Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have developed a soft, stretchable, self-powered thermometer that can be integrated into smart robots and stretchable electronics.
The research was published in the Proceedings of the National Academy of Sciences.
Zhigang Suo is an Allen E. and Marilyn M. Puckett Professor of Mechanics and Materials at SEAS and senior author of the paper.
“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 Suo.
Structure of the Thermometer
The thermometer has three parts: an electrolyte, an electrode, and a dielectric material that separates them. The electrolyte/dielectric interface accumulates ions, and the dielectric/electrode interface accumulates electrodes.
With the charge imbalance between the two, it results in an ionic cloud in the electrolyte. This ionic cloud then changes thickness and generates voltage when the temperature changes. While the voltage is sensitive to temperature, it is insensitive to stretch.
Customizing the Sensor
Yecheng Wang is a postdoctoral fellow at SEAS and first author of the paper.
“Because the design is so simple, there are so many different ways to customize the sensor, depending on the application,” said Wang. “You can choose different materials, arranged in different ways and optimized for different tasks.”
The researchers could arrange the electrolyte, dielectric, and electrode in different configurations, which resulted in four designs for the temperature sensor. They tested it by first integrating the sensor into a soft gripper before measuring the temperature of a hot hard boiled egg. The sensors were more sensitive than traditional thermoelectric thermometers, and they were able to respond to changes in temperature within 10 milliseconds.
“We demonstrated that these sensors can be made small, stable, and even transparent,” said Wang.
The thermometer can measure temperatures of up to 200 degrees Celsius or as cold as -100 degrees Celsius depending on which materials are used.
“This highly customizable platform could usher in new developments to enable and improve the internet of everything and everyone,” said Suo.