Search Results for external magnetic fields

This article describes the mechanisms involved in creating texture for various metal-fabrication processes, namely, solidification, deformation, recrystallization and grain growth, thin-film deposition, and imposition of external magnetic fields. It discusses two experimental and analytical approaches for experimental determination of texture: one using classical diffraction and pole figure measurement techniques and the other using individual orientation measurements. The article also provides information on microtexture, grain-boundary character, and texture gradients. It concludes with information on texture evolution through modeling.

Hyperthermia is a type of cancer treatment that requires directing a carefully controlled dose of heated nanoparticles to the cancerous tumor that leads to the destruction of cancer cells. Nanoparticles are used as the heat generating sources within the cancer cells and the tumors. The problem in controlling the temperature of nanoparticles is solved by the use of induction heating, which uses a high-frequency alternating magnetic field localized in the area of interest. This article provides an overview of this technique along with the description of its major components, namely, nanoparticles, induction heating setup, and magnetic field strength.

Electromagnetic problem solutions are based on the macroscopic theory of the continuous model for the electromagnetic field (EMF). It is described by a system of integral or partial differential equations for five vector quantities, namely, electric field strength, electric flux density, current density, magnetic field strength, and magnetic flux density. This article describes the behavior of the EMF by Maxwell's equations in integral or differential forms. It discusses the definition of potentials; methods of mathematical modeling; boundary conditions; and energy, power density, and electromagnetic forces.

This article discusses the principles and limitations of micromagnetic techniques, namely, magnetic Barkhausen noise (MBN) and magnetoacoustic emission (MAE). It also discusses various factors limiting the establishment of acceptance criteria for test components as they pertain to the successful application of MBN measurement and signal interpretation. The article provides an overview of basic magnetic phenomena and dynamics in ferromagnetic materials that underlie the origin of MBN emissions. It describes the changes in the domain structure of the ferromagnetic material under an applied external field. The relationship between uniaxial stress and angular-dependent strain is also discussed. The influence of stress on domain walls, and therefore, the generation of Barkhausen noise are described. The article also describes the directional and angular MBN measurements and provides information on detection, angular dependence, and advanced analysis methods of MBN emissions.

In an induction heating system, thermal and electromagnetic properties of heated materials make the greatest impact on the heat transfer and performance of induction heating process. This article focuses on major thermal properties, namely, thermal conductivity, heat capacity, and specific heat. It describes the two important electromagnetic properties, electrical resistivity (electrical conductivity) and magnetic permeability, which posses the most pronounced effect on the performance of the induction heating system, its efficiency, and selection of main design parameters. The article also discusses the magnetic properties of diamagnetic, paramagnetic, ferromagnetic, ferrimagnetic, antiferromagnetic, and metamagnetic materials.

Magnetic flux controllers are materials other than the copper coil that are used in induction systems to alter the flow of the magnetic field. This article describes the effects of magnetic flux controllers on common coil styles, namely, outer diameter coils, inner diameter coils, and linear coils. It provides information on the role of magnetic flux controllers for whole-body and local area mass-heating applications, continuous induction tube welding, seam-annealing inductors, and various induction melting systems, namely, channel-type, crucible-type, and cold crucible systems. The article also describes the benefits of the flux controllers for induction heat treating processes such as single-shot and scanning.

Magnetic field testing includes some widely used nondestructive evaluation methods to inspect magnetic materials for defects such as cracks, voids, and inclusions and to assess other material properties, such as grain size, texture, and hardness. This article discusses the principles of such defect detection, providing details on the origin, generation, and assessment of leakage field data. In addition, it discusses the metallurgical and magnetic properties of magnetic materials and the applications of magnetic field testing.

The discovery of the high-critical-temperature oxide superconductors has accelerated the interest for superconducting applications due to its higher-temperature operation at liquid nitrogen or above and thus reduces the refrigeration and liquid helium requirement. It also permits usage of the high-critical-temperature oxides in magnets or power applications in high-current-carrying wire or tape with acceptable mechanical capability. This article discusses the powder techniques mainly based on the production of an oxide powder precursor, which is then subjected to various processing, including powder-in-tube processing, vapor deposition processing, and melt processing. It further discusses the microstructural, anisotropy and weak link influences on these processes.

Premanent magnet refers to solid materials that have sufficiently high resistance to demagnetizing fields and sufficiently high magnetic flux output to provide useful and stable magnetic fields. Permanent magnet materials include a variety of alloys, intermetallics, and ceramics. This article discusses the composition, properties, and applications of permanent magnetic materials, such as hysteresis alloys used in motors. It primarily focuses on the stability of magnetic fields that influences reversible and irreversible losses in magnetization with time, and the choice of magnet material, component shape and magnetic circuit arrangement.

Gears are a common part type for applications of the magnetic Barkhausen noise (MBN) techniques for nondestructive inspection. This article discusses the typical applications for MBN techniques, namely, detection of grinding retemper burn, evaluation of residual stresses, and detection of heat treatment defects, including the evaluation of case depth.

Induction heating is a combination of several interrelated physical phenomena, including heat transfer, electromagnetics, and metallurgy. This article presents a brief review of different heat transfer modes, namely, heat conduction, thermal radiation, and convection. It focuses on the specifics of induction heating and heat treating applications. The article discusses the nonlinear and interrelated nature of a particular heat transfer phenomenon, physical property, and skin effect. It also presents simple case studies and general physical laws governing different heat transfer modes. The article also discusses the basic concepts of direct current and alternating current circuits, and reviews the theory of electromagnetic fields.

Superconductivity has been found in a wide range of materials, including pure metals, alloys, compounds, oxides, and organic materials. Providing information on the basic principles, this article discusses the theoretical background, types of superconductors, and critical parameters of superconductivity. It discusses the magnetic properties of selected superconductors and types of stabilization, including cryogenic stability, adiabatic stability, and dynamic stability. The article also focuses on alternating current losses in superconductors, including hysteresis loss, penetration loss, eddy current loss, and radio frequency loss. Furthermore, the article describes the flux pinning phenomenon and Josephson effects.

This article discusses the chief magnetic characteristics of permanent magnet materials. It provides a detailed description on nominal compositions; principal magnet designations; magnetic, physical, and mechanical properties; selection criteria; and applications of the permanent magnet materials, which include magnet steels, magnet alloys, alnico alloys, platinum-cobalt alloys, cobalt and rare-earth alloys, hard ferrites, iron-chromium-cobalt alloys, and neodymium-iron-boron alloys.