Re: About wireless energy transfer

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Ed Phillips <evp@xxxxxxxxxxx>

Hi all,
Tesla did actually experiment with this form of wireless transmission,
where he ran a loop around the inside perimeter of his lab, powered by
a mercury break disruptive discharge system, i.e. the primary circuit
of a tesla coil. He then picked-up the power with small tuned circuits
mounted inside low pressure air lamps and the like, like the
photographs of him holding an energised lamp. Tesla actually said the
effect was quite stunning to guests, but in fact was a very
inefficient way of broadcasting power, and so concentrated on the
ground current system we all know and love.

Gavin"

   To give the authors a tiny bit of credit, they didn't claim much 
efficiency and were limiting themselves to small power 
levels.  That's all the credit I will give them.  Note that many of 
the current RFID tags use the same principle - energy coupled from a 
tuned loop is received, rectified, stored, and used to power a 
low-power transmitter to convey data back to the source.  Back in the 
1970's a friend of mine and I built a simple demo system based on a 
similar idea.  He wanted to build little receivers which people in 
fast-food restaurants could carry to their tables and which would 
indicate when their orders were ready.
Simple loop around the room excited by a small 180 kHz transmitter 
running around 10 watts.  Receivers had a tuned coil and rectifier 
which fed a decoder (transmissions had simple binary coding) which, 
upon receipt of the appropriate code, lit up an incandescent bulb 
powered by a local D cell.  Worked OK but not enough interest to 
carry the idea further.  We could get several volts of DC anywhere 
inside a 30 x 50 foot square lab.  Efficiency was zilch............

Ed