Read Head Research Articles

Development and Experimental Research of Different Mechanical Designs of an Optical Linear Encoder's Reading Head.

Optical linear encoders are widely used in manufacturing. They are accurate and have a relatively high resolution and good repeatability. However, there are a lot of side effects, which have an inevitable impact on the performance of an encoder. In general, the majority of these effects could be minimized by the appropriate design of an encoder’s reading head. This paper discusses the working principle of and commonly occurring errors in optical linear encoders. Three different mechanical designs are developed and implemented in the experimental reading head of the linear encoder in order to evaluate how mechanical construction influences the displacement measurement accuracy and total performance of the encoder.

Improved Recording Performance With Writer Design and Joint Learning-Based Neural Network for Heat-Assisted Interlaced Magnetic Recording

Heat-assisted interlaced magnetic recording (HIMR) further increases the areal density with the interlaced track layout architecture compared to conventional heat-assisted magnetic recording. However, besides the 2-D inter-symbol interference (ISI) and thermal jitters, the transition curvatures due to the circular thermal profile cause severe erasures after write and obvious nonlinear distortions of readback signals. This deteriorates the recording performance severely. Especially the degrees of transition curvatures for the low temperature written track (LT) and high temperature written track (HT) are distinct, which makes the correction of transition curvature with only the writer design impossible. Correspondingly, a comprehensive method consisting of writer design and multitrack detection algorithm with joint learning-based neural network (JLNN) is proposed to mitigate the effects of transition curvature and 2-D ISI for both LT and HT of HIMR. First, a designed writer with splitting main poles produces the spatially nonuniform write field along the crosstrack direction to correct the transition curvature of LT. Then the multitrack detection with JLNN and improved Bahl–Cocke–Jelinek–Raviv (BCJR) detector (JLNN-IB) algorithm is studied to further mitigate the effects of residual transition curvatures, thermal jitters, and 2-D ISI for both HT and LT. Specifically, the readback signals of read head array and decoded log-likelihood ratio (LLR) outputted by the low-density parity check (LDPC) decoder are fed into JLNN to obtain the equalized signal and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$a$ </tex-math></inline-formula> <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">priori</i> probability (AP) of three tracks. Then the equalized signal as well as AP of current track and corresponding soft bit estimations of adjacent tracks are embedded into the branch metrics of improved BCJR detector for data detection, and the LDPC decoder is cascaded for the error correction. The simulation indicates that at the recording density of 2.11 Tb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , the proposed comprehensive writer design and JLNN-IB algorithm provide 9.2 and 9.7 dB signal to noise ratio (SNR) gains compared to the conventional 2-D neural network equalizer and 2-D linear equalizer under the uniform write field and circular thermal profile, respectively.

A Study of Channel Time-Domain Response on Equalization for Reproducing a Double-Layer Magnetic Recording Medium

To increase the recording density of hard disk drives (HDD), 3-D magnetic recording using microwave-assisted magnetic recording (MAMR) with multiple recording layers is attracting much attention as a next-generation recording method. Developing a signal processing method for 3-D magnetic recording using the multiple conventional recording layers and an magnetoresistive (MR) head reading system is desired. In this article, we evaluate 2-D partial response maximum likelihood (PRML) channels by the bit error rate (BER) performance, where the transfer function of the PR channel is determined by the response of the in-phase or differential-phase bits between layers in a double-layer magnetic recording medium. The results show that a BER of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{-4}$ </tex-math></inline-formula> can be achieved by the PRML channel determined by the differential-phase response with the signal-to-noise ratio (SNR) greater than 26.0 dB for system noise.

