Video Heads Research Articles

Effect of secondary gaps in near-saturated metal-in-gap video heads

Secondary gaps between the ferrite bulk and the Sendust (AlFeSi alloy) shim may occur in metal-in-gap (MIG) heads. Finite-element models are used to explore the effect that these gaps have on the read/write characteristics of single- and double-sided MIG heads. The presence of a secondary gap is shown to cause an additional peak in the writing field and oscillations in the magnitude of the response during replay. The field and response of a double-sided MIG head is affected more than those of the corresponding single-sided MIG head.

DLC coating for video head

The effect of the thickness of DLCs sputtered on video heads upon the value of the playback signal and visibility of the gap in the ferrite surface was examined. It was found that DLCs improve the wear resistance of the heads, whereas the playback quality depends on the probability of the DLC peeling off during friction on the video tape. Technological regimes involving vacuum-pulsed arc sputtering of graphite in combination with ionic bombardment of the ferrite surface and the DLC were worked out. These regimes provide a good adhesion and smoothness of the film surface. Tests of video heads covered with DLCs showed that the wear resistance and the ‘still frame’ time of these heads are several times larger than those of standard video heads. A reliable and highly efficient commercial technology for the production of DLC video heads has been developed.

Video tape recorder head inspection using image processing techniques

In currently selling video tape recorders (VTRs), two or more heads fixed at a revolving drum are used to record or reproduce video signals. To obtain uniform quality, the video heads should have similar characteristics such as geometrical shape and electromagnetic performance. This research is designed to develop a visual inspection system that can measure four geometrical parameters. To obtain reliable results, a digital signal processing-based image board and target-based imageprocessing algorithms were used. A series of experiments were performed on 1000 video heads. From observation of the experimental results, except for the cases of noise on the head and cracklike defects, we were able to obtain high inspection reliability, with an error bound within ±5 ?m.

Magnetization curves of amorphous video heads

Beneath a general electromagnetic characterization of the sandwich layers, measuring the magnetization curve of the assembled video-head allows to detect remanence and coercivity. The eddy current distributions have been also visualized by high resolution thermography. The described measuring methods allow conclusions for the optimization of many parameters of the investigated amorphous CoZrNb sandwich heads.

Magnetization curves of amorphous sandwich video heads

To optimize the layer structure of the magnetic circuit and the parameters of preparation of the layer, several investigation methods have been developed. Besides measuring the magnetization curves in differential transformer arrangements, the eddy current distributions have been measured by thermography. The described measuring methods allow conclusions for the optimization of many parameters. Measuring the magnetization curve of the assembled video-head allows – besides general electromagnetic characterization – to detect remanence and the danger of unintended tape erasing.

Wear mechanisms of sandwich-type video heads

Differential wear between the various material components of composite magnetic recording heads is observed upon running against the magnetic medium. A developing level difference between the magnetic material and the medium bearing surface leads to signal degradation, exponential with the difference and the signal frequency. Experimental evidence is presented for a three-body erosion mechanism in the case of sandwich heads employed in commercial helical scan, Hi-8 video tape recorders. Two sintered ceramic substrates, CaTiO3 and composite Zr-doped CaTiO3, in combination with three soft magnetic materials, amorphous CoNbZr and the nanocrystalline iron alloys FeNbSiN and FeTaN, have been studied. They have been studied in conjunction with commercial metal evaporated (ME) and metal particulate (MP) tapes. Level difference has been measured by interferometry and AFM (atomic force microscopy), the latter also observing level differences between the various components of the sandwich: soft magnetic metal, ceramic laminations and the metallic bonding layer. AFM shows a pull-out of particles from the ceramic substrate with similar sized particles observed on the track. Scanning Auger micrographs have shown the transfer of ceramic particles on to the track and of metal on to the substrate. Wear rates and wear mechanisms have been identified for the materials in isolation by studying single-material dummy heads. This has been identified as plastic deformation controlled microabrasion, transforming to grain pull-out in the crystalline materials in some instances. It is speculated that these pull-outs are responsible for the wear of the soft metallic track when this is out of contact with the tape. The evidence for chemical wear is inconclusive. The involvement of transfer material from the tape to the head is speculated upon.

Frequency characteristics of amorphous multilayered films and video heads using them

Frequency characteristics of amorphous multilayered films and video heads using them

Characteristics of wear and contamination of video heads in consumer VCRs

Head wear and head contamination of video heads is investigated in order to improve the reliability of the head/tape interface. The location of deposits and the shape of the wear scar are studied. The wear rate along the head surface is determined using the so-called "micro-indentation technique". The contact pressure is estimated using the measured area of the wear scar and an average measured contact force. AES spectra from contaminated regions of the head gap are obtained to characterize the head deposits.

