The article doesn't appear to contain the term AC.
It only speaks of an electrical current although it describes the
magnetic field as oscillating at MHz frequencies. Perhaps this is
inaccurate.
Perhaps it is more correct to say the oscillation starts only when both the
power supply ("sender") and a power user ("receiver") are in the same room.
Regarding DC current and radio waves, I was basing my claim on the fact
than electrons made to move in a circle radiate radio waves.
harry
On 9/6/2007 12:26 PM, Michel Jullian wrote:
> Whatever the shape of the wire a DC current can't emit radio waves AFAIK. The
> witricity experimental device uses AC at MHz frequencies (cf the link I
> provided, here it is again
> http://www.mit.edu/~soljacic/MIT_WiTricity_Press_Release.pdf )
>
> Michel
>
> ----- Original Message -----
> From: "Harry Veeder" <[EMAIL PROTECTED]>
> To: <[email protected]>
> Sent: Saturday, June 09, 2007 8:08 PM
> Subject: Re: [Vo]:Tesla Revisted
>
>
>>
>>
>> A DC current in a straight wire won't emit radio waves.
>> A DC current in a coiled wire will emit radio waves, but
>> with little power.
>>
>> Harry
>>
>> On 9/6/2007 6:14 AM, Michel Jullian wrote:
>>
>>>> Essentially it's a transformer primary
>>>> winding with an open secondary winding.
>>>
>>> Indeed a primary with an open secondary behaves like a pure inductor, so
>>> it's
>>> a purely reactive load, so current in it can be made to oscillate non
>>> dissipatively (assuming resistance of the coil is negligible). In terms of
>>> transformer it makes perfect sense. But in terms of antenna, how could the
>>> open air coil antenna help emitting radio waves (which requires power)
>>> towards
>>> infinity?
>>>
>>> Michel
>>
>>
>>> ----- Original Message -----
>>> From: "Robin van Spaandonk" <[EMAIL PROTECTED]>
>>> To: <[email protected]>
>>> Sent: Saturday, June 09, 2007 4:53 AM
>>> Subject: Re: [Vo]:Tesla Revisted
>>>
>>>
>>> In reply to Harry Veeder's message of Fri, 08 Jun 2007 15:00:21 -0500:
>>> Hi,
>>> [snip]
>>>> I can't explain it with em theory, but it behaves like a simple pendulum.
>>>> Ignoring friction, once the pendulum is set in motion it will keep swinging
>>>> with the same amplitude until the pendulum is used to power a clock or some
>>>> other device.
>>>
>>> Precisely, so if no power is drawn, then none is transmitted
>>> (theoretically).
>>> The trick is that the inductance of the transmitting coil remains high until
>>> a
>>> resonant load is attached. Since most things in the environment are out of
>>> resonance the impedance stays high, and the transmitter itself appears as a
>>> high
>>> impendence to its own power source. Essentially it's a transformer primary
>>> winding with an open secondary winding. BTW this implies that losses can be
>>> reduced even further by increasing the Q factor of both transmitter and
>>> receiver. The effect of which is to narrow the bandwidth, ensuring that even
>>> less "spurious receivers" are to be found in the environment, and
>>> consequently
>>> less loss. Of course the flip side is that it's harder to match the resonant
>>> frequency of the receiver to that of the transmitter.
>>>
>>>>
>>>> Harry
>>>>
>>>> On 8/6/2007 11:27 AM, Michel Jullian wrote:
>>>>
>>>>> Maybe it would be possible for the emitter/primary to know there is a
>>>>> receiver/secondary around drawing power from it, if none it could turn
>>>>> off,
>>>>> and turn on for a brief time every few seconds to check of it's needed.
>>>>> Maybe
>>>>> it could even modulate its output power to fit the needs?
>>>>>
>>>>> On the "how it works" side, has anybody understood the difference between
>>>>> this
>>>>> MHz "resonant magnetic coupling" device and a radio emitter with a tuned
>>>>> receiver? They say energy is not radiated away if it's not used by a
>>>>> receiver,
>>>>> I can't really see why.
>>>
>>> I suspect that the receiver is within a wavelength of the transmitter, so
>>> that
>>> this is a near field effect, which would imply that greater distances could
>>> be
>>> achieved by using lower frequencies, though I suspect that one of the
>>> corollaries of Murphy's law says that as the frequency drops, so does the
>>> energy
>>> transfer efficiency. ;)
>>>
>>> Regards,
>>>
>>> Robin van Spaandonk
>>>
>>> The shrub is a plant.
>>>
>>
>
