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.The accelerometers were designed and optimized using the MATLAB simulator and COVENTORWARE simulation tool. Performance Characteristics of Accelerometers 37 2.3.3. Of these different types of accelerometers, differential capacitive sensing and actu ation mechanism is chosen as the principle of the design.
A zoomed view of the surface of Fabricated Silicon 71 Figure 3-31. Hence, the acceleration input that is applied to the sensor is converted to the proof mass displacement in the sensor.
A zoomed in image showing the displacement of the fingers (Finite Element Modelling Using Coventorware) 67 Figure 3-28. Snapshot of the SOl process file used in Coventor Ware 70 Figure 3-30. The magnitude of this displacement is proportional to the magnitude of the acceleration and inversely proportional to the stiffness of the spring struc tures.
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].
DESIGN AND MODELING OF A MEMS-BASED ACCELEROMETER WITH PULL IN ANALYSIS by Akila Kannan B. (Electrical and Electronics Engineering), Anna University, 2005 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF Master of Applied Science in THE FACULTY OF GRADUATE STUDIES (Electrical & Computer Engineering) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) October 2008 © Akila Kannan 2008 Abstract This thesis reports the design and modelling of a MEMS (Micro Electro Mechanical system) based inertial accelerometer. Transverse Comb Capacitance Configuration 16 188.8.131.52. This project is motivated by the fact that the accelerometer will be integrated with a MEMS gyroscope and will be used as an inertial cluster in minimally invasive surgery.
The main motivation to design a differential type of accelerometer is that such a kind of structure allows differential electrostatic actuation and capacitive sensing. This would help in navigation of the surgical tool more reliably and quickly.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). The MEMS-based unit will comprise of accelerometers as well as gyroscopes, together with associated elec tronics.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. A low cost, high precision IMU encompasses in fact a much larger application horizon, ranging from medical to automotive field. 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.This thesis reports the design and modelling of a MEMS (Micro Electro Mechanical system) based inertial accelerometer. • Piezoresistive-Beam or micro machined feature whose resistance changes with accel eration.The main motivation to design a differential type of accelerometer is that such a kind of structure allows differential electrostatic actuation and capacitive sensing. • Hall Effect-Motion converted to electrical signal by sensing of changing magnetic fields.The sim ulation 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. Advanced medical navigation systems require sens ing linear accelerations in the micro-g or lower ranges and very high sensitivities.To characterize the accelerometer a new semi automatic tool was formulated for the noise analysis and noise based optimiza tion of the accelerometer design and the analysis estimation shows that there is a trade off between the SIN ratio and the sensitivity and for the given design could be made much bet ter in-terms of SIN by tuning its resonant frequency. The main objective of this study to construct an accelerometer system which has satisfactory noise-floor/nonlinearity performance for IMUs and is powered with ±12 DC batteries. 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 : • 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 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.