), 2012 IEEE; 01/2012
  • C.D. Emiroglu, Do-Hoon Kwon
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    ABSTRACT: A transmission-line metamaterial design of a material-embedded line source radiating inside a ground recess is presented. The media embedding the recessed line source is designed such that the embedded current creates the same radiation pattern as a line source over a flat conducting ground plane. A numerical example based on circuit simulations is shown to validate the effectiveness of the embedded design at the design frequency.
    Antennas and Propagation (APSURSI), 2011 IEEE International Symposium on; 08/2011
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    ABSTRACT: Metamaterial lenses derived through transformation optics offer control over wave behavior and potential for new antenna structures. A collimating lens is presented with an embedded source that produces up to four orthogonal far-field beams based on the position of the source. As a feasibility confirmation, an example metamaterial design for the lens is presented. Another far-field collimating flat lens allows for fine beam scanning and potential for multiple beamforming based on the position of the sources behind the lens.
    Antennas and Propagation (EuCAP), 2010 Proceedings of the Fourth European Conference on; 05/2010
  • Source
    Caglar D. Emiroglu, Do-Hoon Kwon
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    ABSTRACT: Based on the coordinate transformation technique, a three-dimensional beam expander/compressor design is presented. Spatial coordinates in two orthogonal directions tangential to the device boundary are scaled at the same rate. The reflection and transmission coefficients are obtained in a closed form at the planar boundary for a plane wave illumination at an arbitrary incidence angle. The reflection and transmission characteristics under two-dimensional Gaussian beam illuminations are analyzed by constructing the incident, reflected, and transmitted waves as a superposition of plane wave components via Fourier transform. Numerical examples are provided to demonstrate the small amount of reflection compared with two-dimensional counterparts of the expander/compressor.
    Journal of Applied Physics 05/2010; · 2.21 Impact Factor
  • Do-Hoon Kwon, D.H. Werner
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    ABSTRACT: The recently introduced transformation-electromagnetics techniques provide a new methodology for designing devices that possess novel wave-material interaction properties. They are based on the form invariance of Maxwell's equations under coordinate transformations. These methods provide an extremely versatile set of design tools that employ spatial-coordinate transformations, where the compression and dilation of space in different coordinate directions are interpreted as appropriate scalings of the material parameters. The most famous transformation-optics device is the cloak of invisibility. However, a wide variety of other devices are also possible, such as field concentrators, polarization rotators, beam splitters, beam collimators, and flat lenses. In this paper, an overview of transformation-electromagnetics device design techniques is presented. The paper begins by introducing the underlying design principle behind transformation electromagnetics. Several novel transformation-based device designs are then summarized, starting with electromagnetic cloaks that have spherical shell or cylindrical annular shapes, More general cloaking designs of noncircular annular geometries are treated, and the application of cloaking to RF/microwave antenna shielding is also discussed. Following this, device designs that employ transformations that have discontinuities .on the domain boundary are presented. Unlike those used for cloaks, this type of transformation is capable of modifying the fields outside of the device. Examples of this type of transformation-electromagnetics device are presented, which include flat near-field and far-field focusing lenses, wave collimators for embedded sources (e.g., antennas), polarization splitters and rotators, and right-angle beam benders.
    IEEE Antennas and Propagation Magazine 03/2010; · 1.18 Impact Factor
  • Source
    Do-Hoon Kwon, Caglar D. Emiroglu
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    ABSTRACT: Using the coordinate transformation approach, low-profile material-embedded horizontal linear arrays are designed such that the embedded arrays perform identically to a vertical array of the same length in free space. A vertical array in free space is first rotated by a right angle using a transformation-based rotator. The height of the rotated array is subsequently reduced through a reflectionless compression procedure in the vertical direction. The resulting low-profile array can scan a narrow beam at large scan angles without having a broadening main beam, unlike a linear array in free space. Two transformation material designs are presented based on circular and square annular rotators. Numerical simulation results are provided to verify the scanning performance. The effect of material loss on the radiation pattern is examined numerically.
