An all-electrical system is developed to actuate and detect single biological cells in a microfluidic channel for diagnostic applications. Interdigitated electrodes fabricated on the channel floor transfer a high frequency signal for capacitance detection and a low frequency signal for dielectrophoretic actuation. In the fluid-filled channel, a pressure-driven flow propels single biological cells, which induce time-dependent capacitance signatures as they pass over the electrodes. With a sub-attofarad (~0.15 aF RMS, 53 Hz bandwidth) capacitance resolution, this system detects biological cells (e.g., 1 yeast cell ~ 50 aF) and their deflections (1 micrometer ~ 5 aF) from exerted dielectrophoretic forces (> 5 pN). Electrical detection of cell actuation by strong DEP forces provides an avenue for both inducing and monitoring the deformation of viscoelastic cells. A strong and repulsive dielectrophoretic force can be used to press a biological cell into a channel wall. When this occurs, the mechanical properties of the cell can be investigated by capacitively monitoring the cell-to-wall interaction. The nature of the resulting interaction is shown to depend on the mechanical properties of the cell (surface morphology and viscoelastic properties). Various mammalian cell types such as Chinese Hamster Ovary (CHO) cells, mouse fibroblasts, human blood cells, human breast cells and their tumorogenic phenotypes are investigated using this system. Between these populations, the effective Young's modulus varies widely from 20 Pa (neutrophils) to 1-2 GPa (polystyrene microspheres). The viability and phenotype of a biological cell are known to reflect its mechanical and electrical properties. Consequently, this work investigates whether dielectrophoretically induced cell deformations are correlated with corresponding variations in capacitance, which could be used for discriminating cell phenotypes in the future.

Thesis (MScIng)--University of Stellenbosch, 2007. / Bibliography. Also available via the Internet.

No description available.

An Electrical Capacitance Volume Tomography system has been created for use with a new image reconstruction algorithm capable of imaging high contrast dielectric distributions. The electrode geometry consists of two 4 x 4 parallel planes of copper conductors connected through custom built switch electronics to a commercially available capacitance to digital converter. Typical electrical capacitance tomography (ECT) systems rely solely on mutual capacitance readings to reconstruct images of dielectric distributions. This dissertation presents a method of reconstructing images of high contrast dielectric materials using only the self capacitance measurements. By constraining the unknown dielectric material to one of two values, the inverse problem is no longer ill-determined. Resolution becomes limited only by the accuracy and resolution of the measurement circuitry. Images were reconstructed using this method with both synthetic and real data acquired using an aluminum structure inserted at different positions within the sensing region. Comparisons with standard two dimensional ECT systems highlight the capabilities and limitations of the electronics and reconstruction algorithm.

This thesis presents the analysis and characterization of a low sensitivity dual feedback active RC bandpass filter. Chapter 2 details the analysis of the network and a method of simplifying the resultant transfer function by a single pole/zero cancellation. Chapter 3 characterizes the simplified transfer function through an analysis of the quality factor and of the center frequency gain as functions of the individual variables of the circuit. It also details sensitivity analyses of these characteristic quantities and a stability analysis. Lastly, chapter 3 presents graphical representations of the equations developed so that they can be used as design tools. It then goes through the details of applying these graphs to an example network. Chapter 4 explains the differences between experimental data and predicted data by discussing some of the nonlinearities neglected in the original analysis. Finally chapter 5 restates the design technique in light of the predominant nonlinearities.

No description available.

No description available.

This thesis describes for the first time, how the membrane capacitance of pluripotent human embryonic stem cells (H1, H9, RCM1) increases with their differentiation (H1-MSC, H9-MSC, RCM1-trophoblast) based on the literature review. The method used to determine membrane capacitance was dielectrophoresis (DEP), which is an electrokinetic technique capable of characterising and sorting cells without the need for antibody-based cell surface markers, magnetic beads, or other chemical tags. This finding has potential biomedical importance because human embryonic stem cell (hESCs) isolated from early blastocyst-stage embryos and differentiated progeny have been identified to be of possible use in drug screening and regenerative cell based therapeutic treatment. Current cell sorting methods require membrane surface markers that limit their applicability in stem cell therapeutics, a limitation that is either removed or reduced if DEP-based sorting was used. The work described in this thesis consists of the design, fabrication and testing of DEP based microfluidic devices for characterization and separation of human embryonic stem cells. The cells studied were human undifferentiated hESC lines (H1, H9, RCM1, RH1, and T8) and their differentiated progeny (H1-MSC, H9-MSC, RCM1-trophoblast, hES-MP). The cell membrane capacitance (Cm) of the cells was determined by measuring a parameter known as the DEP cross-over frequency (fxo), where the electrical polarisability of a cell equals that of its suspending electrolyte and so experiences no DEP force. The studies of hESC lines cultured from different sources indicate, on the basis of their similar Cm values, that they have similar membrane morphologies. The change in calculated Cm value upon differentiation of these hESCs indicates that changes occur in their membrane morphology, texturing and possibly of their membrane thickness. Subsequent enrichment of these hESCs from human dermal fibroblasts (hDFs) has been achieved based on fxo measurements. The results presented in this thesis confirm the existence, previously indicated in the literature, of distinctive parameters for undifferentiated and differentiating cells on which future application of DEP in hESC manufacturing can be based.

