Srinivas Tadepalli

Low SNR Signal Processing for Head Media Contact Detection in HDD

The methodology for processing grossly undersampled HDD position error signal (PES) is proposed to improve the head-disk contact detection process. The proposed method is a combination of compressive sampling (CS) and adaptive discrete wavelet transform (ADWT) techniques. Here, CS is employed to reconstruct the PES information from very few revolutions of data while ADWT is utilized for extracting head-disk interface (HDI) modulation changes during thermal protrusion of the read/write element.Copyright

DLC Coatings Characterization on HDD Recording Heads

New magnetic storage technology enhancements are being introduced into the HDD products to facilitate lower head media spacing and reliability. Recently, advanced components such as thermal protrusion devices, Head Disc Interface (HDI) proximity sensors, complex self-compensating AAB designs have been integrated into the recording heads. Component development and product integration teams evaluate performance of these critical head disc interfaces for tribological robustness. New HDI components could potentially bring new HDI wear mechanisms that occur under specific thermo-mechanical conditions. Characterization of recording head DLC overcoat nanoscale wear performance has always been a challenge. Historically, nano-wear tests evolved in conjunction with advances in Scanning Probe Microscopy (SPM) techniques [1] and wear resistive tools [2] like diamond tip cantilevers. Here, by controlling SPM, contact force specified wear patterns can be obtained in contact mode or dynamic mode. Decisions on DLC wear resistance can be made qualitatively by evaluating wear mark topographies.Copyright

Multi-Resolution HDD Contact Detection Technique for Low SNR Applications

A quick and reliable active flying height calibration is critical in today’s hard disc drive short product development and high volume production cycles. In addition to the servo signals, passive HDI acoustic and proximity monitoring techniques are tracking equilibrium of the head gimble assembly and air bearing modes. Passive acoustic HDI monitoring had been proven to be capable in active head protrusion detection applications [1] where derived passive and active Air Bearing flying profiles help to set active flying clearance. With enhanced sensitivity, passive acoustic techniques such as AE can detect embedded particles [2]. The drawback of this technique is that noisy HDD environment causes loss of detectability of the useful AE signal [3]. Special attention has to be paid for extracting desirable HDI information. On the other hand, recording head based proximity probes are immune to torsional HDI modes and operate on pitch mode induced modulation. Advanced HDD today uses a combination of recording head based proximity sensors that are designed to sense HDI modulation at close proximity to the disc. It has to be pointed out that interpretation of proximity probe contact signatures always has been challenging.Copyright