“The Effect of Air Gap Width (S) and the Ratio (P1/D2) on .Minimum Projector Focal Length (Fp)min for the Double Pole-Piece Lens- at Costant Excitation (NI)”, IHJPAS, vol. 21, no. 3, pp. 95–111, Sep. 2017, Accessed: Jul. 16, 2024. [Online]. Available: https://jih.uobaghdad.edu.iq/index.php/j/article/view/1412