Browsing by Subject "Negative refractive index"
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Item Open Access Chiral metamaterials with negative refractive index based on four "U" split ring resonators(American Institute of Physics, 2010-08-23) Li, Z.; Zhao, R.; Koschny, T.; Kafesaki, M.; Alici, K. B.; Colak, E.; Caglayan, H.; Özbay, Ekmel; Soukoulis, C. M.A uniaxial chiral metamaterial is constructed by double-layered four "U" split ring resonators mutually twisted by 90°. It shows a giant optical activity and circular dichroism. The retrieval results reveal that a negative refractive index is realized for circularly polarized waves due to the large chirality. The experimental results are in good agreement with the numerical results.Item Open Access Chiral metamaterials: From negative index to asymmetric transmission(IEEE, 2013) Mutlu, Mehmet; Li, Zhaofeng; Özbay, EkmelChiral metamaterials are attractive for their intriguing properties such as negative refractive index, optical activity and circular dichroism, and asymmetric transmission. In this paper, we review the research we have conducted for the purpose of investigating these exciting properties. © 2013 EurAAP.Item Open Access Complementary chiral metamaterials with giant optical activity and negative refractive index(American Institute of Physics, 2011-04-20) Li, Z.; Alici, K. B.; Colak, E.; Özbay, EkmelA complementary bilayer cross-wire chiral metamaterial is proposed and studied experimentally and numerically. It exhibits giant optical activity and a small circular dichroism. The retrieval results reveal that a negative refractive index is realized for right circularly polarized waves due to the strong chirality. Our numerical results show that the mechanism of the chiral behavior at the resonance of lower frequency can be interpreted as the coupling effects between two sets of mutually twisted virtual magnetic dipoles, while the resonance of higher frequency shows complicated nonlocal features.Item Open Access Conversion from constitutive parameters to dispersive transmission line parameters for multi-band metamaterials(Taylor and Francis Ltd., 2016) Ozturk, Y.; Yilmaz, A. E.; Özbay, EkmelIn this study, we explain an approach including conversion from constitutive parameters to dispersive transmission line parameters using the double-band DNG (double-negative) properties of the circular type fishnet metamaterials. After designing the metamaterial structure, the numerical calculations and the composite right/left-handed (CRLH) modeling of circular-type metamaterials are realized in free space. Detailed dispersion characteristics give us the opportunity to explain the true behavior of the inclusions during the analysis stage. By combining the results coming from the standard retrieval procedure with the conventional CRLH theory, we calculate the actual values of the transmission line parameters for all frequency regimes. The constitutive parameters of an equivalent CRLH transmission line are derived and shown to be negative values. It is shown that the constitutive parameters present the same behavior for all negative refractive index regimes. The double-negative properties and the phase advance/lag behavior of metamaterials are observed based on the dispersive transmission line parameters.Item Open Access Experimental study of subwavelength focusing by lefthanded metamaterials with a negative refractive index(2007) Özbay, Ekmel; Aydin, K.Two dimensional (2D) left-handed metamaterials (LHM) exhibiting negative refraction and subwavelength imaging are studied experimentally. A left-handed transmission band is observed at the frequencies where both dielectric permittivity and magnetic permeability are simultaneously negative. 2D LHM structure is verified to have a negative refractive index by measuring the refraction through a prism-shaped sample. Subwavelength focusing is observed by using a flat LHM superlens.Item Open Access The magical world of metamaterials(SPIE, 2009) Çağlayan, Hümeyra; Özbay, EkmelWe review experimental and theoretical studies performed on left-handed metamaterials (LHM). The metamaterials exhibit quiet unusual electromagnetic properties such as negative refraction, negative phase velocity, subwavelength focusing, subwavelength cavities and enhanced transmission.Item Open Access The magical world of metamaterials(IEEE, 2009-10) Özbay, EkmelIn recent years, there has been a burgeoning interest in rapidly growing field of metamaterials due to their unprecedented properties unattainable from ordinary materials. Veselago pointed out that a material exhibiting negative values of dielectric permittivity (ε) and magnetic permeability (μ) would have a negative refractive index [1]. Generally