Behavior of NiMnGa Under Dynamic Magnetic Fields Considering Magnetic Diffusion and Eddy Current Power Loss

2007 ◽  
Author(s):  
Xiang Wang ◽  
Marcelo J. Dapino
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Eddy Current ◽  
Volume Fraction ◽  
Constitutive Models ◽  
Skin Depth ◽  
Restoring Force ◽  
Magnetic Diffusion ◽  
The Third ◽  
Variant System

Prior experimental measurements by the authors demonstrated large reversible strains of up to –0.41% along the [001] crystal direction of a cylindrical Ni50Mn28.7Ga21.3 rod driven with a magnetic field along the same direction and no external restoring force. This represents an unusual configuration which can lead to solenoid transducers with enhanced energy density and bandwidth relative to standard electromagnet devices. Although a number of constitutive models have been developed which quantify magnetic field induced strain (MFIS) in these materials, models incorporating both the MFIS and transducer dynamics are scarce. This paper presents a transducer model that is built in three steps. In the first step, classic thermodynamics is used to calculate the volume fraction ξ of an ideal two-variant system as a function of magnetic fields and stresses. Bulk strains are then calculated through stochastic homogenization of the volume fraction. The transducer dynamics are quantified in the third step through calculation of magnetic diffusion in the sample, eddy current losses, and skin depth effects. The strain output is quantified at various magnetic field frequencies.

scholarly journals Hydromagnetic dynamos in rotating spherical fluid shells in dependence on the Prandtl number, density stratification and electromagnetic boundary conditions

2014 ◽  
Vol 44 (4) ◽  
pp. 293-312 ◽  
Author(s):  
Tomáš Šoltis ◽  
Ján Šimkanin
Keyword(s):  
Magnetic Field ◽  
Electrical Conductivity ◽  
Magnetic Fields ◽  
Prandtl Number ◽  
Inner Core ◽  
Polar Regions ◽  
Number Density ◽  
Magnetic Diffusion ◽  
Spherical Fluid ◽  
The Magnetic Field

Abstract We present an investigation of dynamo in a simultaneous dependence on the non-uniform stratification, electrical conductivity of the inner core and the Prandtl number. Computations are performed using the MAG dynamo code. In all the investigated cases, the generated magnetic fields are dipolar. Our results show that the dynamos, especially magnetic field structures, are independent in our investigated cases on the electrical conductivity of the inner core. This is in agreement with results obtained in previous analyses. The influence of non-uniform stratification is for our parameters weak, which is understandable because most of the shell is unstably stratified, and the stably stratified region is only a thin layer near the CMB. The teleconvection is not observed in our study. However, the influence of the Prandtl number is strong. The generated magnetic fields do not become weak in the polar regions because the magnetic field inside the tangent cylinder is always regenerated due to the weak magnetic diffusion.

Numerical Simulation of the Effect of Magnetic Fields on Soot Formation in Laminar Non-Premixed Flames

2021 ◽  
Author(s):  
Edison E. Chukwuemeka ◽  
Ingmar M. Schoegl
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Volume Fraction ◽  
Soot Formation ◽  
Premixed Flames ◽  
Premixed Flame ◽  
Pollutant Emissions ◽  
Chemical Mechanism ◽  
Computational Domain ◽  
The Magnetic Field

Abstract Characteristics of non-premixed flames such as flame height and lift-off height are affected by the presence of magnetic fields due to the paramagnetic properties of some combustion species. However, it is unknown whether magnetic fields can be used to reduce the emission of pollutants in non-premixed flames. In general, pollutant emissions are reduced in combustion systems if the mixing of combustion species is enhanced during the process. Since paramagnetic combustion species such as O2, O, OH, HO2, etc have a preferential motion direction in the presence of magnetic fields, there is a potential to harness this effect of mixing by imposing a magnetic field on the flame. This study seeks to provide some insights on the effect of magnetic field on pollutants generated in a laminar non-premixed flame numerically. The non-premixed flame is simulated using a detailed chemical mechanism for propane-air combustion and a modified Moss-Brookes soot model. To simulate the effect of magnetism on the paramagnetic chemical species, the species paramagnetic susceptibility is computed using the Curie relation. The non-premixed flame is placed at three different locations within the magnetic field. The computation predicted that the amount of average pollutants reduction is dependent on the location of the flames within the magnetic fields with respect to magnetic gradients. The mass weighted average of the soot volume fraction over the computational domain decreased when the non-premixed flame is located at certain locations within the magnetic field of the solenoid with respect to the absence of the magnetic fields, but increases in other locations.

scholarly journals High field magnetoresistance of nanocomposites (Co84Nb14Ta2)X(Al2O3)100-X near the percolation threshold

2018 ◽  
Vol 185 ◽  
pp. 01013 ◽  
Author(s):  
Mikhail Blinov ◽  
Ivan Zakharchuk ◽  
Erkki Lähderanta ◽  
Alexander Sitnikov ◽  
Igor Rodionov ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Percolation Threshold ◽  
Volume Fraction ◽  
Ion Beam ◽  
Experimental Studies ◽  
Magnetic Data ◽  
Tunnel Barrier ◽  
Positive Contribution ◽  
Ion Beam Sputtering

