1. Improvement of ultrasonic cross-sectional imagery via the application of coherence weighting and the total focussing method.
Benjamin Knight-Gregson1,2†, Miles Weston2,
Anthony Peyton1, Claire Davis3 and Patricia Scully1
1The University of Manchester, Oxford Road, Manchester, UK 2TWI Technology Centre (Wales), Port Talbot, UK
3The University of Warwick, Coventry, UK
†Corresponding author:

2. Motivation
Cross sectional imagery is common place in ultrasonic inspections
Materials commonly used in various industries for their strength and work hardening properties can cause high levels of background noise due to their grain structure
Background noise can reduce likelihood of detection of defects and indications

3. Motivation
SDH
Backwall

4. Motivation TWI has developed real-time FMC/TFM inspection
Need to find a way of improving imaging performance without degrading inspection speed

5. Introduction
FMC – Synthetic aperture technique.
What is fmc/TFM?

6. FMC Data Acquisition Transmit (tx) 1 2 3 4 … N 1 2 3 4 … N 1 2 3 4
Receive (rx)
Transmitting
element …
Receiving
element N
Full Matrix of Data
Animation courtesy of TWI Ltd.

7. FMC Data Acquisition
Image reconstruction is often done after acquisition
64 elements = 4096 A-scans (642)
Region of interest 100x100px
40.96M TOF calculations (data size >4MB)
TWI Wales has developed a real-time system based on GPU processing

8. TFM Image Reconstruction
Region of interest
1. Select a region of interest
Image courtesy of TWI Ltd.

9. TFM Image Reconstruction
Grid of pixels
2. Region of interest defined as a grid of pixels
Image courtesy of TWI Ltd.

10. TFM Image Reconstruction
Sum A-Scans to single pixel
Grid of pixels
3. Each pixel has a contribution from every tx/rx combination
Image courtesy of TWI Ltd.

11. TFM Image Reconstruction
Sum A-Scans to single pixel
Grid of pixels
4. Iterate for all pixels
Image courtesy of TWI Ltd.

12. Common array imaging Focussed linear scan Unfocussed linear scan
Sectorial scan
FMC/TFM
Images courtesy of TWI Ltd.

13. Introduction
FMC – Synthetic aperture technique.
Coherence weighting

14. Signal coherence Due to the focusing nature of TFM, one
would expect reected signals from a speckle
generating indication to produce coherent
echoes after the signals have been time-shifted
according to the delay-and-sum procedure.

15. Signal coherence Apply time delays High coherence Low coherence

16. α is a sensitivity modifier
Coherence Factor (CF)
Amplitude based
Sign Coherence Factor (SCF)
Phase based
SCF: looking at the standard deviation of the polarity of the data contributing
to the desired pixel
α is a sensitivity modifier
Mallart, and Fink. ‘Adaptive Focusing in Scattering Media through Sound‐speed Inhomogeneities: The van Cittert Zernike Approach and Focusing Criterion’. The Journal of the Acoustical Society of America 96, no. 6 (1 December 1994): 3721–32. doi: /
Camacho, J., M. Parrilla, and C. Fritsch. ‘Phase Coherence Imaging’. IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 56, no. 5 (May 2009): 958–74. doi: /TUFFC

17. Simulation and experimentation
Results
FMC – Synthetic aperture technique.
Simulation and experimentation

18. Simulation setup
Ø= 3.0 mm
Avramidis, Weston, and Liaptsis. ‘Ultrasonic Modelling of Coarse Grained Austenitic Steel’. Proceedings of the 53rd Annual Conference of The British Institute of Non-Destructive Testing. Manchester, UK, 2014.

19. Simulation results

20. TFM & CF
α=1
α=2
α=3
α=4
α=5
α=6

21. TFM & SCF
α=1
α=2
α=3
α=3
SDH
α=4
α=5
α=6

22. Coarse grained steel cast sample
2 mm
SDH Ø= 2.5 mm

23. Coarse grained steel cast sample
2 mm
Optical micrograph courtesy of Neil Hollyhoke, WMG – University of Warwick

24. Coarse grained steel cast sample
α=1

25. Conclusions
Coherence weighting has shown the ability to partially mitigate structural noise in cross section imagery
SDH at 6 dB above background noise in simulation
SDH > 5 dB above background noise on cast steel sample. Unable to be resolved with standard TFM imaging

26. Work supported by

27. Thank you for listening. Any Questions?
Presented by:
Benjamin Knight-Gregson
The University of Manchester, Oxford Road, Manchester, UK
& TWI Technology Centre (Wales), Port Talbot, UK