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A printable, flexible, lightweight temperature sensor: Professor Takao Someya and Dr. Tomoyuki Yokota, Department of Electrical Engineering and Information Systems.Japanese Page

November 10, 2015

A University of Tokyo research group has developed a flexible, lightweight sensor that responds rapidly to tiny thermal changes in the range of human body temperature. This sensor is expected to find healthcare and welfare applications in devices for monitoring  body temperature, for example of newborn infants or of patients in intensive care settings.

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.

In  their  latest research, Professor Takao Someya  and Dr. Tomoyuki Yokota’s research group at the Graduate School of Engineering have developed a new printable, flexible, lightweight temperature sensor that shows a very high change in electrical resistance of up to 100,000 times over a range of just  five  degrees  centigrade,  allowing  accurate  temperature  measurement  without  additional complicated display circuitry.

The key to the new 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 their new 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,” says Professor Someya. He continues, “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.


This work was conducted in collaboration with  the research group of Professor  Walter Voit  at  the University of Texas at Dallas, USA.



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