Hizook (Travis Deyle and Robert Powers) have found some fascinating research:
We were scanning through the upcoming ICRA2012 program and noticed an interesting paper titled, "Resonant Wireless Power Transfer to Ground Sensors from a UAV." This certainly piqued our interest -- especially for Travis, who happens to work with wirelessly-powered sensors at his day job. Come to find out... the article is by Dr. Carrick Detweiler, PI of the NIMBUS Lab at the University of Nebraska-Lincoln (our undergrad alma mater!). Furthermore, he just provided a preprint of the paper (PDF) and a video on his website. Score! Their quadrotor delivers power via magnetic resonance (ie. WiTricity-style) to a load on the ground. This same type of technology is being actively researched for lots of applications, including: consumer electronics, transportation (eg. electric vehicle recharging), and remote sensing (this application). Adding it to a UAV adds a bit of flexibility to the system. Anyway, be sure to check out the video below... and we'll also give a brief overview of a few different wireless power + robotics projects over the ages.
The paper is titled, "Resonant Wireless Power Transfer to Ground Sensors from a UAV" (PDF) by Brent Griffin and Dr. Carrick Detweiler.
Magnetic resonance can be a good method for wireless power transfer at medium distances (ie. a meter or so). Owing to the resonant fields, it is more efficient that inductive coupling, which would require the UAV to be in close proximity to the load (a few centimeters) to get good mutual coupling. Furthermore, the magnetic fields are less susceptible to occlusions or material composition compared to microwave (electromagnetic) or laser-based wireless power transfer.
However, being at least partially familiar with the underlying technology, we know that alignment and (dynamic) frequency tuning are absolutely critical for efficient power transfer using magnetic resonance. Presumably, the quadrotor itself could supply the necessary flexibility in the system to help align the coils -- heck, we've all seen quadrotors perform impressive feats of acrobatics. So kudos to Carrick and Brent for their insights!
Lots more history on this kind of power transfer at the rest of the post here.