Pulsed eddy currents testing using a planar matrix probe

Abstract

This paper presents a new planar matrix eddy currents probe intended for non-destructive testing. The proposed design is composed by multiple independent excitation traces and a matrix of independent sensing coils. Finite element modeling is used to highlight the probe operating principle and to preview its behavior in different measurement conditions. Dedicated on-probe electronics were designed to cope with the requirements of the new probe. Multiple pulse generators are used to drive the excitation traces and a multiplexer enables the selection of the different sensing coils being measured. The sensing coils output voltages are amplified, acquired and digitally processed with an FPGA-based embedded device. Processing of the probe response signals to the pulsed excitation is accomplished in the frequency domain using a dedicated FFT core in the FPGA. The proposed probe and electronics system enables two modes of operation. In the first mode, the probe can be operated selecting a combination of excitation traces to drive and sensing coils to read while is being moved on the tested part. In the second mode of operation, the probe is handheld positioned to measure a specific region and a sequence of measurements are triggered by the user. These measurements results can be arranged to form a color map where the defects can be identified.