Organic–Inorganic Hybrid Interfaces for Spin Injection into Carbon Nanotubes and Graphene

AbstractSpintronics is a quantum technology which aims at adding the spin quantum degree of freedom to conventional CMOS electronics. Since the discovery of the giant magneto‐resistance in 1988, considered as the birth of this field, spintronics continues flooding the market with plethora of devices used in everyday life applications such as hard drive read heads or magnetic random‐access memories, and so on. From a fundamental research perspective, the field is still blooming bringing post‐CMOS perspectives technologically closer to the reality with, for instance, prototypes of all‐spin‐logic circuits and neuromorphic chips. To sustain this intense research activity, a quest for new platform materials is also taking place not only to enhance existing performances but also to generate novel functionalities. In this vein, carbon nanostructures such as molecules, graphene, and carbon nanotubes are among the most sought‐after materials. In this review, spin transport experiments in carbon nanotubes and graphene are first detailed and then, the necessity to consider new hybrid interfaces are highlighted for a better control of the spin injection at the quantum device level.

Comparison of Morphological Organs of Some Quinoa (Chenopodium quinoa Willd.) Genotypes in terms of Nutritional Values

This research was carried out to compare the nutritional values of different morphological organs of 9 quinoa (Cherry Vanilla, French Vanilla, Read Head, Rainbow, Titicaca, China Population, Moqu-Arrochilla, Oro De Valle and Q-52) genotypes in Bingöl conditions. The research was established in the trial field of Bingöl University Genç Vocational School Application and Research area during the 2019 growing period. The study was carried out with randomized block design with four replications. The crude protein, crude ash, acid detergent fiber (ADF), neutral detergent fiber (NDF), digestible dry matter (DDM), dry matter intake (DMI) rates and relative feed value (RFV) of the stems, leaves and bunches of quinoa genotypes used in the research were investigated. According to the results of the research; crude protein ratios of the quinoa genotypes varied between 5.0-9.4% in the stem, 13.7-22.% in the leaf and 19.6-23.2% in the bunch, crude ash ratios between 7.8-14.3% in the stem, 23.9-29.4% in the leaf and 13.1-17.6% in the bunch, ADF ratios between 40.3-51.2% in the stem, 9.9-15.4% in the leaf and 11.9-16.8% in the bunch, NDF ratios between 49.1-68.2% in the stem, 22.5-35.6% in the leaf and 24.3-32.0% in the bunch, DDM rates between 49.0-57.5% in the stem, 76.9-81.2% in the leaf and 75.8-79.6% in the bunch, DMI ratios between 1.76-2.44% in the stem, 3.37-5.33% in the leaf and 3.75-4.93% in the cluster, RFV between 67-101 in the stem, 201-322 in the leaf and 224-298 in the cluster. According to the research result; the best values between the quinoa genotypes in terms of both quality and digestibility were obtained from China population. Therefore; it is recommended that the Chinese population can be raised in Bingöl and similar ecologies.

Exchange bias at the organic/ferromagnet interface may not be a spinterface effect

Exchange bias is a physical effect that is used in many spintronic devices like magnetic read heads, magnetic random access memories, and most kinds of magnetic sensors. For the next generation of fully organic devices, molecular exchange bias, if existing, could have a huge impact for developing mechanically soft and environment friendly devices. The observation of molecular exchange bias has been reported recently in hybrid systems where a metallic ferromagnet is exchanged biased by an organic film, and it is considered to be a spinterface effect. To understand this effect, we investigate if the molecular exchange bias exists in Co/metal tetra-phenyl porphyrin hybrid bilayer systems. The molecular exchange bias is never observed when the samples are properly encapsulated, and when the exchange bias is eventually observed, it is not a spinterface effect, but it results from air-driven partial oxidation of the cobalt film transforming part of the metallic cobalt into a cobalt oxide that is well known to induce exchange bias effects. Surprisingly, oxidation is very difficult to prevent even by using very thick metallic encapsulating layers. A similar effect is observed in the Co/metal-phthalocyanine bilayer system, showing that the molecular exchange bias is not a spinterface effect also in the hybrid system in which this effect was originally discovered.

