Eddy current measurement of the electrical conductivity and porosity of metal foams

This paper presents experimental results characterizing the electrical properties of metallic foams, a relatively new class of material, using nondestructive eddy current sensing techniques. The fundamentals of eddy current sensing, which is based on electromagnetic induction, are described, and the effects on coil impedance change of the representative types of coil sensors are analyzed. It has been found that the phase-frequency response of the normalized eddy current signal of the sensor is relatively immune to coil-to-sample spacing and fill-factor variations, from which key results such as the equivalent conductivity and the porosity of the foams are presented. The paper demonstrates the broad applicability of this technique in characterizing and further recognizing the properties of a variety of sample shapes used.