In most materials, the way heat is absorbed and the way it is emitted are inseparable. If a surface absorbs heat efficiently from a particular direction or wavelength, it also emits heat the same way. This long established principle, known as reciprocity, has made it difficult for scientists to independently control how thermal energy enters and leaves a material.
If those two processes could be separated, however, engineers could direct heat much more precisely. A material could absorb thermal energy from one direction while releasing it in another, potentially improving thermal management, energy conversion, infrared sensing, and thermal communication technologies.
A Material That Can Control Heat
To overcome this limitation, an international team led by Professor Koichi Okamoto and Dr. Shunsuke Murai of Osaka Metropolitan University’s Graduate School of Engineering developed a new type of device using magneto-optical materials. These materials change the way they interact with light when exposed to a magnetic field, making it possible to alter their thermal behavior.
The researchers paired a magneto-optical material with a phase change material known as GST. The resulting device can control the direction in which heat is radiated, switch that behavior on or off, and retain its configuration even after the power has been turned off. In effect, it allows heat to be programmed in a way that resembles how data is stored and controlled inside a computer chip.
“We made heat radiation behave in a ‘smarter’ way,” Dr. Murai explained. “Achieving these capabilities in a working model could enable a new generation of efficient infrared emitters, thermal-energy devices, sensors, and photonic memory technologies.”
Better Performance Than Earlier Designs
The team found that the device responded differently depending on the direction from which light arrived, even when the light struck it almost straight on. Earlier technologies typically required light to hit the material at very steep angles to achieve similar effects, reducing both absorption and radiation efficiency compared with normal incidence.
The new design also addressed other shortcomings of previous systems. Earlier devices produced inconsistent switching between their “on” and “off” states, and they lost their stored configuration once power was removed. In contrast, the new material can reliably switch states while preserving its memory, making it far more practical for future applications.
Toward Programmable Thermal Devices
The researchers see this technology as an important step toward devices that manage heat with the same level of precision that electronic circuits use to control electricity.
“Our ultimate goal is to develop compact devices that can actively control heat radiation, much like electronic circuits control the flow of electricity,” Professor Okamoto said. “Such devices could be used in smarter infrared sensors, more efficient energy systems, and new types of photonic memory that store information using light and heat instead of electrical charges.”