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Robust, Low-cost Sensor Tracks Heat Flow to Boost Efficiency

Worker in a tobacco factory, Kyrgyzstan. 2008 (Photo by V. Pirogov courtesy International Labour Organization) Posted for media use

TOKYO, Japan, July 25, 2023 ( Sustainability News) – Is the machinery in your facility radiating too much heat? Is it dangerous for workers? Is it heating up the building, which then requires cooling? Excess heat from mechanical or electronic devices is a sign or cause of inefficient performance. Now, researchers in Tokyo are demonstrating embedded sensors to monitor the flow of heat that could help engineers alter device behavior or design to improve efficiency. 

For the first time, researchers have exploited a novel thermoelectric phenomenon to build a thin sensor that can visualize heat flow in real time. They say the sensor could be placed deep inside devices where other kinds of sensors are impractical. 

The research team says the sensor they are designing is flexible, robust, inexpensive, and easy to manufacture using well-established methods.

Identifying the Problem 

“According to the law of conservation of energy, energy is never created or destroyed but only changes form from one to another depending on the interaction between the entities involved. All energy eventually ends up as heat,” the University of Tokyo research team states.

“For us that can be a useful thing,” they say, giving the example of needing to heat a building in winter. In any case, the better we can manage the thermal behavior of a device, the better we can engineer around this inevitable effect and improve the efficiency of the device or machine.

But this is easier said than done, the research team says, “as knowing how heat flows inside some complex, miniature or hazardous device is something ranging from the difficult to the impossible, depending on the application.”

Professor Satoru Nakatsuji at the University of Tokyo is interested in developing new materials and their thin film form for spintronics and energy harvesting applications. He also works with Johns Hopkins University’s Institute for Quantum Matter in the United States. (Photo courtesy Johns Hopkins) Posted for media use

Inspired by this problem, Project Associate Professor Tomoya Higo and Professor Satoru Nakatsuji from the Department of Physics at the University of Tokyo, and their team, which included a corporate partnership, set out to find a solution. 

“The amount of heat conducted through a material is known as its heat flux. Finding new ways to measure this could not only help improve device efficiency, but also safety, as batteries with poor thermal management can be unsafe, and even health, as various health or lifestyle issues can relate to body heat,” said Higo. 

“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,” he explained

“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.

Exploring Sensors

The team explored the behavior of a heat flux sensor consisting of certain special magnetic materials and electrodes when there are complex patterns of heat flow. 

The magnetic material based on iron and gallium exhibits a phenomenon known as the anomalous Nernst effect, or ANE, and that is where heat energy is converted to an electrical signal. 

This is not the only magnetic effect that can turn heat into power, though. There is also the Seebeck effect, which can actually create more electrical power, but it requires a large bulk of material, and the materials are brittle, making them difficult to work with. 

ANE, on the other hand, has allowed the University of Tokyo team to engineer their device on a thin, malleable sheet of plastic.

Etching the Right Designs

“By finding the right magnetic and electrode materials and then applying them in a special repeating pattern, we created microscopic electronic circuits that are flexible, robust, cheap and easy to produce, and most of all are very good at outputting heat flux data in real time,” said Higo. 

“Our method involves 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. We then etch our desired patterns into the resultant film, similar to how electronic circuits are made.”

The team designed the circuits specifically to boost ANE while suppressing the Seebeck effect, which interferes with the data-gathering potential of ANE. 

Previous attempts to do this were unsuccessful in any way that could be easily scaled up and potentially commercialized, making this sensor the first of its kind.

“I envisage seeing downstream applications such as power generation or data centers, where heat impedes efficiency,” Professor Nakatsuji said, considering the uses of his new technology. 

“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,” he said.

 “With further developments,” Nakatsuji speculated, “we might even see internal medical applications to help doctors produce internal heat maps of specific areas of the body, or organs, to aid in imaging and diagnosis.”

This technology is another tool that Maximpact energy efficiency experts can add to their toolboxes. Use the contact information on this website to request a consultation.