## 3 Results and Discussion  
In our test, the impact plate of a pushing tester (SPG-01, ATsolution) shown in Figure 4 was used as the charged counterpart causing triboelectrification. The impact plate was made of aluminum, and the test was performed at a frequency of 7 Hz and force of 0.7 N. The pushing tester was driven by an AC speed control motor, repeatedly pushing the plate vertically. The TENG specimen generated triboelectrification by applying repeated pressure at 4-cm intervals due to the pushing tester, and the contact/separation triboelectrification mode was adopted. As for the testing conditions, the temperature and humidity were 27 \({}^{\circ}\)C and 50% RH, respectively. The output of a TENG specimen was measured using the following devices: an oscilloscope (TBS2072, Tektronix Co., Beaverton, OR, USA), a high-voltage passive probe (P5100A, Tektronix Co.), and a low noise current amplifier (DLPCA-200, Femto Co. in Berlin, Germany). The output measurements of TENG specimens were compared with and without the output amplifier. Figure 5a compares the output measurements of the simple PDMS-based TENG specimen with and without the TENG amplifier. Figure 5b shows the output measurements depending on the resistance load. When the output amplifier was applied, both voltage and current were amplified, and the maximum output occurred at 10 mohm. Figure 3: TENG test specimens: (**a**) PDMS-based TENG specimens; (**b**) fabrication process of conductive sponge TENG specimens; (**c**) photos of highly deformable conductive sponge TENG specimens. Figure 5c,d shows the output measurements of the conductive CNT sponge TENG specimen. The porous specimen was pushed deeper at the same pressure. As the internal surface area of the porous specimen was larger than that of the PDMS-based TENG specimen, the basic output was observed to be similar in a smaller area. When the output amplifier was applied, the amplification was larger than in the PDMS specimen. This was because the TENG specimen with a higher charge density per unit area generated larger micro plasma inside the TENG amplifier. The graphs in Figure 6a,b enlarge a single interval of the conductive sponge specimen output. When the TENG output amplifier was used, the peak value of the output certainly increased. However, checking whether the effective power (that is, V rms and I rms) increased was still necessary. Table 1 thus presents the calculations of rms values. It turned out that rms values indicating that the effective power increased by over 20%. Accordingly, the proposed TENG output amplifier could effectively increase the actual electric output. The above increase in the output of TENG is attributable to the increase in the number of flowing electrons that was, in turn, caused by micro plasma continuously occurring in a TENG output amplifier during an external vibration. In this regard, the voltage increased slightly, while the current increased considerably. As the peak value of the increased current was too high and occurred only for a short moment of 1 ms and below, the graphs of the current measured with an oscilloscope could not capture all current values. Those currents that did not appear in the graphs were peak currents occurring at an interval shorter than the sampling rate of the oscilloscope. As this study focused on the overall increase of effective power, such an instantaneous peak current occurring for 1 ms and below was excluded. As the TENG output amplifier utilized the occurrence of micro plasma, its output could be stabilized only by constant micro plasma. Accordingly, if the original TENG has a low output, the threshold voltage for generating micro plasma cannot be satisfied, and the amplifier is therefore hardly applicable. However, if the probe structure for generating micro plasma is moved by vibration, a very short distance can be obtained due to vibration, similar to what was observed in this study. Thus, even if the threshold voltage is very low,