Thanks for sharing Yuval Boger!
Alex Mitchell

Alex Mitchell — thanks for the question. The short answer is that I am not aware of any long-range wireless charging technology that can charge a phone in your pocket. Let me expand on that.

First, let’s establish the basic approximate numbers. The battery capacity of an iPhone X, typical of other smartphones, is about 10 WH. Operating time for an iPhone X under normal conditions is about 20 hours. This means that an iPhone X consumes about 0.5 Watt every hour.

Thus, if you wanted to keep an iPhone X operating ‘forever’, you’d need to deliver at least 0.5 Watt to it. If you can deliver 0.5 Watt, the energy that you are using is going to be equal to the energy you are providing.

RF charging can’t provide 0.5 Watt to a phone even if it’s OUT of your pocket. Under reasonable assumptions of transmitter size, and while keeping within international radiation safely limits, the theoretical limit for RF is about 0.1 Watt, so about 5x less than what you would need to keep an iPhone X operating. Of course when the phone is in your pocket, the situation is even worse because part of the RF energy is reflected, scattered or absorbed by the fabric.

IR charging (at least Wi-Charge’s IR charging) can easily deliver 0.5 W outside the pocket, but is not going to be able to deliver 0.5 Watt inside the pocket because light does not travel well through fabric.

Here’s a graph showing the maximum you can expect from RF and IR at various distances:

This graph is part of a new post we published today that explains these issues. You can find the full post here

I hope this is helpful.

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