Lorentz force sigmometry: A contactless method for electrical conductivity measurements

• Published in: Journal of applied physics 2012-05, Vol.111 (9), p.094914-094914-7
• Main Authors: Uhlig, Robert P., Zec, Mladen, Ziolkowski, Marek, Brauer, Hartmut, Thess, André
• Format: Article
• Language: English
• Subjects: Aluminum; Electrical conductivity; Electrical resistivity; Liquids; Lorentz force; Numerical prediction; Process control; Resistivity
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.4716005

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 σ Al = 20 . 4 MS / m and to a copper sample with σ Cu = 57 . 92 MS / m we obtain σ Al = 21 . 59 MS / m and σ Cu = 60 . 08 MS / m , 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.