# Research Progress in Fluid Energy Collection Based on Friction Nanogenerators
## 2 Recent Developments in Triboelectric Nanogenerator-Based Fluid Energy Harvesting Systems
### Wind Energy Collection
#### 2.1.3 Rotating Self-Adjusting Structure Output Device  
The wind speed acquired through the utilization of a standard rotating mechanism energy harvesting device may not exhibit consistent stability. To address this issue, a strategy is implemented wherein multiple sets of structures are arranged in parallel. Each set of structures is designed to respond to different wind speed intervals. Additionally, another approach involves enhancing the efficiency of the device's response by optimizing the geometry of its structure. However, the performance of the aforementioned mechanisms in capturing wind speed response is still limited. [PERSON] et al. reported a triboelectric nanogenerator (TENG) with a self-adjusting driving torque, as shown in Figure 5a(i). This design was motivated by the feedback structure inherent in the mechanical system. The transition between contact and separation modes is contingent upon the wind speed input. The wind cup and the rotating structure are interconnected with the torque self-adjusting unit, as seen in Figure 5a(ii). The power-generating surface is designed in a trapezoidal form, as seen in Figure 5d. Under the action of different wind speeds, the centrifugal angle of PLA changes with the change of wind speed, resulting in inconsistent contact area with the trapezoidal copper power generation surface to match the input of different wind speeds, as shown in Figure 5e [39]. [PERSON] proposed an SM-Teng that adjusts the working mode according to different wind speeds, as shown in Figure 5f. SM-TENG switches between contact and separation modes according to the input wind speed. As shown in Figure 5g, when the wind speed is less than 5 m/s, the working mode of SM-TENG is sliding F-TENG. When the wind speed exceeds 5 m/s, SM-TENG works in contact with the rotating separated R-Teng [40]. Changing the rotational inertia or driving torque of the device, as well as changing the key characteristics of the mechanism itself at different wind speeds, such as changing the contact area of the friction layer due to the centrifugal angle, achieves good characteristics of the mechanism's self-adjustment output with wind speed changes.  
Table 3 summarizes the performance of some self-adjusting wind power generation devices based on rotating structure in recent years.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**TENG**} & **Operating** & **Short-** & **Open-** & **Power/Power** & **Ref.** \\  & **Wind Speed** & **Circuit** & **Circuit** & **Voltage** & **Density** & **Ref.** \\  & **Range** & **Current** & **Voltage** & **Density** & **Ref.** \\ \hline TENG-EMG & 3.5–6 m/s & 6 mA & 600 V & 0.7 W & [36] \\ WH-EH & 8–9 m/s & 1.48 uA & 204 V & 195.2 mW/m\({}^{2}\) & [37] \\ WNG & 1.65 m/s & 125 nA & 250 V & 0.753 uW & [38] \\ \hline \hline \end{tabular}
\end{table}
Table 2: Performance of wind energy harvesting devices based on rotating structure DC output in recent years.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**TENG**} & **Operating** & **Short-** & **Open-** & **Power/Power** & **Ref.** \\  & **Wind Speed** & **Circuit** & **Circuit** & **Voltage** & **Density** & **Ref.** \\  & **Range** & **Current** & **Voltage** & **Density** & **Ref.** \\ \hline SA-TENG & 5–13.2 m/s & 14 uA & 500 V & 7.69 mW & [39] \\ SM-TENG & 2–25 m/s & 16 uA & 1100 V & 3.47 mW & [40] \\ \hline \hline \end{tabular}
\end{table}
Table 3: Performance of self-regulating wind energy harvesting devices based on rotating structures in recent years.