###### Abstract  
This article presents numerical analysis of an ultrathin concentric hexagonal ring resonator (CHRR) metamaterial absorber (MMA) for ultrawideband visible and infrared optical window applications. The proposed MMA exhibits an absorption of above 90% from 380 to 2500 nm and an average absorbance of 96.64% at entire operational bandwidth with a compact unit cell size of 66 \(\times\) 66 nm\({}^{2}\). The designed MMA shows maximum absorption of 99% at 618 nm. The absorption bandwidth of the MMA covers the entire visible and infrared optical windows. The nickel material has been used to design the top and bottom layer of MMA, where aluminium nitride (AIN) has been used as the substrate. The designed hexagonal MMA shows polarization-independent properties due to the symmetry of the design and a stable absorption label is also achieved for oblique incident angles up to 70 \({}^{\circ}\)C. The absorption property of hexagonal ring resonator MMA has been analyzed by design evaluation, parametric and various material investigations. The metamaterial property, surface current allocation, magnetic field and electric field have also been analyzed to explore the absorption properties. The proposed MMA has promising prospects in numerous applications like infrared detection, solar cells, gas detection sensors, imaging, etc. m 2022  
Ulurowideband Polarization-Independent Nanoarchitectonics: A Perfect Metamaterial Absorber for Visible and Infrared Optical Window Applications. Nanomaterials 2022122849. [[https://doi.org/10.3390/nan012162849](https://doi.org/10.3390/nan012162849)]([https://doi.org/10.3390/nan012162849](https://doi.org/10.3390/nan012162849))  
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M.L. [PERSON]  
M.L. [PERSON]
visible to the infrared regime, which is utilized in various applications [24]. Most of the MMAs are designed the visible regimes and constrained by the limited absorption spectrum, which restricts their uses to thermal emission manipulations and nanoantenna resonators [25; 26; 27]. Wideband absorbers are very attractive for applications like solar energy converters, thermal emitters, and artificial colors with angle and polarization-insensitive features [28; 29; 30]. The near-unity absorption is achieved by electromagnetic (EM) wave-inspired modulation of the interaction between matter and light [23]. EM wave absorbers are categorized into two types, i.e., resonant absorbers [11] and wideband absorbers [23; 31]. According to anomalous diffraction theory, the resonant absorbers are based on the resonance interaction between light and materials at their working frequencies [3]. Wideband absorbers depend on those materials whose characteristics are unrelated to the frequency with the highest intrinsic loss [25]. Multiple methods have been reported to achieve a wide band property, such as perpendicularly standing nanowires, multiple resonators employing in-plane arrangement, multilayer vertically stacked resonant elements etc. [32]. These methods broaden the absorption bandwidth; however, suffer from structural and manufacturing complexities. The merging of multilayer absorbers is challenging with industrial technologies due to its larger size, high cost, and use of new material [29]. Notably, the building process of multiple resonators is cost-efficient compared to the multilayer method. Therefore, designing an absorber with a wideband absorption spectrum, simple fabrication and low cost is necessary for optical window applications. The use of different materials is another potential method opted by numerous researchers to develop broadband absorbers. The idea of using Nickel (Ni) is one of the essential parts of this sequence due to its outstanding optical and chemical characteristics to develop a wideband absorber. The top layer's geometrical shape can provide broad absorption and wide-angle stability. In [20], a Ni-base wideband metamaterial absorber was designed and investigated its performance in visible and near-infrared regimes.