When testing magnetic materials in a magnetic field, increasing the field strength will result in:

When testing magnetic materials in a magnetic field, the relationship between the applied magnetic field strength and eddy current penetration is complex. Initially, as the magnetic field strength is increased, the penetration of eddy currents into the material tends to decrease. This is due to the skin effect, which causes higher frequency currents to flow nearer to the surface of the conductor as they are repelled by the magnetic field.

In this scenario, there is a transition point where the material becomes saturated. When the magnetic material reaches a saturation point, eddy current penetration begins to increase again. This effect occurs because the magnetic permeability of the material becomes nearly constant after saturation, allowing for more eddy current flow deeper into the material.

Therefore, the correct answer captures the essence of this behavior: there is a decrease in eddy current penetration as field strength increases up to a certain point (minimum value), after which, upon reaching saturation, the eddy current penetration starts to increase again.