Magnetic Loss Measurements Research Articles

Measurement of magnetic losses by thermal method applied to power ferrites at high level of induction and frequency

Classically, low frequency losses in soft magnetic materials and ferrites in particular are measured by flux metric method under sinusoidal waveform excitation voltage. However, in typical application of modern power electronics, the frequency currently exceeds 100 kHz. This feature is at the origin of a difficulty: the phase shift between current and voltage can be disturbed by current probe delay. Thus, the results can be affected by large errors. As a consequence, it becomes more and more important to develop alternative methods to measure losses in magnetic materials. It is proposed to use calorimetric method which is by principle free of the above mentioned problems. The experimental device is described in details and the results are reported for experiments conducted on a commercial Mn-Zn ferrite under sinusoidal waveform regime for frequencies varying from 10 to 200 kHz. Comparisons with flux metric measurement show that significant differences appear typically for Bf products above 5000 V/m(2) (50 kHzx100 mT).

Magnetic and dielectric properties of the M-type barium strontium hexaferrite (Ba x Sr1−x Fe12O19) in the RF and microwave (MW) frequency range

This paper presents results for the dielectric permittivity (e′), dielectric loss (tg δE) dielectric permeability (μ′) and magnetic loss (tg δM) in the radio-frequency and microwave frequency range of BaxSr1−xFe12O19 hexaferrite (0 ≤ x ≤ 1). The samples were prepared by a new route of the ceramic method. The magnetic permeability (μ′) and magnetic loss (tg δM) measurements in the range 100 MHz to 1.5 GHz, reveals that 1.32 ≤ μ′ ≤ 1.68 for the permeability of BFO100 (BaFe12O19) and 1.16 < μ′ ≤ 1.88 for SFO100 (SrFe12O19) in the range of studied frequencies. The BFO100 sample presented lower loss (tg δM = 4.10−3 at 1.5 GHz). The permittivity of BFO100 and SFO100 in 1.5 GHz are, respectively 8.18 and 8.19, and in the 1 MHz are, respectively 52.04 and 19.09. The samples presented coercive field in the range of 3–5 kOe and remanence magnetization in the range of 33–36 emu/g. The subjects of paper were study the dielectric and magnetic properties of the barium and strontium hexaferrite, in view of applications as a material for permanent magnets, high density magnetic recording and microwave devices.

Influence of a Stainless Steel Core on Coupling Loss, Interstrand Contact Resistance, and Magnetization of an $\hbox{Nb}_{3}\hbox{Sn}$ Rutherford Cable

Calorimetric and magnetic AC loss measurements were made on a pair of TQ (ldquotechnology quadrupolerdquo) class cables, one with and the other without a stainless steel core. The coupling losses are compared to the cables' hysteretic losses determined at the same time; the latter being compared to the magnetically measured hysteretic losses of individual strand segments. The outcomes of these measurements were: (i) the effective interstrand contact resistances of the uncored and cored cables, (ii) their hysteretic losses translated in terms of ldquoeffective, ICRs (interstrand contact resistances)rdquo for comparison with the above, and hence an evaluation of the real effectiveness of the core in a contemporary cable (iii) a comparison of the cable and strand hysteretic losses and hence an estimate of an effective filament diameter, , for the as-cabled strands.

Measurement and Prediction of Magnetic Losses in Mn-Zn Ferrites From DC to the Megahertz Range

Measurement and Prediction of Magnetic Losses in Mn-Zn Ferrites From DC to the Megahertz Range

Versatile magneto-optic Kerr effect polarimeter for studies of domain-wall dynamics in magnetic nanostructures