    Journal of Applied Physics 03/2010; · 2.21 Impact Factor
  • Do-Hoon Kwon
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    ABSTRACT: A radiation configuration is designed for a monopole antenna embedded within transformation media and buried inside a recess in a conducting ground plane. Both the ground plane near the base of the antenna and the antenna itself, which are physically located inside a recess, are mapped to a virtual location above the ground plane by a negative-index material block. The directivity pattern is identical to that of a monopole on a flat ground plane, radiating the maximum vertically polarized field in the horizon. Radiation characteristics are tolerant to small variations in material parameters from ideal values. Estimates for pattern and impedance bandwidths are provided based on numerical simulations.
    IEEE Antennas and Wireless Propagation Letters 02/2010; · 1.67 Impact Factor
  • Do-Hoon Kwon, D.M. Pozar
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    ABSTRACT: Several fundamental questions about the operation of receiving antennas are addressed, such as ldquoWhy does a receiving antenna scatter an incident field?rdquo and ldquoUnder what conditions does a receive antenna capture all of the available incident power?rdquo A new method is described by which the received power can be maximized for an arbitrary receiving antenna. The technique is first illustrated for two-dimensional infinite receiving arrays of electric and/or magnetic dipole elements, which result in simple plane waves for the scattered (re-radiated) fields. Optimal results (for maximum received power) are derived for several cases, and it is established that half the available incident power may be received by an array of electric (or magnetic) elements in free space, and that all available incident power may be received by an array that combines electric and magnetic elements, or one that incorporates a ground plane. Next, an arbitrary finite three-dimensional antenna enclosed by a mathematical spherical surface is treated using spherical vector wave functions. It is shown that half the available incident power can be received by such an antenna consisting of either TM or TE only elements, while all available incident power can be received when both TM and TE elements are used. It is also shown that the absorption efficiency for any optimal arbitrary antenna is 50%.
    IEEE Transactions on Antennas and Propagation 01/2010; · 2.33 Impact Factor
  • Do-Hoon Kwon, Caglar D. Emiroglu
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    ABSTRACT: A thin low-profile embedded horizontal array design was presented based on the transformation electromagnetics methodology. By applying coordinate transformations to a conductor-backed vertical array in free space, an embedded horizontal array can scan a narrow beam in the angular range near the axial direction. The effect of material loss was investigated numerically. Metamaterials are the prime candidates for realizations. Loss in practical metamaterials will be a key factor in the effectiveness of the embedded horizontal array.
    01/2010;
  • Do-Hoon Kwon, E. Semouchkina, D.H. Werner
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    ABSTRACT: Using the transformation electromagnetics technique, a 2D flat far-zone focusing lens design has been presented. The design was obtained by transforming a circular arc with the center located at the line source position into a planar interface. A near-zone focusing lens was obtained by concatenating two far-zone focusing lenses in a back-to-back configuration. Finally, a non-magnetic version of the lens design was also presented.
    Antennas and Propagation Society International Symposium, 2009. APSURSI '09. IEEE; 07/2009
  • Do-Hoon Kwon, D.H. Werner
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    ABSTRACT: In this paper, a transformation electromagnetic device that changes the polarization of the incoming beam is introduced. Specifically, the embedded coordinate transformation is employed to design a three-dimensional (3D) beam polarization rotator. The material specifications of the design are derived and the performance is verified using full-wave electromagnetic simulations.
    Antennas and Propagation Society International Symposium, 2009. APSURSI '09. IEEE; 07/2009
  • Do-Hoon Kwon, D.M. Pozar
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    ABSTRACT: For lossless receive antennas, the power absorbed and delivered to a conjugate matched load can be obtained by computing a net power lost within a volume that includes the antenna. Maximum achievable received powers by different planar array configurations were analyzed. It was found that both a grounded dipole array, and an array of electric/magnetic dipole combinations, are capable of receiving all of the incident power.
    Antennas and Propagation Society International Symposium, 2009. APSURSI '09. IEEE; 07/2009
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    ABSTRACT: We have proposed to make use of the low-loss characteristic of chalcogenide glass material for infrared filter applications. A stop-band chalcogenide filter design based on a grating structure was presented. The study shows that by varying the grating's geometric structure, the bandwidth can be adjusted and the resonant frequency can be fine-tuned. However, high-Q characteristics can only be realized with thicker grating structures. This initial investigation indicates that a chalcogenide glass stop-band filter can achieve reflectances higher than 90% at infrared wavelengths.
