Literatures suggest that unlike non-ferromagnetic materials that lead to a decrease in impedance of the eddy current sensor, ferromagnetic materials lead to an increase in impedance of the coil. It is stated that this behavior is reversed at sensor frequencies > 1 MHz. Is it true?
The behaviour of eddy currents in ferromagnetic materials differs from that in non-ferromagnetic materials due to their different magnetic properties. Ferromagnetic materials, such as iron or steel, have high permeability and thus can greatly enhance the magnetic field within the material. This leads to the creation of more substantial eddy currents and the associated magnetic fields, which can cause an increase in the impedance of the detection coil.
As for your question about whether this effect reverses at high frequencies, I should note that the interaction between eddy currents and the magnetic properties of materials is a complex phenomenon that depends on many factors, including the exact composition of the material, the geometry of the object and the coil, and the operating frequency.
The eddy currents are confined to a thinner layer near the material's surface at high frequencies due to the "skin effect". This change in the eddy currents' distribution could alter the coil's response. However, the specifics would depend on the details of the system.
The claim that this behaviour reverses at frequencies > 1 MHz could potentially be correct under certain conditions. But it's hard to make a definitive statement without more context or a specific reference to review. I would recommend consulting the specific literature or source where this claim is made for a more detailed explanation. You could also consult textbooks or review papers on eddy current testing for a more thorough understanding of these phenomena.
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Materials
- Inorganic Materials
- Metals
- Alloys
- Steel