Abstract
This study investigated the frequency properties of a flexible printed circuit (FPC) coil and applied it to detect conductivity change of non-ferromagnetic metal materials. Theoretical analysis and measurements showed that the coil’s resistance and inductance are almost frequency-invariant in a particular frequency range; the coil circuit resonates at its self-resonant frequency. With no concern for its thickness, the conductivity of a test object can be measured with high sensitivity and accuracy by using the coil in its frequency-invariant range, based on the “same ωσ, same impedance” principle. In the case that the influence of thickness has to be eliminated, the variation of conductivity can be sensitively detected by using the coil’s resonant properties. The proposed methods have been verified with measurement of standard test pieces whose conductivities were given in advance, and applied to detect conductivity change of deteriorated tube.
Highlights
Electrical conductivity is a fundamental property of metal materials and primarily decided by the number and mobility of electrical charge carriers, which are relevant to the composition, lattice structure, temperature and etc
Measurement based on inductive principle, usually using one or two electromagnetic coil sensors driven by alternating current (AC), is non-destructive and can be applied to test objects directly
We applied the measurement principles described in last section to three standard test pieces (TP) of conductivity 19.70%IACS, 57.70%IACS, and 100.98%IACS, respectively
Summary
Electrical conductivity is a fundamental property of metal materials and primarily decided by the number and mobility of electrical charge carriers, which are relevant to the composition, lattice structure, temperature and etc. The conductivity of a bulk metal material is generally measured by using the so-called 4-point probes method in which DC current is applied to a cut-off sample that the potential drop and current are measured through respective pairs of terminals This method is direct and effective, cutting a sample from a structure is destructive. The signals of inductive measurement change with electrical conductivity, as well as magnetic permeability, geometry and dimension of test object, probe and setup and etc. These factors are difficult to control and might subject to variation. Scitation.org/journal/adv signals showed up remarkably conductivity change, demonstrating the feasibility of the FPC coil and the proposed methods for material characterization
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