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.

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 ($1/14{\mathsf{\lambda }}_{\circ }$, where ${\mathsf{\lambda }}_{\circ }$ 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.

The plasmon-induced transparency (PIT) in planar metasurface comprising of resonators having one S-shaped structure and a rectangular strip (both made of silver) was investigated. It was found that the S-shaped component of metasurface induces a single bright mode, whereas the rectangular strip manifests two bright modes with strong coupling of incident electromagnetic waves. When both the metasurface components were placed in the proximity, the PIT-like phenomenon was observed. The effects of rotational angle of the metasurface as well as the angle of incidence on the transmission spectra (of the metasurface) were also investigated. Both the transverse electric (TE) and transverse magnetic (TM) waves were used to explore the PIT effect. It was noticed that the PIT window could be easily tuned by altering the horizontal distance between the resonator components (i.e., the S-shaped structure and rectangular strip). It is expected that the proposed metasurface structure would be prudent in switching, ultrafast sensing and optical applications.

Metasurfaces, the two dimensional (2D) counterpart of bulky optical metamaterials, facilitate the implementation of abrupt phase discontinuities using an array of ultrathin and subwavelength features. These metasurfaces are considered as one of the propitious candidates for realization and development of miniaturized, surface-confined, and flat optical devices due to their unprecedented capabilities to engineer the wavefront of electromagnetic waves in reflection or transmission mode. The transmission type metasurfaces are indispensable as the majority of optical devices operate in transmission mode. Several transmission type plasmonic metasurfaces have been demonstrated but significant ohmic losses and strong dispersion hampered their performance and integration with state-of-the-art technologies. A high contrast all-dielectric metasurfaces provide a compact and versatile platform to achieve the complete (0−2𝜋) phase control of spin inversed transmitted wave using the concept of Pancharatnam-Barry (PB) phase. Here in this paper, we present ultrathin, highly efficient, all-dielectric metasurfaces implementing the nano-features of silicon on the quartz substrate. With the help of numerical optimization, the cross-polarized transmission efficiency for the operational wavelength of 1.55 𝜇𝑚 with the nanoscale spatial resolution is achieved as high as 95.6%. Significant high cross-polarized transmission efficiency has been achieved due to the excitation of electric quadrupole resonances with a very high magnitude. The highly efficient control over the phase enabled us to realize the riveting optical phenomenon in such a way that the phase profiles of two distinct optical devices, a lens and spiral phase plate (SPP) can be merged together producing a highly Focused Optical Vortex (FOV) with maximum focusing efficiency of 75.3%.