On 22/08/2019 06:49, jeikppkywk wrote:


"Roger Hayter" wrote in message
...
John Rumm wrote:

On 21/08/2019 13:16, dennis@home wrote:
https://www.bbc.co.uk/news/business-48859331

Someone really should tell them that the normal RFID tags in use
are not
powered by radio waves.

You do know what the RF in RFID stands for don't you?

Radio frequency does not necessarily imply radio (electromagnetic)
waves.Â* In fact, if you have an RF magnetic fieldÂ* generated there will
be some EM radiation around.Â*Â* But I believe if is purely the near field
magnetic induction at RF that excites the tag.

Doesnt explain the obvious RF antenna in the pic someone posted.
Thats not a coil.

The lines between coils and antennae are blurred.

Ultimately when you do teh math omn EM radiation (and I did, once) what
pops out is thet 'capacitatative coupling' 'magnetic coupling;' ' RF
power transfer' are all really the same thing - explication of the
nasty tensor calculus that defines 'elecromagnetic fields'.

It is just that in some case you can use a simplified version and get
roughly the right answer and call that 'induction' or 'RF' or
'capacitative coupling'




--
There is something fascinating about science. One gets such wholesale
returns of conjecture out of such a trifling investment of fact.

Mark Twain