The Naked Scientists

The Naked Scientists Forum

Author Topic: When will there be the technology for wireless electricity?  (Read 28421 times)

Offline dentstudent

  • Neilep Level Member
  • ******
  • Posts: 3146
  • FOGger to the unsuspecting
    • View Profile
We still have to plug all our things in - will there soon be a way of getting some sort of signal that creates a current in a remote receiver?


 

Offline xerai

  • First timers
  • *
  • Posts: 5
    • View Profile
When will there be the technology for wireless electricity?
« Reply #1 on: 06/06/2007 11:36:16 »
I'm pretty sure it would be possible already. You could aim an emitter in line with a receiver. Except if you ever walked in between, you would get burned or harmed with the microwaves. So, no, I don't think there will be wireless power available to the general public soon.
 

Offline dentstudent

  • Neilep Level Member
  • ******
  • Posts: 3146
  • FOGger to the unsuspecting
    • View Profile
When will there be the technology for wireless electricity?
« Reply #2 on: 06/06/2007 12:25:08 »
Why microwaves? Why not electromagnetic wavelengths for example that are not so dangerous? It would just need to be some sort of resonant frequency, no?
 

another_someone

  • Guest
When will there be the technology for wireless electricity?
« Reply #3 on: 06/06/2007 12:33:48 »
It depends on what you mean by 'wireless'.  You can have wireless induction loops that work at lower frequencies, but because they are low frequencies, it is not practical to make them directional, so one has to be close to them (you cannot use them to transmit energy a great distance).

Microwaves are not terribly dangerous, but if you are in the path of several kilowatts of power, it doesn't matter how that is delivered, if it is delivered through you, then you are likely to be heated up (if not electrocuted) by that energy.
 

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • Posts: 12656
  • Thanked: 3 times
  • A stitch in time would have confused Einstein.
    • View Profile
When will there be the technology for wireless electricity?
« Reply #4 on: 06/06/2007 12:36:21 »
I used to work for a company that made radar for the navy. We used to play by frazzling things at the open end of the waveguide. I was quite surprised how quickly green leaves turned brown & shrivelled.
 

Offline dentstudent

  • Neilep Level Member
  • ******
  • Posts: 3146
  • FOGger to the unsuspecting
    • View Profile
When will there be the technology for wireless electricity?
« Reply #5 on: 06/06/2007 12:50:38 »
I guess my vision is where I'm in my office and all my equipment (ie PC, PDA, phone, coffee machine, fan, light etc) all operate without leads and plugs. So, it's a very local scale. I guess that this type of thing outside would be very energy inefficient and problematical.
 

another_someone

  • Guest
When will there be the technology for wireless electricity?
« Reply #6 on: 06/06/2007 13:09:22 »
I guess my vision is where I'm in my office and all my equipment (ie PC, PDA, phone, coffee machine, fan, light etc) all operate without leads and plugs. So, it's a very local scale. I guess that this type of thing outside would be very energy inefficient and problematical.

The problem is, it does not matter how local, if you are in the middle of an energy field of sufficient strength to run a major electrical appliance, I would like to have it shown that it will not do damage to you before I sit there.

OK, some of the scare stories about the energy from WiFi systems or mobile phones, that are running at about 1W, is silly; but that is not saying that worrying about a signal that is 3KW in strength is silly.
 

Offline dentstudent

  • Neilep Level Member
  • ******
  • Posts: 3146
  • FOGger to the unsuspecting
    • View Profile
When will there be the technology for wireless electricity?
« Reply #7 on: 06/06/2007 13:24:07 »
So, are you saying that it's not the possibility that's the problem, but the amount of energy required to operate these systems, and the human health impact?

(a thought has just come to me - how big would a solar panel have to be to operate a pc? If the side panels of the pc were photo-voltaic (?) cells, you could put it anywhere!)
 

Offline daveshorts

  • Moderator
  • Neilep Level Member
  • *****
  • Posts: 2583
  • Physics, Experiments
    • View Profile
    • http://www.chaosscience.org.uk
When will there be the technology for wireless electricity?
« Reply #8 on: 06/06/2007 18:50:20 »
A solar panel to power a PC at midday on the equator would have to be about half a square metre, at midday in the UK about 1 square metre, and it would need to cover about 40 rooms inside when it was dark, as it consumes far more power than the lighting in your room use let alone emits.

I think there has been talk of using inductive coupling for low powered devices, by winding the coils right you could make the effect very short range - in fact electric toothbrushes are charged using this principle. However it is never going to be very efficient.

I guess you could build a table with lots of little coils in it, which detects where a device that needs power is and just energises those coils, however it would require you virtually to make a copper table (there would be so many coils), plus a whole lot of electronics, so I don't think it is going to be very cheap...
 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8667
  • Thanked: 42 times
    • View Profile
When will there be the technology for wireless electricity?
« Reply #9 on: 06/06/2007 19:05:46 »
Buld a crystal set like my dad did when he was a kid and you will find out that some power is already transmited wirelessly.
 

