When someone is recovering from joint surgery, it's important for doctors to monitor factors such as their range of motion. A new self-powered sensor could make doing so easier than ever, by wirelessly transmitting movement data from an orthopedic brace on that joint.

Developed by scientists at Canada's University of Waterloo, the prototype sensor takes the form of a small flexible cylinder that is powered by both electromagnetism and triboelectricity – the latter involves the generation of an electrical current via the friction that occurs when one specific type of material rubs against another type, and the sensor incorporates two such materials.

Whenever the brace-mounted sensor is bent or twisted, it generates enough electricity to wirelessly transmit a signal that can be picked up by a device such as a computer, smartphone or smartwatch. These signals could then be analyzed to determine the patient's range of movement, along with other indicators of improvement.

A remotely-located doctor or physiotherapist could subsequently access that information via the internet, instead of requiring the patient to make repeated visits to a clinic for assessment.

The sensors might also conceivably be mounted on the inside of self-driving cars' tires, allowing the vehicles to respond to changing road conditions. "Based on the forces, the interaction between the road and the tires, we could actually detect ice or rain," says engineering doctoral candidate Hassan Askari. "That is extremely important information for autonomous driving."

Currently, the sensor measures about 6 cm long by 1 cm wide (2.4 by 0.4 inches), although the scientists are working on further miniaturizing the technology. A paper on the research was recently published in the journal Sensors and Actuators A: Physical.