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.

The spectral characteristics of nanostructured hyperbolic metamaterial (HMM)-based absorber is investigated. The HMM structure is comprised of periodically arranged assembly of gold nanostrips. The results indicate nearly perfect absorption by the structure in the entire ultraviolet (UV) regime of the electromagnetic spectrum under certain configuration - the feature which would be useful for UV-shield related applications. The absorptivity of the structure can be tailored by altering the slant angle and thickness of gold nanostrips (in the HMM structure). The effect of altering the incidence angle of light is also reported.

A plethora of research in recent years has been reported on biosensing in the surface plasmon resonant systems. However, very little research has reported a tunable and highly sensitive biosensor in a nanoscale platform. In this regard, we propose a nanoscale hyperbolic metamaterial (HMM)-based prism coupled waveguide sensor (PCWS) in the near-infrared range. The HMM layer makes up one of the constituents of the PCWS—comprised of a periodically arranged assembly of silver nanostrips. The structure is numerically simulated by the finite difference time domain method. It is demonstrated that the sensitivity of the reflected light can be tuned through the refractive index (RI) of the solution. Moreover, the effects of alteration of constituents of PCWS on the sensitivity have been analyzed. Results show that the sensitivity of PCWS can be harnessed by altering the thickness, slant angle of HMM layer, volume fraction ($f$) of metal in the HMM layer, and the incidence angle of light. For this purpose, the structure is numerically simulated by the finite difference time domain method. In the optimum design of the proposed sensor, the maximum value of sensitivity is achieved as high as $S=3450\mathrm{nm}/\text{refractive}$ index unit with $\theta =10°$ and $\varphi =10°$ and a metamaterial thickness of 250 nm. Moreover, the structure has a nanoscale footprint of $600\mathrm{nm}\times 400\mathrm{nm}\times 200\mathrm{nm}$.

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.

A specially designed metallic E-shaped fractal-based perfect metamaterial absorber (PMA) with fairly wideband absorptivity in the K- and Ka-bands of the microwave regime was investigated. The PMA top surface is comprised of square-shaped split-ring resonators (SRRs) surrounded with the stated fractal design. The absorptivity of PMA was analyzed in the range of 20 – 30 GHz for the normal and oblique incidence of waves. Both the transverse electric (TE) and transverse magnetic (TM) modes were taken up to observe the robustness of the proposed design. It was observed that the fractal resonators exhibit capacitive effect at low frequencies, whereas the SRRs manifest capacitive effect at higher frequencies. The simulation and measured results were found to be in fairly good agreement. It is expected that the proposed design of PMA would be useful for 5G communication applications.

Graphene-based metamaterials are gaining popularity for developing various reconfigurable and electrically tunable optical devices – especially in terahertz (THz) and infrared (IR) bands. Therefore, in this paper, we aim to investigate the broadband metamaterial-based absorber that efficiently absorbs the THz radiation ranging from 2.2 to 4.6 THz. The proposed absorber comprises a simple meta-square ring of graphene, which possesses different slots in its structure to induce multiple plasmonic resonances. It is observed that the proposed absorber manifests above 95% absorption for the normally incident THz waves, and it also maintains its absorption value over 80% for different obliquely incident operating conditions. Furthermore, the proposed absorber shows polarization-insensitive features. In addition, the absorption characteristics regulate from 95% to 15% by adjusting the chemical potential of graphene from 1 eV to 0.1 eV. Some of the salient features of the proposed absorber is largest reported bandwidth for single layer absorber with smallest footprint without sacrificing polarization insensitivity or amplitude tunability. From the application point of view, it could provide the pathway for implementing switching, cloaking, smart absorbers, and detection phenomena in the THz range.