This article describes a versatile instrument capable of probing magnetic domain-wall dynamics in microstructured thin films. The instrument combines a state-of-the-art scanning magneto-optic Kerr effect polarimeter that incorporates high-bandwidth signal detection, an integrated broadband magnet system, and a microwave probe station. Together, these subsystems enable a broad range of studies of field and current-driven domain-wall dynamics in submicrometer magnetic structures and devices. Domain-wall motion can be probed with ≈2μm spatial resolution and less than 2ns temporal resolution. That motion can be driven by magnetic fields of up to ≈100Oe amplitude with sinusoidal (&amp;gt;20MHz) or user-defined wave forms (20ns rise time) or by electric currents from dc to ≈10GHz. A detailed description of the instrument is provided as well as several experiments highlighting its capabilities, including hysteresis loop shape and magnetic energy loss measurements spanning ten decades of drive frequency; spatially and temporally resolved measurements of domain-wall propagation in submicrometer magnetic wires; and mobility measurements of field- and current-driven domain-wall motion.

Square Helmholtz coil with homogeneous field for magnetic measurement of longer HTS tapes

Magnetic ac loss measurement of HTS tapes and films at various magnetic field orientations becomes a crucial issue from the view point of measurement precision. In principle, due to tiny loss component and anisotropic properties, longer HTS sample subjected to very good homogeneous field could facilitate the accuracy of this kind of measurement. We investigated field profile of Helmholtz coils with square winding as a magnetizer for HTS tape and films. It is found that square winding exhibits better field-homogeneity than that of conventional circular winding with the similar coil dimensions for ideal condition. Being apart from ideal condition, we investigated field profile of square Helmholtz coil with various combinations of coil parameters and made a conclusion for the best combination based on the field homogeneity and field intensity. The design also provides noise reduction facilities by allowing compact and identical pick up-compensation coil arrangement. In addition, we optimized the final design of Helmholtz coil to compensate the influence of difficulties in square winding on the field distribution. Finally, as small as 0.5% field variation was estimated for 50 mm long sample to be magnetized under a proper combination of fabrication parameters. Investigation of field homogeneity, noise effect and a practical design of square Helmholtz coil as a pick-up coil based magnetizer will be reported.

Magnetization Loss of Stacked Bi-2223/Ag Tapes in External Magnetic Field

This paper investigates the magnetization loss of stacked Bi-2223/Ag tapes. A numerical code was developed to estimate the magnetization loss of stacked tapes in parallel and perpendicular external magnetic fields. To calculate magnetization loss and current distribution across the tapes, we used magnetic field dependent current-voltage characteristics of a tape. The numerically calculated result showed good agreement with the measured magnetization loss in a tape. In a perpendicular field, it was observed that the loss per unit volume decreased as the stacking number increased because of the screening current across the tapes. In a parallel field, the loss per unit volume remained virtually unchanged as the stacking number increased. The influence of stacking effect on magnetization loss is addressed with the induced current distribution obtained from numerical calculation.

Calibration free method for measurement of the AC magnetization loss

A calibration free measurement method for determination of the magnetization loss ofsuperconducting samples exposed to the external AC magnetic field is presented. The ideais based on the measurement of the part of the power which is supplied by the ACsource to the AC magnet generating the magnetic field, in which the sample islocated. It uses a coil wound in parallel to the AC field magnet as the measurementcoil. To achieve the necessary sensitivity, two identical systems are used, eachconsisting of an AC magnet and a measurement coil, one of them containingthe sample and the other left empty. No measurement and/or calculation of thecalibration constant is required. To confirm the suitability of this method, theloss of a Cu sample with known dissipation was measured. The applicability tothe AC magnetization loss measurements of superconducting tapes is presented.