Offline hawaiilover

  • First timers
  • *
  • Posts: 5
    • View Profile
When will there be the technology for wireless electricity?
« Reply #10 on: 07/06/2007 09:52:56 »
Indeed this tech has existed for a while. If you've ever seen old radio antenna, like they used to have in England, these not only used the radio waves to generate sounds on the radio, but also absorbed enough of the waves to power the radio. This is why the antenna were so large, because the individual waves are very weak energy.
To generate enough electricity flying through the air to act as a short of wi-fi for electric gadgets would require electromagnetic waves with high energy and at frequencies not used for radio, tv, or cell phones.

They would also have to pack enough energy to power many gadgets, which would require either many transmiters in every conceavable location, or a few very powerful ones, which would put out enough juice to electrocute people.

So, based on my own limited knowledge of this issue, I must agree with previous posters that such large scale wireless electric transport is never going to happen.
 

Offline RD

  • Neilep Level Member
  • ******
  • Posts: 8131
  • Thanked: 53 times
    • View Profile
When will there be the technology for wireless electricity?
« Reply #11 on: 07/06/2007 16:56:24 »
Quote
Tesla demonstrated "the transmission of electrical energy without wires" that depends upon electrical conductivity as early as 1891.

http://en.wikipedia.org/wiki/Nikola_Tesla
 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8667
  • Thanked: 42 times
    • View Profile
When will there be the technology for wireless electricity?
« Reply #12 on: 07/06/2007 19:50:23 »
Hertz had done it before, (in 1886 I think); any advance on 1886?
(Trust me, the story goes back further than Hertz's work.)
 

Offline dentstudent

  • Neilep Level Member
  • ******
  • Posts: 3146
  • FOGger to the unsuspecting
    • View Profile
When will there be the technology for wireless electricity?
« Reply #13 on: 08/06/2007 07:18:23 »
This came up today on BBC webnews.....

http://news.bbc.co.uk/2/hi/technology/6725955.stm
 

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • Posts: 12656
  • Thanked: 3 times
  • A stitch in time would have confused Einstein.
    • View Profile
When will there be the technology for wireless electricity?
« Reply #14 on: 08/06/2007 13:10:13 »
I was just about to post that  >:(
 

Offline Pumblechook

  • Hero Member
  • *****
  • Posts: 569
    • View Profile
When will there be the technology for wireless electricity?
« Reply #15 on: 08/12/2007 23:49:19 »
The efficiency tends to be poor.  The aerials or coils or whatever tend to be big in relation to the gap you are trying to cover.   Microwave transmission would be possible over about 10 metres with 3 metre parabolic dishes which is a bit silly..  Much easier to run a wire..   Even if you could get the transmission loss down the conversions from AC to DC and then to  Radio Frequency and then RF - DC (and then maybe DC-AC) will introduce  considerable extra losses.   
 

Offline Pumblechook

  • Hero Member
  • *****
  • Posts: 569
    • View Profile
When will there be the technology for wireless electricity?
« Reply #16 on: 08/12/2007 23:55:47 »
http://news.bbc.co.uk/1/hi/technology/6725955.stm

That demonstrates my point.. The coils are big with respect to the gap they are covering.

I gather the transmission coupling between the coils was 40%..  (60% waste).

AC(mains) - DC - RF ... 50% maybe (if that)  ...then the 40% coupling.... RF - DC ...70%

Overall efficiency ...50 x 40 x 70  = 14%  AC mains to DC output.   Lot of waste. 

 
 

Offline wolfekeeper

  • Neilep Level Member
  • ******
  • Posts: 1092
  • Thanked: 11 times
    • View Profile
When will there be the technology for wireless electricity?
« Reply #17 on: 08/03/2009 23:16:10 »
It's not necessarily the case that efficiency is poor- there's nothing to stop you just having a big coil set in the floor or ceiling when you build the house. The efficiency tends to only be poor when the distances are several times the coil diameter. Then again cables tend to be quite long as well, and much more cumbersome.
 

lyner

  • Guest
When will there be the technology for wireless electricity?
« Reply #18 on: 09/03/2009 07:54:43 »
It's not necessarily the case that efficiency is poor- there's nothing to stop you just having a big coil set in the floor or ceiling when you build the house. The efficiency tends to only be poor when the distances are several times the coil diameter. Then again cables tend to be quite long as well, and much more cumbersome.
The efficiency just has to be poor if you don't have a huge iron / ferrite core around the reeiving appliance. Unless you do this, the field will spread around in many directions and any conductor will have a current induced in it and consume the power. At higher frequencies, the power will be radiated in all directions.
The toothbrush charger is the only example which I can think of with 'non-contact' transfer of power and that is hideously inefficient. Even that system uses very near contact.
 

Offline wolfekeeper

  • Neilep Level Member
  • ******
  • Posts: 1092
  • Thanked: 11 times
    • View Profile
When will there be the technology for wireless electricity?
« Reply #19 on: 09/03/2009 11:24:56 »
For inductive transfer you don't get significant radiative losses, you mainly get resistive losses in the coil.

