Robots these days often take their inspiration from nature. Now cameras mimicking bug eyes that can look in many directions simultaneously can be made en masse, researchers say. These novel devices, each possessing hundreds of microscopic lenses, could find use as surveillance cameras on flying droids or in minimally invasive surgical operations.
The compound eyes of insects and other invertebrates are each made of up to thousands of relatively simple light-sensing facets known as ommatidia. These cover curved, hemispherical surfaces so that each points in slightly different directions. As such, compound eyes can have much wider fields of view than human eyes or regular cameras, including panoramic ones reaching nearly 360 degrees all the way around.
Scientists have sought to make synthetic compound eyes before for the many benefits they could offer. One could imagine surveillance cameras that can look in many directions at once instead of just one spot at a time — for instance, on miniature airborne drones. Artificial compound eyes could also help in endoscopic surgery that only requires small cuts be made to enter the body instead of more invasive procedures that open patients up more.
However, past techniques for making synthetic compound eyes all had drawbacks. Some placed arrays of microscopic light sensors on flat surfaces, missing the advantages afforded by curved surfaces. Others involved curved surfaces that were each handcrafted, and were therefore not amenable to mass production.
Now researchers may have developed a way to potentially mass-produce cameras with bug’s-eye views.
"We are excited because we feel that we’ve identified a realistic and scalable way to build insect-type cameras," says materials scientist John Rogers at the University of Illinois at Urbana-Champaign.
To make an eye, Rogers and his colleagues start with a flat square of silicone rubber with sides measuring less than 15 millimeters long, enough to line up the heads of nearly 10 pins. This sheet is covered with 180 usable lenses also made of this rubber, with each lens about 400 microns wide, or roughly four times the average width of a human hair.
This rubbery sheet is placed on top of a flexible grid of silicon light sensors, with each sensor capturing light from one of the lenses. Both layers are then dimpled from the bottom to form a curved dome and can be mounted on an electronic circuit board.
"This optical and electronic system can be blown up like a balloon, but in a very controlled fashion that does not crack the silicon or degrade any performance aspect of the system," Rogers says.
All in all, the artificial compound eye is nearly fully hemispherical, offering a field of view of about 160 degrees. These generated clear images without the anomalous blurring or aberrations that can occur with fish-eye lenses, spherical mirrors and other specialized optics that attempt to capture similarly large fields of view. Moreover, the small nature of each lens gives them a nearly infinite depth of field — as an object moves away from the camera, the size of the image decreases but it remains in focus.
"Our camera has an overall design — that is, hemispherical coverage and resolution — that is very similar to, although physically larger than, the eye of a common fire ant or bark beetle," Rogers says.
Although these artificial compound eyes have nearly twice as many light-sensing units as some worker ants, which have compound eyes possessing only 100 ommatidia, Rogers notes praying mantis eyes can have about 15,000 and dragonfly eyes can have roughly 28,000.
"The numbers of artificial ommatidia that we have in our cameras is limited to the low end of the biological world. We feel, however, that the idea can scale," Roger says.
In the future, the researchers would like to cram more lenses and light sensors onto their compound eyes. They would also like higher levels of curvature for even wider fields of view “beyond 180 degrees, to something significantly larger,” Rogers says. “We also feel that we can make cameras of this type with continuously tunable curvature, from flat to hemispherical. In that sense, we can introduce capabilities that are not found in biology.”
Future research could also mimic other kinds of compound eyes, such as ones used by lobsters and shrimp, which employ mirrors instead of lenses.
"We are making progress, but the level of sophistication in a real biological eye exceeds anything that we have done so far," Rogers says.
The scientists detailed their findings in the May 2 issue of the journal Nature.
Top Image: Ectemnius wasp via Shutterstock.