TFM frame rate

A TFM frame costs two things: the time to acquire the full matrix capture, and the time to reconstruct the image from it. Acquisition needs one pulse per transmitting element, so it takes N_tx / PRF seconds. Reconstruction needs one delay-and-sum operation for every transmit-receive pair at every pixel, for every mode imaged: N_tx × N_rx × pixels × modes.

Both scale badly. Doubling the number of elements doubles the acquisition time and quadruples the processing load. Halving the pixel pitch quadruples the processing load alone. Adding a second wave mode set doubles it again. This is why practical TFM setups use a sub-aperture rather than all 64 or 128 elements, and why zones are kept small.

Knowing which of the two limits applies tells you what to change. If acquisition is the limit, reduce the number of transmit elements or raise the PRF. If processing is the limit, shrink the zone, coarsen the grid within the amplitude fidelity budget, or drop a mode. Changing the wrong one buys nothing.

operations per frame = N_tx × N_rx × pixels × modes
processing limit = throughput / operations per frame
acquisition limit = PRF / N_tx
frame rate = the lower of the two