You've read about metamaterials being used to “cloak” antennas to reduce the impact of surrounding structures and to miniaturize antennas. Now a study by researchers at the University of Pennsylvania, the University of Texas at Austin, and the University of Sannio in Italy shows that metamaterials can be designed to do “photonic calculus” as a light wave goes through them.
The University of Pennsylvania news release explains:
“A light wave, when described in terms of space and time, has a profile in space that can be thought of as a curve on a Cartesian plane. The researchers’ theoretical material can perform a specific mathematical operation on that wave’s profile, such as finding its first or second derivative, as the light wave passes through the material.
“Essentially, shining a light wave on one side of such a material would result in that wave profile’s derivative exiting the other side. Metamaterials capable of other calculus operations, such as integration and convolution, could also be produced.”
These calculations are commonly used in applications such as image processing, although they are typically done after the light wave has been converted to digitized electronic signals. The researchers' proposed computational metamaterials could almost instantly perform these operations on the original wave, such as light coming through the lens of a camera, without conversion to electronic circuits.
Nader Engheta, the H. Nedwill Ramsey professor of Electrical and Systems Engineering in Penn’s School of Engineering and Applied Science, and Alexandre Silva, a postdoctoral researcher in Engheta’s research group, are leading the study in collaboration with Francesco Monticone and Andrea Alù of the University of Texas at Austin and Giuseppe Castaldi and Vincenzo Galdi of the University of Sannio in Italy.
Engheta explained: “Compared to digital computers, these analog computers were bulky, power hungry, and slow. But by applying the concepts behind them to optical metamaterials, one day we might be able to make them at micro- and nano-scale sizes, and operate them at nearly speed of light using little power. The thickness of our structures can be comparable with the optical wave length or even smaller. Implementing similar operations with conventional optical systems, such as lenses and filters, would require much thicker structures.”
One of the operations that could be performed by the metamaterial computer is edge detection, which is often used to find faces and identify other objects in pictures.
“When we do edge detection on an image now with currently available image processing techniques, we do it digitally, pixel by pixel,” Engheta said. “We scan an image and compare all of the neighboring pixels, and where there is a big difference between two, we label it an edge. With this computational metamaterial in the future, hopefully we will be able to do it all at once. The light from the image itself could go in and the edge-detected profile could come out the other side.”
For more about the interesting work Nader Engheta is doing with metamaterials, including with antennas, see his home page at the University of Pennsylvania.
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