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͑ a ͒ – ͑ f ͒ , captioned as shown. All parameters, except normalized distance x , are normalized against their maximum values.
Source publication
A method for determining hysteresis losses in thin strips of soft magnetic materials is described. It is based on the measurement of a drag force which arises with the movement of the sample through the strong field existing in the space near a permanent magnet. Not associated with macro eddy currents, the force is shown to originate from the magne...
Contexts in source publication
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... SUT is assumed to have arrived at the position shown in Fig. 1 by motion from left to right, and that in so doing, at least the portion shown, passed under a second, identical PM PM2-not shown, also separated from the SUT by G and located 12G to the left of PM. An element of material of infinitesimal length, dx, at position 1 in Fig. 2a, while presently located where the fields from both PMs are near zero, has been previously exposed to the peak nega- tive field, H p− , from PM2, assumed to be sufficient to result in technical saturation. Thus, when reaching position 1, the start of the AZ, this element of material will be at negative remanence, −M r , indicated as ...
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... where the fields from both PMs are near zero, has been previously exposed to the peak nega- tive field, H p− , from PM2, assumed to be sufficient to result in technical saturation. Thus, when reaching position 1, the start of the AZ, this element of material will be at negative remanence, −M r , indicated as point 1 on the hysteresis loop in Fig. 2b, and transcribed to a plot of M vs x in Fig. 2c. During further rightward motion of the SUT, a distance suf- ficient for the element originally at 1 to arrive at 2, the loca- tion of H p− , M within this element will grow along the path indicated 1 → 2 in Figs. 2b and 2c. During further motion to the right, H L falls to zero and M ...
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... has been previously exposed to the peak nega- tive field, H p− , from PM2, assumed to be sufficient to result in technical saturation. Thus, when reaching position 1, the start of the AZ, this element of material will be at negative remanence, −M r , indicated as point 1 on the hysteresis loop in Fig. 2b, and transcribed to a plot of M vs x in Fig. 2c. During further rightward motion of the SUT, a distance suf- ficient for the element originally at 1 to arrive at 2, the loca- tion of H p− , M within this element will grow along the path indicated 1 → 2 in Figs. 2b and 2c. During further motion to the right, H L falls to zero and M returns to −M r along path 2 → 3 Figs. 2a-2c, ...
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... will be at negative remanence, −M r , indicated as point 1 on the hysteresis loop in Fig. 2b, and transcribed to a plot of M vs x in Fig. 2c. During further rightward motion of the SUT, a distance suf- ficient for the element originally at 1 to arrive at 2, the loca- tion of H p− , M within this element will grow along the path indicated 1 → 2 in Figs. 2b and 2c. During further motion to the right, H L falls to zero and M returns to −M r along path 2 → 3 Figs. 2a-2c, thereby completing the traversal of a minor hysteresis loop. The continuously moving element then experiences a steep growth in H L of opposite polarity, reaching H p+ at 4, relaxing to zero at 5, a growth to H p− at 6, and again ...
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... to a plot of M vs x in Fig. 2c. During further rightward motion of the SUT, a distance suf- ficient for the element originally at 1 to arrive at 2, the loca- tion of H p− , M within this element will grow along the path indicated 1 → 2 in Figs. 2b and 2c. During further motion to the right, H L falls to zero and M returns to −M r along path 2 → 3 Figs. 2a-2c, thereby completing the traversal of a minor hysteresis loop. The continuously moving element then experiences a steep growth in H L of opposite polarity, reaching H p+ at 4, relaxing to zero at 5, a growth to H p− at 6, and again approaching zero at 7, the end of the AZ. If moved slowly enough for quasistatic conditions to prevail, M ...
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... each position within the AZ, the element will have a magnetic moment, MAdx, and by virtue of the field gradient, dH / dx at that location, it will experience a longitudinal force dF = MA dx dH / dx. Variation in dH / dx with position is shown in Fig. 2d; variation in dF plotted as dF / dx is shown in Fig. 2e. Since, at any one instant, there are ele- ments of like size at every location in the AZ, the sum of these elemental forces will comprise a net force acting on the ...
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... each position within the AZ, the element will have a magnetic moment, MAdx, and by virtue of the field gradient, dH / dx at that location, it will experience a longitudinal force dF = MA dx dH / dx. Variation in dH / dx with position is shown in Fig. 2d; variation in dF plotted as dF / dx is shown in Fig. 2e. Since, at any one instant, there are ele- ments of like size at every location in the AZ, the sum of these elemental forces will comprise a net force acting on the ...
