Model-based characterization of homogeneous metal plates by four-point alternating current potential drop measurements

We determined the conductivity, relative permeability, and thickness of homogeneous metal plates from four-point measurements of alternating current potential drop (ACPD) over the frequency range 1 Hz to 10 kHz. We developed simple analytical expressions from which these parameters can be calculated. In the low-frequency regime, in which the measured voltage tends to a constant, real value, the relative permeability of the plate does not influence the ACPD voltage. For known plate thickness, conductivity can be easily determined, even for ferrous metals. For known conductivity, plate thickness can be determined. Relative permeability can be obtained from measurements at higher frequency, for known conductivity and thickness. The inductance of the pickup circuit can also be determined from higher frequency measurements. This practical technique is especially useful for conductivity or plate thickness measurements in configurations where access is restricted to one side of the plate. We studied brass, aluminum, stainless steel, spring steel, and carbon steel plates. Our results agree with available independent measurements.