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Publication Self-Actuated, Thermo-Responsive Hydrogel Valves for Lab on a Chip(2005-06-23) Wang, Jing; Chen, Zongyuan; Mauk, Michael; Hong, Kuang-sheng; Yang, Shu; Li, Mengyan; Bau, Haim HAn easy to fabricate, thermally-actuated, self-regulated hydrogel valve for flow control in pneumatically driven, microfluidic systems is described. This microvalve takes advantage of the properties of the hydrogel, poly(N-isopropylacrylamide), as well as the aqueous fluid itself to realize flow control. The valve was designed for use in a diagnostic system fabricated with polycarbonate and aimed at the detection of pathogens in oral fluids at the location of the sample collection. The paper describes the construction and characterization of the hydrogel valves and their application for flow control, sample and reagent metering, sample distribution into multiple analysis paths, and the sealing of a polymerase chain reaction (PCR) reactor to suppress bubble formation. The hydrogel-based flow control is electronically addressable, does not require any moving parts, introduces minimal dead volume, is leakage and contaminant free, and is biocompatible.Publication STAM: A System of Tracking and Mapping in Real Environments(2004-12-01) Zhang, Ying; Ackerson, Lee; Duff, David; Eldershaw, Craig; Yim, MarkWe have implemented a system of tracking mobile robots and mapping an unstructured environment, using up to 25 wireless sensor nodes in an indoor setting. These sensor nodes form an ad hoc network of beacons, self-localize with respect to three anchor nodes, and then track the locations of mobile robots in the field. The system described here was motivated by search and rescue applications, and has been demonstrated in real physical environments.Publication Fabrication and Characterization of I-cord Knitted SMA Actuators(2021-03-13) Kim, Christopher Y; Chien, Athena; Tippur, Megha; Sung, CynthiaKnitted SMA actuators provide greater actuation stroke than single-strand SMA wire actuators by leveraging its knitted structure. However, due to short-circuiting through interlacing knit loops, existing knitted SMA sheet actuators are unsuitable for joule-heating actuation when uniform contractile actuation is desired. We explore an axially symmetric tubular i-cord knitted actuator as a possible solution. The fabrication process of an i-cord knitted SMA actuator and its electrical, thermal, and mechanics models are presented. After modifying existing models for single-strand SMA wire and adjusting their parameters, the proposed electrical, thermal, and mechanics models were verified with experimental results. Acknowledgements Support for this project has been provided in part by NSF REU EEC-1659190 and by the GeorgiaTech Stamps President's Scholars program.Publication Push-On Push-Off: A Compliant Bistable Gripper with Mechanical Sensing and Actuation(2021-03-13) McWilliams, Jessica; Yuan, Yifan; Sung, Cynthia; Friedman, JasonGrasping is an essential task in robotic applications and is an open challenge due to the complexity and uncertainty of contact interactions. In order to achieve robust grasping, systems typically rely on precise actuators and reliable sensing in order to control the contact state. We propose an alternative design paradigm that leverages contact and a compliant bistable mechanism in order to achieve "sensing" and "actuation" purely mechanically. To grasp an object, the manipulator holding our end effector presses the bistable mechanism into the object until snap-through causes the gripper to enclose it. To release the object, the tips of the gripper are pushed against the ground, until rotation of the linkages causes snap-through in the other direction. This push-on push-off scheme reduces the complexity of the grasping task by allowing the manipulator to automatically achieve the correct grasping behavior as long as it can get the end effector to the correct location and apply sufficient force. We present our dynamic model for the bistable gripping mechanism, propose an optimized result, and demonstrate the functionality of the concept on a fabricated prototype. We discuss our stiffness tuning strategy for the 3D printed springs, and verify the snap-through behavior of the system using compression tests on an MTS machine. Acknowledgements Support for this project has been provided in part by NSF Grant No. 1138847 and DGE-1845298. We also thank Terry Kientz, Jeremy Wang, Peter Szczesniak, and Joe Valdez for their assistance with the fabrication, and Neal Tinaikar for assistance with initial prototypes. We are grateful.Publication Bubble and Pattern Formation in Liquid Induced by an Electron Beam(2013-12-08) Grogan, Joseph M; Schneider, Nicholas M; Bau, Haim H; Ross, Frances MLiquid cell electron microscopy has emerged as a powerful technique for in situ studies of nanoscale processes in liquids. An accurate understanding of the interactions between the electron beam and the liquid medium is essential to account for, suppress, and exploit beam effects. We quantify the interactions of high energy electrons with water, finding that radiolysis plays an important role, while heating is typically insignificant. For typical imaging conditions, we find that radiolysis products such as hydrogen and hydrated electrons achieve equilibrium concentrations within seconds. At sufficiently high dose-rate, the gaseous products form bubbles. We image bubble nucleation, growth, and migration. We develop a simplified reaction-diffusion model for the temporally and spatially varying concentrations of radiolysis species and predict the conditions for bubble formation by . We discuss the conditions under which hydrated electrons cause precipitation of cations from solution, and show that the electron beam can be used to “write” structures directly, such as nanowires and other complex patterns, without the need for a mask.Publication When