A question about front-surface effects on rough surfaces: A widening of the front-surface indication is caused by what phenomenon?

• A. Diffraction from surface roughness
• B. Side-lobe energy reflections
• C. Specular reflection
• D. Multiple scattering

Answer: (B)

The widening of the front-surface indication on a rough surface comes from side-lobe energy reflections. When a transducer emits a pulse, some energy travels in side lobes off the main beam. A rough surface can scatter this side-lobe energy back toward the probe, and because these side-lobe paths have different angles and longer, more varied travel distances, their echoes arrive at different times. The result is a smear or broadening of the leading edge of the front-surface echo on the display. Specular reflection would produce a sharp, well-defined front edge, while other effects like multiple scattering or diffraction can contribute to broadening in other ways, but the specific widening tied to off-axis, backscattered energy from side lobes is why this phenomenon is described this way.