Transparent and Durable Terahertz Absorber Based on Enhanced Wave‐Ion Interaction

Hydrogels, featuring high flexibility and stretchability, have intense wave‐matter interaction in the terahertz (THz) band and high transparency in the visible light band, making them promising materials for transparent THz absorbers in the optical windows of THz devices. However, conventional hydrogels suffer from poor environmental stability, as water evaporation or freezing at subzero temperatures weakens their THz absorption and visible transmittance. Here, An ion‐rich hydrogel film is presented to concurrently boost the THz wave‐ion and intermolecular interactions. The boosted interactions increase the ionic conduction loss and improve the antidrying and antifreezing performance. As a result, with polydimethylsiloxane (PDMS) as the encapsulation layer and antireflection layer, the flexible ionic‐hydrogel‐based THz absorber shows a high maximum reflection loss (RL) of 86.51 dB in the 0.5–4.5 THz range (100% qualified bandwidth) and a high average visible transmittance of 90.87% with a thickness of only 300 µm. Moreover, it still possesses a high average RL of 39.35 dB after 80 days at room temperature and a high average electromagnetic interference shielding efficiency (EMI SE) of 42.30 dB at −10 °C. This work demonstrates the feasibility of transparent ionic THz absorbers, offering inspiration for future ionic THz device designs.