If the transducer diameter increases while keeping frequency constant, what happens to the focal depth?

If the transducer diameter increases while keeping frequency constant, what happens to the focal depth?

• A. No change
• B. Shallower
• C. Deeper
• D. Unpredictable

Answer: (C)

Focal depth is set by the aperture size and the wavelength. With a fixed frequency, the wavelength is fixed, so changing the transducer diameter directly shifts where the beam comes to its tightest focus. A larger diameter acts like a bigger focusing element, and the focal length scales roughly with D^2/λ. Since λ is constant, increasing D pushes the focus farther from the transducer, making the focal depth deeper.

Focal depth is set by the aperture size and the wavelength. With a fixed frequency, the wavelength is fixed, so changing the transducer diameter directly shifts where the beam comes to its tightest focus. A larger diameter acts like a bigger focusing element, and the focal length scales roughly with D^2/λ. Since λ is constant, increasing D pushes the focus farther from the transducer, making the focal depth deeper.