Instead, they devised a simple and clever instrumentation approach of using the receiver to power a small circuit within the implant which, in turn, flashed a tiny LED at a rate proportional to the received power. An optical fibre then conveyed the LED output to an external photodetector and circuit which sensed and counted the flash rate (once again, the RF-free nature of optical fibres opens up new approaches to many problems)very nicely done, indeed.
What's your view on the desirability or viability of wireless charging for consumer products? Would you ever think that transfer efficiency of less than one-tenth of one percent would be sufficient and welcome in a unique application? What power-transfer efficiency would you accept in your application?