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Tham khảo tài liệu 'micro electro mechanical system design - james j. allen part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Scaling Issues for MEMS 131 V AAAAAAAAAAAAAA p - permability B a Electric Field b Magnetic Field FIGURE 4.11 Electric and magnetic fields in a region of space. One way to make this assessment of electric vs. magnetic fields for actuation is to consider the energy density of an electric Uelectric and a magnetic Umagnetic field for a region of space at the appropriate operational condition Figure 4.11 . Equation 4.25 and Equation 4.26 define the electric and magnetic field density respectively where is the permittivity and p is the permeability of the region that contains the electric field E and the magnetic field B. For purposes of this assessment the free space permittivity 0 8.84 X 10-12 F M and the free space permeability p0 1.26 X 105 H M will be used. The maximum value of the electric field E and magnetic field B will be limited by the maximum obtainable operational values. The maximum obtainable electric field is at the point just before electrostatic breakdown. This breakdown occurs when the electrons or ions in an electric field are accelerated to a sufficient energy level so that when they collide with other molecules more ions or electrons are produced resulting in an avalanche breakdown of the insulating medium high current flow is produced. For air at standard temperature and pressure the electric field at electrostatic breakdown in macroscopic scale gaps between electrodes i.e. 10 pm is Emax 3 X 106 V M. 1 E2 2 Uelectric 4.25 Umagnetic 2 1 B2 4.26 The maximum obtainable magnetic field energy density is limited by the saturation of the magnetic field flux density in magnetic materials. In materials the spin of an electron at the atomic level will produce magnetic effects. In many 2005 by Taylor Francis Group LLC 132 Micro Electro Mechanical System Design FIGURE 4.12 An example a magnetization curve. materials these atomic level magnetic effects are canceled out due to their random orientation. However in ferromagnetic materials adjacent atoms have a .
