Showing papers by "Irfan Bulu published in 2006"
TL;DR: In this paper, the existence of a left-handed transmission band in a bulk composite metamaterial (CMM) around 0.3em, 0.5GHz was demonstrated experimentally.
Abstract: The existence of a left-handed (LH) transmission band in a bulk composite metamaterial (CMM) around $100\phantom{\rule{0.3em}{0ex}}\mathrm{GHz}$ is demonstrated experimentally. The CMM consists of stacked planar glass layers on which periodic patterns of micron-scale metallic wires and split-ring resonators are fabricated. The LH nature of the CMM band is proved by comparing the transmission spectra of individual CMM components. Theoretical investigation of the CMM by transmission simulations and an inversion scheme for the retrieval of the effective permeability and permittivity functions supports the existence of LH behavior.
126 citations
TL;DR: In this article, the angular transmission distributions of subwavelength metallic circular annular apertures surrounded by concentric periodic grooves were analyzed and compared with the angular divergence of the beam transmitted from the sub-wavelength circular aperture with a diameter of 8 mm and a periodicity of 16 mm.
Abstract: 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.
45 citations
TL;DR: In this article, the authors studied the grating-coupling phenomena between surface plasmons and electromagnetic waves in the microwave spectrum and demonstrated that a 145-fold enhancement factor could be obtained with a subwavelength circular annular aperture that was surrounded by periodic metallic gratings.
Abstract: 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. Microwave Opt Technol Lett 48: 2491–2496, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22015
26 citations
TL;DR: The experimental results showed that it is in fact possible to focus the source field with half-widths as small as wavelength/4 by using the labyrinth-based metamaterial.
Abstract: We studied focusing in a two-dimensional metamaterial that was based on a labyrinth structure. We theoretically showed that the labyrinth-based metamaterial exhibits negative indices of refraction between 6 and 6.4 GHz. We experimentally studied the focusing effect by measuring electric field intensities on the output side of the metamaterial when the source was placed in front of the input side of the metamaterial. Our experimental results showed that it is in fact possible to focus the source field with half-widths as small as λ/4 by using the labyrinth-based metamaterial.
23 citations
TL;DR: In this paper, left-handed materials (LHM) were employed as negative index materials and experimentally investigated the focusing behavior of such lenses. But the focusing effect occurred at the surface of the LHM with a spot size of 0.16λ.
Abstract: Lenses made of negative index materials exhibit different focusing behaviours compared to positive index material lenses. Flat lens behaviour and imaging below the diffraction limit is possible with negative refractive index lenses. In this study, we employed left-handed materials (LHM) as negative index materials and experimentally investigated the focusing behaviour of such lenses. A point source is embedded inside the LHM lens. We have shown that it is possible to focus electromagnetic (EM) waves by using a planar configuration of lenses that is constructed by using two-dimensional (2D) LHMs. Flat lens behaviour is observed at 3.89 GHz, where EM waves are focused along the lateral and longitudinal directions. At 3.77 GHz, where the reflection is measured to be minimum, the focusing effect occurred at the surface of the LHM with a spot size of 0.16λ. We were able to overcome the diffraction limit with a slab-shaped LHM superlens.
17 citations
TL;DR: In this article, a robust method to tune the plasma frequencies of wire mediums was proposed and demonstrated by using two or more wire arrangements in the unit cell of a labyrinth-based metamaterial.
Abstract: In this work, we suggest and demonstrate a robust method to tune the plasma frequencies of wire mediums. The method we suggest involves the use of two or more wire arrangements in the unit cell. By incorporating the method we suggested it is possible to tune the plasma frequencies of wire mediums effectively by use of lower metal densities. In addition, we study the effective permittivities and permeabilities of labyrinth based metamaterials. Our results show that the effective permeability of the labyrinth based metamaterial medium is negative above a certain frequency. The results of the effective permittivity calculations for the labyrinth based metamaterial medium reveal that the labyrinth structure exhibits a strong dielectric response near the magnetic resonance frequency. Finally, we design labyrinth based left-handed mediums that have several desired properties such as simultaneous μ, ϵ = −1 and μ, ϵ = 0. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2611–2615, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21988
14 citations
TL;DR: In this article, the authors present the experimental and theoretical verification of an impedance-matched LHM to free space using FDTD simulations and retrieval procedures and theoretically verify impedance matching at the surface of left-handed materials.
