## 3 Parameters Related to the Motion of Microrobots  
The swimming speed of a microrobot is a significant parameter to investigate its performance [115]. The speed depends on the parameters such as the length of the microrobot, the strength, and the frequency of the applied magnetic field [116]. A summary of the swimming speed of the microrobots is presented in Table 2. The data presented in Table 2 was analyzed further to identify the effect of the related parameters on the speed of the microrobot and is represented in Figure 9.  
Figure 8: Nanowires for locomotion: (**a**) Nanoswimmer which uses two gold segments to mimic the head and caudal fin of the fish; (**b**) nanoswimmer which uses one PPy segment as the tail [113]; (**c**) four link hydrogel-based biodegradable microrobot which uses microsprings [114].  
Figure 9: Performance analysis of microrobots: (**a**) Variation of maximum speed against body length; (**b**) variation of relative speed against frequency; (**c**) variation of dimensionless maximum speed against magnetic flux density; (**d**) variation of the dimensionless maximum speed of helical microrobots against helical angle. (Blue color dots represents the data points and red color dotted line represents the regression line.)  
The speed of the microrobot is important for microscale applications. Both maximum speed and average speed can be examined to evaluate the performance of the microrobot [37]. In this review, the maximum speeds of the microrobots were collected to analyze the performance of the microrobots. According to Figure 9a, it can be observed that the maximum speed of the microrobots increases with the body length. The effect of the body length can be eliminated by calculating the relative speed (speed per unit body length). The frequency of the rotation or oscillation of the microrobot is another factor that affects the speed of the microrobot. This rotation or oscillation is generated due to the frequency of the applied magnetic field. The variation of the relative speed with the frequency is clearly illustrated in Figure 9b. According to the graph, the relative speed increases with frequency. Using a similar method, the effect of the frequency can be removed by dividing the relative speed by the frequency to obtain the dimensionless maximum speed [37]. In Figure 9c, the variation of the dimensionless maximum speed with the magnetic flux density is analyzed. According to the variation, it can be observed that the dimensionless maximum speed increases when the applied magnetic flux density is increased. Apart from the body length, frequency, and magnetic flux density, the helix angle is an important parameter for helical microrobots. Figure 9d shows the variation of the dimensionless maximum speed of helical microrobots against helical angle. This graph also has an upward trend.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Inspired** & **Body Length** & **Maximum** & **Relative Speed** & **Frequency** & **Dimensionless** & **Helix Angle** & **Magnetic** & **Ref.** \\  & **L (\(\mu\)m)** & **Speed U (\(\mu\)m/s)** & **U/L (\(\mu\)s)** & **f (Hz)** & **Maximum Speed U/L f** & **(Degrees)** & **Flux Density** & **[**51**]** \\ \hline B & 8.8 & 127.0 & 14.43 & 40 & 0.3608 & 65.0 & (R) 1.5 mT & [51] \\ \hline B & 35.0 & 320.0 & 9.14 & 40 & 0.2286 & 65.0 & (R) 1.5 mT & [51] \\ \hline B & 1.5 & 40.0 & 26.67 & 150 & 0.1780 & - & (R) 6.0 mT & [117] \\ \hline B & 30.0 & 140.0 & 4.67 & 30 & 0.1560 & 32.7 & (R) - & [118] \\ \hline B & 2.0 & 2.0 & 1.00 & 10 & 0.1000 & 51.5 & (R) 2.0 mT & [44] \\ \hline B & 16.0 & 45.0 & 2.81