In eddy current testing, what does an increase in the diameter of the testing coil affect?

In eddy current testing, an increase in the diameter of the testing coil leads to a decrease in current density. This phenomenon occurs because as the coil's diameter increases, the area through which the current is distributed also increases. Current density is defined as the amount of electric current flowing per unit area of a conductor. Therefore, with a larger area but the same amount of current flowing, the current density will be lower.

Moreover, larger coils tend to contain and generate eddy currents over a larger area, which can contribute to a reduction in the intensity of the generated magnetic field at specific points compared to smaller coils. Consequently, this effect relates directly to the distribution of eddy currents in the material being tested, as well as the resolution of smaller flaws, which may be influenced by the coil's diameter.

Understanding the relationship between coil diameter and current density is crucial in designing an effective eddy current testing setup. A balance needs to be struck between coil size and the desired depth of penetration and resolution of detection, which is fundamental to achieving accurate testing results.