Which adjustment to the transmitted pulse reduces the number of cycles and improves axial resolution?

Which adjustment to the transmitted pulse reduces the number of cycles and improves axial resolution?

• A. Increasing damping
• B. Increasing pulse length
• C. Increasing wavelength
• D. Increasing frame averaging

Answer: (A)

Shorter transmitted pulses give better axial resolution because the distance info along the beam path is encoded in the pulse length. Increasing damping shortens the pulse by attenuating the later cycles, so the transmitted pulse contains fewer cycles. Fewer cycles reduce the spatial pulse length, and since axial resolution is tied to that length (roughly half the spatial pulse length), objects that are close together along the axis can be distinguished more clearly. If you were to increase the pulse length, you’d have more cycles, which lengthens the spatial pulse length and worsens axial resolution. Increasing wavelength (lower frequency) also lengthens the wavelength itself, tending to degrade axial resolution. Frame averaging affects image noise and frame time but doesn’t change the transmitted pulse’s cycle count or spatial pulse length, so it doesn’t directly improve axial resolution.

Shorter transmitted pulses give better axial resolution because the distance info along the beam path is encoded in the pulse length. Increasing damping shortens the pulse by attenuating the later cycles, so the transmitted pulse contains fewer cycles. Fewer cycles reduce the spatial pulse length, and since axial resolution is tied to that length (roughly half the spatial pulse length), objects that are close together along the axis can be distinguished more clearly.

If you were to increase the pulse length, you’d have more cycles, which lengthens the spatial pulse length and worsens axial resolution. Increasing wavelength (lower frequency) also lengthens the wavelength itself, tending to degrade axial resolution. Frame averaging affects image noise and frame time but doesn’t change the transmitted pulse’s cycle count or spatial pulse length, so it doesn’t directly improve axial resolution.