Throat Height Research Articles

A low inductance metal-in-gap head using a side-core concept

A low inductance metal-in-gap (MIG) head for rigid disk drives using a single crystal ferrite core was developed. Side mounting of a core was adopted to reduce its thickness, thus improving the inductance, and to achieve the ease of controlling the narrow track width and small throat height. It was demonstrated that the side-core composite (SCC) head has several advantages over conventional monolithic and composite heads in terms of electrical performance and manufacturability. Testing methods called swept frequency and swept current were also developed to demonstrate different interpretations of magnetic recording phenomena.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Design and fabrication of thin film heads for the digital compact cassette audio system

The digital compact cassette (DCC) system requires a multitrack recording head which can handle the digital multitrack format but can also playback standard analog compact cassette tapes. The layout and design of a recently developed thin film DCC head are discussed. An analysis of design parameters is presented, which shows why a small throat height of only 3 mu m has been chosen. In order to insure sufficient lifetime of the head, a CrN coating on the tape bearing surface is applied.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Read/write characteristics in a perpendicular recording system

Results of finite-element-modeling and read/write tests of modified thin film heads for perpendicular recording are presented. Yield in fabrication of thin film heads depends heavily on the final mechanical lapping process that determines the gap throat height which has to be adjusted within small tolerances. It is shown that this tolerance window can be enhanced by an improved head design.

Monte Carlo simulation of thin film head read-write performance

Read-write simulations of thin-film head longitudinal recording performance with thin-film disks are described. Acceptable electrical performance of thin-film heads depends on tight control of numerous parameters, and Monte Carlo simulation is used to quantify read-write sensitivity to head variations and to identify the critical parameters. A population of similar heads is assumed, and ten head parameters are subjected to random variations. The resultant electrical performance is dominated by head-disk spacing, with throat height, gap length, trackwidth, and pole thickness following in order of importance. Reasonable variations in coil resistance insulation thickness, yoke thickness, magnetic permeability, or inductance show relatively little influence on recording performance. >

Record characteristics of tape heads with CoZr and NiFe poles

Overwrite and recorded signal are compared for tape heads with Co/sub 91/Zr/sub 9/ and Ni/sub 81/Fe/sub 19/ poles as a function of throat height. The effects of throat height variation on performance are discussed for constant current recording with and without pole saturation. The impact of pole saturation on throat height tolerance is also discussed. Co/sub 91/Zr/sub 9/ and Ni/sub 81/Fe/sub 19/ tape heads have equivalent record performance as long as their poles are not saturated. When pole saturation does affect head performance, it has less impact on CoZr heads, and they record and overwrite better than NiFe heads. In a system that requires at least 25-dB 2f/1f overwrite at 2362 fc/mm (60 kFCI), for example, both CoZr and NiFe heads would perform well on oxide tape over a wide range of throat heights. On metal particle tape the overwrite falls below 25 dB at a throat height of 4.4 mu m for the CoZr heads and 2.3 mu m for the NiFe heads. These throat height limits could be extended with thicker poles or, in the case of NiFe, plated poles that maintain a uniform thickness on sloped areas of the underlying films. Nonetheless, for the conditions described here CoZr heads had nearly twice the throat height tolerance of otherwise identical NiFe heads.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A new concept of magnetic thin-film heads with superconductors

A new concept of the thin-film heads for magnetic recording introduced in this paper is to use the superconductive film as a perfect diamagnet to be the gap medium between the two magnetic poles of a thin-film ring head for the longitudinal magnetic recording. By using the finite-element method, the magnetic field and its distribution for the new designed ring head with a single-layer superconductive film or multilayer structure as the medium between the magnetic poles is calculated. The results show that the diamagnetic film in the gap not only increases the amplitude of the magnetic field in front of the magnetic poles, but also makes the distribution of the magnetic field much sharper, and the amplitude of the field is less influenced by the throat height of the pole tip as well.

燃焼駆動式ＣＯ２ガスダイナミックレーザーの特性 Ｉ 超音速ノズル開口比の影響

Characteristics of a combustion-driven CO2 Gasdynamic Laser (CO2 GDL), which should be a radiation heating simulator for re-entry of a planetary probe and AOTV, are experimentally and theoretically obtained. In the present GDL system carbon dioxide CO2 produced in the combustion process of liquid benzene C6H6 with gaseous oxygen CO2 is used as lasing media associated with the energy-pumping gaseous nitrogen N2. The influence of gas components on the small-signal gain is investigated using four expansion ratios of 5, 7.5, 10 and 15, which have common throat height 1.0mm. The experimental results show that the small-signal gain increases as the nozzle expansion ratio increases and that the maximum gain obtained is 0.2m-1 at the expansion ratio of 10 and 15. Comparison is made between the experimental and theoretical results based on the Anderson model, and fairly reasonable agreement is obtained. The theoretical results show that the small-signal gain decreases when combustion pressure increases and the maximum small-signal gain is obtained by optimum composition of combustion pressure and expansion ratio which are able to be produced in several GDL system.

