Browsing by Subject "Impedance matching"

Now showing 1 - 5 of 5

Open Access
Bismuth-based metamaterials: From narrowband reflective color filter to extremely broadband near perfect absorber
(De Gruyter, 2019) Ghobadi, Amir; Hajian, Hodjat; Gökbayrak, Murat; Bütün, Bayram; Özbay, Ekmel
In recent years, sub-wavelength metamaterials-based light perfect absorbers have been the subject of many studies. The most frequently utilized absorber configuration is based on nanostructured plasmonic metals. However, two main drawbacks were raised for this design architecture. One is the fabrication complexity and large scale incompatibility of these nano units. The other one is the inherent limitation of these common metals which mostly operate in the visible frequency range. Recently, strong interference effects in lithography-free planar multilayer designs have been proposed as a solution for tackling these drawbacks. In this paper, we reveal the extraordinary potential of bismuth (Bi) metal in achieving light perfect absorption in a planar design through a broad wavelength regime. For this aim, we adopted a modeling approach based on the transfer matrix method (TMM) to find the ideal conditions for light perfect absorption. According to the findings of our modeling and numerical simulations, it was demonstrated that the use of Bi in the metal-insulator-metal-insulator (MIMI) configuration can simultaneously provide two distinct functionalities; a narrow near unity reflection response and an ultra-broadband near perfect absorption. The reflection behavior can be employed to realize additive color filters in the visible range, while the ultra-broadband absorption response of the design can fully harvest solar irradiation in the visible and near infrared (NIR) ranges. The findings of this paper demonstrate the extraordinary potential of Bi metal for the design of deep sub-wavelength optical devices.
Open Access
Metamaterials with negative permeability and negative refractive index: Experiments and simulations
(Institute of Physics Publishing Ltd., 2007) Özbay, Ekmel; Guven, K.; Aydin, K.
We report the transmission characteristics of split-ring resonator and left-handed metamaterials (LHM) in the microwave frequency regime. A left-handed transmission band is observed at the frequencies where both dielectric permittivity and magnetic permeability are negative. The reflection characteristics of ordered and disordered LHMs are studied. The two-dimensional LHM structure is verified to have a negative refractive index. We employed three different methods to observe negative refraction: the beam shift method, refraction through wedge-shaped negative-index metamaterial, and phase-shift experiments.
Open Access
Model based anticontrol of chaos
(IEEE, 2003) Morgül, Ömer
We will consider model based anticontrol of chaotic systems. We consider both continuous and discrete time cases. We first assume that the systems to be controlled are linear and time invariant. Under controllability assumption, we transform these systems into some canonical forms. We assume the existence of chaotic systems which has similar forms. Then by using appropriate inputs, we match the dynamics of the systems to be controlled and the model chaotic systems.
Open Access
A narrow-band multi-resonant metamaterial in near-ir
(MDPI AG, 2020) Ali, Farhan; Aksu, S.
We theoretically investigate a multi-resonant plasmonic metamaterial perfect absorber operating between 600 and 950 nm wavelengths. The presented device generates 100% absorption at two resonance wavelengths and delivers an ultra-narrow band (sub-20 nm) and high quality factor resonance. The studied perfect absorber is a metal–insulator–metal configuration where a thin MgF spacer is sandwiched between an optically thick gold layer and uniformly patterned gold circular nanodisc antennas. The localized and propagating nature of the plasmonic resonances are characterized and confirmed theoretically. The origin of the perfect absorption is investigated using the impedance matching and critical coupling phenomenon. We calculate the effective impedance of the perfect absorber and confirm the matching with the free space impedance. We also investigate the scattering properties of the top antenna layer and confirm the minimized reflection at resonance wavelengths by calculating the absorption and scattering cross sections. The excitation of plasmonic resonances boost the near-field intensity by three orders of magnitude which enhances the interaction between the metamaterial surface and the incident energy. The refractive index sensitivity of the perfect absorber could go as high as nm/RIU. The presented optical characteristics make the proposed narrow-band multi-resonant perfect absorber a favorable platform for biosensing and contrast agent based bioimaging.
Open Access
Verification of impedance matching at the surface of left-handed materials
(Wiley, 2006) Aydın, Koray; Bulu, İrfan; Özbay, Ekmel
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.