Re: Worlds best tranducer, Worlds best microphone
Inverse square law applies to all point sources, whether omni or directional, in a linear transmission medium.
In near field, with very large radiators (ie, non-point sources in near field), such as very large phased arrays, it is possible to concentrate energy from a distance of the order of a few wavelengths, but it'll be a frikkin big array with hundreds if not thousands of point sources with appropriate separation.
More of a problem is the non-linearity of air at the power needed to generate enough power to charge a cellphone, the inefficiency, the enormous wall sized arrays, the receiving sleeves, the cost of infrastructure, regulatory barriers, safety implications, innevitable litigation over fillings falling out etc.
It's a complete load of impractical bollocks, and yet another wakeup call (in case they needed one) that the VC industry needs to wake up and stop mis-selling this sort of crap to uneducated investors due to sheer negligence, deliberate or otherwise, on the VCs' part.