A field-modulated electroosmotic flow （FMEOF） in a microchannel can be obtained by applying modulating electric fields in a direction perpendicular to the channel wall. Micro-vortexes are generated around the electr...A field-modulated electroosmotic flow （FMEOF） in a microchannel can be obtained by applying modulating electric fields in a direction perpendicular to the channel wall. Micro-vortexes are generated around the electrodes along with an EOF due to the surface charge on the modulated wall. When polarizable particles are suspended near the electrodes, they experience dielectrophoretic forces due to a non-uniform electric field. In this paper, micro-vortexes and dielectrophoretic forces are combined to achieve separation and trap different sized particles in a continuous flow. Numerical results indicate that by adjusting the driving electric field parallel to the channel wall and the modulating electric field, the ratio of dielectrophoretic and hydrodynamic forces can be altered. One type of particles can be trapped by micro-vortexes （negative dielectrophoresis （DEP））, and the other particles are transported to the downstream so that the particles are separated. The influence of the electrode length and the channel height on the trapping rate is investigated.展开更多
In this paper, a coordinate transformation method (CTM) is employed to numerically solve the Poisson–Nernst–Planck (PNP) equation and Navier–Stokes (NS) equations for studying the traveling-wave electroosmotic flow...In this paper, a coordinate transformation method (CTM) is employed to numerically solve the Poisson–Nernst–Planck (PNP) equation and Navier–Stokes (NS) equations for studying the traveling-wave electroosmotic flow (TWEF) in a two-dimensional microchannel. Numerical solutions indicate that the numerical solutions of TWEF with and without the coordinate transformation are in good agreement, while CTM effectively improves stability and convergence rate of the numerical solution, and saves computational cost. It is found that the averaged flow velocity of TWEF in a micro-channel strongly depends on frequency of the electric field. Flow rate achieves a maximum around the charge frequency of the electric double layer. The approximate solutions of TWEF with slip boundary conditions are also presented for comparison. It is shown that the NS solution with slip boundary conditions agree well with those of complete PNP-NS equations in the cases of small ratios of Electric double layer(EDL) thickness to channel depth(λD/H). The NS solution with slip boundary conditions over-estimates the electroosmotic flow velocity as this ratio(λD/H) is large.展开更多
Dielectrophoresis （DEP） is one of the most popular techniques for bio-particle manipulation in microfluidic systems. Traditional calculation of dielectrophoretic forces of single particle based on the approximation ...Dielectrophoresis （DEP） is one of the most popular techniques for bio-particle manipulation in microfluidic systems. Traditional calculation of dielectrophoretic forces of single particle based on the approximation of equivalent dipole moment （EDM） cannot be directly applied on the dense particle interactions in an electrical field. The Maxwell stress tensor （MST） method is strictly accurate in the theory for dielectrophoretic forces of particle interaction, but the cumbersome and complicated numerical computation greatly limits its practical applications. A novel iterative dipole moment （IDM） method is pre- sented in this work for calculating the dielectrophoretic forces of particle-particle inter- actions. The accuracy, convergence, and simplicity of the IDM are confirmed by a series of examples of two-particle interaction in a DC/AC electrical field. The results indicate that the IDM is able to calculate the DEP particle interaction forces in good agreement with the MST method. The IDM is a purely analytical operation and does not require complicated numerical computation for solving the differential equations of an electrical field while the particle is moving.展开更多
The dielectrophoretic technology has been one of the most frequently applied microfluidic technologies to manipulate particles.The way of a combination of controlled electroosmotic micro-vortices and dielectrophoresis...The dielectrophoretic technology has been one of the most frequently applied microfluidic technologies to manipulate particles.The way of a combination of controlled electroosmotic micro-vortices and dielectrophoresis to manipulate particles of different sizes was proposed in our previous work.However,the thickness of the modulating electrode is neglected.In practice,when the thickness of the modulating electrode increases,the channel flux increases,while the ability of the vortex to capture the particles reduces.In this study,a new method combining the field-modulating electroosmotic vortex and the insulating post is proposed to improve the manipulating capability of the field-modulated electroosmotic vortex to particles.The results indicate that there are three great advantages as the insulating post is placed on the channel wall on the same side of the modulating electrode.First,the capturing ability of the vortex to particles is greater due to the reduction of channel flux and the squeezing effect.Second,the range of regulating channel flux to achieve the optimal separation is extended.Third,the separation efficiency improves since the perfect separation can be achieved at a higher flow rate.Furthermore,the effects of the location and the size of the insulating post on particle separation are analyzed in detail.The present work could provide the reference for the application of the DEP technology.展开更多
A wearable micro-sensor motion capture system with 16 IMUs and an error-compensatory complementary filter algorithm for real-time motion estimation has been developed to acquire accurate 3D orientation and displacemen...A wearable micro-sensor motion capture system with 16 IMUs and an error-compensatory complementary filter algorithm for real-time motion estimation has been developed to acquire accurate 3D orientation and displacement in real life activities.In the proposed filter algorithm,the gyroscope bias error,orientation error and magnetic disturbance error are estimated and compensated,significantly reducing the orientation estimation error due to sensor noise and drift.Displacement estimation,especially for activities such as jumping,has been the challenge in micro-sensor motion capture.An adaptive gait phase detection algorithm has been developed to accommodate accurate displacement estimation in different types of activities.The performance of this system is benchmarked with respect to the results of VICON optical capture system.The experimental results have demonstrated effectiveness of the system in daily activities tracking,with estimation error 0.16 ± 0.06m for normal walking and 0.13 ± 0.11m for jumping motions.展开更多
基金Project supported by the National Natural Science Foundation of China(No.11572139)
文摘A field-modulated electroosmotic flow （FMEOF） in a microchannel can be obtained by applying modulating electric fields in a direction perpendicular to the channel wall. Micro-vortexes are generated around the electrodes along with an EOF due to the surface charge on the modulated wall. When polarizable particles are suspended near the electrodes, they experience dielectrophoretic forces due to a non-uniform electric field. In this paper, micro-vortexes and dielectrophoretic forces are combined to achieve separation and trap different sized particles in a continuous flow. Numerical results indicate that by adjusting the driving electric field parallel to the channel wall and the modulating electric field, the ratio of dielectrophoretic and hydrodynamic forces can be altered. One type of particles can be trapped by micro-vortexes （negative dielectrophoresis （DEP））, and the other particles are transported to the downstream so that the particles are separated. The influence of the electrode length and the channel height on the trapping rate is investigated.
