A Particle Flow Velocity Profiler Using In-Channel Electrodes With Unevenly Divided Interelectrode Gaps

This paper presents a particle flow velocity profiler that employs in-channel electrodes with unevenly divided interelectrode gaps. The proposed electrical method measures both the particle position and velocity from the voltage signals generated by particles passing across three sensing electrodes, thus obtaining the flow velocity profile of the particles in a microfluidic channel. In this paper, we use polystyrene microparticles to characterize the performance of the present particle flow velocity profiler. At flow rates of 1.85, 2.68, and 3.60 muL/min, a flow velocity profile of 6.59-mum-diameter particles is measured with an uncertainty of 5.44%, which is comparable to the uncertainty (5%) in a previous microparticle image velocimetry. From the voltage signals for 6.59- and 5.47-mum particles, we also verify that the present device detects the particle position showing less sensitivity to particle size variation than an existing particle impedance spectroscopy. In addition, in-channel clogging detection using the present electrical method is demonstrated. The present particle flow velocity profiler offers advantages of simpler structure, cheaper cost, and higher measurement stability that is insensitive to particle size for use in integrated microbiofluidic systems.     

Assessment of cross-type optical particle separation system

This paper describes the optical and hydrodynamic characteristics of particle motion in a cross-type optical particle separator. The retention distance modulated by the optical force on a particle was measured in three dimensions for various vertical and horizontal positions via ??-defocusing digital particle image velocimetry. The experimental data showed that the actual retention distance was smaller than the predicted retention distance under the assumption that the approaching velocity was constant through the cross-section of a microfluidic channel. The retention distance was shown to increase as the injection position of the particle shifted toward the channel side wall at a given vertical position due to a higher residence time within the region of influence of the laser beam. In contrast, the retention distance decreased as the injection position shifted toward the channel top/bottom walls at a given horizontal position. A theoretical modeling study was conducted to support and interpret the experimental measurements. The resolution of the particle separation procedure, which did not require adjusting the flow rate, laser power, or working fluid properties, was studied.     

Motion of a rigid cylinder between parallel plates in stokes flow : Part 1: Motion in a quiescent fluid and sedimentation

A general numerical scheme for solution of two-dimensional Stokes equations in a multiconnected domain of arbitrary shape [1, 2] is applied to the motion of a rigid circular cylinder between plane parallel boundaries. Numerically generated boundary-conforming coordinates are used to transform the flow domain into a domain with rectilinear boundaries. The transformed Stokes equations in vorticity-stream function form are then solved on a uniform grid using an iterative algorithm. In Part I coefficients of the resistance matrix representing the forces and torque on the cylinder due to its translational motion parallel or perpendicular to the boundaries or due to rotation about its axis are calculated. The solutions are obtained for a wide range of particle radii and positions across the channel. It is found that the force on a particle translating parallel to the boundaries without rotation exhibits a minimum at a position between the channel centerline and the wall and a local maximum on the centerline.

The resistance matrix is utilized to calculate translational and angular velocities of a free particle settling under gravity in a vertical channel. It is found that the translational velocity has a maximum at some lateral position and a minimum on the centerline; the particle angular velocity is opposite in sign to that of a particle rolling along the nearer channel wall except when the gap between the particle and the wall is very small. These results are compared with existing analytical solutions for a small cylindrical particle situated on the channel centerline, and with solutions of related 3-D problems for a spherical particle in a circular tube and in a place channel. It is shown that the behavior of cylindrical and spherical particles in a channel in many cases is qualitatively different. This is attributed to different flow patterns in these two cases. The motion of a spherical particle in a circular tube has qualitative and quantitative features similar to those for a cylindrical particle in a plane channel.     

Numerical simulations of particle migration in a viscoelastic fluid subjected to Poiseuille flow

In this work we present 2D numerical simulations on the migration of a particle suspended in a viscoelastic fluid under Poiseuille flow. A Giesekus model is chosen as constitutive equation of the suspending liquid. In order to study the sole effect of the fluid viscoelasticity, both fluid and particle inertia are neglected.The governing equations are solved through the finite element method with proper stabilization techniques to get convergent solutions at relatively large flow rates. An Arbitrary Lagrangian–Eulerian (ALE) formulation is adopted to manage the particle motion. The mesh grid is moved along the flow so as to limit particle motion only in the gradient direction to substantially reduce mesh distortion and remeshing.Viscoelasticity of the suspending fluid induces particle cross-streamline migration. Both large Deborah number and shear thinning speed up the migration velocity. When the particle is small compared to the gap (small confinement), the particle migrates towards the channel centerline or the wall depending on its initial position. Above a critical confinement (large particles), the channel centerline is no longer attracting, and the particle is predicted to migrate towards the closest wall when its initial position is not on the channel centerline. As the particle approaches the wall, the translational velocity in the flow direction is found to become equal to the linear velocity corresponding to the rolling motion over the wall without slip.     

