Ultrasound intensity is usually greatest in which part of the beam?

• A. The center of the beam
• B. The edges
• C. Uniform across the beam
• D. Under the transducer housing

Answer: (A)

Ultrasound energy concentrates most strongly along the central axis of the emitted beam. When the transducer’s active surface emits waves in phase across the aperture, the waves reinforce at the center, creating the main lobe with the highest intensity. As the wavefronts spread (diffraction) and move away from the center, the energy is dispersed over a larger area, causing the intensity to decrease toward the edges. The region under the transducer housing doesn’t emit energy, so it wouldn’t be the area of greatest intensity. In short, the center of the beam carries the greatest intensity because energy is most concentrated along the central axis.