With resonant systems you can get maybe ~80% efficiency at distances comparable to the size of the coil and there's little if any coupling to humans because they are non magnetic; or to other conductors if they don't resonate at the right frequency.

« Last Edit: 09/03/2009 11:48:01 by wolfekeeper »
 

lyner

  • Guest
When will there be the technology for wireless electricity?
« Reply #20 on: 09/03/2009 13:24:16 »
If you needto have a lot of power transfered (the whole point of the exercise) then you would have to match the transmit and receive circuits. I cannot envisage a system in which the losses are as small as 20%.
Which frequency would be used? How would you limit radiation losses or just poor flux linkage? A transformer has very poor efficiency if you don't have a good magnetic circuit - i.e. a good amount of iron coupling the primary and secondary circuits.
I don't see how you can get away with the problem of needing a high rate of change of flux in your secondary circuit if most of the flux is going elsewhere.
 

Offline Karsten

  • Hero Member
  • *****
  • Posts: 701
    • View Profile
    • Fortunately still only a game
When will there be the technology for wireless electricity?
« Reply #21 on: 09/03/2009 20:10:47 »
If it is not about increased efficiency, why bother?
 

Offline LeeE

  • Neilep Level Member
  • ******
  • Posts: 3382
    • View Profile
    • Spatial
When will there be the technology for wireless electricity?
« Reply #22 on: 09/03/2009 20:37:36 »
There was the SHARP project:

http://www.friendsofcrc.ca/Projects/SHARP/sharp.html

This was all about powering an aircraft by microwaves.

Incidentally, the professor who designed the airframe went on to design and build a flying ornithopter.
 

Offline techmind

  • Hero Member
  • *****
  • Posts: 934
  • Un-obfuscated
    • View Profile
    • techmind.org
When will there be the technology for wireless electricity?
« Reply #23 on: 09/03/2009 21:42:44 »
The system highlighted by a couple of earlier posters (BBC News website) has a three-page story on it in the recent (Feb 2009) edition of Physics World magazine, pg.23-25. It's not obvious that very much progress has been made in the past 2 years.

http://physicsworld.com/cws/article/print/37532

In the magazine article they state they operate at 10MHz, that the energy is carried almost entirely in the magnetic field, and that the maximum magnetic field strength is only a tiny* 10^-4 Tesla, even very near the coils.

* tiny: the word of the article.

The internationally accepted guidelines for human exposure to EM fields, ICNIRP ( http://www.icnirp.de/documents/emfgdl.pdf ) set an upper limit of 0.1µT for general-public exposure to magnetic fields at 10MHz.

The tiny field of this power-coupling demo is 1000x greater than the currently permissable general-public exposure. This may pose a problem for general deployment ::)


Although the article is at pains to point out that that energy losses in wood, brick, plastics is rather low, I imagine any sheet metal would absorb a lot of energy. With the kind of source/receiver geometries illustrated, the efficiency will inevitably (I would have thought) decrease as the receive coil is made smaller. In general the coupling efficiency will decrease as the source-receiver distance becomes a larger multiple of the antenna size.

I'm also slightly confused that the article appears to place great emphasis on the Q of the receiver coil being very high (as much as 1000) to maxmise coupling and efficiency but it strikes me (although perhaps I'm being naive?) that as soon as you load the receiver coil with a light bulb its Q will drop to something very small...  ???


Some of the comments following the on-line version of the IoP article I reference sound very valid, particularly the "detuning" of the coils if one brings any metal or large modestly conducting object anywhere near them. High-Q coils are easily detuned (this is one of several principles upon which a 'metal detector' can be constructed).


I think this vision of wireless power transmission is rather driven by sci-fi fantasy (and a good headline / enticing photograph for the media). Low-power coupling (eg for mobile phone / mp3 chargers) of 1-2watts over distances comparable or smaller than the physical size of the transmit coil are probably technically feasible - though whether commercially viable or desireable is another matter.

Consider though that, after much wrangling, many of the worlds mobile phone manufacturers have just agreed to standardise on a mini-USB connector as a universal charger input.
« Last Edit: 09/03/2009 22:00:10 by techmind »
 

lyner

  • Guest
When will there be the technology for wireless electricity?
« Reply #24 on: 09/03/2009 22:09:53 »
I think I agree with about every one of your comments techmind.
The wavelength  for 10MHz is 30m. That means a metal structure of 15m would resonate in free space. With dielectric, you'd need, say, 10m.That's about house size. So you wouldn't be allowed to have any mains wiring in the building because that would almost certainly resonate at some stage.

As for mobile phone leads. It's a real scandal, at the moment .  Every time you buy a new phone, you need a whole new set of accessories; sound commercial sense (the bastards).
 

The Naked Scientists Forum

When will there be the technology for wireless electricity?
« Reply #24 on: 09/03/2009 22:09:53 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums