Biblio

The use of rare-earth elements in permanent magnets rises economic, environmental and supply-chain related concerns. Instead, ferrite magnets have been researched as an alternative. The magnetic flux concentration capacity of the Spoke Type Permanent Magnet Synchronous Motor (PMSM) and the low magnetic remanence of the ferrite magnet make them complementary strategies towards the desirable performance. However, if restricted to conventional manufacturing processes and materials, the mechanical design is a challenging step of the development of these machines. This paper explores how mechanical constraints impact electromagnetic performance. To access the interdependency of the performance and the mechanical constraints, finite element analyses are done both in the mechanical and electromagnetic domain. The results show that the mechanical constraints have an impact on the performance, although it is possible to reduce it by adapting the design to the electromagnetic and mechanical properties of the electrical steel.

This paper presents a new micro linear actuator design. The North-South (NS) permanent magnet array configuration is assembled as the mobile part. The fixed part is designed to two-phase planar coils with no crossings avoiding interferences between overlapped conductors. The analytical calculation of the permanent magnet array verifies the feasibility of the finite element simulation. And then electromagnetic optimizations based on simulation to maximize the average thrust and minimize thrust ripple. In order to deal with millimeter level structure design, a microfabrication approach is adopted to process the new micro linear actuator in silicon material. The new micro linear actuator is able to perform millimeter level displacement strokes along a single axis in the horizontal plane. The experimental results demonstrate that the new micro linear actuator is capable of delivering variable strokes up to 5 mm with a precision error of 30 μm in position closed loop control and realizes the maximum velocity of 26.62mm/s with maximum error of 4.92%.

This paper reports electroplated CoPt permanent magnets samples yielding thicknesses up to 100 μm, deposition rates up to 35 μm/h, coercivities up to 1000 kA/m (1.25 T), remanences up to 0.8 T, and energy products up to 77 kJ/m3. The impact of electroplating bath temperature and glycine additives are systematically studied. Compared to prior work, these microfabricated magnets not only exhibit up to 10X increase in thickness without sacrificing magnetic performance, but also improve the areal magnetic energy density by 2X. Using a thick removeable SU-8 mold, these high-performing thick-film magnets are intended for magnetic microactuators, magnetic field sensors, energy conversion devices, and more.

This paper presents a study and analysis of flux linkage performance on 12/8 pole doubly salient permanent magnet machine in square envelope conventional. Analyzed model was using a finite element method. The investigated model was constructed by changing the size of the structure as the main parameters of the speed 500 rpm, PM coercivity 910 kA/m, PM remanence 1.2 T, copper loss 30 W, turns per coil 45, and stator side length 100 mm. The study and analysis of flux linkage, induced voltage, and torque are also included in this paper.

High-temperature magnetic properties of the anisotropic bulk SmCo7/Fe(Co) nanocomposite magnets prepared by multistep deformation have been investigated and compared with the corresponding isotropic nanocomposites. The anisotropic SmCo7/Fe(Co) nanocomposites with a Fe(Co) fraction of 28% exhibit much higher energy products than the corresponding isotropic nanocomposites at both room and high temperatures. These magnets show a small remanence (α = -0.022%/K) and a coercivity (β = -0.25%/K) temperature coefficient which can be comparable to those of the conventional SmCo5 and Sm2Co17 high-temperature magnets. The magnetic properties of these nanocomposites at high temperatures are sensitive to the weight fractions of the Fe(Co) phase. This paper demonstrates that the anisotropic bulk SmCo7/Fe(Co) nanocomposites have better high-temperature magnetic properties than the corresponding isotropic ones.

