Nimbus Lab sends up quadrotors for wireless charging (w/ Video)

May 31, 2012 by Nancy Owano report

( -- Researchers at the University of Nebraska-Lincoln’s Nimbus Lab are exploring wireless power transmission as a way to power devices. They have designed and built a custom power-transfer and receiving system optimized for use on unmanned aerial vehicles (UAVs) to do the job. Brent Griffin and Carrick Detweiler are the creators of these special "quadrotors" which are designed to wirelessly charge electronics making use of “strongly coupled resonances.” The Nimbus team have made a video showing these wireless quadrotor chargers in action. The video caption says the UAV sends nearly 5 watts at 25 cm.

According to a report in IEEE Spectrum, how much gets from quadrotor to the receiver and how efficient is the transmission are linked to how well the quadrotor can keep close to the optimum transmission distance, about 20 centimeters away from the receiver coil. “When everything works perfectly, the quadrotor can wirelessly transfer about 5.5 watts of power with an efficiency of 35 percent, which is easily enough to power a light,” says the report.

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According to the lab team, “We are investigating systems and control algorithms to optimize the power transfer from the UAV to the remote sensor node. In addition, we are investigating energy usage algorithms to optimize the use of the power in networks of that are able to be recharged wirelessly from UAVs.”

They say that applications include powering sensors in remote locations without access to grid or solar energy, such as underwater sensors that surface intermittently to send data and recharge, sensors placed under bridges for structural monitoring, and sensors only activated when the UAV is present.

Moving their research forward, the Nimbus team plans to teach the quadrotor to autonomously keep a stable hover at an optimum distance to transfer power to a receiver. They also hope to be able to boost the amount of power the quadrotor can transfer.

Nimbus stands for Nebraska Intelligent Mobile Unmanned Systems. The lab was partly funded through a grant from the Air Force Office of Scientific Research and UNL support.

“Resonant Wireless Power Transfer to Ground Sensors from a UAV, “by Brent Griffin and Carrick Detweiler, was presented recently at the 2012 IEEE International Conference on Robotics and Automation in St. Paul, Minnesota.

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not rated yet May 31, 2012
What a great tech combo. I can envision beefier versions of these things used to build structures. Having wireless power charging means the UAVs can charge much easier without human intervention.

One quibble: you don't 'teach' the program it.
not rated yet May 31, 2012
Wireless transmission is inherently inefficient.
The larger the distance the larger the transmit and receiving coils.
This is a niche technology and should only be used when direct conection is impossible for some reason.
5.5 watts of power with an efficiency of 35 percent at an optimum transmission distance of 20 centimeters.
5 / 5 (2) May 31, 2012
One quibble: you don't 'teach' the program it.

Actually you do teach them via Machine Learning. This is not your usual programming because you do not program the actual task by hand, but rather feed it examples and let it learn from them.
not rated yet Jun 01, 2012
Wireless power transmission is not inherently inefficient. Old time electronics engineers are probably thinking of something like how transformers work.

This technology is completely different. It is much more analogous to the way radio or wireless RF transmission occurs. Right now only short distances and low amounts of power, but imagine if 20k watts could be transferred at 80% efficiency over a distance of a few feet. This would allow roadways to transmit power to vehicles that wouldn't need internal power (except for entering and leaving the roadway). Tesla invented this technology and planned to transmit megawatts to entire neighborhoods until GE bought the patents and squashed the technology. This is a toy today, like spark gap radio transmitters in the 1910's. In 20 years it will be something altogether more amazing.
not rated yet Jun 04, 2012
Wireless power transmission is simply a transformer without an iron core.
It's not a different technology and is not analogous to wireless RF transmission.
The main difference is that the magnetic field is increased by resonating the inductors(coils) with capacitors. This requires very low resistance in the coils(lots of copper) to achieve high Q(low loss).
Magnetic fields drop in strength rapidly with distance, so to get a reasonable efficiency requires large coil diameters(lots of copper) and a small distance between the coils. Typically the distance between coils should be less than 25% of the coil diameter.

When not supplying power to a receive coil, the transmit coil will consume all of its input power as heat because of the resonant current. An iron based transformer will not.

See, they have graphs showing efficiency versus coil size and spacing.

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