本論文的主軸為探討於高頻交流電場下，非對稱極化現象對於微流體系統中粒子與流體運動的影響，並藉由設計上的變化來操控流道中的非平衡電荷動力現象。而本論文主要分成兩部份，以下我分別加以介紹。
第一部份，我設計兩不同寬度的電極交錯使之成為一陣列，然後在微流道內通入次微米膠體粒子與二次水混合溶液以交流電場作用。我觀察到超高頻(≧1MHz)下為負介電泳(n-DEP)的粒子聚集模式，但是較寬之電極會因尺度差距而造成較明顯的粒子往電極內部移動現象。另外在高頻範(10kHz~100kHz)下，出現非對稱性的交流電滲流現象，會發現到寬度較小的電極上流動速度較快，而寬度較大的電極上流動速度較慢。
論文的第二部份，我在交流電場下觀察二氧化矽粒子運動受傾斜的電極陣列影響。其中在高頻(≧1MHz)為負介電泳的粒子聚集模式，然而角度越傾斜(傾斜角度越小)聚集量越多，這是由於傾斜電極之粒子誘導電偶極與施加電場的方向非等齊。另外加高操作電壓至50Vpp而頻率為1MHz時，會發現聚集粒子被交流電滲流迅速地帶走，此現象有可能是電化學反應所導致。然而在中高頻範圍(1kHz~100kHz)時，主導的歐姆充電作用機制會因傾斜角度而有作用分量產生，導致流體在靠近管壁的地方呈現出螺旋狀轉動的效應後，然後粒子伴隨流體流動且產生局部聚集的效果，另外在特定頻率(100kHz)時加高電壓並搭配非對稱排列的微流道，則會觀察到往電極外流道較短的一方的淨流動現象。最後在低頻(100Hz)下，由於電化學充電作用(Faradaic charging)使得粒子被收集在電極中央處，其流動方向與歐姆充電作用相反且流動速度較快。

In this thesis, I experimentally investigate effects of asymmetric polarization on the motions of particles and fluids under high-frequency ac electric fields. Two strategies are invoked in this work, and constitute the main body of this thesis.
In the first part of the thesis, I employ a series of asymmetric coplanar electrode pairs to design an interdigitated microelectrode array and observe the motion of submicron latex particles in a deionized water subjected to ac electric fields. At high frequencies (≧1MHz), I find particle aggregation of particles due to negative dielectrophoresis and the aggregation occurs near the inner edges between an electrode pair. At low frequencies such as 10kHz~100kHz, the prevailing asymmetric ac electro-osmotic flow leads to rapid particle trapping on the smaller electrodes while the aggregation on the wider ones becomes sluggish.
In the second part of the thesis, I adopt an oblique electrode array to see how it affects the motion of silica particles in ac electric fields. At high frequencies (≧1MHz), I again find negative dielectrophoretic aggregation of the particles. And yet, I find that the larger tilt angle the more aggregated particles, suggesting that the induced dipoles of the particles and the applied field must be disaligned by the oblique electrode arrangement. I also find that the aggregation is rapidly re-suspended by an ac electro-osmotic flow, due possibly to Faradaic charging, at large voltage like 50 Vpp. At moderately high frequencies (1kHz~100kHz), the phenomena are dominated by electrokinetic flow due to Ohmic charging, and exhibit rapid spiral fluid motion toward the sidewalls or pumping toward the end of the channel with a shorter distance to the electrode array. At low frequencies (~100Hz), instead of being re-suspended, the particles are trapped by a flow due to Faradaic charging.

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