Several companies have started to sell power 'pads' that can charge your cellphone when you put it on the pad's surface. But these silicon-based pads are expensive -- and relatively 'specialized.' Now, Japanese researchers have built a plastic sheet which could power all the devices placed close to it. So far, this 4-layer sheet, which uses printed organic transistors and plastic MEMS switches, can deliver up to 40 watts of power -- enough for some laptops. The technology is apparently efficient and inexpensive to produce. But as the devices to recharge will need to incorporate a special receiver, don't expect to see these plastic power sheets on sale before several years. But read more...
Before describing the technology, you can see on the left several examples of how wireless power transmission could be used: "a, Electric power of 2 W is transmitted to a Christmas tree decorated with 21 light-emitting diodes. b, Power transmission to a light-emitting diode in water. c, Power transmission to miniature electronic objects such as home-care robots, automatic cleaners, mobile phones, mobile personal computers, wall-hung televisions and ambient illuminations in the room. Power-transmission sheets to power them are embedded in the wall, floor and table." (Credit: University of Tokyo, via Nature Materials). Here is a link to a larger version of this illustration.
It's also interesting to note that this plastic sheet was invented by an interdisciplinary team of 7 researchers of the University of Tokyo, who belong to very different departments, the Quantum-Phase Electronics Center(QPEC), the VLSI Design and Education Center (VDEC) and the Center For Collaborative Research.
Now, what are the components of this 4-layer plastic sheet? "The plastic has as its base a layer of transistor featuring pentacene, an organic molecule whose electrical conductivity can be controlled. Topping that are layers holding copper coils that can sense whether a compatible electronic device is nearby, microelectromechanical-system (MEMS) switches that serve to turn on and off the power, and copper coils to transmit electricity."
And how does the technology work? "When the sheet itself is plugged in, it can power devices — such as light-emitting diodes (LEDs) strung on a Christmas tree — that are built with a matching receiver coil. When these are placed within 2.5 centimetres of the sheet, the nearest MEMS switch turns on, feeding power to the closest sender coil, which powers the device's receiving coil through induction."
Apparently, the technology is efficient -- "the transmission of power happens with 81.4% efficiency" -- and will not be expensive to produce -- with a target price of US $100 per square meter. But it should take a while before device manufacturers decide to introduce the receiving coils into their products. So don't expect to throw away your chargers before a while...
If you want more information, this research work has been published by Nature Materials as an advance online publication under the name "A large-area wireless power-transmission sheet using printed organic transistors and plastic MEMS switches" (April 29, 2007). Here are two links to the abstract and to an early version of the full paper (PDF format, 4 pages, 676 KB). The researchers also presnted their work at the 2007 IEEE International Solid-State Circuits Conference on February 13, 2007. Here is a link to their presentation.
Sources: Tom Geller, Nature, April 29, 2007; and various websites
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