Scientists Develop Soft, Flexible, Stretchable Thermal Sensors with Simple Structure and Rapid Response to Temperature Changes
In the future, soft robots, smart clothing, and biocompatible medical devices will require the integration of soft sensors that can stretch and twist according to the devices or the wearers. The challenge here is that most components used in traditional sensors are rigid.
Experiment using soft tongs integrated with a thermometer to measure the temperature of hot boiled eggs. (Photo: Harvard SEAS)
However, a research team at the John A. Paulson School of Engineering and Applied Sciences (SEAS) at Harvard University has developed a soft, stretchable, self-powered thermometer that can be integrated into electronic devices and soft robots, Phys reported on January 24. The research was recently published in the journal Proceedings of the National Academy of Sciences.
“We have developed soft temperature sensors with high sensitivity and rapid response time, opening up new possibilities for creating human-machine interaction interfaces and soft robots in the fields of healthcare, engineering, and entertainment,” said Zhigang Suo, a professor of mechanical engineering and materials at SEAS and a member of the research team.
The thermometer consists of three simple components: an electrolyte, electrodes, and a dielectric material for separation. The electrolyte/dielectric interface accumulates ions, while the dielectric/electrode interface accumulates electrons. The charge imbalance between them creates an ion cloud in the electrolyte. When the temperature changes, the ion cloud alters its thickness, generating a voltage. This voltage is sensitive to temperature but not to expansion.
“The design is very simple, allowing for various ways to adjust the sensor depending on its intended use. You can choose different materials, arrange them in various ways, and optimize for specific tasks,” explained Yecheng Wang, a postdoctoral researcher at SEAS and a member of the research team.
By arranging the electrolyte, dielectric, and electrodes in different structures, the team developed four designs for the temperature sensor. In one experiment, they integrated the sensor into soft tongs and measured the temperature of hot boiled eggs. The sensors were more sensitive than traditional thermoelectric thermometers, capable of responding to temperature changes in about 10 milliseconds.
“We have demonstrated that these sensors can be fabricated in a compact, stable, and even transparent manner. Depending on the materials used, the thermometer can measure temperatures as high as 200 degrees Celsius or as low as -100 degrees Celsius,” Wang added.
