4th May 2022
Major advance in microwave power beaming
Researchers from the U.S. Naval Research Laboratory (NRL) have demonstrated the feasibility of terrestrial microwave power beaming by transmitting 1.6 kilowatts (kW) over a distance of 1 kilometre (km) – the most significant advance for this technology in nearly 50 years.
Microwave power beaming is the efficient, point-to-point transfer of electrical energy across free space by a directive microwave beam. A project known as the Safe and COntinuous Power bEaming – Microwave (SCOPE-M), funded by the U.S. Department of Defense (DOD), aims to prove that such technology is feasible at greater scales and distances. Its lead investigator is Christopher Rodenbeck, PhD, Head of Advanced Concepts at the Naval Research Laboratory (NRL).
Just 12 months after initiating this project, the NRL succeeded in beaming 1 kilowatt (kW) of electrical power over a distance of 1 km, using a 10 gigahertz (GHz) microwave beam. SCOPE-M demonstrated power beaming at two locations – one at the U.S. Army Research Field at Blossom Point in Maryland, and the other at the Haystack Ultrawideband Satellite Imaging Radar (HUSIR) transmitter at the Massachusetts Institute of Technology (MIT) in Massachusetts.
"The reason for setting those targets is to push this technology farther than has been demonstrated before," explained Paul Jaffe PhD, Power Beaming and Space Solar Lead. "You don't want to use too high a frequency as it can start losing power to the atmosphere," said Rodenbeck. "10 GHz is a great choice because the component technology out there is cheap and mature. Even in heavy rainfall, loss of power is less than 5%."
In Maryland, the team exceeded their target by 60%, beaming 1.6 kW just over 1 km. At the Massachusetts site, the team did not achieve the same peak power, but had a much higher average, thereby delivering more overall energy. Jaffe believes these demonstrations pave the way for power beaming on Earth, in space, and from space to Earth using power densities within safety limits set by international standards bodies.
"As engineers, we develop systems that will not exceed those safety limits," he said. "That means it's safe for birds, animals, and people."
During past experiments with laser power beaming, using much higher power densities, the engineers incorporated an interlock system – so if something approached the beam it would turn off. But with SCOPE-M, that is no longer necessary, said Jaffe: "We did not have to do that, because the power density was sufficiently low that it was intrinsically safe."
The DOD is particularly interested in wireless power beaming from space. A similar rectenna (rectifying antenna) array as used for SCOPE-M could be used in the harsh vacuum and extreme temperature environment of space, according to Brian Tierney, PhD, electronics engineer for the SCOPE-M project.
"Although SCOPE-M was a terrestrial power beaming link, it was a good proof of concept for a space power beaming link," said Tierney. "The main benefit of space to Earth power beaming for the DOD is to mitigate the reliance on the fuel supply for troops, which can be vulnerable to attack."
Besides being important for military operations, power beaming is the ultimate green technology. Unlike other sources of clean energy, which provide only intermittent and sporadic electrical supplies, power beamed from space to Earth could be supplied continuously, 24 hours a day, 365 days a year.
"That is something no other form of clean energy can do today," said Rodenbeck. "From the standpoint of technology readiness level, I feel we are very close to demonstrating a system we can truly deploy and use in a DOD application."
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