Excimer laser processing of ferrite video heads

The technology of pulsed excimer laser ablation for processing ferrite video heads at 248 nm KrF laser radiation was studied. Using the mask imaging technique two trapezoids were projected onto the surface of the samples producing laser-etched grooves with a depth of approximately 45 μm. A sufficiently sharp contour of the trapezoids was achieved at the workpiece. Since the variations of the critical dimensions with respect to depth were outside the tolerance range the sample was slightly tilted to compensate for the beam divergence and to obtain parallel edges of the trapezoidal grooves with an error of less than 5 μm over the whole depth of the cavities. Micrographs of the samples showed that the surfaces of the laser-etched video heads were covered with ablated material and small droplets of resolidified material. These sediments can be removed easily by a slight polishing of the surface. For the experiments a typical fluence of 5 J/cm 2 was used which allowed etch rates of 50 nm per pulse. The work showed that excimer lasers are useful tools for the precise micromachining of ferrite video heads.

Topographically controlled anisotropy in sandwich video heads

The performance of sandwich heads for high-density video recording can be improved if the soft magnetic layer is given a special profile. This is achieved by sputter deposition of amorphous Co films on substrate tiles that have a grooved surface profile. On the basis of a consideration of the relevant energy terms the critical groove dimensions are estimated. The effect of surface topography on the relative permeability is verified from test structures on strips and ring-shaped substrates. Sandwich heads, manufactured with a groove pattern distributed radially around the coil chamber, perform 3-4 dB better than conventional heads. This demonstrates the feasibility of topographic anisotropy control.

Friction and Wear of Metal Particle, Barium Ferrite and Metal Evaporated Tapes in Rotary Head Recorders

Abstract The friction and wear mechanisms of particulate (metal particle and barium ferrite) and metal evaporated (ME) magnetic tapes were investigated. We conducted tests on these tapes in contact with metal-in-gap (MIG) video heads, using a rotary head recorder in the still (pause) mode. We measured signal degradation and friction during the tests. We conducted chemical and surface analyses of the interface components after the tests. We found discernible differences between the tribological behavior of particulate tapes, and that of the ME tape. The particulate tapes exhibited a more stable friction and head output than the ME tape. We attributed this to a cleaner contact region, due to effective action of the head cleaning agents (HCAs) found in the particulate tapes. The particulate tapes exhibited wear lifetime longer by an order of magnitude, than that of the ME tape. Mild continuous adhesive wear occurred on particulate tapes followed by catastrophic failure. Tape fatigue possibly led to the catastrophic failure. On the ME tape surface, damage initiated at high points or bumps, which resulted in localized delaminations of the tape coating. This led to a catastrophic removal of the entire magnetic coating over the rubbing track. The major difference between the particulate and ME tapes was that signal dropouts concurrent with increases in friction, which resulted from debris accumulation on the video head, preceded the catastrophic failure in the case of ME tapes. We investigated the running-in process of the video head. We found that the durability of a tape and the initial head output increased, and the initial friction force on a tape decreased, as the head ran-in with the tape. We attributed this result to the tape forming a favorable contour on the head rubbing surface. Deposits on the head surface consisted of binder for the particulate tapes, and lubricant and the magnetic coating for ME tape. Tape materials transferred preferentially to the recessed metal core and the recessed glass of the MIG head.

Accelerated wear characteristics of video heads in a helical scan system

Abrasive Al/sub 2/O/sub 3/ tape is used to accelerate wear of video recording heads in consumer helical scan video recorders. The development of the wear scar is studied as a function of time and the increase in the length of the wear scar is measured using optical microscopy. Changes in longitudinal and transverse head radii are determined as a function of time and the dependence of head wear on head position in the scanner window is studied. The results show that the use of abrasive tape is an efficient tool in the acceleration of wear of helical scan heads.

Mechanisms of head-clogging by particulate magnetic tapes in helical scan video tape recorders

The head-clogging processes of video heads by particulate magnetic tapes in helical scan video tape recorders were investigated by continuous microscopic observations of the rotating video heads using a stroboscope. It was found that most wear debris of typical tapes is expelled out of the rubbing surface of a video head and piles up on non-contact area of the exit side of the head. The wear debris which forms an agglomerate contacts a tape surface, and is deposited on the tape surface. The following head picks it up on the rubbing surface (contact area) where the magnetic gap is located. A spacing loss occurs with a consequential decrease in reproduced voltage. >

Practical use of strength and anticorrosion properties of amorphous carbon thin films

A study was made of the protective properties of amorphous C thin films deposited by the method of pulse sputtering of graphite on substrates having a temperature of approximately 175°C. It is shown that the films can be successfully used to improve the service properties of audio or video heads and surgical cutting instruments.

