## 3 Experiments and Results
### The Sensing Performance of H-TENG  
After setting up the test bench, the output signal of H-TENG was tested. Figure 3c shows several voltage waveforms in parallel with H-TENG. It can be seen that when the vibration frequency is the same, the change of the number of parallel H-TENG connections  
Figure 3: Test devices. (**a**) Experimental apparatus diagram; (**b**) physical diagram of H-TENG; (**c**) voltage waveform diagram of multiple H-TENGs’ parallel connections.  
will also lead to the change of the voltage waveform output by the sensor. When the sensor consists of one or two H-TENGs, its output voltage waveform is stable and regular. However, when the number of H-TENG units in the sensor increases, the peak value of its output voltage remains basically unchanged, but the waveform of the signal is gradually disturbed. Due to this, the number of H-TENG units should be selected according to the use requirements in actual working conditions to avoid the measurement function of the sensor being greatly affected. After many tests, when the number of H-TENG units in the sensor exceeds eight, its output voltage waveform will become chaotic, so the number of H-TENG units should not exceed eight in actual working conditions. Moreover, experiments have revealed that vibration frequency and amplitude affect H-TENG. As shown in Figure 4a, H-TENG's output voltage is proportional to the vibration frequency, with a maximum voltage of 15 V, and as the vibration frequency increases, so does the number of voltage pulse signals per unit time. Next, the effect of vibration amplitude on H-TENG was tested. As illustrated in Figure 4b, the maximum output voltage of H-TENG can reach 12 V. However, when the amplitude exceeds 20 mm, the output signal remains stable. The reason for this may be that when the amplitude exceeds 20 mm, the output voltage of H-TENG will not increase because of the limited size and area of the friction layer. As the frequency and amplitude increase, the vibrator accelerates and the extrusion force increases, thereby increasing the contact area between the two friction layers and resulting in an increase in the output voltage.  
The measurement error of vibration frequency and amplitude is obtained through statistical analysis. As illustrated in Figure 4c,d, the vibration frequency error is less than 5%, and the amplitude error is less than 6%, which can meet the actual work requirements of downhole drilling. On the other hand, the downhole temperature increases with the increase of the drilling depth, so the impact of the downhole temperature on the output performance of the sensor is also tested. As illustrated in Figure 4e, when the relative humidity increases from 20% to 80%, the output voltage of H-TENG gradually decreases, but the output voltage after the decrease is still very obvious. The output voltage of H-TENG decreases as temperature rises, and the drop range is within 12% (0 to 300 degrees Celsius). Nonetheless, the decreased range is still inside the noise signal, indicating that the sensor can operate correctly within the range of 300 degrees Celsius. Figure 4f demonstrates that the output voltage of the H-TENG sensor fluctuates minimally after \(10^{5}\) cycles, indicating that the sensor can still maintain a stable output after a long period of continuous operation, and that it has high reliability.