## 4 Current Progress of Magnetic Negative Stiffness in QZS Isolators
### QZS-Based Hybrid Magnetic Negative Stiffness Elements  
A hybrid magnetic negative stiffness mechanism comprises both a permanent magnet and an electromagnet, forming a composite negative stiffness system. The interaction between the permanent magnets and the electromagnets facilitates the adjustment of the structural stiffness. The permanent magnets in hybrid magnetic negative stiffness mechanisms primarily furnish the initial intrinsic stiffness. Endowed with a constant magnetic field, they generate a stable magnetic force, forming the foundational stiffness of the structure. Conversely, the electromagnets facilitate adjustable control over the structure's stiffness. By applying an electric current to the electromagnets, the strength of the magnetic field they emit can be adjusted, thereby influencing the structure's stiffness. Real-time adjustment and control of the structural stiffness are attainable by regulating the current in the electromagnet. The hybrid magnetic negative stiffness mechanism offers the advantage of amalgamating the distinct characteristics of permanent magnets and electromagnets. The permanent magnets exhibit high energy density, independence from external power sources, and rapid responsiveness, ensuring stable initial stiffness. Moreover, the electromagnetic component offers adjustability and flexibility, enabling real-time stiffness modification to suit specific requirements. Performance optimization and the diverse application of the hybrid magnetic negative stiffness mechanism hinge on the judicious design of the permanent magnet and electromagnetic body layout and parameters. Hybrid magnetic negative stiffness mechanisms find extensive applications in structural vibration control, vibration damping systems, robotics, and intelligent structures. These mechanisms enable precise structural control, vibration suppression, and enhancement of the system stability and performance. Moreover, hybrid magnetic negative stiffness mechanisms offer adaptability to various working conditions and requirements through stiffness adjustment, thereby providing remarkable flexibility. [PERSON] [75] explored an orthogonal six-degrees-of-freedom (6-DOF) vibration isolation system designed to mitigate low-frequency vibrations in high-precision instruments while possessing tunable HSLDS characteristics. As shown in Figure 30, employing both experimental and analytical techniques, the researchers formulated a dynamic model for an orthogonal six-degrees-of-freedom electromagnetic nonlinear vibration isolation system to examine the experimental outcomes. They investigated the frequency response function of the force transmissibility through harmonic equilibrium analysis and the arc-length continuation method. The experimental and analytical findings indicate that the isolation frequency range widens with higher control current. Parametric studies reveal that augmenting the electromagnetic coefficient and diminishing the onset distance can lower the isolation onset frequency. The paper offers pertinent interpretations of these findings. The objective of the system is to enhance the orthogonal six-degree-of-freedom low-frequency vibration isolation for variable suspended masses in high-precision instruments. The research innovations encompass the exploration of the electromagnetic nonlinear properties to examine the adaptable orthogonal six-degree-of-freedom HSLDS tailored for variable suspended masses. Additionally, the study employs analytical models to forecast the experimental outcomes of nonlinear phenomena in orthogonal six-degree-of-freedom vibration isolation systems. Furthermore, the section will design and manufacture an orthogonal six-degree-of-freedom isolation system featuring an adjustable HSLDS. It will furnish characteristic curves of the adjustable HSLDS and carry out experiments on a triaxial shaker to investigate and analyze an intriguing phenomenon, namely, magnetic saturation. Utilizing the signals at point 1 and point 2, the researchers computed the force transmissibility.