Narrow Track Width Research Articles

Lateral Stability Performance of Articulated Narrow-Track Tractors

A tractor losing lateral stability starts to rollover. It is a matter of fact that tractor lateral rollover accidents are one of the most frequent causes of death and injuries for farmers. Consequently, tractors are fitted with a specific protective structure to minimize the consequences for the driver during the rollover (ROPS). The narrow-track tractor, designed to operate in vineyards and orchards, is a tractor category with a very narrow track width and the risk of rollover is higher. The aim of the study was to evaluate the compact narrow-track tractor types commercially available, designed to mount a cantilever engine in the forward position with effects on the Center of Gravity (CoG) because more than 50% of the tractor weight is loaded on the front axle, and, specifically, the articulated narrow-track tractors where the stability is affected by the pivot point connecting the two tractor bodies. As a consequence of the typical tractor design of articulated tractors, during the steering action the line passing through the front and rear tire contact points on the ground changes, influencing the tractor’s stability. The approach of the research was based on reproducing the lateral stability tractor condition by developing a kinematic model, with the goal to virtually simulate the tractor behavior and to calculate the lateral stability angle for articulated tractors. The innovative contribution of this paper was the tractor articulation joint modeling, assuming a virtual pivot point to reproduce two relatives’ rotations between the front and rear bodies of the tractor: vertical (yaw angle) and longitudinal (roll angle) rotations. The lowest value of the stability angle was 39.3°, measured at −35° yaw angle. The model at the tractor design stage will allow adjusting of the tractor parameters to improve the lateral stability performance.

A Novel ITI Suppression Technique for Coded Dual-Track Dual-Head Bit-Patterned Magnetic Recording Systems

Generally, an intertrack interference (ITI) is a critical problem in bit-patterned magnetic recording (BPMR) systems that can attain an areal density (AD) up to 4 Tb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Unavoidably, at high ADs, a very narrow track width must be employed, leading to severe ITI and unacceptable system performance. To tackle the ITI; therefore, this article introduces a novel ITI suppression technique for coded dual-track dual-head (DTDH) BPMR systems. At the first turbo iteration, the weighted readback signal of the adjacent track served as an estimated ITI signal is utilized for subtracting from the target readback signal to subside the ITI effect, before passing the refined readback signal to a turbo equalizer. Nonetheless, for the second turbo iteration onwards, the estimated ITI signal generated by the soft information obtained from a decoder at each turbo iteration will be then employed to subtract from the target readback signal during the turbo decoding process. Computer simulation results demonstrate that the proposed system can provide better performance than the DTDH system using a hard ITI suppression technique as well as the conventional system using one read head to decode one data track for all ADs, because the proposed technique can estimate the ITI signal well. Furthermore, when considering the recording system under the effects of media noise and track mis-registration, we also found that the proposed system is more robust than other systems.

Dynamic Stability and Control of Tripped and Untripped Vehicle Rollover

Vehicle rollover accidents have been a serious safety problem for the last three decades. Although rollovers are a small percentage of all traffic accidents, they do account for a large proportion of severe and fatal injuries. Specifically, some large passenger vehicles, such as large vans, pickup trucks, and sport utility vehicles, are more prone to rollover accidents with a high center of gravity (CG) and narrow track width. Vehicle rollover accidents may be grouped into two categories: tripped and untripped rollovers. A tripped rollover commonly occurs when a vehicle skids and digs its tires into soft soil or hits a tripping mechanism such as a curb with a sufficiently large lateral velocity. On the other hand, the untripped rollover is induced by extreme maneuvers during critical driving situations, such as excessive speed during cornering, obstacle avoidance, and severe lane change maneuver. In these situations, the forces at the tire-road contact point are large enough to cause the vehicle to roll over. Furthermore, vehicle rollover may occur due to external disturbances such as side-wind and steering excitation. Therefore, it is necessary to investigate the dynamic stability and control of tripped and untripped vehicle rollover so as to avoid vehicle rollover accidents. In this book, different dynamic models are used to describe the vehicle rollover under both untripped and special tripped situations. From the vehicle dynamics theory, rollover indices are deduced, and the dynamic stabilities of vehicle rollover are analyzed. In addition, some active control strategies are discussed to improve the anti-rollover performance of the vehicle.

