ÖSSUR NEWS – P. 20
Phenomenon
MR f
Once activated, a magneto-rheological fluid can go from liquid to solid within a few milliseconds. This attribute means magnetic fluid can be used in anything from vehicles and earthquake-proof buildings to exercise bikes and washing machines. Text: Anders Lindgren
magneto-rheological fluid (also known as MR fluid or smart fluid) is a fluid with attributes that can be controlled by a magnetic field, usually generated by an electromagnet. Depending on the force of the magnetic field, the fluid can change from behaving like a free-flowing oil to a solid, rubbery material. The viscosity can be controlled very precisely and the transitions between different states take just a few milliseconds. THIS EFFECT IS POSSIBLE THANKS TO the fluid containing small magnetic particles, usually iron, 0.1–10 nanometres in diameter. Without a magnetic field, the particles are randomly dispersed in the oil, which makes the fluid free-flowing. However, when subjected to the current in a magnetic field, the particles align with the flux of the
magnetic field and the fluid becomes rigid. MR FLUID CAN be used in three different ways, depending on the application. In shock absorbers, the fluid flows between two plates that do not move relative to each other. In couplings and brakes, the fluid regulates shear resistance between two or more places that move relative to each other. And, in some applications, the fluid is between two layers that are pressed together or pulled, especially in millimetre-sized movements involving major forces. ALTHOUGH MAGNETIC fluids have been around since the 1940s and have been developed extensively from the 1960s onwards, there were few applications for MR fluids until around 1990. More than anything, this was because of a lack of reliable ways to control the fluid. Today, however, using signal processors and inexpensive computers, the magnetic field can be controlled with a high degree of precision. This has led to a virtual explosion in
