Considerations for high data rate recording with thin-film heads

The significance of head inductance and eddy currents in limiting field rise times is discussed. Poor rise times can cause severe distortion and loss of performance at high data rates. A simple reluctance model is developed to explore the relationship between the geometry of a head and its inductance. The model is extended to include the effects of eddy currents, and to allow the frequency-dependent efficiency (hence the field rise time) to be calculated. Based on this rise time, a geometric model is used to calculate the positions of the recorded transitions and the resulting transition-shift distortion. Experimental results at transition separations down to 6 ns reveal a strong write current dependency which is not seen in the model. This dependence is, however, clearly seen in a simple domain wall model which implicitly includes magnetic saturation. Transition shift distortion can be mitigated by the use of precompensation. It is found that it is possible to successfully recover data at 180 Mbit/s using a conventional thin-film head     

Analysis of electrical coupling parameters in superconducting cables

The analysis of current distribution and re-distribution in superconducting cables requires the knowledge of the electric coupling among strands, and in particular the interstrand resistance and inductance values. In practice both parameters can have wide variations in cables commonly used such as Rutherford cables for accelerators or Cable-in-Conduits for fusion and SMES magnets. In this paper we describe a model of a multi-stage twisted cable with arbitrary geometry that can be used to study the range of interstrand resistances and inductances that is associated with variations of geometry. These variations can be due to cabling or compaction effects. To describe the variations from the nominal geometry we have adopted a cable model that resembles to the physical process of cabling and compaction. The inductance calculation part of the model is validated by comparison to semi-analytical results, showing excellent accuracy and execution speed.     

Understanding the Impact of Inductance in Carbon Nanotube Bundles for VLSI Interconnect Using Scalable Modeling Techniques

In this paper, we develop accurate and scalable models for the magnetic inductance in bundles of single-walled carbon nanotubes, which have been proposed as a means to alleviate the increasingly critical resistance problems associated with traditional copper interconnect in very large scale integration (VLSI) applications. The models consider the density and statistical distribution of both metallic and semiconducting nanotubes within the bundle. We evaluate the speed, accuracy, and scalability of our magnetic inductance modeling techniques and previously proposed inductance models. The inductance model with the best performance evaluates the magnetic inductance of nanotube bundles with excellent accuracy when compared to modeling each nanotube individually and provides orders of magnitude improvement in CPU time as the bundle size increases. Leveraging the magnetic inductance modeling techniques, we determine the relative impact of magnetic and kinetic inductance. Based on our results, the relative value of magnetic and kinetic inductance on single-walled carbon nanotube (SWCNT) bundles is highly dependent on the bundle geometry and the per unit length kinetic inductance     

Practical and adequate approach to modeling light propagation in an adult head with low-scattering regions by use of diffusion theory

A practical and adequate approach to modeling light propagation in an adult head with a low-scattering cerebrospinal fluid (CSF) region by use of diffusion theory was investigated. The diffusion approximation does not hold in a nonscattering or low-scattering regions. The hybrid radiosity-diffusion method was adopted to model the light propagation in the head with a nonscattering region. In the hybrid method the geometry of the nonscattering region is acquired as a priori information. In reality, low-level scattering occurs in the CSF region and may reduce the error caused by the diffusion approximation. The partial optical path length and the spatial sensitivity profile calculated by the finite-element method agree well with those calculated by the Monte Carlo method in the case in which the transport scattering coefficient of the CSF layer is greater than 0.3 mm(-1). Because it is feasible to assume that the transport scattering coefficient of a CSF layer is 0.3 mm(-1), it is practical to adopt diffusion theory to the modeling of light propagation in an adult head as an alternative to the hybrid method.     

Numerical analysis of ferrite recording heads with complex permeability

Numerical methods based on finite differences are applied to the analysis of ferrite recording heads in which the permeability is complex and flux leakage effects are significant. The methods described allow computation of head efficiency, inductance, loss angle, and phase shift. As a specific example, the analysis is performed for a reduced track width version of the Memorex 3650 head for a wide range of the real and imaginary parts of the permeability. Using published values for the frequency dependence of the complex permeability, the frequency dependence of the head performance is estimated. Some experimental data are presented and compared to the theoretical predictions.     

