# Research Progress in Fluid Energy Collection Based on Friction Nanogenerators
## 2 Recent Developments in Triboelectric Nanogenerator-Based Fluid Energy Harvesting Systems
### Wind Energy Collection
#### 2.1.2 Rotary Structure DC Output Device  
In the traditional TENG, the output is alternating current in the direction of change, but in order to achieve reasonable energy storage and energy use, it is likely to add rectifier current to convert AC into DC, and then convert it into the required electrical energy through buck-boost and voltage stabilization circuits. [PERSON] et al. proposed a TENG-EMG, as shown in Figure 4a. Similarly, TENG and EMG are integrated. In terms of EMG, the flipping magnet is combined with the coil to improve the magnetic flux change of the \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**TENG** & **Operating Wind Speed Range** & \begin{tabular}{c} **Short- Circuit** \\ **Current (\(\mu\)A)** \\ \end{tabular} & \
\begin{tabular}{c} **Open- Circuit** \\ **Voltage** \\ \end{tabular} &
\begin{tabular}{c} **Power** \\ **(mW)** \\ \end{tabular} & **Ref.** \\ \hline RS-HG & 5–25 m/s & 8.74 & 1.44 kV & 7.85 & [31] \\ D-TENG & 2.2–16 m/s & 18.9 & 228 V & 2.0 & [32] \\ Hybrid generator & 9 m/s & 14.6 & 190 V & 0.33 & [33] \\ WM-TENG & 1.6–6.7 m/s & 168 & 6.8 V & None & [34] \\ MM-TENG & 0–6 m/s & 7.9 & 490 V & 6.55 & [35] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Performance of wind energy harvesting devices based on rotating structure AC output in recent years. Figure 3: AC output device based on rotating structure. **(a)** RS-HG application scenario and **(b)** RS-HG structural design. Reprinted with permission from Ref. [31]. Copyright 2023, Wiley-VCH GmbH. **(c)** D-TENG structural design. Reprinted with permission from Ref. [32]. Copyright 2021, Wiley-VCH GmbH. **(d)** The hybrid generator structural design. Reprinted with permission from Ref. [33]. Copyright 2021, Wiley-VCH GmbH. **(e)** WM-TENG application scenarios and structural design. (i) T-TENG is used for wind speed measurement, (ii) B-TENG is used for wind direction monitoring. (iii) side view showing the sensing distance between PTFE and Al. Reprinted with permission from Ref. [34]. Copyright 2022, Elsevier. **(f)** MM-TENG application scenarios and structural design **(g)** DLCSC-TENG structure and **(h)** DS-TENG structural design. Reprinted with permission from Ref. [35]. Copyright 2023, Elsevier. cutting coil. In terms of TENG, the output current uses charge accumulation during rotation through the sidewall tip copper structure to achieve gas ionization and increase [36]. A wind energy hybrid harvester (WH-EH) combining soft friction forward triboelectric nanogenerator (SP-Teng) and hierarchical rotating electromagnetic nanogenerator (HR-EMG) was proposed by [PERSON] et al. As shown in Figure 4b, in the columnar structure, the HR-EMG is located at the bottom of the column, and the SP-TENG is on the side of the column, designed by combining electrodes and inner wall beams [37]. An ultralow friction and efficient pinwheel-shaped nanogenerator (WNG) by [PERSON] et al., WNG uses a rotating triboelectric layer with contact-separation mode. As shown in Figure 4c,d, WNG is composed of a circular wedge-shaped plane turntable. When the windmill drives the circular wedge-shaped surface to rotate, the wedge-shaped surface and the disc continue to move closer to reach the contact-separation mode to generate electricity. The contact between the circular wedge surface and the disc reduces the friction resistance between the friction pairs and reduces the threshold of WNG starting wind speed. The optimized WNG maximum load power is 0.753 uW, which can light up nine LEDs at the same time [38]. Introducing magnets and coils or cleverly designing wedge-shaped contact surfaces to control the polarity of charge output without changing, achieving DC pulse output. Table 2 summarizes the performance of some wind energy collection DC output devices in recent years. Figure 4: A DC output device based on a rotating structure. (**a**) TENG-EMG harvesting using a hybrid energy combination of tip discharge and TEMG and EMG integration. Reprinted with permission from Ref. [36]. Copyright 2023, Elsevier.