What is the property of certain materials that enables conversion between electrical energy and mechanical energy?

• A. Mode conversion
• B. Piezoelectric effect
• C. Refraction
• D. Impedance matching

Answer: (B)

The phenomenon at play is the piezoelectric effect. Certain crystals and ceramics generate mechanical strain when an electric field is applied, and conversely produce an electric signal when they are mechanically deformed. In ultrasonic testing, applying a brief electrical pulse to a piezoelectric element makes it physically vibrate, generating ultrasonic waves that travel into the test material. When those waves reflect back and interact with the material, the mechanical vibrations induce a voltage in the element, which the instruments detect as the signal.

The other options describe wave behavior or networking concepts rather than a material’s energy-converting property: refraction is the change in direction of waves at a boundary; impedance matching deals with transferring energy efficiently between materials; mode conversion involves changing between wave types at interfaces, not the intrinsic energy conversion capability of the material itself.