"The Natural Philosopher" wrote in message
...
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. In fact, if you have an RF magnetic field generated there will
be some EM radiation around. 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.

Not with that one, there is no coil at all.

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'.

Irrelevant to whether that RFID has an antenna or a coil.

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'

Irrelevant to whether that RFID has an antenna or a coil.