## 4 Discussion  
According to the Figure 8, the observations were carried out for several cycles where each cycle consist of 10 s demagnetized state and 10 s magnetized state. From the figure, it was seen that the pressure was relatively stable in the initial cycle, while the pressure tended to increase in the subsequent cycles. In Figure 8, it can be seen that there is an increase in the pressure slope in the continuation cycle, due to the accumulation of magnetic particles in the previous cycle. This case occurs because, during demagnetization, the magnetic particles cannot be completely re-distributed in the fluid. It is evident that increases in the magnetic field have caused changes in the MRFs pressure. This is because the pressure sensor detects increases in the barometric pressure of the air above the MRFs. As seen in the boxplot shown in Figure 9, the MRFs pressure readings obtained during the experiment has only small deviations, which indicates the measurement consistency. The most apparent deviation in MRFs pressure occurred at an input current of 2.00 A. In general, the data was normally distributed except for the input current of 1.25 A, where the sole outlier is measured. According to the results, a sudden change of slope was detected when current excitation reached 2.00 A. This condition is slightly different from the other region, which might be the result of the heat dissipated from the coil when excited with a high current. During the experiment, the temperature of the coil bobbin was found to exceed 60 \({}^{\circ}\)C when excited with a 2.00 A current. The heat generated will slightly increase the wire resistance and decreased coil performance which was indicated by an observed decrease in the current input to the coil after few cycles of measurement. A similar case was also reported in the previous work about thermal modeling on heated injectors [35]. During the first cycle, the change in MRFs pressure was measured at 1020.01 Pa as the input current reached \begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline
**Current Input (A)** & **0.25** & **0.50** & **0.75** & **1.00** & **1.25** & **1.50** & **1.75** & **2.00** \\ \hline \(\triangle\)P\({}_{\min}\) (Pa) & 13.06 & 58.98 & 129.17 & 244.49 & 496.04 & 679.79 & 867.36 & 835.50 \\ \(\triangle\)P\({}_{\max}\) (Pa) & 18.39 & 65.91 & 155.64 & 292.53 & 533.77 & 739.02 & 942.50 & 1020.01 \\ \(\triangle\)P\({}_{\mathrm{avg}}\) (Pa) & 15.53 & 62.80 & 144.77 & 267.80 & 517.16 & 709.20 & 904.64 & 918.55 \\ \(\triangle\)P\({}_{\mathrm{median}}\) (Pa) & 15.34 & 63.16 & 147.14 & 267.09 & 519.42 & 708.99 & 904.34 & 909.34 \\ Std Deviation & 2.68 & 3.12 & 11.52 & 21.29 & 15.63 & 25.85 & 38.37 & 78.84 \\ \hline \hline \end{tabular} Note : \(\triangle\)P\({}_{\min}\) is the minimum pressure change that occurs during magnetization at the observation cycle at each given current, \(\triangle\)P\({}_{\max}\) is the maximum pressure change that occurs during magnetization at the observation cycle at each given current, \(\triangle\)P\({}_{\mathrm{avg}}\) is the average pressure change that occurs during magnetization at the observation cycle, Std Deviation is the standard deviation of the measured pressure.  
\end{table} 
Table 1: Experiment Data. Figure 9: A box plot of MRFs pressure (Pascal) and input current (Ampere). 1.88 A. In the subsequent cycles, the change in MRFs pressure is decreased because the input current could only reach 1.85 A, 1.84 A, and 1.83 A. Figure 10 depicts the graph obtained from the experiment at an input current of 1.00 A. It shows that the MRFs pressure had a relatively fast response time and reacted quickly to the input current. Response time is defined as the period that a sensor requires to reach 90% of the total signal response [36]. It took approximately 530 ms to get more values up to 90% of the maximum value. Meanwhile, it took 1810 ms; or less than 2 s, to get to the maximum value based on the data logger.