It's been a dream ever since the days of Nikola Tesla–transmitting electricity without wires.

Massachusetts Institute of Technology spinout Witricity says it's got the science down to do it – if not at the global distances that the father of alternating current contemplated, then at least far enough to charge cars, cell phones and wireless computer keyboards without cords.

Witricity CEO Eric Giler demonstrated the technology Tuesday at the AlwaysOn GoingGreen conference in Sausalito. The company, founded in 2007, has about 55 patents on its method, which involves tuning two coils to the same "magnetic resonance," so that magnetic fields put out by one are picked up by another as electricity.

That's a bit like the way transformers work, except that the two coils in this case can be farther than a few millimeters apart, Giler said.

"Achieving resonance is very difficult to do, even in nature," he said. The technical details of how Witricity does it can be found at its Web site.

The method differs from those promoted by fellow wireless power companies PowerBeam, which uses lasers to power a photovoltaic cell, and Powercast, which uses radio waves, Giler said. The former is limited by line of sight, and the latter is limited by federal regulations on the power of unlicensed radio transmissions, he said.

Witricity's wireless power transmission is limited by distance, he said. While it's about 95-percent efficient at short distances, that can drop to less than 10 percent at distances greater than five times the size of the coils involved, he said.

Still, that's not necessarily a limitation to, say, putting charging coils in desktops to power consumer electronics lying on top of them, or electric vehicle batteries through coils contained in mats laid out in the garage, he noted.

Witricity would like to see both applications taken to market, and is talking with manufacturers of handheld devices and automakers about it, he said. A typical system capable of charging an electric vehicle battery would cost about $2,000, he estimated, and he'd like to see them made available at dealerships as add-on features.

As for the first question he's always asked about the technology, Giler said that no, it does not harm humans or cause pacemakers to go on the fritz. The level of power involved is no stronger than the earth's magnetic field, and bodies appear as empty air to the fields his devices put out, he insisted.