Ultrabroadband Absorbers and Bi-Functional Sensors for Water-Based Metamaterials

In this study, we designed and observed an ultrabroadband absorber and bi-functional sensor based on a water-based metamaterial. The cavity material of the unit cell was photosensitive resin, the internal water layer was formed by connecting two opposite cross-types and rectangles, and the bottom layer was a copper backplate. Simulation results exhibited that the absorption rate for the water-based metamaterial was above 90% in the frequency ranges of 3.01-3.12 GHz and 13.31-57.75 GHz. Experimental results were in good agreement with the simulation results. We observed and analyzed the distribution of electric and magnetic fields at the absorption peaks and determined that the physical mechanism was the strong magnetic resonance between the water layer and the surrounding photosensitive resin. Owing to the irregular shape of the water layer, absorption properties of the proposed metamaterial were sensitive to incidence and polarization angles. At a higher polarization angle of 45°, the corresponding absorption band changed to 3.28-4.34 GHz and 13.31-57.75 GHz, covering the operating bands for 5G communication. The proposed water-based metamaterials were also sensitive to the refractive index and have two detection frequencies. The amplitude and frequency variations with different cover materials can be sensed. The sensitivities corresponding to the two resonance points were 25.58 dB/RIU, 5.04 GHz/RIU, and 27.85 dB/RIU, 4.09 GHz/RIU, respectively, exhibiting good sensing performance. Thus, the designed water-based metamaterials have potential applications in 5G signal shielding and biological detection.