Beam spread and attenuation are measured in which region of the ultrasonic beam?

Beam spread and attenuation are measured in which region of the ultrasonic beam?

• A. Near field
• B. Rear field
• C. Far field
• D. Middle field

Answer: (C)

The main idea is that certain measurements only become meaningful once the beam has moved far enough from the transducer. In the near field, the beam is still in a complex interference pattern and doesn’t spread in a simple, predictable way, so assessing how the beam spreads or how its energy attenuates isn’t reliable there. In the far field, the wavefronts have stabilized into a more uniform, diverging beam with a clear angle of spread, and the amplitude decreases with distance due to geometric spreading and material absorption. This is the region where you can meaningfully quantify both beam spread and attenuation. The rear or middle field aren’t the standard regions used for these measurements.

The main idea is that certain measurements only become meaningful once the beam has moved far enough from the transducer. In the near field, the beam is still in a complex interference pattern and doesn’t spread in a simple, predictable way, so assessing how the beam spreads or how its energy attenuates isn’t reliable there. In the far field, the wavefronts have stabilized into a more uniform, diverging beam with a clear angle of spread, and the amplitude decreases with distance due to geometric spreading and material absorption. This is the region where you can meaningfully quantify both beam spread and attenuation. The rear or middle field aren’t the standard regions used for these measurements.