Thickness measurement of metal coating above moving conductive plate by rectangular coil and electromagnetic method

The electromagnetic NDT method plays an important role in a nondestructive material test. In testing conductive structures, the rectangular coil is more useful than a circular coil due to its asymmetric characteristic. One rectangular coil places above and parallel to the moving conductive plate with metal coating, serving as exciting and sensing coil to measure the thickness of the metal coating. The accurate theoretical expression of the coil impedance variation is derived by analytical method, and the influences of the excitation frequency and the moving speed of conductor to the coating thickness measurement are analyzed. The analytical calculation results are verified with the implementation of finite element method.