A New Wireless Power Transmission Sheet

Roland Piquepaille writes "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."

Re:Environmental reasons why this is stupid.

[zippthorne]

20% of your power.. for LOW POWER DEVICES.

They're not talking about running a refrigerator for these things, they're talking about reducing wall-wart clutter to one wire and one pad. In addition to less clutter, that means that lazy people will leave fewer transformers plugged in without powering anything.

Re:How Efficient?

[Sandbags]

First, the pad only "uses" electricity when there is a device inside of it's field of effect. There's no "sleep mode" it just doesn't use any mower when nothing is near it. The magnetic field generated can easily sense the presence or lack of a device and power on only when necessary.

Second, if you understood the technology, you would know there will never be a 1000 watt version. Magnetic field science works on a multiple of squares system. To generate 80 watts instead of 40 takes a field 4 times larger. to go to 160 watts requires 16 times as much field density. To produce induction coils capable of generating a field large enough to charge large devices, or a field strong enough to charge high voltage devices is prohibitively expensive.

Third, this is a trickle charge technology, taking most of the night to recharge your device instead of an hour. When batteries are rapidly charged, they get hot. This heat is not only energy wasted, but inhibits charge efficiency. Charging times for electric cars are the primary reason they don't exist yet. Trickling the energy into the battery keeps the resistance low, prolongs battery life, and actually makes each charge last longer (rapid charging only gets batteries to about 85% capacity, trickling get it to 100%).

The power efficiency of induction pads is actually quite amazing. 2% on average power loss. In fact, the pad will usually be much MORE efficient that a wall charger since the charger in the wall is 1) always using some power when plugged in, 2) still has 1-2% or more power loss when charging, 3) completes its charge in 1-2 hours, but typically remains plugged in and wasting energy (although not much) for 8-10 hours.

Smart induction only applies power to devices who's antennae resonate on specific frequencies. If you have multiple devices charging at once, the pads can resonate on multiple frequencies at the same time, charging several devices. When one completes its charge, the pad can stop "broadcasting" on that frequency and thus stop wasting that power.