本論文使用鎖頻迴路(frequency-locked loop, FLL)技術研製一種操作於24 GHz之微流體液體濃度感測器。在鎖頻迴路中，將微流道(microfluidic channel)置於非對稱共面波導共振器(asymmetrical coplanar waveguide resonator, ACPWR)上方，作為液體感測元件，並以酒精水溶液與葡萄糖水溶液作為待測液體，不同濃度液體將改變電場分佈，導致對應的相位偏移，再使鎖頻迴路輸出頻率調變訊號。此頻率調變訊號以相位檢測器(phase detector)所製成之頻率解調器解調，輸出對應之電壓。為最佳化感測特性，本論文針對感測元件結構、迴路濾波器與頻率解調器進行改善，最終感測器具備不同濃度待測液體之優異鑑別能力，且輸出電壓與待測液體濃度呈現線性關係。本論文所提出之24 GHz微流體濃度感測器具有低成本、高靈敏度及體積小之優點，具有極佳的系統晶片實現可行性，可搭配物聯網技術，實現居家應用之即時生醫檢體感測。

This thesis develops a 24-GHz microfluidic sensor using frequency-locked loop (FLL) technology for liquid concentration detection. In the FLL, a microfluidic channel is arranged over an asymmetrical coplanar waveguide resonator (ACPWR) and utilized as a sensing device. The ethanol-water mixtures and glucose-water solutions are used as the test liquids. The sensing device will detect the changes in the electric-field distribution caused by the liquids with different concentrations, resulting in transmission phase shifts. The FLL generates a frequency-modulated signal according to these phase shifts. This frequency-modulated signal is then demodulated into a corresponding voltage using a frequency demodulator, which is implemented by a phase detector. In addition, the sensing device configuration, loop filter, and frequency demodulator have been modified to optimize the senser’s performance. As a result, the sensor exhibits an excellent ability to distinguish the tested liquids with different concentrations and provides a linear response relating the output voltage to the liquid concentration. The proposed 24-GHz frequency-locked loop microfluidic sensor offers advantages, such as cost effective, high sensitivity, and compact size. It has a great possibility to implement this sensor using the system-on-chip (SoC) technology. As it combined with Internet of Things (IoT) technologies, it may have a capability of real-time biomedical specimen sensing for daily life.

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