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Quadrotor UAVs used to wirelessly deliver power


June 4, 2012

NIMBUS Lab's quadrotor uses strongly-coupled magnetic resonance to charge devices remotely

NIMBUS Lab's quadrotor uses strongly-coupled magnetic resonance to charge devices remotely

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Not only are quadrotors fun, they're useful for applications like surveillance and are even showing promise in building construction. Here's a practical use we hadn't thought of though - remote wireless charging. The folks from NIMBUS lab at the University of Nebraska-Lincoln are developing a quadrotor equipped with a system that uses strongly-coupled magnetic resonances to transmit power from its batteries to the receiving device without ever needing to make physical contact. The roboticists see this as a solution for powering devices that are otherwise inaccessible to conventional electrical sources.

The quest for wireless charging

The quadrotor as flying charge point is the latest in the over a century-old dream of doing away with wires and batteries for powering electrical devices. That denizen of school physics lab, the Tesla coil is an early example of this as it lights fluorescent tubes across the room by what seems like magic, but is actually basic physics. Its inventor, Nikola Tesla spent decades in the late 19th and early 20th Centuries searching for practical ways to send electric power through the air, but without much success. In the 1920s and ‘30s, one of Tesla’s greatest admirers, the American publisher Hugo Gernsback, filled his science fiction and popular science magazines with all manner of visions of a future time in when power lines have given way to huge antennae beaming power to everything from typewriters to ocean liners.

Not surprisingly, none of this came to pass because the original idea was to basically broadcast power as high-voltage radio waves. This was not only incredibly inefficient, involving blasting out millions of watts all over the place with the power available dropping off alarmingly within a very short distance, but it was also extremely dangerous. Just about anything made of metal would act as a receiving antenna, so it was probably a good thing that it never got past the speculation stage or many people would have suffered the unpleasant fate of being electrocuted by their bridgework.

The alternative plan was to forego broadcast power in favor of beaming it in the form of microwaves or lasers. This was certainly a more efficient alternative, though still hazardous, since a laser or microwave powerful enough to run a device is also liable to be dangerous to anything that got in the way.

Perhaps the only practical form of broadcast power at the moment is induction - a mode of power transmission that's most commonly used in cordless electric toothbrushes and is being developed for electric cars. Induction works on the same principle as an electrical transformer - two electrical coils are placed in proximity to one another, an alternating current is passed through one coil and the continually collapsing electromagnetic field caused by the alternation sets up a current in the second coil. Used in power transmission, one coil is the transmitter and the other is installed in the device being charged. It’s a system that works, but only over very short ranges.

NIMBUS Lab quadrotor

The NIMBUS quadrotor works on a very different principle called “strongly-coupled magnetic resonances.” That sounds intimidating, but coupled resonances are actually a universal phenomenon found in not only electromagnetism, but also mechanics, civil engineering, acoustics and many others. It’s based on the idea that many things have what is called a natural resonance frequency. That’s to say, when they are made vibrate at a particular rate, they store the energy by making the amplitude of the vibrations stronger and stronger. If energy keeps being fed into an object at that resonance frequency long enough, the object will vibrate so violently that it destroys itself.

This is seen in the party trick of having a trained opera singer hitting the exactly right note that makes a wine glass vibrate at its resonance frequency. The glass vibrates, the sound energy is stored in the form of greater and greater vibrations until the glass shatters. But it’s more than a party trick. In 1940, the power of resonance frequencies was demonstrated to terrifying effect when the Tacoma Narrows Bridge in Washington State was buffeted by winds at exactly the right (wrong) frequency and the bridge literally shook itself to pieces.

The important thing about resonance, however, isn’t that it can shatter a wine glass. What is important is that other wine glasses with a different resonance frequency don't shatter. In other words, only that particular glass is affected.

Strongly-coupled magnetic resonance

The same holds true of magnetic resonators. This is what the NIMBUS quadrotor uses, but instead of singers and wine glasses, it uses a pair of magnetic fields that are “coupled” or designed so that one resonates in response to the other. How it works is that the quadrotor has a copper wire wrapped around it. This is configured to act as the power transmitter. The target has a similar wire ring, which is configured to receive. Both of these, when switched on, generate magnetic fields. When these two fields come into contact with one another, they couple and resonate strongly (hence the name “strongly-coupled magnetic resonances”) and power is transmitted from the quadrotor to the target.

Now here’s the clever bit. Until these two fields come together, no power is transmitted. When the quadrotor and the target are apart, their fields become simple, inert magnetic fields like that around a compass needle. This is very different from, for example, a Tesla coil, which is always pumping out energy when it’s on and which will charge anything within range that can act like an antenna. With a strongly-coupled magnetic resonance, the fields will only transmit or receive power when they’re in contact. What’s more, only the target will receive any power. Anything else in the vicinity remains largely unaffected.

