# Fluid Flow-Based Vibration Energy Harvesters: A Critical Review of State-of-the-Art Technologies
## 9 Discussion, Future Prospects and Challenges for FBEHs  
This research discusses FIVs and aerodynamic instabilities employed for energy harvesting technology. In retrospect, the literature shows that several types of harvesting procedures have made tremendous progress in the last few decades. The applications of these FIV systems have been used to lessen reliance on traditional energy sources, such as chemical batteries, etc. Furthermore, the viability of the energy harvesting principle enables a safer environment and consistent energy for remote sensing and monitoring systems. Harvesting vibration energy from induced aerodynamic instability phenomena,  
Figure 14: Rotary wind EHs: (**a**) TE-PE energy harvester reproduced with permission from [206] Elsevier, 2017; (**b**) TE-EM energy harvester reproduced with permission from [207] Elsevier, 2020; (**c**) PE-EM-TE-based RWEH reproduced with permission from [209] Elsevier 2022; (**d**) orientation adaptive EM-based RWEH reproduced with permission from [212] Elsevier 2024. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Transduction Mechanism** & \begin{tabular}{c} **Velocity** \\ **(m/s)** \\ \end{tabular} & **Output Power (mW)** & **References** \\ \hline Tribo-electromagnetic & 9 & \begin{tabular}{c} 0.36 (TE) \\ 18.6 (EM) \\ \end{tabular} & [PERSON] et al. [207] \\ \hline Piezoelectric-triboelectric-electromagnetic & 3.5 & \
\begin{tabular}{c} 0.121 (PE) \\ 0.191 (EM) \\ 0.000168 (TE) \\ \end{tabular} & [PERSON] et al. [209] \\ \hline Piezoelectric & 2 & 1.06 & \\ \cline{2-3} Piezolectric & 5 & 2.21 & [PERSON] et al. [210] \\ \hline Tribo-electromagnetic & 15 &
\begin{tabular}{c} 7.54 (Lateral TE) \\ 7.85 (Top TE) \\ 22.5 (EM) \\ \end{tabular} & [PERSON] et al. [211] \\ \hline Electromagnetic & 5.22 & 0.498 & \\ \cline{2-3}  & 8 & 0.673 & [PERSON] et al. [212] \\ \hline Triboelectric & 12 & \(140\,\mathrm{mW/m^{2}}\) & [PERSON] et al. [213] \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Comparison of rotary wind energy harvesters. such as VIVs, galloping, flutter and wake galloping are typical crossflow vibration-induced aerodynamic phenomena that are considered for energy harvesting applications at large. Enhanced amplitude oscillations of the structures caused by galloping or flutter might result in substantial vibrations and therefore significant levels of captured power. However, due to its self-excitation and self-restriction, the VIV is less severe than flutter and galloping. Due to its small lock-in region, VIV energy conversion experiences large power swings as wind speeds fluctuate; this limits its applicability in environments with unpredictable vibration patterns. Flutter-based wind energy harvesting technology has advanced significantly, and new ideas and technologies have also been put forth recently. However, there are still several difficulties with flutter-based energy harvesting; for instance, these devices are unable to deliver stable output power at low wind speeds because of the existence of the cut-in wind speed. It might not be preferable for real-world applications due to the single structure's low energy harvesting efficiency. For the current challenges, researchers have put forth a variety of improvement techniques, including structural optimization, inducing nonlinearity and energy hybridization. Considering the energy transduction mechanisms, the piezoelectric FBEHs are one of the most promising areas to extract energy from a wide range of fluid flows including wind and water, whereas comparatively, electromagnetic FBEHs are more suitable to gather energy from high-velocity fluid flows. Triboelectric energy harvesting has significant potential for advancing the development of self-powered sensors, wearable devices and other small-scale electronics, as well as contributing to the larger goal of harnessing renewable energy from ambient sources, such as wind and water wave energy.