# Research Progress of Self-Powered Gait Monitoring Sensor Based on Triboelectric Nanogenerator
## 3 Applications of Self-Powered Triboelectric Nanogenerator in Gait Monitoring
### Basic Gait Information Monitoring
The porous structure of this TENG ensures a high degree of sensitivity to pressure and deformation (Figure 3(cii)). Moreover, [PERSON] et al. placed the porous TENG in the shoe sole. Different gait patterns result in different signal outputs, which can reflect that toe-walking, marching, and stomping generate different output signals (Figure 3(ciii)). Thus, it is possible to determine the movement postures and analyze the gait cycle. In addition to integrating TENGs into shoe soles, some researchers have also integrated them with clothing. [PERSON] et al. invented a self-powered cotton sock based on a hybrid piezoelectric and triboelectric mechanism [PERSON] et al. (2018). Compared with integration into insoles and soles, socks with sensing functions can monitor gait states more conveniently and for a longer time. In [PERSON] et al. 's study, a textile TENG was fabricated using PEDOT:  
Figure 3: Applications of self-powered sensors based on TENGs in the field of basic gait monitoring. (**a**) TENG based on electrospun composite nanofibers and used in a self-powered gait analysis system. (**ai**) Distribution of plantar pressure of the human body. (**aii**) Structure design of TENG and its distribution in the shoes. (**aii**) TTL signals generated at different frequencies. (**aiiv**) Application interface for gait parameter analysis. (**b**) Gait monitoring system composed of 4D metamaterials. (**bi**) Preparation process of TENG. (**bi**i**) Signal outputs of different gaits. (**c**) Gait monitoring system constructed based on a porous triboelectric sensor. (**ci**) Schematic diagram of the TENG structure. (**cii**) Stable outputs under different mechanical forces. (**ciii**) Signal outputs under different gait patterns. (**d**) Self-powered cotton socks for gait monitoring based on the hybrid mechanism of triboelectric voltage points. (**di**) Cotton socks composed of the hybrid mechanism. (**dii**) Photos of the polytetrafluoroethylene film and six pairs of aluminum electrodes. (**diii**) Motion tracking output signals from two terminals. (**e**) Application of a non-contact TENG in a gait monitoring system. (**ei**) Working principle of TENG. (**ei**i**) Position of TENG and the movement path of the human body. (**eiii**) Corresponding signals generated by the movement path. (**eiv**) Voltage signals generated during movement through a partition wall. PSS-coated fabric. The TENG was used as part of an integrated piezoelectric sensor (Figure 3(dii)). To better obtain triboelectric signals during contact, [PERSON] et al. constructed an intelligent passage using polytetrafluoroethylene (PTFE) and aluminum electrodes. When the participants walked along the intelligent passage while wearing cotton socks, the signal output at different stages of the gait cycle could be obtained (Figure 3(dii)). After conducting tests on different participants, the researchers verified the stability of the system in gait cycle signal detection applications (Figure 3(diiii)). All the above-mentioned studies involve contact-type TENGs. Non-contact TENGs also have enormous application potential in the field of gait monitoring. For example, [PERSON] et al. proposed a non-contact TENG for human motion monitoring, which can be used for speed monitoring and motion tracking [65]. This TENG operates in a single-electrode mode. The human body serves as the electronegative triboelectric layer of the TENG, while printing paper and metal film act as the positive triboelectric layer and the electrode. Figure 3(ei) depicts the charge transfer pattern followed when the right leg moves. Two TENGs are fixed on the wall as speed sensors (Figure 3(eii)). When a person walks or runs along different paths, [PERSON] et al. achieved real-time monitoring of human movement speed by analyzing the voltage peaks and the passing time (Figure 3(eiii)). In addition, the non-contact TENG can also serve as a human motion tracking sensor.