In the figure below, from a textbook explaining Eddy Currents, a pulse of current is sent and generates a magnetic field $ B_0 $. The magnetic field produces a change in flux in the metal box that generates an electromotive force, driving a current and therefore generating another magnetic field $ B' $
However, I don't understand how this induced magnetic field generates another current $ I' $ in the opposite direction in the receiver coil of the metal detector.