before running out of power at 2am.
Figure 1: The basic WPT process and the logos of the competing inductive standards.
The main principle Tesla seems to have exploited in his demo was based on a static electric field (electrostatics). Whereas in modern WPT, we typically use a time-varying magnetic field — which then induces an electric field (voltage) at some distance in a copper coil. We collect the electrical energy from the coil and condition it to charge our phones. This latter principle was discovered by Michael Faraday way back in 1831. It is our familiar law of magnetic induction, used in every single transformer made. It was the same principle Tesla used to create the high initial voltage and resulting steady electric field in the first place, but perhaps not the principle, or reason, behind the observed glow. It’s not for no reason that Albert Einstein kept pictures of Michael Faraday, Isaac Newton and James Maxwell in his study room — no one else’s.
If we think about it, we do transmit a huge amount of energy between the two adjacent coils of any transformer quite effortlessly. And we do it “wirelessly”, i.e. without galvanic contact between the two distinct coils (before 1831 that too must have sounded like science fiction). The problem however is, the physical distance between the transmitting and receiving coils (windings in this case) is very small, and there is also usually a shared “magnetic core” to channel the magnetic flux more effectively between them. So, physically speaking, this is not a practical configuration to charge our cell phones with. Naturally, we don’t want to be seen walking around with a lump of ferrite