Which zone is closest to the transducer? (Alternative option)

Which zone is closest to the transducer? (Alternative option)

• A. Near zone
• B. Fresnel zone
• C. Far field
• D. Doppler zone

Answer: (A)

In ultrasound, beam geometry creates distinct regions along the path from the transducer. The region closest to the transducer is the near field, where the emitted waves from the aperture are still interacting and the beam is not yet uniform. This zone is sometimes referred to as the Fresnel zone, but when asked for the closest region to the transducer, the near field is the precise label. The end of the near field marks the start of the far field, where the beam begins to spread more steadily and the wavefronts become more planar. How long the near field lasts depends on the transducer diameter and the wavelength: L near ≈ D^2/(4λ). Larger apertures or shorter wavelengths extend the near field. So the closest zone to the transducer is the near field. The far field is farther away, and a Doppler zone isn’t a standard spatial zone in this context.

In ultrasound, beam geometry creates distinct regions along the path from the transducer. The region closest to the transducer is the near field, where the emitted waves from the aperture are still interacting and the beam is not yet uniform. This zone is sometimes referred to as the Fresnel zone, but when asked for the closest region to the transducer, the near field is the precise label.

The end of the near field marks the start of the far field, where the beam begins to spread more steadily and the wavefronts become more planar. How long the near field lasts depends on the transducer diameter and the wavelength: L near ≈ D^2/(4λ). Larger apertures or shorter wavelengths extend the near field.

So the closest zone to the transducer is the near field. The far field is farther away, and a Doppler zone isn’t a standard spatial zone in this context.