Magnetic circuits based on polymer composites for controlled actuation of a ferromagnetic sphere at a microfluidic junction

We present the utilization of polymer composites for the realization of magnetic circuits for flux density engineering. Three-dimensional composite structures for guidance and concentration of the magnetic flux density have been devised and realized, which are used to actuate a ferromagnetic sphere at the intersection of two microfluidic channels. Depending on the position of the sphere the flow in the single branches can be blocked or released, i.e. it resembles the functionality of a microfluidic valve. Additionally, it can also realize some kind of liquid logic in a microfluidic network. At certain positions of the sphere at the x-junction the incoming flow splits up into different fractions for the three outgoing channels. Interestingly enough, permutations of the outward flows can be realized by switching the position of the sphere to predefined positions. In our contribution we describe the technology for creating the desired magnetic flux densities in microstructures based on polymer composites, and we present the application of this approach for the controlled actuation of a ferromagnetic sphere at the x-junction of microchannels for the realization of a valve with multiple switching states.