Improved safety mode considering external shock direction for near-field recording system using SIL

To increase the near-field coupling efficiency in a near-field recording (NFR) system, extremely small air gap (less than 100 nm) between the solid immersion lens (SIL) and media should be maintained. However, maintaining the air gap is very important and difficult. Despite various anti-shock control methods, there are physical limitations to controlling the air gap against external shock. A safety mode that moves the actuator to the initial position for large external shock is currently being used. The existing safety mode exhibits good performance for downward shocks of 6 G amplitude and 10 ms duration time, but some problems arise for upward shocks of 3 G amplitude and 10 ms duration time. To avoid collision for upward and downward shocks, we present an improved safety mode that considers the direction of the external shock for an SIL-based near-field recording system. We analyzed the upward and downward shock responses of the NFR system. The shape of the pulse input was designed to minimize the overshoot of the actuator. Through various experiments, the amplitude and duration time of the pulse input were optimized. Even with an upward shock with 8 G and 10 ms, no collision was observed between the actuator and the media by using the improved safety mode with the optimized pulse input.