本論文開發一款新型的 2.4 GHz液體濃度感測器，主要由感測振盪器與延遲線鑑頻解調器所構成。其中，兩感測振盪器分別以自振式環隙共振器(self-oscillating split-ring resonator, SO-SRR)與自振式互補式環隙共振器(self-oscillating complementary split-ring resonator, SO-CSRR)實現。在此，環隙共振器和互補式環隙共振器作為感測振盪器之選頻元件，同時也扮演著液體感測功能。使用兩型互補式結構共振器設計感測振盪器，係因環隙共振器與互補式環隙共振器分別以聚焦垂直磁場與電場偵測待測液體。本論文將以水-乙醇混合液作為待測液體進行感測器效能驗證。當水-乙醇混合液放置於環隙共振器或互補式環隙共振器上，根據微擾定理(perturbation theory)，將導致共振頻率變化，並伴隨相位變化，亦即在指定頻率下，通過共振器之訊號將轉為相位調變訊號。基於注入鎖定原理(injection-locked theory)，此相位調變訊號注入感測振盪器後，將轉換成頻率調變訊號。此時可在頻譜分析儀觀察到，不同的水-乙醇混合液濃度將對應到不同振盪頻率。實驗結果顯示，水-乙醇濃度上升與振盪頻率偏移呈現線性關係。此外，本論文使用延遲線鑑頻器作為解調器，將頻率偏移結果轉換成電壓值大小，以獲得水-乙醇濃度與輸出電壓值之間的關係。

This thesis proposes a new 2.4 GHz liquid concentration sensor, which is mainly composed of a sensing oscillator and a delay-line frequency discriminator demodulator. Two sensing oscillators are implemented by a self-oscillating split-ring resonator (SO-SRR) and a self-oscillating complementary split-rings resonator (SO-CSRR). Here, the resonators are not only treated as the frequency-selective elements for oscillator design, but also acted as liquid sensing devices. Since SRR and CSRR respectively concentrate vertical magnetic and electric fields for liquid sensing, both complementary resonator structures are employed to design sensing oscillators. In this thesis, water-ethanol mixtures with different concentrations are adopted as liquids under test. As the water-ethanol mixture is placed on the SRR or CSRR, according to the perturbation theory, it leads to a resonant frequency deviation accompanying with a phase shift. Namely, at a specified frequency, the signal, which passes through the SRR or CSRR, will be phase-modulated by the liquid under test. Based on the injection-locked theory, when this phase-modulated signal injects into the sensing oscillator, it will transfer into a frequency-modulated signal. At this moment, different oscillation frequencies will be observed by a spectrum analyzer with corresponding to water-ethanol mixtures having different concentrations. The experimental results reveal that the concentration of water-ethanol mixture is linearly related to the oscillation frequency. In addition, in order to obtain the relationship between the water-ethanol concentrations and the sensor output voltages, this thesis uses a delay-line discriminator as a demodulator to transfer the oscillation frequency deviations to voltage values.

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