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Open Access Publications from the University of California

Scholarly Works (8 results)

  • Article
  • Peer Reviewed
UC Irvine Previously Published Works (2019)
We present a study on the adaptive threshold of the zero-velocity detector, which enables the detector to adjust to gait patterns with different speeds, from as low as walking with 80 steps per minute to as high as running with 160 steps per minute, without any tuning of design parameters during the navigation. This approach enables the zero-velocity update (ZUPT)-aided navigation algorithm to work properly with time-varying speed in a single navigation process. A Bayesian-based approach was applied to determine the adaptive threshold in the likelihood ratio test with a uniform prior information and time-varying cost function. The position error in a velocity-changing navigation scenario was demonstrated to be reduced by 12 times after applying the adaptive threshold instead of a fixed threshold.
    • Thesis
    • Peer Reviewed
    UC Irvine Electronic Theses and Dissertations (2020)

    This Ph.D. dissertation reports on development of inertial sensors and inertial navigation algorithms for pedestrian inertial navigation applications. Toward enabling such applications, this thesis developed new techniques leading to improvements in gyroscopes and navigation algorithms. The main contributions of this thesis include:

    1. Improved structural symmetry and quality factor of Fused Quartz micro-wineglass resonators. We developed an analytical model to predict the resonant frequency of wineglass modes of the resonators with error less than 20%. A model to predict the frequency split of the device was also developed. Directional lapping method was introduced to reduce the as-fabricated frequency split by more than 6X without damaging the integrity of the structure, thus preserving the quality factor of the device. Effects of surface loss were observed and analyzed, and surface reflow was demonstrated to be able to improve the quality factor of the devices. A piezoelectric actuation architecture was explored on the Fused Quartz dual shell resonators, in order to eliminate the metal deposition on the vibratory element to minimize the surface-related energy losses.

    2. Identified and quantified, for the first time, energy dissipation mechanisms in Micro-Electro-Mechanical System (MEMS) resonators. By controlling the temperature, air pressure, and surface moisture of the device, viscous air damping, Thermo-Elastic Damping (TED), the anchor loss, and the surface loss of the resonator were manipulated and identified. At room temperature, the quality factors related to viscous air damping, TED, the anchor loss, and the surface loss were experimentally measured to be 625,000, 200,000, 1,350,000, and 1,146,000, respectively. This study provides insight to understanding the dominant mechanism that limits the quality factors of MEMS resonators.

    3. Developed an analytical model to predict the effect of IMU noise on the navigation solution uncertainty in the Zero-Velocity-Update (ZUPT)-aided pedestrian inertial navigation. A bio-mechanical model for human walking was built in order to numerically simulate the process. A discrepancy of less than 10% was shown between the analytical and numerical results. Experiments have been conducted and the results were on the same level of the analytical prediction. Among many IMU noise contributions, the dominant factor affecting the accuracy of the ZUPT-aided pedestrian inertial navigation was Rate Random Walk (RRW) of the z-axis gyroscope. This result is envisioned to aid in analysis of the effect of errors in sensors, which might lead to a well informed selection of sensors for the task of ZUPT-aided pedestrian inertial navigation.

    4. Improved implementation for the ZUPT-aided pedestrian inertial navigation algorithm for better navigation accuracy. Adaptive threshold based on shock level was first developed for stance phase detection to improve the adaptivity and reliability of the algorithm, demonstrating more than 12X improvement of navigation accuracy. Then, more than 10X reduction in systematic error of position estimation was demonstrated with a careful characterization of the motion of the foot during the stance phases in walking cycles and calibration of IMU in terms of the gyroscope g-sensitivity. Stochastic errors were reduced by 45% when mounting the IMU on the forefoot instead of on the heel.

    This work offers new methods and techniques for further reduction of navigation errors by improving the performance of inertial sensors and inertial navigation algorithms.

