Thermal stealth and camouflage have been intensively studied for blending objects with their surroundings against remote thermal image detection. Adaptive control of infrared emissivity has been explored extensively as a promising way of thermal stealth, but it still requires an additional feedback control. Passive modulation of emissivity, however, has been remained as a great challenge which requires a precise engineering of emissivity over wide temperature range. Here, we report a drastic improvement of passive camouflage thin films capable of concealing thermal objects at near room temperature without any feedback control, which consists of a vanadium dioxide (VO₂) layer with gradient tungsten (W) concentration. The gradient W-doping widens the metal-insulator transition width, accomplishing self-adaptive thermal stealth with a smooth change of emissivity. Our simple approach, applicable to other similar thermal camouflage materials for improving their passive cloaking, will find wide applications, such as passive thermal camouflage, urban energy-saving smart windows, and improved infrared sensors.

为了对物体及其周围环境进行融合以防止远程热图像检测，已经对热隐身和伪装进行了深入研究。红外发射率的自适应控制已被广泛探索为一种有前途的热隐身方式，但它仍然需要附加的反馈控制。然而，发射率的无源调制仍然是一个巨大的挑战，需要在宽温度范围内精确设计发射率。在这里，我们报告了一种被动伪装薄膜的显着改进，该伪装薄膜能够在几乎没有任何反馈控制的情况下隐藏接近室温的热物体，该伪装薄膜由二氧化钒（VO _{2）组成。}）梯度钨（W）浓度层。梯度W掺杂扩大了金属-绝缘体的过渡宽度，实现了辐射率平滑变化的自适应热隐身。我们的简单方法适用于其他类似的热伪装材料，以改善其被动遮盖效果，将找到广泛的应用，例如被动热伪装，城市节能智能窗户和改进的红外传感器。