Polarization-driven Infrared Emissivity Tuning System for Precise Temperature Modulation

Abstract

The global energy and climate challenges require energy-saving solutions to achieve net-zero emissions worldwide. As a result, eco-friendly thermal management has become crucial in various sectors, including residential buildings and mobile devices. In this context, passive radiative cooling has emerged as a promising solution to address the global energy and climate crises by providing energy-efficient and zero-emission cooling. The high emissivity of objects in the mid-infrared (MIR) atmospheric window allows for radiative cooling, where heat is drawn from the objects and emitted to the cold outer space. This unique feature has sparked renewed interest in extensive research on passive radiative cooling, with successful experimental demonstrations in various applications such as wearable devices, solar cells, buildings, display, clothing, roofs, and vehicles [1]. However, conventional radiative cooling technologies suffer from limitations such as undesirable cooling in cold weather, resulting from a single-state of strong thermal emission. Dual-state emitters have recently been developed for self-adaptive thermoregulation, but it still has energy loss in moderate weather [2]. Here, we propose a dynamic temperature modulation system with an infrared (IR) polarization valve as an energy-balancing channel. The system consists of a one-dimensional grating emitter and an IR polarizer. Simple rotation of the polarizer allows continuous temperature modulation. Optical simulations are implemented to optimize the design of the thermal emitter, which comprises a one-dimensional silver grid on a quartz. Our system achieves a wide range of emissivity (2 to 80%) by simple adjustment of the polarizer. This enables precise cooling/heating capabilities (-17 to 51 W/m2). Theoretical calculations estimate the potential energy saving of over 20 GJ/year compared to conventional emitters across different climate zones when applied to roofs of buildings. Outdoor experiments validate the precise temperature regulation within a target range of 17-18℃. This proof-of-concept demonstration in outdoor conditions highlights the reliability and applicability of our approach in various situations such as residential buildings, farms, and wearable devices. Our findings contribute to the advancement of thermal management technologies for achieving net-zero emissions and sustainable energy savings in the face of global energy and climate challenges.