Experiment study on nonlinear oscillator containing magnetic spring with negative stiffness

The concept of negative stiffness may find extensive applications in wave manipulation and low frequency isolation of vibration. Many realizations use prestressed or buckled components, by which the negative stiffness possesses strong nonlinearity and should be taken into account. In this work, based on an air track platform, we propose a scheme to directly test the dynamics of lumped parameter model of a nonlinear vibration system containing negative stiffness spring. Repelling magnets are used to realize negative springs, and different nonlinearity and rigidity are achieved by varying the clearance in between the magnets. A mass spring model of coupled oscillators linked by positive and negative springs in series is first investigated, the nonlinear behaviours of both the free vibration and the frequency response agree well with the theoretical analysis of Duffing's equation adopting cubic approximation of the nonlinear stiffness. A model mimicking the high-static-low-dynamic stiffness isolator is also investigated under nonlinear regime. The proposed facility is flexible and useful for the proof-of-concept validation of relevant systems such as vibration isolators, energy sinkers involving nonlinearity.