Passive acoustic monitoring of head disc interface interactions

A hard disc drive (HDD) recording head thermal protrusion is monitored by the passive acoustic characterization technique where adaptive discrete wavelet (ADW) filtering has been introduced to declare the contact. A phenomenological model is built to demonstrate detectability of the passive acoustic monitoring. The model is based on the mechanical impedance approach where impedances of head disc interface (HDI) and acoustic emission (AE) sensor are compared for matching over air bearing/head gimble assembly frequency bandwidth. A synthesized HDI response signal derived from the HDI mechanical impedance function is compared to the real AE signal obtained during the thermal protrusion based contact detection. A methodology of HDD level AE signal characterization presented in this work consists of the ADW filtering technique where the fifth order DB7 wavelet base function is used in AE signal decomposition. The signal decomposition order is selected by the AE signal entropy minimization.