Bubble sizing with a high spatial resolution

The authors propose a novel method for bubble sizing, based on the double frequency technique, in which f_i (the imaging frequency) is pulsed at a frequency f_r. The received signal from a range cell at a given depth is processed in the same way as in a conventional pulsed Doppler velocimeter. In most cases the pump frequency f_p is greater than f_r, and the demodulated signal is undersampled. If f_p is different from nf_r, it is shown by min|f _p±nf_r| that the longitudinal resolution and the lateral resolution are the same as in conventional Doppler flowmeters (less than 1 mm), and that the measurement of the bubble size is not affected by the pulsed field