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Dynamic Analysis of Microelectromechanical Accelerometers and Designing a Elastic Stopper to Protect Them Against Mechanical Shock

Daeichi, Meysam | 2013

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 45648 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Ahmadian, Mohammad Taghi; Meghdari, Ali
  7. Abstract:
  8. Nowadays, Microelectromechanical accelerometers are of the main parts of inertial navigation systems, and so it is essential to characterize and understand the parameters affecting their performance in order to design them in a way that enables them to survive different practical applications. Mechanical shock is one of the factors existing in almost every industrial environment and cause damages or even permanent failures in MEMS devices. Identifying these damages and protecting the microstructure against them seems inevitable for the designer and engineer of this field.
    In general, approaches of protecting microstructures against mechanical shock are categorized into two major groups. In the first category, the designer tries to design the dimensions of the microstructure in a way that its shock resistance is increased. However, in this method, the performance of MEMS devices would be affected negatively. In the second category, the protection mechanism is designed separately from microstructures. Actually, its main idea is based on the concept of hard stoppers. By limiting the microstructure maximum deflection, stoppers prevent them from undergoing large stresses, but the secondary impact of stopper is another factor which leads to damage the device and hence removing or decreasing this impact is necessary to provide full protection for microstructures.
    In order to do this, firstly, the accelerometer and its stopper are modeled as a distributed model in this study. Then, we derive the equations of motion and investigate the effects of the stopper on the response of microstructure to an applied shock. As our designed stoppers are elastic, the collision time between microstructure and its stoppers would increase, and hence, the secondary impact would decrease. As a result, the device is protected. Moreover, because of the nonlinear stiffness of stoppers, they would stop the microstructure from undergoing large deformation, and therefore, it would not undergo critical stresses.
    In this project, we design a MEMS accelerometer which satisfies basic requirements of automobile application. After designing and analyzing the aforementioned accelerometer, the stopper is designed to protect the microstructure from unallowable shocks. Making use of such a design and protection mechanism, not only the accelerometer performance is not affected, but also it survives unallowable shocks.
  9. Keywords:
  10. Microbeam ; Mechanical Shock ; Microelectromechanical (MEMS)Accelerometers

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