In ET, what does the term "frequency" refer to?

In electromagnetic testing (ET), the term "frequency" specifically refers to the number of cycles per second of alternating current, which is measured in hertz (Hz). In the context of ET, the frequency of the alternating current is crucial because it influences the depth of penetration and the interaction of the electromagnetic field with the material being tested. Different frequencies may be used for various applications and types of materials since the properties of electromagnetic waves change at different frequencies.

For instance, higher frequencies may have less penetration depth, making them more suitable for detecting surface defects, while lower frequencies penetrate deeper into materials, which is useful for detecting subsurface flaws. Understanding the frequency is essential for practitioners to select the appropriate testing conditions that will yield the most accurate results for the specific types of materials and defects they are examining.