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The ωσ method: A new contactless comparison method for measuring electrical conductivity of nonferromagnetic conductors

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4 Author(s)
Miletic, M.B. ; Joint Laboratory for Advanced Materials of SASA, Beograd, Knez Mihailova 35, Yugoslavia ; Nikolic, P.M. ; Vasiljevic-Radovic, D. ; Bojicic, A.I.

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A novel, very simple, eddy current method for measuring the electrical conductivity of nonferromagnetic conductors is described. This method is relative, i.e., we measure the ratio of conductivities of two samples of the same shape and size (this shape and size may be arbitrary). For one of them, conductivity is known, this is the reference sample, whereas the conductivity of the other is unknown and it is to be determined. Consequently, in this method it is necessary to have a reference sample of known conductivity. On the other hand, in this method no other calibration is necessary; the ratio of two conductivities we obtain directly as the ratio of two frequencies, without any calibration. The principle of this method is as follows: It turns out, based on Maxwell’s equations, that if we have a coil through which a sinusoidal current of an angular frequency ω flows and in whose magnetic field a given conductive, nonferromagnetic sample is placed, the effective inductance (i.e., the ratio of the reactive part of the impedance to the frequency ω) depends on ω and on the conductivity of the sample σ only through their product ωσ. Therefore, if it is found that with a sample of conductivity σ 1 at frequency ω1 the effective inductance is equal to that of a sample with conductivity σ 2 and frequency ω2 (the samples being of the same shape and size, both nonferromagnetic, and both placed in the same position relative to the coil), this means that equality ω1σ12σ2 is valid. Hence, if σ1 is known and σ2 is unknown, σ2 can be calculated. © 1997 American Institute of Physi cs.

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Review of Scientific Instruments  (Volume:68 ,  Issue: 9 )