Materials

Rainbow road sign film would be easier for autonomous vehicles to read

Rainbow road sign film would b...
Left: a visible light image of a Stop sign covered in the new microscale concave interface (MCI) material. Right: a LIDAR image of the same sign.
Left: a visible light image of a Stop sign covered in the new microscale concave interface (MCI) material. Right: a LIDAR image of the same sign.
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Left: a visible light image of a Stop sign covered in the new microscale concave interface (MCI) material. Right: a LIDAR image of the same sign.
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Left: a visible light image of a Stop sign covered in the new microscale concave interface (MCI) material. Right: a LIDAR image of the same sign.
A microscope image of the tiny spheres that make up the surface of the new microscale concave interface (MCI) material
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A microscope image of the tiny spheres that make up the surface of the new microscale concave interface (MCI) material
When white light hits the microscale concave interface (MCI), it produces concentric rainbow rings
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When white light hits the microscale concave interface (MCI), it produces concentric rainbow rings
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Autonomous vehicles need to operate in a complex environment, and recognizing traffic signs is an important part of that. A new microstructured material reflects light in rainbow rings, which can make traffic signs easier for computer vision systems to read.

Even outside of fully autonomous vehicles, traffic sign recognition has been part of driver assistance systems for over a decade. Normally the technology is based on recognizing colors or shapes of signs, but it doesn’t always get it right in the real world, where readability can be affected by lighting, weather, obstacles, damage, or something as simple as stickers on the sign.

So for the new study a team of researchers investigated a promising new material that could make the job easier. It’s a new form of retroreflective material, already commonly used to highlight signs and road markings by bouncing light from a vehicle’s headlights straight back at a driver. But rather than focus that light, the new material scatters it to create eye-catching patterns.

When white light hits the microscale concave interface (MCI), it produces concentric rainbow rings
When white light hits the microscale concave interface (MCI), it produces concentric rainbow rings

It’s called a microscale concave interface (MCI) and is made up of a thin film of tiny polymer spheres embedded in tape. When light hits the surface, these microspheres reflect it into a series of concentric circles – white light creates rainbow rings, a single-colored laser produces patterns of bright and dark rings, and infrared lasers have their own similar circular patterns.

The idea is that by covering traffic signs in MCI materials, the patterns produced could be cross-referenced between multiple sensors in a vehicle, to confirm what kind of sign it is.

“Currently, autopilot systems face many challenges in recognizing traffic signs, especially in real-world conditions,” says Qiaoqiang Gan, corresponding author of the study. “Smart traffic signs made from our material could provide more signals for future systems that use LIDAR and visible pattern recognition together to identify important traffic signs. This may be helpful to improve the traffic safety for autonomous cars.”

A microscope image of the tiny spheres that make up the surface of the new microscale concave interface (MCI) material
A microscope image of the tiny spheres that make up the surface of the new microscale concave interface (MCI) material

The team says these MCI materials could also be useful for electronic sensors, anti-counterfeiting tools, and reflective displays. Future tests will experiment with different wavelengths of light and other materials for the microspheres, to see what other effects might emerge.

The research was published in the journal Applied Materials Today.

Source: University at Buffalo

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