Transient simulations of the electrophoretic motion of a cylindrical particle through a 90° corner

The trajectory of a cylindrical particle driven by electrophoresis was transiently simulated as the particle moves through a 90° corner. A variety of system parameters were tested to determine their impact on the particle motion. The zeta potential, channel width, and particle aspect ratio were shown to have a minimal effect on the particle motion. Conversely, the initial vertical position of the particle and initial angle with respect to the horizontal had a significant impact on the particle motion. The presence of the 90° corner acts to reduce the initial distribution of angles to the vertical of 90° to less than 30°, demonstrating the possibility of using a corner as a passive control element as part of a larger microfluidic system. However, the reduction in angle is limited to the area near the corner posing a limitation on this means of control.     

Computational dynamics method for evaluating the mobility of charged biomolecules passing through the electrical potential field within the ion selective channel on an excitable membrane

A mathematical method is introduced to characterize the electrokinetic behavior (electrophoresis) of a biomolecular particle which passes through a specific channel pore on an excitable biological membrane. The basic approach was first proposed by Booth (1950). The system was described by an equation of continuity and an equation of motion in which the driving force involves the diffusion effect, the hydrostatic pressure, and the electrostatic potential. By assuming linear relations between the velocity and the applied electrical field, solutions for the potential, pressure, and velocity were given by a series expansion of the charges on the particle. To examine the influence of ions surrounding the particle and forming an ionic cloud, the Debye–Huckel parameter was introduced. As the thickness of the double layer around the particle increased, the potential, velocity, pressure, and viscosity were changed significantly. The maximum influence was obtained when the radius of the particle became equal to the thickness of the double layer. Although this theory is valid for a charged, spherical, nonconducting particle only, the method is available for evaluating the kinetic behavior of a biomolecule that passes through a channel pore on a cellular membrane.This work was presented, in part, at the 8th International Symposium on Artificial Life and Robotics, Oita, Japan, January 24–26, 2003     

Eccentric electrophoretic motion of a sphere in circular cylindrical microchannels

The eccentric electrophoretic motion of a spherical particle in an aqueous electrolyte solution in circular cylindrical microchannels is studied in this paper. The objective is to investigate the influences of separation distance and channel size on particle motion. A theoretical model is developed to describe the electric field, the flow field and the particle motion. A finite element based direct numerical simulation method is employed to solve the model. Numerical results show that, when the particle is eccentrically positioned in the channel, the electric field and the flow field are not symmetric, and the strongest electric field and the highest flow velocity occur in the small gap region. It is shown that the rotational velocity of the particle increases with the decrease of the separation distance. With the decrease of the separation distance, the translational velocity increases in a smaller channel; while it decreases first and then increases in a relatively large channel. When a particle moves eccentrically at a smaller separation distance from the channel wall, both the translational velocity and the rotational velocity increase with the decrease of the channel size.     

Electrophoresis of a spherical particle in a spherical cavity

The electrophoretic motion of a charged spherical particle situated at an arbitrary position within a charged spherical cavity along the line connecting their centers is studied theoretically for the case of thin electric double layers. To solve the electrostatic and hydrodynamic governing equations, the general solutions are constructed using the two spherical coordinate systems based on the particle and cavity, and the boundary conditions are satisfied by a collocation technique. Numerical results for the electrophoretic velocity of the particle are presented for various values of the zeta potential ratio, radius ratio, and relative center-to-center distance between the particle and cavity. In the particular case of a concentric cavity, these results agree excellently with the available exact solution. The contributions from the electroosmotic flow occurring along the cavity wall and from the wall-corrected electrophoretic driving force to the particle velocity are equivalently important and can be superimposed due to the linearity of the problem. The normalized migration velocity of the particle decreases with increases in the particle-to-cavity radius ratio and its relative distance from the cavity center and increases with an increase in the cavity-to-particle zeta potential ratio. The boundary effects on the electrokinetic migration of the particle are significant and interesting.     

Experimental characterization of electrical current leakage in poly(dimethylsiloxane) microfluidic devices

Poly(dimethylsiloxane) (PDMS) is usually considered as a dielectric material and the PDMS microchannel wall can be treated as an electrically insulated boundary in an applied electric field. However, in certain layouts of microfluidic networks, electrical leakage through the PDMS microfluidic channel walls may not be negligible, which must be carefully considered in the microfluidic circuit design. In this paper, we report on the experimental characterization of the electrical leakage current through PDMS microfluidic channel walls of different configurations. Our numerical and experimental studies indicate that for tens of microns thick PDMS channel walls, electrical leakage through the PDMS wall could significantly alter the electrical field in the main channel. We further show that we can use the electrical leakage through the PDMS microfluidic channel wall to control the electrolyte flow inside the microfluidic channel and manipulate the particle motion inside the microfluidic channel. More specifically, we can trap individual particles at different locations inside the microfluidic channel by balancing the electroosmotic flow and the electrophoretic migration of the particle.     

