Browsing by Author "Lu, Yitong"
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Item Closed-Loop Control of Mesoscale Magnetic Robots Using a Global Magnetic Field(2023-05-11) Lu, Yitong; Becker, Aaron T.; Faghih, Rose T.; Mayerich, David; Kim, MinJun; Ruchhoeft, Paul; Leclerc, JulienThis dissertation investigates three types of mesoscale (milli- and microscale) magnetic robots: magnetic swimmers, magnetic modular cubes, and ferromagnetic micro-particles. Mesoscale magnetic robots show great potential for revolutionizing many aspects of medical and clinical applications. The dissertation investigates Millimeter-scale Magnetic Rotating Swimmers (MMRSs) that could be used to improve surgical procedures. An external rotating magnetic field produces a torque on the swimmers to make them rotate. MMRSs have propeller fins that convert the rotating motion into forward propulsion. The dissertation reports on optimization studies for the MMRS designs and control techniques used experimentally to remove thrombi from a bifurcating vascular model. The dissertation also presents data-driven models to improve MMRS’s 3D path-following performance of a time-delayed sensing system. An algorithm for 2.5D closed-loop control of the MMRS using only 2D ultrasound feedback is proposed and tested experimentally. In addition, a preliminary study of the biocompatibility of the MMRSs is presented. Magnetic Modular Cubes (MMCs) are scalable modular subunits with embedded permanent magnets in a 3D-printed cubic body. Due to the MMC’s cubic design, magnetically connected structures of MMCs are polyominoes in 2D and polycubes in 3D. MMCs represent progress toward a mesoscale manufacturing method controllable by an external force field that combines the precision of modules, the reusability of Legos, and the self-assembly of DNA. The dissertation provides a family of designs of MMCs and a 2D low-fidelity motion planner that computes all reachable polyomino shapes (and their shortest movement sequences) from an arbitrary initial configuration. A closed-loop control method is presented for self-assembling the MMCs in 2D using computer vision-based feedback with re-planning techniques. Furthermore, methods to enumerate polyominoes and polycubes are presented. For biomedical applications in targeted therapy delivery and interventions, a large swarm of micro-scale particles has to be moved through a maze-like environment to a target region. The dissertation demonstrates how to use a time-varying magnetic field to gather ferromagnetic micro-particles to a desired location using reinforcement learning. In addition, methods to overcome the simulation-to-reality gap are explained in the dissertation.Item Simulation Pipeline of Milli-scale Magnetic Robots for Blood Clot Removal(2020-09-29) Ramos, Jocelyn; Lai, Joyce; Lu, YitongMilliscale, magnetically-controlled robots can be used for targeted blood clot removal. This method may provide a more precise, less dangerous, and less invasive removal process than the current methods which utilize blood thinning medication and catheters. These robots have helical threads so that magnetically induced rotation will produce a propulsive force that is controlled by an external magnetic system. The speed at which the robots need to rotate in order to hover in place in human blood is called the hovering frequency, and was used as a measure of the efficiency of the robot designs. We developed a pipeline for simulated testing of the robots using Finite Element Methods and post-processing. The flow of blood around the robots when rotating at various frequencies was modeled with the Navier-Stokes equations and approximated using the penalty method. In post-processing, the simulations were evaluated by visualizing the interaction of flow lines with the design geometries, confirming that the divergence is approximately zero along the geometry's surface, and calculating the generated propulsive forces. Various physical design parameters including thread depth, air pocket size, tip shape, and pitch, were tested with this method to compare the efficiency of hovering frequencies between simulated models. Future work will involve further optimization of the robot's shapes, evaluation of the model, and automation of the simulation process.