The method used to generate eddy currents in a test specimen by means of a coil can most closely be compared with the action of a:

The method of generating eddy currents in a test specimen using a coil is most closely compared with the action of a transformer because both processes involve the principle of electromagnetic induction. In a transformer, alternating current flowing through a primary coil generates a magnetic field that induces a current in a secondary coil. Similarly, when an alternating current flows through the coil used in eddy current testing, it creates a changing magnetic field which penetrates the test specimen, inducing eddy currents within it.

These eddy currents flow in closed loops within the conductive material, much like how the induced current flows in the secondary coil of a transformer. Additionally, both transformers and eddy current testing utilize Faraday's law of electromagnetic induction, highlighting their functional similarity.