Bifunctional Water-Based Frequency-Selective Absorber Regulated by Gravity Field

A bifunctional water-based frequency-selective absorber (FSA) regulated by gravity field realizing the functions of absorptive frequency-selective transmission (AFST) structure and absorptive frequency-selective reflection (AFSR) structure is proposed. The device is made up of two containers with distinct shapes that are connected by locating cylinders. The lossless layer utilizes a bandpass frequency-selective surface with a cross gap. Gravity will shape the water into blocks when the AFST structure is pointed toward the Earth. It is demonstrated that the AFST state obtains a transmission coefficient greater than −3 dB from 2.85 to 4.48 GHz, with an 80% absorptive band from 5.02 to 20 GHz. When the device is turned upside down, the AFSR structure fills with water, making the water shaped like grids. In this state, the device acquires a −3 dB reflection band from 2.42 to 7.78 GHz and an 80% absorption band from 9.66 to 20 GHz. Two equivalent circuit models are proposed to provide insight into the operation mechanism of the FSA. A prototype of the proposed FSA is fabricated and measured to verify its performance. The proposed bifunctional FSA is expected to be used in ground-to-air antijamming communication.