Author(s)

Sohrab Eslami

Advisor(s)

Nader Jalili

Contributor(s)

Ahmed A. Busnaina, Constantinos Mavroidis

Date of Award

8-2011

Date Accepted

8-2011

Degree Grantor

Northeastern University

Degree Level

Ph.D.

Degree Name

Doctor of Philosophy

Department or Academic Unit

College of Engineering. Deparment of Mechanical and Industrial Engineering.

Keywords

Atomic Force Microscopy, Automated Boundary Interaction Force Control, Automated Micro/nanomanipulation, Microrobot, Piezoresistive Microcantilever, Subsurface Cellular Imaging

Disciplines

Mechanical Engineering

Abstract

This dissertation undertakes the theoretical and experimental developments microcantilevers utilized in Atomic Force Microscope (AFM) with applications to cellular imaging and characterization. The capability of revealing the inhomogeneities or interior of ultra-small materials has been of most interest to many researchers. However, the fundamental concept of signal and image formation remains unexplored and not fully understood. For his, a semiempirical nonlinear force model is adopted to show that virtual resonance generation, regarded as the simplest synthesized subsurface probe, occurs optimally when the force is tuned to the vander Waals form. This novel theoretical dynamic multi-frequency force microscopy offers fresh insight into the problem of subsurface probe microscopy that was first experimentally reported by Tetard et al. 2008, 2010.

Owing to the broad applications of microcantilevers in the nanoscale imaging and microscopic techniques, there is an essential feeling to study and propose a comprehensive model of such systems. Therefore, in the theoretical part of this dissertation, a distributed-parameters representation model of the microcantilever along with a general interaction force consisting of two attractive and repulsive components with general amplitude and power terms is studied. This model is investigated in a general 2D Cartesian coordinate to consider the motions of the probe with a tip mass. There is an excitation at the microcantilever’s base such that the end of the beam is subject to the proposed general force. These forces are very sensitive to the amplitude and power terms of these parts; on the other hand, the atomic intermolecular force is a function of the distance such that this distance itself is also a function of the interaction force that will result in a nonlinear implicit equation. From a parametric study in the probe-sample excitation, it is shown that the predicted behavior of the generated difference-frequency oscillation amplitude agreeswell with experimental measurements.

Following the proposed Euler-Bernoulli model, a more comprehensive model is developed by modeling the probe dynamics and including the effects of the rotary inertia and shear deformation under the same proposed tip-sample interaction force. An extensive comparative study between the Euler-Bernoulli and Timoshenko beam assumptions is conducted for different conditions including different base-excitation amplitudes and higher modes. The results underline that the comprehensive Timoshenko and Euler-Bernoulli beam models are able to unveil the realistic behavior of the AFM system in a good fashion.

In addition to extensive modeling efforts on the microcantilever and its interaction with a sample, an adaptive control framework is developed in order to make the microcantilever’s tip follow a desired trajectory. This trajectory can be further considered as an important path acquired by the path planning techniques to manipulate the nanoparticles. There is a base excitation considered for this model which can be considered as the input force control to excite the probe by taking advantage of flexibility of the microcantilever despite its complexity and under existence of the external nonlinear interaction forces between the probe’s tip and sample’s surface.

When building such complicated controller on top of the proposed comprehensive model, the results could be extended to study a macro-micro hybrid rigid-flexible model of a micromanipulator to mimic the realistic behavior of the MM3A®. The MM3A® is equipped with a piezoresistive layer which serves as a force sensor and is capable of measuring very slight forces as small as micro to nano-Newton. Two types of controllers are investigated for the case of the tip force control; the Lyapunov-based PD and the robust adaptive controllers are developed for this purpose and their performances and stabilities are compared together.

In the experimental part, a platform for performing the automated nanomanipulation and realtime cellular imaging is developed by integrating a micromanipulator, a digital signal processor platform (dSPACE®), a computer, and a state-of-the-art light microscope. The closed-loop boundary force control framework is additionally developed for the autonomous in-situ applications. Since the incoming and outgoing signals of the piezoresistive micromanipulator are in the form of the electrical voltage and the string commands (ASCII code), respectively, an intuitive programming code for interfacing the MATLAB® and dSPACE® has been written for the online quasi-data acquisition. As a result, the height of the corneal cell has been obtained and additionally, the microcantilever’s tip force has been automatically controlled by taking advantage of the proposed control framework.

Document Type

Dissertation

Rights Holder

Sohrab Eslami


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