Electromagnetic damping of elastic waves: a simple theory

1970 ◽  
Vol 7 (5) ◽  
pp. 1304-1307 ◽  
Author(s):  
F. E. M. Lilley ◽  
C. M. Carmichael
Keyword(s):  
Magnetic Field ◽  
Electrical Conductivity ◽  
Analytical Solution ◽  
Applied Magnetic Field ◽  
Elastic Waves ◽  
Magnetic Field Gradient ◽  
Magnitude Estimate ◽  
Simple Expression ◽  
Electromagnetic Damping ◽  
Order Of Magnitude

An order-of-magnitude estimate is made to check the effect observed in previously described experiments in which vibrations in a metal bar were damped by an applied magnetic field that was strongly non-uniform. Though the awkward geometry of the experiment has prevented an accurate analytical solution of the problem, some reasonable assumptions allow a simple expression for the effect to be obtained directly. This expression is in agreement with the experimental results regarding the dependence of the effect upon frequency, bar dimensions, density, electrical conductivity, and magnetic field gradient.

Electromagnetic damping of elastic waves: Experimental results

1968 ◽  
Vol 5 (4) ◽  
pp. 825-829 ◽  
Author(s):  
F. E. M. Lilley ◽  
C. M. Carmichael
Keyword(s):  
Magnetic Field ◽  
Elastic Wave ◽  
Applied Magnetic Field ◽  
Elastic Waves ◽  
Applied Field ◽  
Eddy Currents ◽  
Electrical Conductor ◽  
Electromagnetic Damping ◽  
The Waves ◽  
The Magnetic Field

The passage of an elastic wave causes straining and translation in the transmitting material. If a magnetic field is applied, and the medium is an electrical conductor, some of the energy of the wave is dissipated by the flow of electrical eddy currents. Usually the amount of energy lost is very small, but it may be greatly increased if the applied field is strongly non-uniform.Laboratory experiments are described which demonstrate this effect for standing elastic waves in a metal bar. The applied magnetic field changes from almost zero to its full strength over a distance which is short compared to the length of the standing wave. The result of this strong non-uniformity is that the energy lost due to the translation of the bar in the field greatly exceeds the energy lost due to the straining of the bar in the field.The dependence of the attenuation of the waves by the magnetic field is investigated for variation in frequency of vibration, bar thickness, and field gradient.

The effects of wall conductivity in magnetohydrodynamic duct flow at high Hartmann numbers

1971 ◽  
Vol 69 (2) ◽  
pp. 337-351 ◽  
Author(s):  
D. J. Temperley ◽  
L. Todd
Keyword(s):  
Magnetic Field ◽  
Electrical Conductivity ◽  
Applied Magnetic Field ◽  
Hartmann Number ◽  
Classical Model ◽  
Critical Discussion ◽  
Duct Flow ◽  
Rectangular Duct ◽  
Wall Conductivity ◽  
Expansion Procedure

AbstractLaminar motion of a conducting fluid in a rectangular duct is discussed. The applied magnetic field is uniform and parallel to one pair of sides of the duct. Classical theory is used and it is shown that the two successive limiting processes, lim (σwall → ∞; hσ wall → a finite, constant limit) and lim (M → ∞) are not always freely interchangeable; M being the Hartmann number, σwall the electrical conductivity of the duct wall and h the typical ratio of (wall thickness/duct width). A general expansion procedure for M ≫ 1, valid for all types of wall conductivities, is devised. A critical discussion of the deficiencies in the classical model is given.

Notizen: Fluorine Diffusion and Phase Transition in Superionic Conductor KSn2F5 as Studied by 19F NMR, Electrical Conductivity and DSC

1983 ◽  
Vol 38 (5) ◽  
pp. 593-594 ◽  
Author(s):  
W. D. Basler ◽  
I. V. Murin ◽  
S. V. Chernov
Keyword(s):  
Magnetic Field ◽  
Phase Transition ◽  
Activation Energy ◽  
Electrical Conductivity ◽  
Relaxation Time ◽  
Field Gradient ◽  
Magnetic Field Gradient ◽  
Pulsed Magnetic Field ◽  
19F Nmr ◽  
Sharp Transition

The diffusion of fluorine in KSn2F5 has been studied by T1 and T2 relaxation time measurements of 19F NMR (200-500 K) and pulsed magnetic Field gradient tech­niques (390-480 K). Near 423 K a sharp transition into the superionic state has been found, the fluorine diffusion increasing by a factor of 4 within a range of 3 K. Conduc­tivity measurements only show a change in the activation energy.

