## 4 Current Progress of Magnetic Negative Stiffness in QZS Isolators
### QZS-Based Electromagnetic Negative Stiffness Elements
The methodology proposed in this thesis enhances the efficacy of low-frequency measurements by diminishing the overall stiffness, thereby facilitating more  
Figure 27: An adjustable electromagnetic negative stiffness for low-frequency vibration measurement: (**a**) the schematic diagram of the proposed active geophone; (**b**) the experimental setup for evaluating the performance of the proposed active geophone; and (**c**) a comparison between the measured and analytical results of KMS and KS. precise recording and analysis of low-frequency seismic waves by seismologists. Through the integration of the AENS and active control techniques, the researchers successfully augmented the sensitivity and measurement bandwidth of the seismometer whilst upholding the high-frequency stability. Consequently, the seismometer is capable of more effectively detecting seismic signals across a broader frequency spectrum. Notwithstanding the elevated noise level of the prototype seismometer, the authors proposed enhancements to the design through the utilization of tailored components like a capacitive bridge displacement sensor and a lightweight voice-coil motor. Such improvements could lead to a substantial reduction in the instrument's noise floor and a consequent enhancement of the quality of the seismic data. Enhanced seismometers will empower seismologists to discern weak or low-frequency seismic signals that were previously elusive, thereby paving the way for novel research avenues in earthquake prediction, crustal structure analysis, and a deeper understanding of the Earth's interior. As shown in Figure 28, [PERSON] [58] innovatively designed a magnetic-air hybrid QZS vibration isolation system. By integrating electromagnetic technology and air-spring technology, the system effectively addresses the limitations encountered in traditional vibration isolation systems relying on QZS theory, including the constraints related to the mass of the fixed isolation object and the restricted range of QZS. At the heart of the thesis lies the development of a magnetic-air hybrid QZS vibration isolation system, which demonstrates the capability to dynamically adjust initial parameters like the system stiffness and structural specifications to suit the isolation objects of varying masses. Initially, the thesis delineates the constraints of traditional linear vibration isolation systems while introducing the concept of QZS vibration isolation systems. Subsequently, the paper meticulously elaborates on the structural design of the air-spring and electromagnetic components, alongside their static analysis. Furthermore, the paper delves into the parametric relationship between the positive and negative stiffness components, as well as the impact of the isolation object's mass. Ultimately, the performance of the vibration isolation system, particularly in low-frequency vibration isolation, is validated through experimental analysis, elucidating its suitability for isolation objects of diverse masses. In summary, this thesis introduces an innovative solution within the realm of vibration isolation, offering adaptability to various working conditions and showcasing a broad application spectrum. Through a magnetic-air hybrid design, the system attains a broader QZS range compared to conventional systems, thereby enhancing its efficacy in isolating vibrations of varied frequencies. Owing to its design, this  
[PERSON] [74] ingeniously devised a novel compact QZS dynamic vibration absorber (QZS EHDVA) aimed at both low-frequency vibration suppression and energy harvesting. As shown in Figure 29, the paper meticulously delineates the design and modeling of the QZS EHDVA, comprising a negative stiffness magnetic spring, a helical flexure spring, and a coil, tailored to accomplish the dual objectives of vibration suppression and energy harvesting amidst low-frequency vibration scenarios.