Sensors for dynamic characterisation of magnetic storage systems

<jats:p>The areal (surface area density of bits) storage density of magnetic hard disks is continually increasing, with typical available commercial storage densities being around 10Gbits/in<jats:sup>2</jats:sup>. It is predicted that densities in excess of 40Gbits/in<jats:sup>2</jats:sup> will be possible before the year 2003. A number of key issues arise from this development, such as the need to determine and control accurately the dynamic flying height (<jats:italic>z</jats:italic>‐axis) of the read‐write head, which is affected by the apparent distortion of the disk surface due to rotation‐induced disk resonance. As a result of the increasing storage density the positional control of the head in the plane of the disk (<jats:italic>x</jats:italic>‐<jats:italic>y</jats:italic> plane) also becomes more critical. This paper deals generally, but with a particular emphasis on optical and piezoelectric sensors used in our laboratory for characterisation of storage media and systems.</jats:p>