Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2005 / Perhaps more popular than the piezoresistive type are the capacitive type of micromachined accelerometers. The capacitive accelerometer has many fine characteristics, such as simple structure, high sensitivity, strong ability of resisting disturbance, fast dynamic response and so on. It can also work under abominable condition. So it is occupying an important status in the technology of electronical measurement and being used in many kinds of metrical systems. In this paper, the capacitive accelerometer (CA) we will introduce and design is a parallel plate CA with crab-shape. It will detect the acceleration signal by the change of distance between two electrode plates, and its design standard came from the industrial requirements ofKENTRON Company. The whole paper can be divided into four main phases-introduction, study, design and analysis. At first, we have introduced the purpose and background of this thesis, and then the study and the discussion of relative literature. The content of these articles is mainly about the basic principle, types and applications of micro-sensors and this information will be very helpful to the design and analysis ofmy own CA. The course of design is primarily structure design. The main structures of CA are parallel plate structure and cylinder structure. The parallel plate structure is chosen for our CA after we did the comparison of performance and technique of making between these two types of structures. We use the concentrative mass as the top electrode plate and four beams are connected on the two sides of the plate separately.

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Zhang, Yu. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 55-60). / Abstract also in Chinese. / Abstract --- p.i / Acknowledgement --- p.iii / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Background --- p.1 / Chapter 1.2 --- Aim of Research --- p.2 / Chapter 1.3 --- Thesis Organization --- p.3 / Chapter 2 --- Literature Review --- p.4 / Chapter 2.1 --- Carbon Nanotubes in MEMS Devices --- p.4 / Chapter 2.1.1 --- CNT Integration and CNT sensors --- p.4 / Chapter 2.1.2 --- Prior Work in CMNS --- p.6 / Chapter 2.2 --- Overview of Motion Sensors --- p.7 / Chapter 2.2.1 --- Technology Overview --- p.7 / Chapter 2.2.2 --- Categories and Working Principles --- p.9 / Chapter 2.2.3 --- Application --- p.13 / Chapter 2.3 --- Thermal Convective Motion Sensors --- p.14 / Chapter 2.3.1 --- Micro Thermal Flow Sensors --- p.15 / Chapter 2.3.2 --- Research on Thermal Convective Motion Sensors --- p.17 / Chapter 2.3.3 --- Working Principle and Performances --- p.20 / Chapter 3 --- Design and Setup --- p.25 / Chapter 3.1 --- Methodology --- p.25 / Chapter 3.1.1 --- Research Method --- p.25 / Chapter 3.1.2 --- Critical Questions --- p.26 / Chapter 3.2 --- Sensor Chip Design and Fabrication --- p.27 / Chapter 3.2.1 --- Sensor Chip Mask Design --- p.27 / Chapter 3.2.2 --- Fabrication of Sensor Chip --- p.29 / Chapter 3.3 --- Sensor Prototyping --- p.30 / Chapter 3.3.1 --- CNT Deposition --- p.30 / Chapter 3.3.2 --- Sensor Building --- p.32 / Chapter 3.4 --- Setup of Experiment --- p.34 / Chapter 3.4.1 --- Source and Measure --- p.34 / Chapter 3.4.2 --- Acceleration Production --- p.35 / Chapter 4 --- Experiments and Results --- p.39 / Chapter 4.1 --- Hypotheses Verification --- p.39 / Chapter 4.1.1 --- Thermal Detection Using CNT --- p.39 / Chapter 4.1.2 --- Local Heating & Sensing --- p.40 / Chapter 4.2 --- Tilting Test --- p.42 / Chapter 4.2.1 --- Test Result --- p.42 / Chapter 4.2.2 --- Result Discussions --- p.43 / Chapter 4.3 --- Vibration Test --- p.45 / Chapter 4.3.1 --- Test Result --- p.45 / Chapter 4.3.2 --- Result Discussions --- p.52 / Chapter 5 --- Conclusion --- p.53 / Bibliography --- p.55

Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2005 / Having simple structure and high sensitivity, micro accelerometer is a type of popular transducer used to measure the acceleration in a great variety of conditions. The bridge-type micro accelerometer is a typical micro accelerometer and has many types. As one of research project of Kentron in South Africa, the thesis presented here analyzes the bridge-type capacitive nticro accelerometer (BTCMA) and the bridge-type micro accelerometer with two piezoelectric thin films read-out (BTPMA). In this thesis, the similar structures are used on BTCMA and BTPMA For proving the fundamental mode of the structure can measure acceleration and utilizing the structural and electric characteristic to avoid the effect of higher modes, the program CoventorWare for nticro-electric-mechanical system (MEMS) design and analysis is used here to analyze the modes of these two structures, The two group piezoelectric thin films of BTPMA can be connected in serial or parallel configurations. Integrating piezoelectric effect method, strength method and energy method, the analytical analysis of these two configurations has been done with particular emphasis on the elastic characteristics of the thin films. The analytical formulas of transducer, sensitivity, resonance frequency, noise, quality factor, ntinimum detectable signal and maximum detectable range are obtained. According to the comparison results between these two configurations, the charge output in parallel configuration is a little more than that in serial configuration and the sensitivity in serial configuration is much higher than that in parallel configuration. Finally, a calculation of certain practical nticro accelerometer size is used to prove the above conclusions. On the base of capacitance theory, strength method and energy method, the analytical analysis of the BTCMA has been done in this thesis.

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.

M.Ing. / Measurement of acceleration is of importance for several applications such as impact tests and navigation. The design and manufacture of a symmetrical piezoresistive accelerometer, which can measure accelerations up to 60 000 g, are presented in this work. Various accelerometers are discussed and compared. The design of an accelerometer is an interdisciplinary activity which requires knowledge of the mechanical and electronic properties of materials as well as electronic signal processing. Computer design aids such as finite element analysis and semiconductor process modelling are used in this work to optimize first order designs. Since accelerometers with large dynamic range must be small in size in order to cause the minimum disturbance of the measurand, micromachining of silicon is used to manufacture extremely small devices. A substantial part of this work deals with the different materials and methods used in the manufacturing process. Since there is an inevitable spread in the parameters of the accelerometers, each one requires calibration. A test facility was developed to test and calibrate accelerometers up to 20 000 g. Because shock impulse response is determined by the test facility, a Fourier-transform is used to compute the frequency response of the accelerometer. The result of this work is the development and manufacture of an accelerometer with a mass of approximately 1 mg. The extremely small size and mass makes it very useful for measuring high accelerations.

M.Ing. / A two-axis gimbal system in the form of a pitch-roll gimbal and a motion simulating platform were developed to extend the capability of an existing ground-to-air prototype gun-turret. The objective was to stabilize the line of sight (LOS) of the gimbal system despite disturbances introduced by the motion simulating platform in real time. The main sensor used for the stabilization is a two-axis accelerometer which was mounted directly on the inner gimbal (roll gimbal) to form a direct-mass stabilization architecture. The stabilization control algorithm was designed and executed in the Labview® environment on a PC, and the accelerometer data is used to drive the two DC motors used as the actuators of this control system. The design of the motion simulating platform was based on a simplified Stewart-Platform and uses pneumatic cylinders as actuating limbs. All sensors and actuators in the motion simulating platform and the gimbal system are integrated with the National Instrument’s CompactRio® and Labview®. The result was a simple stabilization controller capable of achieving basic stabilization of the LOS. However, the hardware and software of this project are capable of more complex control algorithms and that forms the bulk of the suggestions for further studies.

This dissertation presents the design and development of a mixed-signal low noise second-order integrated circuit (IC) for the open-loop and closed-loop operation of integrated capacitive micro- and nano-gravity accelerometers. The micromechanical accelerometers are fabricated in thick (less than 100 m) silicon-on-insulator (SOI) substrates. The IC provides the 1-bit digital output stream and has the versatility of interfacing sensors with different sensitivities while maintaining minimum power consumption (less than 5 mW) and maximum dynamic range (90 dB). A fully-differential sampled-data scheme is deployed with the ability of low-frequency noise reduction through the use of correlated double sampling (CDS) scheme. In this work, the measured resolution of the closed-loop CMOS-SOI accelerometer system, in the presence of high background accelerations, is in the micro-g (g: gravity) range. In this design, a second-order SC modulator is cascaded with the accelerometer and the front-end amplifier. The accelerometer operates in air and is designed for non-peaking response with a BW-3dB of 500 Hz. A 22 dB improvement in noise and hence dynamic range is achieved with a sampling clock of 40 kHz corresponding to a low oversampling ratio (OSR) of 40. The interface IC consumed a current of 1.5 mA from a supply of 3 V.