    Antennas and Propagation Society International Symposium, 2009. APSURSI '09. IEEE; 07/2009
  • Source
    Do-Hoon Kwon, Douglas H Werner
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    ABSTRACT: Two-dimensional far-zone focusing lenses are designed using the coordinate transformation approach that feature minimized reflections from the lens boundaries. A flat lens of trapezoidal cross section completely converts incident waves with cylindrical wavefronts into transmitted waves with planar wavefronts. A rectangular lens with reduced non-magnetic material parameters that incorporates a nonlinear coordinate transformation features a significantly reduced amount of reflections compared with the non-magnetic lens based on a linear transformation. The improved reflection performance of each new lens design is verified using a full-wave finite-element analysis and compared with previously reported transformation optical lenses.
    Optics Express 06/2009; 17(10):7807-17. · 3.55 Impact Factor
  • Do-Hoon Kwon, D.H. Werner
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    ABSTRACT: A beam scanning/switching method utilizing a transformation electromagnetics device is presented. A flat focusing lens based on the coordinate transformation approach is designed such that the field radiated by an antenna at the lens focus is transformed into a directive beam emitted normal to the lens surface. The main beam can be scanned by moving the antenna in the focal plane. Physical movement of the source or the lens can be avoided by placing an array of radiators in the focal plane. Selective excitations of individual antennas in a linear array configuration result in switched beams. Full-wave numerical simulations are performed, and the results for 2D lens configurations with line sources are provided.
    IEEE Antennas and Wireless Propagation Letters 02/2009; · 1.67 Impact Factor
  • Source
    Do-Hoon Kwon, Douglas H Werner
    [Show abstract] [Hide abstract]
    ABSTRACT: The transformation optics technique is employed in this paper to design two optical devices - a two-dimensional polarization splitter and a three-dimensional polarization rotator for propagating beams. The polarization splitter translates the TM- and the TE-polarized components of an incident beam in opposite directions (i.e., shifted up or shifted down). The polarization rotator rotates the polarization state of an incoming beam by an arbitrary angle. Both optical devices are reflectionless at the entry and exit interfaces. Design details and full-wave simulation results are provided.
    Optics Express 12/2008; 16(23):18731-8. · 3.55 Impact Factor
  • Source
    Do-Hoon Kwon, Douglas H Werner
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    ABSTRACT: The transformation optics technique is applied to design three novel devices—a wave collimator, far-zone and near-zone focusing flat optical lenses and a right-angle bend for propagating beam fields. The structures presented in this paper are all two-dimensional (2D), however, the transformation optics design methodologies can be easily extended to develop 3D versions of these optical devices. The required values of the permittivity and the permeability tensors are derived for each of the three devices considered here. Furthermore, the functional performance of each device is verified using full-wave electromagnetic simulations. A wave collimator consists of a 2D rectangular cylinder where the fields (cylindrical waves) radiated by an embedded line source emerge normal to the top and bottom planar interfaces thereby producing highly directive collimated fields. Next, a far-zone focusing lens for a 2D line source is created by transforming the equi-amplitude equi-phase contour to a planar surface. It is also demonstrated that by aligning two far-zone focusing flat lenses in a back-to-back configuration, a near-zone focusing lens is obtained. Finally, a 2D square cylindrical volume is transformed into a cylinder with a fan-shaped cross section to design a right-angle bend device for propagating beam fields.
    New Journal of Physics 11/2008; 10(11):115023. · 4.06 Impact Factor
  • Source
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    ABSTRACT: Planar chiral metamaterials comprising double-layer dielectricmetal- dielectric resonant structures in the shape of a gammadion are presented in the near-infrared regime. The unit cell of the doubly-periodic metamaterial design is optimized using the genetic algorithm for maximum circular dichroism and for maximum optical activity. A circular dichroism value in excess of 50% is predicted for the optimized design. Maximum polarization rotatory powers in terms of the minimum allowed transmittances are also obtained and presented.
    Optics Express 09/2008; 16(16):11802-7. · 3.55 Impact Factor

Publication Stats

530 Citations
70.43 Total Impact Points

Institutions

  • 2008–2012
    • University of Massachusetts Amherst
      • Department of Electrical and Computer Engineering
      Amherst Center, Massachusetts, United States
  • 2007–2010
    • Pennsylvania State University
      • Department of Electrical Engineering
      University Park, MD, United States
    • Purdue University
      • Birck Nanotechnology Center
      West Lafayette, IN, United States