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27 March 2012 A tunable 'negative' stiffness system for vibration control
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Commonly used variable stiffness methods for vibration control are employed to alter a system's resonant frequency by increasing its stiffness. The concept of "negative" stiffness could be used to decrease the system stiffness; thus, reducing resonant systems' frequency. A tunable stiffness isolation device (TSID) with negative stiffness capability enables a controlled mass to be isolated in a large range of excitation frequencies. This study presents theoretical and experimental investigations of a tunable stiffness system with negative stiffness. The proposed system comprises two electromagnets, two rubber elements and a mass. The negative stiffness effect is obtained from a magnetic force which is nearly a linear function of amplitude in small vibrations. A finite element analysis is performed to obtain a relation between the magnetic force and geometrical dimensions, as well as electromagnets' characteristics. The force transmissibility of the system under different applied currents for a frequency range of 30 to 120Hz is investigated. The results show that the system's resonant frequency decreases with the increased applied magnetic field.
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Zhaochun Li, Xiaojie Wang, Majid Behrooz, Nicholas Maus, and Faramarz Gordaninejad "A tunable 'negative' stiffness system for vibration control", Proc. SPIE 8341, Active and Passive Smart Structures and Integrated Systems 2012, 834122 (27 March 2012);

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