A note on the magnetic spatial forcing of a ferrofluid layer
  We report on the response of a thin layer of ferrofluid to a spatially modulated magnetic field. This field is generated by means of a constant current in a special arrangement of aluminum wires. The full surface profile of the liquid layer is recorded by means of the absorption of X-rays. The outcome is analyzed particularly with regard to the magnetic self focusing effect under a deformable fluid layer. 
Thomas Friedrich, Adrian Lange, Ingo Rehberg, Reinhard Richter
physics.flu-dyn