## 3 Results and Discussion  
In our design, the TE electric field is perpendicular to the \(g_{1}\) parameter, and the transverse magnetic (TM) electric field is perpendicular to the \(g\) parameter. To clarify the electromagnetic responses of the eSRR device, we first simulate the transmission spectra of only two metal bars or two semicircles to figure out the source of the individual resonance. Figure 2a,b show the transmission spectra of  
Figure 1: Schematic drawings of (**a**) 3D view of an electric split-ring resonator (eSRR) array and (**b**) geometrical denotations of an eSRR unit cell. metal bars with different \(L_{1}\) values in TE and TM modes, respectively. By increasing the \(L_{1}\) value of the bottom metal bar from 12 \(\upmu\)m to 24 \(\upmu\)m under the condition of \(L_{2}\) = 12 \(\upmu\)m, there is no resonance in TE mode and the electromagnetic responses can be switched between dual-band and triple-band resonances in TM mode, as shown in Figure 2a,b, respectively. By increasing the gap between two semicircle-shaped metamaterials (\(g_{0}\)) from 6 to 10 \(\upmu\)m under the condition of \(R\) = 20 \(\upmu\)m, there are two stable resonances in TE mode and one stable resonance in TM mode, as shown in Figure 2c,d, respectively. Therefore, we investigate the electromagnetic responses of the eSRR device with different \(L_{1}\) values by keeping the parameters of \(g_{1}\) = 6 \(\upmu\)m, \(L_{2}\) = 12 \(\upmu\)m, and \(R\) = 20 \(\upmu\)m, as shown in Figure 3. In TE mode, there are two stable resonances (\(\omega_{1}\), \(\omega_{2}\)) at 0.69 and 1.21 THz, as shown in Figure 3a. Meanwhile, by increasing \(L_{1}\) values, the electromagnetic responses can be tuned and switched between dual-band (\(L_{1}\) = \(L_{2}\)) and triple-band (\(L_{1}\) \(\
eq\)\(L_{2}\)) resonances in TM mode, as shown in Figure 3b. The first (\(\omega_{1}\)) and second (\(\omega_{2}\)) resonances are both stable at 0.39 and 1.34 THz, while the third (\(\omega_{3}\)) resonance is gradually red-shifted from 1.71 to 0.83 THz by increasing the \(L_{1}\) value from 8 to 24 \(\upmu\)m. The tendencies of resonances and \(L_{1}\) values of the eSRR device are summarized in Figure 3c. The corresponding electric (E) and magnetic (H) field distributions with \(L_{1}\) = 24 \(\upmu\)m are illustrated in Figure 4. In TE mode, the E- and H-field energies are distributed around the semicircles at 0.69 (\(\omega_{1}\)) and 1.21 THz (\(\omega_{2}\)). In the TM mode, the E- and H-field energies are distributed around the semicircles at 0.39 THz (\(\omega_{1}\)). Such a result shows that the first resonance of the eSRR comes from the semicircle structures. The E-field energy is distributed on the upper and lower parts of the upper metal bar, and the H-field energy is distributed in the center of the upper metal bar monitored at 1.34 THz (\(\omega_{2}\)). This means that the second resonance of the eSRR is caused by the upper bar. When \(f\) = 0.83 THz (\(\omega_{3}\)), the E-field energy is distributed on the upper and lower parts of the lower metal bar, and the H-field energy is distributed in the center of the lower metal bar, which indicates that the third resonance of the eSRR is generated by the lower bar. Therefore, when the length of the lower bar changes (different \(L_{1}\) values), the electromagnetic responses of the eSRR can be tuned and switched between the dual-band and triple-band resonances in TM mode. Figure 2: Transmission spectra of metal bars with different \(L_{1}\) values in (**a**) TE mode and (**b**) transverse magnetic TM mode and those of semicircle-shaped metamaterial with different \(g_{0}\) values in (**c**) TE mode and (**d**) TM mode, respectively. When two metal bars are equal at a certain length (i.e., \(L=L_{1}=L_{2}\) by keeping \(R=20\)\(\upmu\)m and \(g_{1}=6\)\(\upmu\)m), the corresponding electromagnetic responses of the eSRR device are shown in Figure 5. There are two stable resonances (\(\omega_{1}\), \(\omega_{2}\)) at 0.69 and 1.21 THz in TE mode, as shown in Figure 5a.