Smart radiators are powerless to adapt

Use of a four layer coated structure will enable the surface of space satellites to radiate energy when they are hot, and retain energy when they are cold. Layer combinations can be devised to regulate temperatures anywhere in the range 100 deg K to 68 deg C or more. While the technology is optimised for space, the underlying ideas are equally applicable to temperature self regulation in products as diverse as cars and solar hot water heaters. Intelligent radiators are the brainchild of Dr John Topping, a post doctoral fellow currently undertaking research at the Department of Engineering Science in the University of Oxford. He describes his invention as a "Thermochromic driven variable surface." It consists of an outer index matching layer on top of a thermochromic layer, a spacer layer and a rear reflective layer in thermal contact with the satellite. When the arrangement is cold, the thermochromic layer is in a state where it has a refractive index below that of the outer layer, and is infra red transparent. The net effect is that heat energy radiated in either direction is reflected without loss either at the first interface or at any of the interfaces within. The combination is thus 'shiny' with a low emissivity, so that in a space environment, where the satellite is much hotter than space, heat energy already within the satellite body is retained. When the arrangement is hot, the refractive index of the thermochromic layer rises to match that of the index matching layer and at the same time, it becomes metallic and absorbing. Incident radiated heat energy thus passes across the boundary between the index matching and thermochromic layers and is absorbed. The combination is thus 'black' with a high emissivity, so the satellite is able to radiate heat into space. The other layers prevent the thermochromic layer from index matching to the metal surface. The index matching layer could be silicon or other high index material or composite and the thermochromic layer, a suitable vanadium, iron or titanium oxide. The development is presently on a laboratory scale. The next stage is proof of manufacture on rolls of polyamide, which with sufficient funds, Dr Topping believes he could accomplish within a few months. The system points the way to smart multi-layer thermal control coatings for cars and solar heaters, but Topping says he would have to do considerable further research to develop and optimise systems for such applications. Isis Innovation Pointers * Multi-layer coating system potentially makes the surface skin of a satellite 'shiny' with low emissivity, retaining heat when cold while becoming 'black' with high emissivity, allowing the surface to radiate heat when hot. * System is optimised to work within infra red wavelengths in a space environment but could, in theory, be used as the basis of terrestrial systems using different materials that could either absorb heat when hot, but retain heat when cold, or perform other useful heat control tasks