Design of Liquid Based Frequency Selective Surfaces Operating as Absorbers

Liquid-based absorbers using frequency selective surfaces (FSSs) rely on 2D periodic lattices. Each unit cell contains one or more resonators filled with liquids, which dissipate electromagnetic energy. Water is preferred because of its wide availability and its high real and imaginary permittivity components. In this paper, we propose and optimize an all-dielectric unit cell structure placed on a metallic plane to function as an absorber when filled with water. A sharp and deep absorption resonance is obtained at 2 GHz, with a relative bandwidth of 14.5%. When optimized to work with methanol as absorbing liquid, the structure presents a resonance frequency of 1.25 GHz, with a relative bandwidth of 36.9%, and a second wide absorption band between 3.56 and 5 GHz. Field images are used to gain insight into the operation of the absorber. The sensitivity of the design to polarization, angle of incidence and temperature has been investigated. The proposed absorber has potential applications in scattering reduction, electromagnetic compatibility and energy harvesting.