During L0° inspections, the amplitude variation of the specimen backwall echo with the probe translation can be used to detect flaws: a decrease in the backwall amplitude is associated with partial shadowing by one or several defects present between the probe and the backwall.
In CIVA 11, the shadowing of the specimen geometry by a defect is modeled very simply: a ray from the probe arriving on a defect before reaching the specimen backwall is stopped and then does not contribute to the backwall echo. It is known that contributions of diffracted rays from the defect edges should be taken into account in the backwall echo calculation.
The presented study consists in evaluating the validity of the simplified shadowing model by comparing the backwall echo of a flat specimen obtained in a non-shadowed area with the one of a zone shadowed by “ribbons” type defects parallel to the specimen surface. The backwall echoes amplitudes are measured and compared to the CIVA11 predictions. The ribbons are located at different depths (between 20mm and 80mm with 20mm step) and 6 probes of 2.25MHz and 5 MHz and of 19mm, 12.7mm, and 6.35 mm were used to detect them.
It should be noted that no publication about the validity of the shadowing model has been yet identified in the literature.