A tunable metamaterial microwave absorber inspired by chameleon's color-changing mechanism.

A metamaterial absorber capable of swiftly altering its electromagnetic response in the microwave range offers adaptability to changing environments, such as tunable stealth capabilities. Inspired by the chameleon's ability to change color through the structural transformation of photonic lattice crystals, which shift the bandgaps of reflection and transmission of visible light, we designed a crisscross structure that transforms from an expanded to a collapsed form. This transformation enables a switch between broadband absorption and peak transmission in the microwave range (4 to 18 gigahertz). The structure, optimized through data-driven design, is mechanically actuated by the rotation of interlinked trusses. This mechanism changes the entire array's response, allowing it to remain undetected by an external radar or to transmit an internal radar signal to a near-field receiver when needed. The mechanical actuation and the shifting electromagnetic response of the arrayed structure are demonstrated.