The dependence of recording characteristics of thin metal tapes on their magnetic properties and on the replay head

A theory is derived to explain the recording properties of thin metal tapes in terms of their magnetic properties and in terms of the losses within the replay head. The tape losses are considered as being due to self-demagnetization and head losses resulting from gap and separation effects. The reproduction of isolated pulses is first considered and then modified to the condition of pulse crowding. A comparison of theory with experiment shows that the theory is sufficient in its prediction of head losses but has some limitations in its prediction of tape losses at high packing densities.     

A magnetoresistive readout transducer

A new type of reproduce transducer for reading magnetically recorded tapes is described. The device structure, which utilizes the magnetoresistive effect in a thin magnetic film deposited onto a nonmagnetic substrate, provides wavelength response characteristics comparable to existing technology. Indigenous noise effects are subordinate to tape noise. No intrinsic frequency limitations are experienced for recording bandwidths in existence today. Since the device detects the tape's fringing fields directly, the output is not a function of tape velocity. The device construction lends itself nicely to multichannel head assemblies. The transducer may also be used to detect digitally recorded information.     

Wear mechanism of particulate magnetic tapes in helical scan videotape recorders

The wear process of particulate magnetic tapes by rotary heads in video tape recorders was investigated. It was found that the plastic flow of the polymer binder in the top layer on the surface asperities (low swellings) of a magnetic layer of a tape caused by head rubbing forms the smoothed surface. The increase in the real contact area on these surfaces asperities by smoothing creates a frictional force increase up to the shear strength of the asperities. When the frictional force exceeds that strength, the asperities are fractured by the shear stress. The wear debris from many fractured asperities gathers into large lumps and retransfers onto the tape surface. The increased frictional force between a rotating head and retransferred lumps of wear debris with an increasing number of head traces causes a larger shear fracture inside a magnetic layer under the retransferred lumps. Wear debris from the scars made by large shear fracture, combined with retransferred lumps, scratches the tape surface as a prow     

MRI-based finite element modeling of head trauma: spherically focusing shear waves

A powerful tool for investigating the physical process producing head trauma is finite element (FE) modeling. In this paper, we present a 3D FE model of the human head that accounts for important geometric characteristics of the various components within the human head through an efficient magnetic resonance imaging voxel-based mesh generation method. To validate the FE model, a previous cadaver experiment of frontal impact is simulated, and this is where heretofore unknown wave patterns are discovered. The model is run under either of two extreme assumptions concerning the head-neck junction—free or fixed—and the experimental measurements are well bounded by the computed pressures from the two boundary conditions. In both cases the impact gives rise to not only a fast pressure wave but also a slow and spherically convergent shear stress wave which is potentially more damaging to the brain tissue.     

Piezotronic Tuning of Potential Barriers in ZnO Bicrystals

Coupling of magnetic, ferroelectric, or piezoelectric properties with charge transport at oxide interfaces provides the option to revolutionize classical electronics. Here, the modulation of electrostatic potential barriers at tailored ZnO bicrystal interfaces by stress‐induced piezoelectric polarization is reported. Specimen design by epitaxial solid‐state transformation allows for both optimal polarization vector alignment and tailoring of defect states at a semiconductor–semiconductor interface. Both quantities are probed by transmission electron microscopy. Consequently, uniaxial compressive stress affords a complete reduction of the potential barrier height at interfaces with head‐to‐head orientation of the piezoelectric polarization vectors and an increase in potential barrier height at interfaces with tail‐to‐tail orientation. The magnitude of this coupling between mechanical input and electrical transport opens pathways to the design of multifunctional electronic devices like strain triggered transistors, diodes, and stress sensors with feasible applications for human–computer interfacing.     

Method of determining the magnetic field of a recording head by using tapes of various coating thicknesses

In magnetic recording, the field configuration of the writing head is of major importance, but it is difficult to measure its actual strength. This paper describes a method of determining both the field geometry of a head and the field strength by using tapes of various coating thicknesses. By differentiating the magnetic flux with respect to the thickness, remanence curves are obtained. These curves may be compared to the remanence which was measured statically. This way, the oersteds of the head field can be determined in a much closer vicinity to the head gap than by previously described methods.     

