Meng H. Lean

Membrane-free microfiltration by asymmetric inertial migration

Membrane-free microfiltration by asymmetric inertial migration is studied and evidence of the filtration capability is presented. Centrifugal force induced by flow in spiral channel geometry modifies the lateral symmetry of straight-channel tubular pinch equilibrium resulting in a focused particle band nearer to the inner sidewall. Bifurcated outlets separately collect the concentrated particle band and remaining effluent. The spiral continuous flow filtration relies solely on internal fluidic shear characteristics, eliminating the need for membrane filters or external force fields. This device has the desirable combinations of high throughput and low cost, making it inherently suited for preparative filtration in the range of micro- to macroscale applications.

On the creation of a generalized design optimization environment for electromagnetic devices

When optimizing designs for practical electromagnetic problems, the number of design constraints and variables is increased drastically. The construction and step-by-step creation of an electrical system, in practice, is a trial and error process. The design may lead to a sub-optimal solution since the success of a design depends on the experience of the designer. Optimization requires that all design goals, of a device, be connected into a single objective function with all independent variables and constraints, In practice, effective pre-processing and post processing of data are necessary In addition to the requirements of high performance computing capabilities. To achieve this process, we propose the utilization of the generalized design optimization environment or the virtual designer described in this paper.

Accurate field computation with the boundary element method

Interface problems in magnetostatics are formulated as boundary integral equations of the second kind involving the appropriate scalar (no current sources) or vector potentials. The boundary element method (BEM), which employs parametric representation of surfaces and sources, is used to solve some two-dimensional examples by way of illustration. A novel approach, automated to address Greens functions singularities over arbitrarily-shaped geometries, is introduced.

Nonlinear boundary element method for two‐dimensional magnetostatics

An interface formulation, successfully used for the solution of magnetostatic fields in piecewise homogeneous media, is extended to nonlinear media problems. The advantage of boundary integral techniques, in the reduction of problem dimensionality, is retained. This nonlinear boundary element method (BEM) algorithm alternates solution of the augmented interface equation with satisfaction of the constitutive media relations. Use of the M‐B chararteristics is shown to guarantee iteration stability because the slope approaches unity as μ tends to infinity. Isoparametric elements of second order are used for both geometry and sources to ensure high solution fidelity. Galerkin’s method is employed for discretization to matrix form. Each iteration requires only the product of the inverted system matrix with the augmented RHS. Examples include saturation of square and circular cylinders of high permeability in a uniform field. It is shown that with an optimal relaxation factor of 0.65, only 3–6 iterations are ...

Dual simple‐layer source formulation for two‐dimensional eddy current and skin effect problems

The integrodifferential expression resulting from a reformulation of the time‐harmonic diffusion equation to accommodate skin effect problems is further transformed, via an approximate average potential A0, to allow solution using a boundary integral technique. Conducting and nonconducting regions are initially separated into subregions. On each subregion boundary a simple‐layer distribution of sources is prescribed resulting in a first kind Fredholm integral equation. Dual simple‐layer sources are therefore distributed on subregion interfaces. The 2n equations derived from enforcing continuity of normal B and tangential H, using point collocation, are added to the current conservation equation for direct solution of the 2n+1 unknowns. This method allows subregion solutions to be decoupled once the sources are determined since the fields in any subregion are adequately prescribed by the corresponding source layer. Curved interfaces are modeled accurately by fourth‐order boundary elements. Numerical resu...

Application of boundary integral equation methods to electromagnetics

The use of boundary integral equation methods for the solution of some electromagnetic field problems are discussed. Boundary integral formulations using simple-layer potentials, and Greens formula, are explained. Readers are drawn to the similarity of discretization methods in use. Some salient features of the boundary element method are presented in review fashion. References are made to sample applications in a few problem areas. The paper concludes with a discussion that attempts to relate boundary integrals to partial differential methods.

Particle simulations of ion cloud in a magnetic field

This work describes a 3D time-dependent particle simulation algorithm used to model the electrodynamics of ion clouds in magnetic fields. The algorithm includes step-wise sequential stages of field evaluation, particle push, and boundary detection. Composite fields due to the ion cloud are computed by superimposing solutions for discrete point sources, together with the use of ground plane and image plane symmetries. A second-order modified Euler predictor-corrector method is used for integration of the equations of motion. Results are presented for an ion cloud under the influence of a bias E-field and the B-field from a magnetized spherical carrier bead used in laser printing applications. We consider cases with the dipole axis oriented parallel and perpendicular to the direction of cloud motion.

Novel integral formulation for scattering from multilayered dielectric cylinders of arbitrary cross section

A novel boundary integral formulation is implemented for the electromagnetic scattering of laser radiation from multilayered dielectric cylinders of arbitrary cross section. Because of the optical frequencies involved, problem size is controlled by a judicious choice of element size. Results for the more compute intensive Galerkin method are generated for comparison against the less time-consuming Moment method using linear isoparametric boundary elements. Singular kernels are integrated numerically using a technique that converges rapidly. Scattered intensities for both TE and TM polarizations on circular cylinders compare extremely well with analytic far-field predictions.

Charge transport in Navier-Stokes flow

The physics of charge transport in steady Navier-Stokes flow is modeled using a novel algorithm that considers full coupling of the electrostatic and fluid equations and is applicable to arbitrary geometries. The hybrid boundary element method-method of characteristics approach is used to solve the nonlinear set of charge transport equations. The fluid problem, inclusive of electrohydrodynamic effects, is solved using a vorticity-stream function boundary-integral-equation formulation that does not require vorticity boundary conditions to be specified a priori. A rapid iterative solution is afforded by the use of influence coefficient matrices that simplify reanalysis and recalculation of fields to the product and sum of matrices. The algorithm is fairly robust, and convergence to less than 2% maximum change is attained, with underrelaxation, in less than 15 iterations for moderately high Reynolds numbers. >

Readback bit shift with finite pole-length heads on perpendicular media

Perpendicular writing fields are calculated for finite pole-length gapped heads, with and without a permeable layer beneath the magnetic medium. These head fields are used to compute readback waveforms from ideal perpendicular transitions, which are detected both by zero-crossings and by inflection points of the waveform. Linear readback bit shift, given by the difference between detected and written transitions, is normalized to half the minimum transition spacing. For detection by waveform zero-crossing, bit shifts are unacceptably large with an under layer. Without an underlayer, detection by inflection point is considerably better than by waveform zero-crossing. Surprisingly, bit shifts from inflection points are only marginally better without an underlayer than with one. A recording system with an underlayer may in fact give superior performance because of other contributions to the total bit shift.