Electronics has already cut the data cord. Can it now cut the power cord as well?
Jun 27th 2015 | Seattle | From the print edition
DRONES may one day transform the way parcels are delivered, crops monitored and suspects apprehended. Those who talk up these possibilities, though, often neglect to mention the drawbacks of such robot aircraft—one of which is that most cannot fly for more than a quarter of an hour before they need to find a human being to swap their batteries for them or plug them into an electrical socket.
He theorized from these experiments that if he injected electric current into the Earth at just the right frequency he could harness what he believed was the planets own electrical charge and cause it to resonate at a frequency that would be amplified in "standing waves" that could be tapped anywhere on the planet to run devices or, through modulation, carry a signal.
That failed, as most other physicists of the time predicted it would. More modest remote power-transmission is, however, now attracting attention again. The technology Tesla pioneered is already being used to charge mobile phones, and researchers are working on similarly wirelessly poweredkitchen appliances, military equipment such as heads-up displays, and medical devices ranging from heart pumps to brain monitors.
Inductively coupled systems like this thus work well for things like repowering electric toothbrushes. They would be impractical, though, for a drone trying to hover over a charging station. Wibotic’s answer is to use tuned electrical circuits in place of simple transmitting and receiving coils. When such circuits are tuned to the same resonant frequency, they exchange energy more efficiently.
For remote charging to take off metaphorically as well as literally, though, devices employing it need to be interoperable. That means establishing industry standards. Unfortunately, in a competition reminiscent of that in the 1890s between alternating current (Tesla’s preference) and direct current (promoted by Thomas Edison), three main consumer standards have emerged.
The Tesla exception
The rise of electric cars opens yet another market for remote power-transmission. Carmakers are keen to avoid the standards war that has broken out among makers of smaller gadgets. If convenient wireless charging lets carmakers halve the size of electric-vehicle batteries, it couldslash thousands of dollars from their prices. That would make a huge difference to the economics of owning and running them. Nikola Tesla failed to beam power between continents but his tricks may yet succeed in something equally dramatic: decarbonising the world’s road vehicles.
make a huge difference to：使产生很大的不同
oscillating magnetic field：震荡磁场