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Magnetics, IEEE Transactions on

Issue 2  Part 2 • Date Mar 2001

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Displaying Results 1 - 12 of 12
  • Optimizing the Jiles-Atherton model of hysteresis by a genetic algorithm

    Publication Year: 2001 , Page(s): 989 - 993
    Cited by:  Papers (34)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (96 KB)  

    Modeling magnetic components for simulation in electric circuits requires an accurate model of the hysteresis loop of the core material used. It is important that the parameters extracted for the hysteresis model be optimized across the range of operating conditions that may occur in circuit simulation. This paper shows how to extract optimal parameters for the Jiles-Atherton model of hysteresis by the genetic algorithm approach. It compares performance with the well-known simulated annealing method and demonstrates that improved results may be obtained with the genetic algorithm. It also shows that a combination of the genetic algorithm and the simulated annealing method can provide an even more accurate solution than either method on its own. A statistical analysis shows that the optimization obtained by the genetic algorithm is better on average, not just on a one-off test basis. The paper introduces and applies the concept of simultaneous optimization for major and minor hysteresis loops to ensure accurate model optimization over a wide variety of operating conditions. It proposes a modification to the Jiles-Atherton model to allow improved accuracy in the modeling of the major loop View full abstract»

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  • Optimal control technique for magnet design in inside-out nuclear magnetic resonance

    Publication Year: 2001 , Page(s): 1015 - 1023
    Cited by:  Papers (10)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (268 KB)  

    The magnets used in a family of inside-out nuclear magnetic resonance (NMR) well-logging tools usually consist of several segments of magnet materials, with each segment magnetized differently. In a tool, the magnet is surrounded with a nonlinear magnetic material, such as ferrite or steel, that is primarily used in the RF coil or in shielding the electronic components from strong magnetic fields. The main objective of the tool design is to find a set of magnetization vectors that result in a desired magnetic field profile in a particular region. A typical nonlinear finite-element method (FEM) model of such a design has about quarter of a million unknowns and requires about 35 h of processor time on a Sun Ultra 60 296-MHz machine with 1 GB of RAM. It generally requires many executions of the nonlinear FEM to arrive at a satisfactory design. In this paper, an optimal control technique in conjunction with FEM is proposed to speed up the design process. A magnet built from the design showed excellent agreement between the measured and computed data and validated the numerical method View full abstract»

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  • Angle dependence of magnetoresistance peaks in thin nickel films

    Publication Year: 2001 , Page(s): 1032 - 1035
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (96 KB)  

    The angle dependence of magnetoresistance (MR) peaks in thin nickel films was investigated by rotating the sample in two different ways. The phase mixing of the positive M and negative MR signals was observed 1) with the sample located in the same plane as the field and rotated through an axis perpendicular to the field and 2) with the sample located in a plane perpendicular to the field and then rotated. In the latter case, the field difference between the two MR peaks increased. This behavior is well explained by the concept of effective magnetic field View full abstract»

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  • Revised core-shell domain model for magnetostrictive amorphous wires

    Publication Year: 2001 , Page(s): 994 - 1002
    Cited by:  Papers (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (180 KB)  

    The radial, circular, and axial components σr, σφ, and σx, of the residual stress tensor in amorphous wires made by quenching in rotating water are derived from the classical elasticity theory on the assumption that the density decreases from the wire surface (r=r0) as r8 /r08. After a small reduction in σx and a small rotation of the easy directions in the core, the current widely applied core-shell domain model is revised. In contrast to the current model, which assumes an axially magnetized core and different core radius rc for wires with positive and negative magnetostriction, the revised model assumes: 1) a fixed core radius τc~0.75 r0 and 2) a helical core magnetization tilting about ±30° from the axial (circular) directions for wires of positive (negative) magnetostriction. This revision is consistent with the existing basic results of domain observations and magnetic measurements and it is further supported by experiments using a new technique described in this paper View full abstract»

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  • Changes in magnetostriction of polycrystalline Tb-Dy-Fe casting alloys after annealing

    Publication Year: 2001 , Page(s): 1003 - 1010
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (304 KB)  

    A study investigated the changes that occur in the structure and magnetostrictive properties of polycrystalline Tb-Dy-Fe casting alloys after annealing. The alloys formed a columnar structure along the thermal flow direction during casting, and the Laves phases tended to show a (110) orientation parallel to the columnar structure. The magnetostriction of the alloys under a condition of compressive prestress changed substantially as a result of annealing, and a pronounced increase in magnetostriction was observed at annealing temperatures above 750°C. After annealing, magnetostrictive properties reflected changes in magnetocrystalline anisotropy and the saturation magnetostrictive coefficient due to differences in the Tb/Dy ratio. Annealing had the effect of homogenizing the alloys and easing lattice distortion of the Laves phases View full abstract»

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  • Minimum-time control of magnetic head flux

    Publication Year: 2001 , Page(s): 1036 - 1048
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (340 KB)  

    This paper presents an optimal shape for a wave traversing a transmission line, incident to a magnetic head's write element, that gives minimum-time control of a magnetic head's yoke flux. The control waveform allows for the effects of the magnetic head's eddy currents as well as of the wave that reflects from the time-varying impedance of the magnetic head write element. It is shown that bringing all magnetic head states to equilibrium for minimum nonlinear transition shift requires excessive time. The preferred solution is to quickly achieve a value of desired yoke flux in minimum time and then to use a subsequent control that maintains the desired flux level in the presence of continuing response from yoke eddy currents. The analysis of a transmission line terminated in a simple RLC magnetic head model gives insight to the choice of transmission line impedance View full abstract»

