Stick-on, wearable wireless sensors track health indicators

Stanford University wearable stick-on sensor
Stanford University researchers have developed stretchable stick-on, wearable sensors to track health and beam these readings to an RFID receiver on a person’s clothing. (Bao Lab, Stanford University)

Stanford University engineers have developed a way to detect physiological signals emanating from the skin, using stick-on sensors that beam wireless readings to a receiver clipped onto clothing.

Stanford University chemical engineering professor Zhenan Bao, whose lab described the system in an Aug. 15 article in Nature Electronics, believes the wearable technology, called BodyNet, will be initially deployed in medical settings such as monitoring patients with sleep disorders or heart conditions. Her lab is already trying to develop new stickers to sense sweat and other secretions to track variables such as body temperature and stress. Bao would like to create an array of stick-on wireless sensors that work in conjunction with smart clothing to more accurately track a wider range of health indicators currently available smart phones or watches.

“We think one day it will be possible to create a full-body skin-sensor array to collect physiological data without interfering with a person’s normal behavior,” said Bao in a statement.  

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Because user comfort was a concern, research team leaders Simiao Niu and Naoji Matsuhisa, both postdoctoral scholars, set out to develop a technology that would have no batteries or rigid circuits to prevent the stickers from stretching and contracting with the skin.

A key hurdle was creating a flexible antenna that could stretch and bend like skin, which the scientists accomplished by screen-printing metallic ink on a rubber sticker. But because human movements would constantly bend and flex the antenna, the other challenge was using a signal technology that could withstand repeated antenna movement.

RELATED: Skin sensors transforming healthcare

To accomplish this, researchers settled on a design with a variation of RFID (radio frequency identification) technology used to control keyless entry to locked rooms. Similar in concept to an ID card, the BodyNet sticker has an antenna that harvests a bit of the incoming RFID energy from a receiver on the clothing to power its sensors. It then takes readings from the skin and beams them back to the nearby battery-powered receiver. The receiver then uses Bluetooth to periodically upload data from the stickers to a smartphone, computer or other permanent storage system.

To demonstrate the wearable technology, the researchers stuck sensors to the wrist and abdomen of one test subject to monitor the person’s pulse and respiration, by detecting how their skin stretched and contracted with each heartbeat or breath. Likewise, stickers on the person’s elbows and knees tracked arm and leg motions by gauging the minute tightening or relaxation of the skin each time the corresponding muscle flexed.

The initial version of the stickers relied on tiny motion sensors to take respiration and pulse readings. The researchers are now studying how to integrate sweat, temperature and other sensors into their antenna systems.

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