Thermal management is ubiquitous and indispensable in the modern world. For instance, batteries, solar cells, transportation vehicles, and electronic chips all require careful thermal management to maintain suitable working temperature ranges. On a larger scale, space heating and cooling maintain the indoor temperature all year round but also consume up to 20% of global energy. Therefore, the development of more effective, energy-efficient, and universal thermal management technology is one of the most critical tasks for a sustainable future. Conventionally, to achieve radiative cooling for low-emissivity objects such as metals, the strategy is to apply a high-*ε* coating to promote thermal emission. For high-emissivity objects, such as the human body, the ideal cooling strategy is to cover them with high-transmittance materials to allow direct radiation from the skin surface. On the other hand, the radiative heating strategy of applying low-emissivity opaque materials works for both low-emissivity and high-emissivity objects. For a radiative heat managing device to be universal and multifunctional - accomplishing both heating and cooling for all kinds of objects - this dependence on the object emissivity demands for better adaptability. Here, for the first time, we demonstrate a triple-mode polymer/metal elastomeric modulator that is able to dynamically switch among emission (*E-mode*), reflection (*R*-mode), and transmission (*T*-mode) to accomplish heat management of the all-surface passive radiative cooling and heating. The device is composed of a surface-textured elastomer coated with a metallic back reflector, which is biaxially strained to sequentially achieve three fundamental modes: emission, reflection, and transmission. We analyze the mechanisms and the scaling relationship between thickness and interface roughness to optimize the coupling between optical and mechanical properties. As a result, we achieve an unprecedented performance of emittance contrast = 0.52, transmittance contrast = 0.48, and reflectance contrast = 0.38, on the same device. This mid-infrared property modulation corresponds to approximately 2X of radiative heat transfer contrast. We point out larger contrast is possible by improving the optical structure to approach the Yablonovitch limit. We also tested its overall heat transfer coefficient (radiative + natural convection) and achieved a 35-45% of inability, which can be customized by different back reflector roughness. Finally, we fabricate a pneumatically-controlled dot-matrix mid-infrared "display" that can independently control the emissivity and heat transfer of the underlying object, thereby emitting artificial thermal image on-demand. The device is low-cost, lightweight, flexible, rapidly responsive, and robust after one hundred cycles, which can provide a new design paradigm for radiation regulation, thermal management, and infrared camouflage technology.


A Triple-Mode Mid-Infrared Modulator for All-Surface Radiative Thermal Management

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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