Sunday, February 24, 2008

Wireless electricity for the classroom?

underfloor wireless power transmission sheetPerhaps floors could be fitted to transmit wireless electricity through the legs of furniture for supply to desktop computers and other low power equipment. This could be useful in flexible classrooms where the furniture was movable.

MIT have been working on WiTricity (wireless electricity), to transmit small amounts of power safely over a few metres. But this requires carefully tuned antennas and electronic circuity.

The large round bases of the Jelly bean desks at RMIT Library reminded me of magnets. It occurred to me that if a non ferrous false floor was used, such as raised plastic interlocking tiles, then coils of wire could be placed under them. Matching coils could be placed under the base plates of the furniture. An alternating current in the floor would produce a magnetic field which would penetrate the floor and induce a current in the coil in the base of the desk. This current could be then carried by a wire up the column of the desk and delivered via a plug to a computer on the desktop.

As the two coils would be only about 10 mm apart (through the floor tile and carpet), the transmission would be much more efficient than with MIT's system. A magnet in the base of the table could be used to only switch on the coil, via a reed switch, when the table is present. Such a system may not need any electronics at all and simply operate at the mains frequency and voltage in the floors system. The desk system could be at a safe low voltage, with the coils acting as as step down transformer.

Inductive coupling is used for charging high capacity batteries in electric cars and can carry kilowatts of power. For low power desktop computers only about 150 Watts per computer is needed. The Dell energy calculator estimates that a Dell Optiplex 745, with a 20 inch LCD monitor uses 296 kW hours a year, or about 142 Watts.

There have been proposals for underfloor power transmission before, such as University of Tokyo's wireless power transmission plastic sheet. But like the MIT WiTricity, this uses complex electronic circuits and tries to cover the whole floor. Instead transmitters might be spaced in a grid pattern or only where tables are likely to be located. With floor tiles it would be possible to raise panels and move the transmitters if needed.

1 comment:

Gye Greene said...

A good thought -- BUT:

What sort of danger does wireless electricity (through EM induction) pose for pacemaker users - and maybe cochlear implant users, as well?

Possibly not a problem whilst they're standing -- but, should they trip and fall (unlikely on a regular basis -- but a feasible occasional hazard), such that their unit is centimeters from the floor...?