We present results of experimental studies of magnetic properties, resistivity and magnetoresistance (MR) of (Co84Nb14Ta2)x(Al2O3)100-x films deposited onto a glass-ceramic substrate by the ion-beam sputtering, focusing on MR in high magnetic fields for compositions close to the percolation threshold (x=47-57 at.%). The samples consist on Co-Nb-Ta metallic nanogranules size of 2-5 nm which are embedded into the non-stoichiometric Al-O matrix. Magnetization was measured by SQUID magnetometer at T=4.2-350 K. MR was studied in the pulsed magnetic fields μ0H up to 20 T at T=70-300 K in three geometries: magnetic field in plane parallel and perpendicular to current, magnetic field perpendicular to plane. The pulse duration was 11-12 ms. For the sample with x=57 at.% the temperature dependence of conductivity follows the lnT behavior that matches a strong tunnel coupling between nanogranules. With decreasing metal volume fraction lnT behavior gradually changes to the T1/2 dependence at 47 at.%. For all samples MR is small (<1%) and negative. For x<57 at.% it is slightly anisotropic at μ0H<1.0 T and almost saturates with increasing magnetic field. There is an evidence of small positive contribution to MR at μ0H=20T. Accordingly to structural and magnetic data a large amount of metallic atoms are located between magnetic nanogranules that diminish the tunnel barrier height and make tunnel MR small and weakly dependent on temperature.

Erklärung stellarer und planetarer Magnetfelder durch einen turbulenzbedingten Dynamomechanismus

1966 ◽  
Vol 21 (8) ◽  
pp. 1285-1296 ◽  
Author(s):  
M. Steenbeck ◽  
F. Krause
Keyword(s):  
Magnetic Field ◽  
Angular Velocity ◽  
Magnetic Fields ◽  
Cross Product ◽  
Skin Depth ◽  
Electrically Conducting ◽  
Magnetic Stars ◽  
The Magnetic Field ◽  
Component Parallel ◽  
Good Agreement

In a foregoing paper 1 the effects of a turbulent motion on magnetic fields were investigated. Especially turbulence was treated under the influence of CORIOLiS-forces and gradients of density and/or turbulence intensity. It was shown that on these conditions the average cross-product of velocity and magnetic field has a non-vanishing component parallel to the average magnetic field. Here we give the consequences of this effect for rotating, electrically conducting spheres.At first a sphere rotating with constant angular velocity is investigated. The quadratic effect provides for dynamo maintainance of the magnetic fields. A field of dipol-type has the weakest condition for maintainance. Applications to the magnetic field of the earth show a good agreement with the conceptions of the physical state of the earth’s core.For a second model differential rotation is included. We have also dynamo maintainance. Since we have to assume that generally the angular velocity is a function decreasing with the distance from the centre of the sphere, the calculations show that we have a preferred self-excited build-up of a quadrupol-type field. This model may be applicable to magnetic stars.Finally we look for dynamo maintainance of alternating fields. We consider the skin-depth to be small compared with the radius of the sphere, then we have plane geometry. The existence of periodical solutions is proved. Applications to the general magnetic field of the sun, which has a period of 22 years, are discussed.

scholarly journals Hydromagnetic dynamos at the low Ekman and magnetic Prandtl numbers

2016 ◽  
Vol 46 (3) ◽  
pp. 221-244 ◽  
Author(s):  
Ján Šimkanin
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Prandtl Number ◽  
Large Scale ◽  
Small Scale ◽  
Polar Regions ◽  
Magnetic Diffusion ◽  
Magnetic Prandtl Number ◽  
Prandtl Numbers ◽  
The Magnetic Field

Abstract Hydromagnetic dynamos are numerically investigated at low Prandtl, Ekman and magnetic Prandtl numbers using the PARODY dynamo code. In all the investigated cases, the generated magnetic fields are dominantly-dipolar. Convection is small-scale and columnar, while the magnetic field maintains its large-scale structure. In this study the generated magnetic field never becomes weak in the polar regions, neither at large magnetic Prandtl numbers (when the magnetic diffusion is weak), nor at low magnetic Prandtl numbers (when the magnetic diffusion is strong), which is a completely different situation to that observed in previous studies. As magnetic fields never become weak in the polar regions, then the magnetic field is always regenerated in the tangent cylinder. At both values of the magnetic Prandtl number, strong polar magnetic upwellings and weaker equatorial upwellings are observed. An occurrence of polar magnetic upwellings is coupled with a regenaration of magnetic fields inside the tangent cylinder and then with a not weakened intensity of magnetic fields in the polar regions. These new results indicate that inertia and viscosity are probably negligible at low Ekman numbers.