A Novel Self-Correction Method for Linear Displacement Measurement Based on 2-D Synthesis Mechanism

With increased range, the accuracy of longer-range linear displacement measurement is difficult to guarantee. According to the analysis, it is inevitable that there will be a certain margin between the direction of the calibration grating and the direction of the reading head, which will impact the longer-range linear displacement measurement. In order to eliminate this measurement error, a self-correction method based on 2-D synthesis is herein proposed. First, we describe the principle of absolute linear displacement measurement based on image recognition. Then, the error model is established, which caused by the included angle between the calibration grating and the reading head. Third, a method is proposed for obtaining the vertical offset of the calibration grating by using the vertical image sensor. Finally, we reach an error self-correction method based on 2-D synthesis. In order to test the feasibility of the proposed method, a linear displacement measuring device with a range of 200 mm was developed. After experiment, the maximum absolute error was reduced from 4.34 to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.03~\mu \text{m}$ </tex-math></inline-formula> with the proposed error correction in the long range of 200 mm. The proposed algorithm does not depend on the assembly and installation position, and can realize self-correction of errors. So the method could lay the groundwork for improving larger range linear displacement measurement technology.

A Reflective-Type Heterodyne Grating Interferometer for Three-Degree-of-Freedom Subnanometer Measurement

A heterodyne grating interferometer (HTGI) able to simultaneously measure the three-axis translational displacements of ultra-precision motion stages with a sub-nanometer resolution is demonstrated. The HTGI is composed of two main parts, a reflective planar grating with a uniform micron-scale period in two orthogonal directions, and a reading head. Thanks to the reflective grating, the reading head design manages to make main optical paths common and located on the same side of this compact structure, potentially resulting in low Abbe errors and environmental variations. Relying on a laboratory-made dual-frequency laser source at 780 nm, two heterodyne interferometric measurement modules for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</i> -/ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Y</i> -direction motions and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z</i> -direction motion were realized based on first-order and zeroth-order diffraction, respectively. Experiments show that the proposed HTGI, in all three axes, can distinguish a 0.5 nm step or even better, perform an up to 2.5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> 10linearity in a range of 80 μm, and hold a 5 nm stability within 300 s. These performances confirm that the proposed HTGI can greatly benefit nanoscience and technology, where multi-axis ultra-precision positioning is required, such as wafer stage in next-generation lithography machine, and so forth.

The MocR/GabR Ectoine and Hydroxyectoine Catabolism Regulator EnuR: Inducer and DNA Binding.

The compatible solutes ectoine and 5-hydroxyectoine are widely synthesized by bacteria as osmostress protectants. These nitrogen-rich tetrahydropyrimidines can also be exploited as nutrients by microorganisms. Many ectoine/5-hydroxyectoine catabolic gene clusters are associated with a regulatory gene (enuR: ectoine nutrient utilization regulator) encoding a repressor protein belonging to the MocR/GabR sub-family of GntR-type transcription factors. Focusing on EnuR from the marine bacterium Ruegeria pomeroyi, we show that the dimerization of EnuR is mediated by its aminotransferase domain. This domain can fold independently from its amino-terminal DNA reading head and can incorporate pyridoxal-5′-phosphate (PLP) as cofactor. The covalent attachment of PLP to residue Lys302 of EnuR was proven by mass-spectrometry. PLP interacts with system-specific, ectoine and 5-hydroxyectoine-derived inducers: alpha-acetyldiaminobutyric acid (alpha-ADABA), and hydroxy-alpha-acetyldiaminobutyric acid (hydroxy-alpha-ADABA), respectively. These inducers are generated in cells actively growing with ectoines as sole carbon and nitrogen sources, by the EutD hydrolase and targeted metabolic analysis allowed their detection. EnuR binds these effector molecules with affinities in the low micro-molar range. Studies addressing the evolutionary conservation of EnuR, modelling of the EnuR structure, and docking experiments with the inducers provide an initial view into the cofactor and effector binding cavity. In this cavity, the two high-affinity inducers for EnuR, alpha-ADABA and hydroxy-alpha-ADABA, are positioned such that their respective primary nitrogen group can chemically interact with PLP. Purified EnuR bound with micro-molar affinity to a 48 base pair DNA fragment containing the sigma-70 type substrate-inducible promoter for the ectoine/5-hydroxyectoine importer and catabolic gene cluster. Consistent with the function of EnuR as a repressor, the core elements of the promoter overlap with two predicted EnuR operators. Our data lend themselves to a straightforward regulatory model for the initial encounter of EnuR-possessing ectoine/5-hydroxyectoine consumers with environmental ectoines and for the situation when the external supply of these compounds has been exhausted by catabolism.

