Nonlinear dynamics of sub-10 nm flying height air bearing slider in modern hard disk recording system

This paper presents an experimental and analytical study of nonlinear dynamics of air bearing slider in modern hard disk recording system. Proximity recording sliders used for commercial hard disk drive were deployed for the experimental investigation. Flying height oscillation signal of the sliders in various proximity regimes (nano-meter level) were measured by using ultra-precision laser doppler vibrometer (LDV), and processed by using Matlab for time–frequency analysis and phase plot analysis. From the experimental results, it was found that two kinds of nonlinear oscillations exist in the system: the slider–disk contact-induced nonlinearity and the air bearing inherent nonlinearity. Primary resonance, superharmonic resonance and sub-harmonic resonance due to the nonlinearity were observed. A numerical–analytical model incorporating the nonlinear features of both slider air bearing oscillation and slider contact vibration was developed to quantitatively estimate spectral signatures. Direct numerical simulations were also carried out to simplified model to obtain phase plots. The analytical and numerical results agree with the experimental results well. It was shown that both the contact vibration and air bearing oscillation render the system to exhibit complex nonlinear features. Particularly, phase plots can be used to identify the slider–disk contact vibration and air bearing nonlinear oscillation, the former is characterized by “sharp corner” when the non-contact phase transferring to contact phase, and latter is characterized by “smooth corner” due to stiffness–softening feature of air bearing.