Printable lightweight temperature sensor aims to improve healthcare
Flexible and wearable devices are increasingly being developed for healthcare and other applications where temperature and other sensors are integrated to provide feedback on patient health and wellbeing. Body temperature is a fundamental measurement and many low-cost flexible temperature sensors have been demonstrated, but devices developed to date require external circuitry to amplify the signal to allow accurate temperature measurement.
Professor Takao Someya and Dr. Tomoyuki Yokota’s research group at the Graduate School of Engineering have developed a printable, flexible, lightweight temperature sensor that shows a high change in electrical resistance of up to 100,000 times across a range of five degrees centigrade which allows accurate temperature measurement without additional complicated display circuitry.
The key to the sensor is the ability to precisely control the target temperature of the sensors. The sensor is composed of graphite and a semicrystalline acrylate
polymer formed of two monomers, molecules that bond together to form a polymer chain. The target temperature range at which the sensor is most precise can be selected simply by altering the proportions of the two monomers. The research group achieved target temperatures between 25 and 50 degrees centigrade, a range which includes average human body temperature, and simultaneously realizing response times of less than 100 milliseconds and a temperature sensitivity of 0.02 degrees centigrade. The device was also stable even under physiological conditions, providing repeated readings up to 1,800 times.
The research group tested the sensor by printing a flexible thermal monitoring device which was placed directly on the lung of a rat to measure lung temperature. The device successfully measured cyclic changes in lung temperature of just 0.1 degrees centigrade as the animal breathed, demonstrating its utility as a sensor for monitoring body vital signs in physiological (internal) settings.
"By printing an array of these sensors it is possible to measure surface temperature over a large area," said Professor Someya. "This sensor array can be attached to biological tissue such as the skin for precise monitoring in medical applications. Because the huge response of the sensor to temperature change allows us to simplify the circuitry, we could print our sensors onto adhesive plasters that could then monitor body temperature. For example, a plaster applied directly to a wound or after surgery could provide warning of infection by detecting local changes in temperature due to inflammation."
Other possible applications include wearable electronic apparel, where the sensor could be applied beneath fabric to measure temperature during sporting and other activities.
Tomoyuki Yokota, Yusuke Inoue, Yuki Terakawa, Jonathan Reeder, Martin Kaltenbrunner, Taylor Ware, Kejia Yang, Kunihiko Mabuchi, Tomohiro Murakawa, Masaki Sekino, Walter Voit, Tsuyoshi Sekitani, and Takao Someya, ‘Ultraflexible, large-area, physiological temperature sensors for multipoint measurements’, Proceedings of the National Academy of Sciences of the United States of America, Online edition 2015/11/09
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