Using Inertial Sensors to Determine Head Motion-A Review.

Human activity recognition and classification are some of the most interesting research fields, especially due to the rising popularity of wearable devices, such as mobile phones and smartwatches, which are present in our daily lives. Determining head motion and activities through wearable devices has applications in different domains, such as medicine, entertainment, health monitoring, and sports training. In addition, understanding head motion is important for modern-day topics, such as metaverse systems, virtual reality, and touchless systems. The wearability and usability of head motion systems are more technologically advanced than those which use information from a sensor connected to other parts of the human body. The current paper presents an overview of the technical literature from the last decade on state-of-the-art head motion monitoring systems based on inertial sensors. This study provides an overview of the existing solutions used to monitor head motion using inertial sensors. The focus of this study was on determining the acquisition methods, prototype structures, preprocessing steps, computational methods, and techniques used to validate these systems. From a preliminary inspection of the technical literature, we observed that this was the first work which looks specifically at head motion systems based on inertial sensors and their techniques. The research was conducted using four internet databases—IEEE Xplore, Elsevier, MDPI, and Springer. According to this survey, most of the studies focused on analyzing general human activity, and less on a specific activity. In addition, this paper provides a thorough overview of the last decade of approaches and machine learning algorithms used to monitor head motion using inertial sensors. For each method, concept, and final solution, this study provides a comprehensive number of references which help prove the advantages and disadvantages of the inertial sensors used to read head motion. The results of this study help to contextualize emerging inertial sensor technology in relation to broader goals to help people suffering from partial or total paralysis of the body.

Femtosecond laser-assisted switching in perpendicular magnetic tunnel junctions with double-interface free layer

Perpendicular magnetic tunnel junctions with double-interface free layer (p-DMTJs), which exhibit enhanced tunnel magnetoresistance (TMR) and thermal stability (Δ) at the nanoscale, have received considerable interest as building blocks for spintronic data storage devices. Heat-assisted magnetic recording (HAMR) techniques have been widely employed in mainstream magnetic storage to enable ultrahigh storage density. However, the data access is achieved by sensing the stray field of the selected magnetic element using a mechanical “read head”, resulting in an unfavorable speed limitation and design complexity. To address this issue, integrating laser-assisted switching with a high-performance magnetic tunnel junction has received interest in spintronic R&D; however, it has not yet been achieved. In this study, we experimentally explored femtosecond (fs) laser-assisted switching in a p-DMTJ device using a direct electrical TMR readout. We demonstrate two reconfigurable switching operations, i.e., binary “write” and unidirectional “reset”, by the interplay of the fs laser and synchronized magnetic field sequence. We further explored the joint effect, and a switching phase diagram was obtained. The effect of the stray field of p-DMTJ, as well as laser helicity, on switching is also discussed. Results show the feasibility of fs laser-assisted writing p-DMTJs, which can pave the way in high-density optospintronic storage applications.

Strategy to Decrease the Angle Measurement Error Introduced by the Use of Circular Grating in Dynamic Torque Calibration.

A circular grating angle encoder is a key component in the dynamic torque calibration system. To improve the accuracy of an angle measurement, in this paper, the source of the angle measurement error of the circular grating is analyzed; an eccentricity error model and an inclination error model are proposed, respectively; further, these two models are combined to establish a total error model. Through the simulation study with the models, the conditions, in which the eccentricity error or inclination error can be ignored, are discussed. The calibration and compensation methods of the angle measurement error are given, and a progressive error compensation function which integrates the first harmonic fitting and the second harmonic fitting is obtained. An experiment is performed to verify the proposed calibration and compensation methods. The peak-to-peak value of the compensated angle measurement error of the single reading head can be reduced by about 93.76%, which approximates to the error of the mean value of the double reading heads. The experimental results show that the error calibration and compensation method based on the proposed error model can effectively compensate the angle measurement error of the circular grating with a single reading head, and obtain a high-precision measurement angle.

