Lower frequency sound beams spread out more in which zone?

Lower frequency sound beams spread out more in which zone?

• A. Near field
• B. Focal zone
• C. Deep far zone
• D. Mid field

Answer: (C)

Beam spreading in ultrasound is governed by diffraction. For a given transducer size, the beam’s divergence in the far field increases with wavelength. Lower frequency means a longer wavelength, so the beam spreads more as it travels. This greater spreading is most evident in the deep far zone, the region beyond the focal area where the beam has had time to diffract and widen. Near the transducer the beam stays relatively narrow, and the focal zone concentrates energy, but once you pass into the deep far zone, the low-frequency beam shows the most divergence. Higher frequencies, with shorter wavelengths, stay more collimated over the same distance.

Beam spreading in ultrasound is governed by diffraction. For a given transducer size, the beam’s divergence in the far field increases with wavelength. Lower frequency means a longer wavelength, so the beam spreads more as it travels. This greater spreading is most evident in the deep far zone, the region beyond the focal area where the beam has had time to diffract and widen. Near the transducer the beam stays relatively narrow, and the focal zone concentrates energy, but once you pass into the deep far zone, the low-frequency beam shows the most divergence. Higher frequencies, with shorter wavelengths, stay more collimated over the same distance.