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... within the AZ there are elements having magneti- zations representative of the traversal of both the minor loop 1 → 2 → 3 and the major loop 3 → 4 → 5 → 6 → 7, F in 2 clearly derives from the total area of both loops. Figure 2f shows the cumulative sum of the elemental forces to the left of each point within the AZ. The existence of a finite final sum, F, clearly seen in this figure, reflects the asymmetry of the plots in Figs. ...
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... loss by drag force measurement is seen to match within 18% those determined by a more conventional method. This unexpectedly close correlation for materials having a wide range of magnetic and geometric characteris- tics seems to indicate that neither normal field components nor the demagnetizing fields arising from the large values of dM / dx Fig. 2c existing within some portions of the AZ have significant effects. The latter was expected on the basis of qualitative reasoning but it has not yet been rigorously proven. The apparent sluggish dependence on the gap is also not unexpected, since peak field excursions of just a few times the coercivity are usually sufficient to develop ...
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Citations
... In such a system, the magnetic stray field of vortices travelling across the superconductor induces a co-moving magnetic polarization in the ferromagnetic material. The local magnetization changes following a minor hysteresis cycle, resulting in a drag force similar to that experienced by a permanent magnet moving along a ferromagnetic thin strip [36]. Extrapolating the results of the magnet/thin strip case to the motion of a single vortex, the magnetic hysteresis drag force is expected to be independent on the vortex velocity and proportional to both the ferromagnetic layer thickness and the lateral extension of the vortex stray magnetic field, L lat ∼ λ (assuming that the characteristic length of the microstructure of the ferromagnetic material is smaller than L lat ). ...
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... This is because that only using this excitation field can magnetic parameters at different magnetic field strengths be obtained under a static magnetization. In addition, a similar field under a static magnetization has been adopted by other researchers to obtain the magnetic hysteresis loss of the inspected members [28]. In the region from L = 55 mm to L = 910 mm, the uniform distribution conditions for the magnetic flux density is satisfied [24]. ...
A new stress measuring sensor is proposed to evaluate the axial stress in steel wires. Without using excitation and induction coils, the sensor mainly consists of a static magnetization unit made of permanent magnets and a magnetic field measurement unit containing Hall element arrays. Firstly, the principle is illustrated in detail. Under the excitation of the magnetization unit, a spatially varying magnetized region in the steel wire is utilized as the measurement region. Radial and axial magnetic flux densities at different lift-offs in this region are measured by the measurement unit to calculate the differential permeability curve and magnetization curve. Feature parameters extracted from the curves are used to evaluate the axial stress. Secondly, the special stress sensor for Φ5 and Φ7 steel wires is developed accordingly. At last, the performance of the sensor is tested experimentally. Experimental results show that the sensor can measure the magnetization curve accurately with the error in the range of ±6%. Furthermore, the obtained differential permeability at working points 1200 A/m and 10000 A/m change almost linearly with the stress in steel wires, the goodness of linear fits are all higher than 0.987. Thus, the proposed steel wire stress measuring sensor is feasible.
... 15. Six magnetic parameters, viz. ...
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... T HE drag force method [1] is based on measuring the force that resists the longitudinal motion of a ferromagnetic strip moving through the magnetic field in the vicinity of a perma- nent magnet. This longitudinal "drag" force originates from the strip's magnetic hysteresis: the forward and backward move- ment through the field close to the magnet causes the local mag- netization to traverse closed magnetization loops; hence, the mechanical work done to move the strip forward and backward equals the hysteresis losses of the strip. ...
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... In the drag force method, the hysteresis loss is obtained by measuring the drag force that arises from the forward and backward movement of a sample relative to the strong field of permanent magnets [1]. The distance between magnet and sample is kept constant in time. ...
... Simulations were carried out for the geometry of the experimental setup [1] in which one NdFeB permanent magnet was moved back and forth over a sample of 1.6 mm thickness. The magnet is positioned as in Fig. 1a. ...
To determine the hysteresis loss in a sample, usually the enclosed area of the B − H loop is evaluated. In the drag force method, based on a proper energy balance, the hysteresis loss is obtained by analyzing the drag force profile when slowly moving the sample forward and backward through the strong field of permanent magnets. A numerical time-stepping model is presented that calculates the drag force profile. At every time step, the sample is slightly moved. The model is based on 2D-FE computations including magnetic hysteretic material behaviour using the Preisach model. In order to improve the numerical stability, we reformulated the Maxwell equations in such a way that the material behaviour is described through differential permeabilities. Consequently, the basic unknown for the FEM becomes the time derivative of the vector potential. The drag force is obtained by using the Maxwell stress tensor. Simulations were carried out in which a sample was moved back and forth through the field of one or two permanent magnets. The numerical model is validated by measurements and by comparing the "drag force" hysteresis losses with the hysteresis losses computed conventionally by the integral of H.dB.
