- 學位論文
楔形體導波於探頭延遲線與音波流動效應之研究
A Study in Wedge Waves with Applications in Delay-line and Acoustic Streaming
摘要
楔形體導波(wedge wave)是沿著楔形體頂端傳遞的導波，在特定頻率下其能量會集中在楔形體尖端產生大振幅的振動，且當頂端無截平時楔形體導波具有無頻散關係之特性。此外楔形體導波還具有振形複雜、低能量衰減以及易受幾何條件與邊界條件影響之特性。有鑑於楔形體導波擁有如此之獨特性與多樣性，但至今仍然沒有以楔形體導波為基礎之前端應用技術。因此本研究將利用楔形體導波頂端大振幅、頂端無截平時無頻散現象以及低能量衰減之特性發展楔形體延遲線(delay-line)。另一方面，針對楔形體導波頂端大振幅與振形複雜之特性探討楔形體導波所造成之音波流動效應(acoustic streaming)。 研究中所開發之楔形體延遲線主要是利用楔形體尖端作為訊號感測用，而所感測到之超音波訊號則利用表面波或橫波探頭作擷取。所開發之楔形體延遲線不但擁有點接觸之高空間解析度優勢以及不需耦合劑之特性。因此非常適合針對小管俓管狀結構、流體模態更甚至是微小尺寸之試片進行超音波量測。且透過不同之實驗架設方式，楔形體延遲線還可分別針對面內橫波、面外橫波以及面內縱波作量測。進一步結合楔形體延遲線與雷射干涉儀更可獲得高達15MHz之訊號量測頻寬。此外，楔形體延遲線還可在點接觸情況下於待測試片中激發面內橫波振動形式之超音波訊號。 另一方面，因楔形體導波具頂端大振幅以及振形複雜之特性，所以楔形體導波對於提昇微流道中流體推進以及混和之效率有很大的幫助，因此本研究亦針對楔形體導波造成之流體音波流動效應進行討論。根據流場分析軟體(CFD-RC)針對楔形體導波造成之音波流動效應分析結果發現，楔形體導波造成之音波流動效應會受到導波振幅、作用週期以及流體黏滯係數的影響。且因楔形體導波之振幅隨著深度增加而遞減，因此不同深度線性音波流動效應之瞬時流速大小與非線形音波流動效應之平均流速分佈都不相同。其中，當楔形體導波振幅增加一倍，瞬時流速會跟著增加一倍，但非線性音波流動效應之最大平均流速值會有大於平方倍的增加趨勢。而當流體之黏滯係數增加1.5倍時，非線性音波流動效應之平均流速最大值會減少28.8％。
並列摘要
This study is focused on wedges waves with applications in delay-line and acoustic streaming. Wedges waves are guided waves with their particle motion anti-symmetric about the apex mid-plane and the energy tightly confined near the wedge-tip. In addition, wedge waves are dispersion-free with small truncation, large amplitude, extremely large amplitude at corner and small energy attenuation. For large amplitude and small energy attenuation, a new ultrasound transducer delay-line has been developed in this research. The wedge delay-line formed by a 5MHz shear piezoelectric transducer and an aluminum wedge with apex angle 60° can detect signals with point-like contact area and without any couplant. In addition, the wedge delay-line can detect the in-plane or out-plane vibration by changing the contact angle between samples and wedge delay-line. Also, the ultrasound transducer delay-line can be used as in-plane SH wave generator. Acoustic streaming is a fluidic phenomenon induced by acoustic waves. In this research, three-dimensional nature of the wedge wave-induced acoustic streaming flow fields are characterized through the computational fluid dynamics (CFD) and flow observation. The wedge waves induced acoustic streaming flow fields are also characterized for several parameters including instantaneous flow direction, time average velocity profile, height of observation plane and exciting amplitude. The acoustic streaming induced by wedge waves is more complex and non-uniform. Therefore wedge waves could be favorable to micro-mixing applications.