Corner echoes with P mode: Echoes analysis for P waves


A contact inspection with P waves is performed in order to study the echoes reflected by a backwall breaking notch. The inspected specimen is a planar stainless steel mock-up of 37.5 mm thickness containing a backwall breaking notch of dimensions 10×20 mm.



The probe used for these measurements is a circular contact probe of Ø12.7 mm diameter and transmitting P45 waves. The transmitted signal has a frequency of 2.25 MHz, a bandwidth of 50 % and a phase of 280°.



The figure below corresponds to B-scans obtained experimentally and with simulation:



P, SV and conversion mode corner echoes appear on the B-scans. Direct and indirect diffraction echoes can also be identified. The corner echoes associated with mode conversion are also called mixed corner echoes. In the simulated B-scan, the SV corner echo is split in two contributions. The splitting is analyzed here.

The main contribution of the mixed corner echo is the one associated with the path “P-defect-P-backwall-SV”. Indeed, the round-trip path “probe-defect-probe” associated with this mode is very favorable (cf. figure below) and the beam associated with the “SV-backwall-P path” is very strong.

The corner echo associated with the path “SV-defect-SV-backwall-P” contributes also to the mixed corner echo but provides smaller amplitude (almost -8 dB relatively to the corner echo “P-defect-P-backwall-SV”).

The figure below shows the paths associated with each of these contributions:



The B-scan can be reconstructed according to the P or SV waves path:



The following results are calibrated relatively to a SDH of Ø2 mm and located at 37 mm depth.


Defect Echo Experimental (dB) Simulated (dB) Difference(dB)
SDH  P direct echo 0 0 0
Notch P corner echo 1.9 2.9 +1.0
Notch Mixed mode corner echo 4.8 6.1 +1.3
Notch SV corner echo 5.0 7.1 +2.1


A similar configuration is studied. It involves a planar steel specimen of 47 mm thickness containing a backwall breaking notch of dimensions 10×15 mm.

The results are calibrated relatively to a SDH of Ø2 mm located at 44 mm depth. They are displayed in the table below:


Defect Echo Experimental (dB) Simulated (dB) Difference (dB)
SDH P direct echo 0 0 0
Notch P corner echo 2.7 3.6 +0.9
Notch Mixed mode corner echo 4.1 4.5 +0.4
Notch SV corner echo 6.3 8.9 +2.6


There is a good agreement between experimental and simulated amplitudes of P and mixed corner echoes.

The SV corner echo amplitude is slightly over-estimated by CIVA and presents on the B-scan two main contributions. However, this has very few consequences on the main contribution since the difference is only 2 dB and because the echo is well positioned on the Bscan. As for the beam splitting phenomenon, it is studied here.


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