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Nondistorting mirror eliminates blind spots

Photonics Spectra
Aug 2012
Ashley N. Paddock, ashley.paddock@photonics.com

PHILADELPHIA – Have you ever been passed on the road by a vehicle that seems to have come out of nowhere? Well, drivers: Take heed. A new subtly curved side mirror that dramatically increases the field of view with minimal distortion could offer an alternative to traditional mirrors that induce blind spots.

Created by Drexel University mathematics professor Dr. R. Andrew Hicks, the new mirror uses a mathematical algorithm to precisely control the angle of light bouncing off its curves; it was recently issued a US patent.

“Imagine that the mirror’s surface is made of many smaller mirrors turned to different angles, like a disco ball,” Hicks said. “The algorithm is a set of calculations to manipulate the direction of each face of the metaphorical disco ball so that each ray of light bouncing off the mirror shows the driver a wide, but not too distorted, picture of the scene behind him.”


A side-by-side comparison of a standard flat driver’s-side mirror with a new slightly curved mirror designed at Drexel University. With minimal distortion, the new mirror shows a much wider field of view; note the wide area to the left of the silver car seen in the distance, behind the tree. Courtesy of R. Andrew Hicks, Drexel University.


Traditional flat mirrors on the driver’s side of a car give an accurate sense of the distance of vehicles and objects behind them, but the field of view is narrow. This results in a region of space behind the vehicle, known as the blind spot, which drivers cannot see via either the rearview or side mirrors.

Now with Hicks’ curved mirror, a driver’s field of view could be as great as 45°, compared with the 15° to 17° field produced by a traditional flat side mirror. The new mirror barely detects any visual distortion of shapes and straight lines, unlike simple curved mirrors that squash the perceived shape of objects and make straight lines appear curved.

US regulations dictate that cars coming off the assembly line must have a flat mirror on the driver’s side; curved mirrors are allowed for the passenger side only if they include the sentence “Objects in mirror are closer than they appear.” Because of such regulations, Hicks’ mirror will not be installed on new cars sold in the US anytime soon.

“The rationale for current regulations that say mirrors must be flat is that flat mirrors give an accurate reflection of depth and distance,” Drexel news officer Rachel Ewing told Photonics Spectra.

“A mirror that is curved to show a wider field of view will make objects appear smaller and farther away, just because things have to look smaller if you want to fit more stuff in,” she added. The Hicks mirror doesn’t solve that problem, but drastically reduces the distortion of shapes you would see in a simple convex mirror.”

The device could be manufactured and sold as an aftermarket product that drivers and mechanics can install on cars after purchase. Slightly curved mirrors are allowed on some new cars in certain European and Asian countries.

Currently, only two prototypes of the mirror exist, Ewing said.


GLOSSARY
photonics
The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
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