      Cover page: Pedestrian Inertial Navigation ---- Development of Sensors and AlgorithmsCreative Commons 'BY' version 4.0 license
      • Article
      • Peer Reviewed
      UC Irvine Previously Published Works (2019)
      In this paper, recent developments in the design and fabrication of micromachined fused quartz hemi-toroidal shells are presented. The fabrication is based on micro glassblowing process, demonstrated to enable the realization of high-Q MEMS resonators and gyroscopes. The design optimization of the shell geometry is performed using parametric finite element analysis. The effect of geometric parameters on the scaling of the resonant frequencies and energy dissipation are discussed. Three variations of the micro-glassblowing process are studied in the paper, concluding that shell resonators with a broad operational frequency range without losing the symmetry and Q-factor are feasible. Finite element models are presented to simulate the presented glassblowing processes, which are used to predict the final geometry of shell resonators accurately. Operational frequency as low as 5 kHz and Q-factor as high as 1.7 million is demonstrated on the fabricated shell resonators. The proposed process modifications demonstrate a low-cost and scalable fabrication of 3D shells for resonators and gyroscopes, which can be used in inertial navigation and timing applications. [2019-0179].
        • Article
        • Peer Reviewed
        UC Irvine Previously Published Works (2017)
        In this paper, we developed an analytical model, supported by experimental results, on the effect of imperfections in glassblown micro-wineglass fused quartz resonators. The analytical model predicting the frequency mismatch due to imperfections was derived based on a combination of the Rayleigh's energy method and the generalized collocation method. The analytically predicted frequency of the n = 2 wineglass mode shape was within 10% of the finite element modeling results and within 20% of the experimental results for thin shells, showing the fidelity of the predictive model. The postprocessing methods for improvement of the resonator surface quality were also studied. We concluded that the thermal reflow of fused quartz achieves the best result, followed in effectiveness by the RCA-1 surface treatment. All the analytical models developed in this paper are to guide the manufacturing methods to reduce the frequency and damping mismatch, and to increase the mechanical quality factor of the device.
          • Article
          • Peer Reviewed
          UC Irvine Previously Published Works (2018)
          We present an analytical relation between the position estimation uncertainty and inertial measurement unit (IMU) characteristics during zero-velocity-update (ZUPT) augmented pedestrian inertial navigation. The effect of angle random walk of gyroscopes and velocity random walk of accelerometers in IMU on circular error probable is studied. Numerical simulation of the ZUPT-augmented navigation algorithm is conducted based on a generated pedestrian trajectory to verify the analytical results, showing the discrepancy less than 15, which supports the fidelity of the results. Experiments are also conducted, and the results match our analytical prediction, with the error less than 20. This study offers a closed-form analytical expression to predict the performance of ZUPT-augmented pedestrian inertial navigation.
            • Article
            • Peer Reviewed
            UC Irvine Previously Published Works (2018)
            We present, for the first time, a permanent structural asymmetry compensation method for fused quartz micro wineglass resonators. Using the technique, we demonstrated a near six times reduction of structural asymmetry (n = 2 wineglass mode), culminating in reduction of the frequency split from 41 to 7 Hz. This is an iterative process. In each iteration, the structural asymmetry was first identified by measuring the mode shape of the resonators. Then, directional lapping was performed with specially designed lapping fixtures to accurately control the lapping angle down to 1°. Analytical predictions and numerical simulations were conducted to study the structural asymmetry phenomenon and the effects of compensation on the quality factor of the structure, showing the ability of this process to reduce the structural asymmetry, while not affecting the overall quality factor of the resonators.
              • Article
              • Peer Reviewed
              UC San Diego Previously Published Works (2016)
              Ocular neovascularization often leads to severe vision loss. The role of bone marrow-derived cells (BMCs) in the development of ocular neovascularization, and its significance, is increasingly being recognized. In this review, we discuss their contribution and the potential mechanisms that mediate the effect of BMCs on the progression of ocular neovascularization. The sequence of events by which BMCs participate in ocular neovascularization can be roughly divided into four phases, i.e., mobilization, migration, adhesion and differentiation. This process is delicately regulated and liable to be affected by multiple factors. Cytokines such as vascular endothelial growth factor, granulocyte colony-stimulating factor and erythropoietin are involved in the mobilization of BMCs. Studies have also demonstrated a key role of cytokines such as stromal cell-derived factor-1, tumor necrosis factor-α, as well as vascular endothelial growth factor, in regulating the migration of BMCs. The adhesion of BMCs is mainly regulated by vascular cell adhesion molecule-1, intercellular adhesion molecule-1 and vascular endothelial cadherin. However, the mechanisms regulating the differentiation of BMCs are largely unknown at present. In addition, BMCs secrete cytokines that interact with the microenvironment of ocular neovascularization; their contribution to ocular neovascularization, especially choroidal neovascularization, can be aggravated by several risk factors. An extensive regulatory network is thought to modulate the role of BMCs in the development of ocular neovascularization. A comprehensive understanding of the involved mechanisms will help in the development of novel therapeutic strategies related to BMCs. In this review, we have limited the discussion to the recent progress in this field, especially the research conducted at our laboratory.
                Cover page: Bone marrow-derived cells in ocular neovascularization: contribution and mechanisms
                • Article
                • Peer Reviewed
                LBL Publications (2019)
                All-polymer organic solar cells offer exceptional stability. Unfortunately, the use of bulk heterojunction (BHJ) structure has the intrinsic challenge to control the side-chain entanglement and backbone orientation to achieve sophisticated phase separation in all-polymer blends. Here, we revealed that the P-i-N structure can outperform the BHJ ones with a nearly 50% efficiency improvement, reaching a power conversion efficiency approaching 10%. This P-i-N structure can also provide an enhanced internal electric field and remarkably stable morphology under harsh thermal stress. We have further demonstrated generality of the P-i-N structure in several other all-polymer systems. Considering the adjustable polymer molecular weight and solubility, the P-i-N device structure can be more beneficial for all-polymer systems. With the design of more crystalline polymers, the antiquated P-i-N structure can further show its strength in all-polymer systems by simplified morphology control and improved carrier extraction, becoming a more favorite device structure than the dominant BHJ structure.
                  Cover page: Simultaneously Improved Efficiency and Stability in All-Polymer Solar Cells by a P–i–N Architecture
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