1Center for Industrial and Governmental Relations, The University of Electro-Communications, 2Graduate School of Informatics and Engineering, The University of Electro-Communications, 3Aichi Institute of Technology
A familiar example of waves are sound wave in air that are used as a medium for communication without being aware of their presence. At the same time, sound waves, particularly ultrasound are positively utilized as a collection tool of information in non-destructive testing and acoustical imaging. Generally, waves exhibit phenomena like diffraction, reflection, and interference. Radiation pressure is also one of the phenomena that waves have in common with each other. Acoustic radiation pressure is exerted on an interface that separates two acoustically different fluids and is provided by the difference of the acoustic energy densities in both fluids. Hence, it is regarded as a non-zero net pressure of the second order of smallness. Practically, acoustic radiation force is of importance in applications where evaluation is performed by integrating the radiation pressure over an obstacle surface. Although the radiation force is small as well, it can be utilized for non-contact levitation and manipulation of small obstacles by focusing ultrasound waves on them. This report overviews second-order classical phenomena caused by acoustic energy; specifically, the phenomena of waveform distortion, radiation pressure, and acoustic streaming.