THE HALL CONDUCTIVITY OF A DOPED GRAPHENE IN A QUANTIZING MAGNETIC FIELD

2012 ◽  
Vol 26 (28) ◽  
pp. 1250188 ◽  
Author(s):  
MIKHAIL B. BELONENKO ◽  
ANASTASIA V. PAK ◽  
ALEXANDER V. ZHUKOV ◽  
ROLAND BOUFFANAIS
Keyword(s):  
Magnetic Field ◽  
Electrical Conductivity ◽  
Energy Spectrum ◽  
Applied Magnetic Field ◽  
Electron Energy Spectrum ◽  
Landau Levels ◽  
Adsorbed Atom ◽  
Doped Graphene ◽  
Quantizing Magnetic Field ◽  
Different Characteristics

In this paper we study the electron energy spectrum corresponding to Landau levels in doped graphene when an external magnetic field is applied in the direction normal to the graphene planar sheet. The derived dispersion relation for the electrons in the doped graphene allows us to determine the dependence of the electrical conductivity on the applied magnetic field. This relationship between electrical conductivity and applied magnetic field is further analyzed for different characteristics of the impurities; specifically the potential of hybridization and the energy of the adsorbed atom.

On the A.C. electrical conductivity of a Lorentz gas

1968 ◽  
Vol 2 (1) ◽  
pp. 1-8 ◽  
Author(s):  
J. H. M. Fu ◽  
R. S. B. Ong
Keyword(s):  
Electrical Conductivity ◽  
Magnitude Estimate ◽  
Lorentz Gas ◽  
Collision Term ◽  
Homogeneous Case ◽  
Spatial Gradients ◽  
Effective Collision Frequency ◽  
Higher Order Terms ◽  
Order Of Magnitude ◽  
Effective Collision

Often one is interested in the electrical conductivity of a plasma for frequencies of the applied electric field comparable to or greater than the effective collision frequency. For the purpose of obtaining an order of magnitude estimate of the conductivity a Lorentz gas model with a Fokker–Planck collision term is used. For this simple model a formula for the a.c. electrical conductivity for two limiting cases is derived in closed form. The first term of the expression for the conductivity in the case where w/k is very large agrees with that obtained by Bernstein & Trehan (1960) for the spatially homogeneous case, while the effect of the spatial gradients is indicated in the higher order terms. In the case where w and k are both equal to zero the expression for the d.c. electrical conductivity of Spitzer (1962) is recovered.

Magnetostrictive gradient in Tb0.27Dy0.73Fe1.95 induced by high magnetic field gradient applied during solidification

2016 ◽  
Vol 09 (01) ◽  
pp. 1650003 ◽  
Author(s):  
Pengfei Gao ◽  
Tie Liu ◽  
Meng Dong ◽  
Yi Yuan ◽  
Kai Wang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Gradient ◽  
High Magnetic Field ◽  
Applied Magnetic Field ◽  
Magnetic Field Gradient ◽  
Gradient Distribution ◽  
Field Gradients ◽  
Magnetic Field Gradients ◽  
The Magnetic Field

We investigated how high magnetic field gradients affected the magnetostrictive performance of Tb[Formula: see text]Dy[Formula: see text]Fe[Formula: see text] during solidification. At high applied magnetic field gradients, the magnetostriction exhibited a gradient distribution throughout the alloy. Increasing the magnetic field gradient also increased the magnetostriction gradient. We attributed the graded magnetostrictive performance to the gradient distribution of (Tb, Dy)Fe2 phase in the alloy and its orientation.

Combined effects of ferromagnetic particles and magnetic field on mixed convection in the Falkner-Skan system using DRA

2019 ◽  
Vol 29 (2) ◽  
pp. 814-832 ◽  
Author(s):  
Mohamed Kezzar ◽  
Nawel Boumaiza ◽  
Ismail Tabet ◽  
Nourreddine Nafir
Keyword(s):  
Magnetic Field ◽  
Electrical Conductivity ◽  
Analytical Solution ◽  
Mixed Convection ◽  
Shooting Method ◽  
Hartmann Number ◽  
Volume Fraction ◽  
Physical Parameters ◽  
Content Type ◽  
Runge Kutta