Motion of a rigid cylinder between parallel plates in stokes flow : Part 2: Poiseuille and couette flow

A numerical solution is presented for the motion of a neutrally buoyant circular cylinder in Poiseuille and Couette flows between two plane parallel boundaries. The force and torque on a stationary particle are calculated for a wide range of particle sizes and poisitions across the channel. The resistance matrix calculated in Ref. [1] (henceforth referred to as Part 1) is utilized to find the translational and angular velocity for a drag- and torque-free particle. The results are compared with analytical perturbation solutions for a small cylindrical particle situated on the channel centerline, and for the motion of a spherical particle in a circular tube or between plane parallel boundaries. It is found the behavior of flow around a cylindrical particle in a channel is qualitatively similar to the behavior of flow around a spherical particle in a tube, while the flow around a spherical particle in a channel frequently exhibits different trends from the above two cases.     

DC dielectrophoretic focusing of particles in a serpentine microchannel

Focusing particles into a tight stream is usually a necessary step prior to separating and sorting them. We present herein a proof-of-concept experiment of a novel particle focusing technique in DC electrokinetic flow through a planar serpentine microchannel. This focusing stems from the cross-stream dielectrophoretic motion induced within the channel turns. The observed particle focusing behavior is consistent with the predicted particle trajectories from a numerical modeling.     

A novel method to construct 3D electrodes at the sidewall of microfluidic channel

We report a simple, low-cost and novel method for constructing three-dimensional (3D) microelectrodes in microfluidic system by utilizing low melting point metal alloy. Three-dimensional electrodes have unique properties in application of cell lysis, electro-osmosis, electroporation and dielectrophoresis. The fabrication process involves conventional photolithography and sputtering techniques to fabricate planar electrodes, positioning bismuth (Bi) alloy microspheres at the sidewall of PDMS channel, plasma bonding and low temperature annealing to improve electrical connection between metal microspheres and planar electrodes. Compared to other fabrication methods for 3D electrodes, the presented one does not require rigorous experimental conditions, cumbersome processes and expensive equipments. Numerical analysis on electric field distribution with different electrode configurations was presented to verify the unique field distribution of arc-shaped electrodes. The application of 3D electrode configuration with high-conductive alloy microspheres was confirmed by particle manipulation based on dielectrophoresis. The proposed technique offers alternatives to construct 3D electrodes from 2D electrodes. More importantly, the simplicity of the fabrication process provides easy ways to fabricate electrodes fast with arc-shaped geometry at the sidewall of microchannel.     

Time correlated fluorescence characterization of an asymmetrically focused flow in a microfluidic device

In this study, we explore and model the behavior of a prototype microfluidic device which employs two non-mixing fluids (sheath and inlet fluids) displaying an asymmetric focused flow, in the presence of a fluorescent dye. Fluorescence correlation spectroscopy is employed, allowing the precise measure of flow speeds across the channels and of the concentration profile of the central focused flux along the flow direction. The system is modeled via a standard Navier–Stokes finite-element approach, coupled to convection–diffusion equations for the solute. Simulations reproduce accurately the shape, the position, and the width of the velocity and concentration profiles along the central channel and across the transversal and vertical sections of the microfluidic device. The observed asymmetric flow with respect to the center of the channel is reproduced numerically with an error in the position determination smaller than 1%.     

Continuous size-based focusing and bifurcating microparticle streams using a negative dielectrophoretic system

Dielectrophoresis (DEP) is an electrokinetic phenomenon which is used for manipulating micro- and nanoparticles in micron-sized devices with high sensitivity. In recent years, electrode-based DEP by patterning narrow oblique electrodes in microchannels has been used for particle manipulation. In this theoretic study, a microchannel with triangular electrodes is presented and a detailed comparison with oblique electrodes is made. For each shape, the behavior of particles is compared for three different configurations of applied voltages. Electric field, resultant DEP force, and particle trajectories for configurations are computed by means of Rayan native code. The separation efficiency of the two systems is assessed and compared afterward. The results demonstrate higher lateral DEP force, responsible for particle separation, distributed wider across the channel width for triangular shape electrodes in comparison with the oblique ones. The proposed electrode shape also shows the ability of particle separation by attracting negative DEP particles to or propelling them from the flow centerline, according to the configuration of applied voltages. A major deficiency of the oblique electrodes, which is the streamwise variation of the lateral DEP force direction near the electrodes, is also eliminated in the proposed electrode shape. In addition, with a proper voltages configuration, the triangular electrodes require lower voltages for particle focusing in comparison with the oblique ones.     

