Showing papers by "Chia-Hsiang Menq published in 2010"

Design, Implementation, and Force Modeling of Quadrupole Magnetic Tweezers

Abstract: This paper presents the design, implementation, and force modeling of quadrupole magnetic tweezers, which are capable of exerting magnetic forces in arbitrary 2-D directions on magnetic particles in the workspace. A lumped-parameter model based on magnetic monopole approximation is employed to describe the magnetic field generated by the quadrupole magnetic tweezers in the workspace. In this model, the magnetic field generated by each magnetic pole is approximated by the field of a point magnetic charge associated with the magnetic pole, and the total magnetic field produced by the system is obtained by applying the principle of superposition. An analytical force model considering the interaction between a magnetic particle and the magnetic field is then developed. The derived force model accurately characterizes the nonlinearity of the magnetic force exerting on the magnetic particle with respect to the applied currents to the coils and the position dependency of the magnetic force in the workspace. The directionality as well as the force generation anisotropy of the designed system is then explored using the force model. The model also facilitates the implementation of a feedback control law to stabilize and control the motion of a magnetic particle. Experimental results in terms of the magnetic force in relation to stable motion control of a magnetic particle are used to validate the force model.

Actively Controlled Manipulation of a Magnetic Microbead Using Quadrupole Magnetic Tweezers

Abstract: This paper presents the theoretical analysis and experimental investigation of actively controlled manipulation of a magnetic microbead using quadrupole magnetic tweezers. Bead dynamics, magnetic actuation, and visual measurement are analyzed. A feedback control law is developed and implemented to stabilize and steer the motion of the magnetic microbead. It is developed in two steps. First, an inverse model, which is associated with a lumped-parameter analytical force model, is derived to enable feedback linearization. Second, linear controllers are designed to achieve motion stabilization and manipulation of the magnetic microbead. A proportional-gain controller along with feedback linearization is implemented to establish a stable trapping of the magnetic bead to facilitate system calibration. Experiments are then performed to validate the derived inverse force model and theoretical analysis. In addition, a minimum-variance controller is designed and employed to reduce the variance of the bead's Brownian motion. The control performance in terms of variance reduction, nanostepping, and large-range steering is then experimentally demonstrated.

Modeling and Design of a Magnetically Actuated Two-Axis Compliant Micromanipulator for Nanomanipulation

Abstract: This paper presents the modeling and design of a novel magnetically actuated compliant micromanipulator based on the atomic force microscope (AFM) probe. The manipulator can control the Z -position of the tip and its orientation about the longitudinal axis. It enables sensitive interaction with the sample along two axes and is therefore a useful 3-D tool for metrology and manipulation at the micro/nanoscale. The model for the actuation scheme is first presented. Subsequently, the quasi-static and dynamic lumped parameter models of the two-axis manipulator are developed. The developed models are used to propose a systematic procedure to design the probe. The design is evaluated by means of finite-element analysis, and the results are compared with the prediction of the lumped parameter model. Finally, the manipulator is fabricated, and the experimentally measured dynamics is shown to agree well with the results of modeling and simulation.

Control of a Two-Axis Micromanipulator-Based Scanning Probe System for 2.5-D Nanometrology

Abstract: This paper presents a versatile atomic-force-microscope (AFM)-based two-axis probing system for 2.5-D nanometrology. Central to this system is a two-axis compliant micromanipulator based on the AFM probe whose orientation and position can be actively changed in the scanning plane. Three enabling technologies are proposed to uniformly scan the section of the sample surface within this plane. First, an orientation control system is developed that controls the tip-orientation to track the changes in normal of the surface section. Second, tapping mode-based tip-sample interaction scheme is developed wherein the direction of tip oscillation and the peak force are controlled, according to the local orientation of the section. Third, a two-axis scanning scheme is developed wherein the scanning and interaction control axes are aligned along the tangent and normal to the local section. Taken together, these technologies enable the entire scanning process to conform to the geometry of the sample in the scanning plane and facilitate metrology of samples with large geometric variation along the two axes. In this paper, the developed probing system is used to scan the entire top surface of a micropipette and demonstrate greater access and absence of artifacts when compared to a conventional scan.

Design and Fabrication of an Active Multiaxis Probing System for High Speed Atomic Force Microscopy

Abstract: The design and fabrication of an active multiaxis probing system for high-speed atomic force microscopy is presented. The probing system employs a multiaxis compliant manipulator that is actuated by two magnetic actuators to control the tip position simultaneously along the vertical and the lateral directions. The manipulator is optimally designed to achieve high bandwidth actuation and large scanning range. A novel process to fabricate multiaxis compliant manipulators reliably by using focused ion beam milling is proposed. The fabricated active multiaxis probing system is demonstrated to have high bandwidth of actuation with the lateral and vertical resonance frequencies at 46.4 and 101.5 kHz, respectively. The lateral scanning range is estimated to be ~350 nm at a magnetic field of 20 × 10-4 T. It enables imaging rate of 10 frame/s with pixel resolution of 100 × 100 pixels.

Mechanical anisotropy and adaptation of metastatic cells probed by magnetic microbeads

Abstract: Metastatic cells have the ability to break through the basal lamina, enter the blood vessels, circulate through the vasculature, exit at distant sites, and form secondary tumors. This multi-step process, therefore, clearly indicates the inherent ability of metastatic cells to sense, process, and adapt to the mechanical forces in different surrounding environments. We describe a magnetic probing device that is useful in characterizing the mechanical properties of cells along arbitrary two-dimensional directions. Magnetic force, with the advantages of biocompatibility and specificity, was produced by magnetic poles placed in an octupole configuration and applied to fibronectin-coated magnetic microbeads attached on cell membrane. Cell deformation in response to the applied force was then recorded through the displacement of the microbeads. The motion of the beads was measured by computer processing the video images acquired by a high-speed CMOS camera. Rotating force vectors with constant magnitude while pointing to directions of all 360 degrees were applied to study the mechanical anisotropy of metastatic breast cancer cells MDA-MB-231. The temporal changes in magnitude and directionality of the cellular responses were then analyzed to investigate the cellular adaptation to force stimulation. This probing technology thus has the potential to provide us a better understanding of the mechano-signatures of cells.

Trapping and Steering a Magnetic Microbead Using 3D Magnetic Tweezers

Abstract: The development of a magnetic micromanipulation system that is capable of trapping and steering a magnetic microbead in three dimensions is presented in this paper. Hexapole magnetic tweezers were designed and implemented to realize three-dimensional (3D) magnetic actuation. Because magnetic actuation is inherently unstable without feedback control, visual measurement based on computer processing of video images was employed to detect the displacement of the microbead, facilitating real-time feedback control. An analytical magnetic force model was developed to characterize the nonlinearity and position dependency of the magnetic force exerted on the magnetic bead by the hexapole magnetic tweezers. Its inverse model was then derived and employed in feedback linearization. A proportionalintegral controller along with feedback linearization was implemented and the motion of the magnetic bead was successfully stabilized. The control results in terms of 100-nanometer stepping and 3D motion steering were experimentally demonstrated.Copyright © 2010 by ASME