Wireless sensors that stick to the skin to track physiological signals

The rubber sticker attached to the wrist can bend and stretch as the person’s skin moves, beaming pulse readings to a receiver clipped to the person’s clothing. (Image credit: Bao Lab)

Stanford engineers have developed experimental stickers that pick up physiological signals emanating from the skin, then wirelessly beam these health readings to a receiver clipped onto clothing. It’s all part of a system called BodyNet.

We tend to take our skin’s protective function for granted, ignoring its other roles in signaling subtleties like a fluttering heart or a flush of embarrassment.

Now, Stanford engineers have developed a way to detect physiological signals emanating from the skin with sensors that stick like band-aids and beam wireless readings to a receiver clipped onto clothing.

To demonstrate this 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.

Zhenan Bao, the chemical engineering professor whose lab described the system in an Aug. 15 article in Nature Electronics, thinks this wearable technology, which they call BodyNet, will first be used 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. Her 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 smart phones or watches consumers use today.

“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, who is also the K.K. Lee Professor in the School of Engineering.

Stretchable, comfortable, functional

Postdoctoral scholars Simiao Niu and Naoji Matsuhisa led the 14-person team that spent three years designing the sensors. Their goal was to develop a technology that would be comfortable to wear and have no batteries or rigid circuits to prevent the stickers from stretching and contracting with the skin.

Their eventual design met these parameters with a variation of the RFID – radiofrequency identification – 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.