AC loss reduction of YBCO coated conductors by multifilamentary structure

The large cross-sectional aspect ratio of YBCO coated conductors leads to alarge magnetization loss in an AC transverse magnetic field. In this work, themagnetization loss of a multifilamentary YBCO coated conductor was studiedexperimentally. A 100 mm length of striated multifilamentary YBCO coated conductor wasprepared where the conductor and filaments were 10 mm wide and 0.4 mm wide,respectively. Striations in the sample were accomplished by laser ablation. Themagnetization loss of this striated conductor as well as a reference non-striatedconductor was measured in AC transverse magnetic fields normal to the conductorat various frequencies. The measured magnetization loss of the 100 mm striatedconductor was less than 9% of the measured loss of the non-striated conductor atf = 11.3 Hzand H/Hcc = 8.8 (Hcc = Ic/πwc;Ic: criticalcurrent, wc: conductor width). Even though the coupling loss component increases the magnetization lossin the striated conductor, the AC loss reduction by striation is still apparent even at 171.0 Hz.The transverse resistance between filaments estimated by a four-probe measurement was38 µΩ for 1 m at 80 K. The coupling length estimated using this transverse resistance is muchlonger than the sample length even at 171.0 Hz, suggesting that the filaments in the striatedconductor are far from ‘completely coupled’ or ‘saturated’.

Configuration and calibration of pickup coils for measurement of ac loss in long superconductors

Pickup coils are widely used for measurements of magnetic susceptibility and hysteretic losses in magnetic and superconducting materials. A general formulation for the calibration of such pickup coils with different geometries is presented. Although the procedure described here is general and can be applied to any coil and sample, special emphasis has been placed on the calibration of saddlelike coils usually used to measure ac losses of long superconductors under ac fields perpendicular to their long dimension. Numerical simulations and experimental measurements have been carried out in order to determine the geometrical limitations of the pickup coil/sample configurations. This is especially important when simple coils of small dimensions and number of turns are used and/or samples of high demagnetization factor are measured. Superconductors of different geometry, in particular, wires and tapes under parallel and perpendicular fields, have been analyzed.

Metrological Support of Measurements of Magnetic Losses in Magnetically Soft Materials in the Sinusoidal Regime of Remagnetization

The modern state of measurements of magnetic losses and their metrological support is briefly reviewed. The reasons of the wide propagation and the high effectiveness of using standard samples of magnetically soft materials are explained. The state of standardization in this form of measurements is characterized and the future trend of the development of the measurement chain is demonstrated.

Magnetic loss measurement and calculation of a DC/DC converter

The use of a tapped inductor in the classical sepic converter leads to a high step-down ratio thus avoiding the extreme duty cycles of the active switch and the high peak currents in the active and passive switches. The function and some stress data of such a converter are summarized and the flux density and the current through the inductor during start-up are measured and simulated by the energetic model of ferromagnetic hysteresis and the magnetic losses of the inductors are calculated.

Collisionless fast electron losses in magnetic toroidal ripples during lower hybrid current drive in Tore Supra

A consistent estimation of the losses of collisionless fast electrons driven by the lower hybrid wave and trapped in magnetic ripples in the Tokamak Tore Supra [Equipe TORE SUPRA, in Proceedings of the 15th Conference on Plasma Physics and Controlled Nuclear Fusion Research, Seville (International Atomic Energy Agency, Vienna, 1995), Vol. 1, IAEA-CN-60/A1-5, p. 105], is carried out using a two-dimensional relativistic bounce-averaged Fokker–Planck solver. A reasonable agreement is found between the simulations and the experimentally observed results obtained by the diagnostic named DRIPPLE (Diagnostic-Ripple) dedicated to magnetic ripple loss measurements. The analysis shows that the radial profile of the ripple loss current is dominated by the shape of the supertrapped domain in momentum space, and is therefore weakly dependent on the lower hybrid wave power absorption.

