Study On Measurement Systemfor Flying Attitude Of Magnetic Head

With the rapid increase of the areal density of the magnetic disk drives, the head-disk spacing is becoming smaller and smaller. As a result, it is critical and difficult to explore the methods to measure the flying height. In this dissertation, three measurement systems are proposed for the measurement of the attitude of magnetic head, that is, the Single-focus Attitude Measuring (SAM) system, the Dual-focus Attitude Measuring (DAM) system and the Four-focus Attitude Measuring (FAM) system.Making use of heterodyne interferometry and dual-differential phase discrimination technology, the Single-focus Attitude Measuring (SAM) system obtains a high measuring resolution, which reaches 0.089nm, and thus is capable of measuring minor displacement as well as minor velocity. Besides, the system has strong ability of overcoming environmental disturbance due to its common path design with a birefringent lens. Experimental results show that, under regular laboratorial condition (temperature variation is 1 degree Centigrade), the phase drift in the SAM system is less than 4 degrees, approximately equivalent to 4 nm, within an hour.In order to measure the three-dimension movements of the magnetic head, the Dual-focus Attitude Measuring (DAM) system and the Four-focus Attitude Measuring (FAM) system are proposed. The pros and cons of each system are compared, based on which the optimal system under different circumstances is established.The design methods of key optical components in the above systems, such as birefringent lens and negative lens, are also presented. The birefringent lens, consisting of a piece of birefringent crystal and a piece of optical glass, is a key component in the dual-focus interference microscope. To design the birefringent lens easily and promptly, we not only introduce the concept of 'pseudo-chromatic aberration' but also define 'the reciprocal of pseudo-chromatic dispersion'. Thereby, with the use of the primary aberration theory and the PW method, a useful table of the primary structure of the birefringent lens is given, with the couple of three kinds of birefringent crystals and optical glasses, according to different demands; the calculation of aberration and optimum design are carried out by OSLO, an optical software, and the desired result is obtained. For the sake of evaluating the specific structure, the compact factor γ is defined as a criteria. This dissertation provides concrete examples, in which calcite and ZF1 are used as materials and the compact factor γ is 0.25.