The output voltage signals generated by the TEG must be reduced to reasonable voltage value, which can be accomplished by the power management circuit, as illustrated in Figure 2.21a [33]. The output voltage signals were decreased to about 12 V, and the current signals were increased to about 0.9 mA, as shown in Figure 2.21b,c. The wireless system consists of a power management circuit, a wireless sensor node, and the TEGs in a transparent gas tube, as shown in Figure 2.21d. The output voltage value could be adjusted to 1.8 V via the power management circuit when the TEG continuity harvest wind energy is about 4.9 S, as shown in Figure 2.21e.
Figure 2.21 The wind‐driven wireless sensor. (a) Schematic diagram of an integral powering circuit. The measured (b) regulative voltage and (c) the current at the transformer output port. (d) Photograph of the self‐powered system. (e) Output voltage of the system.
Source: Reproduced with permission from Wang et al. [33]. Copyright 2015, John Wiley and Sons.
Zhao et al. fabricated a highly efficient TENG, which can harvest wind energy for sustainably powering a wireless smart temperature sensor node [61]. Figure 2.22a shows a photograph of the wireless temperature sensor. A 10 mF capacitor was used to store the energy from the nanogenerator. In the charging stage (process‐1), the capacitor can be charged from 0 to 3.3 V, as shown in Figure 2.22b. The voltage of the capacitor decreased when the sensor stood at the initial stage, and then increased due to the supplement from the nanogenerator. When the TENG was shut down, no electrical energy could be generated, resulting in no temperature data on the screen of the iPhone, as illustrated in Figure 2.22c. When the TENG was working, the temperature sensor can probe the temperature of a human finger, as shown in Figure 2.22d. Lithium ion batteries, which are most effective energy storage devices, have been widely used in numerous electronic devices Jiang et al. used the Li‐ion battery to store electrical energy generated by TENGs [69]. By adjusting the output voltage of the TENG via a power management circuit, the regulative electrical energy can be used to charge the Li‐ion battery, as shown in Figure 2.23a. It was found that voltages of the Li‐ion battery can be increased by increasing the charging time. The voltage of the battery was about 3.6 V, when charged by the TENG for about 40 minutes. Figure 2.23b shows a photograph of the fabricated self‐charging system, which consists of a TENG, a Li‐ion battery, and an LED. The LED can be lit up by the Li‐ion battery, which is charged by the TENG, as shown in Figure 2.23c.
On the other hand, by integrating a WD‐TENG and a pressure‐sensitive elastic polyimide (PI)/reduced graphene oxide (rGO) foam, Zhao et al. fabricated a self‐powered pressure sensor [77]. Figure 2.24a shows a schematic diagram of the self‐powered pressure system. The TENG can generate output voltage signals by harvesting the wind energy. Figure 2.24b shows photographs of the self‐powered pressure system. Figure 2.24c presents four foams with different heights. The resistances of the elastic foam that was connected to the TENG can be changed with the diversification of the external forces, resulting in changes in the measured voltage, as shown in Figure 2.24d.
Figure 2.22 The wind‐driven self‐powered wireless smart temperature sensor. (a) Photographs of the temperature sensor. (b) Charging curve of a capacitor by using the TENG with a PMC. Photographs of the temperature sensor before (c) and after (d) being powered by the TENG.
Source: Reproduced with permission from Zhao et al. [61]. Copyright 2016, American Chemical Society.
Figure 2.23 The wind‐driven self‐charging Li‐ion battery. (a) Charging and discharging curves of the Li‐ion battery via the TENG. (b) Photograph of the self‐charging system. (c) Photographs of lighting up a green LED via the Li‐ion battery charged by the TENG.
Source: Reproduced with permission from Jiang et al. [69]. Copyright 2018, American Chemical Society.
Figure 2.24 The wind‐driven self‐powered pressure sensor. (a) Schematic diagram of the as‐fabricated self‐powered pressure sensor. (b) Photograph of the prepared pressure sensor. (c) Photograph of foams with heights. (d) The output voltage of the foam connected to the TENG.
Source: Reproduced with permission from Zhao et al. [77]. Copyright 2019, John Wiley and Sons.
2.4 Comparison
With the fast development of modern industry, energy shortage has become an important problem that restricts the further development of the human society. Conventional wind harvesters based on the electromagnetic effect have been created as one of the most important ways for harvesting wind energy. Recently, TENGs based on the cooperation of the triboelectric effect and the electrostatic induction have been used to harvest wind energy. Figure 2.25 shows the comparison between two wind harvesters, focusing on the mechanism, characteristics, and disadvantages [78]. Compared to conventional wind harvesters, TENGs can be considered as current sources with a large internal resistance, leading to characteristics of high voltage and low current. In addition, WD‐TENGs possess many advantages such as low cost, high efficiency, and easy fabrication, providing them the potential to be utilized as self‐powered electronics.
Figure 2.25 The comparison between conventional wind harvester and new wind harvester based on a triboelectric nanogenerator.
Source: Reproduced with permission from Chen et al. [78]. Copyright 2018, John Wiley and Sons.
2.5 Conclusion
With the development of wearable electronics and wireless sensors, WD‐TENG, which can convert wind energy to electrical energy, are researched not only to enhance output performance but also to improve compatibility with other electrical devices. It has become a new trend in the further development of self‐powered
