Nano-structure based metamaterial absorbers have been getting enormous interest owing to their widespread applications in solar cells, thermal emitters and integrated photonic devices. This paper presents a novel and ultrathin broadband metamaterial absorber comprised of a hexagonal nano-ring shaped fractal structure. The designed fractal metamaterial absorber (FMA) is composed of a three-layer device having a metal-insulator-metal (MIM) configuration. Based on the numerical simulations, the proposed FMA manifests more than 97% absorptivity for the operating wavelength from 820 to 2520 nm. However, it shows above 80% absorption value for the entire operating wavelength from 200 to 4000 nm. To predict the angular stability of this broadband absorption device, the absorptivity was investigated under different oblique incident angles of the exciting wave by considering both transverse electric (TE)- and transverse magnetic (TM)-polarization. Further, multiple reflection theory was employed to calculate the absorption value of FMA, and it shows appreciable agreement with the simulation results. It is also anticipated that this kind of FMA has not been investigated yet with these ultrabroadband absorption characteristics. Large operating bandwidth, angular robustness, ultra-compact thickness and inclusion of low-cost and temperature-endurable nickel metal (Ni) make this nanostructure-based absorber an attractive candidate for solar photovoltaics, thermal emission, and infrared spectroscopic applications.
Achieving the broadband response of metamaterial absorbers has been quite challenging due to the inherent bandwidth limitations. Herein, the investigation was made of a unique kind of visible light metamaterial absorber comprising elliptical rings-shaped fractal metasurface using tungsten metal. It was found that the proposed absorber exhibits average absorption of over 90% in the visible wavelength span of 400-750 nm. The features of perfect absorption could be observed because of the localized surface plasmon resonance that causes impedance matching. Moreover, in the context of optoelectronic applications, the absorber yields absorbance up to ~ 70% even with the incidence obliquity in the range of 0°-60° for transverse electric polarization. The theory of multiple reflections was employed to further verify the performance of the absorber. the obtained theoretical results were found to be in close agreement with the simulation results. in order to optimize the results, the performance was analyzed in terms of the figure of merit and operating bandwidth. Significant amount of absorption in the entire visible span, wide-angle stability, and utilization of low-cost metal make the proposed absorber suitable in varieties of photonics applications, in particular photovoltaics, thermal emitters and sensors. In recent years, optical metamaterials have gained considerable attention in both the engineering and scientific lexicons owing to the exotic electromagnetic (EM) response, that led to varieties of technological applications 1-6. As has been in reports, these artificially engineered materials allow the versatile utility to manipulate the amplitude, phase, and polarization of the incidence radiation at a deep subwavelength scale 7. Metamaterials are generally comprised of nano-resonators, scatterers and meta-molecules of different size, shape, geometry, orientation, and arrangement. Within the context, the negative refractive index (RI)-based metasurfaces enable intriguing applications in super lensing 8 , planar filters 3 , optical cloaking 9,10 , wavefront manipulation 11,12 , optical chirality 13 , medical imaging 14 , and perfect absorption 15-17. These are also tremendously exploited in various other EM applications, namely asymmetric transmission, plasmon-induced transparency, holography, and bio-sensing 6,17-19. Extensive studies have been reported on metamaterial absorbers operating in different frequency regimes 20-22 owing to the prevalent applications in bolometer, holograms, stealth technology, solar energy harvesting, wireless communications, and sensors 15-17,23-27. From the perspective of absorption bandwidth, the narrowband metamaterial absorbers covering the visible and infrared (IR) regimes find applications, such as thermal emission manipulation, nano-antennas, sensors, and resonators 28,29. On the other hand, wideband absorbers have potentials in solar energy converters, artificial colors, thermal emitters, and many other optoelectronic applications 30,31. Within the context, photovoltaics have im...
Broadband metasurface-based devices are essential and indispensable in modern wireless communication systems. This paper presents an ultra−wideband and wide incident angle reflective cross−polarization converter metasurface. The unit cell of the proposed structure is a 45° rotated anisotropic meta−sheet developed by cutting the rhombus−shaped patch from the central part of the square patch. The unit cell’s top structure and ground blocking sheet are made of copper, whereas a dielectric substrate (FR−4) is used as an intermediate spacer between them. The unit cell thickness is minimal compared to the operating wavelength (1/14λ∘, where λ∘ is the wavelength of the starting frequency of 13 GHz of the operating band). The proposed structure efficiently converts linearly polarized waves into their orthogonal component, with a polarization conversion ratio of (PCR > 90%) over a broad frequency spectrum of 13 GHz to 26 GHz. The physical origin of polarization conversion is also depicted using surface current distribution plots. An ultra−wideband and highly efficient polarization conversion (above 90%) is achieved with the help of strong electromagnetic resonance coupling between the upper and lower layer of the metasurface. This kind of ultra−wideband polarization conversion metasurface can be employed in satellite communication, radar cross−section reduction, and navigation systems.
Broadband absorption in the terahertz regime is a challenge and onerous to realize with a single layer metasurface. Self-similarity in fractal structures are exploiting metamaterial characteristics that offer a promising platform to design wideband microwave and optical devices. This paper presents a metamaterial absorber that consists of fractal geometry of Pythagorean-tree. The proposed metamaterial absorber demonstrates the wideband absorptivity in a terahertz spectrum ranging from 7.5–10 THz. Both transverse electric (TE)–and transverse magnetic(TM)–mode are taken up under different obliquity incidence angles to deeply study the angular dependence on absorption features of the Pythagorean-tree fractal meta-absorber (PTFMA). A numerical approach of interference theory is employed to verify the simulation results of the designed PTFMA. Further, the performance of the PTFMA was analyzed in terms of the figure of merit (FOM) and operational bandwidth (OBW) for different geometric parameters. Furthermore, surface electric field patterns and current distributions were studied to understand the absorption mechanism of the suggested PTFMA. The designed absorber would be a promising contender for bolometers, THz detection, and communication.
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