# Advancements in Semi-Active Automotive Suspension Systems with Magnetroheological Dampers: A Review
## 3 Magnetorheological Dampers (MRDs)  
MRDs represent a novel class of intelligent damping devices utilizing MRF as their filling material, widely employed in semi-active suspension systems. Their operational principle involves altering the viscosity of the MRF by manipulating magnetic fields that orderly align magnetic particles within the fluid under magnetic influence, thereby increasing its viscosity [5,25], as illustrated in Figure 3[25]. They are distinguished by rapid response speed, excellent reversibility, compact size, low energy consumption, the ability to adjust damping force continuously across a wide range, and high reliability. Currently, they have found extensive applications in the aerospace, construction, and automotive industries. In recent years, there has been a notable upsurge in research efforts focused on MRDs at prominent universities and research institutions [26]. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Suspension Type** & **Advantages** & **Disadvantages** & **Applications** \\ \hline \multirow{2}{*}{Passive} & \multirow{2}{*}{Simple, reliable, low cost} & Fixed damping, less effective in & \multirow{2}{*}{Most common, entry-level vehicles} \\  & & varying conditions & \\ \hline \multirow{2}{*}{Semi-active} & Improved damping, & \multirow{2}{*}{Complex design, \multirow{2}{*}{control-dependent}} & \multirow{2}{*}{Mid to high-end vehicles, aerospace} \\  & energy-efficient, reliable & & \\ \hline \multirow{2}{*}{Active} & Best performance, real-time & High energy consumption, & \multirow{2}{*}{High-end vehicles, racing cars, limited use} \\  & adjustment & expensive, less reliable & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Advantages, disadvantages, and applications of different suspension types. The design of MRDs is intricate, involving multiple physical factors such as fluid dynamics, circuits, magnetic fields, and dynamics. Their dynamic characteristics depend on factors such as magnetic field distribution, current intensity, fluid properties, and damper structure, posing significant challenges in research. The technology of MRF was initially discovered and successfully developed by American scholar [PERSON] in 1948 [27]. In 1953, [PERSON] proposed the application of controllable fluids in dampers and designed a controllable damper capable of smoothly adjusting damping force over a wide range [28]. However, over subsequent decades, this technology did not attract widespread attention from industry and research institutions. In recent years, MRF has garnered attention compared to electrorheological fluid (ERF) due to its exceptional material properties and performance advantages, leading to the introduction of various new MRF products. The American company Lord Corporation is a pioneer in applying MRF technology to the commercial sector. In 1994, [PERSON] and [PERSON] proposed the use of MRF in controllable dampers, addressing issues associated with ERF, such as low yield strength, high input requirements, and vulnerability to environmental contamination [29]. Following this, numerous researchers began applying MRF in dampers and conducted extensive experimental studies. By adjusting the intensity and direction of the magnetic field, they controlled the rheological properties of MRF to achieve regulation and control of the dampers. Studies have demonstrated that MRF exhibits excellent characteristics such as reversibility and fast response speed. With continuous development and improvement of MRF technology, the performance and control precision of MRDs have been further enhanced, laying a solid foundation for their widespread application in automotive, aerospace, and architectural fields [5]. Between 1990 and 1995, Lord Corporation filed numerous patents related to MR technology, with a primary focus on research into MRF formulations and damper designs [29; 30].