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I phoned a friend.  Here was his response in RED.

The receiver device can have a coil of only 8mm diameter, but it can be quite long in a cylindrical-length direction.

The transmitter coil can be concentrically located around the outside receiver's coil, as in inserting into a tube, (if this is an advantage) and can also be as long in the z-direction..

1)      Is this an advantage - for the coils to be concentrically mated vs. the typical, flat, co-planar system?

>> Coupling coefficient between the two coils for both planar and cylindrical designs depends on the gap between them.

I don’t think one design has an intrinsic advantage over the other.
On the other hand in the concentrically mated design the transmitter coil can be equipped with a ferromagnetic core, which will make the mutual inductance higher. Higher mutual inductance should let you transmit more power, but not necessarily more efficiently; ferromagnetic cores have losses which depend on a number of factors (e.g. size, frequency, type of material).

2)      How much current might I be able to transfer between a large(er) transmitter coil and a very small (8mm) receiver coil?  The air gap can be made VERY small in this application.

>>

Hard to say. This will mainly depend on your design, especially whether you use a core or not, what type of core and what type of wire you use and what your thermal constraints are.

Based on my limited experience I would expect between 5 and 10W if you have a decent heat-sinking mechanism.

If you want to find more information onTI wireless power solutions you can find them at

http://www.ti.com/lsds/ti/analog/powermanagement/power_portal.page

Look for the link on the bottom left of the page

Regards,

Marc