Electromagnetic materials

Case Study 10 Terahertz Imaging for Electromagnetic Materials Research... 

Magnetic hysteresis loops (a) electromagnetic material and (b) permanent magnetic material. 

Engdahl, G. A time dependent radially resolved simulation model of giant magnetostrictive materials, in Mechanical Modelling of New Electromagnetic Materials, R.K.T Hsieh, Elsevier, pp. 131-138 (1990)... 

The full derivation of this approach can be found in ref. 29. In summary, from Maxwell s equations we first consider the general case of a 4x4 transfer matrix for electromagnetic materials, followed by the specific case of a screwlike electrical axis. 

An electromagnetic material supplied as a molded or extruded preform located at the bond interface. Special hot melt or liquid systems can also be employed. 

The distance between the work coil and the electromagnetic material should be as close as possible, generally, between 1/32 in. to 3/32 in. In many applications, the work coil is set into a non-conductive holding fixture and acts as a pressure medium with direct contact on the surface of the plastic to be bonded. 

The electromagnetic material at the bond interface becomes molten when activated and flows. This flow can be directed, if desired, to fuse a greater interfacial bond area than the original contact surface of the electromagnetic layer. However, ideally, the molten flow should be contained and subjected to an internal pressure against the nonconductive thermoplastic bonding surfaces. Thus, a void area should be provided. ... 

Electromagnetic materials are micron-sized ferromagnetic powders of different types, particle sizes, and concentrations. They can be metallic (iron, stainless steel) or nonmetallic, ceramic (ferrite) material. For bonding thermoplastics, they are enclosed in a thermoplastic matrix that is compatible with the plastics being joined.f ]f ]f ]... 

Figure 14.33 Various forms of electromagnetic materials used in induction welding.

Figure 14.34 A typical induction welder, showing components of the welding process induction generator, work coils, fixtures or nests, and the electromagnetic material. The inset shows the joint area, with placement of work coils and electromagnetic material.

The sample should be liquid or in solution. It is pumped and nebulized in an argon atmosphere, then sent through a plasma torch that is, in an environment where the material is strongly ionized resulting from the electromagnetic radiation produced by an induction coil. Refer to the schematic diagram in Figure 2.8. 

The development of Remote Field Eddy Current probes requires experience and expensive experiments. The numerical simulation of electromagnetic fields can be used not only for a better understanding of the Remote Field effect but also for the probe lay out. Geometrical parameters of the prohe can be derived from calculation results as well as inspection parameters. An important requirement for a realistic prediction of the probe performance is the consideration of material properties of the tube for which the probe is designed. The experimental determination of magnetization curves is necessary and can be satisfactory done with a simple experimental setup. 

H.A. Sabbagh and R.G. Lautzenheiser. Inverse problems in electromagnetic nondestructive evaluation. International Journal of Applied Electromagnetics in Materials, 3 253-2614, 1993. 

Geller and others Evaluation of Electromagnetic Rope Testers Joint Canadian/US Work, Materials Evaluation, vol. 50, no. 1, 1992, 56-63. 

Electromagnetic Evaluation of Material Discontinuities Shape and Severity. 

The purpose of the nondestructive control consists in detecting local modifications of the material parameters which, by their presence can endanger the quality of the half-finished or finished products. The electromagnetic nondestructive control permits to render evident surface and subsurface discontinuities in the electroconductive material under test. The present tendency of this control is to pass from a qualitative evaluation (the presence or absence of the material discontinuities which give at the output of the control equipment a signal higher or at least equal to that coming from a standard discontinuity whose shape and severity has been prescribed by the product standards) to a quantitative one, which enables to locate as exactly as possible the discontinuity and to make predictions over its shape and severity. 

The electromagnetic field created by the transducer propagates through the examined material as a wave with the length... 

In this section we consider electromagnetic dispersion forces between macroscopic objects. There are two approaches to this problem in the first, microscopic model, one assumes pairwise additivity of the dispersion attraction between molecules from Eq. VI-15. This is best for surfaces that are near one another. The macroscopic approach considers the objects as continuous media having a dielectric response to electromagnetic radiation that can be measured through spectroscopic evaluation of the material. In this analysis, the retardation of the electromagnetic response from surfaces that are not in close proximity can be addressed. A more detailed derivation of these expressions is given in references such as the treatise by Russel et al. [3] here we limit ourselves to a brief physical description of the phenomenon. 

In the previous sections we have described the interaction of the electromagnetic field with matter, that is, tlie way the material is affected by the presence of the field. But there is a second, reciprocal perspective the excitation of the material by the electromagnetic field generates a dipole (polarization) where none existed previously. Over a sample of finite size this dipole is macroscopic, and serves as a new source tenu in Maxwell s equations. For weak fields, the source tenu, P, is linear in the field strength. Thus,... 

In order to describe the second-order nonlinear response from the interface of two centrosynnnetric media, the material system may be divided into tlnee regions the interface and the two bulk media. The interface is defined to be the transitional zone where the material properties—such as the electronic structure or molecular orientation of adsorbates—or the electromagnetic fields differ appreciably from the two bulk media. For most systems, this region occurs over a length scale of only a few Angstroms. With respect to the optical radiation, we can thus treat the nonlinearity of the interface as localized to a sheet of polarization. Fonnally, we can describe this sheet by a nonlinear dipole moment per unit area, -P ", which is related to a second-order bulk polarization by hy P - lx, y,r) = y. Flere z is the surface nonnal direction, and the... 

As discussed in more detail elsewhere in this encyclopaedia, many optical spectroscopic methods have been developed over the last century for the characterization of bulk materials. In general, optical spectroscopies make use of the interaction of electromagnetic radiation with matter to extract molecular parameters from the substances being studied. The methods employed usually rely on the examination of the radiation absorbed. 

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