To design an ultra-low frequency (ULF) isolator, a magnetic spring composed of a pair of ring magnets is employed in parallel with the conventional pendulum. The magnetic spring can produce magnetic torque to cancel the gravitational torque of the pendulum and hence reduce the resonance frequency. The magnetic torque is calculated based on the Amperian current model. After establishing the analytical dynamic model of the ULF isolator, the transfer function is achieved and the isolation performance is evaluated from two aspects analytically: the resonance frequency and the center of percussion effect.
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