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A novel method for micro bubble manipulation by ultrasonic waves is proposed. This method uses seed bubbles in order to manipulate the target bubbles. First, if the seed bubbles are introduced into an incident ultrasonic wave field, they start to oscillate, radiating secondary ultrasonic waves around them. These waves produce Bjerknes force between the bubbles. This produces seed bubble aggregation with a certain size. Then, the target bubbles are introduced, the Bjerknes force between the aggregated seed bubbles and the target bubbles trap the target bubbles, producing a bi-layer bubble mass of (inner layer: seed bubbles, outer layer: target bubbles). Experiments are carried out using bubbles with PVC shells. It is observed that the target bubbles, which are not trapped when they flow into the ultrasonic wave field, are trapped as a bi-layer bubble mass by the proposed method.