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MIT Stealth Startup Charges Up Wireless Power Competition
gthuang88 writes: Wireless charging of electronics is an old concept, but there's a new player in the competition between companies like WiTricity, Energous, and tech giants Apple, Samsung, and Qualcomm. A new spinout from Dina Katabi's lab at MIT, called Pi, may have a new take on how to charge mobile devices at a distance. The company isn't talking yet, but Katabi's research suggests the system uses an array of coils to produce a magnetic field and detect when a device is within range, like a Wi-Fi router. The array can then focus the magnetic field on a coil attached to a phone or mobile device and induce a current to charge the battery. But it's still very early, and the field of wireless charging needs to settle on technical standards and work out its commercial kinks.
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).
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Unless you have a conducting loop in or around your body when it fires, such as a wedding ring, or a magnets in your body, such as are found in some medical electronics, or if you've got any accidentally embedded magnets such as those swallowed by children..
http://www.npr.org/sections/he...
Or unless there is a bulky, conducting metal object in the room, such as an oxygen tank:
http://www.nytimes.com/2001/07...
I'm not suggesting that a modest hom recharger will create such risks. But please, do not extrapolate armchair physics to assume you understand the real risks of a real electromechanical device without doing the research.