As the test frequency increases while the field strength remains constant, the surface eddy current density:

As the test frequency increases while maintaining a constant field strength, the surface eddy current density increases due to the relationship between frequency and the generation of eddy currents. In simple terms, higher frequencies induce changing magnetic fields at a faster rate, which results in more rapid oscillations of the magnetic field lines and a greater interaction with the conductive material.

This phenomenon can be understood through the principles of electromagnetic induction. According to Faraday's law of electromagnetic induction, the induced electromotive force (EMF) is proportional to the rate of change of the magnetic field. Therefore, as the frequency increases, the induced EMF and, consequently, the resulting eddy currents increase as well. The higher the frequency, the more energy is imparted to the electrons in the conductor, leading to a greater density of eddy currents near the surface of the material.

Moreover, when considering the skin effect – which is the tendency of alternating current to distribute unevenly in a conductor – increasing frequency reduces the depth of penetration of the currents into the material. This causes the currents to be concentrated more significantly near the surface, further increasing the surface eddy current density.

Overall, with a constant field strength, the interaction between the higher frequency and the material leads to an increase