Browsing by Author "Saenz, E."

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Open Access
Decoupling of multifrequency dipole antenna arrays for microwave imaging applications
(Hindawi Publishing Corporation, 2010) Saenz, E.; Guven, K.; Özbay, Ekmel; Ederra, I.; Gonzalo, R.
The mutual coupling between elements of a multifrequency dipole antenna array is experimentally investigated by S -parameter measurements and planar near-field scanning of the radiated field. A multifrequency array with six dipoles is analyzed. In order to reduce the coupling between dipoles, a planar metasurface is placed atop the array acting as superstrate. The mutual coupling of the antenna elements in the absence and presence of the superstrate is presented comparatively. Between 3 and 20dB mutual coupling reduction is achieved when the superstrate is used. By scanning the field radiated by the antennas and far-field measurements of the radiation pattern, it is observed that the superstrate confines the radiated power, increases the boresight radiation, and reduces the endfire radiation.
Open Access
Electromagnetic cloaking with canonical spiral inclusions
(Institute of Physics Publishing Ltd., 2008) Guven, K.; Saenz, E.; Gonzalo, R.; Özbay, Ekmel; Tretyakov, S.
We report an electromagnetic cloaking structure that is composed of identical canonical spiral particles. By using the Clausius-Mosotti formula, the electric and magnetic polarizabilities of a single spiral particle are related to the relative permittivity and permeability of the sparse distribution of particles. The permittivity and permeability of the distribution are, in turn, defined according to the coordinate transformation, which leads to the cloaking effect. Spirals are optimized to exhibit equal permittivity and permeability response so that the cloak consisting of these spirals will work for both transverse electric (TE) and transverse magnetic (TM) polarizations. Measurement of the cloaking device surrounding a metal cylinder inside a parallel waveguide was performed. The steady-state propagation of an electromagnetic wave was reconstructed from the amplitude and phase data, which demonstrates that the field largely restores to a free-space propagation pattern after the cloak.
Open Access
Enhanced directed emission from metamaterial based radiation source
(AIP Publishing LLC, 2008) Saenz, E.; Guven, K.; Özbay, Ekmel; Ederra, I.; Gonzalo, R.
The enhanced directed emission from a metasurface which is illuminated at its resonance frequency by a dipole source is experimentally demonstrated. The metasurface consists of two cutwire layers and a continuous wire layer in between, which exhibits strong magnetic dipole resonance under excitation normal to the plane. The scanned near-field patterns show the confinement of the field in the presence of metasurface, which, in turn, provides an enhanced and directional radiation in the far field. The far-field patterns are obtained by direct measurement and by a far-field transformation of the scanned near field, which are found to be in good agreement.
Open Access
Metamaterial based cloaking with sparse distribution of spiral resonators
(SPIE, 2010) Guven, K.; Saenz, E.; Gonzalo, R.; Özbay, Ekmel; Tretyakov, S.
We investigate the application of a metamaterial that is formed by the sparse distribution of spiral resonators as an optical transformation medium is in order to achieve electromagnetic cloaking. The well-known Clausius-Mossotti formula relates the microscopic polarizability of a single resonant particle to the macroscopic permittivity and permeability of the effective medium. By virtue of transformation optics, the permittivity and permeability of the medium, in turn, can be designed according to a coordinate transformation that maps a certain region of space to its surrounding. As a result, the mapped region can be cloaked from electromagnetic waves. In this study, the spirals are optimized to exhibit equal permittivity and permeability response so that the cloak formed by these spirals will work for both the TE and TM polarizations. An experimental setup is developed to visualize the steady state propagation of electromagnetic waves within a parallel plate waveguide including the cloaking structure. The measured and simulated electromagnetic field image indicates that the forward scattering of a metal cylinder is significantly reduced when placed within the cloak. © 2010 SPIE.
Open Access
Modeling of spirals with equal dielectric, magnetic, and chiral susceptibilities
(Taylor & Francis Inc., 2008) Saenz, E.; Semchenko I.; Khakhomov, S.; Guven, K.; Gonzalo, R.; Özbay, Ekmel; Tretyakov, S.
In this article, we study spiral particles with optimized design parameters, which can make possible the realization of media with equal dielectric, magnetic, and chiral susceptibilities. Two different spiral structures are investigated: the canonical spiral (which consists of a split loop with two straight-wire sections, orthogonal to the loop plane and connected to the edges of the gap) and the true helix (which is obtained by bending a wire with a constant pitch angle). The transmission and reflection coefficients of arrays of spiral particles are obtained under plane wave excitation by numerical simulation. The properties of slabs formed by periodic chiral and racemic arrays of spirals are investigated. Good agreement is found between the presented results and the previously reported theoretical and experimental studies.
Open Access
Near-field measurement of a planar meta-surface illuminated by dipole antennas
(IEEE, 2008-03) Saenz, E.; Güven, Kaan; Ederra, I.; Özbay, Ekmel; De Maagt, P.; Gonzalo, R.
In this paper, the uniform illumination of a meta-surface that is fed by a single dipole antenna or an array is experimentally investigated by means of near-field measurements. The results of the scanned field, when the dipoles are radiating in free space and when the meta-surface is placed atop them are presented. By means of this measurement, the coupling reduction between dipoles of an array due to the presence of the meta-surface is observed. ©2008 IEEE.