Theses and Dissertations at Montana State University (MSU)
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Item Developing bio-inspired methodologies for encoding angular position from strain(Montana State University - Bozeman, College of Engineering, 2020) Lange, Christopher William; Chairperson, Graduate Committee: Mark JankauskiAs mechanical systems rely more on closed-loop control, the sensors which supply feedback information are essential. Additionally, in systems where sensor function is critical, sensor redundancy is important to retain functionality if one or more sensors fail. Redundancy can be achieved through multiple high-fidelity sensors which measure the same type of information, such as gyroscopes or accelerometers. However, multiple high-fidelity sensors can increase cost significantly. This thesis explores the potential to replace or augment the functionality of angular position sensors using strain measurements. Strain gauges are already used in system health monitoring systems. By utilizing these already implemented sensors to measure angular position, we can remove the additional cost of redundant angular position sensors. However, for complex systems, the mapping between strain and angular position is unclear. By incorporating reduced order, physics-based models into machine learning techniques, we can efficiently transform high-order strain data into angular position. To demonstrate the potential of using alternative sensing methods, we developed a reduced order model of a parametrically excited flexible pendulum. Inspiration for this simplified system comes from insect halteres, which are small sensory organs evolved from insect hind wings which provide rapid information about body rotation. The parametrically excited flexible pendulum allows a single axis of rotation and single direction of flexibility to be paired, and their relationship studied. By varying parameters within the model such as pendulum length and modulus as well as parametric excitation amplitude and frequency, the Gaussian process regression learning can be optimized to reduce training time and increase untrained prediction accuracy. Inputs of strain and parametric excitation position along with their respective first and second derivatives are then analyzed to determine which inputs are interrelated and therefore un-necessary, thus reducing the input required. This provides the essential first steps towards using machine learning to implement multiple sensor, deformation based, multi axial angular position sensing in complex systems.Item Design, fabrication, and testing of the van der Paw piezoresistive structure for pressure sensing(Montana State University - Bozeman, College of Engineering, 2008) Cassel, Robert Douglas; Chairperson, Graduate Committee: Ahsan MianThe project characterizes a piezoresistive sensor under variations of both size and orientation with respect to the silicon crystal lattice for its application to MEMS pressure sensing. The sensor to be studied is a four-terminal piezoresistive sensor commonly referred to as a van der Pauw (VDP) structure. The VDP sensor is used primarily in sheet resistance measurements, but has also been determined to be useful in determining the stress components at a point on (100) and (111) silicon wafer surfaces. In a previous study, our team has determined the relation between the biaxial stress state at a point and the piezoresistive response of the VDP by combining the VDP resistance equations with the equations governing silicon piezoresistivity. It was found that the theoretical sensitivity of the VDP sensor is over three times higher than the conventional filament type resistor. With MEMS devices being used in applications which continually necessitate smaller size, understanding the effect of size on VDP performance is important. In order to test the validity of the theoretical calculations which were done by our group, appropriate devices were manufactured on a (100) silicon test wafer. The wafer was designed to have numerous pressure sensitive diaphragms which can reliably sustain a pressure difference of approximately 50kPa. Each diaphragm was doped with a VDP or other sensor designed to test the sensitivity of the VDP vs. a certain parameter. These parameters include size, misalignment, and diaphragm position, in addition to the comparison of sensitivity to conventional sensor types. A test strip was also included in the design in order to determine an empirical relationship between stress and resistance. In testing the VDP devices for comparison with conventional sensor types, it was found that the VDP devices had a linear response as expected, were the most sensitive, and provided a number of additional advantages. Specifically, the VDP device allows for significant miniaturization, because its resistance value is independent of size, and the measurement technique is independent of line resistance. The simple geometry of the VDP also simplifies fabrication.