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Lorentz force sigmometry: A contactless method for electrical conductivity measurements
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1.
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Figures

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FIG. 1.

LoFoS sample problem—conducting plate moving with a constant velocity below a permanent magnet.

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FIG. 2.

Calibration curves for plates obtained analytically (anl.) and numerically (num.) (anl.—infinite plate with thickness 50 mm, num.— ) for various velocities (a) lift-off distance δz = 3 mm (b) lift-off distance δz = 5 mm.

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FIG. 3.

Sketch of experimental measurement setup containing (1) a three-component force sensor, (2) a permanent magnet, and (3) the specimen mounted on a linear belt-driven drive.

Image of FIG. 4.

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FIG. 4.

Dependency of force on velocity for Al-alloy at a lift-off distance of δz = 3 mm and Cu at δz = 5 mm (a) drag force (b) lift force.

Image of FIG. 5.

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FIG. 5.

Dependency of the ratio between lift force and drag force on velocity for Al-alloy and Cu (lift-off distance δz = 3 mm and 5 mm, respectively).

Image of FIG. 6.

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FIG. 6.

Dependency of force on lift-off distance for Al-alloy (different magnet sizes, ), (a) drag force, (b) lift force.

Image of FIG. 7.

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FIG. 7.

Dependency of the ratio between lift force and drag force on lift-off distance for Al-alloy, where the permanent magnet is PM ø15 mm  × 25 mm.

Image of FIG. 8.

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FIG. 8.

Dependency of measurement uncertainty on fixed parameters of (a) lift-off distance δz = 3 mm and (b) velocity (PM ø15 mm ×25mm).

Image of FIG. 9.

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FIG. 9.

Numerically obtained calibration curves for the used bar geometry ( ) for different velocities (a) lift-off distance δz = 3 mm, the particular example from Table IV is visualized colorfully (b) lift-off distance δz = 5 mm.

Tables

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Table I.

Geometrical and material properties used for comparison of the analytical with the numerical model and experiments.

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Table II.

Basic linear fitting coefficients for plate calibration.

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Table III.

Basic linear fitting coefficients for numerical bar calibration.

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Table IV.

Conductivity calculation using LoFoS.

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/content/aip/journal/jap/111/9/10.1063/1.4716005
2012-05-15
2014-04-19

Abstract

The present communication reports a new technique for the contactless measurement of the specific electrical conductivity of a solid body or an electrically conducting fluid. We term the technique “Lorentz force sigmometry” where the neologism “sigmometry” is derived from the Greek letter sigma, often used to denote the electrical conductivity. Lorentz force sigmometry (LoFoS) is based on similar principles as the traditional eddy current testing but allows a larger penetration depth and is less sensitive to variations in the distance between the sensor and the sample. We formulate the theory of LoFoS and compute the calibration function which is necessary for determining the unknown electrical conductivity from measurements of the Lorentz force. We conduct a series of experiments which demonstrate that the measured Lorentz forces are in excellent agreement with the numerical predictions. Applying this technique to an aluminum sample with a known electrical conductivity of and to a copper sample with we obtain and , respectively. This demonstrates that LoFoS is a convenient and accurate technique that may find application in process control and thermo-physical property measurements for solid and liquid conductors.

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Scitation: Lorentz force sigmometry: A contactless method for electrical conductivity measurements
http://aip.metastore.ingenta.com/content/aip/journal/jap/111/9/10.1063/1.4716005
10.1063/1.4716005
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