On 8 Jun 2007 at 11:49, Andy Talbot wrote:

> *http://news.bbc.co.uk/1/hi/technology/6725955.stm*<http://news.bbc.co
> .uk/1/hi/technology/6725955.stm>
> 
> They clain to have acheived 40% efficiency - that doesn't seem very
> good.
> 
> Andy  G4JNT
> 

By coincidence there is an article in this month's Engineering & 
Technology, the magazine of the IET, which discusses these 'power 
wireless' techniques, it dropped through the letter box this morning. 

It covers the MIT research and other, inductive coupling and near 
field techniques, in some depth. They cover how they place resonant 
receivers in the near field of the radiation and can get 50% or so 
efficiency at short ranges. But there is absolutely no mention of 
what they do to stop the radiation getting any further - and the only 
mention of frequency is 'a wavelength of 30m' at one point, which 
sounds suspiciously like our 30m band.... You really do have to take 
with a pinch of salt how much these chaps actually claim to know.

Another technique involves burying a sheet of resonant coils 
underneath the floor of the building to couple the rf into the room. 
The editor has added a snide remark at the end 'If the public is 
unwilling to allow mobile phone masts to be built close to schools, 
it seems unlikely they'll welcome the installation of underfloor 
grids delivering large amounts of power'. Hopefully this will kill 
these cloud cuckoo ideas stone dead...

In due course you will be able to read the article at 
http://www.theiet.org/engtechmag (only the May edition is there at 
the moment).

72 Dave G3YMC

http://www.davesergeant.com