Abstract
High-Frequency Eddy Current Techniques (HFEC) refer to special Eddy Current Techniques which work in the frequency range of around 100 kHz to 100 MHz. The techniques are based on the normal Eddy Current technique. Using a coil, an electromagnetic field is induced in the surface of the component, which has to be evaluated. The electromagnetic field induces circling currents, the so called eddy currents. Depending on the electrical properties of the material in the area of this exciting field, a second electromagnetic field is induced, which is directed perpendicular to the exciting field. By analyzing the complex impedance of the measurement coil, variations of the electric properties of the medium can be analyzed. In the higher frequency range of HFEC, special sensors and hardware filters must be used. HFEC is better suited for applications in materials with very low electrical conductivity, such as titanium alloys, nickel-based superalloys and similar materials, Carbon composites, ceramic composites, and polymers and lossy dielectrics may be evaluated as well. With HFEC, it is possible to reach an improvement in the measurement effect as well as better lateral resolution with matching penetration depths for these applications in comparison to lower eddy current frequencies. Additionally, the measurement effect is not only influenced by inductive processes in the area affected by the eddy currents but also by capacitive effects and an increase in displacement currents, which increases the gathered information as well. Regarding the applications, measurement process, sensors and hardware, different specifics must to be considered.
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Hillmann, S., Schulze, M.H., Heuer, H. (2018). High-Frequency Eddy Current Techniques. In: Ida, N., Meyendorf, N. (eds) Handbook of Advanced Non-Destructive Evaluation. Springer, Cham. https://doi.org/10.1007/978-3-319-30050-4_49-1
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DOI: https://doi.org/10.1007/978-3-319-30050-4_49-1
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