What benefit would you obtain by choosing a transducer having a large diameter compared to one having a small diameter?

• A. It can focus at greater depths
• B. Increases the frequency
• C. It increases the beam diameter in the far field
• D. Both A and C

Answer: (D)

A transducer with a larger diameter acts like a bigger optical lens for ultrasound. The larger aperture concentrates the emitted energy more tightly and reduces how quickly the beam spreads as it travels. That means the beam stays narrow to greater depths, so focusing at deeper locations becomes possible and lateral resolution is improved at those depths.

Frequency, on the other hand, is set by the transducer’s material and the drive signal and isn’t determined by the aperture size, so it isn’t a benefit gained from choosing a larger diameter.

Regarding the beam in the far field, a bigger aperture actually reduces beam divergence, producing a narrower beam as it travels farther, not a larger beam diameter.

So the key benefit is the ability to focus at greater depths (with a tighter beam as it propagates).