Resistance-frequency eddy current method for electrical conductivity measurement

In eddy current measurements of electrical conductivity, adverse effects from lift-off effects are inevitable, especially for relatively large lift-offs. In this work, a new method of electrical conductivity measurement, the resistance-frequency eddy current method, is proposed. The method uses an LC resonator as the measurement probe and characterizes the conductivity of the measured material by exploiting the physics that the ratio of the resonant frequency to the resonant resistance of the probe is linearly related to the logarithm of the conductivity. Furthermore, a two-dimensional resistance-frequency plane (RF plane) consisting of resonant frequency and resonant resistance is established. The resistance frequency lift-off curves in the RF plane have good linearity in the med-high lift-off range, which can be used to eliminate lift-off effects. Experimental results show that the proposed method can perform conductivity measurements in the med-high lift-off range of 1 mm to 2.5 mm independent of lift-off, with relative errors within 5 %. Therefore, the proposed method is particularly suitable for conductivity measurements in the med-high lift-off range, especially for metallic materials with thicker surface coatings.