The article should have said: &quot;by magnetic induction&quot;.  An AC current driven electromagnet induces a current in the metal, the induced current in the metal also has a magnetic field (basic physics), and it is this magnetic field that is then used to &quot;sort&quot; the conductors (metals) from the non-conductors (non-metals).<p>But then, the article was likely written by someone lacking an engineering&#x2F;physics background, and so &quot;extracted by magnets&quot; was likely as much as they could comprehend of the process.