Researchers at Harvard University have developed a self-powered soft temperature sensor that is simple to design and portable. A dielectric/electrode interface coupled with a dielectric/electrolyte interface form a charged capacitor that responds to temperature changes within milliseconds.
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Soft sensors that adapt well at human-machine interfaces are going to be crucial in next-generation soft robotics and wearable devices. However, many of the components used in these applications are too rigid for advanced applications. This new sensor paves the way for stretchable, self-powered sensing devices.
Soft Robotics and Sensors
In contrast to traditional robotics, where robots are built from metals and rigid plastics, soft robotics is concerned with building robots out of malleable (“soft”) materials. Soft robots are often inspired by and mimic the functions of living organisms.
Plants, for example, can change their shape by controlling the movement of ions through their cell membranes. This has inspired soft robots that can change their shape using adaptive pressure materials.
The aim of soft robotics is to design robots with flexible bodies that are safer for human-machine interaction, industrial process optimization and various biomedical applications. Furthermore, self-learning soft robots that learn through artificial intelligence are multiplying the opportunities in industry, commerce and society.
Flexible electronics and soft sensors are crucial in the development of soft robotics. Soft sensors detect pressure, force, bend or stretch. They rely on various physical quantities such as capacitance, piezoresistivity, optical and acoustic loss to affect their measurements.
The Harvard team developed a capacitance-based temperature sensor that measures differences in voltage between two dielectric/electrolyte and dielectric/electrode interfaces.
Building a Self-Powered Soft Temperature Sensor
The researchers at the School of Engineering and Applied Sciences at Harvard University developed a stretchable, self-powered temperature sensor that can be used in stretchable electronics and integrated into soft robots and wearable devices.
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.
Prof. Zhigang Suo, School of Engineering and Applied Sciences, Harvard University
The soft thermometer consists of an electrode, an electrolyte and a dielectric separating the two. Electrons accumulate at the dielectric/electrode interface, while ions accumulate at the dielectric/electrolyte interface.
The difference in voltage between the interfaces creates an ionic cloud in the electrolyte. Changes in temperature alter the thickness of the cloud, thereby altering the voltage between the interfaces. Thus, temperature can be calculated.
Because the design is so simple, there are so many different ways to customize the sensor, depending on the application.
Yecheng Wang, Postdoctoral Fellow, School of Engineering and Applied Sciences, Harvard University
In one test, the team fitted the sensor into a soft robotic hand which measured the temperature of a boiled egg. The soft sensor responds to changes in temperature within ten milliseconds. It can measure temperatures ranging between -100 ℃ and 200 ℃.
This highly customizable platform could usher in new developments to enable and improve the internet of everything and everyone.
Prof. Zhigang Suo, School of Engineering and Applied Sciences, Harvard University
References and Further Reading
Suo, Z., et. al., (2022) Temperature sensing using junctions between mobile ions and mobile electrons. Proceedings of the National Academy of Sciences, [online] Available at: https://www.pnas.org/content/119/4/e2117962119
Burrows, L. (2022) A soft, stretchable thermometer. [online] Available at: https://www.seas.harvard.edu/news/2022/01/soft-stretchable-thermometer
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