the manipulation of superparamagnetic microbeads for lab-on-a-chip applications relies on the steering of microbeads across an altering stray field landscape on top of soft magnetic parent structures. Using ab initio principles, we show three-dimensional simulations forecasting the controlled movement of microbeads. Simulated aspects of microbead behaviour include the looping and lifting of microbeads around a magnetic circular structure, the flexible bead movement along symmetrically distributed triangular structures, and the dragging of magnetic beads across an array of exchange biased magnetic microstripes. the unidirectional motion of microbeads across a string of oval elements is predicted by simulations and validated experimentally. each of the simulations matches the experimental results, proving the robustness and accuracy of the applied numerical method. the computer experiments provide details on the particle motion not accessible by experiments. the simulation capabilities prove to be an essential part for the estimation of future lab-on-chip designs. Downsizing and integrating the functionality of traditional laboratory capabilities onto a microchip is a focus of research on lab-on-a-chip devices 1-8. The building blocks of these devices are functional elements like sensors or valves connected by microfluidic channels 9. At the same time the controlled manipulation of magnetic particles has gathered much attention for possible bio-applications, allowing transport, separation, and detection of magnetic micro-or nanoparticles 7,10-12. Functionalized superparamagnetic microbeads (MB) are widely used in labelling and detection of biomedical species 13-15. The movement of MBs on magnetic parent structures has been investigated experimentally using different schemes utilizing structured hard magnets 14,16,17 , soft magnets 7,12,18,19 , or magnetic thin full films as the parent structure 10,20-22. For soft magnetic structures, a large number of designs such as rings 12,23 , stripes 20,24 , periodic arrays of elements 7,19,25 , and mixed structures 26 can be employed to generate particle specific paths of motion. In general, the behaviour of the MBs on the magnetic structures is defined by the magnetostatic interaction between the MBs and the magnetic structures over which an external magnetic vector field is applied. By changing the external field and thereby the magnetic microstructure of the employed magnetic structures, motion of the MBs is achieved by changing the correlated potential energy landscape. In these cases, the speed of motion is limited by the hydrodynamic drag and surface friction acting on the MB for a fixed potential energy gradient. The modelling of MB behaviour by quantitative descriptions of the magnetic forces between the superparamagnetic MBs and the micromagnetic state of the parent structure, as well as the hydrodynamic drag forces, is of great interest for the design of new structures to achieve specific functionalities 12,16,27,28. Various simulations considered different aspects ...
