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Author Topic: new source of RFI  (Read 720 times)
KC6TOA
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Posts: 2




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« on: June 07, 2007, 12:03:11 PM »

i was reading on the BBC
http://news.bbc.co.uk/2/hi/technology/6725955.stm

they are lighting a light bulb by transferring energy across two coils spaced two meters apart, using a 10MHz frequency.

It says 40% of the energy reaches the light bulb.

So where does the other 60% go?

once again, a complete disregard for other users of the radio spectrum.
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WB2WIK
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« Reply #1 on: June 07, 2007, 01:29:49 PM »

The rest goes to radiation loss.  The signal's still there, just not intercepted to help illuminate the bulb.

Unfortunately, that means it is QRMing us on the 30m band instead.
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AA4PB
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« Reply #2 on: June 07, 2007, 04:24:38 PM »

Amazing that professors at MIT are impressed by this. Transfering energy via wireless means has been proven many times over the years. I did it as a teenager on a smaller scale (#47 bulb). The reason its use has not been practical is because it is so inefficient. Who can affort to loose 60% of the power. Actaully its probably a lot less efficient than stated. To light a 60W bulb I need 120W of RF. To generate 120W of RF I need 240W of DC power. Add another 20W for power supply loss for a total of 260W. That puts the real efficiency at about 23%. Now when they come up with a system that is small and 90% efficient and doesn't clobber the HF spectrum then we can be impressed :-)
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N3OX
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« Reply #3 on: June 08, 2007, 02:44:01 PM »

Before everyone goes off the deep end, they should read the paper here:

http://arxiv.org/ftp/physics/papers/0611/0611063.pdf

A quote from the introduction:

"Radiative modes of omni-directional antennas (which work very well for information transfer) are not suitable for such energy transfer, because a vast majority of energy is wasted into free space. Directed radiation modes, using lasers or highly-directional antennas, can be efficiently used for energy transfer, even for long distances (transfer distance LTRANSĀ»LDEV, where LDEV is the characteristic size of the device), but require existence of an uninterruptible line-of-sight and a complicated tracking system in the case of mobile objects."

They are trying to avoid radiation of any radio waves.    I haven't read the paper through yet, so I don't know how to build an antenna that only couples to other antennas through evanescent wave coupling, but this is what they seem to be doing.

They've been doing this with optical fiber for years:  take a fiber which keeps all of the waves propagating inside of it, right?  Total internal reflection happens at the outside of the fiber, keeping the light beam in the fiber.

However, if you bring another fiber *NEAR* the first one, light from one fiber can *tunnel* into the other....the probability of a photon jumping the gap between the fibers is very, very small, and if the second fiber weren't present, it would be ZERO.  It also goes down a great deal as you increase the distance... tunneling is a quantum effect... no electromagnetic waves actually travel in the space between the fibers!

What I don't know is if you can tunnel between the 10MHz charger and your 10MHz dipole... let me read the paper and I'll get back to you.  

What I do know is that tunneling does NOT launch electromagnetic waves into free space.

Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
N3OX
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« Reply #4 on: June 08, 2007, 03:02:54 PM »

OK, well, the antennas are just little tiny magnetic loops... nothing special here, so they *will* radiate.  The other possible transducer is a dielectric disk cavity with resonances in the microwave, obviously not a threat at 10MHz.

I think that this would cause interference if located within the 30m band, but a couple of things stand out as suggesting that it will a minor threat.

1) They consider radiation a loss, a drain on efficiency... because it is a loss for their system, just like has been suggested here.

2) They're using very high Q circuits... it'll be a spot frequency interference, not a wideband one.

Something to keep an eye on, but they're not *trying* to radiatively beam power from one antenna to another.

I think they have some work to do on that front if they're suggesting using 1/35th wavelength diameter magnetic loops at 10MHz though ;-)  

Dan  

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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
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