Trapping of micrometer size bubbles by ultrasonic waves

An ultrasonic trapping method of small objects is applied to micrometer size bubbles. The experiments are carried out using an ultrasonic contrast agent of mean diameter 1.3 mum. An ultrasonic focused wave of opposite phase with frequency 5 MHz is applied to produce sequential traps for the microbubble flow. It is found that the microbubbles aggregate forming large masses of bubbles which are trapped inside the ultrasonic wave field. The effects of viscosity of the surrounding liquid are also examined.