Magnetic forces produced by rectangular permanent magnets in static microsystems

Abstract

Finite element numerical simulations were carried out in 2D geometries to map the magnetic field and force distribution produced by rectangular permanent magnets as a function of their size and position with respect to a microchannel. A single magnet, two magnets placed in attraction and in repulsion have been considered. The goal of this work is to show where magnetic beads are preferentially captured in a microchannel. These simulations were qualitatively corroborated, in one geometrical case, by microscopic visualizations of magnetic bead plug formation in a capillary. The results show that the number of plugs is configuration dependent with: in attraction, one plug in the middle of the magnets; in repulsion, two plugs near the edges of the magnets; and with a single magnet, a plug close to the center of the magnet. The geometry of the magnets (h and l are the height and length of the magnets respectively) and their relative spacing s has a significant impact on the magnetic flux density. Its value inside a magnet increases with the h/l ratio. Consequently, bar magnets produce larger and more uniform values than flat magnets. The l/s ratio also influences the magnetic force value in the microchannel, both increasing concomitantly for all the configurations. In addition, a zero force zone in the middle appears in the attraction configuration as the l/s ratio increases, while with a single magnet, the number of maxima and minima goes from one to two, producing two focusing zones instead of only one.

Magnetic track array for efficient bead capture in microchannels

“…static bead solution in the microchannel), (f) the particle-fluid or inter-particle interaction are not considered. This numerical model has been previously validated showing a good correlation with published results [39,49].…”

“…The field line curvatures are at the origin of the F mag force maxima in these regions (due to the BrB term in Eq. 3) [8,39].…”

“…The process is simplified and larger magnetic fields (>0.5 T) and forces can be reached. In a recent study, the distribution of magnetic field and force in a microchannel surrounded by permanent magnets was simulated [39]. It has been shown that the magnetic field and force is restricted to a specific location defined by the magnet geometry and pole orientation (attraction, repulsion, single magnet).…”

Ring magnets for magnetic beads trapping in a capillary

“…28,38 In the case of permanent magnets and in the absence of charges in movement, the magnetic field H is irrotational and as the calculation domain is simply connected, H derives from a scalar magnetic potential f (H ¼ ÀVf). As the magnetic flux density B is conservative, the equation to be solved (using a Galerkin formulation, ESI 1 †) is written as:…”

Fabrication of Nanopillar Micropatterns by Hybrid Mask Lithography for Surface-Directed Liquid Flow

“…The reason for this is that magnetic fields can be a suitable power source for an on-chip robot, because of their non-contact drive, low invasiveness with respect to a cell and low production cost. Thus, a considerable amount of research has been carried out on magnetic actuators [6,7,[9][10][11][12][13][14]. We have achieved the high speed actuation of MMTs with high output force by applying the magnetic field of horizontally arranged permanent magnets.…”