Phase Coherence Imaging 

PCIPhase Coherence Imaging is an ultrasonic technique combining the advantages of both time-of-flight diffraction (TOFD) and phased array using the total focusing method (TFM). It uses the phase information from captured A-scans to generate TFM images. By comparing the coherence of A-scan phases for each position within the TFM grid, each spatial position receives a coherence amplitude from 100% (strong) to 0% (weak).
A strong phase coherence is received from reflections and diffractions from defects. A weak phase coherence is received from other signals, such as high-frequency background noise. Therefore, this technique offers an improvement in signal-to-noise for inspecting noisy/attenuative materials and identifying defects in such materials.

As with TOFD, PCI is capable of detecting small defects, including those of unfavourable orientation for standard phased array techniques. PCI is capable of locating, positioning and sizing defects volumetrically using the TFM process and has an advantage over TOFD because it is amplitude independent.

For more information on PCI see:
J Camacho et al, ‘Phase coherence imaging’, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, Vol 56, No 5, pp 958-974, May 2009. DOI: 10.1109/TUFFC.2009.1128. Available at: https://ieeexplore.ieee.org/document/4976281 
J Camacho et al, ‘Phase coherence imaging: principles, applications and current developments’, Proceedings of Meetings on Acoustics, 2019 International Congress on Ultrasonics, Vol 38, 055012, 2019. Available at: https://asa.scitation.org/doi/10.1121/2.0001201 and www.olympus-ims.com/en/insight/5-main-advantages-of-phase-coherence-imaging-pci/

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