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Title: Design and analysis of a levitated proof mass accelerometer
Author: Houlihan, Ruth
ISNI:       0000 0001 3582 2846
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2004
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This work describes the design, analysis and development of a novel MEMS capacitive accelerometer. The device is based on the principle of electrostatic suspension of the proof mass. As such, multi-axial sensing with comparable sensitivities in all degrees of freedom is achievable. The levitated proof mass is controlled by incorporating it into an electromechanical ∑∆ modulator loop, for which the proof mass itself assumes the role of the double integrator. A thorough analysis of the dynamics, electrostatics and control of the accelerometer is presented. Being untethered, the dynamics of the proof mass are completely described by the squeeze film damping coefficients. These are determined, for both transverse and rotational motion of the proof mass, using finite element modelling. Analytic models are derived to describe the electrostatic sensing and force feedback operations. The equations are based on a Taylor's series and are validated using the finite element method. The electrostatic fringing fields and passive electrostatic restoring forces that they produce are also modelled analytically. Based on the extracted damping coefficients and derived analytic models, a five degree of freedom, system level model was developed to validate the concept of electrostatic suspension of the proof mass and to identify the key parameters defining the performance of the sensor. In particular, the effects of ambient pressure, multi-axial operation, damping holes, electrode design and controlling electronics on the performance of the sensor is established. Several different electrode configurations were designed and optimised. A fast generation prototype of the device was fabricated and initial measurement results are presented. The design and fabrication process for the second generation prototypes is also presented.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available