This work is an experimental study of the evolution of magnetic losses in DC-04 steel under static mechanical stress. The material was subjected, in the elastic regime, to uniaxial stress at levels ...from -90 MPa to 90 MPa, and the evolution of magnetic losses, from quasi-static regime to 300 Hz (under controlled sinusoidal magnetic induction), was monitored. The analysis of the experimental results (remanent induction, coercive field, different component of losses) shows the non-trivial dependency of the stress-loss relationship to frequency. A loss separation analysis was performed to interpret the results. Considering the skin effect and its evolution with stress, hysteresis, eddy current, and anomalous losses are analyzed. The observed variations with frequency are then attributed to the change in the balance between the different components of losses, each showing a different sensitivity to stress depending on frequency. The study provides a phenomenological description of the frequency-dependent loss behaviour of magnetic materials under tensile and compressive mechanical stress.
•Magnetic characterization of Mn-Zn sintered ferrites up to 160 °C from DC to 1 GHz.•Increased doping by CaO, Nb2O5, ZrO2, and SiO2 favors loss reduction.•The temperature-dependent phenomenology has ...been assessed.•The role of eddy currents and spin damping are demonstrated.•The temperature dependent effective magnetic anisotropy < Keff > is calculated.
We investigate the effect of different doping schemes on the broadband magnetic losses and their temperature dependence in Mn-Zn ferrites. CaO, Nb2O5, ZrO2, and SiO2 are added with increasing proportions to TiO2-doped prefired powders and, after sintering at either 1275 °C or 1300 °C, the obtained ring samples are tested versus frequency f (DC-1 GHz) and peak polarization Jp (2 mT – 200 mT) up to T = 160 °C. Appropriately enhanced impurity contents are shown to induce further decrease of the energy loss in materials already prepared for best performance at high temperatures (140 – 160 °C). This behavior can be hardly ascribed to the impurity-related increase of the electrical resistivity brough about by extra-doping, being it rather connected to a corresponding monotonical decrease of the effective magnetic anisotropy < Keff > with T. The decreasing anisotropy makes the balance between the contributions of domain wall (dw) displacements and reversible rotations to the magnetization process evolving in favor of the latter. The energy loss correspondingly develops with frequency and peak polarization in a complex fashion, according to the specific dissipative mechanisms sustained by the spins precessing either inside the moving walls or in the bulk. A dividing line in the (Jp − f) plane is identified, which separates dominant dw- and rotation-generated losses. It moves downward (i.e. lower f) with increasing temperature, the higher T the lower the frequency at which the rotations, theoretically assessed via the Landau-Lifshitz equation, supersede the domain wall contribution. Once accomplished, however, the transition to rotations can lead, according to the theoretical model, to higher losses when moving to higher temperatures. Following the experimental trend of the complex resistivity versus frequency at different T values, the calculations and the experiments show that eddy currents start to contribute to the energy loss, in the 5 mm thick ring samples, around a few MHz, accounting for about 50 % of measured loss beyond some 50 MHz. The chief dissipative process at applicative frequencies and induction values is therefore identified with spin damping, to which the generalized loss decomposition method can be applied.
We propose an innovative fast 3D approach for the accurate computation of electromagnetic losses in the metallic armors of submarine cables. In order to develop a scheme that is more efficient with ...respect to most commonly used 3D simulation methods, typically based on the Finite Element Method (FEM), we proceed by proposing a suitable discretization of an integral formulation. In the proposed approach, each wire of the armor is modeled as filamentary which leads to a dramatic reduction in the number of degrees of freedom in the numerical model and in the overall computational burden. The new approach can be applied to cables where armor wires are stranded either with opposite (contralay) or same (equilay) orientation as the central phase cables. The efficiency of the proposed method is especially notable in latter case for which FEM is very demanding due to the extremely large model size. The reduction in both computation times and memory footprint allows performing extensive sensitivity studies with respect to geometrical parameters and material properties that would be otherwise unaffordable with existing 3D methods.
Abstract
In this review article we present basic principles of magnetically induced heat generation of magnetic nanoparticles for application in magnetic particle hyperthermia. After explanation of ...heating mechanisms, the role of particle-particle as well as particle-tissue interactions is discussed with respect to achievable heating power of the particles inside the tumour. On the basis of heat transfer theory at the micro-scale, the balance between generated and dissipated heat inside the tumour and the resulting damaging effects for biological tissue is examined. The heating behaviour as a function of tumour size is examined in combination with feasible field strength and frequency. Numerical calculations and experimental investigations are used to show the lower tumour size limit for tumour heating to therapeutically suitable temperatures. In summary, this article illuminates practical aspects, limitations, and the state of the art for the application of magnetic heating in magnetic particle hyperthermia as thermal treatment of small tumours.
