A team from the Massachusetts Institute of Technology lit a 60 watt light bulb from a power source two meters away and with no physical connections between the source and the appliance. The ‘WiTricity’ device – the term coined by the MIT team to describe the wireless power phenomenon – uses magnetic fields to deliver power to the gadgets remotely.”
And what strength of magnetic fields are they using?
battery-free mouse
(DIY mod replacing the batteries by a coil under the pad and in the mouse)
Wacom has been making tablets with battery and wire free mouse and stylus for years…
I read somewhere that Tesla did it a long long time ago. What is the difference now?
Also, did they made any study of the impact of this on live cells close to the source? Just wondering because in this case the power is not as low as is in the devices we use now.
Tesla is alleged to have afaik. I don’t anyone’s ever been able to reproduce his work though.
From http://www.geocities.com/Area51/Shadowlands/9654/tesla/projecttesla…
“Although Tesla was not able to commercially market a system to transmit power around the globe, modern scientific theory and mathematical calculations support his contention that the wireless propagation of electrical power is possible and a feasible alternative to the extensive and costly grid of electrical transmission lines used today for electrical power distribution.”
I would also suggest reading the book “Prodigal Genius” for an insight into his life, repeated failures and extraordinary successes…highly recommended.
Edited 2007-06-11 16:28
While I agree he had a wonderfully creative mind, I feel he did the world a great disservice by not documenting his work so it could be recreated later.
While I agree he had a wonderfully creative mind, I feel he did the world a great disservice by not documenting his work so it could be recreated later.
Well, he did some notes on what he was doing, but they were often written so that only he could understand them. Also, he’s lab was destroyed in a fire (may be some people didn’t like what he was doing…) along with all he’s notes covering the larger part of his life work.
Some say a lot of material exist today, but kept from public exposure. interpret that as you like.
As interesting as it sounds, I have a hard time taking something seriously that calls itself Project Tesla (objectivity anyone?), is hosted at geocities.com/area51, and contains sections called Market Analysis/Projections/Size.
Both these methods work on the principle of magnetic induction. This way of transferring energy is well known. One example of the application of this principle is in cooktops; Google the words magnetic induction cook.
Tesla’s method transferred power wirelessly over long distances. To do Tesla’s method of wireless power transmission, you need the sky and the ground to get the magic happening i.e., you can’t use Tesla’s method of wireless power distribution indoors; you’d need an outdoor receiver then wire that energy inside. This method of power distribution would for anything located located outdoors.
In the “WiTricity” method, people are also using the principle of magnetic induction to transfer energy. The problem with magnetic induction is that it is very wasteful way of transferring energy over distances. From what I understood from the article a team has found a way to minimise the amount of energy wasted; they have devised a way so that sender and receiver applications transfer energy over a “coupled resonated frequency”.
For me, this looks interesting. I’m going to have to brush up on my physics to really understand what is happening; I’m not particularly versed about resonance coupling as I glossed over it during my studies.
I’m thinking I could use one of these about 2 meters away from me on a Monday morning. For now, I’ll settle with liquid beans!
Also, did they made any study of the impact of this on live cells close to the source? Just wondering because in this case the power is not as low as is in the devices we use now.
Like me, I have a Pacemaker that I am sure it would mees up.
Even if this were safe, no-one’s going to trust it. Look at all the people kicking up a fuss about WiFi and mobile phone signals. They’ll never accept large amounts of power flying through the air.
It reminds me of my granny, who thought that if you left an empty power socket switched on, the electricity would leak out.
It reminds me of my granny, who thought that if you left an empty power socket switched on, the electricity would leak out.
It doesn’t?!?!
you are right though, I hear things from people periodically about brain tumors ’caused’ by cellhpones…
I think having communication and data services where ever I am is nice enough to take the 1 in a million chance ill get a brain tumor. If I do, well, I’ll die happy
This is not exactly uncommon. In Denmark there’s a law against “theft” (unauthorized used) of wireless power
– and that law is several decades old.
Edited 2007-06-11 15:47
Two copper coils with 20 inches diameter, and roughly 40% efficiency?
Sorry, but i would like to have my wires back please…
Any museum of science and industry worth it’s salt has at least one large Tesla coil, and will happily demonstrate it’s ability to light a 4′ florescent tube as someone carries it around the room.
I’ve seen this demonstration, numerous times, at COSI and the McKinley Meuseum of Sciene and Industry: Both in Ohio.
It’s pretty freakin’ cool.
