Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2007 / Micro Electro-Machnical Systems (MEMS) applications are fastest development technology
present. MEMS processes leverage mainstream IC technologies to achieve on chip sensor
interface and signal processing circuitry, multi-vendor accessibility, short design cycles, more
on-chip functions and low cost. MEMS fabrications are based on thin-film surface
microstructures, bulk micromaching, and LIGA processes. This thesis centered on
developing optical micromaching inertial sensors based on MEMS fabrication technology
which incorporates bulk Si into microstructures. Micromachined inertial sensors, consisting of
the accelerometers and gyroscopes, are one of the most important types of silicon-based
sensors. Microaccelerometers alone have the second largest sales volume after pressure
sensors, and it is believed that gyroscopes will soon be mass produced at the similar
volumes occupied by traditional gyroscopes.
A traditional gyroscope is a device for measuring or maintaining orientation, based on the
principle of conservation of angular momentum. The essence of the gyroscope machine is a
spinning wheel on an axle. The device, once spinning, tends to resist changes to its
orientation due to the angular momentum of the wheel. In physics this phenomenon is also
known as gyroscopic inertia or rigidity in space. The applications are limited by the huge
volume.
MEMS Gyroscopes, which are using the MEMS fabrication technology to minimize the size
of gyroscope systems, are of great importance in commercial, medical, automotive and
military fields. They can be used in cars for ASS systems, for anti-roll devices and for
navigation in tall buildings areas where the GPS system might fail. They can also be used for
the navigation of robots in tunnels or pipings, for leading capsules containing medicines or
diagnostic equipment in the human body, or as 3-D computer mice. The MEMS gyroscope
chips are limited by high precision measurement because of the unprecision electrical
readout system.
The market is in need for highly accurate, high-G-sustainable inertial measuring units
(IMU's). The approach optical sensors have been around for a while now and because of the
performance, the mall volume, the simplicity has been popular. However the production cost
of optical applications is not satisfaction with consumer. Therefore, the MEMS fabrication
technology makes the possibility for the low cost and micro optical devices like light sources,
the waveguide, the high thin fiber optical, the micro photodetector, and vary demodulation
measurement methods. Optic sensors may be defined as a means through which a
measurand interacts with light guided in an optical fiber (an intrinsic sensor) or guided to (and
returned from) an interaction region (an extrinsic sensor) by an optical fiber to produce an
optical signal related to the parameter of interest. During its over 30 years of history, fiber
optic sensor technology has been successfully applied by laboratories and industries
worldwide in the detection of a large number of mechanical, thermal, electromagnetic,
radiation, chemical, motion, flow and turbulence of fluids, and biomedical parameters. The
fiber optic sensors provided advantages over conventional electronic sensors, of survivability
in harsh environments, immunity to Electro Magnetic Interference (EMI), light weight, small
size, compatibility with optical fiber communication systems, high sensitivity for many
measurands, and good potential of multiplexing. In general, the transducers used in these
fiber optic sensor systems are either an intensity-modulator or a phase-modulator. The
optical interferometers, such as Mach-Zehnder, Michelson, Sagnac and Fabry-Perot
interferometers, have become widely accepted as a phase modulator in optical sensors for
the ultimate sensitivity to a range of weak signals. According to the light source being used,
the interferometric sensors can be simply classified as either a coherence interferometric
sensor if a the interferometer is interrogated by a coherent light source, such as a laser or a
monochromatic light, or a lowcoherence interferometric sensor when a broadband source a
light emitting diode (LED) or a superluminescent diode (SLD), is used.
This thesis proposed a novel micro electro-mechanical gyroscope system with optical
interferometer readout system and fabricated by MEMS technology, which is an original
contribution in design and research on micro opto-electro-mechanical gyroscope systems
(MOEMS) to provide the better performances than the current MEMS gyroscope. Fiber
optical interferometric sensors have been proved more sensitive, precision than other
electrical counterparts at the measurement micro distance. The MOMES gyroscope system
design is based on the existing successful MEMS vibratory gyroscope and micro fiber optical
interferometer distances sensor, which avoid large size, heavy weight and complex
fabrication processes comparing with fiber optical gyroscope using Sagnac effect. The
research starts from the fiber optical gyroscope based on Sagnac effect and existing MEMS
gyroscopes, then moving to the novel design about MOEMS gyroscope system to discuss
the operation principles and the structures.
In this thesis, the operation principles, mathematics models and performances simulation of
the MOEMS gyroscope are introduced, and the suitable MEMS fabrication processes will be
discussed and presented. The first prototype model will be sent and fabricated by the
manufacture for the further real time performance testing.
There are a lot of inventions, further research and optimize around this novel MOEMS
gyroscope chip. In future studying, the research will be putted on integration three axis
Gyroscopes in one micro structure by optical sensor multiplexing principles, and the new
optical devices like more powerful light source, photosensitive materials etc., and new
demodulation processes, which can improve the performance and the interface to co-operate
with other inertial sensors and navigation system.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:cput/oai:localhost:20.500.11838/1101 |
| Date | January 2007 |
| Creators | Zhang, Bo |
| 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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