Fig. 2.

(a). COMSOL simulation of bi-pole structure coils with and without application of shield arrays (Gray colored objects are copper wire coil and copper rings shield array, and blue parts are the iron core and frame of the coil; however, its conductivity is adjusted to zero since the real experimental setup is using laminated iron sheets to inhibit eddy current in magnetic materials.); (b). The shield formation consists of two layers of ring arrays. Each layer has 6 stacks of rings arranged in a way to gradually reduce the formation opening; (c). Magnetic field distribution along x direction at a cut line 5mm above the pole without shield and field distributions at a cut line 5mm above the shield surface with the diameter of the shield formation opening of 8mm, 9mm, 10mm, 11mm and 12mm.