What does hydrophone measurement characterize in a transducer beam?

• A. It measures the transducer's electrical impedance.
• B. It measures mechanical resonance frequency.
• C. It maps acoustic pressure to determine beam width, near/far-field characteristics, peak pressures, and intensity distribution; parameters include lateral/axial beam profiles and focal region measurements.
• D. It assesses battery life.

Answer: (C)

Hydrophone measurement characterizes the acoustic pressure field produced by a transducer beam. By sampling pressure at many positions in water, it creates a map of how pressure varies in space and time. This lets you determine the beam’s width and shape, both laterally and axially, how the beam behaves in the near field versus the far field, the peak pressures within the focal region, and how the intensity is distributed throughout the beam. In short, it’s about the actual sound pressure and its distribution, which underpins how the beam delivers energy.

The other options don’t fit because electrical impedance, mechanical resonance frequency, and battery life pertain to the transducer’s electrical properties, mechanical construction, or power status rather than the acoustic pressure field that a hydrophone is used to measure.