how much data do you need to transfer, or to be more exact, how long =
does it take? If you have stored up data over some hours say, and then =
need to transfer it in a burst, can you get a situation where the =
subject sits in a chair, or can be located in some other way, so the =
transponder can be at a (relatively) known point. What I envisage is a =
chair which has a loop in the floor say a couple of feet diameter that =
the shoe is going to be in proximity of to pick up the signal to tell it =
to transmit.

Another possibility I thought of while writing the above is contact =
anyone doing hearing aids and sound loops for buildings. I was involved =
in doing this for a church, and started out with a 100 meter reel of =
three core figure 8 wire. I used 1.5mm cross section, and taped it to =
the floor in a square around the outside of the pews. The DC resistance =
of this was very close to 8 ohms, so I connected it to the output of a =
100 watt audio amplifier, and using a sense coil arrangement that they =
use for testing these things, got acceptable magnetic field about three =
times the "diameter" ( if a square loop has such a thing) of the loop. =
As you are going one direction with your signal this sort of technology =
may be what you require.

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