Can ferrohydrodynamic instabilities be useful in transducers? [Instrumentation Notes]

Magnetic fluids are formed when magnetic particles are dispersed in a carrier liquid and suitably coated [1], [2]. Coating the particles provides an elastic shield which avoids particle friction, and it can be also used to implement bio-assay strategies. There are two types of magnetic fluids: magneto-rheological fluids and ferrofluids. The size of the dispersed particles is what distinguishes the two types of magnetic fluids: magnetorheological fluids containing magnetic particles with a diameter on the order of microns and the fluids change from a liquid to a solid in response to a high magnetic field while ferrofluids are colloidal suspensions of magnetic nanoparticles that maintain their liquid state in the presence of a strong magnetic field. In the case of ferrofluids, the higher the magnetization strength, the greater the magnetic pressure exerted by the fluid [3]. Magnetic fields applied to a ferrofluidic volume and the consequent magnetic force causes the alignment of the ferrofluidic particles in the direction of the field and modifies the viscosity and the control of the ferrofluid mass position. Interest in ferrofluids and magnetic particles exists because of the possibility of efficiently converting valuable elastic energy into mechanical energy in many applications. In this column, we describe some of the uses of ferrofluids and highlight ways to exploit its ferrohydrodynamic instabilities.