Most wireless sensors today communicate via embedded Bluetooth chips powered by small batteries. But experts believe these conventional chips and power sources will be too bulky for next-generation sensors, which are taking on thinner, more flexible forms.
The researchers “e-skin” is made from an ultrathin, high-quality film of gallium nitride, a material that is known for its piezoelectric properties – meaning it can both produce an electrical signal in response to mechanical strain and mechanically vibrate in response to an electrical impulse.
The MIT team found they could harness gallium nitride’s two-way piezoelectric properties and use the material simultaneously for both sensing and wireless communication.
In their new study, published in Science, the team produced pure, single-crystalline samples of gallium nitride, which they then paired with a conducting layer of gold to boost any incoming or outgoing electrical signal.
They showed that the device was sensitive enough to vibrate in response to a person’s heartbeat, as well as the salt in their sweat, and that the material’s vibrations generated an electrical signal that could be read by a nearby receiver.
The device was able to do all this without the need for a chip or battery.
“Chips require a lot of power, but our device could make a system very light without having any chips that are power-hungry,” says the study’s corresponding author, Jeehwan Kim, an associate professor of mechanical engineering and of materials science and engineering, and a principal investigator in the Research Laboratory of Electronics at MIT. “You could put it on your body like a bandage, and paired with a wireless reader on your cellphone, you could wirelessly monitor your pulse, sweat, and other biological signals.”
The research team see the e-skin research as a first step toward chip-free wireless sensors. They believe that the current device could be paired with other selective membranes to monitor other vital biomarkers.
“We showed sodium sensing, but if you change the sensing membrane, you could detect any target biomarker, such as glucose, or cortisol related to stress levels,” says co-author and MIT postdoc Jun Min Suh. “It’s quite a versatile platform.”