The extraction of metallic nanoparticles (MNPs) from waste electrical and electronic equipment (WEEE) has gained extensive attention from researchers for eco-friendly, reliable, and sustainable alternative protocol over the traditional linear economic approach (make-use-dispose) for boosting the circular economy. A plethora of MNPs including metals/metal oxide nanoparticles having a size dimension ranging from 1–100 nanometers (nm) have been extracted from these WEEE by using different chemical, physical, and biological methods. Recovery of certain precious MNPs can be achieved by dismantling and recycling electronic waste items in the form of gold (Au), platinum (Pt), zinc oxide (ZnO), silver (Ag), and copper oxide (CuO). These MNPs provide a huge range of applications such as antibacterial, therapeutic, target drug delivery, and biotechnological applications. This comprehensive review provides in-depth knowledge of the synthesis of MNPs using different techniques from WEEE and delves into their potential applications in biomedical fields with in-depth mechanisms. This article also discussed global challenges and opportunities in this area for adopting the concept of circular economy to conserve natural resources for future generations and hence create a greener environment and protect our planet.

Metasurfaces have been widely investigated across the disciplines of optical biosensing due to their exceptional ability to manipulate electromagnetic fields. Consequently, over the past few years, there has been growing interest in the application of metasurfaces in optical biosensors in the field of biomedical sensing. While being label-free and offering real-time tracking, high sensitivity, and a quick response are among the benefits of conventional optical biosensors, the incorporation of metasurfaces improves their wavefront manipulation, selectivity for versatile sensing, and capacity for device miniaturization to satisfy increasingly complex application requirements. Furthermore, there is a lack of comprehensive evaluations that address the current research developments and future possibilities, despite the encouraging advancements in this emerging field. Hence, this work provides a comprehensive review and serves as a valuable resource for researchers exploring metasurface-based optical biosensors. This review delves into defining the basic sensing concepts, design procedures, and important figures of merit (FOM) for metasurface-based optical biosensors and their applications, including the detection of numerous analytes, such as viruses, toxins, antibodies, tumors, and drugs and the monitoring of blood sugar. Furthermore, presenting a critical evaluation of structural fabrication techniques with a view toward potential future commercialization, this review ends by highlighting several fascinating areas for further investigation. For this review article, a total of 5844 effective documents about metasurface optical biosensors were retrieved from the Scopus database. The VOSviewer version 1.6.20 bibliometric software was used for the scientific analysis of the data retrieved from the Scopus database from 2010 to 2025.

The remarkable abilities of metamaterial-based microwave absorbers (MMA) to regulate electromagnetic (EM) waves have attracted a lot of interest since they facilitate effective energy absorption at a variety of frequency ranges. The design ideas, material choices, and structural advancements that support MMA performance are the main topics of this comprehensive review. The mechanisms of absorption, such as resonance, reduction of plasma frequency, and impedance matching, have been highlighted, along with the function of material and geometric tunability in attaining wideband, angle-independent, and polarization-insensitive absorption. A special emphasis is provided to the classification of MMA based on the material composition, including dielectric, metal, magnetic, carbon, polymer, plasma, and hybrid along with their impacts on the performance characteristics. The emerging utilization of MMA is being investigated in areas such as wireless communication, electromagnetic interference (EMI) shielding, stealth technologies, antennae, and sensing. Recent developments in fabrication of MMA that use flexible, reconfigurable, and multipurpose materials to increase their potential in dynamic contexts are also highlighted in this review. Future directions for performance optimization and application scope expansion are examined, along with challenges about scalability, manufacturing accuracy, and integration with current technology.

Background: Circular antenna arrays are widely used in 5G, IoT, and beamforming applications of next-generation communications, however attaining the subsidiary lobes along with directivity is still a challenge. The array parameters could be estimated in real-time using a variety of standard approaches, but these methods would tends to lag in maintaining appropriate directivity and even a low side lobe level. Methods: To suppress the subsidiary lobe, achieve the required primary lobe direction, and enhance directivity, an optimization problem is applied in this study. Also with the circular antenna array problem, an artificial hummingbird algorithm (AHA) is used to accurately determine the regulating parameters. Results: Simulations are performed, and the outcomes are analyzed with those achieved using other accepted techniques. The results indicated that the artificial hummingbird technique significantly reduces side lobes while preserving acceptable directivity Conclusion: In this work based on the dimensional analysis, it is also possible to achieve high directivity values alongside low side lobe levels using reduced antenna elements.