Abstract: The reluctance of the magnetic core (RMC) has a great influence on the Pull-in phenomena of the magnetostatic micro-devices (MMD). Based on Ohm’s law and the energy approach, the Pull-in characteristics of different kinds of MMD are analyzed with the consideration of the RMC according to the condition needed when Pull-in phenomena occurr. The results indicate that in the MMF (magneto-motive-force)-controlled model, the vertical and the point-vortical MMD have the same Pull-in characteristics. r increases linearly from 1／3 to 1 with the increase of m from 0 to 2, with r being the ratio of instable displacement to the initial air gap, and m being the ratio of RMC to the magnetic reluctance of the initial air gap. However in the surface-vertical MMD, r₁ increases gradually from 0.4404 to 0.6910 with the increase of m from 0 to 12, where r₁ is the ratio of the instable angle to the maximal rotating angle with the limiting value of r₁ being about 0.7106. In the flux-controlled model, there is no influence of RMC on the Pull-in phenomena of the MMD. No Pull-in phenomena occur in the vertical and the point-vortical MMD, with r₁ in the surface-vortical MMD remaining constant, of about 0.7106.

Key words: magnetostatic actuated, micro-devices, Pull-in characteristics, reluctance of the magnetic core