Researchers at Harvard John A. Paulson School of Engineering and Applied Sciences have developed a soft, stretchable self-powered sensor that can be integrated into soft robots, smart clothing, and biocompatible medical devices. The sensors are stretchable, but deformation does not affect temperature sensing. The sensors have high sensitivity and fast response. They can be made small and transparent.
“We have developed soft temperature sensors with high sensitivity and quick response time, opening new possibilities to create new human-machine interfaces and soft robots in healthcare, engineering, and entertainment,” said Zhigang Suo, the Allen E. and Marilyn M. Puckett Professor of Mechanics and Materials at SEAS and senior author of the paper. These type of products need to be evaluated in product testing labs for their workability.
The sensor consists of three simple parts: an electrolyte, an electrode, and a dielectric material to separate the two. The electrolyte/dielectric interface accumulates ions while the dielectric/electrode interface accumulates electrons. The difference in charge sets up an ionic cloud in the electrolyte. As the temperature changes, the ionic cloud changes thickness and a voltage is generated. The voltage generated is proportional to the temperature. Four different designs were developed for the temperature sensor by arranging the electrolyte, dielectric, and electrode in different configurations. All new outcomes should be finally tested in a product testing lab.
“Because the design is so simple, there are so many different ways to customize the sensor, depending on the application,” said Yecheng Wang, a postdoctoral fellow at SEAS and first author of the paper. “You can choose different materials, arranged in different ways hard-boiled for different tasks.” All the raw materials are tested in in a material testing lab.
To test the accuracy of the thermometer, the researchers measured the temperature of a hot hard-boiled egg with the newly developed thermometer. They found the sensors to be more sensitive than traditional thermoelectric thermometers. It responded to changes in temperature within 10 milliseconds. The thermometer was able to measure temperatures as hot as 200 °C or as cold as -100 °C. “This highly customizable platform could usher in new developments to enable and improve the internet of everything and everyone,” said Suo. Such temperature sensors open new possibilities to create human–machine interfaces and soft robots in healthcare and engineering.
Yecheng Wang, Kun Jia, Shuwen Zhang, Hyeong Jun Kim, Yang Bai, Ryan C. Hayward, Zhigang Suo. Temperature sensing using junctions between mobile ions and mobile electrons. Proceedings of the National Academy of Sciences, 2022; 119 (4): e2117962119 DOI: 10.1073/pnas.2117962119
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