Testing hard disk drives’ resonances

Hard disk drives – with their ever growing storage densities and shorter access times – require an extremely high level of stability as regards the read/write head’s location and positioning in relation to the disk drive interface. The flying height is a compromise between competing effects. A lower flying height enables better local resolution for read/write operations and thus a higher data density; meanwhile the risk of collisions with the medium grows at the same time. The flying height is just a few nanometers and very much depends on the ambient pressure due to the aerodynamic bearing. The aerodynamic bearing, however, has resonances that depend on the ambient pressure too and that may lead to instabilities.

Since the measurement process is both non-contact and non-intrusive, in this situation using laser vibrometers is the only way of measuring the response behaviour of the read/write head including its suspension following dynamic excitation. When performing resonance test measurements with single-point and scanning vibrometers, the frequency spectrum of the read/write head’s deflection is measured as a function of the ambient pressure. You can use this to identify critical conditions and then make constructive changes. The goal of the optimization process is to develop read/write units that respond robustly to resonances caused by aerodynamic excitation.