Head-medium contact detection using an oscillating electromagnetic force

An apparatus, comprising:

• circuitry configured to apply an AC signal having a frequency to one of a slider of a recording head and a magnetic recording medium, the applied AC signal causing an oscillation in an electrostatic force and clearance between the slider and the medium at the frequency of the AC signal;
• a thermal sensor configured to generate a sensor signal at the AC signal frequency in response to sensing changes in temperature resulting from the oscillating clearance;
• and
• a detector coupled to the circuitry and the thermal sensor, the detector configured to detect one or both of head-medium spacing changes and head-medium contact using a change in a phase delay between a phase of a first harmonic of the thermal sensor signal and a phase of the applied AC signal.

A method, comprising:

• applying an AC signal having a frequency to one of a slider of a recording head and a magnetic recording medium, the AC signal causing an oscillation in an electrostatic force between the slider and the medium at the frequency of the AC signal;
• causing, by the oscillating electrostatic force, an oscillation in a signal produced by a thermal sensor at the slider, the thermal sensor signal oscillating at the AC signal frequency;
• and
• detecting one or both of head-medium spacing changes and head-medium contact using a phase of a first harmonic or an amplitude of a second harmonic of the thermal sensor signal;
• wherein:
• electrical noise is introduced in the recording head in a frequency range that includes a first harmonic of the thermal sensor signal;
• and
• detecting using the amplitude of the second harmonic avoids the noise.

An apparatus, comprising:

• circuitry configured to apply an AC signal having a frequency to one of a slider of a recording head and a magnetic recording medium, the applied AC signal causing an oscillation in an electrostatic force and clearance between the slider and the medium at the frequency of the AC signal;
• a thermal sensor configured to generate a sensor signal at the AC signal frequency in response to sensing changes in temperature resulting from the oscillating clearance, the circuitry comprising the thermal sensor;
• and
• a detector coupled to the circuitry and the thermal sensor, the detector configured to detect one or both of head-medium spacing changes and head-medium contact using a phase of a first harmonic or an amplitude of a second harmonic of the thermal sensor signal;
• wherein:
• electrical noise is introduced by bond pad sharing between the circuitry and the thermal sensor, the noise falling within a frequency range that includes a first harmonic of the thermal sensor signal;
• and
• detecting one or both of head-medium spacing changes and head-medium contact by the detector avoids the noise.