speaking, the dielectric permittivity (ε) and the magnetic permeability (μ) are both positive for natural materials. In fact it is possible to obtain negative values for ε and μ by utilizing proper designs of metamaterials. Left-handed electromagnetism and negative refraction are achievable with artificially structured metamaterials exhibiting negative values of permittivity and permeability simultaneously at a certain frequency region. The first steps to realize these novel type of materials were taken by Smith et al., where they were able to observe a left-handed propagation band at frequencies where both dielectric permittivity and magnetic permeability of the composite metamaterial are negative [2]. Soon after, left-handed metamaterials with an effective negative index of refraction are successfully demonstrated by various groups [3].Item Open Access Negative refraction and subwavelength focusing in two-dimensional photonic crystals(Springer-Verlag, 2007) Özbay, Ekmel; Özkan, Gonca; Krowne, C. M.; Zhang, Y.We experimentally and theoretically demonstrate negative refraction and focusing on electromagnetic (EM) waves by using two-dimensional photonic crystal slabs at microwave frequencies. 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 negative refractive index. Subwavelength imaging and flat lens behavior of photonic crystals are successfully demonstrated. We have been able to overcome the diffraction limit and focus the EM waves to a spot size of 0.21θ. Metallodielectric photonic crystals are employed to increase the range of angles of incidence that results in negative refraction. Experimental results and theoretical calculations are in good agreement throughout the work.Item Open Access Negative refraction and subwavelength focusing using left-handed composite metamaterials(SPIE, 2008-01) Özbay, Ekmel; Aydın, KorayWe review experimental studies performed on left-handed metamaterials (LHM) at microwave frequencies. The metamaterial structure is composed of periodic arrays of split-ring resonators and wire meshes and exhibits a left-handed propagation band at frequencies of negative permittivity and negative permeability. Negative refraction is verified using prism shaped LHM and also by beam-shifting method. Subwavelength focusing of a point source is achieved with a resolution of 0.13λ, through a flat LHM superlens.Item Open Access A planar metamaterial with dual-band double-negative response at EHF(IEEE, 2009-10-02) Gundogdu, T. F.; Guven, K.; Gokkavas, M.; Soukoulis, C. M.; Özbay, EkmelWe report the fabrication and electromagnetic characterization of a planar composite metamaterial (CMM) that is designed to achieve dual-frequency double-negative response at the lower end of the extremely high-frequency (EHF) band. The CMM is based on cut wire pairs and continuous wire elements. Dual-frequency operation is obtained by employing cut wire pairs of two different lengths within the unit cell of the CMM. The magnetic response of the cut wire pairs and the left-handed transmission band of the CMM are demonstrated by experiment and numerical simulations. It is found that the combined electric response of the dual-band CMM is complicated and imposes certain restrictions to the structure design in achieving true left-handed response at both designated frequencies.Item Open Access Science meets magic: photonic metamaterials(Society of Photo-Optical Instrumentation Engineers, 2012-05) Özbay, EkmelThe word "magic" is usually associated with movies, fiction, children stories, etc. but seldom with the natural sciences. Recent advances in metamaterials have changed this notion, in which we can now speak of "almost magical" properties that scientists could only dream about only a decade ago. In this article, we review some of the recent "almost magical" progress in the field of meta-materials. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).Item Open Access Two-dimensional left-handed metamaterial with a negative refractive index(IOP, 2006) Aydın, Koray; Güven, Kaan; Özbay, EkmelWe present a two-dimensional metamaterial with left-handed properties in a certain frequency range where both effective dielectric permittivity and magnetic permeability is simultaneously negative. A wedge-shaped metamaterial structure is employed for refractive index measurements. At the left-handed frequency range the structure is shown to have negative refractive index. Phase shift between consecutive number of layers of metamaterial structures are measured and a negative refractive index value is calculated from the amount of the phase shift. The structure is shown to have negative phase velocity. The refractive index values obtained from two different and independent methods are in good agreement.