Scientists produce wireless electricity

Scientists produce wireless electricity
By Sadie Gray
Published: 08 June 2007
Independent UK

Plugs and cables could become obsolete after scientists devised a way of recharging electrical devices ranging from laptop computers to lights from a distance.

A team from the Massacussetts Institute of Technology made a 60-watt lightbulb glow using electricity sent wirelessly between copper coils set seven feet apart.

Scientists have known for years that electricity can be transferred without wires, but had struggled to find a practical and efficient way of making it work.

Professor Marin Soljacic used the concept of resonance. Energy can be efficiently transferred between objects that resonate at the same frequency, so he used two copper coils, one transmitting and the other receiving power.

The breakthrough, which has been dubbed WiTricity, was announced by the researchers in the online version of the journal Science. They believe they are between three and five years away from developing a system which could recharge laptops, mobile phones and other devices wirelessly. It could also mean some gadgets would no longer need batteries, eliminating the potential for pollution caused by discarded cells.

Professor Soljacic said: "We have promising ideas as to how to achieve this, so now is a good time to start seriously thinking about commercialisation."

However, up to 45 per cent of the transmitted power was lost before it reached the lightbulb, and Professor Soljacic said the system needed to be twice as efficient before it would be as effective as chemical batteries. Also the copper transmitting coils were two feet high, although there was potential for miniaturising them.

He said the project was inspired by his annoyance at being woken up by his mobile phone beeping when he had forgotten to recharge it.

light can only travel in a straight line, wut if u are in between the 2 coils u would be electrecuted??

MonkeyMan09 wrote:

light can only travel in a straight line, wut if u are in between the 2 coils u would be electrecuted??

When you wear a hat with a visor on it, it blocks the direct line of sight between you and the sun -- yet the world does not become pitch black to you. Although light does mostly travel in straight lines, it is still reflected off of any surface in all directions -- it still gets around.

Furthermore, it does not always have to bounce around obstacles -- it can go through some of them if they aren't too thick.

If you are still not convinced, consider wireless internet -- you can still get a signal when there is crap in the way. However, the more crap there is, the harder it is for the signal to get there.

I haven't heard of this before...I can't wait for the new technology wave!

but that reflection does not curve the light when it bounces of it meerly shoots off into another straight line..

MonkeyMan09 wrote:

but that reflection does not curve the light when it bounces of it meerly shoots off into another straight line..

I am aware of the law of reflection. There is also refraction, and diffusion, diffraction...interference. And yes light can travel in curved lines...but we can use the straight line approximation to understand it well enough. I don't think you are aware of the amount of reflection that goes on. Diffuse reflection is the primary means for global illumination.

When light waves hit an object, some of those photons are absorbed, some are refracted and some are reflected. The higher the reflectance the brighter the object will look. Objects that appear solid are diffuse reflectors, meaning that they scatter light randomly in all directions in a hemisphere from the reflection angle. It still follows the law of reflection but it is at the atomic scale -- an object that appears to be smooth is actually quite bumpy, and this causes the light rays to be scattered in all directions.

Some objects appear mirror-like, in that you can see a reflection in them. This is because the light rays are reflected mostly according to the law of reflection because they are very smooth at the atomic level. The rays being reflected are coherent.

So for example, if you see a white object, then you know it has very high reflectance/low absorption in all wavelengths but it reflects light in random directions.

If you see a bright red object, then you know it has very high reflectance /low absorption in the red wavelength, and it scatters light in random directions.

If you see a perfect mirror, you know it has high reflection/low absorption in all wavelengths, and is smooth at the atomic level.

If you see a matte black object, then it has low reflectance/high absorption in all wavelengths and scatters light in all directions that it does reflect.

If you see a shiny black object, then it has low reflectance/high absorption in all wavelengths but it is smooth at the atomic level so it reflects coherent light.

If you curtain up all the windows in your house and turn the lights off, chances are you will still be able to see a little bit. This is because a tiny amount of light still gets in...that little ray of light hits 1 object, bounces into a billion directions, and each one of those rays hits a billion objects and bounces off in a billion directions, and it does not matter that they are traveling in straight lines because there are light rays hitting practically every single surface in your house.

thats almost wut i said or i think... but we are tlking about electricity not harmlerss visible light..

between copper coils set seven feet apart.

One more observation: I suspect that primary loss of signal would come from phase changes due to reflections that take different path lengths, and not just loss of signal due to scattering like with WiFi.

MonkeyMan09 wrote:

thats almost wut i said or i think... but we are tlking about electricity not harmlerss visible light..

Uh...no.

Quote:

between copper coils set seven feet apart.

Obviously they are using electromagnetic induction which has been around for 2 centuries, and has been happily providing customers with wireless power for charging devices like toothbrushes and laptops and cell phones and ipods for many years. The waves are still electromagnetic waves. Light is an electromagnetic wave. It is the same thing. The difference is that they have found a way to increase the effective range of these devices from millimeters to feet.

Still, for laptop-sized coils, power levels more than sufficient to run a laptop can be transferred over room-sized distances nearly omni-directionally and efficiently, irrespective of the geometry of the surrounding space, even when environmental objects completely obstruct the line-of-sight between the two coils.

I spoke too soon...from BumbleBee's summary it sounded like they were using induction; they're not.

Still, it is nothing like a stun gun; there is no spark jumping the gap.

However, I believe this addresses your question re: obstacles:

Quote:

Still, for laptop-sized coils, power levels more than sufficient to run a laptop can be transferred over room-sized distances nearly omni-directionally and efficiently, irrespective of the geometry of the surrounding space, even when environmental objects completely obstruct the line-of-sight between the two coils.