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  • Electromagnetic separation techniques in metal casting. II. Separation with superconducting coils

    Publication Year: 2001 , Page(s): 1024 - 1031
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (152 KB)  

    The second part of this paper is devoted to the use of dc superconducting coils for electromagnetic separation of small nonconducting inclusions in metal casting. We theoretically analyze two methods: 1) magnetohydrodynamic separation with an electric current induced by a mean flow (conical separator) and 2) electromagnetic separation with an externally injected electric current (helical separator). First, the paper develops a model of the conical separator proposed by Gillon and Pillin in 1998 and compares it with experiments. It states that the main reason for poor separation efficiency can be flow inhomogeneity and turbulence in the separation channel. Second, the paper introduces a model of the electromagnetic separator with an injected current. Such a model has a number of advantages including better performance and higher flow homogeneity. It is capable of separating of nonconducting inclusions on the order of 10 μm in size in a magnetic field of 8 T with a flow rate of 1 kg/s. Power efficiency of the electromagnetic separation is studied with respect to the accompanying Joule's heating of molten metal. It is found that the electromagnetic separator with a superconducting coil and an injected current has the highest power coefficient, at least 100 times greater than the efficiency of conventional separation devices View full abstract»

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  • Demonstration of 35 Gbits/in2 in media on glass substrates

    Publication Year: 2001 , Page(s): 1052 - 1058
    Cited by:  Papers (20)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (156 KB)  

    A recording density of 35 Gbits/in2 was achieved in longitudinal recording media with high-sensitivity GMR heads. The media displayed excellent thermal stability as a result of a CoPtCrB alloy with high magnetocrystalline anisotropy and relatively narrow grain size distribution. The degree of Co easy-axis orientation in the plane of the μm was greatly improved and the grain size was reduced in the media on glass substrates. Estimates of the switching volume from dynamic coercivity and signal-to-noise measurements are larger than the physical grain size, suggesting that intergranular interactions improve stability. A potential path to further increases in recording density above 35 Gbits/in2 is to use antiferromagnetically coupled magnetic layers in the media View full abstract»

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  • Analytical calculation of ironless loudspeaker motors

    Publication Year: 2001 , Page(s): 1011 - 1014
    Cited by:  Papers (10)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (124 KB)  

    This paper analyzes a concept for ironless loudspeaker motors. The structure is a torus with a cylindrical air gap, formed by toroidal permanent magnets with a triangular cross section. The advantage of this design is that it permits control of the magnetic field inside the structure. The result is ironless self-shielding devices with small flux leakage View full abstract»

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  • Two-dimensional finite element magnetic modeling for scalar hysteresis effects

    Publication Year: 2001 , Page(s): 982 - 988
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (140 KB)  

    A general transient simulation method accurately models the magnetic state of a device containing a ferromagnetic core by incorporating a scalar hysteresis model into the standard finite element framework. The method numerically implements the Jiles-Atherton hysteresis model to simulate hysteresis without introducing additional parameters to simulate minor loops. Additionally, it extends the finite element geometry to two-dimensional space by predefining directional vectors or element coordinate systems that specify the local field directions for which the scalar material model applies. The method is verified by applying it to a rotationally symmetric ferromagnetic core with a time harmonic current excitation. Finally, the verified technique is applied to model a square-shaped inductor core having a more general two-dimensional magnetic field distribution View full abstract»

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  • Time domain network analysis of write head coil impedance

    Publication Year: 2001 , Page(s): 1049 - 1051
    Cited by:  Papers (1)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (48 KB)  

    In this paper, time domain network analysis methods are used to measure the electrical impedance of a magnetic disk drive write head, An incident step capable of delivering ±73 mA to the write coil simulates typical operating levels. The paper compares results to more common vector network analysis measurements, which are done at small-signal levels. It discusses the application of the measured transient response to high data rate recording View full abstract»

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  • Quantifying advanced tape medium noise

    Publication Year: 2001 , Page(s): 1059 - 1066
    Cited by:  Papers (12)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (200 KB)  

    An investigation of the tape medium noise mechanism analyzed the magnetization fluctuation produced by an incremental dc erase process in a variety of modern metal-particle tape media. It examined the wavelength characteristics of the noise and compared the integrated noise during the reverse dc erase process with in situ remanent hysteresis curves. The integrated noise power followed the square of the first field derivative of the remanent hysteresis curve, (dM/dH)2 , showing that spatial fluctuation of the recording field inside the medium is a major source of the tape medium noise. It excluded spatial fluctuation of the medium coercivity as a possible noise source by comparing results from recording heads with two very different gap lengths. A quantitative analysis of the medium noise spectra at different erase currents indicated that interfacial roughness at the magnetic coating backside in some dual-layer media is a major source of medium noise. The conclusion: The main mechanism of the medium noise in advanced tape media is the head medium spacing fluctuation due to surface roughness View full abstract»

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Aims & Scope

IEEE Transactions on Magnetics publishes research in science and technology related to the basic physics and engineering of magnetism, magnetic materials, applied magnetics, magnetic devices, and magnetic data storage.

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Meet Our Editors

Editor-in-Chief
Pavel Kabos
National Institute of Standards and Technology