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Cota – wireless charging through walls with a 40 foot range means you may never need another charger cable again


The goal of delivering real remote wireless charging to the world’s gadgets seems to be cracked with the demonstration this month of a new system which can charge a smartphone in a user’s pocket from 40 feet away, through two walls and closed doors.

The Cota technology makes use of what’s called time reversal symmetry to beam 1W of power (which is a fifth of that you get from a USB charger) wirelessly to any receivers within range. When you wander within range of a power charger unit, the phone or other device in your pocket sends an ‘I’m here’ signal to the charger, which then sends back a focused beam of power along the exact same route. Thereby avoiding obstacles or people in the way, which might absorb the beam.


The result should be a safe, and yet effective way to trickle charge all the devices in your home or office using one simple system, with no cables or contact needed. Think of it like a WiFi signal, but instead of delivering the Internet, it delivers power.

It all sounds incredibly wonderful, but there are still a few questions we’d like to see answered before the tech is widely deployed sometime next year. For one thing, it’s incredibly inefficient, delivering only 15% of the power to the device (we assume the remainder is dissipated en route, on walls or whatever). This means a considerably increase in power needed to charge up our many gadgets.


For another thing, it’s supposed to be safe, because the microwave radiation is routed around people in the vicinity, and not absorbed, but that assumes the body stands perfectly still while the charging is going on. Since people typically move, there’s definitely going to be a need for the system to ‘ping’ the location of the body at short regular intervals, each of which will no doubt involve radiation hitting the body.

However, for now we’ll give it the benefit of the doubt and applaud what seems to be a very innovative solution to the problem of getting power to our lives quickly, conveniently and with a minimum of infrastructure disruption.


  • I’m always dubious about the safety claims of a technology supposed to beam several watt of energy in closed place with several people inside.

    The “time reversal symmetry” technique never meant that the beams won’t touch or travel trough people, even if they are still.

    It means that the beams will “bounce back”, carrying more energy, on the same path as the “I’m here” signal.

    If that signal bounced on or slightly travelled through people inside the place, the energy beam will do the same.

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