Sensitive multi-level thermal camouflage patterns via intelligent fabry-perot cavity with multi-trend behavior

Achieving multi-level dynamic patterns within a narrow temperature range is vital for infrared (IR) thermal camouflage and encryption. Conventionally, phase change materials like VO₂, with tunable phase-transition temperatures achieved through doping, are used to create multi-level patterns. However, the inherent monotonic relationship between IR emission and temperature in phase change materials leads to overlapping emissivity curves rather than intersecting ones within narrow temperature ranges, restricting pattern reversibility and variability. Here, we introduce a scalable, lithography-free multi-layer nanostructure (Al/Si/VO₂/Al) that enables precise multi-level IR emissivity control by leveraging both the VO₂ metal-insulator transition and Fabry-Perot (F-P) cavity effects. The thickness of the top metal layer plays a critical role in determining the light absorption characteristics of the F-P cavity. By simply tuning the thickness of the top Al layer in conjunction with the VO₂ phase transition within the same temperature range, the equivalent metal layer thickness can be modulated, resulting in distinct F-P cavity behaviors. This approach unlocks unique IR emission trends, including monotonic increase, non-monotonic fluctuations (low-high-low), and monotonic decline, all within the same phase transition temperature range. Through the strategic spatial design of these multi-trend films, multiple intersection points on emissivity-temperature curves are realized within a narrow temperature range of 61–71 °C, enabling 11 levels of adaptive thermal pattern manipulation. This practical approach offers a simple yet effective solution for highly sensitive thermal camouflage and encryption applications.