Some topics developed at SiMMaS

Windmill-like concentrators

We have investigated how a thin windmill-like ferromagnetic system can hugely concentrate a magnetic field at its core. We have described the different effects that provide this enhancement: the thickness of the device and its unique windmill-like geometry. The idea is to use the central part of the windmill as a sensor that would enhance its sensitivity by a large factor due to the presence of the blades. Factors up to 150 times stronger than the applied field can be achieved.

Generic representation of a concentration device comparing the magnetic field modulus B in (a) a bare ferromagnetic cylindrical core with (b) the same ferromagnetic core but with a shell of windmill blades, both exposed to the same uniform in-plane magnetic field, B0.

These windmill-like concentrators have also been studied in the dimensional transition from 3D to 2D. Their properties have been analysed in detail, both theoretically and experimentally. This is a collaborative work together with ICMAB-CSIC in Barcelona, Université de Liège (Belgium), University of Bath (UK), and CEITEC of Brno University of Technology (Czech Republic) in the context of the METAMAGIC project.

Simulation of the variation in concentration gains with the concentrator thickness (outer radius Ro = 400 µm and inner radius Ri = 100 µm.). Panels (a) and (b) illustrate the differences in results obtained with a concentrator without a central core with a ferromagnetic core, respectively.
Schematic representation of the system and the XPEEM experiment employing X-ray Magnetic Circular Dichroism (XMCD) for magnetic contrast. The evolution of the average magnetic contrast as a function of the applied field is also depicted.

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Transformation of magnetic fields

We are interested in different ways of “controlling” static magnetic fields. That is, using different types of materials (i. e ferromagnets and/or superconductors) that can shape the field lines of a given source, we are studying how to manipulate these fields to cloak, transform, and, in general, mould them in a desired fashion.

Magnetic field B modulus for several sets of wires demonstrating the capacity of zero magnetic permeability media to add (a), subtract (b), confine (d,e), concentrate (f), or separate (g) their influence in different regions of space.
Finite-element simulations of the 3D colour map of the magnetic-field strength created by a superconducting toroid with a toroidal cavity and several circular loops immersed in the superconductor (a,d). The image also shows magnetic flux surfaces (b,e) at the superconducting-air boundary in the cavity.