Apple Patent Hints At Wirelessly Charging Your iPhone Via Wi-Fi Routers (appleinsider.com)

According to AppleInsider, "Apple is experimenting with medium- to long-distance wireless charging technologies that could one day allow users to charge up their iPhones with nothing more than a Wi-Fi router." From the report: Detailed in Apple's patent application for "Wireless Charging and Communications Systems With Dual-Frequency Patch Antennas" is a method for transferring power to electronic devices over frequencies normally dedicated to data communications. In its various embodiments, the invention notes power transfer capabilities over any suitable wireless communications link, including cellular between 700 MHz and 2700 MHz, and Wi-Fi operating at 2.4 GHz and 5 GHz. More specifically, the document's claims apply to millimeter wave 802.11ad spectrum channels currently in use by the WiGig standard, which operates over the 60 GHz frequency band. Theoretically, the proposal opens the door to wire-free charging from in-home Wi-Fi routers to cellular nodes and even satellite signals. Of course, amplitude in a wireless system is normally a function of distance. Like conventional wireless charging techniques, Apple's design requires two devices -- a transmitter and receiver -- to function. Each device contains one or more antennas coupled to wireless circuitry capable of making phase and magnitude adjustments to transmitted and received signals. Such hardware can be employed in dynamic beam steering operations.

Comments

Re:Wireless charging? NOT POSSIBLE. Breaks Phys la

[rgbatduke]

t's really weird how people who know NOTHING about PHYSICS assume they can make decisions about technology.

I teach physics. In fact, I teach electrodynamics, off and on. Is it possible to charge a cell phone with wireless technology? Sure. All you need is a big enough tesla coil and a big enough loop and the ability to rectify broadband noise. If you are radiating a couple of hundred watts you can probably pull a watt out of it if you aren't too far away. Of course, you can also cook a hot dog if it isn't too far away.

Now let's consider 802.11 signals. The signal strength is limited to 1 watt by the FCC, but IEEE specs peg it at 23 to 24 dBm (200-250 mW). One whole watt is 30 dBm in decibels(milliwatt), and you can get an effective gain of 6 dBm (x4) or 4 watts with the antenna:

https://www.air802.com/fcc-rul...

Most wireless receivers operate with signal power (coming into the receiver antenna) in the ballpark of -10 dBm to -100 dBm, where at the low end of that range one is likely down in the noise. That is (translating to power) 100 microwatts down to 10^{-13} watts (10^{-10} milliwatts). If one takes the average cell phone's surface area -- maybe 50 or 60 cm^2 -- and compare it to the radiating solid angle of a transmitter just 50 cm away, it is a very small fraction -- order of 50 to 50^2 or order of 1%. So if one starts with 200 mW and receive it with 100% efficiency around a half meter away, one would be lucky to get more than around 1 mW. USB cell phone wall chargers, OTOH, typically use 1 to 2 W, and still take hours to charge a discharged phone. We could anticipate charging times of order 1000 hours, then, at a mW trickle.

The one place and way this MIGHT work, then, is if one places the phone ON the 802.11 transmitter, just outside of the antenna, close enough that the phone subtends at least 1/10 of its radiation pattern. Assuming a 36 dBm antenna signal strength (4 W), picking up 0.4W, with maybe 0.1 to 0.2 W usable power input after accounting for RMS power and efficiencies, you would be to the point where one might be able to recharge a partially discharged phone in a day.

The big question is then, who would want to do this? A normal 23 dBm transmitter would take weeks to charge the phone even sitting on top of it, and the phone itself would be sucking up the signal you need for your devices to operate. It would still take all day to charge instead of a few hours. It would (probably) cost more than existing "charging pads" that do the same thing and charge your phone wirelessly through induction and an inverter. It would interfere with your 802.11 device and likely reduce its effectiveness at the purpose for which it was intended. It's like "hey, we can build an antenna so that if we put your phone in the microwave oven, it will recharge it really quickly, if we shield the phone and don't mind possibly ruining the microwave". Sure, but why would we, when wall-warts and a cable cost $15, when solar chargers that actually work and don't leach power from 802.11 devices cost less than $100, etc?

The one thing you will NOT be able to do is to recharge your phone from across the room, or keep your phone charged by just sitting in the same room as an 802.11 transmitter. You'd need a phased array of antennae a half-meter wide to get enough directional concentration across a room, and it would make your transmitter pretty much useless as an actual transmitter for 802.11 devices long before that. Even if you pulled ALL the power from a 23 dBm transmitter the numbers just don't make sense for this.