Which of the following is not an advantage of contact ultrasonic search units adapted with lucite shoes?

• A. Allows ultrasound to enter a part's surface at oblique angles
• B. Eliminates most of the crystal wear
• C. Increases sensitivity
• D. Permits adaptation to curved surfaces

Answer: (C)

Lucite shoes provide a protective, replaceable window that lets the ultrasonic beam be directed into the part under more favorable conditions, especially on curved surfaces or when you need to approach the surface at oblique angles. The shoe takes wear and abrasion away from the crystal, extending transducer life, and its shape or window design helps maintain coupling on curved geometries so you can reach areas that would be hard with a bare crystal.

However, adding the lucite layer between the crystal and the test piece introduces additional impedance and attenuation. That extra interface and material path tends to reduce the signal amplitude reaching the part and the returned signal, so sensitivity isn’t increased by using the shoe. The benefits come from wear protection and adaptable beam paths, not from higher sensitivity.