What is the primary purpose of acoustical lenses in ultrasonic testing?

• A. To focus the beam
• B. Contour correction
• C. To adjust frequency
• D. To replace wedges

Answer: (D)

Acoustical lenses shape and control the ultrasonic beam by bending it so that it converges to a focal point inside the test material. The lens material has a different speed of sound than the surrounding medium, so the wavefront is refracted according to Snell’s law. This focusing tightens the beam at a chosen depth, increasing energy density and improving lateral resolution and flaw detectability at that depth.

Wedges serve a different purpose: they change the path and angle of the beam entering the material, not the beam’s focus. Frequency is determined by the transducer and drive electronics, not by the lens. Contour correction is not the primary role of the lens.