Electrorheological Fluid (ER fluid) is a type of smart fluid that changes its viscosity in response to an electric field. When an electric field is applied, the particles within the fluid align and form structures, making the fluid behave more like a solid. This property allows ER fluids to be used in various applications, such as in clutches, dampers, and shock absorbers. The unique behavior of ER fluids makes them valuable in industries requiring precise control of movement and force. They can quickly switch between liquid and solid states, enabling innovative designs in automotive, aerospace, and robotics technologies.