Microsilicon luminous flux switch controlled by means of magnetic field

The construction of a silicon beam which is used as a optical switch was presented. The investigated beam consists of three layers: on the silicon base the iron layer is put and it is followed by the aluminium layer. The change of the external magnetic field intensity causes the beam end displacement as well as the change of the luminous flux reflection angle. The influence of the magnetic transducer parameters as well as the field intensity on the luminous flux reflection angle are analysed. The optical system which is steered by the magnetic field was described. 1 THE CONSTRUCTION OF THE OPTICAL SWITCH Microsilicon structures are commonly applied in the sensors or actuators in which piezoelectric, electrostatic, electromagnetic and magnetic transducers are used (Ciudad, 2004). The scheme of the magnetic transducer with the silicon microbeam is shown in Fig.1. Figure 1: The scheme of the magnetic transducer with the silicon beam The structure with the micro-mirror on the surface (aluminium layer) can be used to the luminous flux switching in scanners, display units as well as in the optical path switchers for communication (Cho, 2002). Figure 2: The cross section of the microstructure with the monocrystalline silicon, Si <100>, base and the magnetic (Fe) and metallic (Al, Cu ) layers The beam structure we studied is shown schematically in Figure 1 and 2 (Wagner, 1992). It consists of a narrow silicon beam (monocrystalline silicon <100>) with of thin magnetic layer (Fe) and metallic layer (mirrorAl). A planar coil was used for the magnetic field generation (Fig.1, Fig.2) (Ripka, 2001). If a uniform magnetic field is applied to this structure, a pure moment without a translational force is induced. The pure moment or torque generated by the magnetic transducer rotates the beam end through an angle φ (Fig.3). 301 Golebiowski J. and Prohun T. (2005). MICROSILICON LUMINOUS FLUX SWITCH CONTROLLED BY MEANS OF MAGNETIC FIELD. In Proceedings of the Second International Conference on Informatics in Control, Automation and Robotics, pages 301-306 Copyright c © SciTePress 2 THE ANALYSIS OF THE LUMINOUS FLUX REFLECTION ANGLE IN THE TRANSDUCER CONTROLLED BY MEANS OF THE MAGNETIC FIELD The beam with the thin ferromagnetic layer is analysed.. It is assumed that the material is isotropic and homogenous as well. The torque generated under the influence of the external magnetic field can be expressed as (Judy, 1997) : α sin ⋅ ⋅ ⋅ = × = H M V H M V Tfield r r (1) where M is magnetization vector, α is an angle between the magnetization vector and the external field intensity and V is the magnetic material volume. The magnetic field direction is normal to the normal beam axis as it is shown in Fig. 3. The torque formed at the external field H causes the magnetization vector M rotation and the rotation angle towards the normal beam axis is equal to β. When β angle increases the field of the magnetic anisotropy increases as well (Tumanski 1997) according to the equation: s anis M K H ⋅ = 2 (2) where Ms is the saturation value of the magnetization and K is magnetic anisotropy constant. The anisotropic field generates the torque Tanis which shifts the magnetization vector M towards the beam axis. The beam is under the influence of the torque of opposite sense -Tanis. As a results the beam dislocation is observed. For the silicon beam with the ferromagnetic layer and the elasticity coefficient kmech the dislocation generates the mechanic torque which counteracts the magnetic torque -Tanis and is equal to: φ ⋅ − = mech mech k T (3) At the equilibrium state the absolute values of torques are equal. Figure 3: The beam deflection under the influence of the magnetic field H. (Judy, 1996) The investigated beam consists of three layers: monocrystalline silicon, iron and aluminium. The analysis is carried out basing on the following assumptions: For the crystallographic orientation <100> silicon is an orthotropic material with: Young’s modulus E = 1.31*10N/m, Poisson ratio ν = 0.0625, Density ρ = 2330kg/m. The iron layer parameters are equal to: Young’s modulus E = 2*10N/m, Poisson ratio ν = 0.29, Density ρ = 7870kg/m. The aluminium layer parameters are equal to: Young’s modulus E = 0.7*10N/m, Poisson ratio ν = 0.33, Density ρ = 2700kg/m. The model allows to create the dislocation net which reflects the influence of the external magnetic field on the transducer magnetic layer. At first the density of magnetic energy accumulated in the ferromagnetic layer is calculated. It consists of the external magnetic field energy and the energy of the magnetic anisotropy field. The value of the accumulated energy is used to the determination of the force which influences the beam and causes its displacement. Regarding the existence of ferromagnetic layer anisotropy the finite element and the coupling field methods as well as FEMLAB program are used in the calculations. As the FEMLAB programme uses the coupling field method it is possible to take into accounts a variety of physical phenomena and their interactions. The finite element method MES allows to simulate the miscellaneous mechanical structures including ICINCO 2005 INTELLIGENT CONTROL SYSTEMS AND OPTIMIZATION