Which statement about the frequency content of ultrasound pulses is true?

Which statement about the frequency content of ultrasound pulses is true?

• A. The pulse contains only the center frequency
• B. The pulse contains a range of frequencies around the center frequency
• C. The pulse contains frequencies only above the center frequency
• D. The pulse contains no frequency components

Answer: (B)

Finite-duration ultrasound pulses cannot be a single pure frequency. The short time length of a pulse requires a spread of frequencies around the center frequency, forming a bandwidth. The energy is concentrated near the center frequency but includes frequencies both above and below it, depending on the pulse shape. The shorter the pulse, the wider the bandwidth. So the pulse contains a range of frequencies around the center frequency.

Finite-duration ultrasound pulses cannot be a single pure frequency. The short time length of a pulse requires a spread of frequencies around the center frequency, forming a bandwidth. The energy is concentrated near the center frequency but includes frequencies both above and below it, depending on the pulse shape. The shorter the pulse, the wider the bandwidth. So the pulse contains a range of frequencies around the center frequency.