If frequency increases, the near zone length is:

If frequency increases, the near zone length is:

• A. decreased
• B. unchanged
• C. constant
• D. increased

Answer: (D)

As frequency goes up, the near zone length grows. This is because the near (Fresnel) zone depends on the transducer’s aperture D and the wavelength λ, with the relationship N = D^2 / (4λ). The wavelength in tissue is about λ = c/f, so N = D^2 f / (4c). Higher frequency means shorter wavelength, which makes the near zone extend farther from the transducer. In practical terms, doubling the frequency roughly doubles the near field length. For a typical 2 cm aperture in tissue, increasing from 5 MHz to 10 MHz increases the near zone from about 32 cm to about 65 cm.

As frequency goes up, the near zone length grows. This is because the near (Fresnel) zone depends on the transducer’s aperture D and the wavelength λ, with the relationship N = D^2 / (4λ). The wavelength in tissue is about λ = c/f, so N = D^2 f / (4c). Higher frequency means shorter wavelength, which makes the near zone extend farther from the transducer. In practical terms, doubling the frequency roughly doubles the near field length. For a typical 2 cm aperture in tissue, increasing from 5 MHz to 10 MHz increases the near zone from about 32 cm to about 65 cm.