Electrorheological fluid

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Electrorheological fluids or electrorheological fluids (abbreviated: ERF ) are adaptive materials, the flow behavior of which can be controlled quickly and reversibly over a wide range by an electric field .

Underlying physical effect

A distinction is made between homogeneous and heterogeneous electrorheological fluids. The homogeneous ERF exist z. B. from aluminum salts of stearic acid. The mechanism of action of the homogeneous ERF is not known with absolute certainty. The heterogeneous ERF consist of polarizable particles or droplets which are immersed in an electrically non-conductive carrier liquid, e.g. B. silicone or mineral oil, are dispersed.

Dipoles are induced in the particles by an external electric field . The particles form chains and columns along the lines of the electric field. This so-called chain model according to Winslow is the simplest structural model to explain the electrorheological effect. Macroscopically, the rheological behavior of such fluids can be explained with the Bingham model .

Practical application and areas of application

Electrorheological fluids are mostly used as a central component of a mechatronic system. Together with a housing, a high-voltage power supply and a corresponding control or regulation , these systems can react to different framework conditions.

For example, the damping properties of hydraulic bearings can be controlled by using an electrorheological fluid. When using such a bearing as an engine mount in an automobile, the damping could be dynamically adapted to the speed of the engine and the nature of the ground in order to reduce the noise pollution for the occupants.

When transporting sick people or sensitive goods, conventional passive dampers are only suitable to a limited extent. Actively controllable dampers based on ERF can help here.

With the help of ERF, haptic sensor-actuator systems can also be implemented. Other areas of application are actuators , valves, clutches and brakes.

Electrorheological fluids are just as resilient as their raw materials. When used as a variable brake, modern ERF, unlike solid brakes, are not abrasive and are comparatively temperature-stable. However, there are also ERF formulations that could be used as abrasives due to their high abrasiveness.

Current development trends

Research and development over the past few years have resulted in significant improvements in both the rheological and electrical properties of electrorheological fluids. The development has particularly focused on ERF made of polymer particles . With these electrorheological suspensions z. B. from polyurethane particles , dispersed in a silicone oil as a carrier, abrasion and wear no longer play a role. On the one hand, the soft and elastic particles have no abrasive influence on the mechanical components of the ER systems (pumps, valves), on the other hand, due to their flexibility, they are themselves extremely resistant to mechanical wear, so that no degradation of the ERF even under extreme mechanical stress is to be recorded.

By skillfully modifying the particle surface with a chemical dispersant , the remaining tendency to sedimentation of the suspension can now be well controlled by the remaining density difference between particles and carrier fluid. This surface adaptation also helps with the redispersion of the ER fluids after a longer standing time. As a result of these measures, ERFs are available today, which are characterized by good constancy of the characteristic values ​​even over long periods of time.

Web links

Individual evidence

  1. ^ Winslow, Willis M. (1949). "Induced vibration of suspensions". J. Appl. Phys. 20: 1137-1140.
  2. ↑ Christoph Stiebel: The sky hook - transport goods seem to float above the road. ( Memento of the original from January 16, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. In: Magazin forschung 2/2000, pp. 34–38. @1@ 2Template: Webachiv / IABot / www.uni-saarland.de
  3. ↑ hasasem.de: Haptic sensor-actuator system
  4. ↑ M. Gurka, D. Adams, L. Johnston and R. Petricevic: New electrorheological fluids - characteristics and implementation in industrial and mobile applications , 11th Conference on Electrorheological Fluids and Magnethorheological Suspensions 2008 Proceedings 012008.
  5. ↑ Patent WO 2007/121942 A1