## 2 Structural Design and Working Principle of H-TENG
### Structure and Working Principle  
Figure 2a is an explosion diagram of H-TENG, and Figure 2b is a structural diagram of H-TENG. The exterior of the H-TENG consists of a base, a top cover, and housing, and inside is a vibrating body that can move freely and come into direct contact with the base. Rectangular magnets are embedded in all six sides of the housing to allow free assembly, and perforations are made on the sides of the housing to connect wires. According to the triboelectric sequence table [42], Al and Kapton are selected as friction materials, which can achieve a good output effect. Therefore, we chose these two materials as the friction layer of H-TENG. The drill string is fixed to the outside of the base, and the inside is attached to the aluminum (Al) and polyimide (Kapton). Al is attached to the underside of the vibrating body; Kapton (PY11 YG, Lingmei Co., Ltd., Dongguan, China) serves as a friction layer to produce friction charge and Al serves as the electrode output to produce friction charge, while Al also serves as a friction layer and an electrode layer at the same time, and is connected with the copper (Cu) electrode through wires. When axial vibration occurs, the vibrator moves up and down under the action of inertial forces, causing Kapton to contact the Al to generate an electric charge; thus, the measurement of the vibration frequency and further processing of the vibration energy are made possible. The whole H-TENG is 3D printed with polylactic acid (PLA) material, the printing temperature is 210 degrees Celsius, and the printing layer thickness is 0.3 mm. The hexagonal base and top cover edge are 20 mm long, the housing length is 50 mm, the magnet size is 20 \(\times\) 10 mm\({}^{2}\), and the cylinder size in the vibrator is 19 mm.  
Figure 1: Application environment and basic composition of the H-TENG. (**a**) The sensor’s actual installation position; (**b**) honeycomb; (**c**) H-TENG’s schematic diagram.  
Figure 2c is a cross-sectional view of H-TENG showing how the sensor works and the charge distribution. In the initial state (Figure 2c(i)), Kapton is exposed to Al because of gravity. Because Al and Kapton have different abilities to gain and lose electrons, at this point, the Al surface is positively charged, whereas the Kapton surface is negatively charged. Since the polymer has strong insulation, it can maintain the charge on the surface of the material for a long time. Then, when axial vibration occurs, the two friction layers are separated under the action of inertial forces. Due to electrostatic induction, the open circuit voltage between the two electrodes gradually increases at this time (Figure 2c(ii)). When the vibrator is running to the top (Figure 2c(iii)), the distance between the two friction layers is maximized and the open circuit voltage reaches its peak value. Subsequently, the separation distance between the two friction layers is gradually reduced (Figure 2c(iv)), and to balance the potential, the charge is transferred in reverse to produce a reverse current. Finally, the distance between the two friction layers is gradually reduced back to its initial value. It can be seen that each vibration of H-TENG produces a voltage pulse, and by counting the number of pulse signals per unit of time, the vibration frequency can be determined.