Ionic Liquids-Based Reconfigurable Frequency Selective Rasorber with Thermally Tunable Absorption Band

This article proposes a novel ionic liquids-based reconfigurable frequency selective rasorber (FSR) at microwave bands. The ionic liquids-based FSR consists of a bandpass-type frequency-selective surface, a 3D resin container, and an ionic liquid layer. Numerical simulation analysis demonstrates that the transmission loss of the FSR is less than 3 dB within the range of 4.3–5.3 GHz, and the absorption rate exceeds 90% within the range of 8–27.5 GHz. The FSR exhibits reconfigurable characteristics: when the cavity is filled with the ionic liquid [EMIm][N(CN)₂], it demonstrates low-frequency transmission and high-frequency absorption. In contrast, when no ionic liquid [EMIm][N(CN)₂] is in the cavity, it exhibits low-frequency transmission. The proposed ionic liquids-based FSR also has a wide incidence angle with polarization-insensitive characteristics. By studying the electromagnetic characteristics of frequency-selective rasorbers at different temperatures, it is found that the frequency-selective rasorber has a stable passband at low frequencies and the absorption bandwidth decreases with increasing temperature at high frequencies. Finally, a prototype of the FSR based on ionic liquid has been fabricated, and the experimental results are presented to demonstrate the validity of the proposed structure, indicating potential applications in antenna stealth technology.