Wear mechanisms of Co-Cr sputter deposited magnetic tapes in helical scan video tape recorders

The wear mechanisms of Co-Cr sputter-deposited tapes for perpendicular magnetic recording by rotary video heads in the still mode of video tape recorders were investigated by using two kinds of experimental apparatus. One is a rotary-head-type friction tester in which the surface of the rotating head can be observed continuously by a microscope with a stroboscope synchronized with the head rotation; the other is a scratch tester in which the scratched surface of a tape specimen can be observed in situ through the transparent hemispheric slider. It was found that the wear debris of the Co-Cr layer transfers onto the head surface, forms the asperities on the head, and scars the tape surface, with the increasing amount of head tracing. A carbon protective layer can prevent the Co-Cr layer from transferring onto the head and being subsequently scarred. However, the carbon protective layer may be peeled by the rotating head when the frictional force increases up to the interfacial shearing strength between the carbon layer and the Co-Cr layer.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High abrasion resistance laminated Sendust VTR heads

High-performance laminated sputtered Sendust (LSS) video heads with high abrasion resistance have been realized by using a newly developed CaO-TiO/sub 2/-NiO ceramic substrate. For acceptable head abrasion for practical use of 15 mu m, head life is more than 1000 h at more than 20 m/s relative tape-head speed. Low magnetostriction Sendust films provide high reproduce voltage for the head. The LSS head, with CaO-TiO/sub 2/-NiO substrate, has sufficient performance for use as high-definition television (HDTV) video tape recorder (VTR) heads.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A 384 track fixed recording head

A multiplexed write magnetic head has been realized, constructed with the ability to record a very large number of parallel tracks on a magnetic tape. The multiplexed concept is presented along with a practical component. Recording performance is similar to that of the state-of-the-art 8 mm MIG (metal-in-gap) video heads. Multiplex-induced crosstalk is analyzed and is measured in the worst case to be below -23 dB. The head-to-media contact is very homogeneous, and only limited by the tape roughness. A raw bit error rate of 10/sup -5/ has been measured for the complete channel. >

Read/write characteristics for laminated high moment Fe-Ta-N film heads for HDTV VTR

Laminated Fe-Ta-N film video heads have been developed using high-wear-resistance ceramic. The heads achieve a recording capability more than 1.5 dB superior to Sendust heads and more than -35 dB overwrite values for 1- mu m wavelength signals over 2- mu m wavelength signals with high coercive (>1500 Oe) metal particle tapes. Sufficient wear resistance is also shown with 21.4 m/s tape head relative velocity for high-definition television (HDTV) video tape recorders (VTRs). It should be possible to improve the read/write characteristics for the Fe-Ta-N head by magnetoelastic energy control to a negative value.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The effect of head cleaning agents on the wear mechanisms of video heads

Wear mechanisms occurring at the video head were examined for a Mn-Zn ferrite single-crystal head in sliding contact with iron oxide formulation video tape. Of particular interest was the effect on wear due to the inclusion of a head cleaning agent (HCA) in the tape formulation. Wear tests were performed in situ using specially formulated iron oxide video tape samples containing a range of levels of two types of HCA: Al2O3 and Cr2O3. Head performance was monitored by measuring the degradation of the RF signal during wear, and wear to the head was measured using Knoop diamond indentation. The resulting wear surfaces were examined using optical and scanning electron microscopy. The tape was examined in cross section using transmission electron microscopy. Results showed that the dominant mechanism of wear was abrasive, characterized by the ploughing of isolated asperities on the tape surface through the ferrite head, and damage to the head gap by three-body abrasion. Evidence is presented which suggests that the isolated asperities are a result of poor dispersion of tape particles. The addition of an HCA to the tape formulation reduced the abrasion damage. Wear increased with increasing HCA content, but the total signal degradation did not vary significantly with HCA level for either HCA. Substantial differences in wear were observed between the two types of HCA, and evidence is presented which suggests that the differences are a product of the relative quality of dispersion of the two HCA materials.

Submicron‐powder starting materials for advanced ferrites

Research News: The dependence of the microstructure on the processing route and conditions has a profound effect on the performance of ferrites (magnetic oxides) in applications such as cores for transformers and inductors, and in video heads. Methods of optimizing the microstructures of the materials for particular applications are discussed with special emphasis on a consolidation method which is a combination of sedimentation and filtration.