Abstract: Impedance matching at the surface of left-handed materials (LHM) is required for certain applications including a perfect lens. In this study, we present the experimental and theoretical verification of an impedance-matched LHM to free space. Reflection characteristics of both one-dimensional and two-dimensional LHM were investigated. The reflection was observed to be very low at a narrow frequency range. FDTD simulations and retrieval procedures were used to theoretically verify impedance matching. By varying the number of layers along the propagation direction, the ultralow reflection at specific frequencies was shown to be independent of the sample thickness. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2548–2552, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22003
9 citations
TL;DR: In this paper, the negative refraction and focusing of electromagnetic (EM) waves by two-dimensional photonic crystal slabs at microwave frequencies was demonstrated. But the negative reflection was not observed for transverse magnetic (TM) and transverse electric (TE) polarized incident EM waves.
Abstract: We experimentally and theoretically demonstrate the negative refraction and focusing of electromagnetic (EM) waves by two-dimensional photonic crystal slabs at microwave frequencies. The negative refraction is observed both for transverse magnetic (TM) and transverse electric (TE) polarized incident EM waves. Gaussian beam shifting method is used to verify the negative refractive index. The Subwavelength imaging and flat lens behavior of photonic crystals are succesfully demonstrated. We have been able to overcome the diffraction limit and focus the EM waves to a spot size of 0.21λ. Metallodielectric photonic crystals are employed to increase the range of angle of incidence that results in negative refraction. Experimental results and theoretical calculations are in good agreement throughout the work.
7 citations
01 Apr 2006
TL;DR: In this article, the negative refraction and focusing effect of a metallodielectric photonic crystal was studied for aflat-lens with large incidence angles, and it was shown that by using the metallodelectric reflector, it is possible to obtain negative refractive index for large incidence angle.
Abstract: In this work, we study the negative refraction and focusing effect by a metallodielectric photonic crystal. We show that by using a metallodielectric photonic crystal it is possible to obtain negative refraction for large incidence angles. In addition, our experimental and theoretical work reveal that the metallodielectric photonic crystal can be used as aflat-lens.
5 citations
01 Apr 2006
TL;DR: In this paper, the angular transmission distributions from circular annular apertures and circles surrounded by concentric periodic grooves have been studied and it was shown that at the surface mode resonance frequency, the transmitted electromagnetic waves from the sub-wavelength circle with a diameter of 8 mm have a strong angular confinement with an angular divergence of ± 3°.
Abstract: We studied the diffraction of electromagnetic waves from subwavelength metallic circular apertures in the microwave spectrum. 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 to the angular divergence of the beam transmitted from the subwavelength circular aperture.
2 citations
21 May 2006
TL;DR: In this article, the magnetic resonance of split-ring resonators (SRR) was investigated experimentally and the dependence of the geometrical parameters on the resonance frequency of SRR was studied.
Abstract: We investigated the magnetic resonance of split-ring resonators (SRR) experimentally. The dependence of the geometrical parameters on the resonance frequency of SRR is studied. We further investigated the effect of disorder on performance of SRRs.
01 Mar 2006
TL;DR: In this article, a labyrinth-based metamaterial was proposed to solve two major problems related to split-ring resonator-based structures, i.e., bianisotropy and electric coupling.
Abstract: We propose and demonstrate a new labyrinth based metamaterial structure that solves two major problems related to the split-ring resonator based structures One of the problems related to the
split-ring resonator structure is the bianisotropy, and the other problem is the electric coupling to the magnetic resonance of the split-ring resonator structure These two problems introduce difficulties in obtaining isotropic left-handed metamaterial mediums The new structure that we propose here solves both of these problems We further show that in addition to the magnetic resonance, when combined with a suitable wire medium, the structure that we propose exhibits left-handed transmission band A two-dimensional metamaterial based on the labyrinth structure is used to study imaging of a point source Our experimental results show that it is possible to image the point source with half widths as small as λ/4 by using the labyrinth based metamaterial
TL;DR: In this paper, the authors reported a true left-handed (LH) behavior and focusing in a composite metamaterial consisting of periodically arranged split ring resonator (SRR) and wire structures.
Abstract: 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 = 0.5e and e. The full width at half maximum of the focused beams is 0.36e and 0.4e, respectively, which are both below the diffraction limit.