In order for it to be truly soft, a soft-bodied robot can't contain any hard, rigid components. That's why we've already seen soft batteries, circuits and actuators. Now, a squishy, stretchable thermometer has joined that list.
Currently in development at Harvard University's John A. Paulson School of Engineering and Applied Sciences, the self-powered device is made up of three layers: a salt-containing hydrogel electrolyte, an electrode, and a dielectric (non-conductive) material separating the two.
Ions accumulate at the interface between the dielectric material and the electrolyte, while electrons accumulate at the interface between the dielectric material and the electrode. This produces an imbalance in the electrical charge of the two interfaces, which in turn causes an electrochemical phenomenon known as an ionic cloud to form in the electrolyte.
When the temperature around the thermometer changes, the thickness of the ionic cloud changes correspondingly, causing the electrode to produce an electrical current. Since the strength of that current changes with the temperature – but is unaffected by the thermometer being stretched or compressed – it serves as an accurate and precise indicator of the ambient temperature.
In tests conducted so far, the soft thermometer proved to be more sensitive than a traditional thermoelectric thermometer – it reacted to changes in temperature within approximately 10 milliseconds. Additionally, depending on the materials used in their construction, various versions of the thermometer were capable of measuring temperatures as high as 200 ºC (392 ºF) and as low as -100 ºC (-148 ºF).
"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 Prof. Zhigang Suo, senior author of a paper on the research. That paper was recently published in the journal Proceedings of the National Academy of Sciences.
Source: Harvard John A. Paulson School of Engineering and Applied Sciences
