## 3 Results  
The simulation models of the gastrointestinal tract and triangular IDEs are illustrated in Figure 1. The gastrointestinal tract was composed of the mucosal layer (ML), submucosal layer (SL), and muscularis propria (MP). The triangular IDEs were located inside the gastrointestinal tract. The electrical and thermal properties of gastrointestinal tract were based on the literature, and the electrode was set to be gold in the COMSOL built-in library (Table 1). The electrical conductivity response according to the change in the temperature and electric field of the tissue is shown in Figure 2. The electrical conductivity was calculated through Equation (3) within the temperature range of 37-57 \({}^{\circ}\)C and the electric field range of 100-800 V/cm. The ranges of electrical conductivity change for the ML, SL, and MP used in this study were 0.511-1.638, 0.251-0.803, and 0.202-0.586 S/m, respectively. The above values were used in FEM simulation for the electric field distribution in the tissue and for probability of cell death due to EI (PEI). In addition, it should be noted that the influence of temperature on conductivity was small enough to be negligible compared with the change in electrical conductivity for electric field strength [33]. In order to investigate the effect of triangular IDEs, the electrical performances of rectangular and triangular IDEs with an identical electrode distance were compared. The rectangular IDEs had a finger length of 15 mm, finger width of 5 mm, electrode distance of 5 mm, and three fingers, as shown in Figure 3a. Two triangular IDEs were designed with (1) three fingers with a finger length of 15 mm, a base length of 5 mm, and a \(\sim\)2 times longer electrode distance (d \(\approx\) 11 mm) than rectangular IDEs as shown in Figure 3b; and (2) five fingers with a finger length of 15 mm, a base length of 5 mm, and an identical electrode distance (d \(\approx\) 5 mm) of rectangular IDES as shown in Figure 3c. The voltage distribution for each electrode configuration is shown in Figure 3. A set of 10 pulses with a duration of 100 us and a frequency of 1 Hz were delivered to the tissue, and the voltage of each pulse was set to be 1 kV. As shown in the voltage profile of the rectangular (d = 5 mm) and the triangular IDEs (d \(\approx\) 11 mm, d \(\approx\) 5 mm) at x = 20 mm and z = 3.5 mm in Figure 3d, the slopes of the rectangular IDEs (d = 5 mm) and the triangular IDEs (d \(\approx\) 5 mm) in the region shaded in green were similar at 159.8 and 145.7, respectively, but the slope of the triangular IDEs (d \(\approx\) 11 mm) was 83.2, showing a large difference. Figure 2: Electrical conductivity response of the (**a**) mucosal layer, (**b**) submucosal layer, and (**c**) muscularis propria during irreversible electroporation (IRE). The electric field distribution in the rectangular and triangular IDEs was evaluated as shown in Figure 4. The top panel shows the electric field distribution in the x-y plane view and the bottom panel shows the y-z cross-sectional view. The electric field was strongly focused on the edge of the rectangular IDE (d = 5 mm), and the maximum electric field was about 1.09 \(\times\) 10\({}^{6}\) V/m. For the triangular IDE, a strong electric field was observed at the tip region, and the maximum magnitudes were about 2.54 \(\times\) 10\({}^{6}\) V/m at d \(\approx\) 11 mm and 3.17 \(\times\) 10\({}^{6}\) V/m at d \(\approx\) 5 mm. Compared to the triangular IDEs with a d \(\approx\) 11 mm, the triangular IDEs with a d \(\approx\) 5 mm had a smaller effective electrode spacing, so the magnitude of the electric field appears larger. Figure 5 shows the distribution of PEI calculated from Equation (7) for the rectangular IDE (d = 5 mm), triangular IDE with three fingers (d \(\approx\) 11 mm), and triangular IDE with five fingers (d \(\approx\) 5 mm). From these results, a relative area ratio of PEI > 0.90 was calculated. The relative area ratio of PEI was defined as the ratio of the valid area of PEI > 0.90 to the total cross-sectional area.