Printed Sensor Monitors Tire Tread in Real Time

A carbon nanotube sensor measures millimeter-scale changes in rubber thickness

Close up of a tire depth sensor in a tire
Photo: Kevin Seifert/Duke University

A flexible, printed sensor that accurately measures tire wear in real time could warn drivers when the tread on their tires has gotten uneven or precariously thin. The sensor, made with carbon nanotube ink, spots millimeter-level changes in tire tread with 99 percent accuracy.

Today’s cars are laden with sensors that keep tabs on many variables including engine temperature and fuel pressure as well as environmental conditions and approaching obstacles. But there is no technology to monitor tire wear, says Duke University professor of electrical and computer engineering Aaron Franklin, who led the team that reported the new tire sensor in IEEE Sensors Journal last year.

The researchers’ spinout Tyrata, Inc. raised US $4.5 million from several investors last week. Franklin says the startup should have a sensor package that’s ready to go into cars by mid-2019. “The device is so simple and the need is so great since no existing competitor is available, that response from the industry has been astonishing,” he says.

The new tire sensor is simple: it consists of just two millimeter-scale electrodes that the researchers print on a plastic substrate using carbon nanotube ink. The device goes on the inside wall of a tire. An oscillating voltage is applied to one electrode and the other is grounded to create an electric field, part of which arcs over the electrodes and passes through the tire rubber. The sensor system measures the magnitude of the oscillating signal reflecting off the grounded electrode, which changes with slight changes in the rubber’s thickness.

In their research paper, the team had focused on measuring capacitance. But, the capacitance changes are very tiny and required expensive electronics to measure, Franklin says. The low-frequency reflectance signal, meanwhile, can be measured with low-cost electronics.

The printed sensors alone should cost a few cents apiece. By putting arrays of these sensors on the insides of tires, it’s possible to create a high-resolution map of the tread depth of the entire tire area, the researchers say. The sensors could even be inkjet-printed directly on the inside rubber wall.

A full sensor system should also be relatively cheap, Franklin says, and could be built with off-the-shelf parts: a low-cost battery that lasts for the life of a tire, control electronics to drive the sensor, and a Bluetooth chip to transmit measured signals to a phone app or the vehicle’s control unit.

Even better, the carbon nanotube sensors could piggyback on the tire pressure monitoring systems that already exist in cars. Those systems, mounted on tire stems, include a battery, microcontroller, and a wireless transmission chip.

Tyrata is pursuing both of these paths to integrate its sensor into cars and trucks.

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