In reply to Michel Jullian's message of Sat, 9 Jun 2007 19:26:17 +0200: Hi, [snip] >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 I see no reason why a MHz device wouldn't also emit common radio waves since the transmitting coil can be seen as a multi-coil hoop antenna. Unfortunately I don't know the formulae governing the efficiency of such antennae, however my guess is that one could design the coil such as to make it as inefficient as possible as a normal antenna (e.g. choose the wavelength to be a bad match for the actual size of the antenna - a transcendental number comes to mind e.g. Pi thus also eliminating transmission at harmonic frequencies). However I also think that the impedance of the transmitter will be much lower when a tuned receiver is present than when it isn't. Another means of keeping the normal radio transmission losses to a minimum is to lower the frequency.
Regards, Robin van Spaandonk The shrub is a plant.
