Scientists at the Hong Kong University of Science and Technology claim to have developed a robotic eye they say mimics the equivalent human organism and even out-performs it on some measures.
Zhiyong Fan and his team developed a hemispherical artificial retina containing light-sensitive nanowires made from perovskite to mimic the photoreceptors of the human eye. In a paper in Nature, they detail how the device can "see" by reconstructing images (the letters "E", "I" and "Y") viewed by the artificial eye.
A detailed structure of EC-EYE. a) Exploded view of EC-EYE and b) side view, complete with liquid metal wires. Diagram via: "A biomimetic eye with a hemispherical perovskite nanowire array retina", Nature, 20 May
Previous attempts to develop robotic eyes were limited by the fact the scientists created an artificial retina by laying out receptors on a flat plane and then attempted to fold or curve them, compromising the density of sensors, an accompanying article explains.
Fan's team got around this problem by placing photosensors directly inside the pores of a hemispherical membrane of aluminium oxide.
"Thin, flexible wires made of a liquid metal sealed in soft rubber tubes transmit signals from the nanowire photosensors to external circuitry for signal processing. These wires mimic the nerve fibres that connect the human eye to the brain," the researchers revealed in the paper, "A biomimetic eye with a hemispherical perovskite nanowire array retina," which appeared in the 20 May edition of Nature.
The artificial retina detects an average of 86 photons per second, on a par with the sensitivity of photoreceptors in human retinas. The performance results from perovskite being a compound which shows great promise in optoelectronic and photonic applications, such as solar cells.
On other measures, the robotic eye out-performs its human counterpart, the researchers said. It can take 19.2 milliseconds to respond to a pulse of light and then 23.9 milliseconds to return to its inactive state when a pulse has ended. The response-and-recovery times show how quickly it might respond to light signals. The time for a human retinas ranges from 40 to 150 ms.
But the team's work is just the start. The paper is based on a proof-of-concept consisting of just 100 pixels, each with three nanowires. The authors say their design can be built with better resolution than human eyes by increasing the density of nanowires to more than 10 times the human equivalent.
In an accompanying news article, Hongrui Jiang of the Department of Electrical and Computer Engineering at the University of Wisconsin, said Fan and co's "work adds to the breakthroughs that have been made in the past few decades, which have been achieved by mimicking not only camera-like eyes (such as those of humans), but also compound eyes similar to those of insects. Given these advances, it seems feasible that we might witness the wide use of artificial and bionic eyes in daily life within the next decade." ®