## 3 Performance Comparison of the Proposed and Other Models
As illustrated in Figure 2, the magnetic path of the proposed motor is reduced, reducing the magnetic resistance and improving the motor performance, as indicated in Equation (9):  
\[B=\frac{\mu NI}{L} \tag{9}\]  
A longer magnetic path causes greater magnetic resistance and lower magnetic density. In contrast, a shorter magnetic path causes a greater magnetic density. In Equation (9), \(B\) denotes the magnetic field, \(\mu\) is the permeability, \(N\) indicates the number of turns, \(I\) denotes the current, and \(L\) represents the length of the magnetic path. In other words, Figure 2 indicates that the length of the magnetic path is shorter than that in Figure 1, resulting in less magnetic resistance and increased magnetic density. As presented in Figure 6, a salient pole is used to generate magnetic poles according to the electromagnet polarity. Installing the salient pole has advantages in solving the problem due to magnetic short circuits and reducing the use of PMs using rare-earth elements. \begin{table}
\begin{tabular}{c c} \hline \hline
**Items** & **New DHPM Vernier Motor** \\ \hline Angle of inclination of saddle motor & 7.5\({}^{\circ}\) \\ Maximum Outside diameter & 82 mm \\ Motor length & 35 mm \\ Air gap length & 0.5 mm \\ Coil & 0.8 mm, 1.09 \(\Omega\) \\ Coil turn number & 150 \\ Magnetic material & 50 JN400 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Specification of the proposed DHPM vernier motor. In Figure 7, we compare the inductive voltage of the SPM, DHPM, and model \"with salient poles.\" The induced voltage is (1) 1.24 V for the SPM vernier motor, (2) 1.61 V for the model with salient poles, and (3) 1.68 V for the DHPM motor. The comparison results indicate that the motor performance with salient poles is similar to or better than that of the DHPM. As displayed in Figure 8, the back EMF of the inductive voltage is similar to the DHPM model with only PMs in the stator or a model with salient poles to replace the PMs. The magnetic flux in the DHPM vernier motor is more robust than that in the SPM motor. However, the generated magnetic flux is limited between the teeth and rotor because it does not move sufficiently. Figure 9 presents the magnetic flux flow that occurs when replaced by salient poles instead of a PM in the slot in the DHPM vernier motor. Moreover, the magnetic flux density and flow pattern are similar to the motor model with a salient pole. Figure 6: Comparison of the surface permanent magnet (SPM) vernier motor, double half permanent magnet (DHPM) (with a PM in the stator) motor, and model with salient poles. Figure 7: Comparison of the induced voltage of the surface permanent magnet (SPM) vernier motor, double half permanent magnet (DHPM) motor, and motor with salient poles. Table 3 presents the comparison results of the performance of the SPM and proposed DHPM vernier motor using saddle coils with salient poles. The SPM and DHPM vernier motors have no slope, but the proposed DHPM vernier motor replaces the PM in the stator with the salient poles, employing an inclination angle. In addition, the coils of the predecessor and proposed model are wound in the same slot evenly. Moreover, the number of turns is the same, so resistance values are about the same. The proposed model focuses on reducing the magnetic resistance due to the smaller space and the circumference's smaller surface area. The inclination angle changed from 0\({}^{\circ}\) to 7.5\({}^{\circ}\). From the comparison results, the maximum external stator diameter is 82 mm, and the motor length is 35 mm. The air gap is 0.5 mm, and the coil diameter is 0.8 mm. The external rotor diameter is 42 mm, and the thickness of the PMs is 2 mm. The inclination angle between the stator's surface circumference and the axis of rotation of the rotor is 7.5\({}^{\circ}\). In a motor, as the magnetic flux of the \(d\)-axis transmits a low permeability magnet, the inductance is low, and the magnetic flux of the \(q\)-axis passes through the iron core.