Ultra-thin water-based metasurface with dual-broadband perfect absorption

The rapid development of the 5 G technology can be attributed to its outstanding penetration in the low frequency bands ranging from 600 MHz to 6 GHz, particularly in specific frequency ranges like 700 MHz, 2.3 GHz, and 3.5 GHz. Simultaneously, the technology excels in the millimeter-wave spectrum, spanning from 24 GHz to 52 GHz, notably in bands such as 24.25-27.5 GHz and 37-40 GHz, showcasing impressive capabilities for high-speed data transmission. Nevertheless, these signals frequently encounter electromagnetic interference from electronic equipment in practical applications, which compromise the quality of communication. To address these issues, this paper presents the design, fabrication, and measure of a dual-broadband ultra-thin water-based metasurface absorber (WBMA). The unit cell is composed of a 4 mm thick photoresist shell encasing a water layer and metal plate, and features an irregular octagonal prism and a rectangular annulus cavity within the water layer. Simulation and experimental outcomes indicate that the proposed metasurface achieves near-perfect absorption at frequencies from 4.2 GHz to 4.8 GHz and from 23.6 GHz to 51.1 GHz in the transverse electric mode. Additionally, the proposed metasurface exhibits more than 90% absorption in the transverse magnetic mode for frequency ranges from 4.3 GHz to 4.9 GHz and from 23.2 GHz to 50.8 GHz. The designed water-based metasurface also exhibits features of polarization insensitivity and capability to handle wide-angle incidence. Analysis of the electric and magnetic field distribution within the metasurface suggests that the absorption mechanism is driven by strong magnetic resonance within the water layer's structure. Furthermore, the effective impedance of the metamaterial absorber is explored. Given the unique absorption frequency bands, the proposed WBMA has potential applications in the realm of 5G communication.