text: how to increased the depth of penetration of a magnetic field?   when you wrap a coil of wire around an iron bar and pass an electrical current through the bar, you create an electromagnet that is capable of temporarily aligning the iron atoms in the bar.  perhaps all the atoms are aligned a little.  by increasing the current or adding additional turns to the coil or both the strength (flux) of the electromagnet can be increased and the alignment of iron atoms also increased until saturation when maximum strength is obtained.  rather than increasing penetration, this is likely more like increasing strength at depth (penetration).