A portable embedded contactless system for the measurement of metallic material conductivity and lift-off

This paper describes the development, implementation and characterization of a portable embedded measurement system for the contactless estimation of a metallic material conductivity and of the lift-off between the system probe and the metallic material surface. The system consists on an absolute probe with compensation and is capable of measuring the in-phase and in-quadrature components of the probe output voltage using as a reference the probe stimulus voltage. The stimulus module includes a direct digital synthesizer (DDS) to set the measurement frequency, while the acquisition module includes analog voltage amplification and analog-to-digital conversion. A microcontroller is used to control the measurement, process the acquired voltage samples, estimate the desired parameters and perform USB communication. The final dimensions of the pen-like system, its capability of communication with a smartphone and its ability to power the system from the smartphone make it highly portable and especially suited for non-destructive testing (NDT) and field measurements.