Distortion of the electric field distribution induced in the brain during transcranial magnetic stimulation

In this study, the effects of various parameters, such as the geometrical head model, conductivity condition and stimulus position, on the electric field induced in the brain during transcranial magnetic stimulation are thoroughly examined. It is revealed that the distortion of the induced field causes the movement of the maximum field point and also leads to the deviation of the field focusing region from the stimulus centre. Numerical results show that the induced field distortion is primarily caused by the spatial asymmetry of the head geometry with respect to the stimulus centre and the induced field distribution is further deformed by imposing the heterogeneous conductivity condition. For verification purposes, an elaborate phantom head model has been constructed and the experimental results have been compared to the predicted fields yielding good agreement.     

Comparison of reproduction performance of a single pole head and a ring head

The reproduction pulse amplitude of a single pole head from double-layer perpendicular media has been analyzed. We derived an analytic expression to relate the pulse amplitude to the head and medium parameters. Experimental data are also presented to verify the calculated results. The reproduction performances of a single pole head and a ring head are theoretically compared and found to be comparable when both are normalized to the same head inductance.     

Calculation and Analysis of Stator End-Winding Leakage Inductance of an Induction Machine

This paper proposes an improved method for calculating the value of and for analyzing the frequency-dependence of the stator end-winding leakage inductance of an induction machine. The method was based on the stored magnetic energy, which was calculated by a 3-D time-harmonic finite element analysis. In this method, there were no rotary parts in the model of the simulated machine. The results of the analysis show that the stator end-winding is capable of influencing the end of the active region of the machine whereas the influence on the central part of the active region is small. In addition, the phenomenon that the stator end-winding leakage inductance, as well as the magnetic energy in the machine, relates to the frequency of the stator current is explored.      

Evaluation of head response to ballistic helmet impacts using the finite element method

Injuries to the head caused by ballistic impacts are not well understood. Ballistic helmets provide good protection, but still, injuries to both the skull and brain occur. Today there is a lack of relevant test procedure to evaluate the efficiency of a ballistic helmet. The purpose of this project was (1) to study how different helmet shell stiffness affects the load levels in the human head during an impact, and (2) to study how different impact angles affects the load levels in the human head. A detailed finite element (FE) model of the human head, in combination with an FE model of a ballistic helmet (the US Personal Armour System Ground Troops’ (PASGT) geometry) was used. The head model has previously been validated against several impact tests on cadavers. The helmet model was validated against data from shooting tests. Focus was aimed on getting a realistic response of the coupling between the helmet and the head and not on modeling the helmet in detail. The studied data from the FE simulations were stress in the cranial bone, strain in the brain tissue, pressure in the brain, change in rotational velocity and translational and rotational acceleration. A parametric study was performed to see the influence of a variation in helmet shell stiffness on the outputs from the model. The effect of different impact angles was also studied. Dynamic helmet shell deflections larger than the initial distance between the shell and the skull should be avoided in order to protect the head from the most injurious threat levels. It is more likely that a fracture of the skull bone occurs if the inside of the helmet shell strikes the skull. Oblique ballistic impacts may in some cases cause higher strains in the brain tissue than pure radial ones.     

Efficiency and data correction for OFAPT sensors with fiber receivers

This paper addresses the problem of calculations of the efficiency, as well as the necessary raw data correction, essential for the design of an optically induced fluorescence auto-projection tomography (OFAPT) sensor head. Instead of discretizing an analytically derived equation, relevant to a certain symmetry, discretization is implemented on the algorithmic level, thus developing a universal, fully numerical approach to sensitivity and efficiency calculations. The algorithm is built around the calculation of the efficiency of the fluorescence collection from a small discrete voxel. Further, the contributions from all voxels, excited by the OFAPT laser beam at a given distance from the receiver's tip, are added together, to yield the efficiency of the sensor head. OFAPT measurements are simulated on a 64/spl times/64 phantom and the proposed algorithm for correction of the raw data is implemented and assessed. The effect of the magnitude of the absorption coefficient on the data, collected under certain sensor head geometry, is studied in detail. On this basis, optimal excitation beam and receiver configurations are discussed.     

