# Effect of Pole Head Profile on Torque Performance of a Disc-Type Multipole Magnetorheological Brake
## 3 Pole Head Geometry  
The pole head geometry should be improved to obtain maximum shear stress, which helps in increasing braking torque. The magnetic field induced by the coil winding flows through the shank and reaches the pole head assembled inside the nonmagnetic stator case in the form of flux lines. The pole head can be divided into three regions: the central region, where the pole is responsible for passing the maximum flux; the high field region, where the pole head experiences the maximum flux flow after the central region; and the low field region, which occurs at the edges of the poles where the flux flow is less. A smaller magnetic field allows the flow to drop more rapidly at the edge of the pole heads. Pole head profiles have to be changed appropriately to enhance the braking torque in compact magnetorheological brake configurations. The effective working area of MR fluid depends on the pole head area: if the area increases, then shear stress developed in the MR fluid increases, resulting in higher braking torque. So, square and trapezoid pole head shapes were considered in this study for larger pole head areas. Magnetic flux flow is another factor that is influenced by the pole head's area. If the gap between poles is smaller, the flux flow from one pole to the adjacent pole might be bypassed. Considering this aspect, the hexagon and pentagon pole head shapes with larger areas are arranged in a symmetrically linear configuration. The radial distance between the center of the pole to the center of the brake affects the final torque. An ellipse pole head profile is considered to achieve a larger radial distance and also a larger gap between the poles. To obtain higher torque and overcome the bypass of flux flow in this compact design, different geometric \begin{table}
\begin{tabular}{c c} \hline \hline
**Properties** & **MRF-140 CG** \\ \hline Viscosity at 40 \({}^{\circ}\)C & 0.280 Pa-s \\ Density & 3.64 g/cm\({}^{3}\) \\ Thermal conductivity & 0.28–1.28 W/m\({}^{\circ}\)C \\ Operating temperature & \(-\)40 to +130 \({}^{\circ}\)C \\ Yield strength at 200 kA/m & 57 kPa \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Properties of magnetorheological fluid (MRF-140 CG). Figure 2: (**a**) Elliptical shank and circular shank; (**b**) flux flow between adjacent poles in a magnetorheological brake poles. pole head profiles--as shown in Figure 3--such as square, trapezoid, pentagon, ellipse, hexagon and circle were analyzed. For the simulation study, electromagnetic analysis was carried out to calculate the amount of magnetic field generated. It is a flexible platform that allows users to model all relevant physical aspects of any type of design and is used to support the optimization process of torque enhancement. In this analysis, the resulting magnetic field intensity distribution within the magnetorheological brake configuration was analyzed. The magnetorheological brake can be modeled and evaluated using finite element analysis software like COMSOL, which is commonly used for electromagnetic modeling. To develop a 3D model of a magnetorheological fluid brake, Solid Works was used, and COMSOL Multiphysics was used to calculate magnetic flux with changing pole head shape. One of the benefits of utilizing COMSOL is the material definition feature, which allows us to define the nonlinear connection between magnetic flux and magnetic field, known as the B-H curve. The surface integration tool helped us to compute the magnetic flux on the core surface and MR fluid, which led us to use a 2D graph that illustrates the magnetic flux density on the disks. The simulation was performed with various numbers of turns in a coil and also by varying the current. The load in the present problem is the current flowing through the coil, responsible for the magnetic flux. Another benefit of COMSOL for accuracy in the output is the ability to modify the size of the elements in the mesh section.