Electrorheological fluid
Electrorheological fluids, electrorheological fluids, respectively (abbreviated: ERF ) are adaptive materials whose flow behavior can be controlled rapidly and reversibly within a wide range by an electric field.
Underlying physical effect
A distinction is made between homogeneous and heterogeneous electrorheological fluids. The homogeneous ERF consist, for example, 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 in an electrically non-conductive carrier liquid, such as Silicone or mineral oil are dispersed.
By an external electric field induces dipoles in the particles. The particles form chains along the field lines and columns of the electric field. This so-called chain model to Winslow is the simplest structural model for the explanation of the electrorheological effect. Macroscopically can be explained with the Bingham model, the rheological behavior of such fluids.
Practical Application and areas of
Electrorheological fluids are mostly used as a central component of a mechatronic system. With a housing, a high voltage power supply and an appropriate control or regulation of these systems can respond to different parameters.
Thus, the damping characteristics of the hydraulic bearing through the use of an electrorheological fluid, for example, be controlled. When using such a camp as an engine mount in an automobile, the attenuation could be dynamically adapted to the speed of the motor and the nature of the subsurface to reduce the noise level for the occupants.
When transporting sick people or sensitive goods, conventional, passive dampers are limited. Active variable damper based on ERF can help here.
With the help of ERF also haptic sensor-actuator systems can be realized. Other applications include actuators, valves, clutches and brakes.
Electrorheological fluids are as durable as their raw materials. When used as a variable brake modern ERF are different than solid brakes are not abrasive and relatively temperature stable. However, there are ERF formulations which could be used due to their high abrasive as an abrasive.
Current trends
Researches and developments of recent years have led to significant improvements in both the rheological and electrical properties of electrorheological fluids. Here, the development has particularly focused on ERF of polymer particles. With these electrorheological suspensions, for example, polyurethane particles dispersed in a silicone oil as a carrier, abrasion and wear no longer play a role. The soft and elastic particles to a no abrasive effect on the mechanical components of the ER- systems (pumps, valves), on the other hand they are extremely durable due to its flexibility even against mechanical wear, so that even under the most violent mechanical stress, no degradation of the ERF is to list it.
By a clever modification of the particle surface with a chemical dispersant may now be readily controlled by the remaining difference in density between the particles and the carrier fluid, the remainder of sedimentation of the suspension. This also helps in the matching surface of redispersion of the ER fluids after a prolonged service life. These measures are now available ERF, which are characterized by a good constancy of parameters over longer periods of time.