Current Progress of Magnetoresistance Sensors

Magnetoresistance (MR) is the variation of a material’s resistivity under the presence of external magnetic fields. Reading heads in hard disk drives (HDDs) are the most common applications of MR sensors. Since the discovery of giant magnetoresistance (GMR) in the 1980s and the application of GMR reading heads in the 1990s, the MR sensors lead to the rapid developments of the HDDs’ storage capacity. Nowadays, MR sensors are employed in magnetic storage, position sensing, current sensing, non-destructive monitoring, and biomedical sensing systems. MR sensors are used to transfer the variation of the target magnetic fields to other signals such as resistance change. This review illustrates the progress of developing nanoconstructed MR materials/structures. Meanwhile, it offers an overview of current trends regarding the applications of MR sensors. In addition, the challenges in designing/developing MR sensors with enhanced performance and cost-efficiency are discussed in this review.

Large magnetoresistance in Heusler alloy-based current perpendicular to plane giant magnetoresistance sensors

Increasing the data storage in next-generation hard disk drives requires a reduction in the physical dimensions of read sensors. Tunneling magnetoresistance heads yield high magnetoresistance (MR) ratio but with a high resistance-area product (RA) that is suboptimal for devices. Giant magnetoresistance (GMR) head using different materials is an alternative way to improve reader performance with high MR ratio and low RA. In this paper, we theoretically study the effect of material properties and the layer thickness on RA and MR ratio in a trilayer system via an atomistic model combined with the spin transport model. The GMR stack can be constructed by the atomistic model and the RA and MR ratio can be directly calculated by considering the spin accumulation and spin current from the spin transport model. It is found that the spin valve using the Heusler alloy electrode with high spin polarization exhibits a high MR ratio and RA of 64 which is better than the spin valves using conventional ferromagnets such as Co, NiFe and CoFe. Moreover, we consider the thickness dependence of the change of RA (). Increasing the free layer thickness yields the increase in and MR ratio because of the enhancement of the bulk spin scattering. Additionally, the results show that the depends on the spin diffusion length of the nonmagnetic materials (). The increases from 3 up to 10 when increases from 35 to 1200 nm. This investigation shows the possibility for read head design of HDDs with areal density beyond 2 Tb in−2.

Two-channel six degrees of freedom grating-encoder for precision-positioning of sub-components in synthetic-aperture optics.

We investigate a novel two-channel grating encoder that can perform simultaneous measurements of six-degree-of-freedom (DOF) motions of two adjacent sub-components of synthetic-aperture optics such as pulse-compression gratings(PCGs) and telescope-primary mirrors. The grating encoder consists of a reading head and two separate gratings, which are attached to the back of the sub-components, respectively. The reading head is constructed such that there two identical optical probes can share the same optical components. The two probes are guided to hit each of the two gratings and can detect six-DOF motions simultaneously and independently. For each probe, the incident beam propagates through both a three-axes grating interferometry module and a three-axes diffraction integrated autocollimator-module, which detects translational and rotational movement, respectively. By combining the two modules it is possible to perform six-DOF measurement for a single point. The common-path configuration of the two probes enable identical responses to environmental variation, which ensures high accuracy.

Giant magnetoresistance effect due to the tunneling between quantum anomalous Hall edge states

A recent work predicted the tunneling effect between topological edge states where the tunneling probability is tuned by a transverse electric field [Xu et al., Phys. Rev. Lett. 123, 206801 (2019)]. Here we study this tunneling effect between quantum anomalous Hall edge states under a perpendicular magnetic field. It is shown that the tunneling probability depends exponentially on the magnetic field. We propose a magnetic transistor based on a quantum anomalous Hall ribbon to observe this effect experimentally. Numerical simulations show that the conductance of the device is very sensitive to the strength and direction of the magnetic field. The positive/negative magnetic field results in the on/off state of the transistor. A giant magnetoresistance is found, and the on/off ratio reaches up to greater than 1010 for a long ribbon. These findings should be useful for potential applications in magnetic read heads and magnetic field sensors.

