What if you could take your temperature without a thermometer?
Researchers at the University of Tokyo have developed a wearable device that can continuously monitor a patient's temperature – and sound an alarm when a fever develops to alert a nurse or caretaker. Wireless and imperceptibly thin, the "fever alarm armband" is superior to a traditional thermometer in two ways: hygiene and patient comfort.
Reusable devices can easily spread germs from patient to patient in a hospital setting, but the armband can be printed from a modified inkjet printer and is inexpensive enough to toss out after use.
To ensure patient comfort, the solar-powered device is built entirely out of flexible components, including circuits made from carbon, hydrogen and oxygen. These so-called organic circuits replace the need for the rigid silicon circuits found in conventional electronics.
"Organic semiconductors are inherently soft and cheap," said Takao Someya, an electrical engineer who helped lead the project.
The armband combines a flexible solar panel, speaker, temperature sensor and a power supply circuit in a device that's only hundreds of micrometers thick. It's the first device to achieve both flexibility and a wireless, solar-powered interface, said Hiroshi Fuketa, a research associate in the university's Institute of Industrial Science who worked on the device.
Someya and Takayasu Sakurai, an electrical engineer, led the research groups behind the armband, which was presented last month at the 2015 IEEE International Solid State Circuits Conference in San Francisco.
At 12 inches around and 7 inches wide, the armband fits around the patient's upper arm and can be worn on the skin or over clothing. Much of the armband's surface is covered in a thin, flexible solar panel, eliminating the need for wires.
A tiny temperature sensor rests between the arm and the body and sounds a high-pitched alarm if the body reaches a pre-set value between 97.7 and 101.3 degrees Fahrenheit. A normal body temperature is 98.6 degrees.
The armband represents an initial step into a world of functional everyday items.
Last year, the researchers unveiled a sensor system that was both flexible and wireless. They demonstrated their new technology in the form of a diaper – its organic circuit could wirelessly alert parents when it got wet.
The stiff, bulky circuits that are commonplace today are not practical for wearable sensor devices. Instead, consumers want disposable devices with "imperceptible softness," the researchers said – features you can't get from conventional electronics.
Researchers fabricated the temperature detector and organic circuits onto a flexible polyimide film – a sturdy kind of plastic found in many consumer electronics – and attached the solar cells and speaker on top. The solar cells cover a large portion of the armband's outer surface, making the device look like it was cut from a scaly suit of armor.
Together, the organic circuits and temperature detector are 50 micrometers thick and the solar cells add another 200 micrometers. Still, the armband is only about twice as thick as a human hair, Fuketa said.
Before the armband is ready for hospitals, the researchers still need to develop a rechargeable battery for the device, which relies on constant sun or indoor light. A fever detector that works in the dark is still a few years away, Someya said.
Once that hurdle is overcome, the armband could also be used in homes, to take care of infants or the elderly, he added.
Fever detection is only the first application of this technology, the researchers say.
In the future, the system could be combined with other sensors to detect heart rate, wetness or pressure, Someya said. But those measurements are more difficult to make using wireless circuitry and will require more complicated techniques that are still in development, Fuketa said.