Electric field strength from AC conducting wire in form of a loop along z-axis?
If same amount of Q is flowing in the loop wire as out of it (I_in = I_out), then net charge of the loop is Q=0 and there is no E-field (But there is a H/B-field). 

There can only be Q in the wire if I_in != I_out for some time. Then the loop wire is behaving like a capacitor and there is some Q != 0 left in the loop of wire.

The site you linked shows a setup where there is "a ring of charge". So there is no current I involved. (There maybe was a current I_in to bring that charge Q onto the ring).