# 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  
Human gait parameter information includes gait cycle, kinematic parameters, spatio-temporal parameters, kinetic parameters, etc. These parameters can objectively reflect an individual's walking characteristics. In recent years, an increasing number of researchers of TENGs have shown great interest in self-powered gait monitoring sensors. Among them, some researchers have achieved gait monitoring by integrating TENGs into insoles or shoe soles. For example, [PERSON] et al. fabricated a TENG based on electrospun composite nanofibers to construct a self-powered gait analysis system. The system can monitor walking speed and acceleration and realize data visualization [61]. There are three TENGs in this system, and the placement of the sensors is determined through plantar pressure simulation analysis (Figure 3(ai)). Two of the TENGs form a sensing module and are placed at the forefoot and heel positions, and one TENG is used as a charging module and placed at the heel position (Figure 3(aii)). Gait monitoring is achieved by relying on the two TENGs in the sensing module to collect the electrical signals generated during walking. The original output signals are processed by a charge amplifier circuit and then converted into sensing signals readable by the microcontroller unit (MCU). The processed signals present as transistor-transistor logic (TTL) signals (Figure 3(aiii)). The two TENGs used for obtaining signals can acquire stable signals, and the TENG of the charging module can drive the MCU to collect and calculate data. Based on the above mechanism, [PERSON] et al. developed an application program that can not only record the gait parameters of the exerciser, but also realize the visualization of gait parameters (Figure 3(aiiv)). Placing TENGs on the soles of the feet for signal collection poses greater requirements for the mechanical properties and electrical output performance of the TENG materials. To date, many researchers have focused on developing triboelectric materials with mechanical properties and device structures to improve performance output. For instance, [PERSON] et al. proposed an origami-shaped metamaterial [62]. This metamaterial can modulate its mechanical properties through geometric design modification. Subsequently, it was fabricated into a shoe sole via 4D printing technology. This kind of shoe sole is a TENG with self-power and self-sensing capabilities. The TENG operates based on the vertical contact-separation working mode. In terms of its structure selection, the structure of three topological units is used as the substrate (Figure 3(bi)). Aluminum foil is pasted on the dark-colored part, which serves as the conductive layer and the positive triboelectric layer. On the opposite part, the aluminum foil acts as the electrode, and the piezoelectric and flexible thin film (PFF) is fixed above the aluminum foil as the negative triboelectric layer. [PERSON] et al. integrated the TENG into the shoe sole to monitor the voltage signals generated during walking in real time, and analyzed the foot pressure situation through the signal output. In addition, voltage signals generated by slow walking, fast walking, jogging, and running are different. Different walking patterns can be identified by analyzing the signal types, thus enabling gait pattern monitoring (Figure 3(bi)). [PERSON] et al. fabricated an integrated TENG with numerous pores for gait cycle monitoring [63]. It is worth noting that, compared with the same type of TENG without a pore structure, its electrical output performance is increased by approximately 10 times. The porous TENG operates in a single-electrode working mode. Each individual pore can be regarded as a separate TENG (Figure 3(ci)). Its principle of electricity generation lies in the periodic contact-separation between the carbon nanofibers (CNFs) in the pores and the rubber.