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

我们知道，强超声波对液体的照射使液体向波的传播方向流动。这种现象被称为声流。作者报告说，使用高频超声波可以大大增强这种现象。这个项目的最终目标是观察空气中的声流。为此，我们致力于开发高频、高效的空气超声换能器。首先，详细研究了溶胶-凝胶沉积压电陶瓷薄膜在超声换能器中的应用。研究了热过程中温度分布和环境气体对薄膜质量和压电性的影响。然后，对超声换能器的制作工艺进行了研究。我们开发了一种在热处理之前对PZT前驱体凝胶进行图像化的方法。此外，我们还开发了一种制造任意形状的相对厚的扁平PZT结构的技术。该技术的优点是简单，重现性高。将这些方法应用到高频超声换能器的实现中。制作了厚度为1 μm、直径为160 μm的超声换能器。换能器工作在2 GHz，估计机电耦合达到20%。为了有效地将超声波激发到空气中，必须对换能器进行减薄以激发断裂振动。目前，我们正在开发这种细化过程。我们希望我们能尽快建立这个过程，然后将尝试观察空气中的声流。

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.