## 4 Current Progress of Magnetic Negative Stiffness in QZS Isolators  
### QZS-Based Permanent Magnet Negative Stiffness Elements  
The utilization of permanent magnets in QZS vibration isolators has garnered significant attention from scholars in recent years, and their distinctive properties render them an optimal material for vibration isolation. With the ongoing advancement of science and technology, the investigation into QZS vibration isolators has progressively delved deeper, encompassing diverse realms ranging from fundamental theory to practical implementations. From an academic perspective, research on the utilization of permanent magnets in QZS vibration isolators primarily centers on several key areas. Firstly, employing theoretical modeling and numerical simulation, we investigate the functional mechanisms of permanent magnets within QZS vibration isolators and explore optimization design methodologies. Secondly, we conduct a comprehensive examination of the practical implications of permanent magnets within vibration isolation systems, coupled with experimental validation, to discern the influencing factors. Additionally, we meticulously scrutinize the performance and durability of permanent magnet materials, along with potential long-term usage issues. This endeavor not only furnishes a crucial theoretical framework for the design and enhancement of QZS vibration isolators but also establishes a robust groundwork for the advancement of associated fields. Notably, the integration of permanent magnets into QZS vibration isolators has commenced practical application in various domains. For instance, in precision instrument manufacturing, QZS vibration isolators effectively mitigate the external vibration effects on instrument accuracy, thereby enhancing the measurement precision and stability. Similarly, in aerospace applications, QZS vibration isolators proficiently attenuate aircraft vibrations during flight, thus augmenting the equipment reliability and operational efficiency. Moreover, amidst escalating concerns regarding environmental noise and vibration impacts, the QZS vibration isolator, as a novel vibration isolation apparatus, harbors extensive application prospects. Magnetic rings constitute a pivotal component of QZS vibration isolators. Extensive research endeavors have centered on the utilization of magnetic rings within negative stiffness architectures. As shown in Figure 23, the study by [PERSON] [69] introduces an innovative passive airborne quasi-zero stiffness platform (APQZSP) comprising upper and lower planes, a vibration-resistant framework, and six QZS leg components. This configuration primarily aims to mitigate low-frequency vibrations in airborne electro-optical systems, consequently enhancing the measurement precision. The QZS leg components of the platform are fabricated through the parallel integration of folded beam springs and magnetic negative stiffness springs (MNSSs). The magnetic force and negative stiffness characteristics of the MNSSs are meticulously elucidated within the thesis, alongside a comprehensive discussion on the influence of frictional damping imparted by the seismic structure on the platform's isolation efficacy. The study scrutinizes the platform's isolation efficacy under frictional damping by employing the harmonic balance methodology, and it delves into the impacts of damping and excitation on said performance. The findings indicate that the adoption of the QZS technique diminishes the platform's resonance frequency, efficaciously isolating low-frequency vibrations. Additionally, the study elucidates that frictional damping mitigates resonance by maintaining the displacement transfer rate within specified bounds when the excitation frequency falls below the isolation frequency.