The Quest for Electromagnetic ‘Full Absorption’ and the End of Power Lines

​”Harvesting the energy of electromagnetic waves” sounds redundant. As energy is a thing at all in its most reduced, pristine senseit is just that: electromagnetic waves. These waves, which can be viewed as electric and magnetic waves traveling separately but joined together, are just charged particles accelerated, reflecting changes within electric and magnetic fields. This is how energy freed from mass gets from place to place at the speed of light.

Harvesting these waves is the subject of a​ paper out this week in the Applied Physics Letters boasting the possibility of “full absorption.” This means the conversion of electromagnetic waves within a given range of frequencies with almost 100 percent efficiency. Fully absorbent materials reflect nothing and waste nothing.

In the new paper, researchers at the University of Waterloo describe the use of metasurfaces etched with different patterns of shapes, with each variation acting as a resonator that can be tuned to target a particular frequency. This tunability allows the material to achieve “full unity” (or very close to it) in its absorption of electromagnetic waves. This absorbed energy is then shuttled away from the surface through a conducting path connected to a resistant load (sort of an electrical sponge).

Image: AIP/Waterloo

“In this work, we present the design of a metamaterial harvester slab operating in the microwave regime based on an array of electric-inductive-capacitive resonators,” the Waterloo researchers write. “The experimental results showed that 93 percent of the incident power was channeled to the load resistance.” Pretty close to perfect.

“Conventional antennas can channel electromagnetic energy to a load-but at much lower energy absorption efficiency levels,” said study co-author Omar M. Ramahi, an electrical engineering professor at Waterloo, in ​an American Institute of Physics statement. “We can also channel the absorbed energy into a load, rather than having the energy dissipate in the material as was done in previous works.”

The idea is that a material like this could employed in such a way to match the ambient electromagnetic radiation of a given environment, or free-space impedance.

One potential application is in space-based solar energy harvesting. Via conventional solar panels, some satellite power plant would capture energy, which would then be converted into microwaves. These microwaves could then be beamed down at surface microwave collector farms. This could be a lot more bang per solar buck.

Another related possibility, according to Ramahi, is “wireless power transfer-directly adaptable to power remote devices such as RFID devices and tags or even remote devices in general.” In other words: the end of wires.

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