Abstract-Improvement of multiband absorption with different technics (graphene, ito, and hole) for metamaterial absorber at optical frequencies

Batuhan Mulla,  Cumali Sabah

https://www.spiedigitallibrary.org/journals/Journal-of-Nanophotonics/volume-12/issue-4/046017/Improvement-of-multiband-absorption-with-different-technics-graphene-ito-and/10.1117/1.JNP.12.046017.short?SSO=1

Three absorption improvement techniques are numerically applied to a multiband metamaterial absorber design for solar energy harvesting. These techniques are the following: the reshaping of the back metallic plate, the integrating of graphene sheets, and the utilizing of indium tin oxide (ITO), in the design. Based on numerical simulation results, each of these methods has the capacity to enhance total absorption rates. In addition to the enhancement in the total absorption rates, new absorption peaks are also obtained within the various frequency regions (infrared and ultraviolet). Furthermore, the absorption enhancement abilities of the mentioned methods are also compared. Among all the techniques, ITO provides the highest absorption rates, as it enhanced the total absorption rate by 48.5%.

© 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)

Abstract-Polarization independent triple-band (5,4) semiconducting carbon nanotube metamaterial absorber design for visible and ultraviolet regions

Madina Obaidullah,  Volkan Esat, Cumali Sabah,

https://www.spiedigitallibrary.org/journals/Journal-of-Nanophotonics/volume-11/issue-4/046011/Polarization-independent-triple-band-54-semiconducting-carbon-nanotube-metamaterial-absorber/10.1117/1.JNP.11.046011.short?SSO=1

Various metamaterial absorber designs operating in the microwave, infrared, visible, and ultraviolet frequency regions have been proposed in the literature. However, only a few studies have been done on the metamaterials that absorb in both visible and ultraviolet solar spectra. A triple-band polarization-insensitive metamaterial absorber structure with semiconducting single-walled carbon nanotube as the dielectric layer is proposed to efficiently absorb the incident electromagnetic radiations in visible and ultraviolet frequency regions. A unit cell of this design comprises three basic components in the form of metal–semiconductor–metal layers. The metallic part of the structure is aluminum, and the (5,4) single-walled carbon nanotube is used as the semiconducting material. The electromagnetic response of the proposed design is numerically simulated in the visible and ultraviolet regions with the maximum absorption rates of 99.75% at 479.4 THz, 99.94% at 766.9 THz, and 97.33% at 938.8 THz with corresponding skin depths of 13.0, 12.8, and 12.9 nm, respectively. Thus, solar cells based on this metamaterial absorber can offer nearly perfect absorption in the suggested frequency regions. The simple configuration of the design provides flexibility to control geometric parameters to be used in the solar cell and possesses the capability to be rescaled for other solar spectrum.

© 2017 Society of Photo-Optical Instrumentation Engineers (SPIE

Abstract-Stepwise technique for accurate and unique retrieval of electromagnetic properties of bianisotropic metamaterials

Ugur Cem Hasar, Joaquim J. Barroso, Cumali Sabah, Yunus Kaya, and Mehmet Ertugrul  »View Author Affiliations 
http://www.opticsinfobase.org/josab/abstract.cfm?uri=josab-30-4-1058

Metamaterials (MMs) are artificial materials that have received attention recently because their built-in features create collective electromagnetic effects that are otherwise impossible, such as negative refraction, and because of their exotic electromagnetic applications, namely, perfect lens and invisibility cloaks. Depending on wave propagation characteristics, MMs possessing normally weak magneto-electric coupling coefficients start to exhibit stronger bianisotropic effects. Therefore, accurate electromagnetic characterization of these MMs is important. In this study, we adapt a stepwise method based on the Nicolson–Ross–Weir technique for accurate and unique retrieval of electromagnetic properties of bianisotropic MM slabs. For this goal, we have derived explicit expressions for unique retrieval of electromagnetic properties of these slabs and compared these expressions with those in the literature in the retrieval process. From the comparison, we note that derived expressions are appropriate for unique determination of electromagnetic properties of bianisotropic MM slabs. In the performance analysis of the stepwise method for different measurement scenarios, we considered different bianisotropic MM cell configurations (split-ring and Omega-shaped resonators as well as the same resonators with wire strips) and extracted their electromagnetic properties when measured/simulated scattering parameters have some thermal noise. We note that for most of the frequencies, the stepwise method retrieves correct electromagnetic properties even when a relatively higher normally distributed noise with zero mean value and with standard deviations of 0.015 is present. In addition to the influence of thermal noise on performance of the stepwise method, we also analyzed the effect of both increasing length slab and the frequency band on retrieved electromagnetic properties of the analyzed various bianisotropic MM slabs.

© 2013 Optical Society of America