Wireless Charging, at a Distance, Moves Forward for uBeam
bits.blogs.nytimes.com
bits.blogs.nytimes.com
Also imagine embedded medical devices.
edit: The article is not referring to resonant induction or standard induction, but using ultrasound instead.
However, I'm skeptical that they can actually create a kilowatt of sound energy, and while you can focus the power (certainly you could do something more efficient than fully-spherical propagation), you're also going to have significant losses.
All this for a charging rate that's about 1/5 of what you get from a 1 amp USB charger.
[1] https://en.wikipedia.org/wiki/Acoustic_power#Table_of_select...
1: http://www.npr.org/2011/08/23/139854129/young-entrepreneur-h...
That said, the tech just to locate the phones in space to allow the beamforming would be a significant accomplishment itself. But forming the beam or multiple beams to charge multiple devices is probably quite feasible.
If you can also make a reasonable initial guess of it's location (to within a few degrees) you could narrow down the guess and check search area considerably.
1-http://www.midwiferytoday.com/articles/ultrasoundrodgers.asp
A system like this is going to have at least the energy density of sunlight and that transfers enough heat into your body you can feel it.
I'd be particularly concerned if the thing somehow shot a beam right at your eyes, which are the thing most vulnerable to damage from internally generated heat (i.e. microwaves)
High energy focused ultrasound like you'd probably need to charge, less so. It's used to destroy tissue. https://en.wikipedia.org/wiki/High-intensity_focused_ultraso...
Across the house? Yea, that'd be a huge problem, I think.
This is not even thinking about the efficiency of converting electricity into sound and back again.
You could focus the sound beam to improve things but then you lose the convenience of putting the device anywhere.
Could homes be built with a giant coil in the whole attic that could then power things in the house?
The limiting factor for distance of induction charging is the strength of the magnetic field per unit area or flux. Technically you could create a magnetic field large enough to pass through an entire house, I can think of two big problems with that off the bat however. First, the Magnetic field strength drops as the cube of the distance from the source. The further you are, the less effective the charging at the same power rate. As well the magnetic permeability of air is so small (µ_0 = 4π×10−7 V·s/(A·m)), this is the reason why iron cores are used in transformers as you would lose a lot of flux to the surrounding area unless it is channeled through a permeable material. The second reason is that there would be unintended effects on other conductive materials located within the magnetic field, eg computers, copper piping. The energy losses by induction charging are usually very very high when compared to charging by traditional means (Cable).