Purpose This paper aims to traitted the combined effects of ferromagnetic particles and magnetic field on mixed convection in the Falkner Skan equation using analytical solution by the Duan–Rach method. Design/methodology/approach Visualization and grouping of effects of various physical parameters such as electrical conductivity of ferro-particles (electrical conductivity calculated using Maxwell model), ferro fluid volume fraction for Magnetite-Fe3O4-water and magnetic field represented by the Hartmann number in a set of third- and second-order nonlinear coupled ordinary differential equations. This set of equations is analytically processed using the Duan–Rach Approach (DRA). Findings Obtained DRA results are validated using a numerical solution (Runge–Kutta–Fehlberg-based shooting method). The main objective of this research is to analyze the influence of physical parameters, in particular electrical conductivity, Ferrofluid volume fraction in the case of Magnetite-Fe3O4-water, in addition to the types of solid nanoparticles and Hartmann number on dynamic and thermal distributions (velocity/temperature). Results of the comparison between the numerical solution (Runge–Kutta–Fehlberg-based shooting method) and the analytical solution (DRA) show that the DRA data are in good agreement with numerical data and available literature. Originality/value The study uses Runge–Kutta–Fehlberg-based shooting method) and the analytical solution (DRA) to investigate the effect of mixed convection, in the presence of Ferro particles (Magnetite-Fe3O4) in a basic fluid (water for example) and subjected to an external magnetic field on the Falkner–Skan system.

scholarly journals An analytical solution to electromagnetically coupled duct flow in MHD

2015 ◽  
Vol 771 ◽  
pp. 595-623 ◽  
Author(s):  
Michael J. Bluck ◽  
Michael J. Wolfendale
Keyword(s):  
Magnetic Field ◽  
Analytical Solution ◽  
Applied Magnetic Field ◽  
Homogeneous Solution ◽  
Duct Flow ◽  
Mean Flow ◽  
Validation Data ◽  
Electrically Conducting ◽  
Fusion Applications ◽  
Fusion Blankets

The flow of an electrically conducting fluid in an array of square ducts, separated by arbitrary thickness conducting walls, subject to an applied magnetic field is studied. The analytical solution presented here is valid for thick walls and is based on the homogeneous solution obtained by Shercliff (Math. Proc. Camb. Phil. Soc., vol. 49 (01), 1953, pp. 136–144). Arrangements of ducts arise in a number of applications, most notably in fusion blankets, where liquid metal is used both as coolant and for tritium generation purposes. Analytical solutions, such as those presented here, provide insight into the physics and important benchmarking and validation data for computational magnetohydrodynamics (MHD), as well as providing approximate flow parameters for 1D systems codes. It is well known that arrays of such ducts with conducting walls exhibit varying degrees of coupling, significantly affecting the flow. An important practical example is the so-called Madarame problem (Madarame et al., Fusion Technol., vol. 8, 1985, pp. 264–269). In this work analytical results are derived for the relevant hydrodynamic and magnetic parameters for a single duct with thick walls analogous to the Hunt II case. These results are then extended to an array of such ducts stacked in the direction of the applied magnetic field. It is seen that there is a significant coupling affect, resulting in modifications to pressure drop and velocity profile. In certain circumstances, counter-current flow can occur as a result of the MHD effects, even to the point where the mean flow is reversed. Such phenomena are likely to have significant detrimental effects on both heat and mass transfer in fusion applications. The dependence of this coupling on parameters such as conductivities, wall thickness and Hartmann number is studied.

scholarly journals Anisotropic Purcell Factor Control of an Emitter in Graphene Under the Modulation of a Static Magnetic Field

2021 ◽  
Author(s):  
Zenghong Ma ◽  
Zijian Chen ◽  
Lian Zhang ◽  
Xiaocui Lu ◽  
Jian Xu ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Spontaneous Emission ◽  
Static Magnetic Field ◽  
Applied Magnetic Field ◽  
Great Promise ◽  
Polarization Angle ◽  
Polarization Direction ◽  
Purcell Factor ◽  
Order Of Magnitude ◽  
Definition Of

Abstract Spontaneous emission control of emitters hold great promise for applications in pho-tonics and quantum optics. As a definition of the spontaneous emission lifetime of an atom or molecule, the Purcell factor of an emitter coupled with graphene plasmons by a static magnetic field is studied. The results show that the Purcell factor can be effectively modulated by the applying of external magnetic field to graphene at lower terahertz frequencies. In addition, in the presence of a magnetic field, the coupling between the graphene and emitter becomes stronger, which results in a strong enhancement of the emission of the emitter and the numerically calculated Purcell factor is increased. More specifically, the Purcell factor increases by almost an order of magnitude when the applied magnetic field is 10T. Moreover, the Purcell factor also depends on the polarization direction of the emitter, especially when the polarization direction of the emitter is parallel to the graphene plane, the Purcell factor will show anisotropy with the change of polarization angle. Bias of the applied magnetic field extends a new path for the realization of Purcell factor modulation based on graphene-emitter interaction, it may provides a promising application value for the design of the photo-magnetic based quantum devices.

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