Scientists proved the fundamental limits of electromagnetic energy absorption

Mathematical solution evaded discovery for over two decades.


Duke University electrical engineers have calculated the maximum electromagnetic energy a see-through material may absorb in terms of its thickness. This finding will assist engineers in creating radiation-blocking devices that allow specific radiation to get through while blocking others, which will be helpful for things like enhancing wireless communication and hiding from radar.

According to Duke professor Willie Padilla, finding a precise solution like this is unusual and intriguing because many physics concepts are either too complex or well known.

Sometimes, whether you’re building sunscreen or an antenna, you need to absorb specific wavelengths of light. Increasing the thickness of the absorbing material is one approach to absorbing more light.

Until recently, researchers were unsure of the minimum thickness of a transparent substance required to take in a given quantity of light.

Konstantin N. Rozanov of the Institute for Theoretical and Applied Electrodynamics in Russia discovered more than two decades ago the amount of light that a gadget might absorb at various wavelengths if one side of it was coated in metal. This metal establishes a barrier where light is absorbed or bounced back, simplifying the mathematical solution.

However, on the electromagnetic spectrum, everything changes dramatically when that metal edge is removed, and light can flow through.

Yang Deng, a research assistant in Padilla’s laboratory, said, “Rozanov used a clever trick: He worked in wavelength instead of frequency. But several researchers have since tried using that approach to this problem and failed.”

Scientists collaborated with Vahid Tarokh, a Duke University professor who is well-known for his broad research interests and creative approaches to dataset analysis, to create a novel mathematical approach.

Tarokh managed to reframe the problem and make it solvable without getting bogged down in intricate mathematical details; it was almost like conjuring a brilliant answer out of thin air.

Willie Padilla, professor of electrical and computer engineering at Duke, said“Hindsight is 20/20, but even mathematicians call these creative strategies tricks.”

In addition to providing an answer to a long-standing mystery, the researchers think their study will have practical applications in various sectors. Metal-backed absorbers block all forms of electromagnetic energy; however, there are circumstances in which you might wish to let certain frequencies through while blocking others.

For example, mobile phones may need to filter out dangerous radiation while allowing Bluetooth or GPS signals to pass through. Comprehending the essential boundaries for accomplishing this objective aids engineers in determining when they have arrived at the optimal design and when more refinement will not yield significant improvements.

Journal Reference:

  1. Willie J. Padilla, Yang Deng, Omar Khatib and Vahid Tarokh. Fundamental absorption bandwidth to thickness limit for transparent homogeneous layers. Nanophotonics. DOI: 10.1515/nanoph-2023-0920
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