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A Conceptual Introduction to the Fundamentals of Magnetic Fields, Magnetic Materials, and Magnetic Particles for Biomedical Applications
Published in Jeffrey N. Anker, O. Thompson Mefford, Biomedical Applications of Magnetic Particles, 2020
Magnetic materials that retain a magnetization in the absence of an applied magnetic field are sometimes known as permanent magnets (as opposed to “temporary” magnets, which are magnetized only in the presence of an applied magnetic field and lose their magnetization when the applied field is reduced to zero). Permanent magnets must necessarily exhibit the phenomenon of magnetic hysteresis as shown in Figure 2.11. The magnetization of a permanent magnet in zero applied magnetic field is the remanent magnetization. Heating a magnetized specimen in zero applied field tends to reduce the magnetization (Figure 2.12). The temperature at which the remanent magnetization is reduced to zero is known as the Curie temperature (Tc). Heating a sample above its Curie temperature is a way of demagnetizing it. The process is known as thermal demagnetization.
Magnetic Circuits
Published in Zeki Uğurata Kocabiyikoğlu, Electromechanical Energy Conversion, 2020
This is associated with the phenomenon of hysteresis. Hysteresis loss is due to heat that occurs in reversing the directions of the magnetic domains when trying to magnetise ferromagnetic materials. All ferromagnetic materials exhibit this phenomenon called hysteresis which is defined as the lagging of magnetisation or flux density (B) behind the magnetising force (H) (Figure 2.46).
Magnetic Separation in Integrated Micro-Analytical Systems
Published in Nguyễn T. K. Thanh, Clinical Applications of Magnetic Nanoparticles, 2018
Magnetization is the vector field induced in a material when it is exposed to a magnetic field. When a magnetic field H is imposed to a sample, its response in magnetization M is characterized by the magnetization hysteresis loop, as shown in Figure 11.1. As H increases, an initially unmagnetized material reaches the saturated state (M = Ms), and remains magnetized (M = Mr) when H is reduced to 0. Ms and Mr are called the saturated magnetization and the remanence. The coercive field H = −Hc is needed to change the sign of M. Based on Ms, Mr, and Hc in the hysteresis curve, magnetic materials are classified into soft or hard magnetic materials. Hard magnetic materials, or hard magnets, have broad magnetization loops and retain their magnetization in zero magnetic field. Soft magnetic materials, or soft magnets, have narrow loops and lose their magnetization when the magnetic field is removed. Soft magnetic materials are sometimes called electromagnets because they are often used in electrically induced magnets whose magnetization can be actively switched or flipped.
Quantitative Analysis of Aeroengine Turbine Disk Surface Crack under Natural Magnetic Field
Published in Research in Nondestructive Evaluation, 2022
Ping Fu, Bo Hu, Weitao Luo, Shaofei Wang, Xiwang Lan
Geomagnetic field is a natural excitation source with a magnetic field intensity of approximately T [25]. Material in the magnetic field shows certain magnetism, which is called magnetization. Paramagnetic, diamagnetic, and ferromagnetic materials can be magnetized by the geomagnetic field [26]. The principle of weak magnetic detection is shown in Figure 1. The geomagnetic field can be regarded as the excitation source of weak magnetic detection. When the test block is placed in the geomagnetic environment, if the relative permeability of the defect is less than that of the test block itself (i.e., ), then the magnetoresistance increases in the local area near the defect because the magnetic resistance is inversely proportional to the relative permeability. The defect repels the magnetic induction line, then the collected magnetic induction intensity curve shows a downward convex magnetic anomaly. If the relative permeability of the defect is greater than that of the test block itself (i.e., ), and the defect attracts the magnetic induction line, then the collected magnetic induction intensity curve shows an upward convex magnetic anomaly.
Multiphysics finite element model for the computation of the electro-mechanical dynamics of a hybrid reluctance actuator
Published in Mathematical and Computer Modelling of Dynamical Systems, 2020
F. Cigarini, E. Csencsics, J. Schlarp, S. Ito, G. Schitter
The electromagnetic material parameters of the steel have to be defined to compute the influence of the eddy currents and of the hysteresis on the electromagnetic dynamics. Eddy currents arise in conductive materials in response to an external variable electromagnetic field. The intensity of these currents is dependent on the electrical conductivity of the material [34]. Hysteresis is due to the cycle of magnetization and demagnetization of the ferromagnetic material as a result of the variable electromagnetic field. This is graphically represented by the hysteresis loop (shown in Figure 5 for EN 10025 S235JR), which is univocally defined by the intrinsic coercivity , the remanence and the magnetizing curve (dashed line in Figure 5). In order to compute the effect of hysteresis on the torque in the time domain, the magnetizing curve, as well as the values of , and need to be defined for EN 10025 S235JR [26,35] and are listed in Table 2.
Interpreting geology from geophysics in poly-deformed and mineralised terranes; the Otago Schist and the Hyde-Macraes Shear Zone
Published in New Zealand Journal of Geology and Geophysics, 2019
Casey C. Blundell, Robin Armit, Laurent Ailleres, Steven Micklethwaite, Adam Martin, Peter Betts
Two forms of magnetisation are possible; induced and remanent magnetisation (also known as remanence). Induced magnetisation is proportional to the magnetic susceptibility of the material being magnetised by a ratio that depends on magnetic permeability (μ), a factor which describes how easily a magnetic field can exist within a material (Dentith and Mudge 2014). Induced magnetisation may have the same orientation as the Earth’s magnetic field. Magnetic susceptibility describes the degree of magnetisation of a material in response to an applied external magnetic field. The higher a material’s magnetic susceptibility (and/or a stronger external magnetic field), the stronger the magnetism induced in the material. Remanent magnetisation is carried by ferromagnetic minerals (magnetite, monoclinic pyrrhotite), may have any orientation and be several orders of magnitude larger than the induced magnetisation. Further, the amplitude and shape of a magnetic anomaly may be stongly influenced by remanent magnetisation, and remanence can be affected by metamorphism and deformation (Airo 2015). The ratio of remanent to induced magnetisation (Konigsberger ratio) can be used to predict the contribution of induced and remanent sources to the anomaly, and consequently be used to predict magnetic mineralogy (Airo 2015). Typical magnetic susceptibilities for lithologies in the study area are shown in Figure 3.