A predictive analysis for optimum contour-after-wear for magnetic heads

Reliable reproduction of recorded signals is dependent upon a good head-tape interface, and particularly, upon adequate contact pressure at the gap. In the case of grooved magnetic heads the pressure profiles are complex 3-dimensional surfaces. The head contours, as machined, may cause pressure profiles which are unfavorable to good signal reproduction. A mathematical analysis is outlined, which forecasts the progressively changing head contours and pressure profiles in terms of the average depth of head wear due to passage of tape (magnetic or lapping tape). The analysis indicates the amount of wear needed to substantially improve the pressure profile. Good correlation is shown between the theoretical predictions and actual test values.     

Failure Analysis of a Cracked Gasoline Engine Cylinder Head

This article presents a failure analysis on a gasoline engine cylinder head made of aluminum alloy, which has been used in passenger cars. During an endurance test, a crack initiated from the interior wall of a hole in the center of the cylinder head and then propagated through the thickness of the cylinder head. The metallurgical examinations are conducted in the crack origin zone. The results show that there are many casting pores due to poor quality of casting in the failed cylinder head which has certainly played a crucial role in initiating the crack. Finite element analysis of the cylinder head is performed to identify the stress components. Modeling of a bolt for the hole shows that the plastic stresses are occurred. Moreover, the lower strength of the material due to high assembly stress caused the failure in the cylinder head.     

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.     

Magnetic domains in thin-film recording heads as observed in the SEM by a lock-in technique

In a thin-film magnetic recording head, a magnetic circuit made from two Permalloy thin films, one above the other, is magnetized by a spixally plated thin-film copper coil which is located (together with insulating layers) between those two films. The magnetic domains in a thin Permalloy film can be studied by type-2 magnetic constrast using backscattered electrons (BSE) in the scanning electron microscope (SEM) provided that the film has a smooth surface and is deposited on a flat substrate. In practice, the upper Permalloy film follows the contours of the underlying layers. This gives a topographic signal which is large enough to mask the type-2 magnetic contrast signal in its simple form. The domain walls can, however, be seen if the magnetic recording head is excited with a sinusoidal current and if the video waveform is processed with a lock-in amplifier referenced either to the fundamental or to the second harmonic of the excitation frequency. This lock-in image processing technique has now been applied to obtain images of the magnetic domains both from the upper Permalloy film of an incompletely fabricated head and also from the exposed cross sections of the Permalloy films in an operational thin-film head.     

Thin-film inductive heads for perpendicular recording

A modified thin-film magnetic head for perpendicular recording in rigid disk drives with improved read/write characteristics, especially at high areal bit densities, is presented. The head on which the modified design is based is described. It combines the advantages of single-pole heads and thin-film heads, writing with the sharp field edge of the leading pole and reading like a thin-film head. To increase the writing efficiency and improve the yield, the sequence of magnetic layers in the head is changed; the second layer of the four-layer head is embedded in the substrate, where it can be placed much closer to the pole tip of the first layer. The improved write capability depends mainly on the position of the embedded layer. In addition, there results an improved magnetic flux guidance from the embedded layer into the pole tip layer, providing the potential for a significant improvement in fabrication yield. The embedded-layer approach also allows a further increase in areal density. The results of read/write tests and the write-wide and read-narrow characteristics are presented     

The effect of magnetic interaction between medium and head on perpendicular magnetic recording characteristics

The high density recording characteristics of perpendicular magnetic recording using a single-pole head are affected by the magnetic interaction between the medium and the head. By decreasing the relative thickness of the Co-Cr layer in the double-layer medium to that of the main-pole of the head, and increasing the saturation magnetization of the Co-Cr layer, the high density recording characteristics are enhanced. When requisite conditions are realized, the reproduced voltage vs. bit density characteristics are improved considerably for a thinner main-pole of the single-pole head.     

