Sensors use nanotubes to measure tyre wear Friday, 16 June 2017

A team of electrical engineers have invented an inexpensive printed sensor that can monitor the tread of car tyres in real time, warning drivers when the tread has grown dangerously thin.

The researchers from Duke University in North Carolina in collaboration with Fetch Automotive Design Group have demonstrated a design using metallic carbon nanotubes that can track millimetre-scale changes in tread depth with 99 percent accuracy.

"With all of the technology and sensors that are in today's cars, it's kind of crazy to think that there's almost no data being gathered from the only part of the vehicle that is actually touching the road," said Aaron Franklin, associate professor of electrical and computer engineering at Duke.

"Our tyre tread sensor is the perfect marriage between high-end technology and a simple solution."

The technology relies on the interactions of electric fields with metallic conductors. The core of the sensor is formed by placing two small, electrically conductive electrodes very close to each other. By applying an oscillating electrical voltage to one and grounding the other, an electric field forms between the electrodes.

While most of this electric field passes directly between the two electrodes, some of the field arcs between them. When a material is placed on top of the electrodes, it interferes with this so-called 'fringing field'.

By measuring this interference through the electrical response of the grounded electrode, it is possible to determine the thickness of the material covering the sensor. While there is a limit to how thick a material this setup can detect, it is more than enough to encompass the several millimetres of tread found in today's tyres. And with evidence of sub-millimetre resolution, the technology could easily tell drivers when it's time to buy a new set of tyres.

"When we pitch this idea to industry experts, they say to each other, 'Why haven't we tried that before?' It seems so obvious once you see it." said Franklin.

While the sensor could be made from a variety of materials and methods, the paper explains how the researchers optimised performance by exploring different variables from sensor size and structure to substrate and ink materials. The best results were obtained by printing electrodes made of metallic carbon nanotubes on a flexible polyimide film.

Besides providing the best results, the metallic carbon nanotubes are durable enough to survive the harsh environment inside a tyre. Tests also proved that the metal mesh embedded within tyres does not disrupt the operation of the sensors.

Franklin's group also wants to explore other automotive applications for the printed sensors, such as keeping tabs on the thickness of brake pads or the air pressure within tyres.

[A demonstration of the printed carbon nanotubes on a flexible surface. Photo: Duke University]