Switched reluctance motor (SRM) has become a competitive selection for many applications of electric machine drive systems recently due to its relative simple construction and its robustness. The advantages of those motors are high reliability, easy maintenance and good performance. The absence of permanent magnets and windings in rotor gives possibility to achieve very high speeds (over 10000 rpm) and turned SRM into perfect solution for operation in hard conditions like presence of vibrations or impacts. Such simple mechanical structure greatly reduces its price. Due to these features, SRM drives are used more and more into aerospace, automotive and home applications. The major drawbacks of the SRM are the complicated algorithm to control it due to the high degree of nonlinearity, also the SRM has always to be electronically commutated and the need of a shaft position sensor to detect the shaft position, the other limitations are strong torque ripple and acoustic noise effects.

The goal of this thesis is to experimentally characterize the flyability of current generation read/write heads over media patterned to densities above the superparamagnetic limit. The superparamagnetic limit is the physical limit to magnetic storage density. In magnetic storage, superparamagnetism is the uncontrollable switching of stored bits during the lifespan of a hard disk. Theoretical analysis has predicted that densities of ~50 Gbit/in2 are not possible using traditional continuous media. One strategy to achieve high storage density, above the superparamagnetic limit, is patterned media. With patterned media the physical separation of magnetic domains increases their stability. One of the major challenges of development of patterned media is achieving acceptable flyability of the read/write head. In that vein, a test stand is built to measure head liftoff speed, head to disk intermittent contact and head fly height. Tangential friction, an indicator of head liftoff is measured by a Wheatstone bridge strain circuit attached to a cantilever beam. Intermittent contact is quantified by the amount of noise emanating from the interface, which is measured by a high frequency acoustic emission sensor. Head fly height is measured indirectly with a capacitance circuit built around the head to disk interface. Experimental samples of current generation read/write heads and media are obtained from industry. Current generation media is patterned using focused ion beam milling to a density of 10 Gbit/in2. Other, extremely dense samples, above 700 Gbit/in2, are created via thin film self assembly on silicon substrate. Conclusions on slider head flyability over patterned media are based on comparison with flyability over non-patterned media. It is demonstrated that loss of hydrodynamic lubrication is small for small pattern regions with high conserved surface area ratio. Conserved surface area ratio is defined as total surface area minus etched surface area all divided by the total surface area of the storage media. For wafer scale patterned media with low conserved surface area ratio, head liftoff cannot be achieved at designed normal load. However, a 50% reduction of load allows slider head liftoff.

A measurement method of small-capacitance using transient waveforms is proposed in this thesis. A pi-circuit is used to express the stray capacitors between terminals and those from each terminal to ground. Two measuring modes, differential and common modes, are required to obtain the parameters of the circuit. The parameters are determined by transient current waveforms of the modes with an applied voltage, i.e., the open circuited voltage at the end of the current injection cable. The parameters of the pi-type circuit are obtained from a slope of the transient current waveforms or a waveform fitting by a nonlinear method. These methods enable the derivation without a voltage measurement by a probe connecting across the small capacitance, since the parasitic capacitance of the voltage probe obscures the small capacitance. / 博士(工学) / Doctor of Philosophy in Engineering / 同志社大学 / Doshisha University