Nonlinear aspects of air-bearing modeling and dynamic spacing modulation in sub-5-nm air bearings for hard disk drives

A new analytical model and method of analysis are proposed for understanding the dynamical behavior of ultralow flying height air-bearing sliders in proximity based on nonlinear dynamics. It is found that for sub-5-nm flying height air-bearing sliders, the nonlinear effects cannot be neglected. These nonlinear effects cause a slider´s response to become highly nonstationary, making frequency domain analysis by fast Fourier transforms (FFTs) an insufficient means of analysis. Joint time-frequency analysis is applied for accurately analyzing the nonstationary slider responses and to verify the nonlinear nature of the air bearing for both experimental and simulation results. One degree-of-freedom (DOF) and 2-DOF nonlinear lumped parameter models are proposed showing the effect of nonlinearities on the FFT representations of air-bearing slider responses. The 2-DOF model is used to further investigate the nonlinear coupling effect, and it shows high correlation with experimental results from two different slider designs when in unsteady proximity. These findings suggest that the nonlinearities of the air-bearing slider must be considered when modeling slider-disk interface dynamics. Also, complex frequency domain representations of slider responses in proximity can be explained by the nonlinear nature of the air-bearing slider without contact between the slider and disk as previously proposed by other models.