... In the drag force method, based on a proper energy balance, the hysteresis loss is obtained by analyzing the measured drag force profile when slowly moving the sample forward and backward through the strong field of a permanent magnet. In [1], it was shown that a good correspondence was obtained between the measured losses by the drag force method and the losses obtained by Epstein measurements. The distance between the magnet and the sample is kept constant in time. ...
... Simulations were carried out for the geometry of the experimental setup [1] in which one NdFeB permanent magnet with dimensions 3.17 × 12.7 × 50.8 mm (along x, y and z axis respectively) was moved back and forth over a sample of 1.6 mm thickness. The magnet is positioned as in Fig. 1a. ...
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The initial magnetization curve is closely related to the stress in ferromagnetic material, thus it could be used to evaluate the stress in ferromagnetic member online. However, the initial magnetization curve measurement system recommended by the technical standard IEC 60404-4 is not suitable for online application. It is inevitable to use excitation coils to generate the excitation field and induction coils to obtain the magnetic flux density, however winding coils closely and uniformly online is not easy to operate. To obtain the initial magnetization curve easily, a calculation method for initial magnetization curve under constant magnetization based on time-space transformation is put forward in this paper. The theoretical correctness of this method is validated through simulation with the constant current coil magnetization. Considering the fact that the constant magnetic field could also be provided by permanent magnets and that magnetizing ferromagnetic members online by permanent magnets are convenient to achieve, in this paper, we put forward the measuring principle of initial magnetization curve based on a constant magnetic field excited by permanent magnets further and set up the corresponding measurement system. This system employs permanent magnetizers as the excitation magnetic source, and adopts symmetric magnetization methods to produce a constant magnetic field on a cylindrical rod-shaped member. The excited constant magnetic field changes along the axial position of the member. Under this exciting field, the axial and radial magnetic flux densities at different lift-offs from the surface of the member are measured by a testing probe including Hall chip array. Then, the axial and radial magnetic flux densities at the interface between the member and air are calculated based on the extrapolation method through utilizing polynomial function fitting and the Gauss's law for magnetism. Furthermore, the axial magnetic field strength within the member is calculated from the axial magnetic flux density at the interface according to the continuity of the tangential magnetic field strength. On the other hand, the induced magnetic flux density within the member is calculated from the radial magnetic flux density at the interface on the basis of the Gauss' law for magnetism, the basic equation of magnetization curve in Rayleigh region and the law of approach to saturation. Finally, the initial magnetization curve could be measured. System measurement results show that with no excitation coils nor induction coils, the initial magnetization curve of the cylindrical rod-shaped member can be easily obtained from the axial and radial magnetic flux densities at the interface of the member under the constant magnetic field excited by permanent magnetizers. The measurement error is less than 10%, and the standard deviation of the error is less than 0.01, which shows that the measurement repeatability is good. Therefore, this proposed system could provide a new approach to measuring the initial magnetization curve of cylindrical rod-shaped members online conveniently.
The increase in hysteresis loss associated with the altered microstructure and residual stress fields in regions near the cut edges of electrical steels is investigated by means of drag force measurements. Measurements are made using relatively narrow magnets on samples of two grades of nonoriented steels cut by laser or mechanical processes. Largest drag forces, hence losses, are consistently found in slow laser cut samples, smallest drag forces with fast laser cut samples, and moderately higher losses in mechanically cut samples. These results are consistent with other measurement methods.
Variations in the longitudinal drag force on a magnet close to a slowly moving strip sample of electrical steel are shown to provide sensitive, nondestructive indications of local inhomogeneity in the permeability, dimensions, and hysteresis loss of the sample. Measurements of both grain-oriented and nonoriented electrical steels showed drag force variations of unexpectedly large amplitude for movements of just a few millimeters, often with quasiperiodic features. Hysteresis variations were smaller and less drastic. © 2008 American Institute of Physics.
The effects of varying shot peening process parameters on drag force signatures are examined. The salient features of such signatures are found to compare favorably with those expected from consideration of the effects of peening on magnetic properties combined with analysis of the actual force sources. The potential utility of the drag force method for automatic assessment of peening quality and uniformity is encouraged by experimental results. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3072378]
