本研究探討由壓電元件做為振動源在毫米尺度模型內產生超音駐波
(ultrasonic standing wave, USW)來凝聚溶液中微粒之現象，並採用流場可視化
(Flow Visualization)與微粒影像測速儀(Particle Image Velocimetry)技術觀察在共
振腔室內超音波駐波現象，以及超音波駐波與聲射流流動之交互作用。
本研究中使用阻抗分析儀測得壓電片的共振頻率，並以波形產生器設定驅動頻率、電壓、與波形，並以功率放大器將振幅放大以驅動壓電片，透過超音波傳導膠將超音波導入壓克力製模型以產生駐波。流場可視化與微粒影像測速儀實驗則以展開之雷射光頁照射模型內部，使用sCMOS 高速攝影機拍攝腔室流場流動情形進行分析。實驗中使用粒徑為5 ~ 18 微米之聚醯胺(Polyamide)與聚苯乙烯(Polystyrene)微粒做為攝影機的循跡微粒，得到腔室內超音波駐波與聲射流間的交互作用關係，並測試於0.8~2MHz 中頻率與微粒聚集效率之關係，探討微粒與水分離的效果。
實驗結果顯示成功的產生出超音波駐波的現象，其實際駐波波長與理論波長間誤差不超過6%；超音波駐波現象產生同時伴隨聲射流流動，在相同驅動頻率下，聲學控制能力是18μm>10μm>5μm。在0.847、1.016、1.355、1.863、2.032MHz 之測試條件下，18μm 聚集效率皆大於10μm。不論在何種驅動頻率下，聲射流在開啟壓電片時便開始產生，影響腔室內部流場，使流體產生流動，微粒因而開始移動。在10μm、18μm 驅動頻率為0.847、1.863、2.032MHz 下，超音波駐波與聲射流同時發生且互不干擾。此項結果顯示未來可結合流道設計穩定其流動情形，進而用以收集微粒。

In this study, ultrasonic standing waves (USW) are generated using the
piezoelectric plate as a vibration source in a millimeter-scale chamber to agglomerate
the particles in the suspension solution, and the interaction between USW and induced
acoustic streaming flow patterns is studied by Flow Visualization (FV) and Particle
Image velocimetry (PIV).
The driving oscillation frequency is set to the natural frequency of the piezoelectric plate measured by an impedance analyzer. Driving parameters including frequency, voltage and waveform are set to the waveform generator and amplified by a power amplifier to enlarge the amplitude of the driving signal. The oscillation of the
piezoelectric plate is conducted to the acrylic resonated chamber by the ultrasonic
coupling gel for the experiments. FV and PIV experiments are performed using the laser light sheet as illumination and the flow patterns are recorded by a high-speed sCMOS camera. There are 3 different tracer particles (polyamide and polystyrene particles, 5 ~18μm) used as the tracers of the flow to investigate the interaction between USW and acoustic streaming. Relationships of the driving frequency(0.8~2MHz) to the particle aggregate efficiency are investigated.
Experimental results show that the ultrasonic standing wave is successfully
generated, and the error between the standing wavelength in the theory and in the
experiment does not exceed 6%. The ultrasonic standing waves is accompanied by the
acoustic streaming flow, and the acoustic control capability of the acoustic radiation
force of particles in different diameters is 18μm>10μm>5μm. Within the aggregation
efficiency range of 0.847,1.016,1.355,1.863 to 2.032 MHz, the aggregation efficiency
of 18μm particle are all greater than the 10μm one. With all driving frequencies it is
found that the acoustic streaming flow starts as the oscillation is turned on and affecting the flow patterns immediately.At driving frequencies of 0.847,1.863,2.032MHz for 10μm and 18μm particles, the acoustic streaming flow does not interfere with USW and both effects coexist. This finding suggests potential applications of combining both phenomena for better collection of particles.

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