The discovery of the interstitial rare earth nitride Sm2Fe17N3 came about seven years after the discovery of the rare earth iron boride Nd2Fe [1],[2], and the nitride initially seemed to offer intrinsic magnetic properties that were superior (Curie temperature TC, magnetocrystalline anisotropy K1 or comparable (spontaneous magnetization Ms to those of its illustrious predecessor. However, the promise of the new material to seriously challenge Nd2Fe14B was not realized. The 2:17 nitride powder, prepared by a low-temperature gas-phase interstitial modification process proved difficult to orient and worse still, it lost its nitrogen at the temperatures needed to process dense sintered magnets [3]. Attempts at explosive compaction [4] or spark sintering [5] failed to yield material with good enough coercivity. Nevertheless, work continued in Japan and China to develop a coercive powder that could be used for bonded magnets. An early realization was zinc-bonded Sm2Fe17N3 [6] with an energy product of 84 kJm3 but a rather low coercivity of 480 kAm-1, less than 5 % of the anisotropy field (Ha = 2K1/Ms ≈ 11 MAm-1). The anisotropy field of Nd2Fe14B is significantly less (6 MAm-1) yet several decades of intensive development have led to higher values and continuous improvements of the coercivity, even in unsubstituted material. Historical experience with permanent magnets shows that a long period of materials development is needed to arrive at the best composition and processing conditions for a microstructure that allows the hard magnetism to be optimized. Coercivities of about 25% of the anisotropy field are ultimately achieved. Here we compare the magnetic properties of melt-spun material. Our Nitroquench powder, produced by Daido Steel, was in the form of flakes 10 μm thick and up to 100 μm in diameter. A crystal-lite size of approximately 15 nm deduced from Scherrer broadening of the X-ray reflections. Composition was checked by EDX microprobe analysis. Hysteresis loops have been measured in applied fields of up to 14 T, at room temperature and at 4 K.The material exhibits a room-temperature coercivity of 690 kAm-1 after saturation in 14 T, with a remanence of 700 kAm-1 in zero applied field and an extrapolated saturation magnetization of 1230 kAm-1. The remanence ratio Mr/Ms of 63% when the remanence is corrected to zero internal field, is reflected in a preferred orientation seen in the X-ray powder diffraction patterns and in 57Fe Mössbauer spectra of magnetized powder. Spectra obtained after saturation of an immobilized powder absorber either in-plane or perpendicular to the sample plane exhibit distinctly different relative intensities of the ΔM=0 absorption lines. The maximum energy product for the powder, assuming full density, is 162 kJm-3. The remanence enhancement is attributed to fact that the nanocrystallite size is not much greater than the exchange length. Melt-spun Sm-Fe-N powder has superior corrosion resistance and thermal stability compared to melt-spun Nd-Fe-B. The Nitroquench powder may be used to produce polymer-bonded magnets with an energy product in excess of 100 kJm-3.

This article is dedicated to the study of an innovative architecture for the conversion of renewable marine energy into electrical energy. It consists of a Permanent Magnet Synchronous Generator (PMSG) combined with a three-phase Vienna rectifier. This last converter is not reversible but has the advantage of minimizing the number of active switches. This improves the operational reliability of the chain, which is necessary in the context of marine energy exploitation where access to the installations is not easy. The study focuses on the behavior analysis of electrical chain conversion, and the study of phase and neutral current according to the conduction’s states of the switches of the Vienna rectifier is being investigated. Despite the high non-linearity of this architecture, this control is made possible through to the dynamic performance and control of the maximum switching frequency of the self-oscillating controller called the Phase-Shift Self-Oscillating Current Controller (PSSOCC).

Back-end-of-line compatible integration of NdFeB-based micro magnets onto 8 inch Si substrates is presented. Substrate conditioning procedures to enable further processing in a cleanroom environment are discussed. It is shown that permanent magnetic structures with lateral dimensions between 25μm and 2000μm and a depth up to 500μm can be fabricated reliably and reproducibly with a remanent magnetization of 340mT at a standard deviation as low as 5% over the substrate. To illustrate post-processing capabilities, the fabrication of micro magnet arrangements embedded in silicon frames is described.

This paper investigates the temperature demagnetization modeling method for permanent magnets (PM) in permanent magnet synchronous linear motor (PMSLM). First, the PM characteristics are presented, and finite element analysis (FEA) is conducted to show the magnetic distribution under different temperatures. Second, demagnetization degrees and remanence of the five PMs' experiment sample are actually measured in stove at temperatures varying from room temperature to 300 °C, and to obtain the real data for next-step modeling. Third, machine learning algorithm called extreme learning machine (ELM) is introduced to map the nonlinear relationships between temperature and demagnetization characteristics of PM and build the demagnetization models. Finally, comparison experiments between linear modeling method, polynomial modeling method, and ELM can certify the effectiveness and advancement of this proposed method.

