# Design and Performance Research of a Wearable Airbag for the Human Body
## 6 Discussion  
In this study, a pedestrian-vehicle FEA model has been established, and a wearable airbag is used to protect pedestrians in the accident, which is rare in previous studies. The protective performance of the wearable airbag is evaluated, demonstrating that the wearable airbag can reduce the injury of pedestrians in the collision.  
Figures 9 and 18 show the motion posture of the HBM at an impact speed of 30 km/h. At 50 ms, the HBM's thigh collides with the edge of the hood. During the collision, the lower leg gradually detaches from the bumper with a bending action, and the head collides with the edge of the hood and windshield at 180 ms. The posture of the pedestrian during collision agrees well with the results of [PERSON]'s study [30]. However, the difference is that the vehicle impact speed was 40 km/h and the pedestrian's head hit the windshield in their study. Apparently, the different impact speeds resulted in different head impact positions, as confirmed by [PERSON] [2]. With an increase in car speed, the collision possibility between the head and the windshield increases.  
Figure 16: HIC\({}_{15}\) head injury index distribution under different combinations of gas mass and pulling atrap length.  
Figure 17: Comparison of airbag impact invasion: (**a**) gas mass is 20 g; (**b**) gas mass is 24 g.  
In recent studies, wearable airbags have been used to prevent falls after stroke [31], to protect elderly people with broken hips [7; 32], and to protect cyclists and motorcycle riders [12; 15], but they are rarely used to protect pedestrians in collision. This study combines inflatable helmets, vests, and hip airbags to protect pedestrians from collision in all directions. The finite element simulations carried out in this study confirm that a wearable airbag can reduce the injury of pedestrians, as shown in Table 1. Some studies [15; 16] have shown that inflation pressure and airbag thickness play a decisive role in the protection performance of wearable airbags. They have demonstrated that a larger airbag deployment thickness is always beneficial, and an optimal inflation pressure that minimizes chest deflection can be found. These findings are consistent with our research showing that the maximum airbag inflation thickness provides the best protection, but the maximum inflation mass is not favorable because high inflation pressure increases rigidity and weakens the airbag's protection effect. These results have important implications for the selection of the appropriate inflator and the optimal structure of the wearable airbag.  
According to the protection of vulnerable road users (VRU) in the European New Car Assessment Program (E-NCAP), the hood and windshield are divided into 24 areas for adult head impact tests, as shown in Figure 19. Correspondingly, we will conduct multiple crash simulations to study the protective effect of the airbag when the head hits in different positions. Crash simulations at different speeds will also be carried out to evaluate the airbag's protective performance at higher impact speeds in our future work.  
The current research is focused on evaluating the protective performance of wearable airbags using numerical models. In other studies, wearable airbags were evaluated by conducting a drop test [15; 33]. Therefore, the newly designed wearable airbag should be manufactured and tested for further calibration of the numerical model of the airbag, such as the characteristics of the airbag material. In addition, gyroscopes are crucial in the practical application of wearable airbags, but the signal collection and process of the gyroscope is out of scope of current study. These issues will be addressed in future work.  
Figure 19: The area of adult head impact test in E-NCAP.  
Figure 18: Pedestrian motion posture during collision.