All of this ^^^
Wireless charging tech has been in a bit of a of a PR pickle due to the fact that around the same time (~2010) that the industry introduced a couple of inductively coupled protocols (the main one that has become ubiquitous is Qi, there’s also a PMA and maybe a couple others) for allowing different manufacturers equipment (chargers and devices) to cooperate there were also announcements in distance charging. What has caused widespread confusion is around that same time some bright folks at M.I.T. demoed a compelling and impressive power-transfer-over-distance using resonant techniques. I think that helped boost the marketing of the tech, but also created some confusion over what ranges could be expected.
Resonant coupling of energy is more like radio transmission - it can traverse long distances of space. Unless bean-forming techniques are employed to aim at the target (5G and some new Bluetooth specs do this) - the energy dissipates more. The article linked below gets into some of the resonant system physics - it’s less efficient overall than inductive.
Inductive coupling uses closely linked coils and is basically an air-core transformer, it’s what is in most phones these days. In best case conditions it can be very efficient but it’s super picky about alignment because the Rx and Tx coils need to have their inner diameter apertures mostly aligned for the fields to link/harmonize. These are usually around the size of a dime, any substantial offset lessens the efficacy. The coils need to be very low impedance - Litz wire is often used to reduce skin effects.
Yeah, Qi uses in-band signalling - toggling the transmitted electrical field itself - to communicate between the charger and device and set up the “contract” between them in order to transmit the appropriate amount of power and shutdown if power is leaking into some other unintentional receiver. Totally agree that sort of fine grained control is hard to imagine in the system in the linked article.