Design Concepts of Optimized MRI Magnet

This paper describes a simple technique to design compact air core magnets for magnetic resonance imaging (MRI). The optimum geometry is obtained by a combination of analytical and numerical methods. The technique emphasizes achieving the required field homogeneity with a shorter magnet having a minimum amount of ampere turns. The code calculates the total inductance of the set of coils, total conductor length, force, and maximum field on each coil. The code also calculates the allowable geometrical tolerance to achieve the field uniformity. The code is flexible and can be used for various geometries. Here, we present three different cases to demonstrate the efficiency of the code. First, we present the design details of a 1.5 m long 1.5 T actively shielded magnet, where the stray field is reduced to less than 4 gauss outside the sphere of radius 3.65 m using a pair of shielded coils. A total of four pairs of coils provide a field uniform to within 5.2 parts per million (ppm) within a sphere of 50 cm diameter. Calculated values of all the higher order moments lie within a few ppm. Second, we describe optimized geometry of unshielded 1.5 T symmetric magnets having three pairs of coils. Third, we optimize the geometry of a 1.2 m long 1 T asymmetric magnet having five coils. Here, the good field region starts at 20 cm from one of the edges of the magnet, providing the attending physician better accessibility to the patient. But the ampere turns and computation time required are quite large compared to a symmetric magnet.      

POWDER COATING PROCESS PARAMETERS FOR A TRANSFER EFFICIENCY MODEL

The trajectories of charged powder particles in a powder coating system are governed by the electrostatic, gravitational and aerodynamic forces acting on the particles. A mathematical model of particle trajectories inside a powder coating booth must consider (1) the aerodynamic flow field, (2) particle size and charge distributions, (3) the electrostatic field distribution, and (4)the geometry of the target. Our approach is to employ a grid generation and flow solver to examine the air flow pattern and an iterative technique where the Charge Simulation Method can be used to compute the electric field strength and the Method of Characteristics can be used to compute the charge density in the gun-to-target region. The electrostatic forces due to the deposited powder layer and image charge are to be taken into account to determine if the particle will deposit on the substrate or not. The model is applied to the geometry of a high-voltage electrode consisting of a long thin rod with a hemispherical end cap and a grounded flat disk substrate. An experimental system to measure transfer efficiency, with the ability to control various parameters effecting transfer efficiency, has been developed to verify the theoretical model. The simulation results can provide valuable information concerning particle deposition and optimization of transfer efficiency. This paper describes (1) system parameters involved in modeling the transfer efficiency, (2) an approach to develop such a model with preliminary data on the simulation of particle track, and (3) experimental data on the real-time measurements of first pass transfer efficiency.     

Shells of revolution with local deviations

A finite element model that is suitable for the analysis of shells of revolution with arbitrary local deviations is presented. The model employs three types of shell elements: rotational, general and transitional. The rotational shell elements, which are most efficient, are used in the region where the shell is axisymmetric. The general shell elements, which can simulate almost any shell geometry, are used in the local region of the deviation. The transitional shell elements connect these two distinctively different types of elements and make it possible to combine them in a single analysis. The form of the global stiffness matrix is somewhat unique in the new model. Non-zero terms are not confined to a narrow band along the diagonal, but occur throughout the matrix. This is due to the following: (1) two different types of nodes, ring nodes and point nodes, are combined in a single analysis; and (2) a locally non-axisymmetric geometry creates a coupling of the Fourier harmonic coefficients of the rotational elements. Yet, the matrix still contains many scattered zero terms that should be considered for numerical efficiency. In this paper an efficient solution procedure that is effective for this situation is developed. The steps include the use of a substructuring technique and separate partial harmonic analysis. A numerical example is presented and compared with existing solutions to demonstrate the capabilities and the efficiency of the new model.     

Tunable superconducting nanoinductors

We characterize inductors fabricated from ultra-thin, approximately 100 nm wide strips of niobium (Nb) and niobium nitride (NbN). These nanowires have a large kinetic inductance in the superconducting state. The kinetic inductance scales linearly with the nanowire length, with a typical value of 1 nH μm(-1) for NbN and 44 pH μm(-1) for Nb at a temperature of 2.5 K. We measure the temperature and current dependence of the kinetic inductance and compare our results to theoretical predictions. We also simulate the self-resonant frequencies of these nanowires in a compact meander geometry. These nanowire inductive elements have applications in a variety of microwave frequency superconducting circuits.     

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.     

