[BrianG]

Yeah, old tech for sure. IIRC, pacemakers are recharged in a similar way, and they have been around for quite some time. Maybe the current generation of pacemakers use the body's natural bioelectrics to power them, I dunno.

With something as general-purpose as this, there must be a substantial amount of losses. In a real transformer, the primary and secondary coils are physically very close together and are magnetically coupled via some type of core. And even then, there are some decent amount of losses. Without a focusing core, the flux goes everywhere being wasted and only a little makes its way to the secondary. Convenient? Yes. Efficient? Probably not.

I also wonder what effect the stray magnetic flux has on other inductive devices?