Experimental research on resist filling behavior in microimprint lithography by using defocusing digital particle image velocimetry

The resist filling behavior is crucial to the quality of the final imprinted patterns in microimprint lithography. To achieve the microscale velocity field of resist, a 3-D defocusing digital particle image velocimetry (DDPIV) system was established. The spatial coordinates of 500 nm fluorescent tracer particles were inferred from their DDPIV images generated by a mask with three apertures forming an equilateral triangle. Time-resolved 3-D particle field inside the resist was obtained with the spatial coordinates of particles. Particle tracking velocimetry was utilized to derive the velocity field from the particle spatial position in the imprinting sequence. Velocity history of particles along the extracted track was described. The results showed that the maximum velocity of the resist was always located in the region between the mold corner and the supporting substrate; meanwhile, the velocity component of the resist in the vertical direction is approximate to zero. The volume transfer characteristics of resist was illustrated from the view of particle field and velocity field, which will help reveal the resist filling mechanism and provide useful guidance for the mold structure optimization.     

Quality assessment of SRTM C- and X-band interferometric data: Implications for the retrieval of vegetation canopy height

The Shuttle Radar Topography Mission distinguished itself as the first near-global spaceborne mission to demonstrate direct sensitivity to vertical vegetation structure. Whether this sensitivity is viewed as exploitable signal or unwanted bias, a great deal of interest exists in retrieving vegetation canopy height information from the SRTM data. This study presents a comprehensive application-specific assessment of SRTM data quality, focusing on the characterization and mitigation of two primary sources of relative vertical error: uncompensated Shuttle mast motion and random phase noise. The assessment spans four test sites located in the upper Midwestern United States and examines the dependence of data quality on both frequency, i.e., C-band vs. X-band, and the number of acquired datatakes. The results indicate that the quality of SRTM data may be higher than previously thought. Novel mitigation strategies include a knowledge-based approach to sample averaging, which has the potential to reduce phase noise error by 43 to 80%. The strategies presented here are being implemented as part of an ongoing effort to produce regional- to continental-scale estimates of vegetation canopy height within the conterminous U.S.     

On an adaptive control system for angular motion of a communication satellite

Synthesis of adaptive control system with adjustable model of the communication satellite without using data on angular velocity is considered. Information on deflection angles from the local vertical sensor and tachometers measuring angular velocities of rotation of rotors of three flywheels, and on angular mismatch about the local vertical is used in the control block. The information on the angle of rotation of the satellite about the local vertical is formed on the Earth based on the variation of the polarization plane of the radio signal transmitted from the satellite. The convergence of estimates of the parameters of angular motion to their actual values and the stability of the feedback control with respect to these estimates are studied. This algorithm can be applied as a reserve algorithm in case of failure of angular velocity sensors for prolonging the resource of the communication satellite.     

Time-optimal control of a particle in a dielectrophoretic system

We study the time-optimal control of a particle in a dielectrophoretic system. This system consists of a time-varying nonuniform electric field which acts upon the particle by creating a dipole within it. The interaction between the induced dipole and the electric field generates the motion of the particle. The control is the voltage on the electrodes which induces the electric field. Since we are considering the motion of a particle on an invariant line in a chamber filled with fluid flowing at low Reynolds number, the dynamics have a two dimensional state; one for the particle position and the other for the induced dipole moment. In regard to time-optimal control, we address the issue of existence and uniqueness of optimal trajectories, and explicitly compute the optimal control and the corresponding minimum time. Finally, we cast our analysis in the framework of symplectic reduction theory in order to provide geometric insight into the problem.     

Optimization of Intelligent Approach for Low-Cost INS/GPS Navigation System

Due to the inherent highly nonlinear vehicle state error dynamics obtained from low-cost inertial navigation system (INS) and Global Positioning System (GPS) along with the unknown statistical properties of these sensors, the optimality/accuracy of the classical Kalman filter for sensor fusion is not guaranteed. Therefore, in this paper, low-cost INS/GPS measurement integration is optimized based on different artificial intelligence (AI) techniques: Neural Networks (NN) and Adaptive Neuro-Fuzzy Inference System (ANFIS) architectures. The proposed approaches are aimed at achieving high-accuracy vehicle state estimates. The architectures utilize overlapping windows for delayed input signals. Both the NN approaches and the ANFIS approaches are used once with overlapping position windows as the input and once with overlapping position and velocity windows as the input. Experimental tests are conducted to evaluate the performance of the proposed AI approaches. The achieved accuracy is presented and discussed. The study finds that using ANFIS, with both position and velocity as input, provides the best estimates of position and velocity in the navigation system. Therefore, the dynamic input delayed ANFIS approach is further analyzed at the end of the paper. The effect of the input window size on the accuracy of state estimation is also discussed.