# A Review of Bioinspired Vibration Control Technology
## 4 Other Bionic Vibration Control Devices  
Some studies have shown that the heads of pigeons, chickens, and other birds are able to maintain a stationary state in the hold phase when moved forward or back, and that this is not affected by movement [61; 62]. The necks of birds, which usually consist of 8-25 vertebrae (Figure 13), play an important role in this process. [PERSON] et al. combined the function of the bird's neck with a quasi-zero stiffness vibration isolation system to propose a new bionic vibration isolation device (Figure 14) [63]. They equivalented the whole body of the bird to the rigid support of the bionic system. The head was simplified as a mass block at the top of the system. Multiple quasi-zero stiffness damping mechanisms with springs and dampers were used to simulate the necks of birds. The system had an excellent vibration isolation effect under low and ultra-low frequency vibration, which provided a new solution for the nonlinear bionic vibration control system.  
Figure 12: (**a**) Limb structure of a frog [59], (**b**) bionic QZS device: a1, the rods in the second layer; a2, the supporting plate; a3, the torsion springs in the second layer; a4, the rods in the first layer; a5, the bottom plate; a6, the torsion springs in the first layer [60].  
Figure 13: (**a**) Test of head’s gazing stability, (**b**) 3D reconstruction model of the neck [64].  
In daily life, people encounter various types of vibration caused by a variety of situations such as running, jumping, and walking on rough roads [55; 65; 66]. The human body acts as a shock absorber to prevent brain injury caused by the vibration and impact. On the one hand, the swing of both arms can maintain the stability of the human body and weaken the harm of vibration to the human body [67; 68]. The arm swing can significantly reduce the vertical reaction moment of the ground against the person and reduce the vertical displacement of the body's center of mass. On the other hand, the leg plays an excellent role in low-frequency vibration isolation [69], preventing a large amount of vibration damage to important organs of the human body [66; 70]. Elastic muscles and tendons can act as nonlinear energy-conserving springs and shock absorbers during locomotion. Vibration energy is absorbed to prevent brain injury caused by vibration and impact during lengthening contractions of the muscles and tendons.  
The motion state and simplified model of the human arm and leg when walking is displayed in Figure 15. According to the above analysis and a simplified human motion model, a new bionic vibration isolation device based on the structure of the human body was reported [69]. The device consists of two parts: a swing rod and a rotating plate, which imitate the swing of human arms, and an X-shaped supporting structure with spring and damper, which imitate legs (Figure 16). The experimental results showed that the device not only had the nonlinear performance of X-type structures, but also had ultra-low tunable frequency and excellent anti-vibration characteristics.  
Figure 14: Bionic vibration isolation device based on a bird’s neck [63].  
Figure 15: Motion (**a**) and simplified model (**b**) of hand and leg when walking [69].  
Later, [PERSON] et al. proposed another nonlinear anti-vibration device [71]. As shown in Figure 17, the difference between this device and the previous one was that it adopted the structure of up and down distribution and used two small X structures with a spring or damper to replace the large X structure. The results demonstrated that the bionic vibration isolation device had a lower resonance frequency, which was conducive to its performance in low frequency vibration control. The device had good nonlinear coupling characteristics, and these nonlinear parameters could be adjusted according to actual needs.