Comment Engineer Comments (Score 3, Informative) 63
I design near field low frequency RFID readers.
It's kind annoying to WiTricity claim they invented something (resonant charging) that the LF RFID industry has been doing for the last 30 years. ie Very HiQ coils to efficiently transmit to passive RFID tags (which also have HiQ resonant coils).
Magnetic fields can be well directed by permeable materials like ferrites, but as soon as you have to bridge the air-gap, you get 1/r^3 power loss. Can you do phased array effects like steerable antennas like the article claims? Yes, but probably not in a way that is beneficial to bridging the air-gap loss.
Here is a challenge. I give you 4 little round neodymium super magnets, and I'm going to let you rotate them into whatever static position you like, with the goal of producing twice as much magnetic attraction a distance 4x their diameter. Think you can do it?
Besides terrible efficiency you are also limited in power as described in ESTI EN 300-330-1
There is a specific allowance for magnetic near field from 119 to 135kHz of 70dBuA/m.
As for safety. These magnetic fields are fairly benign. We have thousands of these transmit at the legal limit on big 1200mmx600mm air coils, and have to our knowledge have not had an incident (ie with a pacemaker).