Real-Time Processing of Multifrequency Eddy Currents Testing Signals: Design, Implementation, and Evaluation

The design, implementation, and evaluation of a real-time digital signal processing architecture to generate and process multifrequency signals for eddy currents testing is described in this paper. This architecture is implemented on a dedicated instrument whose processing core is a field-programmable gate array. Stimulus generation is achieved using direct digital synthesis with some important improvements to reduce spurious frequency components. An in-phase and in-quadrature demodulation scheme is implemented to estimate the real and imaginary parts of the probe output signal. A cascaded integrator comb decimator is used to lower the sampling frequency and then allow narrowband filtering with low resources. The proposed architecture is able to generate and process the stimulus and input data at 125 MSamples/s and to estimate the input data components at 1.25 MSamples/s rate for eddy-currents with multiple simultaneous testing frequencies between 2.5 kHz and 10 MHz. Experimental validation is performed using a set of synthetic defects and two stimulus with different spectral composition.