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Transmitarray antenna performance is limited by the amplitude and phase uniformity of the illumination source. Horns are a common feed-source for transmitarrays, but require large separation distances in order to provide uniform illumination, thus, limiting the ability to realize low-profile horn-fed transmitarray systems. In order to overcome this challenge, transformation optics inspired lenses...
Through the careful consideration of field enhancement observed in individual unit cells, metamaterials can be designed for use in high power microwave (HPM) applications. However, power handling considerations are only one aspect of any metamaterial design's performance. Presented here are two metamaterial unit cell geometries which feature reconfigurable reflection phase behaviors intended for HPM...
A metamaterial design that can rapidly reconfigure its reflection phase angle and safely operate under high incident field strengths is presented for use in a high power microwave (HPM) reflectarray system. The design offers switching between reflection phase angles to allow for beam control with a stationary reflector and feed horn. Two variations of the design are presented which offer (a) fixed...
In recent years, there has been immense interest in two-dimensional metallic gratings based on plasmonic nanoparticles. The enhanced fields in these structures due to the plasmonic resonance of nano-particles, makes them ideal candidates for a variety of applications. Many of these studies have utilized spherical nano-particles which have a well-known localized surface plasmon resonance condition...
A metamaterial design that can rapidly reconfigure its reflection phase angle and safely operate under high incident field strengths is presented for use in a high power microwave (HPM) reflectarray system. The design offers switching between three sufficiently unique reflection phase angles to allow for beam control with a stationary reflector and feed horn. The metamaterial unit cell is fairly lightweight...
A multi-octave polarization splitting anisotropic metasurface is presented. The metasurface is comprised of a periodic array of metal structures synthesized via Bézier surfaces. An analytical solution for broadband polarization splitting is presented followed by a candidate design which exhibits multi-octave polarization splitting from 3µm to 15µm.
A reconfigurable dual-band circularly polarizing conformal patch antenna is demonstrated in the S-band. The dual-band behavior is achieved via the implementation of reactive end-loading without the use of shorting pins or any other connection to ground. Through the integration of variable capacitive or resistive elements into the reactive end-load, it is demonstrated that the second resonance frequency...
A reconfigurable long-wave infrared circularly polarizing anisotropic metasurface is presented. The polarizing metasurface is comprised of an anisotropic impedance surface consisting of a periodic array of metal structures synthesized via optimized Bézier surfaces. Additionally, a phase change material that facilitates reconfigurability is integrated into the metamaterial substrate.
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...
For simplicity, most ultra-wideband aperiodic array layout design approaches use only isotropic sources as elements during optimization. However, since the selected antenna element can have a large impact on the total radiation pattern of the final array, it would be beneficial in such cases to use realistic antenna element patterns when designing array layouts. In this paper, a realistic spiral antenna...
A novel approach for analysis of the scattering response of aperiodic quasicrystalline gratings is proposed. The method exploits the fact that mathematically quasicrystals can be obtained as irrational projections of higher-dimensional periodic structures onto the physical space. The periodicity in the super-space allows for application of plane wave expansion methods such as Rigorous Coupled-Wave...
Optical properties of aperiodic arrays of gold cylinders in the visible range are studied experimentally and analytically. Aperiodic samples based on Ammann-Beenker and Danzer tilings were fabricated and illuminated with visible light. The arrays are composed of gold cylinders with a diameter of 175 nm and a height of 50 nm in a fused silica medium. The images of the arrays showed multiple colors...
Local field enhancements in aperiodic arrays of gold nanospheres are studied. The arrays are based on three aperiodic tilings of the plane which display 5, 7, and 8 fold rotational symmetries that are not possible in conventional periodic arrays. Electromagnetic (EM) field calculations are based on the analytical generalized Mie theory (GMT). It will be shown that despite the fact that aperiodic arrays...
A reconfigurable near-infrared circularly polarizing reflector is presented. The circular polarizing reflector is comprised of a birefringent impedance surface consisting of a periodic array of reconfigurable split ring resonators. Integrated into the metamaterial surface is a phase change material that facilitates the reconfigurability.
Optical properties of aperiodic aggregates of gold nanospheres are studied. The optical response of these arrays can be explained in terms of the grating response of the array (photonic resonance) and the plasmonic response of the spheres (plasmonic resonance). In particular the couplings between the photonic and plasmonic modes are studied. In periodic arrays this coupling leads to the formation...
An overview of current high performance, nature-inspired ultra-wideband antenna array design techniques is given. The polyfractal, raised-power series (RPS), compact direct, and aperiodic tiling methods are discussed, which utilize nature-inspired optimization strategies such as the genetic algorithm or the recently developed covariance matrix adaptation evolutionary strategy. These methods have yielded...
Classical evolutionary strategies such as the genetic algorithm and particle swarm technique have long been the most called upon methods for optimization of electromagnetic design problems. Due to their capability for robust global search and their ease of implementation, they have been fruitfully applied to the design of antennas, arrays, frequency selective surfaces, metamaterials and other electromagnetic...
A new method for designing broadband transmission gratings with wide field of view for solar cell applications is proposed. The method is based on forming the sidewalls of the gratings according to polynomial functions. To achieve the optimal response, the roots of the polynomial are optimized. This method allows for generating complex sidewall profiles while keeping the number of variables at a manageable...
A prismatic-mesh periodic finite element boundary integral (P-FEBI) simulation tool is paired with a high performance real-valued evolutionary strategy to efficiently design frequency selective surfaces. The irregular, triangular meshing scheme is used to produce metallic structures of nearly any arbitrary shape and contour inside of the unit cell. The unit cell is bound by a parallelogram which permits...
A new all-dielectric metamaterial design methodology based on effective medium theory is proposed for perfect optical mirrors. The optical metamaterial parameters required to obtain a high reflection are derived. A robust genetic algorithm technique is then employed to evolve the optimal design for an optical mirror targeting near-perfect reflection at 3.3 µm (3.5 µm with substrate loading effects...
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