應用液晶之微可變電容研究

Study on Liquid-Crystal Based Micromachined Tunable Capacitors

鐘晟原(Sheng-Yuan Chung)

指導教授 ： 張培仁

共同指導教授 ： 施文彬(Wen-Pin Shih)

國立臺灣大學/工學院/應用力學研究所/碩士(2007年)

https://doi.org/10.6342/NTU.2007.02569

摘要

本文製作出一高分子分散型液晶可變電容，並且理論上驗證可以將此可變電容用來提高可調式能量擷取系統的能量擷取效率。此可調式能量擷取系統利用一壓電懸臂樑將外界的振動機械能轉換成電能儲存。為了改善能量擷取的效率，本文中所發展的高分子分散型液晶可變電容配合適當的電路，可以用來即時調變所使用的壓電懸臂樑共振頻，使得此壓電懸臂樑的共振頻可以即時的和外界的隨機振動匹配，如此可以得到最大的能量輸出。高分子分散型液晶可變電容的製程以及量測結果將在文中詳述。在75kHz的量測頻率下可以得到高達117.5%的電容調變量，此外在施加12V的偏壓情況下，仍然可以得到55%的電容調變量。另外此高分子分散型液晶可變電容的介電常數特性和光學特性也會在文中詳細討論。從量測的結果我們對此可變電容建立一個集總元件等效電路，並且藉由理論模擬驗證其可以改善可調式能量擷取系統的能量擷取效率。

關鍵字

可變電容 ； 能量擷取 ； 高分子分散型液晶

並列摘要

This thesis presents a tunable power harvesting device and explains how a tunable capacitor based on polymer-dispersed liquid crystal (PDLC) can be used to optimize the power harvesting efficiency. The power harvesting device utilizes piezoelectric micro-cantilever excited by environmental random vibration to transfer mechanical energy to electric power. For improving the power harvesting efficiency, we have developed a PDLC tunable capacitor to adjust the resonance frequency of the piezoelectric micro-cantilever beam to match the frequency of environmental random vibration in real time. Fabrication process and measurement results of the PDLC tunable capacitor are detailed. Large tuning ratio up to 117.5% of the PDLC tunable capacitor is measured at 75kHz signal frequency. At 12V driving voltage, tuning ratio as 55% can be achieved. The dielectric and optical properties of the fabricated tunable PDLC capacitor have been examined thoroughly. Based on the experimental results, we have also developed an equivalent lumped-element model of the PDLC tunable capacitor. The simulation results show that the impedance of the developed model agrees well with that of the fabricated tunable capacitor. This model can be incorporated into the equivalent circuit of the integrated power harvesting system for efficiency optimization in the future.

並列關鍵字

tunable capacitor ； power harvesting ； polymer-dispersed liquid crystal

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