High Track Pitch Density for HAMR Recording: 1M TPI

Differences between heat-assisted magnetic recording (HAMR) and conventional perpendicular magnetic recording at narrow track widths are compared. We can see that HAMR appears to have similar adjacent track interference, but increased readback signal from the adjacent tracks (side reading). This background interference signal appears to be a consequence of the media architecture, and can be decreased if the media soft underlayer spacing to the hard layer, and transducer is reduced. The impact is also reduced for very high linear densities, due to a smaller fraction of unbiased flux from the neighbor tracks reaching the test track. The use of two reader multiple sensor magnetic recording at high track density appears to address some of this issue, and we can demonstrate viable track writing for HAMR beyond 1M tracks per inch using this readback technique.

An Engineering Review of the Farm Tractor's Evolution to a Dominant Design

This paper explains the origin and merits of the dominant farm tractor design, which has endured since the 1940s. Understanding the origins and rationale for this dominant design enables engineers to appreciate its merits, and understand its drawbacks, which could be addressed in future designs. Additionally, the methods used in this paper to study tractor evolution are applicable to the study of other products with a longstanding dominant design. Two themes are covered in this paper: first, the historical context that directed the farm tractor's design evolution is presented; and second, a terramechanics-based tractor model is used to analyze why the dominant design is conducive to good performance. The prominent characteristics of the dominant tractor design are its weight distribution, wheel layout, tool location, and construction. Its weight distribution maximizes drawbar pull by placing 70 to 80% of the total vehicle weight on the rear wheels. Shifting the weight forward reduces pulling force while shifting it backward produces a negligible increase in pulling capacity while dangerously increasing the risk of upending the tractor. The tractor has four wheels arranged in a rectangular pattern—the rear wheels are driven while the front ones are usually idle. Rear wheels are of large diameter to increase ground clearance and tractive efficiency. Front wheels are of small diameter to allow for a large steering angle despite a narrow track width. A narrow track width reduces the space required for making a U-turn at field ends and improves access to farm spaces. Inline front and rear wheels are desirable for ease of driving between rows and to best harness soil compaction. Attaching implements behind the rear axle leverages tillage forces to increase maximum drawbar pull and enables using large tools. The tractor's crankcase and transmission housing are structural components—this reduces mass and manufacturing complexity.

Effective Field Analysis of Segmented Media for Microwave-Assisted Magnetic Recording

In current perpendicular magnetic recording, a high-recording signal-to-noise ratio (SNR) always accompanies wide track width, limiting the area density capability. To overcome this difficulty, we propose a novel media design with notched anisotropy distribution along the film depth for microwave-assisted magnetic recording (MAMR). The micromagnetic modeling presented in this letter shows that MAMR with the notched medium significantly improves recording SNR while maintaining narrow track width. The effective field analysis clearly demonstrates the advantage of combining MAMR with the notched medium. With the notched medium design, the viability of MAMR for substantial area density capability gain is further enhanced.

Transient evolution of the target erosion profile during magnetron sputtering: Dependence on gas pressure and magnetic configuration

The growth of the target erosion profile (racetrack) in DC magnetron sputtering has been experimentally studied at a modest target power. Unbalanced magnetron sputtering (UBMS) and balanced magnetron sputtering (BMS) of a copper target were conducted at Ar gas pressures between 0.38–2.0Pa at a constant DC discharge power of 100W. At time intervals of several hours throughout the target life, the target was removed from the chamber, and its erosion profile was measured with a height gauge. The racetrack width was found to have an interesting pressure dependence. Higher argon gas pressure resulted in a wider initial track width in both the UBMS and BMS configurations. As the sputter erosion of the target proceeded, the track width became narrower at higher gas pressures (≥1.0Pa). At lower gas pressures, the track width was mostly unchanged and even showed a slight increase in the case of 0.38Pa in UBMS. As a result, the order of the final width was reversed: the higher gas pressure resulted in a narrower track width. The origin of this behavior was ascribed to the difference in the plasma sheath thickness and the free path of secondary electrons.

