Dennis Siegel, a student at the Unviersity of Arts Bremen in Germany, has created a device capable of charging an AA battery by "stealing" electromagnetic energy out of thin air. The device comes in two versions; one that harvests 50/60Hz signals from mains power, and another one for capturing megahertz (radio, GSM) and gigahertz (Bluetooth/WiFi) radiation.
It's an interesting concept, but the efficiency of the wireless charging strongly depends on the range and orientation of the transmitting source. Siegel mentions the device charges one AA battery per day, but presumably that's only the case when you're sitting next to a huge power substation.
Full details at ExtremeTech.
Dennis Siegel, of the University of Arts Bremen, does away with the charging pad, but the underlying tech is fundamentally the same. We don’t have the exact details — either because he doesn’t know (he may have worked with an electrical engineer), or because he wants to patent the idea first — but his basic description of “coils and high frequency diodes” tallies with how wireless power transfer works. In essence, every electrical device gives off electromagnetic radiation — and if that radiation passes across a coil of wire, an electrical current is produced.