Adaptive ionic liquid polymer microwave modulation surface with reprogrammable dielectric properties.

Adaptive microwave surfaces have the capability to dynamically adjust their electromagnetic transmission to meet specific needs, offering significant potential for efficient integration and flexible use in reconfigurable communication systems. In this work, we utilize temperature induced break and reconstruction of hydrogen bonds to drive the orientational motion and charge mobility of the ionic liquid [EtA⁺][NO₃⁻] in the poly-2-hydroxyethyl-acrylate, resulting controllable modulation of dielectric properties at microwave frequencies. Building on this mechanism, we applied machine learning algorithms to establish correlations between temperature, ionic liquid concentration, and dielectric constant, enabling the design of a reprogrammable dielectric microwave modulation surface. For example, the 2 mm-thick switchable microwave absorbing surfaces fabricated here can operate in two distinct modes during the temperature transition from low to high, namely, off-to-on and on-to-off. The corresponding tunable effective absorption bandwidths and reflection loss values reach 5.69 GHz, -6.04 dB to -46.21 dB, and 5.34 GHz, -50.48 dB to -6.47 dB, respectively. Using the developed active surface, we also demonstrate various device architectures fabricated by three-dimensional printing, including pixelated surfaces and self-sensing functionalities, which provide valuable guidance for the development of next-generation intelligent electromagnetic devices.