Dismounted soldiers and Marines often carry upwards of 100 pounds of gear, much of it power-hungry radios and night-vision goggles and sensors (like these tiny drones ). Each requires batteries and extra batteries — and that makes the prospect of delivering electricity over a Wi-Fi signal very attractive indeed.
Last week, researchers from the University of Washington unveiled a paper, “ Powering the Next Billion Devices With Wi-Fi ,” that describes how to power a small camera with a Wi-Fi signal. In essence, the camera’s 2.4-GHz antenna becomes an energy harvester that transforms radio frequency signals into DC power. Unlike some other ambient power schemes, this one doesn’t interfere with the functioning of the router. ( WIRED took note, declaring “ Wi-Fi to power your gadgets is closer than you think ,” and then walked back expectations with “ Wi-FI charging is real, but probably won’t charge your iPhone .”)
But is this breakthrough relevant for the men and women who lug hot and heavy batteries across mountaintops in places like Afghanistan?
Wi-Fi power has “any number of applications” on the battlefield, said Paul Roege, a retired Army colonel who also served as chief of the Army Operational Energy Office. Those include “inductive charging pads in a vehicle seat that could recharge soldier batteries on the ride to battle to a laser beaming power from an aerostat to a small patrol, either moving or stopped.” Over the last few years, he said, he has encouraged the Army to explore wireless energy for a variety of uses. “The Army actually has it on their screen today,” he said.
The amount of power that Vamsi Talla and his UW colleagues demonstrate in their paper might be enough for a wide variety of devices. “For example, if you have a bunch of sensors that could be arrayed near a hotspot, you can expand the idea a bit by having a battery or capacitor that charges up over time for use during the occasional powered activity — picture-taking, measurement, or even transmission,” said Roege. He added that there were some big limitations, including proximity to the hotspot. They might also power very small LED lights, of the sort that the Air Force Research Laboratory is implanting into gloves as part of the Batman program . But it’s not going to power your drone-killing laser — at least not yet.
The Past and Future of Wireless Power Beaming
The idea of beaming power from an aerostat — a big, tethered drone blimp — is not that far-fetched. On June 5, 1975, the NASA Jet Propulsion Laboratory used microwaves to transmit 34 kilowatts of power some 1.5 kilometers. Two years later, the Department of Energy and NASA began an ambitious research initiative to explore beaming power from space to Earth. It’s 10 times more efficient to generate solar power in space, free of interference from clouds, ozone, and airborne particles. But much of that surplus is lost in the effort to get the energy to the ground.
One of the more interesting space-based power schemes to emerge lately, the LUNA RING proposal from Japanese construction company Shimizu, involves sending robots to the moon to construct solar panels around the lunar equator from moon dirt. The hope was to harness the 13,000 trillion watts (terawatts) of energy that flows continuously from the sun to the lunar surface — some 650 times the amount that all human civilization needs to sustain economic growth. The collected energy would be beamed from the lunar surface via microwave and laser to satellites and finally to power receiving stations at sea. It is—to say the least—a lofty notion.
The Silicon Valley rush to space could push space-based power from fiction to fact in coming years. Last month, SpaceX founder and Silicon Valley megafauna Elon Musk filed a petition with the FCC to orbit 4,000 mini satellites that would beam Internet signals to Earth. It’s not much of a leap to think that such a constellation might some day double as power stations.
Back on Earth, Wi-Fi as a battlefield power source remains at least several tweaks away from practicality, says Roege. For instance, most wireless routers send out signals in all directions. That’s ideal for a home or office where lots of devices may be scattered about. But for an environment with fewer devices, focusing the Wi-Fi signal through a series of directional antennas makes more sense, according to Roege. “The [Talla] article at hand speaks to common existing Wi-Fi technology. Imagine using a dynamic directional antenna that tracks the soldier’s antenna and concentrates its radiatiave power on that location. You could deliver much more power, use less transmitting power, and be harder to detect,” he says.
Another key will be making the devices much more power-efficient. “Radio transmission currently takes the lion’s share of soldier power — so, try to minimize bits of information being sent — or create a passive communicator that passes information by virtue of selective absorption of the RF energy in the Wi-Fi signal,” Roege suggests.
But Roege believes these are just bumps on the road to an unwired world. “The power/Wi-Fi concept not only will soon be available for soldiers, but will become common to hotspots in the civilian world,” he said.