The chinese article on this is clearer, by avoiding the completely confusing wine-glass analogy: http://news.xinhuanet.com/english/2007-06/08/content_6215681.htm
The gist of it is that this technique uses inductance, the phenomenon that a coil subject to changing magnetic fields will experience a flow of electric current. What they’ve found is that modulating the magnetic field at the magnetic resonance frequency of the receiver coil gives you particular efficient energy transfer. Meanwhile, since most materials (including biological ones) don’t interact strongly with magnetic fields, nor have the same resonance frequency as the receiver, a lot of power isn’t absorbed by your surroundings.
This technique seems neat. I never thought we’d see efficient wireless power, because the obvious radiative methods have horrible efficiency*.
*) A spherical radiator with a power P has a power density of P / (4 * pi * r^2) at any range R. So to send 10W to a target the size of a piece of paper (~0.06 meters) across a room (say 5 meters), a purely radiative technique with no other losses would require a source of roughly 52,000 watts.
Edited 2007-06-11 16:09
The oral-b electronic toothbrush uses this technology.
The toothbrush is being charged from the base by a such field. In fact the toothbrush is “touching” the base, but there are no wires from the toothbrush to the charger.
BTW, I ve read somewhere that they were planning a such “power base” and some compatible batteries installed on devices like PDA, mobile phones. All you have to do is to lay that devices on that base.
Edited 2007-06-11 18:22
… evanescent wave coupling rather than a transformer-type induction? That would prevent wastage of power when not charging.
Maybe, but evanescent waves ranges are really low… So maybe something like a mouse charger.
Evanescent wave coupling requires that your transmitter and receiver be within one wavelength or thereabouts of the transmitted wave. The effect is that the waves start tunneling from the transmitter to the receiver. Outside this range, the coupling effect drops off exponentially. So if you have a few kilohertz frequency, you easily have a range of several meters.
The problem with wireless power transmission is that broadcasting energy in all directions can be very wasteful because a vast majority of power ends up being squandered into free space.
Soljacic and his colleagues devised WiTricity based on resonance.
How does using resonance frequency of a device resolve the problem of the power radiating in all directions? Indeed, it doesn’t… You would still need to radiate energy, with the inverse squared radius law.
Unless you find something to focus that energy.
The coil’s magnetic field will look like a magnet’s. By making it oscillate, you will still fill the room with the magnetic field.
Original article:
http://www.sciencemag.org/cgi/content/abstract/1143254v1?maxtoshow=…
(need subscription…)
i.e., the receiver uses a tuned circuit to discriminate between the frequencies of interest and all the other background noise? The power levels are not the same, but transmitter and receiver are usually much farther apart
I agree with big_gie; unless you use directional antennas or other means to prevent the omnidirectional radiation, that is what it is going to happen. One of those Tesla articles talks about the earth/ionosphere being a resonant cavity, which does prevent the scattering.
I think that battery manufacturers won’t be happy about this
This transfer method is NOT based on radiation. It is based on inductivity, which is a completely different phenomenon. It is direct interaction between electrons of two coils, by the EM force. While irradiated photon cannot be “returned” (as it is extremely unprobable, i.e. entropy of system is increased with radiation), in this case exactly that happens: if frequencies of oscillators don’t match (clasically, average force over time will be 0 in that case), oscillator will most of time accelerate and slow down those electrons (therefore giving and regaining energy), assuming that those don’t have enough time to relax(=loose) this energy into their system. For that reason energy gets transferred only to oscillators that have same frequency, as with the pendulum that you push back and forth at the right rate.
Indeed, exactly this was proposed by Tesla a century ago, though he imagined it on a much larger scale.
The wikipedia article about this technology sheds some light about why this technology can achieve high efficiency ratios, as well as about suspected dangers:
— quote —
Their theoretical analysis showed that by sending electromagnetic waves around in a highly angular waveguide, evanescent waves are produced which carry no energy. If a proper resonant waveguide is brought near the transmitter, the evanescent waves can allow the energy to tunnel (specifically evanescent wave coupling, the electromagnetic equivalent of tunneling) to the power drawing waveguide, where they can be rectified into DC power. Since the electromagnetic waves would tunnel, they would not propagate through the air to be absorbed or dissipated, and would not disrupt electronic devices or cause physical injury like microwave or radio wave transmission might.
— end of quote —
In other words, the energy does not decrease by 1/r^2 because it is not radiated into directions where no (resonant) receiver is placed, and it won’t fry you if you’re standing in between the source and the receiver (unless your body happens to have just the matching resonant frequency by accident).
Now, of course, you’d have a hard time explaining this to Joe Average who is afraid of a brain tumor from his cellphone