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/sub i/ (the imaging frequency) is pulsed at a frequency f/sub 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/sub p/ is greater than f/sub r/, and the demodulated signal is undersampled. If f/sub p/ is different from nf/sub r/, it is shown by min mod f/sub p/+or-nf/sub r/ mod 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.<>