Magneto-inductive element

A novel sensitive magnetic head using a magnetoinductive (MI) effect in zero- or negative-magnetostrictive amorphous wires is described. The MI effect refers to the change of an inductance L for an external magnetic field in a ferromagnetic wire element magnetized with a wire AC current I_AC. A 5-mm-length MI element using a folded almost zero-magnetostrictive amorphous wire having a 120-μm diameter showed a sensitive rate of change of its inductance of more than 50% for an external low frequency field of about 10 Oe (800 A/m) applied in parallel with the element. The a-wire MI element works for a wire current having frequencies up to 1 MHz     

Compact scalable diode-pumped Nd:YAG ceramic slab laser

We describe our preliminary studies of the use of neodymium-doped slab-shaped ceramic YAG media in the construction of compact, rugged, high-power diode-pumped solid-state lasers. A maximum extraction of more than 160 W at a 20% slope efficiency level, with a narrow transverse direction beam-parameter product of the order of 4 mm mrad(-1) is experimentally obtained from an extremely simple and compact (overall dimensions 160 mm x 100 mm x 60 mm) laser head in a quasi-continuous-wave regime. Experimental data together with finite-elements method simulations indicate that power extraction can be scaled up at least to 900 W cw with this laser head geometry.     

NON-WETTING ELECTROSTATIC ASSISTED NOZZLE FOR SPRAYING A CATALYTIC MELT

In this paper we present how a normal pressure nozzle can be adapted into a successful electrostatic assisted atomiser for one particular industrial application. The “Reverse Modelling” technique for the design of the nozzle head, induction electrode and counter 'wetting' electrode using finite element method is of universal value and can be used widely in induction charging electrostatic spraying applications where wetting is a problem. Experimental results showed that under the same operating condition, an optimised geometry and position of electrodes can give a spray current an order of magnitude higher than the previous design without any wetting problem. An optimum combination of an induction and a counter electrode geometry and positions will ensure a non-wetting induction nozzle assembly with very high charging efficiency.     

High-efficiency, medium-caliber helical coil electromagnetic launcher

Research progress in the development of a 40 mm/spl times/750 mm helical-coil electromagnetic launcher (HCEL) is presented and discussed. Significant technical problems that have been solved in this research include efficient stator commutation methods and the ability to simultaneously implement high-inductance gradient armatures. The HCEL is able to launch a 525-gram projectile to a velocity of 140 m/s. Power for the HCEL is derived from a 62.5 kJ sequentially fired pulse forming network (PFN) of 900 V (maximum) electrolytic capacitors. The experimentally measured HCEL efficiency of 18.2% is substantially greater than a conventional or augmented railgun of similar scale (i.e., equivalent mass, bore-size, and velocity). The HCEL's high launch efficiencies result from its 150 /spl mu/H/m inductance gradient, which is approximately 300 times greater than the inductance gradient of a conventional railgun. HCEL computer model predictions are given and compared to experimentally measured HCEL and PFN parameters including peak current, inductance gradient, acceleration time, parasitic mass ratios, and electrical-to-kinetic conversion efficiency. Scaling relationships for the HCEL are also presented and used to predict launcher operation at higher velocity and with a larger diameter bore size.     

A numerical study of the coupling coefficients for pot coretransformers

When a circuit containing a transformer is to be simulated, one must know the coupling coefficient or equivalent leakage inductances in addition to the other transformer properties. When other inductances in series with a transformer winding are large compared to the leakage inductance the leakage inductance may be neglected in a simulation. Otherwise, the coupling coefficient must be known or the simulation will be inaccurate. Since the degree of coupling depends on the nature of the winding as well as the core, and is difficult to estimate accurately, we have used numerical techniques to study the trends in coupling with geometric parameters for cores having cylindrical symmetry. Magnetic vector potential has been found using the TOPAZ2D finite element code, and then correspondingly interpolated numerical integration has given the inductances for an equivalent circuit. Results from our calculations show that although the magnetizing inductance changes greatly as a core saturates, the coupling coefficient changes slowly so long as some reasonable effective permeability remains. Actual values depend on the turns ratios and any air gaps present. For a typical pot core geometry without an air gap the coupling coefficient ranges from 0.997 to 0.999 for effective permeabilities from 600 to 1800. With air gaps the coupling coefficient drops, but stays even more constant with permeability