Advanced Dual-Free-Layer CPP GMR Sensors for High-Density Magnetic Recording

All-metal current-perpendicular-to-plane (CPP) giant magnetoresistance (GMR) read sensors with a shield-to-shield spacing (S2S) of 16–21 nm and a narrow track width of down to 25 nm were fabricated using ferromagnetic CoFeMnSi Heusler-alloy-based spin valves. Room temperature GMR ratios from these read sensors are obtained of up to 6% and 14–24% ( $\Delta \textrm {RA}= 7.1$ –12.0 $\text{m}\Omega \mu \text{m}^{2}$ ) at $\mathrm {S2S} = 16$ and 21 nm, respectively. Studies and results of electron transport and CPP GMR support the sustainability and scalability of the CPP GMR process for Tb/in2 the areal density of magnetic recording. A universal parameter defined as magnetic resistivity for a sensor device, $\Delta \textrm {RA}/\mathrm {S2S}$ in ohm micrometers, is proposed to gauge the practically and rationally applicable CPP GMR for the read sensor process. The investigation of the CPP GMR operation range and micromagnetic simulation demonstrates the feasibility of the CPP GMR read sensors at $\mathrm {S2S} = 21$ nm for sustaining 1.0 Tb/in2 and of those at $\mathrm {S2S}= 16$ nm for marginally supporting 2.0 Tb/in2 the areal density of magnetic recording, The future path to and potential of the technology for ever increasing areal density beyond 2.0 Tb/in2 are addressed with emphasis on the importance of further enhancing the CPP GMR for process margin improvement.

Defining the Biological Effectiveness of Components of High-LET Track Structure.

During space travel, astronauts are exposed to a wide array of high-linear energy transfer (LET) particles, with differing energies and resulting biological effects. Risk assessment of these exposures carries a large uncertainty predominantly due to the unique track structure of the particle's energy deposition. The complex damage elicited by high charge and energy (HZE) particles results from both lesions along the track core and from energetic electrons, δ rays, generated as a consequence of particle traversal. To better define how cells respond to this complex radiation exposure, a normal hTERT immortalized skin fibroblast cell line was exposed to a defined panel of particles carefully chosen to tease out track structure effects. Phosphorylation kinetics for several key double-strand break (DSB) response proteins (γ-H2AX, pATF2 and pSMC1) were defined after exposure to ten different high-LET radiation qualities and one low-LET radiation (X ray), at two doses (0.5-2 Gy) and time points (2 and 24 h). The results reveal that the lower energy particles (Fe 300, Si 93 and Ti 300 MeV/u), with a narrower track width and higher number and intensity of δ rays, cause the highest degree of persistent damage response. The persistent γ-H2AX signal at lower energies suggests that damage from these exposures are more difficult to resolve, likely due to the greater complexity of the associated DNA lesions. However, different kinetics were observed for the solely ATM-mediated phosphorylations (pATF2 and pSMC1), revealing a shallow induction at early times and a higher level of residual phosphorylation compared to γ-H2AX. The differing phospho-protein profiles exhibited, compared to γ-H2AX, suggests additional functions for these proteins within the cell. The strong correspondence between the predicted curves for energy deposition per nucleosome for each ion/energy combination and the persistent levels of γ-H2AX indicates that the nature of energy distribution defines residual levels of γ-H2AX, an indicator of unrepaired DSBs. Our results suggest that decreasing the energy of a particle results in more complex damage that may increase genomic instability and increase the risk of carcinogenesis.

Effect of stripe height on the critical current density of spin-torque noise in a tunneling magnetoresistive read head with a low resistance area product below 1.0 Ω μm2

To understand the spin-torque effect on the noise in tunneling magnetoresistive (TMR) read heads, the GHz range noise spectra of TMR read heads with a narrow track width (w = 36 nm), and various stripe heights (h) are investigated as a function of the external magnetic field (Hex) and dc bias current density (j). The strong noise peak intensity depends on both Hex and j, indicating that the spin-torque affects the thermal mag-noise under a positive (negative) j for a positive (negative) Hex, regardless of h in the TMR heads. Due to the increased shape anisotropy, the critical current density (jc), where the non-thermal fluctuation noise originates from the spin-torque, increases markedly as the head dimension is reduced, and the maximum value of jc is approximately +1.5 × 1012 A/m2 for a head with w = 36 nm and h = 15 nm. These results demonstrate that the non-thermal fluctuation noise originating from the spin-torque in the TMR head can be suppressed in the current density range below 1012 A/m2, as the head dimension is reduced and the shape anisotropy is increased.

