Nonradiative Cooling

Radiative cooling is a key technology that reduces the temperature of sky-facing objects through radiative energy transfer between the objects and outer space at 4 K. However, this technology is not applicable when objects and spaces are surrounded by opaque absorbers. Here, we report a nonradiative cooling technology that can reduce the temperature of space surrounded by an opaque container. When a metamaterial-loaded thermoelectric device is placed in an opaque and sealed container, the metamaterial absorber absorbs the thermal radiation inside the container and the thermoelectric element converts the thermal energy to electric current. The generated current flows to the resistor placed outside the container, releasing thermal energy to free space as Joule heating. Consequently, the temperature inside the container was reduced.