利用環形壓電致動器產生供霧化用表面聲波之研究

Abstract

本研究旨在開發一種在不鏽鋼環盤上產生徑向雷利波的新型環型表面聲波致動元件，此設計不同於以往的單向表面聲波裝置，透過環形的結構設計以及環形指叉電極，在不鏽鋼表面上產生向心的徑向表面聲波。本研究使用有限元素法來分析不同環寬下、不同厚度下和不同指叉電極對數下對雷利波產生的影響及放大倍率進行研究。根據本研究的設計，發現使用不鏽鋼層1.5 mm厚度以上的環型表面聲波元件可在7.26 MHz的驅動頻率下在不鏽鋼表面產生徑向雷利波，由外向內的表面聲波會向中心匯聚，並在內表面處振幅會逐漸增強，接著透過有限元素法模擬這種表面聲波會以雷利角34.43∘輻射進液滴中並產生聲流力，此機制可在液滴表面產生霧化之效果。本研究從分析中整理出壓電層環寬並不會影響振幅放大比例，而隨著不鏽鋼層環寬變長，振幅放大比例則會增大，並且不鏽鋼內徑越靠近中心時，振幅放大比例會增得越快。此外，電極對數會影響位移大小，當電極對數越多時，位移則會越大，從雷利波產生區至圓中心的振幅可以達到4.85倍。本研究總結環型表面聲波致動元件的最佳設計方法，以供使用者可以以最有效率的方法依所需驅動頻率設計出環形表面聲波元件。

This study aims to develop a new annular surface acoustic wave (SAW) actuator that generates radial Rayleigh waves on a stainless-steel ring disk. This design is different from the standard unidirectional SAW devices. This device has a unique annular structural design and annular interdigitated electrodes, which can generate centripetal radial surface acoustic waves on the stainless-steel surface. To study the effectiveness of this design, the finite element method is used to analyze the effect and magnification of the amplification ratio and displacement on the generation of Rayleigh waves under different ring widths, thicknesses, and pairs of interdigital electrodes. It was found that when using an annular surface acoustic wave element with a stainless steel thickness of more than 1.5 mm, radial Rayleigh waves can be generated on the surface of stainless steel at a driving frequency of 7.26 MHz. The surface acoustic waves can be activated from the outer ring and propagate toward the center of the stainless-steel ring disk. The amplitude at the inner surface will gradually increase. Based on the finding of the finite element analysis, this surface acoustic wave will radiate into a droplet at a Rayleigh angle of 34.43∘with a concentric acoustic force. This mechanism can produce an acoustic atomization effect on the droplet surface. In summary, this study concludes that the ring width of the piezoelectric layer does not affect the amplification ratio. As the ring width of the stainless-steel ring dish becomes longer, the amplification ratio also increases. Furthermore, when the inner diameter of the stainless steel is closer to the center, the amplitude amplification ratio will increase. In addition, the number of electrode pairs can affect the amplitude of the displacement at center. More electrode pairs can have a larger displacement and amplitude from the Rayleigh wave generation area to the central region. The amplification ratio can be 4.85 times. Lastly, this study also summarizes the best design criteria for ring-shaped SAW actuators so that users can follow this guidance to design a ring-shaped surface acoustic wave devices.