Long range wireless charging feasible?

[JimRemington]

but from the little I do know, it's about creating a highly focused beam

Obviously, you are convinced by the empty talk and the near field demo. The rest of us certainly aren't.

[orolo]

I think if people understood the inverse square law alot of these videos wouldn't be made.

What's the law for inductive coupling ignoring environmental/ohmic losses? Does the power which needs to slosh around in the primary tank increase by the square of distance too to transmit the same energy per cycle?

Quick googling suggests an inverse cube law.  My basic theory isn't good enough to know if this is power or current though!

To first order, the magnetic field is dipolar, \$H \sim r^{-3} \$. So the magnetic flux also decays with the cube of the distance and, from Faraday's law, the induced voltage decays with the cube of the distance. That implies that power decays as \$ r^{-6}\$, which is also obvious from the energy density being \$\sim \vert H\vert^2\$.

Anyway, magnetic coupling is good enough, and in fact better, for very short distances, where the inverse power law doesn't matter. At greater distances,both square and cube laws aren't good enough. A very narrow beam is useless: if I have to be in a very precise position to charge my phone, I better use a cable or close magnetic coupling. As soon as you abandon the very narrow beam idea, inefficiency gets overwhelming.

[Marco]

They say they can do resonant transfer upto around 5 times the diameter of the coils.

Might be able to make charging pads for under seat cushions which charge mobiles in your trouser pocket.

[Ian.M]

They say they can do resonant transfer upto around 5 times the diameter of the coils.

Might be able to make charging pads for under seat cushions which charge mobiles in your trouser pocket.

Well at least that should improve the IQ of the general population, as male frequent users who haven't yet reproduced will be eligible for Darwin Awards!
See https://en.wikipedia.org/wiki/Diathermy

[rfeecs]

Some market research based on supply chain, patent filings, claiming Apple is not going to incorporate long range wireless charging:
https://www.scribd.com/document/337322317/Energous-Corporation-WATT-Game-Over

Apple could not have been clearer in its critique of
WATT’s base technology (RF) when highlighting:

i) The technology is inherently inefficient delivering energy because massive power is lost in transmission.

ii) The complication of forcing a charging source to track charged devices and steer radiation to them, (which Apple notes still fails if an object blocks the line-of-sight between the transmitter and the device  being charged),

iii) The radiation poses hazards to people who find themselves in the path of such directed radiation beams

Energous is hyping the Apple connection to raise more money:

Does this mean Apple will ever use WATT’s technology?

No. Based on the overwhelmingly conclusive mosaic, Apple will deploy in-house inductive charging on the next iPhone.

Story over.

We believe WATT’s management recognizes its window to raise capital will close once inductive charging is confirmed for the next iPhone.

[Marco]

Well at least that should improve the IQ of the general population, as male frequent users who haven't yet reproduced will be eligible for Darwin Awards!
See https://en.wikipedia.org/wiki/Diathermy

Don't think double digit kHz magnetic field fluctuations can couple much energy into people.

[Ian.M]

Double Digit KHz wont get much energy transfer to small receiver coils at a range of 5 diameters.  Increasing the frequency increases the number of flux reversals per unit time and thus the energy that can be received, but strong fields at even a few hundred KHz can cause detectable deep tissue heating.

Then you've got the direct heating from losses in the under-seat transmitter coils . . .

[JiggyNinja]

You know what else is a coil? Rings. How many people are going to be happy getting fingers toasted by their wedding bands?

[JimRemington]

My wife's father was in the Navy in the 1940s.
 
He said that the sailors often used to stand in front of the radar dishes on cold days, in order to warm up.

[rfeecs]

There's the famous urban legend:
http://www.snopes.com/horrors/techno/microwave.asp

(25 December 1998, Canada) Telephone relay company night watchman Edward Baker, 31, was killed early Christmas morning by excessive microwave radiation exposure. He was apparently attempting to keep warm next to a telecommunications feedhorn.

Baker had been suspended on a safety violation once last year, according to Northern Manatoba Signal Relay spokesperson Tanya Cooke. She noted that Baker's earlier infraction was for defeating a safety shutoff switch and entering a restricted maintenance catwalk in order to stand in front of the microwave dish. He had told coworkers that it was the only way he could stay warm during his twelve-hour shift at the station, where winter temperatures often dip to forty below zero.

Microwaves can heat water molecules within human tissue in the same way that they heat food in microwave ovens. For his Christmas shift, Baker reportedly brought a twelve pack of beer and a plastic lawn chair, which he positioned directly in line with the strongest microwave beam. Baker had not been told about a tenfold boost in microwave power planned that night to handle the anticipated increase in holiday long-distance calling traffic.

Baker's body was discovered by the daytime watchman, John Burns, who was greeted by an odor he mistook for a Christmas roast he thought Baker must have prepared as a surprise. Burns also reported to NMSR company officials that Baker's unfinished beers had exploded.

[raspberrypi]

There's the famous urban legend:
http://www.snopes.com/horrors/techno/microwave.asp

(25 December 1998, Canada)  Baker had not been told about a tenfold boost in microwave power planned that night to handle the anticipated increase in holiday long-distance calling traffic.

ported to company officials that Baker's unfinished beers had exploded.

Increasing the power would not be wise to increase traffic. Reduced power and more site increases traffic. Plus the beer would be isolated from the microwaves.

This sounds more and more like a solar roadways company. Get as much money as you can before people realize the idea doesn't actually work. What gets me is how people who have nothing to gain still will advocate that these BS technologies actually work. That or they do actually work but solve a problem thats a non issue; the spinning solar panels that reduce heat even though energy loss through heat is very small loss and easily dealt with by installing a small air gap, like on daves roof. If he really wants to get more power he should spin his whole house on those magnetic copper coils that made the tony hawk skate board, which is totally unrideable, and uses a huge amount of power. These companies take the money then say "Tried. Can't. Sorry, not sorry".