MHD-Based Microfluidics is Equivalent to Pressure-Driven Flow(2011-01-01) Qin, Mian; Bau, Haim HMagnetohydrodynamics (MHD) provides a convenient, programmable means for propelling liquids and controlling fluid flow in microfluidic devices without a need for mechanical pumps and valves. When the magnetic field is uniform and the electric field in the electrolyte solution is confined to a plane that is perpendicular to the direction of the magnetic field, the Lorentz body force is irrotational and one can define a “Lorentz” potential. Since the MHD-induced flow field under these circumstances is identical to that of pressure-driven flow, one can utilize the large available body of knowledge about pressure-driven flows to predict MHD flows and infer MHD flow patterns. In this note, we prove the equivalence between MHD flows and pressure-driven flows under certain conditions other than flow in straight conduits with rectangular cross-sections. We determine the velocity profile and the efficiency of MHD pumps, accounting for current transport in the electrolyte solutions. Then, we demonstrate how data available for pressure driven flow can be utilized to study various MHD flows, in particular, in a conduit patterned with pillars such as may be useful for liquid chromatography and chemical reactors. Additionally, we examine the effect of interior obstacles on the electric current flow in the conduit and show the existence of a particular pillar geometry that maximizes the current.Publication Electrical Detection of Cellular Penetration during Microinjection with Carbon Nanopipettes(2014-04-07) Anderson, Sean E.; Bau, Haim H.The carbon nanopipette (CNP) is comprised of a pulled-glass pipette terminating with a nanoscale (tens to hundreds of nm) diameter carbon pipe. The entire inner glass surface of the CNP is coated with a carbon film, providing an electrically conductive path from the carbon tip to the distal, macroscopic end of the pipette. The CNP can double as a nanoelectrode, enabling electrical measurements through its carbon lining, and as a nanoinjector, facilitating reagent injection through its hollow bore. With the aid of a lock-in amplifier, we measured, in real time and with millisecond resolution, variations in impedance as the CNP penetrated into the cytoplasm and nucleus of adherent human osteosarcoma (U20S) cells. The capacitance change associated with nucleus penetration was, on average, 1.5 times greater than the one associated with cell membrane penetration. The experimental data was compared and favorably agreed with theoretical predictions based on a simple electrical network model. As a proof of concept, the cytoplasm and nucleus were transfected with fluorescent tRNA, enabling real-time monitoring of tRNA trafficking across the nuclear membrane. The CNP provides a robust and reliable means to detect cell and nucleus penetration, and trigger injection, thereby enabling the automation of cell injection.Publication A Scalable Strategy for Open Loop Magnetic Control of Microrobots Using Critical Points(2016-05-11) Guerrero-Bonilla, Luis; Bhattacharya, Subhrajit; Kumar, VijayA novel scalable strategy for open loop control of ferromagnetic microrobots on a plane using a scalable array of electromagnets is presented. Instead of controlling the microrobot directly, we create equilibrium points in the magnetic force field that are stable and attractive on the plane in which the microrobot is to be controlled. The microrobot moves into these equilibrium points rapidly in presence of low viscous forces, and thus controlling the equilibrium points let us control the microrobot precisely. An unit/cell in the array of electromagnets allows precise control of the microrobot in the unit/cell’s domain. Motion synthesis across multiple overlapping domains allows control of the microrobot in large regions across the array. We perform numerical analysis and demonstrate the control of the ferromagnetic microrobot using the proposed method through simulations.Publication Visual Servoing of Quadrotors for Perching by Hanging From Cylindrical Objects(2016-01-01) Thomas, Justin; Daniilidis, Kostas; Kumar, Vijay; Loianno, GiuseppeThis paper addresses vision-based localization and servoing for quadrotors to enable autonomous perching by hanging from cylindrical structures using only a monocular camera. We focus on the problems of relative pose estimation, control, and trajectory planning for maneuvering a robot relative to cylinders with unknown orientations. We first develop a geometric model that describes the pose of the robot relative to a cylinder. Then, we derive the dynamics of the system, expressed in terms of the image features. Based on the dynamics, we present a controller which guarantees asymptotic convergence to the desired image space coordinates. Finally, we develop an effective method to plan dynamically-feasible trajectories in the image space, and we provide experimental results to demonstrate the proposed method under different operating conditions such as hovering, trajectory tracking, and perching.Publication The Penn Haptic Texture Toolkit for Modeling, Rendering, and Evaluating Haptic Virtual Textures(2014-02-12) Culbertson, Heather; Lopez Delgado, Juan Jose; Kuchenbecker, Katherine J.The Penn Haptic Texture Toolkit (HaTT) is a collection of 100 haptic texture and friction models, the recorded data from which the models were made, images of the textures, and the code and methods necessary to render these textures using an impedance-type haptic device such as a SensAble Phantom Omni. This toolkit was developed to provide haptics researchers with a method by which to compare and validate their texture modeling and rendering methods. The included rendering code has the additional benefit of allowing others, both researchers and designers, to incorporate our textures into their virtual environments, which will lead to a richer experience for the user.