The ultrasonic beam consists of two different zones or fields called the:

• A. Near field and far field
• B. Front field and rear field
• C. Near field and middle field
• D. Apex field and base field

Answer: (A)

Ultrasonic beams behave differently as they travel, so they are described in two zones: the near field and the far field. In the near field, the waves from different parts of the transducer interfere in complex ways, producing a pattern that can be irregular and highly variable in intensity. As distance increases, the waves spread out and the beam settles into a more uniform, narrow main cone with predictable divergence—this is the far field. The boundary between these zones depends on the transducer’s size and the sound wavelength; a common rule of thumb is near field length roughly D^2/λ, with the far field starting at about 2D^2/λ. Understanding these zones helps explain where you’ll get higher lateral resolution and how the beam will interact with flaws at different depths. Other terms like front/rear field or middle/apex/base aren’t used to describe the beam’s two regions, so the standard and most accurate description is near field and far field.