Tham khảo tài liệu 'an introduction to mems engineering - nadim maluf and kirt williams part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 160 MEM Structures and Systems in Photonic Applications The Lorentz force is planar to the mirror for the normal field Bn. The Lorentz force is normal to the plane of the mirror for the radial fringing field Br. Figure a An illustration of the rare-Earth magnet and the four independent drive coils. The magnetic flux density outside of the magnet has a normal component Bn and a fringing radial component B . b The normal magnetic component interacts with a counterclockwise current to induce a Lorentz force that is in the plane of the coils. The radial component of the magnetic field results in a force that is normal to the plane of the coil. Only the fringing radial component of magnetic field Br contributes to the angular and piston vertical displacement of the micromirror. A counterclockwise current in a drive coil interacting with the radial field results in a Lorentz force that is normal to the plane of the coil and acting to pull the coil towards the magnet see Figure b the peripheral portion of the coil contributes to the force whereas the radial portions have little effect. Switching the polarity of the current results in an opposite force that pushes the coil away from the magnet. It thus becomes evident that two adjacent coils carrying currents in opposite directions induce a torque around an axis of symmetry that divides them. Torques of arbitrary magnitude can be generated around the two axes of symmetry by the proper selection of the current direction and magnitude in each of the coils. Furthermore an additional vertical piston motion can be induced by driving all four coils simultaneously with a current in the same direction. For example a clockwise current in all coils moves the mirror away from the surface of the magnet. The differential drive of the coils provides an added benefit the developed torque stays relatively constant throughout the full range of motion of 5 . As the mirror tilts the side that is closer to the magnet develops a .