Because the resonance fields interact very poorly with anything they don’t resonate with, other devices, people, animals, walls or other obstacles are more or less transparent as far as the field is concerned. What all this adds up to is that a strongly-coupled magnetic resonance field is more efficient for transmitting power, operates over a longer range and can’t electrocute someone, for example, who’s carrying a steel pole in the vicinity.

Experiments with strongly-coupled magnetic resonance have already been carried out at places like MIT, but these have been with stationary equipment while NIMBUS is working with a mobile system. The idea is to bring the power source to the device instead of the device to the power source. So far, there's been a measure of success, with 5.5 watts of power transmitted over 20 cm (8 inches) with 35 percent efficiency.

The purpose of the quadrotor is to recharge devices such as remote sensors, buried equipment or devices that are inaccessible, like those installed on bridges or atop radio masts or ones that can’t use solar panels for aesthetic reasons. A variation on the quadrotor could periodically visit the device and feed power to it without ever needing to come into contact.

The current design is still very much in the experimental stage and NIMBUS plans to make improvements to handle greater power as well as making the quadrotor operate autonomously so it can seek out and hover near its target without flitting about as the current version does.

There’s still a ways to go, but it may be that someday you may see someone being followed down the road by a quadrotor and you’ll have to decide whether he’s being spied on or the ‘rotor is just charging his tablet for him.

The video below shows NIMBUS Lab's quadrotor remotely charging an experimental target.

Sources: NIMBUS Lab, IEEE Spectrum

About the Author
David Szondy David Szondy is a freelance writer based in Monroe, Washington. An award-winning playwright, he has contributed to Charged and iQ magazine and is the author of the website Tales of Future Past.   All articles by David Szondy

"so it was probably a good thing that it never got past the speculation stage or many people would have suffered the unpleasant fate of being electrocuted by their bridgework..."

That was the preliminary stage. That's like saying, "it's good that no one got past the beta stage of jet plane flight or biotechnology because many people might get hurt. Your ulterior motive is clearly to deride Tesla's Work."

Randolph Fabian Directo
5th June, 2012 @ 09:41 am PDT

Please get your science about Tesla right. Tesla's device used the exact same principle you are talking about here, but for much greater distances. He used the natural resonance of the earth and atmosphere as the frequency to transmit power. Once the losses of setting up the resonance were overcome, the rest was free to be transmitted to a receiver coil tuned to the same frequency. The reason that it did not fly was because it was free. His backers pulled his funding because they could not meter and charge for the power.

5th June, 2012 @ 12:22 pm PDT

Efficiency of only @35%, and there will be a power loss at every conversion. While the copter is charging, flying, correcting for any wind, (unless you intend to fly up a static wire) transference to the target power receiving unit, all to be clever and avoid Solar panels? Use a different form of power. There is still wind, thermal, hydro, and kinetic. Not to mention Grid power. Use the water draining off the surface of a bridge to power it's sensors. Use the flutter of a flagpole to power it's spotlight, use the heat of the sun on upper surfaces in addition to solar printed films on railings and signage, those could produce power on a smaller scale all day, without even being visible.

5th June, 2012 @ 01:30 pm PDT

@ see3d,

Thanks for setting the record strait!

Damn J.P. Morgan.

Billy Brooks
5th June, 2012 @ 10:14 pm PDT

Nikola Tesla was the first American Scientist who gave the concept of wireless or free energy. There are many others and the list is long. I am satisfied now that some how or the other , the thing is started. Great people.....

6th June, 2012 @ 02:11 am PDT

Both transmitter and receiver highly tuned to a single frequency with high 'Q'. Hats Off Again, Dr. Tesla.

Jim Hinds
6th June, 2012 @ 04:04 am PDT

This technology will be a success even if it is only practical

for its most obvious application: Using an UAV to recharge

remote sensors, such as the ones the US Army has placed

here and there in Afghanistan.

M. Report
6th June, 2012 @ 09:51 am PDT

What might be mostly overlooked regarding what Tesla accomplished was that he had many receivers tuned to one transmitter. I think it may have occurred to JP Morgan that ~anyone might be able to build a power receiver and tap the power for free.

To use this article as an example, ie " This is seen in the party trick of having a trained opera singer hitting the exactly right note that makes a wine glass vibrate at its resonance frequency. The glass vibrates, the sound energy is stored in the form of greater and greater vibrations until the glass shatters ", what is the limit of the number of perfectly matched wine glasses that would resonate with the opera singer? Does the opera singer have to exert more energy to shatter more wine glasses?

What would happen if you had 10 (or 100) perfectly matched tuning forks in close proximity, and struck only one? How many might vibrate in sympathy?

For interesting reading, google Alfred M. Hubbard Coil Generator

David Mott
9th June, 2012 @ 02:31 pm PDT
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