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Stretchy graphene sensor feels the strain

Fish scales of graphene oxide on stretchable tape could make for a highly sensitive, wearable sensor

by Neil Savage
August 24, 2016

Photo of graphene strain sensor and scanning electron micrograph of graphene fish scales
Credit: ACS Nano
A strain sensor built on flexible tape (left) works thanks to graphene broken into small pieces in a fish-scale pattern (right).

Sensors that could detect body motion as subtle as a pulse or as large as the bending of a knuckle would be useful as health monitors or other kinds of wearable electronics. Existing sensors based on metals, semiconductors, or nanomaterials, however, can measure only a small range of motion. Now researchers have built a simple device by layering graphene atop a piece of stretchable adhesive tape, which they say can be used as inexpensive, highly sensitive strain sensors (ACS Nano 2016, DOI: 10.1021/acsnano.6b03813).

To build their sensors, chemist Gaoquan Shi and his colleagues from Tsinghua University placed a film of reduced graphene oxide on a piece of commercially available elastic tape, then stretched the tape by 50%, causing the graphene oxide to crack and break into smaller pieces. With the film still stretched, they deposited another graphene film on the surface and stretched the tape to double its original length, breaking up the new layer. The team then let the tape return to its original length and attached copper wires to the ends. The resulting graphene structure resembled fish scales, with larger pieces on top of smaller ones.

To sense strain, the researchers simply stick the device on whatever is being measured—a human wrist, for example. As the device is stretched or bent, the graphene layers slip, and the contact area between overlapping layers changes. Measuring the change in electrical resistance reveals the amount of strain. Shi says the device can measure an increase in strain from 0.1 to 82%. And it works for both stretching and bending motions.

The device is sensitive enough to measure a pulse from a person’s wrist, allowing it to be used as an inexpensive pulse monitor outside of a hospital setting, Shi says. The team also placed the device on a person’s throat and was able to detect different signals when the person spoke different words. Such a device might be used to retrain someone having trouble speaking, or provide a new means of controlling a computer, Shi suggests.



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