The AL-value varies greatly depending on gap width, so it is effective for the advance study of a design to accurately obtain the AL-value dependency on the gap width (air gap versus AL characteristics) for the geometry of a choke coil by using a finite element analysis (FEA).
This Application Note explains a case example that obtains the air gap versus AL characteristics of a choke coil.
Air Gap-AL Characteristics
Fig. 1 demonstrates the relationship between the gap width and the AL-value. This makes it possible to obtain the AL-value from the gap width and estimate the number of turns to achieve the specified inductance.