Half-metal CPP GMR sensor for magnetic recording

Current-perpendicular-to-plane (CPP) giant magnetoresistance in magnetic CoFeMnSi Heusler alloy based spin valves and its potential application for high areal density recording are investigated, given that film stack design and crystalline structure matching during film growth are considered. Modeling of electron transport in spin valves predicts the CPP GMR of up to 130% and 25% in pseudo and antiferromagnet pinned spin valves at large bulk diffusive scattering asymmetry in Heusler alloy layers. Experimentally, the testing structures of pseudo spin valves, which have the L21 ordered Huesler alloy layers grown on single crystal MgO substrates, were built and demonstrate the CPP GMR of 55% or larger with ΔRA≥27.5mΩμm2. CPP GMR reader sensors were fabricated based on antiferromagnet pinned spin valves using the same Huesler alloy materials albeit on AlTiC wafers, with narrow track widths of down to 35nm. The CPP GMR obtained is up to 13% (18%, ΔRA=9.0mΩμm2 after correction of current distribution in device). Reader test results show that the low frequency track averaged output amplitude is 3.14mV with the electrical SNR=28dB. These read heads have the transition width of readback waveform T50 of ~22nm and the magnetic read track width of 35.6nm. The obtained on-track bit error rate is close to 10−3 decade at a linear density of 1800KFCI, potentially realizing a magnetic recording with an areal density of up to 800Gb/in2.

Microwave Assisted Magnetic Recording Utilizing Perpendicular Spin Torque Oscillator With Switchable Perpendicular Electrodes

In this paper, we present a systematic micromagnetic modeling study on microwave assisted magnetic recording (MAMR) utilizing a perpendicular spin torque oscillator (PSTO) to generate localized circular ac field. The PSTO at narrow track width naturally produces a circular field rotating at desired high frequency within the plane of the media, resulting in a substantially enhanced effective write field gradient. With the STT oscillator generated ac field waveform, recording simulations show that area recording density exceeding 3 Tbits/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> can be readily achieved with a medium signal-to-noise ratio above 13 dB (1T-SNR) and thermal stability at K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> V = 60 k <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">300°K</sub> .

Bus Structure Behaviour under Driving Manoeuvring and Evaluation of the Effect of an Active Roll System

One of the main causes of traffic accidents in which heavy vehicles are involved is lateral stability loss. It is well known that heavy vehicles have relatively high centres of gravity and narrow track widths and can lose roll stability at moderate levels of lateral acceleration. The influence of several parameters (i.e. height of the centre of gravity, weight distribution between axles, chassis torsional stiffness, etc.) on bus roll stability during a lane change manoeuvre, as well as the bus structure stress level has been analyzed by means of a six degrees of freedom beam finite element model. In addition, due to the use of active systems to prevent excessive roll motions in heavy vehicles, the effect of an active system based on anti-roll bars in a bus structure under a lane change manoeuvre is carried out by means of a bus dynamic finite element model. Results show that the fuzzy logic controller implemented in the anti-roll bar system significantly reduces both the vertical displacements at the corners of the bus structure and the stress level.

Recording over 15 ktpi using multichannel heads in a tape system

In magnetic recording systems, it has been reported that sufficient signal-to-noise ratio (SNR) was obtained with a narrow track width, using a spin-valve head and metal-evaporated tape. In order to apply this to a helical-scan tape system, techniques for writing narrow tracks and reading them exactly were required. However, the degree of mechanical accuracy demanded was too high to realize. With this in mind, we have developed multichannel heads which can write and read certain tracks with a single scan, as well as a nontracking technique removing the need for such precise mechanical accuracy. A prototype tape drive employing these techniques was developed, and a track density exceeding 15 ktpi was achieved.

Side-Shielded Tunneling Magnetoresistive Read Head for High-Density Recording

To reduce the side-reading effect and obtain a narrower effective read track width, the side-shield effect was studied by computer simulations and experiments. Computer simulations show that the side shield, which consists of a soft magnet, can reduce the effective read track width. To examine the effect, a side-shielded tunneling magnetoresistive head was fabricated. In the head, to place a soft magnet by the sensor side, a closed-flux structure was applied for longitudinal bias instead of a conventional abutted junction. Microtrack profile measurements agreed with simulated results, and the side-shield effect was clearly demonstrated.

Patterning damage in narrow trackwidth spin-valve sensors

Using a combination of electron-beam lithography and Ar ion milling, we have fabricated spin-valve sensors with widths ranging from 30 to 250 nm. Although the resistance of the sensors scales as expected with width, the giant magnetoresistance (GMR) ratio decreases with decreasing width, consistent with the presence of a region with negligible GMR at the edges of the sensors. Sensors patterned using a focused ion beam showed a similar but much greater effect. We attribute this behavior to edge damage associated with the patterning process.