Magnetization loss measurements of Bi-2212 round wires fabricated by stranded-and-formed method

Round high Tc superconducting wires are sometimes preferred to flat tapes, because they are easy to assemble to obtain large current carrying capacity, and their performance in the external magnetic field is isotropic. Ag- or Ag/Au-sheathed Bi-2212 round wires were fabricated by the stranded-and-formed method. In this method, first, 54 filaments are bundled to make a segment, and then, three segments are stranded, drawn, and formed to a final round-shape wire. Advantages of the round wires fabricated by the stranded-and-formed method include higher tolerance against bending strain and higher critical current density than usual round wires. Another potential advantage of this type of round wires is the reduction of AC losses due to their multiply twisted structures. The magnetization losses of four types of the Bi-2212 round wire with multiply twisted structure were measured. The effect of the multiply twisted structure for the AC loss reduction was confirmed by the experimental results.

Magnetization and AC loss in a superconductor with an elliptical cross-section and arbitrary aspect ratio

An analytical approximation is developed for the magnetization of an infinitely long superconductor with an elliptical transverse cross-section. The superconductor is modeled in the critical state with a critical current density that is not dependent on the magnetic field. The aspect ratio of the ellipse is varied from one (=circle) to infinitely large. The magnetic field is applied perpendicular or parallel to the broadest face. The analytical expression is compared with a more detailed model that utilizes a numerically optimized contour for the boundary of the saturated zone. The two methods are compared and the maximum error is estimated at 2% for the optimized contour approach and 5% for the analytical approximation. The analytical model is compared with a magnetization loss measurement on a high- T c superconducting tape with an aspect ratio of nearly 20. A good agreement is obtained for a magnetic field pointing perpendicular as well as parallel to the broadest face of the tape. An interesting result for the magnetic behavior determined for the ellipse is that it contradicts with the behavior that is predicted for an infinitely thin strip in perpendicular field. The difference is attributed to the two specific assumptions made in the thin strip model: the constant critical current density distribution across the tape and the magnetic-field profile that does not exclude unsaturated currents in the shielded zone.

AC loss in cored, stabrite-coated, superconducting cables in response to external compaction and variation of core thickness and width

AC loss due to coupling currents in a Rutherford cable can be modified by changing the interstrand contact resistance (ICR) by: adjusting the level of native oxidation of the strand, coating it, or by inserting a ribbon-like core into the cable itself. With regard to cored cables further effective-ICR adjustments can be achieved by changing: (i) the degree of compaction during manufacture, (ii) the thickness of the core at fixed overall thickness, and (iii) the width of the core. We report on the results of magnetic and calorimetric AC loss measurements on stainless-steel-cored stabrite cables which had been: (i) externally compacted by rolling to thicknesses of 0%, 6%, 9%, and 11% below the standard thickness, (ii) internally compacted by being furnished with cores of thicknesses 1 mil ( 25 μm ) and 2 mil ( 50 μm ), and (ii) furnished with cores whose widths, w core, were about 20%, 50%, 75% and 100% of the maximum available width. The measurements were made in applied AC fields that were directed perpendicular (face-on, FO) and parallel (edge-on, EO), respectively, to the broad cables faces. It was noted that: (i) the introduction of the core dramatically reduced the FO loss, (ii) core-induced compaction moderately increased the side-by-side ICR at higher curing temperatures and hence increased the EO loss, (iii) increases in either external or internal compaction still further increased the losses, particularly those in the FO direction (which of course had already been strongly core-suppressed). The loss results were interpreted in terms of the FO-measured effective ICRs, R ⊥,eff, which were found to decrease from 198 to 37 μΩ during the compaction of a 170 °C-heat treated (“cured”, HT) cored cable and from 38 to 10 μΩ in the case of a 200 °C HT one. With increase in the w core of a 170 °C HT cable R ⊥,eff increased from 2.5 to 123 μΩ , passing through 15 μΩ at a w core of 57% w core,max. The results show that there is an opportunity for achieving the LHC-target R ⊥,eff of 15±5 μΩ either by compacting the standard cored cable ( T f=200 °C) by 4–7% or by reducing the width of the core ( T f =170 ° C ) to within 57±7% of w max. We prefer the latter route since it exposes more of the strands to crossover-type current sharing.

