Passive stretchable infrared modulator and reversible strain sensor based on a nano/microstructured metal-elastomer...

We report the design, fabrication, and characterization of a stretchable composite material with mechanically tunable optical properties in the thermal infrared spectral range. The device consists of an elastomeric substrate of Styrene-Ethylene-Butylene-Styrene (SEBS) patterned at the micro‑scale coated with an optically active gold layer whose morphology and optical response evolve under mechanical deformation. Stretching or compressing the composite modifies the geometry of both the surface pattern and the active layer, leading to reversible changes in transmittance and reflectance in the infrared range. The resulting composite operates without external electrical power, relying exclusively on mechanical actuation. A comparison between two active layer thicknesses (30 and 60 nm) on micropatterned SEBS elastomer reveals distinct optical behaviors. The 30 nm layer exhibits a transmission increase from 10% to 43% (+ 33%) under 100% strain, making it suitable for transmission-based IR modulation. In contrast, the 60 nm layer exhibits a reflectance decrease from 55% to 15% (-40%), making it suitable for reflectance-based thermal camouflage. We demonstrate its performance as a flexible strain sensor and infrared modulator and assess its stability over 1000 cycles of repeated deformation. The optical response remains stable despite nanoscale crack formation in the metal layer, highlighting the decoupling between electrical and optical behavior. These results define a simple design strategy in which metal thickness governs the dominant modulation mode (transmission vs. reflectance), providing a versatile platform for passive, mechanically driven infrared devices Part of this work has previously been disclosed in a patent (ES 2 950 877 A1), highlighting its technological relevance.