Influence of installation error of grating interferometer on high-precision displacement measurement

We investigated a high-precision grating interferometer displacement measurement system that can be applied to high-end immersion lithography machines and explained its composition and measurement algorithm. By analyzing the optical path variation caused by the installation error of the grating interferometer, we calculated the influence of the installation error on the displacement measurement. A displacement measurement model of a grating interferometer using three read heads was established, and the influence of the model coefficients on the displacement measurement model was analyzed. The simulation results show that, under the condition that the error of the measurement model in the X direction and the Y direction is <0.1 nm, the translation error of the read head should be within ±100 μm, and the relative rotation deviation between the two read heads or two gratings placed along the diagonal should be within ±50 μrad. The methods and results of studying the influence of grating interferometer installation error on the displacement measurement provide a theoretical basis for the application of a grating interferometer displacement measurement system in immersive high-end lithography scanners.

Research on High Precision Angle Measurement and Compensation Technology Based on Circular Grating

In this paper, the angle measurement method of high-precision circular grating is studied. The principle analysis of circular grating angle measurement, the principle analysis of multi reading head, and the design of rotary servo control system are carried out. After analyzing the error model of circular grating angle measurement, the research based on harmonic compensation model is carried out respectively. Aiming at the problem of zero crossing oscillation of compensation algorithm, the piecewise compensation strategy is designed, which fully demonstrates the application value of circular grating angle measurement method in high-precision angle measurement system.

Synthesis and study of the structural and dielectric properties of La0.67Ca0.2Ba0.13Fe1−xMnxO3 ferrites (x = 0, 0.03 and 0.06)

The La0.67Ca0.2Ba0.13Fe1−xMnxO3 perovskite compounds with different manganese concentrations (x = 0.0, 0.03, 0.06) were synthesized by the autocombustion method and annealed at 700 °C. The X-ray diffraction (XRD) data indicated that all obtained compounds crystallize in the cubic structure with the Pm $$\overline{3}$$ m space group. The increase in the substitution rate has been found to lead to the decrease in the crystallite size value characterized by X-ray diffraction. The dielectric properties of these samples, using a complex impedance spectroscopy technique, were also performed as a function of frequency and temperature. A suitable equivalent electrical circuit was used to assess the contributions of electrode, grains, and grain boundaries in the complex impedance results. Activation energies were determined from different methods. Nyquist plots were consistent with three circuits in series, each one with a capacitance in parallel with a resistance. The conduction mechanism follows the NSPT model for the three samples at T < 280 K, in which the rise in substitution rate increases the binding energy of carriers. Above 280 K, the appropriate model is the Correlated Barrier Hopping (CBH) for x = 0, while the overlapping large polaron tunneling (OLPT) process has been confirmed for both samples x = 0.03 and x = 0.06. Our compounds have high electrical properties, and good thermal and chemical stability. They are susceptible to many technological applications, such as gas sensors, capacitors, filters, resonators, new read heads, and solid oxide fuel cells.

Rotated read head design for high-density heat-assisted shingled magnetic recording

In heat-assisted shingled magnetic recording, recorded tracks are erased on one side. The transitions are no longer symmetric relative to the track center, especially when the transitions are highly curved as a result of the temperature profile generated by the near-field transducer. To optimally utilize these asymmetrically curved transitions, the read head is rotated to match the curvature. For a single rotated head, a more than 10% improvement in user density is achieved compared to that of a single non-rotated head. We found that the optimal rotation angle generally follows the transition shape. With an array of two rotated heads, a track pitch of 15 nm, and a minimum bit length of 6.0 nm, the user areal density reaches 6.2 Tb/in2, more than 30% above previous projections for recording on granular media.