Engineers at Stanford University have developed a skin monitoring system that uses a network of stretchable sensors to wirelessly relay physiological signals.
Known as BodyNet, the system uses rubber patches that are screen printed with flexible metallic ink antennas. Depending on where on the body the patches are placed, the way in which they move and stretch can determine things like heart and respiration rates, as well as limb movements. The battery-free sensors transmit their signals with a form of RFID (radiofrequency identification) whereby small amounts of energy are harvested from a receiver clipped to clothing. The receiver then uses Bluetooth to upload the physiological data to a smartphone or computer.
To demonstrate the technology, the Stanford team stuck sensors to the wrist and abdomen to monitor the subject’s pulse and respiration by detecting how their skin stretched and contracted with each heartbeat or breath. Stickers on the elbows and knees tracked arm and leg motions by gauging the minute tightening or relaxation of the skin each time the muscle flexed.
According to Zhenan Bao, the chemical engineering professor whose lab led the work, the team is now hoping to develop new sensors that can detect changes in sweat and other secretions to determine things like stress and body temperature. The work is described in the journal Nature Electronics.
“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 behaviour,” said Bao, the K K Lee Professor at Stanford’s School of Engineering.
Key to the sensors’ design is the lack of any rigid components or circuits that would make wearing them uncomfortable. Problems arose with the stretchable antenna, however, as the signals it emitted when deformed became weak and unusable. To counter this, the engineers developed a new type of RFID system that could beam strong and accurate signals to the receiver despite constant fluctuations.
Another challenge comes with the receivers, which must be in close proximity for signals to be transmitted. Its envisioned that future iterations of the BodyNet system will use receivers embedded in clothing and sportswear to create a more user-friendly product.