聲波懸浮系統中懸浮物之參數討論

Abstract

本研究我們建立了非共振型懸浮系統，並探討薄片狀物體的面積、密度等參數如何影響聲波懸浮的難度。測試結果顯示薄片樣本的密度、厚度越大，會越難被懸浮。而樣本的面積在臨界面積以下，面積越大會越容易懸浮，超過臨界面積則相反，我們由實驗數據的擬合結果得到面積公式。而樣本形狀的測試結果顯示正方形會比長條形容易懸浮、實心圓會比圓環容易懸浮。我們由水平聲場量測結果定義了形狀參數，此參數越大代表樣本接收聲波輻射力的程度越好。我們將此參數與實驗結果進行擬合，得到形狀公式，但此公式對於小面積物體的預測與實驗結果是相反的，可能是因為聲場的非軸對稱或懸浮物的質心並非落在懸浮器中心軸上等原因。最後，藉由形狀公式與面積公式，我們預測不同密度、尺寸的圓球與橢球被懸浮所需的聲壓。

In this research, we established a non-resonant acoustic levitation system. We also discussed the effects of thicknesses, areas, densities, and shapes of planar objects on the difficulty of levitation. The experimental results show that sound pressure required to levitate the objects increases as their thicknesses or densities increase. As for the objects’ areas, the difficulty of levitation decreases with the increasing areas of the objects when the areas are lower than a critical value. Otherwise, the larger the areas of the objects are, the harder they are to be levitated. We defined a shape factor by results of sound field measurement. This factor can describe the extent of acoustic radiation forces that the objects received in the same sound field. Then we got the area formula and the shape formula by curve fitting. However, the prediction of the shape formula is contrary to the experimental data for the objects of low areas. We thought it is because the sound field inside the levitator was not axisymmetric and the centroids of the levitated objects were not located on the central axis of the levitator. Finally, by the area formula and the shape formula, we predicted the sound pressure required to levitate a sphere or an ellipsoid of arbitrary density.