A new lightweight temperature sensor that's printable and flexible



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From workouts to weight loss, from infants to invalids, keeping track of fluctuations in body temperature can make all the difference to health. But traditional electronic thermometers have always had practical drawbacks. Now a research group at the University of Tokyo has developed a flexible, lightweight sensor that responds rapidly to tiny thermal changes in the range of human body temperature with potential benefits for athletes, newborn babies and intensive care patients.


Feel the heat

The printable sensor is thin and flexible enough to wrap around a pencil, or adapt to the form of the human body or another substrate. Device performance is largely unaffected by bending. Credit: 2015 Someya Laboratory

Body temperature is one of the most important measurements needed to provide feedback on a patient's health and wellbeing. Though wearable devices are increasingly being developed for healthcare and other applications, many low-cost flexible temperature recorders require external circuitry if they are to amplify the signal enough to allow accurate temperature measurement.

Professor Takao Someya and Dr. Tomoyuki Yokota's team have developed a new printable, flexible, lightweight sensor that has proved to be highly sensitive to temperature change over a range of just five degrees Celsius. This, they say, will allow accurate temperature measurement without additional complicated display circuitry.


Muscle in plastic

What makes the new sensor different is its ability to precisely control the temperature of the sensors which is made of graphite and a special heat sensitive thermoplastic — technically known as a semicrystalline acrylate polymer. The target temperature range at which the sensor is most precise can be selected simply by altering the proportions of the chemical makeup of the plastic.

The researchers say they have achieved target temperatures between 25 and 50 degrees Celsius — a range which includes average human body temperature — a response time of less than 100 milliseconds and a temperature sensitivity of 0.02 degrees Celsius. This allows them to very quickly and accurately measure even slight changes in body temperature.


Sticking with it

The team tested the new flexible thermal monitoring sensor on a rat by positioning the device to measure the creature's lung temperature. They successfully measured variations of just 0.1 degree as the animal breathed, demonstrating the sensor's potential use for monitoring body vital signs in internal — or physiological — settings.

"This sensor," says Someya, "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 — and maybe even powered by physical activity — during sporting and other activities.