A technology that would control the flow of heat the way electronic devices control electrical current is the subject of research by engineers at Purdue University, LaFayette, Ind. If successfully developed for commercial use, the advance could have applications in a diverse range of fields from electronics to textiles, say the engineers.
The concept uses tiny triangular structures to control "phonons," quantum-mechanical phenomena that describe how vibrations travel through a material's crystal structure.
Findings in research using advanced simulations show the triangular or T-shaped structures — if small enough in width — are capable of "thermal rectification," or permitting a greater flow of heat in one direction than in the opposite direction, said Xiulin Ruan, an associate professor in Purdue University's School of Mechanical Engineering and Birck Nanotechnology Center.
Rectification has made possible the transistors, diodes and memory circuits central to the semiconductor industry. The new devices are thermal rectifiers that might perform the same function but with phonons instead of electrical current.
"In most systems, heat flow is equal in both directions, so there are no thermal devices like electrical diodes. However, if we are able to control heat flow like we control electricity using diodes, then we can enable a lot of new and exciting thermal devices including thermal switches, thermal transistors, logic gates and memory," said Ruan, whose research group collaborated with a group led by Yong Chen, an associate professor in Purdue's Department of Physics and School of Electrical and Computer Engineering. "People are just starting to understand how it works, and it is quite far from being used in applications."
Findings are detailed in a research paper that has appeared online in the journal Nano Letters. The paper was authored by doctoral students Yan Wang, Ajit Vallabhaneni and Jiuning Hu and former doctoral student Bo Qiu; Chen; and Ruan.
A potential, although speculative, future application could be thermal transistors. Unlike conventional transistors, thermal transistors would not require the use of silicon, are based on phonons rather than electrons and might make use of the large amount of waste heat that is already generated in most practical electronics, said Chen.
The research was funded by the U.S. Air Force Office of Scientific Research.