Approximating of the Axial Magnetic Field Distribution By A Modified Form of Grivet-Lenz Model

A modified mathematical expression of the Grivet-Lenz model has been put forward for approximating axial magnetic flux density distribution. The main feature of this form is that it’s more flexible to spreading along the optical axis. Influence of the optimization parameters arises from the suggested expression on the objective focal properties and the reconstructed polepieces are investigated in details. Results have been shown that as the number of the optimization parameters increased the degree of freedom to handling the model increases. Further more, as the parameter lead to localizing the field its properties become better.