Optical methods of the head positioning in magnetic disk systems

This paper reports a new method of head positioning by applying optics to magnetic disk systems. To increase the accuracy of head positioning, several methods in which a servo disk is not used have been investigated. Until now these methods were unsuccessful because of interference between the head positioning signal and the data signal, both of which were recorded on the same data surface. In the method explained here, the head can be positioned on the disk by an optically detected positioning signal without disturbing operation of the magnetic disk system. A unique structure for both the disk and head was investigated. Optical patterns depicting position of the data tracks were formed by coloring the anode oxidized surface layer of an aluminum substrate, and by forming a magnetic film over that. Three optical fibers were imbedded in a hole in the central rail of a Winchester-type ferrite head and were used to read the optical pattern. A stable positioning signal was optically detected from the rotating disk. By using the signal to assemble a simple servo loop, the head could be positioned with ±3 μm accuracy. Potential accuracy was found to be ±0.7 μm.     

An investigation of the failure envelope of granular/discontinuous-columnar sea ice

The three-dimensional failure envelope for granular/discontinuous-columnar sea ice has been investigated over a range of nominal strain rates from 9 × 10^?6 s^?1 to 4.4 × 10^?4 s^?1 by using confined compression tests. Both the applied load and side-confining load were measured. The tests were performed on samples cut from a solid block of ice in the Beaufort Sea which structurally was granular with some banding of discontinuous-columnar ice to a depth of 1.2 m. The results indicate the overall shape and size of the failure envelope of this ice, and show that although the shape is independent of loading rate, the size increases with loading rate. An analytical expression is derived which mathematically describes the failure envelope in three-dimensional space.     

Thermodynamics of helium in the rotating frame between 3.0 and 6.0 K

Experiments on helium with a large diameter (1 m) rotating cryostat at speeds up to 50 Hz are described. Radial temperature distributions have been measured with axial pressures ranging from 25 × 10³ to 2.0 × 10⁵ Nm^?2. It is concluded that the temperature distributions are isentropic to within 30 mK (ie the uncertainties in the published equation of state) in a radial duct of diameter 18 mm.     

The crosstie memory

The crosstie memory stores information in magnetic domain walls in permalloy films about 350 Å thick. The domain walls are also used as shift register tracks. Serrated edges on narrow thin film permalloy strips are used to center a domain wall in each strip and to provide stable positions for crossties and Bloch lines. A magnetoresistance detector uses the same information bearing permalloy film as the magnetoresistive element. The entire crosstie memory can be fabricated on a silicon wafer or chip using conventional photolithographic procedures as are used in fabricating integrated circuits. Thus, a magnetic memory can be combined with semiconductor drivers, decoders, and sense amplifiers on the same chip. The memory is intended to serve as a block oriented random access memory (BORAM). Important background information such as static and dynamic stability conditions, Bloch line mobility, propagation and observation techniques are reviewed. Also, design goals and the role such device is expected to play in memory technology are presented. Anticipated performance includes a shift rate of 20 × 10⁶bits/sec, a bit density greater than 1.5 × 10⁵bits/cm², an operating temperature range from -50 °C to 100 °C, nonvolatility, low cost, and low power consumption.     

On the fatigue behaviour of quenched and tempered at 300 and 600 °C SAE 1045 steel in an environment of sugar cane juice

SAE 1045 steel is widely used for manufacturing shafts in the sugar cane mills of the sugar industry. These shafts are designed with an expectation of a long lifetime. However, fatigue failures occur frequently. The sugar cane juice processed in these mills has corrosive properties that can alter the fatigue life of these shafts. In this research, the fatigue strength of SAE 1045 steel between 1 × 10⁴ and 2 × 10⁵ cycles in air and in sugar cane juice, with two different microstructures (tempered martensite at 300 °C and tempered martensite at 600 °C), was determined in rotating bending. The microstructure of the materials was characterized using optical microscopy, and the fracture surfaces were characterized using scanning electron microscopy. The results show that the fatigue strength at 2 × 10⁵ cycles for the tempered condition at 600 °C decreases 7% because of the sugar cane juice effect, and for the tempered condition at 300 °C, the fatigue strength decreases 15%.     

