Long range wireless charging feasible?

[elliottveares]

Just seen the below linked video from a tech person in the US. Talking about how the next iPhone could have wireless charging built in. (Not close coupled inductive charging but medium/long range wireless charging).



Is this even possible or is it complete BS as I suspect? I don't know that much about electronics and RF related stuff, but seems rather impassible without having a massive energy loss involved in the process.

Transmitting data/signals over long range is one thing, but doing the same with enough power to charge a smart phone!?

Sure RF energy is all around us from AM/FM radio to Wi-Fi, but proportionally the power transmitted involved is minuscule in regards to Wi-Fi and is equally minuscule for the amount of  power that can be absorbed by your typical TV Arial under a normal conditions.

Should it be possible (Say to charge your average smart phone from 2-4 meters away), how much input power would be required at the transmitters end?

Reagrds: Elliott.

[orolo]

If you place an isotropic radiator 2 meters away, with a power emission P, the power per square meter you get at a two meter distance is P/50 (inverse square law). If a phone has a cross section of 100cm^2 = 0.01 m^2, the power it will harvest from the radiator will be at best P/5000. So, to get 1Watt in your phone, the radiator must be rated for 5000W. Not practical. The only way to get some efficiency would be for the radiator to use a very directional beam, at extremely high frequencies (diffraction), which would not be very practical or safe, either.

[Ian.M]

Not possible.  FCC limits for long term human exposure microwave band power density are 1mW/cm² (5mW/cm² short term peak under controlled circumstances).  Assume a max pocket size of 10cm x 18cm, and a 90% efficiency rectenna, that's only 162mW under ideal conditions (phone directly facing power transmitter with clear line of sight).  That's 1.6% of the output of a normal 2A USB charger, or about 4 days to charge an iPhone 6!

[IanB]

Very likely "wireless charging" means putting the phone on a special charging pad. This would naturally be very convenient since most people will put their phone on the nightstand next to the bed when they go to sleep at night.

[The Magic Rabbit]

I don't think you can say "not possible" when it's already being done...

https://youtu.be/GNgUdWW0y-s

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[JimRemington]

I don't think you can say "not possible" when it's already being done

The video does demonstrate short range charging/powering, like my decade old electric toothbrush.
The rest is just talk.

[amyk]

Feasible, yes.

Safe, probably not.



http://www.industrytap.com/florescent-bulbs-unplugged-and-shinning-tapping-electromagnetic-fields/1763
https://en.wikipedia.org/wiki/File:TeslaWirelessIllustration.png

[Ian.M]

Yes. I should have qualified that "Not Possible." as 'Physically possible but could not legally be sold in North America or other parts of the 1st world, so not commercially possible'

You should note that in most developed countries it's not legal to build under or adjacent to overhead high voltage power lines.  e.g. from the W.A. Powerlines, Electromagnetic Fields and Health, Environmental Health Guide:

Each power line runs along a corridor of land called an easement. The width of the easement is determined by a number of factors, including the electrical load on the line. The widest easements, naturally, are given to the lines with the highest loads e.g. an easement width of 60 metres is typical for 330kV lines.
Public access to an easement is permitted, but building and long-term occupation are not. At the edge of an easement, the EMFs are appreciably lower than they are in the centre. The WHO limits are not exceeded anywhere within easements; the EMFs outside easements are consequently well below these limits.

[BrianHG]

Give me the patent number, I'll read it and tell you if it's possible, feasible & will pass FCC.

[IanB]

You should note that in most developed countries it's not legal to build under or adjacent to overhead high voltage power lines.

However, this is not apparently the case in the UK: https://goo.gl/maps/bcSgwySzUfQ2

Land is too expensive to have a "dead zone" underneath power lines. I have seen it here in the USA but in the UK power line towers just put their footings wherever needed and hop over whatever lies beneath.

[Edit: fixed broken link]

[Ian.M]

That's a good case for requiring either a well grounded metal roof or a well grounded wire mesh lining the rafters.    You don't see a lot of overhead lines in UK urban and suburban residential areas as the high population density and high land values + perceived blight of overhead lines makes it economic to use buried HV lines.   

[BrianHG]

That's a good case for requiring either a well grounded metal roof or a well grounded wire mesh lining the rafters.    You don't see a lot of overhead lines in UK urban and suburban residential areas as the high population density and high land values + perceived blight of overhead lines makes it economic to use buried HV lines.

Forget grounding your roof, I would use it as an antenna, put it though a step-down transformer and siphon power, use it + feed the surplus backwards through my houses power meter & have the power company pay me.  If the power company wants to radiate my house, I'll use that radiation to my benefit & profit.

[IanB]

Forget grounding your roof, I would use it as an antenna, put it though a step-down transformer and siphon power, use it + feed the surplus backwards through my houses power meter & have the power company pay me.  If the power company wants to radiate my house, I'll use that radiation to my benefit & profit.

In the picture I linked the power lines were there long before the houses were built. I am frankly surprised they found buyers for the houses. I wouldn't want to buy a house situated like that.

