Browsing by Subject "Electromagnetic wave diffraction"

Now showing 1 - 6 of 6

Open Access
Analysis of circular reflectors by complex source-dual series approach
(IEEE, 1993-06-07) Oğuzer, Taner; Altıntaş, Ayhan; Nosich, A. L.
In the present paper, two dimensional circular reflector antennas are analyzed by a rigorous analytical-numerical technique for both E and H polarization cases. The method is used in combination with the complex source approach. The convergence of the solution is guaranteed and any desired accuracy can be obtained. Some principal results of reflector antennas are examined by the exact circular reflector solution.
Open Access
Beaming of electromagnetic waves emitted through a subwavelength annular aperture
(Optical Society of American (OSA), 2006) Caglayan, H.; Bulu, I.; Özbay, Ekmel
We study the diffraction of electromagnetic waves from subwavelength metallic circular apertures in the microwave spectrum. The theoretical and experimental demonstration of the near- and far-field electromagnetic distributions for subwavelength circular annular apertures and circular annular apertures surrounded by concentric periodic grooves are reported here. The metallic samples had a subwavelength hole with a diameter of 8 mm and had concentric grooves with a periodicity of 16 mm. We present the angular transmission distributions from circular annular apertures, and circular annular apertures surrounded by concentric periodic grooves. At the surface-mode resonance frequency the transmitted electromagnetic waves from the subwavelength circular annular aperture surrounded by concentric periodic grooves have a strong angular confinement with an angular divergence of ±3°. This represents a fourfold reduction when compared with the angular divergence of the beam transmitted from the subwavelength circular aperture. © 2006 Optical Society of America.
Open Access
Experimental demonstration of negative refraction and subwavelength imaging by left-handed composite metamaterials
(Cambridge University Press, 2006) Özbay, Ekmel; Aydın, Koray; Özkan, Gonca; Bulu, İrfan
We report a true left-handed (LH) behavior and focusing in a composite metamaterial consisting of periodically arranged split ring resonator (SRR) and wire structures. The magnetic resonance of the SRR structure is demonstrated by comparing the transmission spectra of SRRs with that of closed SRRs. We confirmed experimentally that the effective plasma frequency of the LH material composed of SRRs and wires is lower than the plasma frequency of the wires. A well-defined left-handed transmission band with a peak value of -1.2 dB (-0.3 dB/cm) is obtained. We also report the transmission characteristics of a 2D composite metamaterial (CMM) structure in free space. At the frequencies where left-handed transmission takes place, we experimentally confirmed that the CMM structure has effective negative refractive index. Phase shift between consecutive numbers of layers of CMM is measured and phase velocity is shown to be negative at the relevant frequency range. Refractive index values obtained from the refraction experiments and the phase measurements are in good agreement and the experimental results agree extremely well with the theoretical calculations. By measuring the refracted electromagnetic (EM) waves from a LHM slab, we found an effective refractive index of -1.86. A 2D scanning transmission measurement technique was used to measure the intensity distribution of the electromagnetic (EM) waves that radiate from the point source. The flat lens behavior of a 2D CMM slab was demonstrated for two different point source distances of ds = 0.5λ and λ. The full width at half maximum of the focused beams is 0.36λ and 0.4λ, respectively, which are both below the diffraction limit. © 2006 Materials Research Society.
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
The method of analytical regularization in the electromagnetic wave scattering by thin disks
(Institution of Engineering and Technology, 2007) Balaban, M. V.; Nosich, A. I.; Altıntaş, Ayhan; Benson, T. M.
We consider the problem of diffraction of an arbitrary electromagnetic wave by a thin disk made from different materials and located in free space. Here we imply a zero- thickness perfectly electrically conducting (PEC) disk, and also thin electrically resistive (ER) and dielectric disks whose thickness is much smaller than the disk radius and the free space wavelength, and also much smaller than the skin-layer depth in the ER disk case. The method used for the modeling is based on the integral equation (IE) technique and analytical regularization. Starting with Maxwell's equations, boundary conditions and the radiation condition at infinity we obtain a set of coupled dual IEs (DIEs) for the unknowns and then reduce this set of equations to the coupled IEs of the Fredholm second kind. To verify our results we calculate the far field characteristics in the case of the PEC disk with the incident field being the field of horizontal electrical dipole located on the disk axis.
Open Access
Scaling of diffractive and refractive lenses for optical computing and interconnections
(Optical Society of America, 1994-06-10) Özaktaş, Haldun M.; Urey, H.; Lohmann, A. W.
We discuss both numerically and analytically how the space-bandwidth product and the information density of lenses scale as functions of their diameter and f-number over many orders of magnitude. This information may be useful for the design of optical computing and interconnection systems. For diffractive lenses, cost is defined as the number of resolution elements the lithographic production system must have; the relationship of this quantity to the space-bandwidth product and information density is also given.