用于原子重力仪的扫频频率源系统

原子重力测量实验中,需要通过扫频频率源来实现主从Raman激光的线性啁啾,进而补偿原子在自由下落过程中产生的多普勒频移,实现当地重力加速度g的测量。针对传统扫频频率源体积大、发热量大的问题,通过AD9959数字芯片设计了一款扫频频率源,可用作原子喷泉扫频控制和Raman光锁相环鉴频鉴相本振参考。最终通过实验测得：该扫频信号源的相位噪声为-112 dB@1 kHz,频率稳定度为1.38×10^-11@1 s,对原子重力仪灵敏度影响为2.81×10^-9 g/Hz^1/2,600 s积分时间对原子重力仪实验影响为1.15×10^-10 g。该系统具有低噪声、高稳定度的特点,可满足搬运式原子重力仪分辨力10^-10 g需求。研究结果为原子重力仪从原理样机向工程化可搬运实验测试仪器发展提供了一定参考。     

The propagation of magnetic bubbles on permalloy disks

A magnetic bubble generator consisting of a Permalloy disk and a current conductor loop has been used recently in a mass memory design utilizing magnetic bubble technology. The bias field range in which the disk can hold the seed bubble is measured in this report as a function of of the rotating field frequency. Above a critical frequency fc, the bias field margins begin to decrease. The dependence of fcon disk size is obtained for disks with diameters from 16 μm up to 43 μm at rotating fields of 20 and 30 Oe. The separation between Permalloy disks and the garnet film is kept at 0.8 μm or 1.6 μm. Results show that at a fixed rotating field, a smaller disk is preferable at higher frequency for a magnetic bubble material with a given mobility. The critical frequency fcobtained is in good agreement with a theoretical calculation using the viscous damping model by Rossol et al. For frequencies below fc, the bias field margin on the disk is equal to that of the propagating channel and circuit failure due to the loss of the generator seed bubble can be eliminated.     

Typical flow between enclosed corotating disks and its dependence on Reynolds number

Abstract

The flow in an enclosed co‐rotating disk pair is investigated by Laser Doppler Velocimetry (LDV) measurements and flow visualizations. First, the typical flow structure at Re = 5.25 × 10⁵ and S = 0.09 is clarified. The flow fields in the r – θ and the r – z planes are both investigated and then divided into several flow regions based on the distinct flow types observed. The flow regions found in the two different planes are also compared and integrated. Second, with S fixed, the dependence of the flow field structure upon the Reynolds number is discussed. Three regimes of the r – θ plane flow with different Reynolds numbers are identified based on the measured mean velocity and spectral intensity. When Re < 1.6 × 10⁵, no solid body region is found and the flow is in a laminar regime. In the range 1.6 × 10⁵ ≤ Re ≤ 2.0 × 10⁶, the solid body region and the outer region vortices coexist, and an empirical equation is developed to estimate the number of vortices. When Re > 2.0 × 10⁶, the flow becomes turbulent. As Re increases from 9.3 × 104 to 5.25 × 10⁵, the spectral intensity initially increases and then decreases before increasing again to an even higher level, resulting in an increasing sawtooth pattern.     

The effect of microstructure on thermal expansion coefficients in powder-processed Al2Mo3O12

Orthorhombic Al₂Mo₃O₁₂ was investigated as a model anisotropic phase to understand the influence of powder preparation routes and bulk microstructure (mean grain size) on the bulk coefficient of thermal expansion (CTE) and to compare it to the intrinsic CTE of powder samples. A co-precipitation route was used for the synthesis of pure single-phase nanopowders, while a polyvinyl alcohol-assisted sol–gel method was utilized for the synthesis of micron-sized powders. Sintered samples prepared from both powders exhibited different microstructures in terms of mean crystal sizes and porosity. Bulk samples obtained from nanopowders were highly porous and contained crystals of approximately 100-nm diameter, while the bulk pieces produced from the micron-sized powders were denser, contained crystals larger than 5 μm, and showed occasional intergranular and transgranular microcracks. Such different microstructures hugely impact the bulk CTE: the nanometric sample possesses a bulk CTE (0.9 × 10^?6 °C^?1, from 200 to 700 °C) closer to the instrinsic CTE (2.4 × 10^?6 °C^?1) than for the micrometric sample, which showed a negative CTE (?2.2 × 10^?6 °C^?1) from 200 to 620 °C, and an even more negative CTE above 620 °C (?35 × 10^?6 °C^?1). A finite element analysis showed that the local maximum thermal tensile stresses could be as high as 220 MPa when simulating a temperature drop of 700 °C as an example of thermal treatment following sintering. This tensile stress is expected to exceed the tensile strength of Al₂Mo₃O₁₂, explaining the origin of microcracks in bulk samples prepared from the micron-sized powders. The thermal behavior of the microcracks leads to differences between the intrinsic and bulk thermal expansion; we show experimentally that such differences can be reduced by nanostructuring.     

Magnetic bubble mass memory

An experimental magnetic bubble mass memory module complete with all control function and detection electronics has been built and operated. The module contains twenty-eight 16 448-bit mass memory chips and operates at a nominal rotating field frequency of 100 kHz. The module has an average access time of 2.7 ms, a read/write cycle time of 5.14 ms, and a data rate of 700 kbit/sec. A read error rate of <1.6 × 10¹²and error-free propagation in excess of 8.4 × 10¹⁵bubble cycles have been demonstrated.     

