Ultra broadband microwave metamaterial absorber with multiple strong absorption peaks induced by sandwiched water resonators

Water-based metamaterial microwave absorbers have been proposed recently due to their potential for versatility such as optically transparence and flexibility. In this study, a sandwiched metamaterial absorber with cross-connect water rings is designed, which achieves an absorptivity of more than 90% in the ultra-broadband from 7.74 to 36.76 GHz, and the relative bandwidth can reach as high as 130.4% with a thickness of 3.8 mm. The multi-peak resonance characteristic of the absorption spectra of the proposed absorber is discussed in 6–40 GHz, and the strong resonance absorption is believed to be highly correlated to shape of the designed water unit cells. The impedance matching as well as the lossy mechanism is discussed based on the permittivity of water and periodic unit cells. Additionally, the proposed absorber shows a comprehensive performance with temperature insensitivity and broad absorption characteristics at wide incidence angles. Therefore, the proposed water-based metamaterial absorber shows excellent absorption performance while greatly reduces the difficulty of its preparation and implementation, which could be applied in a wider range of applications for different scenarios.