New device enables flexible control of heat
Heat is absorbed from the right, heating the structure, where it is radiated to the left, cooling the structure.
Image Credit: Osaka Metropolitan University
Scientific Frontline: Extended "At a Glance" Summary: Programmable Thermal Radiation
The Core Concept: Programmable thermal radiation refers to the ability to independently control the absorption and emission of heat, allowing thermal energy to be directed, switched on and off, and stored like data in a microchip. This circumvents the traditional thermodynamic rule of reciprocity, which dictates that a material must absorb and emit heat symmetrically.
Key Distinction/Mechanism: Unlike conventional materials that exhibit reciprocal thermal behavior, this new device separates absorption and emission by combining magneto-optical materials with a phase-change material known as GST. This integration allows the material to absorb heat from one direction and emit it in another even at near-normal angles of incidence, while retaining its thermal state without continuous electrical power.
Major Frameworks/Components:
- The Reciprocity Principle: The fundamental thermodynamic limitation being bypassed, which normally links a surface's efficiency in absorbing heat at a specific wavelength and direction to its emission.
- Magneto-Optical Materials: Substances manipulated by an external magnetic field to alter their interaction with light, allowing the separation of thermal absorption and emission behaviors.
- Phase-Change Material (GST): A specialized compound integrated into the device that acts as a switch and a memory cell, enabling the system to "remember" its thermal configuration after power is disconnected.
- Metagratings: The structural nanoscale architecture used to achieve nonreciprocity at near-normal incidence, overcoming the limitations of previous devices that required extreme, highly inefficient angles of incoming light.
Branch of Science: Materials Science, Thermodynamics, Photonics, and Optical Engineering.
Future Application: Applications include highly efficient infrared emitters, advanced thermal management architectures, directional energy conversion systems, and novel photonic memory capable of storing information using light and heat rather than electrical charges.
Why It Matters: By enabling heat to be actively steered and programmed like electrical currents in a circuit, this technology fundamentally advances thermal management. It maximizes energy efficiency and enables completely new paradigms for thermal communication, sensing, and computing components.
Normally, a material absorbs and emits heat in a linked way: a surface that absorbs heat well at a certain wavelength and direction will also emit heat in the same way. This fundamental relationship, known as reciprocity, limits our ability to independently control heat absorption and heat emission.
If absorption and emission could be separated, engineers could design devices that absorb heat from one direction while emitting it in another. By "steering" thermal energy, they could create more efficient thermal management, energy conversion, infrared sensing, and thermal communication technologies.
To create a material that behaves differently for incoming and outgoing radiation, an international research team led by Professor Koichi Okamoto and Dr. Shunsuke Murai from Osaka Metropolitan University's Graduate School of Engineering turned to magneto-optical materials. In these materials, the interaction with light can be altered using a magnetic field.
By combining a magneto-optical material with a special phase-change material called GST, the team created a device that can not only control the direction of heat radiation but also switch this effect on and off. Furthermore, the device remembers its state even when power is removed, allowing heat to be programmed like data in a microchip.
"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."
The researchers found that their device exhibited different responses depending on light direction, even when light arrived nearly at normal incidence. This marked a significant improvement compared to previous devices that required light to arrive at very large angles, at which the absorption and radiation efficiencies dropped relative to those at normal incidence. In addition, the "on-and-off switch" effect of the previous devices was highly variable, and their memory was lost when power was removed, limiting reconfiguration.
"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."
Funding: This work was supported by the National Natural Science Foundation of China (62305173); the Japan Society for the Promotion of Science (JSPS) Postdoctoral Fellowships for Research in Japan (P25357) and KAKENHI (25K01501, 25K21709, and 25KF0265); the Youth Talent Support Program of the Jiangsu Association for Science and Technology (JSTJ-2024-390); the Agency for Science, Technology, and Research (A*STAR) under its Japan-Singapore Joint Call for Quantum 2025 (R25J4IR112); and the National Research Foundation (NRF), Singapore (NRF-CRP30-2023-0003).
Published in journal: Laser & Photonics Reviews
Authors: Ye Ming Qing, Yi Shen, Jun Wu, Shunsuke Murai, Zhaogang Dong, and Koichi Okamoto
Source/Credit: Osaka Metropolitan University
Edited by: Scientific Frontline
Reference Number: ms070726_01