Browsing by Subject "Electromagnetic wave transmission"

Now showing 1 - 9 of 9

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
Enhanced transmission of microwave radiation in one-dimensional metallic gratings with subwavelength aperture
(American Institute of Physics, 2004) Akarca-Biyikli, S. S.; Bulu, I.; Özbay, Ekmel
We report a theoretical and experimental demonstration of enhanced microwave transmission through subwavelength apertures in metallic structures with double-sided gratings. Three different types of aluminum gratings (sinusoidal, symmetric rectangular, and asymmetric rectangular shaped) are designed and analyzed. Our samples have a periodicity of 16 mm, and a slit width of 2 mm. Transmission measurements are taken in the 10–37.5 GHz frequency spectrum, which corresponds to 8–30 mm wavelength region. All three structures display significantly enhanced transmission around surface plasmon resonance frequencies. The experimental results agree well with finite-difference-time-domain based theoretical simulations. Asymmetric rectangular grating structure exhibits the best results with ,50% transmission at 20.7 mm, enhancement factor of ,25, and ±4° angular divergence.
Open Access
Laser-micromachined millimeter-wave photonic band-gap cavity structures
(American Institute of Physics, 1995) Özbay, Ekmel; Tuttle, G.; McCalmont, J. S.; Sigalas, M.; Biswas, R.; Soukoulis, C. M.; Ho, K. M.
We have used laser-micromachined alumina substrates to build a three-dimensional photonic band-gap crystal. The rod-based structure has a three-dimensional full photonic band gap between 90 and 100 GHz. The high resistivity of alumina results in a typical attenuation rate of 15 dB per unit cell within the band gap. By removing material, we have built defects which can be used as millimeter-wave cavity structures. The resulting quality ~Q! factors of the millimeter-wave cavity structures were as high as 1000 with a peak transmission of 10 dB below the incident signal. © 1995 American Institute of Physics.
Open Access
Microwave transmission through metamaterials in free space
(2002) Aydın, Koray; Bayındır, Mehmet; Özbay, Ekmel
To investigate properties of metamaterials, composite structures which consists of periodical arrangement of thin copper wires and SRRs on a circuit board was constructed. Through this, the transmission properties of composite metamaterials at microwave frequencies were investigated. It was observed that a pass-band was formed within the forbidden transmission bands of thin wire and SRR structures.
Open Access
Near-field light localization using subwavelength apertures incorporated with metamaterials
(Elsevier, 2012-03-12) Ates, D.; Cakmak, A. O.; Özbay, Ekmel
We report strong near-field electromagnetic localization by using subwavelength apertures and metamaterials that operate at microwave frequencies. We designed split ring resonators with distinct configurations in order to obtain extraordinary transmission results. Furthermore, we analyzed the field localization and focusing characteristics of the transmitted evanescent waves. The employed metamaterial configurations yielded an improvement on the transmission efficiency on the order of 27 dB and 50 dB for the deep subwavelength apertures. The metamaterial loaded apertures are considered as a total system that offered spot size conversion ratios as high as 7.12 and 9.11 for the corresponding metamaterial configurations. The proposed system is shown to intensify the electric fields of the source located in the near-field. It also narrows down the electromagnetic waves such that a full width at half maximum value of λ/29 is obtained.
Open Access
Negative refraction through an impedance-matched left-handed metamaterial slab
(Optical Society of American (OSA), 2006) Aydin, K.; Özbay, Ekmel
We report the transmission and reflection characteristics of a two-dimensional (2D) left-handed metamaterial (LHM). A well-defined left-handed (LH) transmission band with a peak value of -9.9 dB is obtained at frequencies where both effective permittivity and permeability are negative. A very sharp dip (-38 dB) at the reflection spectrum due to impedance matching at the surface of a 2D LHM is observed. Gaussian beam shifting experiments are performed to study the LH properties of a LHM structure. The structure has a negative refraction of electromagnetic waves in a certain frequency range. The negative refractive index values obtained for four different incident angles are in good agreement. © 2006 Optical Society of America.
Open Access
One-way transmission through the subwavelength slit in nonsymmetric metallic gratings
(Optical Society of America, 2010-07-27) Cakmakyapan, S.; Serebryannikov, A. E.; Caglayan, H.; Özbay, Ekmel
An approach for obtaining one-way transmission in the beaming regime is suggested that is based on the directional radiation of surface plasmons in nonsymmetric metallic gratings with a single slit. In contrast to the various nonsymmetric one-way diffraction gratings that have recently been proposed, the possibility of obtaining of narrow beams is demonstrated. Strong directional selectivity can appear a wide range of the observation angles, while the angle of incidence is retained.
Open Access
Plasmonic structures with extraordinary transmission and highly directional beaming properties
(Wiley Periodicals, 2006) Cağlayan, H.; Bulu, I.; Özbay, Ekmel
We studied the grating-coupling phenomena between surface plasmons and electromagnetic waves in the microwave spectrum. We first present the experimental and theoretical results of an enhanced microwave transmission though a subwavelength circular annular aperture with and without metallic gratings. We demonstrate that a 145-fold enhancement factor could be obtained with a subwavelength circular annular aperture that was surrounded by periodic metallic gratings. This was assisted by the guided mode of the coaxial waveguide and by coupling to the surface plasmons. 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°. We demonstrate that only the output surface is responsible for the beaming effect. Furthermore, we present the field distributions and showed that there is no beaming effect at the off-resonance frequency. © 2006 Wiley Periodicals, Inc.
Open Access
Reflection properties and defect formation in photonic crystals
(A I P Publishing LLC, 1996-08-05) Özbay, Ekmel; Temelkuran, B.
We have investigated the surface reflection properties of a layer-by-layer photonic crystal. By using a Fabry-Perot resonant cavity analogy along with the reflection-phase information of the photonic crystal, we predicted defect frequencies of planar defect structures. Our predictions were in good agreement with the measured defect frequencies. Our simple model can also predict and explain double defect formation within the photonic band gap.