When pulsed and continuous-wave sound beams have the same SPTP or SATP intensities, which has the higher SPTA or SATA intensity?

When pulsed and continuous-wave sound beams have the same SPTP or SATP intensities, which has the higher SPTA or SATA intensity?

• A. The pulsed beam
• B. The continuous wave beam
• C. They are equal
• D. Cannot be determined

Answer: (B)

The main idea is how time-averaged intensity relates to how long the beam is on. SPTP (or SATP) is the peak intensity during the pulse, while SPTA (or SATA) is the average intensity over time. The average is reduced in a pulsed beam by the duty factor, which is the fraction of time the pulse is actually on. For a continuous wave, the beam is always on, so the time-averaged intensity equals the peak intensity: SPTA = SPTP and SATA = SATP. For a pulsed beam, the beam is on only part of the time, so SPTA = SPTP × (duty factor) and SATA = SATP × (duty factor), with the duty factor less than 1. If the two beams have the same SPTP or SATP, the pulsed beam’s time-averaged intensity is lower by the duty factor, while the continuous wave keeps the full peak value as its time-averaged intensity. Therefore the continuous wave beam has the higher SPTA or SATA intensity.

The main idea is how time-averaged intensity relates to how long the beam is on. SPTP (or SATP) is the peak intensity during the pulse, while SPTA (or SATA) is the average intensity over time. The average is reduced in a pulsed beam by the duty factor, which is the fraction of time the pulse is actually on.

For a continuous wave, the beam is always on, so the time-averaged intensity equals the peak intensity: SPTA = SPTP and SATA = SATP. For a pulsed beam, the beam is on only part of the time, so SPTA = SPTP × (duty factor) and SATA = SATP × (duty factor), with the duty factor less than 1.

If the two beams have the same SPTP or SATP, the pulsed beam’s time-averaged intensity is lower by the duty factor, while the continuous wave keeps the full peak value as its time-averaged intensity. Therefore the continuous wave beam has the higher SPTA or SATA intensity.