Mode Ordering in Anti-Phase Driven MEMS Gyroscopes and Accelerometers
Inertial sensors have a wide spectrum of applications, ranging from consumer electronics to precision navigation. As these devices continue to maximize performance, while minimizing Size, Weight, and Power (SWaP) requirements, these opportunities will only continue to expand. Vibratory Micro Electro Mechanical System (MEMS) inertial sensors are uniquely positioned in this landscape due to their low SWaP metrics and high potential for enhanced performance. In this dissertation, the fundamental challenges behind the further advancement of these devices are explored, with a number of potential solutions proposed.
For vibratory gyroscopes, one of these fundamental challenges is the tradeoff between rate and acceleration sensitivity; both of which are enhanced by low frequencies of operation. Anti-phase resonances are typically employed to decouple this influence; however, when conventional flexures are used, the anti-phase vibratory mode is forced to a higher frequency, reducing rate sensitivity. For this reason, a novel coupling structure has been designed, analyzed, modeled, fabricated, and tested. This structure is experimentally shown to selectively stiffen in-phase vibration, creating a high degree of modal separation in excess of 120%, a value that is believed to be the highest in published literature, along with reducing acceleration sensitivity by over 20 fold. Theoretical analysis shows that the observed frequency separation can continue to be expanded with this technique, which is only limited by fabrication constraints. This type of structure was also applied to a new frequency modulated accelerometer, and shown to enhance the mechanical scale factor by over 20 times.
Resonator quality factor is another critical element that can be maximized to enhance the performance of some inertial sensors. By identifying the primary energy loss mechanisms within the frequency range of interest, each mechanism was modeled and minimized through design and fabrication. The result of this work was a resonator with quality factor of 2.34 million and decay constant of 1300 s, both of which are also believed to be the highest in published literature for microfabricated structures. In addition to these highlights, investigations also include an in-run scale factor calibration method, through the use of an integrated torsional rate stage, as well as packaging considerations for enhanced temperature robustness.