| MEMS micro scanning mirrors,with advantages such as small size,low cost,and multiple scanning modes,have been widely used in laser radar,medical imaging,and free-space optical communication.However,the MEMS micro scanning mirrors currently in the research and development phase still have limitations in terms of flexibility in scanning modes and low driving efficiency due to factors such as size,structure,and fabrication processes.This paper presents the design of a three-dimensional MEMS micro scanning mirror applicable to free-space optical communication,based on a vertical comb structure and electrostatic driving.The proposed MEMS micro scanning mirror features a frameless structure,allowing for not only deflection modes around the x-axis and y-axis but also a vibration mode along the z-axis.Moreover,the x-axis and y-axis can have the same scanning speed,providing increased flexibility in scanning modes.By improving the comb structure in the electrostatic driver of the MEMS micro scanning mirror to an inclined comb structure,the number of comb pairs in a single vertical comb driver is increased from 120 pairs to 148 pairs without changing the area of the vertical comb driver.This enables larger deflection angles under the same driving voltage.The research in this paper focuses on the working principle,simulation,optimization design,fabrication,and testing of the MEMS micro scanning mirror.The main contributions include:(1)Proposing a design scheme for a three-dimensional MEMS micro scanning mirror based on a vertical comb structure and electrostatic driving.The driving principle of the bidirectional driver of the micro scanning mirror is described,and the application of driving forces on the mirror during deflection and vibration modes is explained.The theoretical calculation of the electrostatic driving force in relation to the driving voltage is conducted,considering the deflection angle during mirror deflection and the displacement during mirror vibration without considering damping effects.Various damping mechanisms in the micro scanning mirror system are analyzed,with a focus on simplifying and deriving theoretical models for the sliding film damping and diaphragm damping in the air damping mechanism.The damping ratio and Q-factor are calculated,concluding that the main air damping mechanism in the MEMS micro scanning mirror system is the sliding film damping between vertical combs.(2)Performing modal analysis of the three-dimensional MEMS micro scanning mirror using Ansys finite element analysis software and calculating the resonance frequencies of the first six modes.By varying a single parameter among the undetermined parameters and observing its impact on the resonance frequency while maintaining consistency between the vibration modes and working modes of the micro scanning mirror in the first three modes,resonance frequency versus parameter relationship curves are plotted.The goal is to ensure that the resonance frequencies of the second and third torsional vibration modes are above 700 Hz and maximize the difference between the resonance frequencies of the interfering mode and the third working mode.Based on these premises,appropriate parameters are selected for the micro scanning mirror.Finite element analysis using COMSOL software is employed to simulate thermoelastic damping and anchor damping and calculate the damping ratio and quality factor Q.Combining the theoretical calculation of the air damping mechanism from Chapter 2,it is determined that the main damping mechanism affecting the MEMS micro scanning mirror is air damping,while the influence of thermoelastic damping and anchor damping is negligible.Finally,harmonic response analysis of the micro scanning mirror is conducted,and the corresponding curves are plotted.(3)Developing a complete fabrication process for the designed three-dimensional MEMS micro scanning mirror.The micro scanning mirror layout is designed using L-edit software,and the fabrication of the MEMS micro scanning mirror is carried out according to the process flow.The micro scanning mirror is then packaged.The resonance frequencies of the micro scanning mirror under vertical vibration and deflection modes are measured by applying physical driving signals.Piezoelectric ceramic actuators and a scanning laser Doppler vibrometer are used for resonance frequency detection,and amplitude-frequency response curves are plotted.The measured resonance frequency of the micro scanning mirror under vertical vibration mode is approximately 342.50 Hz,with a quality factor of approximately 29.22.The measured resonance frequency of the micro scanning mirror under deflection mode is approximately 686.09 Hz,with a quality factor of approximately 55.57. |
PDF Full Text Request