[james_s]

I'm not aware of any conclusive evidence showing harm to humans caused by EMR from 50/60Hz power lines. There has been some paranoia out there, but ask around and for anything you can think of you'll find someone who thinks it causes all manner of health problems.

As far as wireless charging goes, sure it's possible to transmit significant amounts of energy over the air, I can light up lamps across the room with my tabletop tesla coils, but it knocks out radio reception all over the house and probably a much larger area than that. It's also extremely inefficient.

[The Magic Rabbit]

I don't think you can say "not possible" when it's already being done

The video does demonstrate short range charging/powering, like my decade old electric toothbrush.
The rest is just talk.

I doubt Apple would be in testing with them etc. if it was just talk.

The power transfer on the short range transmitter is nothing like your toothbrush. The toothbrush chargers are essentially just magnetic induction.

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[ConKbot]

In the far field?  Lol no, definitely not. Any wireless charging system for public consumption is going to be some sort of near field coupling, with some sort of antenna magic and fiddling to keep them physically small for their frequency.

[raspberrypi]

I don't think you can say "not possible" when it's already being done

The video does demonstrate short range charging/powering, like my decade old electric toothbrush.
The rest is just talk.

I doubt Apple would be in testing with them etc. if it was just talk.

The power transfer on the short range transmitter is nothing like your toothbrush. The toothbrush chargers are essentially just magnetic induction.

Sent from my Moto G (4) using Tapatalk

I think if people understood the inverse square law alot of these videos wouldn't be made. Its like how people think teslas wireless electricity is still viable. We rely on radio freq. spectrum distribution so much that these generators would reak havoc on communications, wifi, etc... Plus it seems like people would get RF burns when they touched metal. 

[The Magic Rabbit]

Well I don't have the in depth understanding to give you the solution, but from the little I do know, it's about creating a highly focused beam, hence the need for so many aerials inside the unit.

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[james_s]

I think if people understood the inverse square law alot of these videos wouldn't be made. Its like how people think teslas wireless electricity is still viable. We rely on radio freq. spectrum distribution so much that these generators would reak havoc on communications, wifi, etc... Plus it seems like people would get RF burns when they touched metal.

I'm sure they would, I got a painful RF burn on my finger when it brushed the grounded screw that holds the cover plate on a light switch while I had my small SSTC running on the table. Tesla had some brilliant ideas, but he was also off his rocker, especially as he got older. He was under-appreciated for a long time but lately the myths surrounding him have grown to ridiculous levels.

[DBecker]

There is strong evidence that Tesla didn't quite 'get' EM waves.  He apparently was very good at visualizing magnetic fields, and devising novel devices.  But he didn't understand far-field behavior, and didn't have the mathematic skill to compensate.  There is a big difference between rotating magnetic flux and wave behavior.  Having an intuitive grasp of one doesn't automatically mean you understand the other.

[Marco]

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?

[JiggyNinja]

I think if people understood the inverse square law alot of these videos wouldn't be made. Its like how people think teslas wireless electricity is still viable. We rely on radio freq. spectrum distribution so much that these generators would reak havoc on communications, wifi, etc... Plus it seems like people would get RF burns when they touched metal.

Not even RF burns, there would be a very real possibility of real burns too.

The biggest downside to wireless power transmission is the same as for wireless information broadcasting: you can't control who can receive it. And before someone mentions "encryption", encryption does nothing to prevent the signal from being received, it only makes the received signal useless to the eavesdropper (if done right). You can't "encrypt" power in the same way you can encrypt information anyway.

So the biggest flaw for wireless power transmission isn't transmission efficiency, but that you can't control what receives the power. And it's not a problem because of Big Business conspiracy theories about "not being able to bill for usage", because that's a solvable problem. Most countries already use taxation to subsidize building and maintaining infrastructure (such as roads, water, electric grid, and telecomms), and this would not be majorly different.

No, the real problem is that now every piece of metal within range of the power transmitter becomes an induction heater. Your car. Building frames. Pots and pans. Metal cases. Jewelry. EVERYTHING. Not only is it doubly wasteful (extra greenhouse gases + directly heating the environment), it is dangerous. With that much power there would definitely be some pieces of metal with the right shape and orientation to get hot enough to burn things.

Large scale wireless power transmission is a stupid idea, and no amount of "OMG oppressed genius TESLA!!!11!" can change that.

[rch]

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!

[rfeecs]

There was a lot of talk about this from MIT about 10 yrs ago.  Marin Soljacic using wireless resonant power transfer.  It looks like they went off and started a company called WiTricity: http://witricity.com/

They demonstrated powering a 60 watt bulb over a distance of a few meters.

Here's a TED talk about it:

[rfeecs]

Give me the patent number, I'll read it and tell you if it's possible, feasible & will pass FCC.

Here you go:
https://www.google.com/patents/US9086864

Edit.  Seems like Google's images are messed up.
From the US Patent office:
US9008864