In this thesis, the Method of Moments has been applied to calculate capacitance between two arbitrary 3D metal conductors or a capacitance matrix for a 3D multi-conductor system. Capacitance extraction has found extensive use for systems involving sets of long par- allel transmission lines in multi-dielectric environment as well as integrated circuit package including three-dimensional conductors located on parallel planes. This paper starts by reviewing fundamental aspects of transient electro-magnetics followed by the governing dif- ferential and integral equations to motivate the application of numerical methods as Method of Moments(MoM), Finite Element Method(FEM), etc. Among these numerical tools, the surface-based integral-equation methodology - MoM is ideally suited to address the prob- lem. It leads to a well-conditioned system with reduced size, as compared to volumetric methods. In this dissertation, the MoM Surface Integral Equation (SIE)-based modeling approach is developed to realize electrostatic capacitance extraction for 3D geometry. MAT- LAB is employed to validate its e?ciency and e?ectiveness along with design of a friendly GUI. As a base example, a parallel-plate capacitor is considered. We evaluate the accu- racy of the method by comparison with FEM simulations as well as the corresponding quasi-analytical solution. We apply this method to the parallel-plate square capacitor and demonstrate how far could the undergraduate result 0C = A ? "=d' be from reality. For the completion of the solver, the same method is applied to the calculation of line capacitance for two- and multi-conductor 2D transmission lines.

Yeung Nang Ching. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (leaves 72-74). / Abstracts in English and Chinese. / ACKNOWLEDGMENTS --- p.I / ABSTRACT --- p.II / 摘要 --- p.III / TABLE OF CONTENTS --- p.IV / LIST OF FIGURES --- p.VII / LIST OF TABLES --- p.X / Chapter CHAPTER 1 --- INTRODUCTION --- p.1 / Chapter 1.1 --- Overview of filter --- p.1 / Chapter 1.1.1 --- History --- p.1 / Chapter 1.1.2 --- Application of analog filter --- p.2 / Chapter 1.1.3 --- Category of continuous time filters --- p.3 / Chapter 1.1.4 --- Problem issued from Active RC filter --- p.7 / Chapter 1.2 --- Motivation --- p.7 / Chapter 1.3 --- Outline --- p.8 / Chapter CHAPTER 2 --- FILTER FUNDAMENTAL --- p.9 / Chapter 2.1 --- Overview --- p.9 / Chapter 2.2 --- Terminology --- p.9 / Chapter 2.3 --- General Goals of Filter Design --- p.11 / Chapter 2.4 --- Standard Lowpass Filter Characteristic --- p.11 / Chapter 2.4.1 --- Butterworth --- p.11 / Chapter 2.4.2 --- Chebyshev --- p.12 / Chapter 2.4.3 --- Elliptic-Function --- p.13 / Chapter 2.5 --- Study on Different Tuning Approaches --- p.13 / Chapter CHAPTER 3 --- CURRENT DIVISION NETWORK (CDN) --- p.18 / Chapter 3.1 --- Overview of Current Division Technique --- p.18 / Chapter 3.2 --- Second Order Effects --- p.23 / Chapter 3.3 --- Working Principle of CDN --- p.23 / Chapter 3.4 --- Performances of CDN --- p.25 / Chapter 3.4.1 --- General Properties of CDN --- p.25 / Chapter 3.4.2 --- Input Resistances of CDN --- p.26 / Chapter 3.4.3 --- Noise Performance of CDN --- p.27 / Chapter CHAPTER 4 --- REALIZATION OF THE FILTER --- p.31 / Chapter 4.1 --- Overview --- p.31 / Chapter 4.2 --- Traditional Kerwin Huelsman Newcomb (KHN) Biquad --- p.31 / Chapter 4.2.1 --- State Variable Method --- p.31 / Chapter 4.2.2 --- KHN Biquad --- p.32 / Chapter 4.3 --- Proposed Filter --- p.33 / Chapter 4.3.1 --- Biquad with CDN --- p.33 / Chapter 4.3.2 --- A dvantages of Proposed Filter --- p.36 / Chapter 4.3.3 --- Schematic of Proposed Filter --- p.38 / Chapter CHAPTER 5 --- LAYOUT CONSIDERATION --- p.41 / Chapter 5.1 --- Overview --- p.41 / Chapter 5.2 --- Process Information --- p.41 / Chapter 5.3 --- Transistor Layout Techniques --- p.42 / Chapter 5.3.1 --- Multi-finger Layout Technique --- p.42 / Chapter 5.3.2 --- Common-Centroid Structure --- p.43 / Chapter 5.3.3 --- Guard Ring --- p.45 / Chapter 5.4 --- Passive Element Layout Techniques --- p.45 / Chapter 5.5 --- Layout of Whole Design --- p.47 / Chapter CHAPTER 6 --- SIMULATION RESULT --- p.49 / Chapter 6.1 --- Operational Amplifier --- p.49 / Chapter 6.2 --- Overall Performance of filter --- p.55 / Chapter CHAPTER 7 --- MEASUREMENT RESULT --- p.60 / Chapter 7.1 --- Measurement Setup --- p.60 / Chapter 7.2 --- Time Domain Measurement --- p.62 / Chapter 7.3 --- Frequency Domain Measurement --- p.63 / Chapter 7.4 --- Measurement of Non-Linearity --- p.66 / Chapter 7.5 --- Summary of the Performance --- p.69 / Chapter 7.6 --- Comparison on Tuning Ability --- p.70 / Chapter CHAPTER 8 --- CONCLUSION --- p.71 / BIBLIOGRAPHY --- p.72