Open thermal cloak based on active thermal metasurfaces

The enclosed configuration of conventional thermal cloaks prevents the passage of matter across their boundaries. To overcome this limitation, we propose an open thermal cloak (OTC) that simultaneously provides effective thermal cloaking and incorporates a functional exit that allows unimpeded passage and exchange of matter. The OTC integrates a closed thermal cloak with an exit (CTCE) and a thermal shifter designed via coordinate transformation. The thermal shifter compensates for performance degradation caused by the exit by transferring the thermal regulation function of the removed segment back to the exit location, using a material with equivalent negative thermal conductivity derived from transformation thermotics. For practical implementation, this idealized material is replaced with discrete active thermal metasurfaces (ATMs) at the boundary to replicate the required heat flux conditions. Numerical simulations show that the ATM-based OTC exhibits excellent cloaking performance under varying heat flow directions and across exits of different sizes and shapes, maintaining background temperature field integrity and a near-uniform temperature distribution inside the protected region. The average temperature disturbance induced is significantly lower than that of CTCE and a directly exposed object, with performance approaching that of an ideal closed thermal cloak (CTC). This work breaks the enclosure limitation of traditional thermal cloaks and shows promise for infrared thermal protection of underground shelters and the thermal management of heat-sensitive electronics.