It is well known that “Secondary Bjerknes Force” works attractive and repulsive force between microbubbles by acoustic radiation. But it has not cleared that effective way to trap microbubbles aggregations. Hence, in this report, we aimed to design an acoustic field that is capable of trapped large microbubbles per unit acoustic power by aligning the acoustic power passing through the flow channel. First, we examined the relation between the total trapped area of microbubbles and the elevation angle of the transducer in an opposite direction to the suspension flow, so that we can minimize the influence caused by irradiating acoustic beam angle deviating from the centralaxis of the transducer. Next, we designed 19 kinds of acoustic field using a 2D-array transducer, and examined the acoustic pattern's capability of the amount of trapped microbubbles per unit acoustic power. Through these experiments, we found that the trapped amount of microbubbles was stable according to the variation of the irradiation angle of ultrasound with the condition of flow rate of 20 mm/s and elevation angle of 40 deg. Furthermore, we have succeeded to form an acoustic field which has been able to trap 1.87 times greater microbubbles than a conventional focused acoustic field.
