It is difficult for me to be objective because I am opposed to RF wireless charging methods of electronic devices. While the inductive charging solutions make sense, then the use of radio waves for this is a kind of nonsense. But Apple thinks otherwise, or at least wants to try to master this technology. I am very curious how it will come out and whether we will ever find a working solution that charges our smartphone using the surrounding radio waves.
The whole problem is that the energy radiated by the antennas of all devices dissipates very quickly. The power that reaches the receiver decreases with the square of the distance from the transmitter. This means that the Wi-Fi signal received at a distance of 10 meters will be 4 times weaker than at a distance of 5 meters. We also have a lot of regulations which limit the maximum power of transmitted signals. So how does Apple want to overcome all these adversities?
Apple has just patented wireless charging using cellular signals and Wi-Fi.
This is a fairly recent patent application. It is based on a set of dual frequency microstrip antennas that will be used for both charging and data transfer. Apple wants to use all possible mobile systems that work at frequencies between 700 MHz and 2700 MHz (i.e. all LTE, 3G, and 2G bands), Wi-Fi networks operating at 2.4 GHz and 5 GHz bands, and even 60 GHz band used by 802.11ad WiGig standard. So in short, Apple wants to charge smartphones using every supported wireless technology. I have to admit that in this madness is the method, because the energy carried by the radio waves is spreaded as a function of frequency.
Broadband RF wireless charging systems may make sense.
Normal radio receiver works only in the selected frequency channel. For example, if you use a home Wi-Fi network, you do not want to receive signals from your neighbours routers. As a matter of fact, each Wi-Fi router works on another channel so that each other does not interfere. However, in case when we want to transform the radio signal into electricity, then it is no longer a problem. We really want to receive signals from all Wi-Fi routers in order to charge the battery. We also want to receive signals from all base stations, including those which belong to other operators networks.
The innovation proposed here by Apple consists in integration of the RF wireless charging system with the systems used to exchange data. Interestingly, the patent also mentions the possibility of using an antenna beam forming method to increase the efficiency of the charging system. Theoretically, the smartphone would have to determine where the transmitter is, from which you can get the most power. This solution would partly solve the problem of the range and the efficiency of RF wireless charging solutions. Will it work in practice?