Phase coherence factor (PCF) and sign coherence factor (SCF) are usually considered as weighing terms for dynamic range improvement and side lobes removal of ultrasonic imaging delay-and-sum (DAS) algorithms [1]. Over the years, extended work was carried out to evaluate the potential of this approach for different applications. Especially, images produced by the coherent summation of instantaneous phase or sign can be directly used for defect identification and sizing [2]. This strategy presents many advantages such as removing the effect of the signal amplitude, reducing the number of artefacts and improving the sensitivity to highly diffractive and weak discontinuities such as crack tips. However, specular reflectors are usually badly reproduced due to the inherent behavior of the coherent summation. Recently, [3] suggested a different approach by differentiating the instantaneous phase so as to obtain the instantaneous frequency of recorded signals and feed it to a DAS algorithm. By doing so, reflectors are identified by constant frequency values corresponding to the central frequency of the input signal. Through successive summations, a reflector is then clearly reconstructed while uncorrelated frequencies are destroyed. Finally, dynamic range is related to the selected frequency range which can be tweaked according to the center frequency, the sampling frequency and the number of elements. While presenting many benefits related to instantaneous phase or sign imaging, this new concept could also alleviate some of the drawbacks such as the restitution of specular reflectors. In this study, instantaneous frequency imaging performances are assessed in terms of specular reflectors restitution and multi-view capabilities. Experiments were conducted on two samples. The first one is a stainless-steel block of thickness 50 mm comprising regularly spaced side drilled holes (SDH) of diameter 2 mm which is used to characterize backwall restitution compared to SDH features. The second sample is a 3/4” thick mid-steel plate with EDM notches at several angles used to characterize restitution of crack-like defects when performing multi-view DAS. Results show better performances in terms of specular reflectors reconstruction compared to instantaneous phase or sign imaging while also being complimentary to these methods. Additionally, instantaneous frequency imaging presents interesting features for multi-view reconstructions while remaining difficult when using a wedge and very sensitive to the frequency range selection.[1] J. Camacho, M. Parrilla, and C. Fritsch. Phase Coherence Imaging. IEEE Transactions onUltrasonics, Ferroelectrics, and Frequency Control, 56(5):958–974, 2009.[2] Baptiste Gauthier, Guillaume Painchaud-April, Alain Le Duff, and Pierre B ́elanger. Towardsan Alternative to Time of Flight Diffraction Using Instantaneous Phase Coherence Imaging for Characterization of Crack-Like Defects.Sensors, 21(3):730, January 2021. Number: 3 Publisher: Multidisciplinary Digital Publishing Institute.[3] V. T. Prado and R. T. Higuti. Instantaneous Frequency Image.IEEE Transactions on Ultrasonics,Ferroelectrics, and Frequency Control, pages 1–1, 2021. Conference Name: IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control.

Performances Evaluation of Instantaneous Frequency Imaging for Specular Reflectors and Multi-View Ultrasonic Inspection

Paper Proceedings: https://asmedigitalcollection.asme.org/qnde/QNDE2021/volume/85529

ASME 2021 48th Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE2021)

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