According to the NRL, this is the most significant demonstration of power beaming in nearly 50 years.
The concept is simple: Electricity is converted to microwaves, which are then focused in a tight beam at a receiver made up of rectenna elements. These components consist of an x-band dipole antenna with an RF diode. When the microwaves strike the rectenna, the elements then generate DC current.
Microwave power beaming is a point-to-point transfer of electrical energy across free space using a directed microwave beam. It is received with the rectifying antenna, which consists of large numbers of small microwave antennas. These works in the X-Band, which is the frequency range falling between seven and 11.2 gigahertz (GHz). A diode then converts the incoming electromagnetic waves back into the DC electrical power. In this particular demonstration system, the NRL used a 10 GHz band as the technology being used is considered to be mature and available at low costs.
Paul Jaffe, a researcher on power beaming and space-based solar power, explained that the NRL set its targets to push the technology farther than has been demonstrated before. The frequency was chosen because it can beam even in heavy rain with a loss of power of under five percent, but it is also safe to use under international standards in the presence of birds, animals and even people.
Despite initial doubts, microwave beaming turned out to be surprisingly efficient, and the the Advanced Concepts Group team led by Christopher Rodenbeck has been tasked to develop the Safe and Continuous Power Beaming-Microwave (SCOPE-M) project that could explore the practicality of fielding the technology.
The NRL also stated that power beaming is the ultimate green technology. Unlike other sources, power beamed from space to Earth could provide power continuously for an entire year. (Related: Green power dangers: Scientists review the downside of renewable energies.)
"That is something no other form of clean energy can do today. 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 [Department of Defense] application." Rodenbeck said.
The project was carried out in two locations. In the Maryland test version of the project, the beam operated at a 60 percent efficiency rating. The Massachusetts test did not reach the same peak, although it did have a higher power level, which meant that it delivered more energy. The technology is expected to one day be used to transmit power on Earth or from large orbital solar power stations, which could provide electricity to national grids 24 hours a day, 365 days a year.
Meanwhile, the DOD would like to use the technology for wireless power transmission from space. According to drawn-up plans by the military, troops that are deployed abroad are to be supplied with energy via power beaming that would make them independent of fuel deliveries. China is also working on a similar concept for civilian use. (Related: US Navy's solar satellite can open the way for solar farms in space.)
While the project was a terrestrial power-beaming link, SCOPE-M electronics engineer Brian Tierney said it was a good proof of concept for space power beaming. "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."
Jaffe also said past experiments with laser power beaming using much higher power densities allowed engineers to successfully implement interlock systems, so if something were to approach the beam, it will turn itself off. "We did not have to do that with SCOPE-M because the power density was sufficiently low that it was intrinsically safe," he said.
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