AC losses in superconducting Ag/Bi-2223 composite tapes with interfilamentary barrier

Power dissipation in multifilamentary Ag/Bi-2223 composite tapes was measured using AC magnetization loss measurement method. In order to decrease the interfilamentary electromagnetic coupling currents in the tapes the filaments were separated by resistive ceramic barriers, made of Bi-2201 phase or Al 2O 3 powder. The tape samples used in this study were with twisted and untwisted filaments. The magnetization loss measurements were performed in a sinusoidally varying external magnetic field (parallel to the plane of a tape) and with a DC transport current flowing along a tape. The frequency range of the sinusoidal varying field was 11–115 Hz. Some anomalies in magnetic losses due to DC current flowing distributions are observed. The obtained results are compared with the critical state model predictions.

Advanced ac loss measurement methods for high-temperature superconducting tapes

Advanced ac loss measurement methods for superconducting tapes are described in detail and demonstrated on BSCCO/Ag (Bi2Sr2Ca2Cu3Ox with a Ag matrix) tapes in liquid nitrogen at 77 K. The aim of the measurements is to simulate the situation of a tape conductor in an electric power application like a transformer coil or a power cable. In this class of devices the conductor is fed with an alternating transport current and simultaneously exposed to an alternating magnetic field. In many devices the magnetic field vector points in a single direction but in some devices such as three-phase power cables and motors the magnetic field rotates around the conductor. In all cases described above an electromagnetic approach with pick-up coils and voltage taps is used to measure the ac loss. This method enables a separate study of magnetization loss and transport current loss when both the magnetic field and transport current are present simultaneously. The magnetization loss measurement setup for unidirectional and rotating magnetic field is described. The transport current loss measurement setup is described, focusing on the suppression of cross effects of ac transport current and ac magnetic field that disturb accurate measurements. Finally several relevant examples of the results obtained are shown.

Power dissipation in composite Ag/Bi-2223 tapes with twisted and untwisted filaments

Power dissipation in a set of multifilamentary Bi2223 silver sheathed composite tapes (with 61 filaments) was measured using AC magnetization and transport loss measurement techniques. In order to decrease the interfilamentary bridging and thus electromagnetic coupling, the space between filaments was considerably increased. The tape samples used in this study were with twisted (twist pitch 15 mm) and untwisted filaments. Critical currents were of the order of 55 Amps, as measured by a standard four-point technique, and corresponds to a critical current density of approximately 9 kA cm/sup -2/. The AC transport current losses were measured by a standard four-point lock-in method; in the range of-the transport current frequency of 40-160 Hz. The magnetization loss measurements were performed in a sinusoidally varying external magnetic field, at the frequency range of 11 to 155 Hz. The external magnetic field was oriented parallel to the plane of a tape. The obtained results are compared with theoretical predictions of the critical state model.

Coupling loss and contact resistance in cored stabrite cables-influences of compaction and variation of core width

AC loss due to coupling currents in a Rutherford cable can be modified by changing the interstrand contact resistance (ICS) by: adjusting the level of native oxidation of the strand, coating it, or by inserting a ribbon-like core into the cable itself. With regard to cored cables further effective-ICR adjustments can be achieved by changing: (i) the degree of compaction during manufacture; (ii) the thickness of the core at fixed overall thickness; and (iii) the width of the core. The authors report on the results of magnetic and calorimetric AC loss measurements on stainless-steel-cored stabrite cables which had been: (i) externally compacted by rolling to thicknesses of 0, 6, 9, and 11% below the standard thickness; (ii) internally compacted by being furnished with cores of thickness 1 mil (30 /spl mu/m) and 2 mil (50 /spl mu/m); and (iii) furnished with cores whose widths, w/sub core/, were about 20%, 50%, 75% and 100% of the maximum possible width. The measurements were made in applied AC fields that were directed perpendicular (face-on) and parallel (edge-on), respectively to the broad cables faces.