This is a quick video showcasing the wave propagation and echo generation in a plane-strain steel plate with a small hole in the middle. This is a finite-element model I developed, using standard steel properties and a 1MHz sine actuating wave of 1 period long.
Although you can clearly see the hole generate a considerable echo, by the time the echo returns back to the listening surface it has spread out significantly which results in an "arc" shape on the resulting ultrasound scan rather than the expected circular shape.
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