Towards a model-based integration of co-registered electroencephalography/functional magnetic resonance imaging data with realistic neural population meshes

Brain activity can be measured with several non-invasive neuroimaging modalities, but each modality has inherent limitations with respect to resolution, contrast and interpretability. It is hoped that multimodal integration will address these limitations by using the complementary features of already available data. However, purely statistical integration can prove problematic owing to the disparate signal sources. As an alternative, we propose here an advanced neural population model implemented on an anatomically sound cortical mesh with freely adjustable connectivity, which features proper signal expression through a realistic head model for the electroencephalogram (EEG), as well as a haemodynamic model for functional magnetic resonance imaging based on blood oxygen level dependent contrast (fMRI BOLD). It hence allows simultaneous and realistic predictions of EEG and fMRI BOLD from the same underlying model of neural activity. As proof of principle, we investigate here the influence on simulated brain activity of strengthening visual connectivity. In the future we plan to fit multimodal data with this neural population model. This promises novel, model-based insights into the brain's activity in sleep, rest and task conditions.     

Recording with magnetic bubbles

We propose to use the stray field of a magnetic domain (e.g, a bubble) for magnetic recording. It is shown that these stray fields are large enough to write information into a conventional disc or tape. An experiment in which an audio signal is recorded on a conventional tape with the aid of a stripe domain is described. We consider the feasibility of an integrated recording head for "one head per track recording" by using a multitude of bubbles in one crystal plate as well as the possibility of realizing a scanning head for video recording. Our preliminary experiments demonstrate the feasibility of recording based on this new principle.     

Domain structures due to induced anisotropy and stresses in filmheads

The local anisotropy near the backgap closure of inductive-film heads is generally the result of two superimposed anisotropies. One is the anisotropy induced during deposition of the magnetic yoke in the presence of a magnetic field, and the other is a stress anisotropy whose magnitude and direction depend on the sign and magnitude of the stress-magnetostriction product. The authors present a simple model for these combined anisotropies and the associated domain wall patterns, assuming that the stress-magnetostriction product falls off as r^-2, where r is the distance from the center of the backgap closure, which in this case is assumed to be circular. One of the features of the predicted domain wall patterns is a three-wall intersection occurring where the two anisotropies cancel, i.e. where the yoke material is isotropic. Examples of domain walls in the vicinity of a backgap closure of an experimental film head are shown and discussed     

Magnetic scan head for high-frequency recording

A stationary magnetic head scans the width of a record magnetically, enabling successive lines of video information to be recorded on a slowly moving tape. The head contains a large number of laminations. All except one of these are blocked from transducing action with the tape by currents through sweep windings. As the sweep currents are changed, every lamination becomes active in succession. For playback, such a head operates on a magnetic-modulator principle which is sensitive to flux rather than to its rate-of-change.     

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.     

Properties, preparation, advances and limitations of materials andmedia for perpendicular recording

The trends in perpendicular magnetic recording research are discussed, with emphasis on clarifying the trend of research on recording media, their materials, and head materials. Among numerous proposed perpendicular recording media materials, barium ferrite powder and evaporated Co-Cr films seem to lead in practical applications, since their mass production seems to be very successful. There still exist crucial points in their development. However, improvements are continuously taking place. Other candidate perpendicular recording media for a device which has a ring head are also discussed. It is concluded that, for future high-density magnetic recording, utilizing fully the perpendicular component of media magnetization will furnish the key to success     

Magnetic analysis of contact head/tape spacing

A new magnetic analysis method is used to determine the mean magnetic spacing of a contact head/tape interface. The initial part of the curve of readback signal amplitude versus recording current is measured at a low recording density and is fitted by using theoretical approximations to obtain the head/tape spacing. A tape looper test stand, inductive heads, and various high-density metal particle tapes are used in the recording measurements. The mean head/tape spacing obtained from magnetic analysis agrees well with the results from numerical analysis of mechanical measurements     

Dynamic micromagnetic field measurement by stroboscopic electronbeam tomography

A stroboscopic electron beam tomography system for measuring the dynamic micromagnetic field of recording heads is presented. A pulsed electron beam, which is synchronized with the recording head driver, is scanned along the recording head surface from all directions. Integration of the magnetic field intensity along the beam path is calculated from the electron beam deflection angle. Intensity distributions of the dynamic magnetic field are calculated using a tomographic reconstruction algorithm. To obtain enough current even in pulsed electron beam operation, a high-brightness Ti/W thermal field emitter is used. This system was successfully applied in measuring the field distributions of a thin-film recording head, with 0.1 μm spatial resolution and 1 ns time resolution at an operation frequency of 30 MHz