Engineers have developed a way to detect physiological signals emanating from the skin with sticky sensors that beam wireless readings to a receiver clipped onto clothing. To demonstrate the wearable technology, the researchers stuck sensors to the wrist and abdomen of a 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 wearable technology, called Body-Net, could be used in medical settings such as monitoring patients with sleep disorders or heart conditions. Additional stickers are being developed to sense sweat and other secretions to track variables such as body temperature and stress. The ultimate goal is to create an array of wireless sensors that stick to the skin and work in conjunction with smart clothing to more accurately track a wider variety of health indicators than the smartphones or watches consumers use today.
The BodyNet sticker is comfortable to wear and has no batteries or rigid circuits to prevent the stickers from stretching and contracting with the skin. The design uses a variation of the radio-frequency identification (RFID) technology used to control keyless entry to locked rooms. When a person holds an ID card up to an RFID receiver, an antenna in the ID card harvests a tiny bit of RFID energy from the receiver and uses this to generate a code that it then beams back to the receiver. The BodyNet sticker is similar to the ID card. It 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 receiver.
To make the wireless sticker work, the researchers had to create an antenna that could stretch and bend like skin. This was done by screen-printing metallic ink on a rubber sticker; however, whenever the antenna bent or stretched, those movements made its signal too weak and unstable to be useful. To solve the problem, researchers developed a new type of RFID system that could beam strong and accurate signals to the receiver despite constant fluctuations. The battery-powered receiver then uses Bluetooth to periodically upload data from the stickers to a smartphone, computer, or other permanent storage system.
The initial version of the stickers relied on tiny motion sensors to take respiration and pulse readings; the team is now studying how to integrate sweat, temperature, and other sensors into the antenna systems. To move the technology beyond clinical applications into consumer-friendly devices, another challenge had to be overcome: keeping the sensor and receiver close to each other. The researchers clipped a receiver on clothing just above each sensor.
One-to-one pairings of sensors and receivers would be adequate in medical monitoring but to create a BodyNet that someone could wear while exercising, antennas would have to be woven into clothing to receive and transmit signals no matter where a person sticks a sensor.