Micro-electromechanical systems (MEMS) are micro-devices or systems that integrate micro-structures, micro-sensors, micro-actuators, and corresponding signal processing control circuits into interfaces, communications, and power supplies. In the micro-actuator, the electrostatic motor is usually the first choice. It is responsible for converting the electrical signal into mechanical motion. The size and performance of the volume of the electrostatic actuator directly affect the overall quality of the MEMS. The development of the electrostatic motor as the key component of the MEMS More and more people are paying attention.
At present, there are many researches on structural analysis of MEMS devices, and there are few analysis on static electricity. The flat electret micro-motor analyzed in this paper is different from the previous silicon micro-electrostatic motor. The rotor is made of PTFE electret material. The surface of the rotor is stored with a surface charge, and the charge decay time constant is much longer than the period of formation of the electret. For micron-sized pitches, smaller voltages can generate larger electrostatic forces. In order to optimize the design of the electrostatic motor, finite element analysis of the electrostatic field between the stator and the rotor of the micromotor is necessary.
By using the ANSYS program to analyze the electrostatic field of the three-dimensional solid model of the electret electret micromotor, the electric field energy of the entire system and the static driving force of the rotor are obtained.
1 The principle of electret micromotor shows flat electret micromotor, (b) is 20Um in Pro/E shaft diameter, 1Um in aluminum stator thickness, and h=0.5Pm in electret rotor thickness; its relative Dielectric constant £;. = 2.1; air body disc outer radius is 175Um; disc thickness is 5Um; air gap between stator and rotor is di = 1.25 from m; air gap between stators is center = 3Um; upper and lower stators of aluminum are applied between The square wave voltage with a peak value of V=500V; the force per unit length of the surface charge rotor on the surface of the electret rotor is 匕 (whose direction is perpendicular to the rotor radius). The force F per unit length can be seen; it is a quadratic function of the voltage V.
2 3D Finite Element Analysis 2*1 Creating a Basic Model Because the motor structure is more complex, Pro/E's powerful 3D modeling capabilities are used to draw and assemble parts, and finally, IGES format files are formed.
2.2 Setting the Unit Type The unit type determines the degree of freedom of the attachment (displacement, corner, temperature, etc.).
Many units also have some cell options, such as cell properties and assumptions, print output options for cell results, and more. The work of this article belongs to the electrostatic analysis of the microscopic field, so the electrostatic three-dimensional element SOLID122 is selected. 2.3 Definitions of material properties Material properties are constitutive properties unrelated to the geometric model, such as the amount of Young's film, relative permittivity, etc. Although the material properties are not tied to the element type, because the material properties are needed to calculate the element matrix, ANSYS lists the appropriate material properties for each element type for the user's convenience.
Depending on the application, the material properties can be linear or non-linear. Similar to the unit type, a variety of materials can be defined in an analysis, and a material number is set for each material. It is easy to know the relative permittivity of the air body is 1; the rotor is the electret material, and the relative permittivity is 2.1. 2.4 Grid division For the electrostatic field analysis, it is not necessary to perform every conductor in the grid division. Divided because they are all isopotential bodies. Therefore, it is only necessary to mesh the dielectric and air bodies that can be reached in the electric field. In addition, the rotor is made of PTFE electret material, and the surface charge density needs to be applied to the upper and lower surfaces thereof. Therefore, the rotor needs to be meshed. Grid diagrams such as
Flat electret micro rotor grid. 5 Load the square wave voltage of 500V peak on the node of the stator surface, add the surface charge density of 6.4x10-5UC/m2 directly on the upper and lower surfaces of the rotor, and then add the Maxwell force flag on the surface; A zero voltage is applied to the node on the outer surface of the cylinder of the air body so that the loading is completed.
2.6 Solving 2.6.1 Selecting the Solver After all the preprocessing, meshing, applied loads, and control loads have been completed, the program is assigned to the solver before the program enters the analytical solution. The calculation method used.
The incomplete Joulev conjugate gradient method (ICCG) is more stable for bad matrices, and this method is faster than direct solution. So, this time select the ICCG solver.
Set to start solving.
2.7 Post-processing When the calculations are complete, you can view the results through the postprocessor. Click GeneralPostproc in the main menu to go directly to the generic post-processing module (POST1) and export the result list.
3 Results Analysis Through ANSYS analysis, the electric field energy of the entire system and the electrostatic driving force of the rotor were obtained. Change the peak value of the square wave voltage and compare the derived electrostatic force Fz with the theoretical value, see Table 1. Table 1 Fz theoretical value and calculated value Voltage between stators (V) System Electric field energy calculated value (pJ) (Continued on page 85) Table 1 Experimental data for 1 and 2 pressure sensors 1 Pressure sensor 2 Pressure sensor Pressure center wavelength Wavelength drift Pressure center wavelength Wavelength drift 4 Conclusion Studies and experiments have shown that this type of pressure sensor can measure the lateral pressure of an optical fiber. Therefore, The size of the pressure acting direction is very small and can be made into a miniature pressure sensor with a small thickness. And compared to similar sensors have a very high pressure sensitivity. At the same time, this new type of grating pressure sensor is easy to package and can be quantitatively machined. The sensor has the advantages of compact structure, light weight, small size, high accuracy, good repeatability, etc. It can be applied to all kinds of pressure measurement and sensor size. And demanding application environments.
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