Electromagnetic methods

Electromagnetic flowmeters are mainly applied to single-phase conducting fluids, for example liquid metals, water-based industrial liquids, and blood. However, they are also being used to measure solid/liquid flows such as water-based slurries and sludge as long as conductivity of the liquid medium exceeds 50 microsiemens per centimeter (pS/cm). Output signals from an EM flowmeter are basically proportional to the volumetric flow rate, which is applicable to solid/liquid flows only if the solids particles are uniformly distributed in the liquid. Moreover, to obtain the mass flow rate of a solid/liquid flow, the EM flowmeter requires other means to measure solids concentration. 

In the conventional EM flowmeter, point electrodes are used in a circular pipe. This flowmeter is normally overly sensitive to flow near the two electrodes it may accurately measure flow rate if the magnetic field is uniform and flow is rectilinear (i.e., parallel to the flowmeter axis) and axisymmetric. For a rectilinear, axisymmetric flow, Eq. 6.2 can be written as 

FIGURE 6-2 Weight Junction contours for the uniform-field point 

Electromagnetic methods such as eddy current, capacitance, microwaves, and terahertz radiation are not traditional inspection methods for composites, but they can be used in some circumstances [36]. Microwaves (300 MHz—300 GHz, 1000—1 mm) and terahertz (300 GHz—3 THz, 1—0.1 mm) are applicable to fiberglass composite inspection and have been successful at the detection of damage and internal features [37—45]. However, electromagnetic radiation at these wavelengths does not penetrate conductive materials. For CFRP, which is mildly conductive, they are only useful for sensing very near the surface. Capacitance measurements can be used to measure dielectric property changes in composites such as moisture uptake or cure condition. 

Eddy current inspection is typically performed in metallic components for cracks or thickness inspections. The method uses a changing magnetic field to create eddy currents in the substrate under test. Those eddy currents create a secondary field back in the eddy current coil. Changes in the substrate that affect the eddy current flow will alter the secondary electromagnetic fields and therefore affect the originating coil 

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Although isotopes have similar chemical properties, their slight difference in mass causes slight differences in physical properties. Use of this is made in isotopic separation pro cesses using techniques such as fractional distillation, exchange reactions, diffusion, electrolysis and electromagnetic methods. 

Zaitzev, V.M., Pokhil, P.F., and Shvedov, K.K. (1960), An Electromagnetic Method for Measurement of the Velocity of Explosion Products, Dokl. Akad. Nauk. SSSR 132, 1339-1340. 

In 1929 Lawrence invented the cyclotron, which instrument played (and still plays) an important role in nuclear physics. That work led directly to the award of the Nobel Prize in Physics for 1939, just one of his many honors. During World War II E. O. Lawrence made vital contributions to the development of the atomic bomb holding several high-level appointments in the Manhattan Project. He played an influential role in the decision to develop and later employ electromagnetic methods for uranium isotope separation (Calutrons) during the early 1940s. (Photo credit http //wikipedia.org, public domain)... 

Zirconium silicate occurs in nature as mineral zircon. Ore is mined from natural deposits and concentrated by various techniques (See Zirconium, Recovery). It is separated from sand by electrostatic and electromagnetic methods. 

Dremin Shvedov (Ref 3) measured by an electromagnet method the CJ pressure time of reaction in detonation waves of RDX, TNT, PETN, Tetryl, DINA, and of some of their mixts. The results obtd were significantly different from previous data. An attempt was made to explain this difference Refs 1) W.E. Deal, "Measurement of Chapman-Jouguet Pressure for Explosives", JChemPhys 27, 796-800(1957) 2) N.L. 

V.M. Zaitsev et al, "Electromagnetic Method for Measuring the Speed of Explosive... 

Aleksandrov et al (Ref 19) used the electromagnetic method to obtain what they term reaction times fas a function of input press P. For RDX of 1.8mm particle size at l.Og/cc they obtained the following ... 

Electromagnetic geophysical methods arc based on the study of the propagation of electric currents and electromagnetic fields in the earth. There arc two major modifications of electromagnetic methods one is based on direct current (DC), and another employs a transient electromagnetic field. 

Gusarov s theorem is a further generalization of this result for a 2-D geoelectrical model with a piecewise analytic distribution of electrical conductivity. The last two theorems make it feasible to apply the electromagnetic method for examining inhomogeneous geological structures of the earth. 

In most geophysical applications of electromagnetic methods, it is necessary to model geoelectrical structures of quite arbitrary shape and size, with anomalous conductivity varying in an arbitrary manner and not necessarily restricted to a local region. The most widely used approach to forward modeling of such problems is through the use of finite difference and finite element methods to find numerical solutions to Maxwell s equations written in differential form (Weaver, 1994 Zhdanov et ah, 1997). 

Electromagnetic potential equations and boundary conditions Another approach to the formulation of electromagnetic boundary-value problem is to use the electromagnetic potentials introduced in Chapter 8. This approach has been used in a number of publications on numerical electromagnetic methods (Biro and Preis, 1990 Everett and Schultz, 1996 Everett, 1999 Haber et aJ., 1999). 

Rogge also calcd that for propelling by electromagnetic method of a projectile weighing 750kg with muzzle velocity of lOOOm/sec from a barrel cal 38cm and 20 meters long, would require 100000 kilowatts, which is extremely hi ... 

In addition, electromagnetic methods are subject to interference from many cultural features and the presence of nearby electrical fields. Finally, the ability of electromagnetic conductivity surveys to identify groundwater contaminant plumes requires that a significant electrical conductivity contrast exists between contaminated and natural groundwater (2). 

Electrical resistivity measurements were also taken at 28 locations selected across the site to verify the data collected by electromagnetic methods. The data obtained was in agreement with the results of the electromagnetic conductivity survey. 

Although the basic requirement of most of the separation and purification methods is the formation of second phase, there are some methods e.g. the electromagnetic method of separation of isotopes, fractional diffusion and thermal diffusion for the separation of gases, that do not need to meet that requirement. 

The method can be successfully used to get separation of appreciable quantities of isotopes of an element. Perhaps, the most important case of separation by the electromagnetic method was that of the separation of U from U carried out... 

It was in the investigation of berylfium disintegration in 1932 that the neutron was discovered. Since the neutron has no charge, the typical electromagnetic methods of detection were useless. Chadwick bounced the mystery particle off atomic nuclei that were detectable, and, by the conservation of momentum and energy, he was able to determine that the neutron had a mass slighdy greater than that of a proton. 

Monitoring of solid/gas flow is important to safe and efficient operation of pneumatic transport that is used in many industrial processes such as coal mining and powder transport. Commonly employed techniques to measure particle velocity are a radioactive tracer method (Somerscales, 1981), optical techniques (Lee Srinivasan, 1978), electromagnetic methods (Bobis et al., 1986) and conventional mechanical approaches (Soo, 1990). 

Daev, D. S. High frequency electromagnetic methods of investigation in boreholes. Nedra, Moscow, 1974. 

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