Magnetically Controlled Fluids and Solids

Magneto-rheological fluids (MRF) and magnetically controlled elastomers (MCE) respond to a magnetic field immediately and reversibly with a change in rheological or elastic behaviour, respectively, acting as magnetically functional materials.

In both cases ferromagnetic iron particles (3-10 micron in diameter) are suspended in a carrier liquid such as mineral oil (MRF) or in a rubber matrix (MCE), respectively.

 The active principle of a MRF can be seen schematically in the sketch demonstrating the influence of an applied magnetic field resulting in a controllable yield strength.

A design form of magnetorheological (MR) fluid usage: direct shear mode with moving magnetic poles. Can be used in clutches, brakes and dampers.

In the frame of the European project VAST-IMAGE (completed 2006) elastomer seismic isolators and vibration mitigation dampers were developed. The stiffness can be semi-actively controlled by means of a variable magnetic field able to modify the mechanical parameters of the natural rubber compound. These composites consist of magnetically polarisable particles in an elastomer matrix. The complete systems contain additionally  permanent magnet circuits to ensure a constant high stiffness without energy input. In case of a detected seismic wave these  circuits are being compensated instantaneously by electromagnetic coils which have a local energy supply. At IFW Dresden, we designed, modelled and calculated (Finite Elemente Method) both systems: the seismic isolator and the vibration damper.

Shaking table with 15 tons mock-up and 3 Magnetically Controlled Elastomer Isolators. Tests (Earthquake Simulation) performed at our Italic industrial partner ENEA. View video demonstration (1.2MB).