Smart fluid

A smart fluid is a fluid whose properties (most commonly the viscosity) can be changed by applying an electric field or a magnetic field.

The most developed smart fluids today are fluids whose viscosity increases when a magnetic field is applied. Small magnetic dipoles are suspended in a non-magnetic fluid, and the applied magnetic field causes these small magnets to line up and form strings that increase the viscosity. As of 2004, these materials are being used in the suspension of cars: depending on road conditions, the dampening fluid's viscosity is adjusted. This is more expensive than traditional systems, but it provides better control. Similar systems are being explored to reduce vibration of washing machines, air conditioning compressors, in rockets and satellites, and one has even been installed in Japan's National Museum of Emerging Science and Innovation in Tokyo as an earthquake shock absorber.

Some current haptic devices whose resistance to touch can be controlled are also based on these fluids.

Other smart fluids change their surface tension in the presence of an electric field. This has been used to produce very small controllable lenses: a drop of this fluid, captured in a small cylinder and surrounded by oil, serves as a lense whose shape can be changed by applying an electric field.