Wireless Power Over Distance: Just a Parlor Trick?

Lucas123 writes "Companies like U.S.-based WiTricity and China-based 3DVOX Technology claim patents and products to wirelessly powering anything from many feet away — from smart phones and televisions to electric cars by using charging pads embedded in concrete. But more than one industry standards group promoting magnetic induction and short-distance resonance wireless charging say such technology is useless; Charging anything at distances greater than the diameter of a magnetic coil is an inefficient use of power. For example, Menno Treffers, chairman of the Wireless Power Consortium, says you can broadcast wireless power over six feet, but the charge received will be less than 10% of the source. WiTricity and 3DVOX, however, are fighting those claims with demonstrations showing their products are capable of resonating the majority of source power."

Re:Tesla

[Pentium100]

You also have to consider the efficiency. Running a 1GW power plant just to light a 100W light bulb a few kilometers away does not seem a good idea.

Yes, it is possible to transfer power without wires - radio has been doing it for a long time (a simple crystal radio set does not need any power other than what it gets from the antenna, but you'd better have some sensitive headphones, a big antenna and a station that is relatively close). The problem is transferring a lot of power efficiently and without huge antennas.

Re:No it isn't

[StripedCow]

Power drops with the square of distance.

Not if you have a directed beam of energy.

The beam could be directed based on some set-up protocol between the energy-source and the energy-consumer.
And you can easily direct beams by using some antenna array.

Such direction-sensitivity could also be used to (partly) solve the billing problem.

http://en.wikipedia.org/wiki/Antenna_array_(electromagnetic) [wikipedia.org]

Re:No it isn't

[Anonymous Coward]

Even directed beams drop off with distance squared once you get outside the near field. A directed beam is a lot more efficient than an omnidirectional beam, but for any given directional beam, power will drop off with distance squared, and narrowing the beam will require larger antennas setups.

Re:What about the dangers? Does it cause cancer?

[metaconcept]

From the very PDF you link to, Question 1, right at the beginning:

• the more recent epidemiological studies show little evidence that either power lines or "electrical occupations" are associated with an increase in cancer (see Q19);
• laboratory studies have shown little evidence of a link between power-frequency fields and cancer (see Q16);
• an extensive series of studies have shown that life-time exposure of animals to power-frequency magnetic fields does not cause cancer (see Q16B);
• a connection between power line fields and cancer is physically implausible (see Q18).

... Overall, most scientists consider that the evidence that power line fields cause or contribute to cancer is weak to nonexistent.

(Emphasis mine.)

Re:No it isn't

[Anonymous Coward]

ever heard of lasers?

Or optical masers, as they used to be called!

how about a radio wavelength laser?

So, regular masers, then?

Okay, cool.

Now go read about diffraction [wikipedia.org], and see if you can realize that lasers, masers, etc. aren't magic, and that every finite beam loses power like 1/r^2 in the far field.

Re:Tesla

[girlintraining]

There's only one problem with people like you: You're always wrong [teslatech.info]. Tesla did do exactly what I said he did. Sorry it took me so long to check in and see some moron had gotten +5'd for handwaving while I got -1'd for telling the truth guys. Hopefully the mods will read the link and attached pictures and realize that yes, Tesla did have wireless power in the 1890s. Oh, and I was severely understating the distance: "Furthermore, the power loss experienced by Teslaâ(TM)s pulsed, electrostatic discharge mode of propagation was less than 5% over 25,000 miles. Dr. Van Voorhies states, âoe...path losses are 0.25 dB/Mm at 10 Hz,â which often is difficult for engineers to believe, who are used to transverse waves, a resistive medium, and line-of-sight propagation modes that can dissipate 10 dB/km at 5 MHz."

I'm waiting for my apology.

Re:Tesla

[Areyoukiddingme]

The problem with Tesla's system is the frequency on which it operates. 10 Hz has a wavelength of 34.73 meters. Properly receiving power at that frequency requires an antenna sized to match. Needless to say, it's not going into a handheld device. Tesla intended his system to be used in relatively large scale fixed installations. You could power your house with it, but the individual pieces of equipment in the house would be wired to the receiver. So yes, in theory his system could eliminate the grid as we know it and that does indeed address "power over long distances" as the headline does (really long distances). However, it's solving a different problem, that of very long distances using very large equipment, rather than the handheld gear over tens of feet as the articles are arguing over.