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. >> >