Microstructural investigation of AA 2195 T81 chips formed during a metal-cutting process

In this study, the microstructure of AA 2195 T81 metal-cutting chips formed during a turning operation were characterized using microscopy and diffraction techniques. At a constant strain of 2, the resulting strain rate imposed on the metal was varied from 0.8 × 10⁴ to 2.6 × 10⁵ s^?1. At strain rate of 0.8 × 10⁴ s^?1, the resulting microstructure contained regions of 100 nm ultrafine grains. At the highest strain rate of 2.6 × 10⁵ s^?1, 150–200 nm ultrafine grains were observed plus overaged precipitates. The grain size increment and appearance of overaged precipitates with the higher strain rate is conjectured to be a result of temperature increment and not of direct strain rate.     

State-space model of grid-connected inverters under current control mode

Growth of distributed generation has led to distribution systems with a mixture of rotating machine generators and inverter interfaced generators. The stability of such networks needs to be studied through the analysis of state-space models, and so suitable models of inverters are needed to complement the well-established models of rotating machines. As machine models include features such as automatic voltage regulators and wash-out functions, the inverter model also includes phase-locking functions and internal control loops. The model for voltage source inverters with an internal current control loop, an outer power regulation loop, a measurement of average power and a phase-locked loop has been developed. The model is presented in detail and is formed with a state-vector, similar to that used for rotating machines. The model includes nonlinear terms but can be linearised about an operating point. The state-space model is verified against a component-level time-step simulation in Simulink/PLECS     

High Density Direct Read after Write (DRAW) Recording

Burning holes into a thin layer of bismuth film is the basis for the development of a large capacity store for DRAW operation (2 × 10¹⁰ bits). In 600 Å bismuth films deposited on a rotating disc, storage is achieved at a data rate of 1 Mbit/s using a He-Ne laser source. Reading the record in transmission, an optical contrast ratio of 2–3 was observed. Storage densities close to 10⁸ bits/cm² are achievable.     

High-performance dc SQUIDs with submicrometer niobium Josephson junctions

We report on the fabrication and performance of low-noise, all-niobium, thin-film planar dc SQUIDs with submicrometer Josephson junctions. The junctions are evaporated obliquely through a metal shadow evaporation mask, which is made using optical lithography with 0.5 µm tolerance. The Josephson junction barrier is formed by evaporating a thin silicon film and with a subsequent oxidation in a glow discharge. The junction parameters can be reproduced within a factor of two. Typical critical currents of the SQUIDs are about 3 µA and the resistances are about 100 Ω. With SQUIDs having an inductance of 1 nH the voltage modulation is at least 60 µV. An intrinsic energy resolution of 4×10^?32 J/Hz has been reached. The SQUIDs are coupled to wire-wound input coils or with thin-film input coils. The thin-film input coil consists of a niobium spiral of 20 turns on a separate substrate. In both cases the coil is glued onto a 2-nH SQUID with a coupling efficiency of at least 0.5. Referred to the thin-film input coil, the best coupled energy resolution achieved is 1.2×10^?30 J/Hz measured in a flux-locked loop at frequencies above 10 Hz. As far as we know, this is the best figure achieved with an all-refractory-metal thin-film SQUID. The fabrication technique used is suited for making circuits with SQUID and pickup coil on the same substrate. We describe a compact, planar, first-order gradiometer integrated with a SQUID on a single substrate. The gradient noise of this device is 3×10^?12 T m^?1. The gradiometer has a size of 12 mm×17 mm, is simple to fabricate, and is suitable for biomedical applications.     

Canadian developments in superconducting Maglev and linear synchronous motors

Canadian developments in the application of superconducting magnets for levitation, synchronous propulsion, and guidance of high speed inter-city ground transport are described. At 480 km h^?1 a 100 passenger vehicle weighing 300 kN is levitated 15 cm clear of a flat guideway (minimizing ice and snow accumulation) by eight 3.85 × 10⁵ ampere-turns 100 × 30 cm magnets interacting with eddy currents induced in two 80 × 1 cm aluminium strips. The variable speed LSM uses fifty 5 × 10⁵ ampere-turns 40 × 150 cm magnets interacting with split three-phase windings energized in 5 km sections and phase angle controlled to give 72% efficiency and 0.82 power factor. A lateral restoring force of 10⁴ N cm^?1 is produced by the propulsion magnets interacting with the levitation strip edges and with flat null-flux loops overlying the LSM windings. A review of cryogenic systems indicates that isochoric dewar operation is best suited for Maglev vehicles. The test facility, using stationary full-scale superconducting magnets and guideway components mounted on a 100 km h^?1 vertical axis 7.6 m diameter wheel, is now fully operational and LSM tests are being performed.     