Analysis and design of a metal-in-gap head for rigid disk files

Design improvements of the metal-in-gap head for rigid disk files, using a finite-element method that takes into account magnetic saturation, are discussed. The saturation flux density and the thickness of the alloy film and the throat height of the head are discussed analytically in order to obtain a more intensive and sharper field. The proposed analytical design is confirmed by measurements using an improved scanning electron microscope. The calculated and measured field results are in close agreement. >

Electrical detection of end point in polishing process of thin-film heads (invited)

A novel method for detecting the polishing process end point was developed for thin-film heads to achieve a gap depth (throat height) of smaller than 1.5 μm. Special thin-film heads whose magnetic paths are closed at the front end of the gap films were used. As the throat height of these gap films are much the same as the maximum tolerable value of the gap depth, the end point can be detected by monitoring the opening of the magnetic paths of the thin-film head themselves. Electrical detection of the opening was studied, utilizing the bias current dependence of the head inductance. Both inductance values of the head, with and without the bias current, Lb and Lnb, change when the magnetic path opens. The Lnb and Lb values at 3-mA bias current are 250 and 95 nH for the head having a closed magnetic path, and 180 and 155 nH for an open one, respectively. The difference Lnb−Lb decreases to about 1/6 when the magnetic path is opened. An apparatus was developed to measure the amplitude of Lnb−Lb. It utilizes a Wheatstone bridge circuit, excited with a 10-MHz sinusoidal signal for measuring inductance, and a 0.2-Hz rectangular pulse train as a bias current, respectively. Experimental results indicate that polishing can be stopped within 0.6 μm of the front edge of the gap films.

Optimization of ferrite heads for thin media

A flat write-current response (signal amplitude vs. write current) is a desirable feature of magnetic-recording heads, because it provides increased tolerance to variations in various system parameters. It is shown by theory and experiment that the write-current response of ferrite heads can be made flat by proper choice of throat height and apex angle.

Investigations of transonic diffusers. (1st report Behavior of a shock wave in a two-dimensional circular diffuser)

The behavior of shock waves in a two-dimensional transonic circular diffuser has been experimentally investigated by a schlieren optical method and by pressure measurements. When the overall pressure ratio of the diffuser, φ, increases, a few weak shock waves appear near the throat section before the flow is completely choked at the throat. These weak shocks are not stable but fluctuate in the channel, and the pressure at the throat p* increases with an increasing φ, although it is not in proportion to φ. when the flow is completely choked, these weak shocks coalesce into a single normal shock, and p* increases in proportion to φ. The behavior of the shock waves in diffusers with different geometries can be plotted on a single curve in an x/√(h*R)-φ plane if the position of the shock from the diffuser throat x is non-dimensionalized by the characteristic length √(h*R), where h* and R are the throat height and the radius of curvature of the diffuser, respectively.

Two-dimensional viscous simulation of inlet/diffuser flows with terminal shocks

Two-dimensional Navier-Stokes solutions of the flow through three inlet/diffuser configurations with terminal shock systems are reported. Calculations without bleed indicate that the terminal shock location is very sensitive to the outflow back pressure. For cases where there are little or no available experimental results, it becomes difficult to estimate the back pressure that will result in a terminal shock. Estimates based on quasi-onedimensional analysis are not found adequate for complex two-dimensional flows. It is found that since the flow downstream of the terminal shock is subsonic, and what happens at the outflow boundary affects the flow inside the inlet, enough of the subsonic diffuser must be modeled to accurately predict the terminal shock region. The diffuser portion should be fairly long with the outflow boundary occurring in a region of more or less uniform flow to be able to prescribe a uniform back pressure. The second configuration studied was investigated with and without incorporating bleed in the code. It is found that the use of bleed stabilizes the shock location and allows solutions which, without bleed, result in unstarting of the inlet. The third configuration required a significant amount of bleed through the ramp and cowl surfaces (both ahead and behind the throat) to avoid separation and provide uniform flow at the engine-face station. Comparisons are made with available experimental data. Nomenclature h - throat height M = Mach number P = pressure, N/m2 Re = Reynolds number T = temperature, K x = streamwise location from the inlet face a. = angle of attack Subscripts b = outflow boundary conditions / = inflow boundary conditions 0 = stagnation oo = freestream condition

Theoretical analysis of combustion-driven 16µm CO&amp;lt;inf&amp;gt;2&amp;lt;/inf&amp;gt;gas dynamic lasers

A numerical analysis is presented with a combustion-driven 16 μm CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> gas dynamic laser operating on liquid fuel and liquid oxidizer constituted of benzene (C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> ) and nitrous oxide (N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O), respectively. Adopting a sharp-edged nozzle with an area ratio of 100, optimization of equivalence ratio φ, reservoir pressure P <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> , and nozzle throat height <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h*</tex> was performed by considering conditions of no steam condensation and exhausting the combustion gas to the atmosphere. The analysis showed that the maximum value of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G_{16} = 0.48</tex> m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> for small-signal gain and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E_{16}^{max} = 9</tex> mJ/(l . atm . pulse) for available specific energy would be attainable with the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P(15)</tex> line of the (02 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sup> 0)-(01 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> 0) transition.

