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Position sensors other than the R/W heads are not embedded into current hard-disk drives (HDDs) due to cost, resolution, and signal-to-noise ratio (SNR) issues. Moreover, the "optimal" location for placing these sensors is still unknown. In this paper, the Pb-Zr-Ti (PZT) elements in the PZT suspension-based microactuator are used as a secondary actuator and a displacement sensor simultaneously with self-sensing actuation. The proposed displacement estimation circuit produces an estimated PZT microactuator's displacement with high SNR and nanometer resolution comparable to that measured from the laser doppler vibrometer (LDV). A robust active mode damping controller is then designed to damp the PZT microactuator suspension's torsion modes and sway mode, as well as decoupling the HDD dual-stage servo into two distinct loops for individual sensitivity optimization. Our results show attenuation of …