Aliased Narrow-Band Disturbance Rejection Using Phase-Stabilization Above Nyquist Frequency

Lightly damped resonant modes at above the Nyquist frequency which are not phase-stabilized result in aliased narrow-band disturbances. In this paper, an elliptical transformation-based scheme is proposed for phase-stabilization of resonant modes at above the Nyquist frequency. Our experimental results on the Pb-Zr-Ti active suspension in a commercial 3.5 ${\´\´}$ dual-stage hard disk drive show that narrow-band disturbances are suppressed without large spillover effects at an aliased resonant mode at 4.23 kHz, which is in close proximity with an out-of-phase resonant mode at 3.50 kHz.