FIG. 5.

(Color online) (a) Subharmonic, (b) second harmonic, and (c) fundamental components of the scattered responses from droplets, microbubbles, propylene glycol stream, and control at an excitation frequency of 2.25 MHz. Central frequencies of transmitting (T) and receiving (R) transducers are indicated in the legends. The data sets were scaled by 10⁵ for easier display. The ADV threshold determined from each curve is denoted by ($*$).