Hierarchical Phase-Change Materials as Passively Adaptive Microwave Shields

Stealth Armor Labs proposes to develop a passively adaptive microwave shield based on hierarchical phase-change materials (PCM). This novel shield will continuously protect Army platforms from hostile microwave radiation (e.g. jamming signals, electronic countermeasures, energy weapons) while selectively allowing desired communications signals to pass through unimpeded and without increasing detectability. The clear benefits of microwave communications, such as long-distance penetration through the atmosphere, communication without line of sight, and readily available, low cost microwave sources also make electronics and systems that rely on microwave communications potentially vulnerable. Electronics can be jammed or destroyed with a moderate amount of microwave power at the right frequency. Materials exist which can completely reflect incoming radiation (metallic enclosures), or completely absorb it (iron-based magnetic paints), but these also prevent communications in and out during times when there are no hostile incoming signals. There is a need for materials which can allow such communications during normal operation but quickly, effectively and automatically switch to block incoming signals without increasing the RF signature and detectability of the system. In Phase I we aim to demonstrate a novel material system and superstructure with novel functionality that (i) admits low-power communication signals in a narrow frequency band, (ii) rejects all incident radiation outside of this band, and (iii) passively (i.e. automatically) closes the passband upon adversarial attack with high-power radiation without increasing detectability. In our innovative design, two coupled metasurface layers, upon heating due to high-power microwave irradiation, drive a semiconductor-to-metal transition in a third phase-change material composite layer. This approach allows communication signals to pass through during normal operation and rapidly switches from narrow band transmission to broadband absorption in response to incoming threats.