A method of inspecting a material comprising: producing at least one eddy current excitation in a material under test; sensing said at least one eddy current excitation in the material under test; wherein the method comprises using a low cross-correlation coded spread spectrum to produce said at least one eddy current excitation, and using a correlation technique to make a determination of amplitude and phase of the sensed eddy current excitation; wherein the method further comprises using the determination to make an assessment of the material under test.