What you are referring to is demodulation of AM signals in much the same way a crystal receiver operates. That requires a fairly strong signal and a nonlinear device, i.c. a diode formed by two different metals in your brace, a germanium diode (crystal set) or iron/rust junctions in barb wire, which also exhibits this phenomenon.
The article is about a modulation of a pre-existing radio wave, similar to a spy device the Russians used during the Cold war. A difference is that the Russians transmitted a dedicated carrier to be modulated, while this technique piggybacks on existing radio waves.