Mechanically tunable radiative cooling for adaptive thermal control

Passive radiative cooling is currently the frontier technology in renewable-energy research. In terms of extraterrestrial applications, radiative cooling is a critical component to the thermal management system of a spacecraft, where the extreme environment of space can cause large temperature variations that can break and damage equipment. For terrestrial applications, nocturnal or daytime radiative cooling is expected to lead to cost-effective passive heat management without the need of inefficient and costly artificial refrigeration technologies. However, most currently available radiative cooling systems cannot be changed dynamically and radiate a constant static amount of thermal power. Dynamically tunable adaptive radiative cooling systems will be a critical development to prolong the lifetime of spacecraft or improve the efficiency of terrestrial cooling systems. Here we propose stretchable radiative cooling designs that can be substantially tuned by using the simple physical mechanism of mechanical strain. When their structure is stretched, the radiated power is significantly reduced. We develop a modeling method that can simulate mechanical stretching combined with electromagnetic response to compute the tunable thermal emission of these new adaptive radiative cooling systems. The presented photonically engineered structures can be used as coatings to achieve efficient adaptive thermal control of various objects in a cost-effective and environmentally friendly way. The proposed designs are much simpler to be realized than others found in the literature and the best design achieves a high thermal emission power with a tunable range on the order of 132 W/m2.