Water-based thermally controlled multifunctional switchable frequency selective rasorber

In this paper, a multifunctional switchable frequency selective rasorber (FSR) incorporating water-based active thermal control devices is proposed. Compared with other FSRs, the proposed design, on the basis of reconfigurability, exploits the thermochromic dispersion and fluidity characteristics of water-based materials to achieve enhanced functional integration. The proposed design consists of a water-filled chamber absorber, a bandpass frequency selective surface (FSS), and integrated micropumps and thermal control devices. The proposed absorber is fabricated using 3D printing technology, whereas the bandpass FSS is manufactured using printed circular board (PCB) technology. Experimental results demonstrate that, under the FSS transmission mode, the proposed design achieves a −3 dB bandwidth of 10.3–11.6 GHz with a minimum insertion loss of 0.74 dB within the passband. Under the integrated absorption–attenuation mode, the in-band attenuation exceeds 5.0 dB, while the absorption rate is greater than 80% in the out-of-band frequency ranges of 11.9–13.6 GHz and 20.9–21.4 GHz. The two operating modes can be reversibly switched by loading and unloading water via the micropump. Additionally, the proposed design incorporates a water-cooling circulation system with thermal control devices to enable effective thermal management and tunable absorption performance. In the cooling mode, the temperature can be rapidly reduced from 53.2 °C to 32.3 °C within 60 s. By activating the temperature control mechanism, adjustable absorption levels can be achieved. The proposed multifunctional switchable FSR not only reduces manufacturing costs but also satisfies the requirements for thermal stability in complex communication and detection environments, demonstrating significant potential for radome applications.