Electrical engineers at Duke University have determined the theoretical fundamental limit for the way much electromagnetic energy a transparent material with a given thickness can absorb. The finding will help engineers optimize devices designed to dam certain frequencies of radiation while allowing others to go through, for applications equivalent to stealth or wireless communications.
“Much of the physics of the known universe have already got fundamental solutions or are too complex to get a precise answer,” said Willie Padilla, professor of electrical and computer engineering at Duke. “In any field, finding a really novel, fundamental, exact result like that is rare.”
The research appeared online March 8in the journal Nanophotonics.
Whether constructing an antenna or developing sunscreen, there are a lot of instances where certain kinds of light have to be absorbed. One trick to maximizing that quantity is increasing the thickness of the fabric absorbing the energy.
Nevertheless, the needed thickness for a transparent material to supply that absorption was unknown till now.
Greater than 20 years ago, Konstantin N. Rozanov of the Institute for Theoretical and Applied Electrodynamics in Moscow, Russia, discovered essentially the most light over a variety of wavelengths that a tool of a certain thickness could absorb if one side was lined with metal. This scenario creates a boundary on one side where all light either reflects back or is absorbed, providing a constraint that permits a certain mathematical approach to crack the issue.
Taking away that metal edge and allowing the sunshine to proceed through, nonetheless, is a horse of a wholly different color on the electromagnetic spectrum.
“Rozanov used a clever trick where he worked in wavelength as an alternative of frequency,” said Yang Deng, a research assistant working in Padilla’s laboratory. “But several researchers have since tried using that approach to this problem and failed.”
To provide you with a brand new mathematical approach, Padilla and Deng collaborated with Vahid Tarokh, the Rhodes Family Professor of Electrical and Computer Engineering at Duke. Tarokh’s research spans a wide selection of topics while pursuing latest formulations and approaches to getting essentially the most out of datasets.
Without getting too deep into the mathematical weeds, it might probably be said that Tarokh was in a position to determine the right way to shape the issue in order that it might be solved, pulling a rabbit from a mathematical hat.
“Hindsight is 20/20, but even mathematicians call these creative strategies ‘tricks,'” Padilla said.
Beyond the novelty of solving a long-sought-after problem, the researchers say their work has practical implications in several areas. Metal-backed absorbers won’t let any kind of electromagnetic energy go through. But there are particular applications where it is advisable to block some frequencies while letting others pass.
For instance, cellular phones might wish to find a way to dam certain kinds of harmful electromagnetic radiation while letting others like GPS or Bluetooth through. Knowing what the elemental limits of this kind of goal will allow engineers to know when more work optimizing their design won’t be well worth the effort.
This research was supported by the Department of Energy (DESC0014372).
