Observation of Acoustic Streaming in Air and Application to Micro-Manipulator

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It is known that irradiation of powerful ultrasonic waves to liquid causes its flow toward the direction of wave propagation. This phenomenon is called the acoustic streaming. The authors reported that this phenomenon can be enhanced considerably by the use of high frequency ultrasonic waves. Final goal of this project was to observe the acoustic streaming in air. For this purpose, we have devoted ourselves to the development of high frequency and highly efficient ultrasonic transducers for air. First, sol-gel deposition of piezoelectric PZT films was investigated in detail for the application to the ultrasonic transducers. It was shown how the film quality and piezoelectricity are influenced by the temperature profile and environmental gas during the thermal process. Then, the fabrication process for the ultrasonic transducer was investigated. We developed a method to pattern PZT precursor gel prior to the thermal process. In addition, we also developed a technique to fabricate relatively thick and flat PZT structures of arbitrary shape. This technique is advantageous due to its simplicity and high reproducibility. These methods were implemented into the realization of high frequency ultrasonic transducers. The ultrasonic transducer of 1 μm thickness and 160 μm diameter was fabricated. The transducer operates at 2 GHz, and estimated electromechanical coupling was attained to 20%. For the efficient excitation of ultrasonic waves to air, the transducer must be thinned to excite fracture vibration. Presently, we are developing this thinning process. We hope that we will establish this process very soon, and then will try to observe the acoustic streaming in air.