Sensor monitors heat flow in devices to improve efficiency

Excess heat from electronic or mechanical devices is a sign or cause of inefficient performance; in some cases, embedded sensors that monitor the flow of heat can help engineers alter device behaviour or designs to improve their efficiency. Now, researchers have exploited a novel thermoelectric phenomenon to build a thin sensor that can visualise heat flow in real time. The sensor could be built deep inside devices where other kinds of sensors are impractical.

Project Associate Professor Tomoya Higo and Professor Satoru Nakatsuji, from the University of Tokyo, said that the amount of heat conducted through a material is known as its heat flux; finding new ways to measure this could help improve device efficiency and safety, as batteries with poor thermal management can be unsafe.

“But finding a sensor technology to measure heat flux, while also satisfying a number of other conditions, such as robustness, cost efficiency, ease of manufacture and so on, is not easy. Typical thermal diode devices are relatively large and only give a value for temperature in a specific area, rather than an image of the heat flux across an entire surface,” Higo said.

The researchers explored the way a heat flux sensor consisting of certain magnetic materials and electrodes behaves when there are complex patterns of heat flow. The magnetic material based on ion and gallium exhibits a phenomenon known as the anomalous Nernst effect (ANE), which is where heat energy is converted to an electrical signal. This is not the only magnetic effect that can turn heat into power — there is also the Seebeck effect, which can create more electrical power, but requires a large amount of material, and the materials are brittle and difficult to work with. ANE allowed the researchers to engineer the device on a thin and malleable sheet of plastic.

Higo said that by finding the right magnetic and electrode materials and applying them in a special repeating pattern, the researchers created microscopic electronic circuits that are flexible, robust, easy to produce and good at outputting heat flux data in real time. Their method involved rolling a thin sheet of clear, strong and lightweight PET plastic as a base layer, with magnetic and electrode materials sputtered onto it in thin and consistent layers. The researchers then etched their desired patterns into the resultant film. The circuits are designed in a particular way to boost ANE while also suppressing the Seebeck effect, as this interferes with the data-gathering potential of ANE.

“I envisage seeing downstream applications such as power generation or data centres, where heat impedes efficiency. But as the world becomes more automated, we might see these kinds of sensors in automated manufacturing environments where they could improve our ability to predict machine failures, certain safety issues and more,” Nakatsuji said.

Image credit: iStock.com/Petrovich9