Affiliated with the
Communication & Space
Sciences Laboratory

Novel Electromagnetic Metamaterials

Transformation Electromagnetics/Optics

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..: References :..

1-) Transformation Optical Designs for Wave Collimators, Flat Lenses and Right-angle Bends
by Do-Hoon Kwon and Douglas H. Werner
New Journal of Physics, 10 (2008) 115023, 27 November 2008.

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 equiphase contour to a planar surface. It is also demonstrated that by aligning two farzone 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.

2-) Polarization Splitter and Polarization Rotator Designs Based on Transformation Optics
by Do-Hoon Kwon and D. H. Werner
Optics Express, Vol. 16, Issue 23, pp. 18731-18738.

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

3-) Flat Focusing Lens Designs Having Minimized Reflection Based on Coordinate Transformation Techniques
by Do-Hoon Kwon and D. H. Werner
Optics Express, Vol. 17, Issue 10, pp. 7807-7817.

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.

4-) Beam Scanning Using Flat Transformation Electromagnetic Focusing Lenses
by Do-Hoon Kwon and Douglas H. Werner
IEEE Antennas and Wireless Propagation Letters, Vol 8, pp. 1115-1118, 2009.

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.

5-) Conformal Mappings to Achieve Simple Material Parameters for Transformation Optics Devices
by Jeremiah P. Turpin, Ayah T. Massoud, Zhi Hao Jiang, Pingjuan L. Werner, and Douglas H. Werner
Optics Express, Vol 18, Issue 1, pp. 244 - 252, 2010.

ABSTRACT: The transformation optics technique for designing novel electromagnetic and optical devices offers great control over wave behavior, but is difficult to implement primarily due to limitations in current metamaterial design and fabrication techniques. This paper demonstrates that restricting the spatial transformation to a conformal mapping can lead to much simpler material parameters for more practical implementation. As an example, a flat cylindrical-to-plane-wave conversion lens is presented and its performance validated through numerical simulations. It is shown that the lens dimensions and embedded source location can be adjusted to produce one, two, or four highly directive planar beams. Two metamaterial designs for this lens that implement the required effective medium parameters are proposed and their behavior analyzed.

6-) Transformation Electromagnetics: An Overview of the Theory and Applications
by Do-Hoon Kwon, and Douglas H. Werner
IEEE Antennas and Propagation Magazine, Vol 52, Issue 1, pp. 24 - 46, 2010.

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.

7-) Experimental demonstration of a broadband transformation optics lens for highly directive multibeam emission
by Zhi Hao Jiang, Micah D. Gregory, and Douglas H. Werner
Phys. Rev. B, vol. 84, pp.165111(1)-(6), October 2011.

ABSTRACT:The emerging field of transformation optics, with its powerful ability to manipulate and control electromagnetic waves, represents a promising new approach to tailor the radiation properties of antennas. However, previously reported source transformation designs have been severely limited by their narrow operating bandwidth, as well as the number and directions of radiated beams. In this paper, we design, fabricate, and characterize a new type of broadband transformation optics lens capable of converting the radiation from an embedded isotropic source into any desired number of highly directive beams pointing in arbitrary directions. We exploit the dispersive properties of the metamaterial building blocks to greatly enhance the impedance bandwidth of the embedded antenna. Moreover, the simple material parameters required by the demonstrated transformation make it amenable to the development of practical beam collimating devices that operate in both the microwave and the optical regimes.

8-) Body-of-revolution finite-difference time-domain for rigorous analysis of three-dimensional axisymmetric transformation optics lenses
by Xiande Wang, Qi Wu, Jeremiah P. Turpin, and Douglas H. Werner
Optics Letters, vol. 38, pp. 67-69, January 2013.

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.

9-) Design of Metamaterial-Coated Arrays through Quasi-Conformal Transformation Optics
by Ephrem T. Bekele, Giacomo Oliveri, Jeremiah P. Turpin, Douglas H. Werner, and Andrea Massa
Proceedings of The 8th European Conference on Antennas and Propagation (EuCAP), The Hague, The Netherlands, 6-11 April 2014.

ABSTRACT:This paper presents synthesis of conformal arrays enhanced by metamaterial lenses. The synthesis uses a multi-step Quasi-Conformal Transformation Optics technique to compute lens parameters that allow an arbitrary-shaped conformal array to acquire properties of another desirable conformal array. The approach is demonstrated by numerical experiments including a full wave simulation.

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