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Highly Stretchable Sensors Devised for Wearable Devices

Glove with finger sensors

Glove with finger sensors (University of British Columbia, Okanagan)

23 February 2018. Engineers in Canada developed graphene sensors with a great deal of flexibility that can measure fine human movements and minute functions for wearable medical devices, and be made with an economical process. A team from the University of British Columbia campus in Okanagan describe 3 applications of the sensors in a recent issue of the journal Sensors and Actuators A: Physical (paid subscription required).

UBC-Okanagan researchers from the lab of mechanical engineering professor Homayoun Najjaran are seeking materials for sensors in wearable medical devices that do a better job of capturing muscle movements and measuring vital human functions. Many of today’s wearable devices can measure large muscle movements, such as walking, but cannot capture complex muscle movements or key vital signs, such as heart beats, without additional technologies. In order to be feasible, their solution needed to conform to the human physique, be light in weight, stable, and durable, as well as easy and inexpensive to produce.

Najjaran and colleagues based their stretchable sensors on graphene, a material closely related to graphite like that used in pencils, one atom in thickness and arrayed in an hexagonal atomic pattern. The material is very light, strong, chemically stable, and can conduct both heat and electricity, with applications in electronics, energy, manufacturing, distribution, and health care. The team fabricated nanoscale flakes of graphene infused into an adhesive pad made from a common rubber-like material. The conductivity of the graphene makes it possible to measure piezoelectric effects, or electric fields from compression of the material, to create the sensors.

The researchers found the material can stretch well beyond its original shape. Tests by the team show the material can withstand strains as high as 350 percent. Other tests stretched and relaxed the sensors more than 10,000 times, with the material still able to maintain its electronic responses. In addition, the material’s wide gauge factor range, a measure of electrical resistance to mechanical strain, indicates it can monitor a variety of human motions and functions.

The team made the material into 3 wearable devices, with tests also reported in the paper. A knee band measures larger muscle movements, used in standing, sitting, walking, and running. A wrist band with the material can measure heart beats from a person’s pulse. A glove with sensors in the fingers can measure finger movements on humans and robotic hands.

“We have introduced an easy and highly repeatable fabrication method to create a highly sensitive sensor with outstanding mechanical and electrical properties at a very low cost,” says UBC-Okanagan engineering professor and co-author Mina Hoorfar in a university statement. “Not only did it maintain its form,” adds Najjaran, “but more importantly it retained its sensory functionality.”

Najjaran and Hoorfar take part in the university’s SmarT Innovations for Technology Connected Health or STITCH Institute, developing technologies for wearable devices. The institute so far spun-off 3 companies, with the newest enterprise, Texavie, developing smart fabrics for augmented and virtual reality.

Najjaran and Hoorfar tell more about their project in the following video.

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