[quote=@Prince of Seraphs]
Could you tell me exactly what "Aura powered" means. As far as I'm aware aura is a shield manifested from the soul of the wielder, it doesn't power machinery.
[/quote]

Frankly I'm taking a lot of liberties based on what we know about Penny, but if they created a machine that can produce Aura, than surely they could have made machines that react and possibly be powered by Aura. And not that I'm trying to drag someone else into this conversation, but if I remembered correctly Aura-powered machines is something we're allowing since you said that Ebon's R-Types react to his telepathic semblance, which is an extension of his aura. 

Of course that's also assuming Penny is being powered solely by this aura generating machine, though this is where Gren is different because he was once a normal fuanus and can produce his own Aura (Despite most of his fleshy bits mostly being in his head).

[hider=Spoilers for those who haven't watched the episode]
Which is why an EMP wouldn't work on Gren because if Penny is solely powered by this aura machine, I can see how Pyrhha's magnetism may have effectively "Shut down" Penny's aura, which is what allowed her body to be cut apart. Gren's Aura isn't produced by a machine, but his own "soul", which he still has even if he's missing a large amount of his body. Hence why a magnetic pulse, or EMP, wouldn't adversely affect him the same way it would Penny.
[/hider]