BITS Faculty Publications
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Item Coupled Field Analysis of Hemispherical Resonator Gyroscope(International Journal of Vehicle Structures & Systems, 2022) Rao, Venkatesh K.P.This work deals with the electromechanical analysis of the Hemispherical Resonator Gyroscope (HRG). The HRG is a type of Coriolis vibratory gyroscope (CVG), which uses Coriolis force to measure the input angular rate. For any CVG drive and sense mode, frequencies play a critical role, which decides the sensitivity and bandwidth of a sensor. In this study, we carry out modal analysis to evaluate the natural frequencies and corresponding mode shapes of an HRG. As HRG is an electromechanical structure, the device is driven at resonance in the drive direction, and the Coriolis force leads to motion in the sense direction. In this study, we present the piezoelectric based HRG; coupled field simulations are carried out to evaluate the performance characteristics of a sensorItem Design and Analysis of General Purpose MEMS Accelerometer(KTH, 2007) Rao, Venkatesh K.P.Inertial sensors including accelerometers and gyroscopes play an important role in vibration sensing, health monitoring, automotive applications etc. Here we design, fabricate and characterize the set of accelerometers with natural frequencies varying from 8 to 18 kHz. The design is compatible with PolyMUMPs process and has an ease of integrability with the electronic circuits. The operating voltage of the sensor is less than 3.5 V and both the structural and electrode layers are in polysilicon. The user is given an option of choosing the accelerometer in terms of sensitivity and the working range of g (acceleration due to gravity) based on the need of the application. Analytical, Numerical and experimental studies are carried out to determine the sensitivity, frequency range, maximum measurable acceleration and the pull-in voltage of each device. Effect of residual stress on the static and dynamic response characteristics of the accelerometer has been explored and the effect of same on its sensitivity.Item System integration design in MEMS — A case study of micromachined load cell(Springer, 2009-10) Rao, Venkatesh K.P.One of the critical issues in large scale commercial exploitation of MEMS technology is its system integration. In MEMS, a system design approach requires integration of varied and disparate subsystems with one of a kind interface. The physical scales as well as the magnitude of signals of various subsystems vary widely. Known and proven integration techniques often lead to considerable loss in advantages the tiny MEMS sensors have to offer. Therefore, it becomes imperative to think of the entire system at the outset, at least in terms of the concept design. Such design entails various aspects of the system ranging from selection of material, transduction mechanism, structural configuration, interface electronics, and packaging. One way of handling this problem is the system-in-package approach that uses optimized technology for each function using the concurrent hybrid engineering approach. The main strength of this design approach is the fast time to prototype development. In the present work, we pursue this approach for a MEMS load cell to complete the process of system integration for high capacity load sensing. The system includes; a micromachined sensing gauge, interface electronics and a packaging module representing a system-in-package ready for end characterization. The various subsystems are presented in a modular stacked form using hybrid technologies. The micromachined sensing subsystem works on principles of piezo-resistive sensing and is fabricated using CMOS compatible processes. The structural configuration of the sensing layer is designed to reduce the offset, temperature drift, and residual stress effects of the piezo-resistive sensor. ANSYS simulations are carried out to study the effect of substrate coupling on sensor structure and its sensitivity. The load cell system has built-in electronics for signal conditioning, processing, and communication, taking into consideration the issues associated with resolution of minimum detectable signal. The packaged system represents a compact and low cost solution for high capacity load sensing in the category of compressive type load sensor.Item Design and characterization of in-plane MEMS yaw rate sensor(Springer, 2009-10) Rao, Venkatesh K.P.In this paper, we present the design and characterization of a vibratory yaw rate MEMS sensor that uses in-plane motion for both actuation and sensing. The design criterion for the rate sensor is based on a high sensitivity and low bandwidth. The required sensitivity of the yawrate sensor is attained by using the inplane motion in which the dominant damping mechanism is the fluid loss due to slide film damping i.e. two–three orders of magnitude less than the squeeze-film damping in other rate sensors with out-of-plane motion. The low bandwidth is achieved by matching the drive and the sense mode frequencies. Based on these factors, the yaw rate sensor is designed and finally realized using surface micromachining. The inplane motion of the sensor is experimentally characterized to determine the sense and the drive mode frequencies, and corresponding damping ratios. It is found that the experimental results match well with the numerical and the analytical models with less than 5% error in frequencies measurements. The measured quality factor of the sensor is approximately 467, which is two orders of magnitude higher than that for a similar rate sensor with out-of-plane sense direction.