## 4 Results and Discussion  
With a driving voltage of 200 V\({}_{\mathrm{PP}}\) and a resonant frequency of 10.4 kHz, the actuator can move forward outside or inside the endoscopic channel (see Figure 4) and thus modulate the distance between the actuator and disease part, proving that the piezoelectric actuator and permanent magnet orbit can meet the size requirements of the endoscope and also be applicable for linear driving of the micro ultrasonic transducer or other dosing devices in the biopsy channel for drug penetration in an unresectable or non-abatable archenteric gastrointestinal tumor. To correlate the speed upon the application of driving voltage, duty ratio, and magnetic induction intensity, a performance test platform is established to obtain the motion performance of the piezoelectric actuator on the permanent magnet track. The permanent magnet orbit has an effective working distance of 10 mm and its motion process is given in Figure 5a. Shown in Figure 5b is the speed versus applied voltage performance of the actuator on the permanent magnet orbit, whose magnetic induction intensity is 145 mT. An upward trend in the speed with the increasing driving voltage is observed. A maximum speed of 168 mm/s is achieved with a driving voltage of 200 V\({}_{\mathrm{PP}}\) at 10.4 kHz. Meanwhile, a minimum speed of 25 mm/s is achieved with a driving voltage of 120 V\({}_{\mathrm{PP}}\). In addition, the amplitude of the leg is too small and it is difficult for the actuator to work stably when the driving voltage is lower than 120 V\({}_{\mathrm{PP}}\), and the piezoelectric ceramics can be easily broken down when the driving voltage is higher than 200 V\({}_{\mathrm{PP}}\). To characterize the effect of the magnetic induction intensity on the speed of the actuator, we measured the speed under various magnetic induction intensities and the obtained data are given in Figure 5c. The magnetic induction intensity can be changed by alcohol lamp heating permanent magnets and the grinding of permanent magnets. As can be seen from Figure 5c, the speed of the actuator under different magnetic induction intensities basically presents a linear distribution, and the speed of the actuator increases with the increase of the magnetic induction intensity. When the magnetic induction intensity of the permanent magnet orbit is 43 and 145 mT, the corresponding actuator speed is 41 and 168 mm/s, respectively. In this paper, because the permanent magnet orbit is ground to a thickness of 0.35 mm when the actuator is installed in the endoscope, its magnetic induction intensity is 43 mT. According to the experimental measurement methods of Section 2, the maximum temperature of the front end of the actuator working in the endoscopic channel in the first 3 min is shown in Figure 6 for when the driving voltage is 200 V. From the figure, it is obvious that the endoscopic biopsy channel displayed the highest temperature because of the existence of the piezoelectric actuator being operated, while the temperature of the remaining regions was also affected by the operation of the piezoelectric actuator. Moreover, it shows that the temperature rises from 36.4 \({}^{\circ}\)C to 44.4 \({}^{\circ}\)C with an  
Figure 4: The motion process of the piezoelectric actuator: (**a**) outside the endoscopic biopsy channel (Video S2); (**b**) inside the endoscopic biopsy channel (Video S1). increasing operation time, which is beyond the safe temperature of the human body. In particular, the temperature of the actuator is more than 42 \({}^{\circ}\)C just after 1 min. As shown in Figure 7a, the temperature field distribution of the actuator is obtained and the maximum temperature appears on the surface of the piezoelectric ceramics. Moreover, the results of Figure 7b show that the calculated maximum temperature of the front end of the actuator (it is same measurement area as the experimental measurement area) rising curves corresponds to the experimental results, proving the effectiveness of this FEM method.