The manuscript presents the quadruple circular with plus shaped resonators based multi-band metamaterial absorber (QCPSRMBMA). The unit cell of QCPSRMBMA  consisted of 0.035 mm frequency selective surface as top layer that comprises of circular patches within which the plus shaped patches are embedded in each quadrant inside the square patch, middle layer is 0.8 mm FR-4 substrate and the lowermost layer is 0.035 mm thick copper ground metallic layer. The unit cell has dimensions of 9 mm X 9 mm X 0.8 mm and it is simulated in “CST microwave suite”. The simulated results for QCPSRMBMA design exhibited absorption bands at 6.44 GHz, 14.32 GHz, 31.16 GHz, and 34 GHz with absorptance of 99.33%, 98.07%, 81.68%, and 90.03% respectively whereas experimentally with some deviations the proposed design exhibited absorption bands at 6.36 GHz, 14.28 GHz, 31 GHz, and 33.96 GHz with absorptance of 99.48%, 99.04%, 86.83%, and 95.89% respectively . The three different shaped patches-plus shaped, circular shaped and square shaped contribute to high absorptance bands lying within frequency range from 6GHz – 35GHz with potential applications in stealth technology, reducing RCS, absorption in 5G spectrum.

 A high-gain and compact size 2 × 2 multi input multi-output (MIMO) antenna with a half mode substrate integrated waveguide (SIW) antenna is introduced in this paper for sub-6GHz 5G applications. The material used to develop the structure is FR-4 substrate, which has a dielectric constant of 4.3 and a thickness of 1.6mm. The HMSIW antenna is designed for size miniaturization and further enhancing the substrate for improving gain, and extended to a 4-port MIMO antenna. The CST software is used to create the antenna, extract the simulation results, and fabricate the antenna. The antenna is measured and vali dated using a Vector network analyzer (VNA) and an anechoic chamber. The proposed work achieves superior performance with high gain (>11.2 dBi), ultra-low ECC (<0.00001), high diversity gain (>9.96 dB), and over 90% radiation efficiency, making it significantly better than previously re ported designs for Sub-6 GHz 5G applications. 

The Doped process is an essential issue in the solid-state electronic engineering field. This paper presents a z-scan study to reveal the nonlinear optical characteristics of microstructure layers of Nitrogen Doped Graphene by varying pumping power. Nitrogen-Doped Graphene was prepared by chemical reaction and exposed to high temperature sequentially at room temperature to synthesize it. The nonlinear optical characteristics of Nitrogen-Doped Graphene were related to peak absorptions revealed by UV-VIS-NIR, and observations from FESEM images indicate that morphology layers look like crumpling sheets with diameters of several micrometers. The Z-Scan technique investigates the nonlinear optical characteristics run by a femtosecond laser with 800nm wavelength that revealed the two-photon absorption denoted by nonlinear absorption (NLR) with coefficient(a) and Kerr effect denoted by nonlinear refraction (NLR) with coefficient (n2) of Nitrogen-Doped Graphene. Increasing the pumping power in a femtosecond pulse laser from 42mW to 80mW enhances nonlinear optical properties, shows a negative lens, and causes thermal relaxation in Nitrogen-Doped Graphene. 

Flexibility with appropriate dopant concentration in vacant orbitals may significantly influence the  TM2O5 optical properties. Dopant induced oxygen defects may considerably affect the optical-transitions between the filled oxygen states and empty transition metals 3d states. This work introduces tunable design of photonic devices through Titanium (Ti) ion intercalation in transition metal pentoxides (TM2O5), specifically V2O5, Nb2O5, Ta2O5, and Db2O5. Unlike previous approaches limited to static properties, this approach dynamically modulates the optical characteristics by varying the Ti molar concentration (x = 0, 0.05, 0.075). Result is a wideband tunable device demonstrating significant enhancements in Peak Normalized Circular Dichroism (PNCD) and Normalized Handed Preserving Reflectance (NHPR). It has been observed that with an increase in molar concentration to x = 0.05, Nb2O5-based device shows a slight increase in circular dichroism at 1400 nm, which subsequently decreases as Ti content is increased to x = 0.075. For Db2O5, when the Ti content is raised to x = 0.05, circular dichroism increases to 0.548 at 1375 nm, but then decreases to 0.45 as the Ti content reaches x = 0.075. Similarly, highest value reported for NHPR is 0.910 using Db2O5. Moreover, as Ti content is increased to x = 0.05 in the Nb2O5-based device, there is a modest increase in NHPR at 1400 nm, which then starts to decline with a further increase in Ti content to x = 0.075. In the case of Db2O5, when Ti content is increased to x = 0.05, NHPR drops to 8.03 at 1600 nm, and further reduces to 0.500 when Ti content is raised to x = 0.075.This can be attributed to the fact of lowered energy gap and elevated photo-response. The behaviour of device can be attributed to the occurrence of half wave dipole resonance (HWDR) and guided mode resonance (GMR) that are surviving the losses and manipulating the light. Intercalation of Ti is resulting into polarization dependent phase shift. The interplay between localized Aluminium plasmonic resonances and delocalized TixT M2O5 resonances underpins improved performance. These findings offer a novel pathway for tunable, polarization-sensitive optical systems in photonic circuits, sensing, and energy efficient applications. The device can be tuned for specific wavelength by incorporating the variations in materials and intercalation factor.