Wireless Electricity Update Summer 2009

This is an update on recent developments in wireless electricity. I’ve been writing about wireless electricity for several years now and have corresponded with Marin Soljacic at MIT on one occassion regarding his progress as well.

The MIT Technology Review is doing a good job of following along with the race between their team (now operating within the independant VC funded startup WiTricity) and Intel (who appears to be building on top of some of their own technology) to bring a wireless electricity product to market first . Thanks to my buddy Jim for pointing me to this article last week. The article talks pretty much all about Intel and their June 18th presentation at the Computer History Museum in Mountain View, California. At the event they showed a wireless electricity prototype which charged an iPod speaker at a distance of one meter using a 60 cm diameter loop transmitter and a 30 cm diameter loop receiver both tuned to a frequency (electrical current oscillation) of seven megahertz. Electrical power was transmitted with 80% efficiency through the specific arrangement they demonstrated.

This display is similar to one they showed in the Fall of 2008 which lit a lightbulb over a similar distance with only slightly less (75%) efficiency. Because of the small improvement in efficiency (5% increase in 10 months) I wonder if they are approaching a unique design limitation or a fundamental limitation with the transfer of a magnetic field through the air. It’s also worth wondering whether the 20% of energy lost is falling out as the magnetic field passes through the air (currently a distance of one meter) or through the process in which electric energy is converted into magnetic energy and back within the wire loops that comprise the transmitter and receiver. I figure the magnetic field transfer through the air is to blame for most of the energy lost in this model. Does anyone know?

I also haven’t heard anyone talking about efficiency gained or lost when a single transmitter is used in combination with multiple transmitters. If a transmitter is able to send a magnetic field out in multiple directions (which I don’t know if it does) then it seems to me that a receiver in a location far away from another receiver would not reduce the ability of the other receiver to be driven by the magnetic field. Could this technique be used to increase efficiency to a level that the current energy losses would be more than compensated for? I don’t see why this wouldn’t work… but my physics knowledge is based mostly on Physics 26 and 27 in the undergrad program at UNC from eight years ago 🙂 At least the classes did include sections on electricity and magnetism.

Another note about WiTricity, the company pushing MIT’s research forward that I mentioned earlier, their website contained a few things I found interesting:

1) It mentions that WiTricity has an exclusive license to the wireless electricity prototype intellectual property developed by Marin Soljacic and his team at MIT. There are also some other interesting details on the about us page of the WiTricity website as well.

2) It contains a nice illustrated description about how wireless electricity works which is a great read for a wireless electricity novice and probably great content for a lesson plan if you are a teacher.

3 thoughts on “Wireless Electricity Update Summer 2009”

  1. Very interesting stuff. I’d like to learn more about the differences between the wireless transmission occurring here and that of a cell phone to its radio tower. I don’t think we’ll ever get to the point where batteries are regularly charged anywhere (kind of a blanket similar to wifi), but I would love to have a box in my home where I just drop my laptop / phone and it charges away (maybe built in to the desk?)

  2. Great points Jeremy. Thanks for your note. From what I’ve seen it looks like a widespread geographical roll out of wireless electricity, similar to what we’ve seen with wireless phone and data signals, will be extremely challenging.

    Induction charging at little to no distance actually already exists for a number of devices. Years ago I used to own an electric shaver that would charge while sitting on its base without making contact with any physical electrical connections. A magnetic field produced in the base unit induced a current within the shaver itself which charged the battery. It worked great and probably had great efficiency as well considering the distance the magnetic field traveled was probably about 5 millimeters.

    All of the most recent research has been pretty consistent with prototypes transferring energy around one meter in distance. With these types of tests being conducted I believe they are hoping to create technology that would allow a house or office to be powered by one or a few small broadcast power sources. Essentially starting by removing the need to run a wire from your desk to the wall, but not replacing the electrical wiring within the walls or within the larger grid outside.

    We might have to wait a long time for that but the implications of the larger scale are simply incredible, ie: think what mobile phone networks have done for developing countries.

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