Variation of the electrochemical potential difference in a gravitational field

We have determined the variation of the electrochemical potential difference in a gravitational field, and the results agree to within 4% with the predictions of the Equivalence Principle (EP). Thus, EP has again been verified, but unlike previous experiments, this experiment involved charged particles. The results were obtained using a DC SQUID in which the two junctions were separated vertically by about 7 cms. The junctions, which were phase-locked to an external microwave source, acted as two very precise batteries. Because of the gravitational red-shift of the radiation, a voltage difference of 1:10¹⁷existed between these batteries, giving a net EMF in the SQUID loop in the absence of other effects of about 2×10^-21volts. The loop EMF determined by the rate of change of flux in the loop was however less than 1×10^-22volts, thus demonstrating the additional variation in the potential difference due to the gravitational field.     

A low inductance strip-line recording head

A prototype high energy-efficiency recording head for use in a high packing density recording system has been developed. The operation of the head in the writing mode depends on the magnetic field round a thin strip conductor rather than flux leakage from the magnetic circuit as in a conventional ring-type head. The presence of ferrite in the vicinity of the strip increases the field produced for a given strip current. Since its low input impedance is unsuitable for direct connection to electronic circuits, it has been necessary to use an intermediate pulse transformer. By making this transformer an integral part of the recording head, a very compact unit is realizable. Care has been taken in the design of the structure to minimize any stray inductance which may be comparable to that of the head element. Advantages of the proposed head are its good high-frequency performance and suitability for high track densities.     

High Precision Robust Automatic Alignment Method for Rotating Shaft

Rotating Shaft is widely used in various high precision instruments on scientific and industrial metrology. This paper proposes a high precision and robust method to automatically align a rotating shaft perpendicular to the horizontal plane. Firstly, an alignment model consisting of a dual-axis inclinometer and four motors is designed. Then the rotating shaft tilt angle between the practical and the ideal shaft is projected to two orthogonal planes, and generates a rotation angle in each plane. The two rotation angles are calculated by differential measurement method based on the inclinometer outputs, and then the relationship of shaft tilt angle against inclinometer outputs is obtained. According to these two rotation angles, the relative heights of the three supporting points of the platform attached to the rotating shaft are calculated. Employing an angle closed loop strategy; the rotating shaft tilt angle is aligned by three linear stepping motors. Experiment results show an alignment precision of 0.003º is achieved using an inclinometer with the resolution of 0.0005º and a linear stepping motor with the regulation precision of 0.89 μm. The proposed method is suitable for a wide variety of precision machines that require the use of rotating shaft.     

A temperature-variable sample rotating cryostat in high magnetic fields

A temperature-variable sample rotating cryostat has been developed in order to measure the angular and temperature dependence of the upper critical field in several single crystal Chevrel phase superconductors. In the cryostat, the temperature of the sample can be varied from 2 to 15 K within an accuracy of ±10 mK. The sample can be rotated in an adiabatic vacuum can around a horizontal axis at the centre of our superconducting magnets up to 16.5 T within an accuracy of ±1°.     

Elevated temperature sliding wear behavior of WCP-reinforced ferrous matrix composites

WC_P-reinforced ferrous matrix composites were processed by direct addition of WC_P (100–150 μm) and the melt of the matrix alloy to a rotating mold at 1000 rpm. Dry sliding wear behaviors of the composites containing about 80 vol.% of WC_P and high-speed steel counterpart were investigated at room temperature and 400 °C against a rotating die steel ring. And wear experiments were performed under loads of 50, 100, and 150 N and a fixed sliding velocity of 30 m/s. Results show that at room temperature, both materials exhibited a marked increase in wear rate with load applied. Wear rates of the composites and high-speed steel under loads of 50, 100, and 150 N at room temperature achieved 1.61 × 10⁻⁶, 2.14 × 10⁻⁶, 3.56 × 10⁻⁶, and 3.11 × 10⁻⁶, 23.08 × 10⁻⁶, 57.39 × 10⁻⁶ g/m, respectively. At a testing temperature of 400 °C, the composites exhibited a marked increase in wear rates and high-speed steel exhibited mild wear (characterized by extremely low wear rates) over the range of loads considered in these experiments. Wear rates of both the composites and high-speed steel at 400 °C achieved 2.42 × 10⁻⁶, 5.19 × 10⁻⁶, 6.64 × 10⁻⁶, and 4.1 × 10⁻⁶, 8.92 × 10⁻⁶, 26.02 × 10⁻⁶ g/m, respectively, under different loads. Finally, the wear-mechanism was discussed in this article.