In eddy current testing, how is the specimen coupled to the test coil?

In eddy current testing, the specimen is coupled to the test coil primarily through the coil's magnetic field. When an alternating current flows through the test coil, it generates a varying magnetic field that interacts with the conductive material of the specimen. This interaction induces eddy currents within the material. The strength and characteristics of the eddy currents are influenced by the conductivity, permeability, and geometrical configuration of the specimen.

This coupling is essential for effectively detecting surface and subsurface flaws, as the induced eddy currents change in response to any variations in the material properties. The feedback from these changes is utilized to assess the integrity of the specimen being tested. This makes the coil's magnetic field the fundamental mechanism for coupling the test equipment with the specimen, allowing for accurate measurements and evaluations during testing.