This paper presents a new class of high-performance permanent micro-magnets based on the controlled assembly of cobalt nanorods for the electromagnetic transduction of MEMS. Micromagnets are fabricated using a low temperature fabrication process that yields a dense material exhibiting high coercive field and remanence to saturation magnetization ratio. The cartography of the magnetic induction produced by the sub-millimeter size magnets was obtained using a scanning Hall effect micro-probe microscope. Silicon microcantilevers placed in the vicinity of these magnets were successfully actuated using the Lorentz force with low currents. The good signal to noise ratio measured at resonance demonstrates the potentiality of these nanostructured micro-magnets.

Having significant role in the storing, delivering and conversion of the energy, the permanent magnets are key elements in the actual technology. In many applications, the gap between ferrites and rare earths (RE) based sintered permanent magnets is nowadays filled by RE bonded magnets, used in more applications, below their magnetic performances. Therewith, the recent trends in the RE market concerning their scarcity, impose EU to consider alternative magnets (without RE) to fill such gap. The paper presents the chemical synthesis of the exchange coupled SrFe12O19/CoFe2O4 nanocomposites, based on nanoferrites. The appropriate annealing leads to the increasing of the main magnetic characteristics, saturation magnetization MS and intrinsic coercivity Hc, in the range of 49 - 53 emu/g, respectively 126.5 - 306 kA/m. The value reached for the ratio between remanent magnetization and saturation magnetization is higher than 0.5, fact that proved that between the two magnetic phases occurred exchange interaction.

Alternatives to rare earth permanent magnets, such as alnico, will reduce supply instability, increase sustainability, and could decrease the cost of permanent magnets, especially for high-temperature applications, such as traction drive motors. Alnico magnets with moderate coercivity, high remanence, and relatively high-energy product are conventionally processed by directional solidification and (significant) final machining, contributing to increased costs and additional material waste. Additive manufacturing (AM) is developing as a cost effective method to build net-shape 3-D parts with minimal final machining and properties comparable to wrought parts. This paper describes initial studies of net-shape fabrication of alnico magnets by AM using a laser engineered net shaping (LENS) system. High-pressure gas atomized pre-alloyed powders of two different modified alnico “8” compositions, with high purity and sphericity, were built into cylinders using the LENS process, and followed by heat treatment. The magnetic properties showed improvement over their cast and sintered counterparts. The resulting alnico permanent magnets were characterized using scanning electron microscopy, energy dispersive spectroscopy, electron backscatter diffraction, and hysteresisgraph measurements. These results display the potential for net-shape processing of alnico permanent magnets for use in next generation traction-drive motors and other applications requiring high temperatures and/or complex engineered part geometries.

We present an optimization approach that can be employed to calculate the globally optimal segmentation of a 2-D magnetic system into uniformly magnetized pieces. For each segment, the algorithm calculates the optimal shape and the optimal direction of the remanent flux density vector, with respect to a linear objective functional. We illustrate the approach with results for magnet design problems from different areas, such as a permanent magnet electric motor, a beam-focusing quadrupole magnet for particle accelerators, and a rotary device for magnetic refrigeration.

This paper presents the analysis and the design of a ferrite permanent magnet synchronous generator (FePMSG) with flux concentration. Despite the well-known advantages of rare earth permanent magnet synchronous generators (REPMSG), the high cost of the rare earth permanent magnets represents an important drawback, particularly in competitive markets like the wind power. To reduce the cost of permanent magnet machines it is possible to replace the expensive rare earth materials by ferrite. Once ferrite has low remanent magnetization, flux concentration techniques are used to design a cheaper generator. The designed FePMSG is compared with a reference rare earth (NdFeB) permanent magnet synchronous generator (REPMSG), both with 3 kW, 220 V and 350 rpm. The results, validated with finite element analysis, show that the FePMSG can replace the REPMSG reducing significantly the active material cost.