Effects of Initial Boundary-Layer Thickness on Transonic Diffuser Flows

Transonic flows displaying self-induced fluctuations were explored in a two-dimensional diffuser for shock Mach numbers to 1.4 and for approach boundary-layer displacement thicknesses from 2 to 5.8% of throat height. Steady and fluctuating properties were measured, including positions of shock, separation, and reattachment. Boundary-layer effects were moderate below and weak above a shock Mach number of 1.3, contrary to expectations of strong dependencies. Surface pressure power spectra were bimodal, reflecting both shock motion (100-200 Hz) and shear-layer turbulence (300-6000 Hz). The peak frequency for the latter decreases in the streamwise direction and becomes comparable to the shock-related frequency near the end of the divergent duct section.

Shock-tube CO2 gas-dynamic laser operating on the (0310)⇄(10°0) transition at 18.4 μm

Laser action at 18.4 μm has been obtained between the (0310) and (1000) levels in a shock-tube-driven CO2/Ar gas-dynamic laser. The pulse duration was equal to about 4 ms, giving the output power up to 2 W extracted from a 10-cm3 volume cavity mounted within a nozzle of 60° divergence angle and 0.5-mm throat height 67-mm downstream of the nozzle throat.

Numerical analysis of writing and reading with multiturn film heads

The effect of various parameters (film thickness, pole-face length, gap length, throat height, permeability, number of turns) on performance (resolution, peak shift, efficiency, saturation current) of multiturn film heads has been investigated using a numerical solution of the integral form of Maxwell's equations. It is found that very small throat heights are required not only to achieve adequate efficiency, but also to prevent saturation at currents lower than the required write current. Gap length and pole-face length are the critical dimensions which control resolution and peak shift.

Analysis of Gain Coefficients for CO2-N2-He Nozzle Flows with Boundary Layer

Experimental measurements and theoretical calculation of gain coefficients were made for vibrationally nonequilibrium nozzle flows, with relatively low reservoir pressure. A simple and semi-empirical method to estimate the effective cross section of the expansion core was proposed and applied to the calculations. Gain coefficients versus the reservoir pressure, throat height, and the distance along a nozzle were measured. Experimental results agreed well with the theoretical ones.

Portable, Adjustable Flow-Measuring Flume for Small Canals

ABSTRACT A portable flume capable of throat height adjust-ment above a canal bottom and special stilling well and depth sensing arrangements is being used as a field-survey device before casting low-cost concrete throat sections. This caliper-flume can be installed and removed from a flowing canal by two persons.

Method for Increasing Wind Tunnel Mach Number for Large-Scale Inlet Testing

FOR the development of efficient mixed-compression inlet systems for supersonic aircraft, relatively large'-scale models are required to accurately assess the inlet performance. Large-scale models are particularly essential as design inlet Mach numbers increase above about M°° = 2.2. That is, for mixed-compression inlets the throat contraction ratio increases, resulting in small throat heights and large negative pressure gradients; under these conditions accurate measurements of the inlet performance parameters would be difficult without large models. For inlet tests above Mach numbers of 3.5, few wind tunnels exist that are suitable for large-scale (50 cm capture diam) models. To overcome this problem, a simple and inexpensive technique to extend the Mach number range in existing wind tunnels for large-scale inlet testing has been investigated. The technique involves an expansion plate, wherein flow is expanded two-dimensionally around the sharp leading-edge to create a local uniform flow field with higher than freestream Mach numbers. Previously, flow expansion plates have been used to vary the Mach number in supersonic tunnels,' and occasionally they have been used to achieve special test conditions. The objective of the investigation was to show the feasibility of using locally expanded flow to extend the Mach number range of supersonic wind tunnels for large-scale inlet testing. The primary considerations of this investigation were to determine the Mach number increase possible and to define the uniformity of the expanded flowfield.

Experimental investigation of the expansion of moist air around a sharp corner

The results of an experimental study of two-dimensional supersonic expansions of moist air around a sharp corner are reported. Condensation of water vapor by homogeneous nucleation occurs within the expansion fan. Measurements of the location of the onset of condensation show that the leading edge of the condensation zone is concave with respect to the oncoming flow. Density measurements, obtained from the analysis of flow-interfer ograms, indicate that the flowfield within the condensation zone is a function of both expansion angle and radial distance from the corner. An empirical relation between experimentally determined adiabatic supercooling and expansion cooling rate is obtained. Nomenclature C = constant, Eq. (5) h* = nozzle throat height K = Gladstone-Dale constant L = optical path length M = Mach number n = exponent, Eq. (5) p = pressure R = universal gas constant r = radial distance measured from the corner A$i2 = nondimensional fringe shift T = temperature ATad = adiabatic supercooling 7 = ratio of specific heats X = wavelength JLI = molecular weight p = density 3> = relative humidity <£ = expansion angle measured from the vertical at the corner a) = specific humidity Subscripts a = air c = saturated conditions, condensed phase k = onset of condensation v — water vapor 0 = stagnation conditions 1 = reference conditions 2 = measured properties oo = plane surface