Accelerometer Thesis

Accelerometer Thesis-44
Simulink Model of the accelerometer 54 Figure 3-14. Snapshot of the showing a stable DC Operating point of the system 61 Figure 3-21. Displacement to determine the stiffness of the beam 62 Figure 3-22. Displacement Qim) variation with respect to time 65 Figure 3-25. Meshed Solid Model of the Accelerometer 67 Figure 3-27. An accelerometer is defined as a “device that can be usedfor measuring linear acceleration.” They can be used to measure tilt, inertial acceleration and shocks or vibra tion as shown in Figure 1-1.. An external acceleration will displace the proofmass from its rest position. SEM Picture showing the entire structure 53 Figure 3-13. Saber Schematic showing the design for the differential accelerometer 60 Figure 3-20. Saber simulation showing the resonant frequency (phase and magnitude) 64 Figure 3-24. The large volume demand for accel erometers is due to their diversified applications which covers a much broader spectrum where their small size and low cost have even a larger impact. The Fuctionality of an Accelerometer r.1c TIDN INPUT TI1 0 fr IW .d*t H,n ACCELEROMETER __________ OJIr O OIfl EU m L DJt I Il WJ 1 To extract the acceleration value, the sensor has a movable proof mass which is connected to a fixed frame via spring structures.The simulation tests show that the SOl accelerometer system yields 8.8k Hz resonant frequency, with a quality factor of 10 and 2.l2m V/g sensitivity. The main ques tion that would tend to arise will be the significance of this particular accelerometer.

Simulink Model of the accelerometer 54 Figure 3-14. Snapshot of the showing a stable DC Operating point of the system 61 Figure 3-21. Displacement to determine the stiffness of the beam 62 Figure 3-22. Displacement Qim) variation with respect to time 65 Figure 3-25. Meshed Solid Model of the Accelerometer 67 Figure 3-27. An accelerometer is defined as a “device that can be usedfor measuring linear acceleration.” They can be used to measure tilt, inertial acceleration and shocks or vibra tion as shown in Figure 1-1.. An external acceleration will displace the proofmass from its rest position. SEM Picture showing the entire structure 53 Figure 3-13. Saber Schematic showing the design for the differential accelerometer 60 Figure 3-20. Saber simulation showing the resonant frequency (phase and magnitude) 64 Figure 3-24. The large volume demand for accel erometers is due to their diversified applications which covers a much broader spectrum where their small size and low cost have even a larger impact. The Fuctionality of an Accelerometer r.1c TIDN INPUT TI1 0 fr IW .d*t H,n ACCELEROMETER __________ OJIr O OIfl EU m L DJt I Il WJ 1 To extract the acceleration value, the sensor has a movable proof mass which is connected to a fixed frame via spring structures.The simulation tests show that the SOl accelerometer system yields 8.8k Hz resonant frequency, with a quality factor of 10 and 2.l2m V/g sensitivity. The main ques tion that would tend to arise will be the significance of this particular accelerometer.

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Some of them include Capacitive, Piezoresistive, Piezoelectric, Tunnelling, Optical, Heat Transfer, Hall Effect, Thermal, Interferometric etc.

3 • Lately it has been used in medical industry along with micro gyroscopes which form a microinetrial unit which helps in the navigation of the tools during surgeries. TYPES OF ACCELEROMETERS There are different types of accelerometers which are classified on the basis of transduction principle.

Experimental verification of the pull-in voltage and the release voltage 78 Figure 4-5. The mea surement ofacceleration is used as an input into some types of control systems.

Experimental Verification of pull in voltage 77 Figure 4-4. But In-plane accelerometers offer the following advantages: (i) fabrication of beams and seismic mass in one etching step, and (ii) a high degree of symmetry which allows one to increase the seismic mass without changing its gravitational center[3]. Applications of Accelerometers Acceleration is a measure of the physical characteristic of any system.

The accelerometers were designed and op timized using the MATLAB simulator and COVENTORWARE simulation tool. One of the main goals is to improve the resolution and accuracy of the present MEMS-based inertial sensors.

First set of devices is fabricated using a commercial foundry process called SOIMUMPs. The presently avail able resolutions of (commercial) MEMS sensors are in the range ofmg for accelerometers, 6 and around 0.1 deg/sec for gyroscopes. SEM picture of the fabricated SOl Differential Accelerometer 73 Figure 4-1. One can divide the sensors as [2]: * Out-of-plane accelerometers where the sensitive axis is perpendicular to the wafer surface. Simulink Model of the Pull-in Accelerometer 93 4.3. Surface Roughness of the Silicon in the Y direction 72 Figure 3-32. The sensor then extracts the magnitude of this displace ment using its sensing scheme.11 Table of Contents Abstract ii Table of Contents iii List of Tables vi List of Figures vii Acronyms x Acknowledgements xi Dedication xii CHAPTER 1. The system is to yield a voltage output proportional to the externally applied acceleration. A few of the types are explained below: • Capacitive-Metal beam or micro machined feature produces capacitance; change in capacitance related to acceleration[l]. The different application areas for accelerometers [5] 4 • Piezoelectric-Piezoelectric crystal mounted to mass -voltage output converted to accel eration[6].One is in the field of minimally invasive surgery where accelerometers will be combined with gyroscopes to be used in the navigation of surgical tools as a inertial micro unit (IMU). • Tunneling-A cantilever structure with a variable gap between an integrated tunneling tip and a conducting electrode causes electron tunneling in the gap and this principle can be used to detect extremely sensitive accelerations[ 11].The choice for the design of a structure with 1 Degree of Freedom(DOF) , instead of a 2-DOF device was instigated by the simplicity of the design and by a more efficient 1-DOF dynamic model. Design Challenges for MEMS Accelerometers 40 CHAPTER 3. • Interferometric- The inter digital system forms an optical diffraction grating where the displacement of the proof mass relative to the support substrate is measured with a standard laser diode and photo detector[ 12].They can be operated at the border of stability also so that the “pull in” operation mode can be explored. Medical navigation systems are mainly used for monitoring the position of surgical instruments relative to patient body.Such kinds of structures have a wide range ofapplications because of their high sensitivity. The idea is to attach the micro inertial measurement unit (IMU) to the instrument to track its position. Here for Asymmetric mode(V1V and V20) and for Symmetric mode(V1V2=V) 82 Figure 4-8. Based on this its wide rage of applica tions include mlitary,aerospace,medical systems,navigation,automotive industry. The typical functions an accelerometer can be used are [4]: • Tilt/Roll Sensing • Vibration-Can be used to isolate vibration of the mechanical system from the outside sources. • Vehicle Skid Detection- Often used with systems that deploy smart breaking to regain the control of vehicle. Generation of the 2D Layout and Solid Model with Mesh 67 3.3. EXPERIMENTAL VERIFICATION AND DEVICE CHARAC TERIZATION 75 4.1. Lumped model of the accelerometer for pull-in analysis. Some common “g” reference points[4] Description I] “g” level Earth’s Gravity 1 g Parked car ig Bumps in a road 2g Car Driver in a corner 3g Bobsled driver in a corner 5g Human Unconsciousness 7g Orbiting Space Shuttle 1 Og Depending on the characteristics, there is diverse range of applications for acceler ometers. are some of the factors that determine the type of the applications for the accelerometer.

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