scholarly journals The Measurement of Solar Magnetic Fields

1971 ◽  
Vol 43 ◽  
pp. 3-23 ◽  
Author(s):  
Jacques M. Beckers
Keyword(s):  
Magnetic Field ◽  
Energy Density ◽  
Kinetic Energy ◽  
Magnetic Fields ◽  
Solar Atmosphere ◽  
Zeeman Effect ◽  
Kinetic Energy Density ◽  
Solar Magnetic Fields ◽  
The Third ◽  
The Magnetic Field

The different methods which have been used, or which may be used in the future, to measure solar magnetic fields are described and discussed. Roughly these can be divided into three groups (a) those which use the influence of the magnetic field on the electromagnetic radiation, (b) those which use the influence of the field on the structure of the solar atmosphere (MHD effects), and (c) those which use theoretical arguments. The former include the Zeeman effect, the Hanle effect, the gyro and synchrotron radiations and the Faraday rotation of radiowaves. The second includes the alignment of details at all levels of the solar atmosphere, and the calcium network, and the third makes use, for example, of the assumption of equipartition between magnetic and kinetic energy density.

Solidified microstructure evolution of Mn-Sb near-eutectic alloy under high magnetic field conditions

2009 ◽  
Vol 24 (7) ◽  
pp. 2331-2337 ◽  
Author(s):  
Qiang Wang ◽  
Ao Gao ◽  
Tie Liu ◽  
Feng Liu ◽  
Chao Zhang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Flux Density ◽  
Volume Fraction ◽  
Primary Phase ◽  
Structure Evolution ◽  
Magnetic Flux Density ◽  
High Magnetic Fields ◽  
Magnetic Field Direction

Mn-90.8 wt%Sb alloys were solidified without and with high magnetic fields to investigate the effects of high magnetic fields on the structure evolution of the alloys. It was found that there were only MnSb/Sb eutectics without any primary phase in the alloy at 0 T, whereas a small amount of primary MnSb dendrites appeared in the MnSb/Sb eutectic matrix when the magnetic flux density was 4.4 T. In magnetic fields of 6.6, 8.8, and 11.5 T, both of two primary phases, i.e., MnSb and Sb, occurred in the matrix. In addition, the volume fraction of these two primary phases increased with increasing magnetic flux density. In magnetic fields of 8.8 and 11.5 T, primary MnSb dendrites aligned parallel to the magnetic field direction and gathered at the edge of the specimens. In contrast, primary Sb dendrites gathered in the center region of the specimens.

Giant ac electrical response of La0.7Sr0.3MnO3in sub-kilogauss magnetic fields

2010 ◽  
Vol 1256 ◽  
Author(s):  
Alwyn Rebello ◽  
Vinayak Bharat Naik ◽  
Sujit Kumar Barik ◽  
Mark Choong Lam ◽  
Mahendiran Ramanathan
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Electrical Transport ◽  
Electrical Response ◽  
Skin Depth ◽  
Abrupt Increase ◽  
Device Applications ◽  
Ac Current ◽  
Metallic Ferromagnet ◽  
And Shifts

AbstractWe report ac electrical transport in the metallic ferromagnet La0.7Sr0.3MnO3. Both ac resistance (R) and reactance (X) were measured as a function of temperature (T= 400-100 K), frequency of the ac current (f= 100 kHz – 20 MHZ) and external dc magnetic field (H= 0-100 mT) applied parallel to the current direction. It is shown that, whileR(H= 0 T) decreases smoothly around the Curie temperature (TC) forf= 100 kHz, an abrupt increase followed by a peak close toTCoccurs forf≥ 500 kHz. The peak decreases in magnitude, broadens and shifts down in temperature with increasing values ofH. The peak inRis completely suppressed underH= 100 mT resulting in a huge low-field ac magnetoresistance (R/R= -53 % forf= 2MHz) whereas the dc magnetoresistance only -31 % even at H = 7 T. While the reactanceX(H= 0 T) also shows an abrupt increase atTCforf< 10 MHz, it decreases abruptly atTCforf≥ 12 MHz. The magnetoreactance is largest (X/X= -47 %) atf= 100 kHz and it changes sign from negative to positive with increasing frequency. It is suggested that the observed huge ac magnetoresistance arises from decrease of magnetic permeability which enhances skin depth under a magnetic field. Our results indicate that the extraordinary sensitivity of the ac magnetoresistance to low dc magnetic fields can be exploited for device applications.

scholarly journals Magnetic fields generated by the Rayleigh-Taylor instability

1986 ◽  
Vol 4 (3-4) ◽  
pp. 325-328 ◽  
Author(s):  
R. G. Evans
Keyword(s):  
Magnetic Field ◽  
Growth Rate ◽  
Magnetic Fields ◽  
Taylor Instability ◽  
The Self ◽  
Magnetic Diffusion ◽  
Rayleigh Taylor Instability

In the absence of magnetic diffusion the self-generated magnetic field in a plasma is proportional to the fluid vorticity. The ratio of magnetic to fluid energy then shows that self-generated magnetic fields can only affect the Rayleigh Taylor growth rate for large k (wavelengths less then a few microns).

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