文摘In this paper, a coordinate transformation method (CTM) is employed to numerically solve the Poisson–Nernst–Planck (PNP) equation and Navier–Stokes (NS) equations for studying the traveling-wave electroosmotic flow (TWEF) in a two-dimensional microchannel. Numerical solutions indicate that the numerical solutions of TWEF with and without the coordinate transformation are in good agreement, while CTM effectively improves stability and convergence rate of the numerical solution, and saves computational cost. It is found that the averaged flow velocity of TWEF in a micro-channel strongly depends on frequency of the electric field. Flow rate achieves a maximum around the charge frequency of the electric double layer. The approximate solutions of TWEF with slip boundary conditions are also presented for comparison. It is shown that the NS solution with slip boundary conditions agree well with those of complete PNP-NS equations in the cases of small ratios of Electric double layer(EDL) thickness to channel depth(λD/H). The NS solution with slip boundary conditions over-estimates the electroosmotic flow velocity as this ratio(λD/H) is large.
基金Project supported by the National Natural Science Foundation of China(No.11172111)
文摘Dielectrophoresis （DEP） is one of the most popular techniques for bio-particle manipulation in microfluidic systems. Traditional calculation of dielectrophoretic forces of single particle based on the approximation of equivalent dipole moment （EDM） cannot be directly applied on the dense particle interactions in an electrical field. The Maxwell stress tensor （MST） method is strictly accurate in the theory for dielectrophoretic forces of particle interaction, but the cumbersome and complicated numerical computation greatly limits its practical applications. A novel iterative dipole moment （IDM） method is pre- sented in this work for calculating the dielectrophoretic forces of particle-particle inter- actions. The accuracy, convergence, and simplicity of the IDM are confirmed by a series of examples of two-particle interaction in a DC/AC electrical field. The results indicate that the IDM is able to calculate the DEP particle interaction forces in good agreement with the MST method. The IDM is a purely analytical operation and does not require complicated numerical computation for solving the differential equations of an electrical field while the particle is moving.
基金Project supported by the National Natural Science Foundation of China(No.11572139)。
文摘The dielectrophoretic technology has been one of the most frequently applied microfluidic technologies to manipulate particles.The way of a combination of controlled electroosmotic micro-vortices and dielectrophoresis to manipulate particles of different sizes was proposed in our previous work.However,the thickness of the modulating electrode is neglected.In practice,when the thickness of the modulating electrode increases,the channel flux increases,while the ability of the vortex to capture the particles reduces.In this study,a new method combining the field-modulating electroosmotic vortex and the insulating post is proposed to improve the manipulating capability of the field-modulated electroosmotic vortex to particles.The results indicate that there are three great advantages as the insulating post is placed on the channel wall on the same side of the modulating electrode.First,the capturing ability of the vortex to particles is greater due to the reduction of channel flux and the squeezing effect.Second,the range of regulating channel flux to achieve the optimal separation is extended.Third,the separation efficiency improves since the perfect separation can be achieved at a higher flow rate.Furthermore,the effects of the location and the size of the insulating post on particle separation are analyzed in detail.The present work could provide the reference for the application of the DEP technology.
基金supported by the National Natural Science Foundation of China(Nos.61431017,81272166)
文摘A wearable micro-sensor motion capture system with 16 IMUs and an error-compensatory complementary filter algorithm for real-time motion estimation has been developed to acquire accurate 3D orientation and displacement in real life activities.In the proposed filter algorithm,the gyroscope bias error,orientation error and magnetic disturbance error are estimated and compensated,significantly reducing the orientation estimation error due to sensor noise and drift.Displacement estimation,especially for activities such as jumping,has been the challenge in micro-sensor motion capture.An adaptive gait phase detection algorithm has been developed to accommodate accurate displacement estimation in different types of activities.The performance of this system is benchmarked with respect to the results of VICON optical capture system.The experimental results have demonstrated effectiveness of the system in daily activities tracking,with estimation error 0.16 ± 0.06m for normal walking and 0.13 ± 0.11m for jumping motions.
