Re: Inverse Square 'law' Re: About wireless energy transfer

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Original poster: Ed Phillips <evp@xxxxxxxxxxx>

>...Inverse Square 'law'...
   Welllllll.
   And i am NOT proposing New Physics.
   Really.
   8)>>

   "inverse quare' is The Law FOR OMNIDIRECTIONAL sources.
   Each unit radius out from the source the energy gets
   'spread more widely', becomes 'thinner'.  (To put it in
   non mathematical terms.)

   However.
   Ponder, please, a 'Very Well Collimated' beam.
   Parallel.  BIG 'reflector', meaured in wavelengths.
   The beam (laser, microwave) does not get bigger.
   I believe this was the concept for the 'rectenna'
   driven concept.

   Now no real beam will beperfect, but, maybe,
   close enough for 'all practical purposes'.

   best
    dwp"

   You have of course moved from "non radiative" transfer to 
conventional radiation but the point is worth discussing.  As you 
point out, "no real beam will be perfect".  In the case of the "well 
collimated beam" there will be a region (usually called the "far 
field") determined by the wavelength and the dimensions of the 
antenna beyond which propagation DOES follow an "inverse square law" 
of received energy PER UNIT AREA of receiver.  If the receiving 
antenna is made big enough to intercept ALL of the transmitted power 
then the "efficiency" is high but the dimensions involved really 
preclude serious consideration of such "energy beaming" or at least 
make it incredibly expensive if long distances are involved.  People 
have proposed the idea to provide microwave power to high-altitude 
airships and there is at present at least one outfit trying to get 
someone to pay them to develop a system.

   The "rectenna" is the "receiving end" of such a scheme and 
involves the use of distributed rectifiers throughout the 
structure.  Some workers have claimed efficiencies as high as 80% for 
such a device.
Proponents of using an orbiting array of solar panels whose output 
drives a microwave transmitter composed of many distributed magnetron 
amplifiers would use such a receiver.  The whole subjected has been 
treated seriously in the literature and there are many publications 
which discuss "real" systems.  They involve antennas with dimensions 
of the order of several miles on both the transmit and receive ends 
of the link.  There are so many practical problems with the idea that 
I think it will always remain in the talking stage although some 
short-range relatively low-power demos have been made.

Ed