Electromagnetic Nondestructive Testing of Cylindrically Layered Conductors

We extend a previous analysis for the series impedance of a long solenoid to allow for the cylindrical layering of the encircled conductor. The results are discussed in the context of nondestructive testing of steel ropes that may have external or internal corrosion. It is shown that even an internal layer of reduced conductivity and permeability will be detectable if the frequency is sufficiently low to permit penetration of the primary field.