A discontinuity with a concave surface will cause the reflected beam to:

• A. Diffuse the sound energy throughout the part
• B. Cause the reflected beam to focus at a point
• C. Cause mode reinforcement of the ultrasonic wave
• D. None of the above

Answer: (B)

A concave surface acts like a focusing reflector for sound waves. When the ultrasonic beam strikes this curved surface, the reflections from different parts of the surface bend toward a common point along the axis, causing the wavefronts to converge. This concentrates the energy at a focal point, producing a stronger echo at that location. If the surface were flat, you’d get a directionally reflected beam (specular), and if it were rough, the energy would scatter rather than focus. Mode reinforcement isn’t the inherent effect of a concave reflector, so the focusing at a point is the best description of what happens.