Frequency ratio, f/fg, can be defined as:

Frequency ratio, defined as f/fg, is specifically the ratio of the test frequency (f) to the limit frequency (fg). This concept is crucial in Eddy Current Testing (ET) as it allows inspectors to understand the relationship between the frequency at which they are testing and the limit frequency that characterizes the maximum frequency that can be used without loss of sensitivity to specific material properties or flaws.

The limit frequency essentially marks a threshold beyond which the testing technique may not adequately respond to the types of defects being assessed in the material, and the test frequency is the frequency applied during the actual inspection process. By using the frequency ratio, one can analyze the effectiveness of the test at different frequencies and how it relates to detection capabilities, depth of penetration, and material properties.

Therefore, understanding this ratio aids technicians in optimizing their testing parameters to achieve accurate and sensitive assessments of the material under investigation.