There is no way to avoid the fact that the power is being transfered via a magnetic field. Could you imagine what would happen if someone's keyfob with some enamled wire or some such weirdness resonated? You'd inductivly heat the key's. Anyone ever burned by even a 30 watt iron knows they can get a little hot, and they're talking about 100watts as a goal. I finally found an efficiency rateing for the device which was about 40%, really respectable for wireless power, but the possible environmental interactons are impossible to determine until a full size power distribution network was tried, and so little is known about what extended exposure to strong magnetic fields does to living tissues. I've seen frogs magnetically levitated in super conducting coils, and it's kind of creepy to think how high the flux density must be to do that to organic tissue and what might be going on. You just can't pump that much power through something without expecting some sort of interaction. Perhaps some specific chemicals or molecular structures resonate, even at a harmonic some power will be absorbed.