In this work, polypyrrole-coated ZnFe2O4 (ZnFe2O4@PPy) nanocomposites were successfully synthesized via a simple in-situ polymerization process, then evaluated as electromagnetic wave (EMW) absorbers ...over the 2–40 GHz frequency range. The ZnFe2O4@PPy nanocomposites exhibited excellent EMW absorption properties, including very low reflection losses (−42.31 dB at 30.24 GHz and a thickness of 2.5 mm) and a broad absorption bandwidth of 28.20 GHz (from 9.66 to 37.86 GHz). The EMW absorption properties of the ZnFe2O4@PPy nanocomposites could be adjusted by changing the PPy shell thickness and also the thickness of the absorber (1–2.5 mm). The excellent microwave absorption performance of the ZnFe2O4@PPy nanocomposites is attributable to the synergistic effects of magnetic losses (ZnFe2O4 nanoparticles), dielectric losses (ZnFe2O4 and PPy) and interfacial relaxation losses at ZnFe2O4-PPy interfaces.
This paper presents an effective design method for inductors which is based on the multi-objective optimization accelerated by the artificial neural network (ANN). In the learning phase prior to the ...optimization phase, ANN is trained for 1000 input-output data sets obtained from the finite-element analysis for randomly generated dimensional parameters. The magnetic hysteresis of the ferrite core is modeled by the play model to evaluate the hysteresis losses. The multi-objective optimization problems are solved by the genetic algorithm in which the magnetic loss is effectively computed by the trained ANN to reduce the core volume as well as magnetic loss. The Pareto solutions for an EI-shaped ferrite core are obtained for different inductances. It is shown that the proposed method works much faster than the conventional optimization, and the magnetic loss and the inductance of the optimized inductor agree well with the experimental results.
Accurately analyzing power losses in inductive wireless power transfer including lossy magnetic sheet is challenging, as coils have mutual influences on each other's power dissipation. This paper ...proposes a precise analytic model for inductive wireless power transfer (WPT) with lossy magnetic sheets. Combining a partial element equivalent circuit (PEEC) with a 2-port network, both self- and mutual impedances of coupled coils are accurately calculated considering eddy current effects. Furthermore, the proposed PEEC-based model incorporates the complex permeabilities of lossy magnetic sheets, thus addressing a critical gap in previous studies that have not considered magnetic sheets with losses in their analysis. The suggested model is verified with finite element method (FEM) simulations and measurements. Compared with an FEM simulator, the proposed model calculates impedances about 31 times faster, substantially reducing the number of meshes. Finally, the ohmic and magnetic losses in coil windings and magnetic sheets are investigated with the proposed model, demonstrating that the phase adjustment of currents using the compensation capacitor is effective to reduce the losses caused by eddy currents and lossy magnetic sheets. The proposed model offers more detailed and accurate loss analysis, compared to conventional methods based on circuit analysis.
Calculation of core loss is essential in the design of magnetic components especially in high frequency applications. Existing empirical approaches still present some limitations such as the ...inaccuracy and the difficulty to apply under nonsinusoidal waveforms. In particular, these methods fail to predict core loss with low duty cycle and when there is a significant change in the frequency. In addition to that, the use of different solutions of Steinmetz parameters for different frequency range can present some discontinuity problems at the boundary of each frequency interval. The main contribution of this study is to develop a new empirical method to estimate magnetic core losses under nonsinusoidal induction. The developed method is enough accurate and user-friendly to apply by designers. The effects of the frequency and the duty cycle are considered. The developed model is verified and compared with the improved generalized Steinmetz equation and measurement data from literature with 3F3 and N67 ferrite materials.
Aim to improve the power efficiency of the dual-active-bridge (DAB) dc-dc converter, an efficiency optimization scheme with triple-phase-shift (TPS) modulation using reinforcement learning (RL) is ...proposed in this article. More specifically, the Q-learning algorithm, as a typical algorithm of the RL, is applied to train an agent offline to obtain an optimized modulation strategy, and then the trained agent provides control decisions online in a real-time manner for the DAB dc-dc converter according to the current operating environment. The main objective is to obtain the optimal phase-shift angles for the DAB dc-dc converter, which can achieve the maximum power efficiency by reducing the power losses. Moreover, all possible operation modes of the TPS modulation are considered during the offline training process of the Q-learning algorithm. Thus, the cumbersome process for selecting the optimal operation mode in the conventional schemes can be circumvented successfully. Based on these merits, the proposed efficiency optimization scheme using the RL can realize the excellent performances for the whole load conditions and voltage conversion ratios. Finally, a 1.2-KW prototyped is built, and the simulation and the experimental results demonstrate that the power efficiency can be improved by using the optimization scheme based on the RL.
Manganese-zinc (Mn-Zn) ferrites are the primary choice for high-frequency and high-power magnetic components. Optimum material selection is essential for high-performance magnetic component design. ...However, the manufacturers' material specifications usually do not provide sufficient information to optimize the design. Complex permeability and permittivity, as well as specific power loss, are typically provided as one value, regardless of the core shape and size. Magnetic component design based on these incomplete specifications can result in a poorly optimized component. This article proposes methods to determine the properties of Mn-Zn ferrite at high frequencies, with tests up to 20 MHz. This article also presents experimental complex permeability and permittivity frequency characteristics for four ferrite materials: 3E10, 3F36, 3E65, and 3C95. The resulting fitted parameters for the equivalent-circuit model can be used in any design algorithm or simulation tool. The impacts of physical size, temperature and force on complex permeability and permittivity are also considered.
