> 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.
So they do, my mistake, that's called synchrotron or cyclotron radiation (or light). All accelerated charges radiate, so I suppose that in theory a radio emitter could work in DC. But that's not how the witricity device works in any case, since it operates at a resonant frequency of a few MHz. Michel ----- Original Message ----- From: "Harry Veeder" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Saturday, June 09, 2007 9:10 PM Subject: Re: [Vo]:Witricity scheme (was Re:Tesla Revisted) > > 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. >>>> >>> >> >
