During reception, time delays are used to align echoes from different elements to a common depth.

• A. To align echoes from different depths
• B. To align echoes from a given depth
• C. To attenuate noise
• D. To change the frequency

Answer: (B)

Time delays on reception implement focusing at a specific depth. By delaying the signals from each element so that echoes coming from the same depth reach the processor at the same time, those echoes can be summed coherently. This makes the signal from that depth stand out and improves lateral resolution at that depth. As you scan through depths, you adjust the delays to keep focusing on one depth at a time, rather than trying to align echoes from multiple depths simultaneously. So the purpose is to align echoes from a given depth. The other ideas aren’t the primary function: aligning echoes from different depths isn’t how receive focusing works, and while coherent summation can boost SNR, the goal isn’t to attenuate noise directly, nor to change the frequency.