Micromagnetic study of side-writing phenomena using thin-film heads and Co–CoO metal-evaporated tape

The recording process and the relationship between the side-written band and the pole shape of thin-film recording heads, which have an upper pole with a narrow track width and a trimmed lower pole, using Co–CoO, obliquely evaporated magnetic tape, have been investigated. In nonazimuth recording, the lower pole of the thin-film head on the trailing side is better than that on the leading side for generating a sharp-edged, side-writing band. In azimuth recording, the relationship between side-writing phenomena and the pole shape of a thin-film head is complicated, because the position recorded by the leading gap-field shifts across the track width from that recorded by the trailing gap-field due to the azimuth angle. The thin-film recording head with trapezoidal upper and lower poles to minimize the effect of the side-fringing field can generate a sharp-edged, side-writing band, particularly in azimuth recording, but it is critical that the lower pole be on the trailing side. The thin-film recording head, which has a trapezoidal upper pole on the leading side and a trapezoidal lower pole on the trailing side, is most effective in generating a sharp-edged, side-writing band.

Understanding single-turn write head design at narrow track widths

This paper provides a systematic micromagnetic analysis on the magnetization processes-in various miniaturized single-turn head designs. The calculation results show that a thick yoke yields the formation of a magnetization vortex through the yoke thickness, resulting in efficient flux conduction at small yoke dimensions. A vortex structure is also important for the pole tips to maintain zero remanence after writing. Following this understanding, a hollow yoke structure has been studied to promote the efficient flux conduction in the yoke and flux closure mode in the pole tips at the remanent state. The simulation results are elucidating for efficient single-turn head designs at small yoke dimensions.

Spin-valve head with specularly reflective oxide layers for over 100 Gb/in/sup 2/

We have developed spin valves with thin oxide reflective layers, which exhibit a greatly improved magnetoresistance (MR) performance while keeping other good properties, such as an exchange bias field of over 1000 Oe and a coercivity and an interlayer coupling field of less than 10 Oe. The giant magnetoresistance (GMR) values reached over 12% for the spin valve with a single specular layer and over 15% for the spin valve with double specular layers. The oxide reflective layers helped improve MR performance due to enhanced specularity at the oxide interfaces. Evidence of enhanced specularity was provided by the observed reduced sheet resistance and oscillatory interlayer exchange coupling between the free layer and the spacer in the spin valve. The observation of the oscillation was possible due to amplified Ruderman-Kittel-Kasuya-Yoshida (RKKY) coupling, as seen in a multilayered superlattice composed of ferromagnetic layers with nonmagnetic spacers. We successfully fabricated read heads by incorporating such spin valves. In particular, very narrow read track width was achieved in the head with double reflective layers. The read track width was estimated to be less than 0.14 /spl mu/m. The head was tested on a low noise CoCrPt-based alloy disk with a coercivity of 3170 Oe and an areal moment of 0.36 memu/cm/sup 2/. The head showed a normalized output of 8.6 mV//spl mu/m with an asymmetry of 0.5% at 2 mA sense current, a /spl sim/40% increase over that of the head with a single reflective layer that was used in the demonstration of 56.1 Gb/in/sup 2/. We have therefore demonstrated that our head with the specular layers can be used for an areal density of over 100 Gb/in/sup 2/ in magnetic recording with the help of advanced media and integration techniques.

3223 空気静圧軸受けを用いた高精度リニア・トラッキング

The areal density of hard disk drives (HDD) is expected to reach 1 Tbits/in^2 with very narrow track width heads below 50nm in the near future. Assuming that the allowable tracking error is 10% of the track width, the tracking accuracy should be less than 5nm. Moreover, when we will investigate track profiles and off-track characteristics using a read-write performance tester, the tracking actuator should have capability of positioning at sub-nanometer resolution. Therefore, an actuator consisting of a linear air bearing and a linear VCM(Voice Coil Motor) was designed for precise tracking. The stiffness of the air bearing was strong enough so that the moving coil of a VCM fixed to the air bearing slider arm could form a cantilever system. The linear actuator showed a much higher resonance frequency than a conventional rotary actuator. Due to the high resonance frequency the servo bandwidth became significantly wider. The linear actuator could be stepped at 1nm resolution without overshoots and undershoots and the rise time was less than 0.15msec.