Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2005. / Due to an increasing in industrial micromation need in recent years, the use of micro
accelerometers has been highly increased. Consecutively, this has promoted research
activities in this field; capacitive accelerometers also have got high concern at large.
As a research project of the Kentron in South Africa, this thesis deals with a
theoretical model for a one-dimensional micro capacitive accelerometer with U-shape
cantilever beam. The properties of the small angle tilted-plate capacitor have been
analyzed; the capacitance equation and electrostatic force equation of this kind
capacitor have been derived. The sensing element of this accelerometer consists of an
inertial mass connected with two cantilever beams. The vibration modes analysis to
the sensing element was accomplished by using CoventorWare2004's MemMech
module, the result indicates that the main vibration mode can cause the capacitance
change observably and the effect of the other modes to the capacitance can be ignored,
which satisfied the purpose of the design.
In the process of deriving the linearizing acceleration equation, the angle of the
inertial mass caused by the deformation of the U-shape cantilever beam was taken
into account as well as the electrostatic force between the two electrodes, thus the
more precise acceleration linear equation was obtained. The sensitivity equation was
derived through the acceleration linear equation, the relationship between the main
parameters of the system and the sensitivity has been analyzed. The differential
structure of this micro capacitive accelerometer was also analyzed; the linearizing
acceleration equation and sensitivity equation of this kind structure were derived, it
has been proven that the sensitivity of this structure is twice than the normal structure
approximately. The maximum detectable signal was obtained in terms of the fracture
strength of the cantilever beam and the maximum displacement of the inertial mass.
The minimum detectable signal was obtained in terms of the thermal noise analysis.
In the process of the dynamic analysis, the forced vibration produced by the
sinusoidal periodic force and sinusoidal periodic moment was analyzed and the
transient capacitance equation was derived, this proved the system has good dynamic character in theory.
The system was simulated and analyzed by using CoventorWare2004's Saber module.
The initial capacitance analysis indicates the relationship between the voltage and the
initial capacitance, the result is close to the analytic model. The resonance frequencies
analysis indicates that the main dimensions of the sensing element can determine the
resonance frequencies and each vibration mode's sequence, the initial dimensions of
the sensing element was proved reasonable by analyzing. Sensitivity analysis and
Monte Carlo analysis indicate the effect of the sensing element's normal
manufacturing tolerance to the system's frequency is small. Impact of plate curvature
analysis indicates the effect of the inertial mass's deformation caused by the surface
stress to the capacitance is small. Transient analysis obtained the system's transient
displacement curve of six directions and transient capacitance curve in normal terms;
this proved the system has good dynamic character in the simulating environment.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:cput/oai:localhost:20.500.11838/2616 |
| Date | January 2005 |
| Creators | Wang, Lin |
| Contributors | Sun, Bohua |
| Publisher | Cape Peninsula University of Technology |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Rights | http://creativecommons.org/licenses/by-nc-sa/3.0/za/ |
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