非對稱微波耦合傳輸線具雙埠出口與其非平面感測應用

Abstract

相較於傳統微波感測器多以集中元件電路（Lumped element circuit）進行設計與分析，雖然在窄頻範圍可提供準確預測，然而在面對寬頻的需求時，常受限於模型簡化造成準確性下降。為克服此限制，本文提出利用分布元件電路（Distributed element circuit）建構耦合傳輸線模型，並以奇模態與偶模態分析電磁場的分佈特性，實現由主傳輸路徑向兩個獨立通道的能量分配，最後應用於非平面式分裂共振環增強型微波感測器（Non-Planar SRR-Enhanced Microwave Sensor, NPSRREMS），此方法不僅展現良好的感測靈敏度與場能集中效果，亦提供一套結合理論分析與實務設計的快速建模途徑，有助於未來針對複雜三維結構之感測器進行更高效率之設計與驗證。此結構在兩通道分別配置共振環，使電磁場得以集中於感測腔體內部區域，將待測物置於該區域時，待測物介電係數的變化會影響感測腔體內部電場分佈，使得散射參數中的共振頻率產生偏移。此機制使該結構在感測過程中具有明確的頻率響應，對不同材料的變化有靈敏的辨識能力。此外，本文亦提出一項額外設計，透過注射幫浦使液體流經流道，從而實現即時的液體感測。 為驗證本感測架構之可行性，本文採用高頻性能穩定的Rogers RO4350B板材製作感測器，並透過向量網路分析儀進行散射參數量測，以分析實際感測響應。最後模擬結果與實驗數據比對顯示，此結構具良好的共振靈敏度，裝置本身設計的共振頻率為5.0792 GHz，最大電場強度達到1012.49 kV/m，而對於介電係數靈敏度可達到4.23 MHz/Δε，驗證了耦合傳輸線分支結構應用於非平面感測器之潛力。在葡萄糖溶液感測上，靈敏度也達到了382.82 kHz/(mg/dL)，而乙醇水溶液則是有2.30 MHz/%的效果，展現出本研究所提出三維能量分佈設計於高靈敏度液體介電係數感測中的應用可行性與優勢，具備進一步擴展至多通道感測應用的發展潛力。

Compared to conventional microwave sensors that are typically designed and analyzed using lumped element circuits, which provide accurate predictions within narrowband ranges, such models often suffer from reduced accuracy when applied to broadband applications due to oversimplified assumptions. To overcome this limitation, this study proposes the use of distributed element circuits to construct a coupled transmission line model. By employing even-mode and odd-mode analysis, the electromagnetic field distribution characteristics are thoroughly examined, enabling the division of energy from the main transmission path into two independent channels. This methodology is further applied to the design of a Non-Planar SRR-Enhanced Microwave Sensor（NPSRREMS）. The proposed approach not only demonstrates excellent sensing sensitivity and field concentration capability, but also provides a fast modeling framework that bridges theoretical analysis with practical design. This modeling strategy facilitates efficient development and validation of complex three-dimensional sensing structures. In the designed sensor, split-ring resonators（SRRs）are strategically positioned along both transmission channels, allowing the electromagnetic field to concentrate within the central sensing cavity. When a material under test is placed in this region, changes in its dielectric constant perturb the local electromagnetic field, resulting in a shift in the resonance frequency observable in the scattering parameters. This mechanism ensures a well-defined frequency response during the sensing process and enables sensitive detection of material property variations. Additionally, this work introduces a real-time sensing configuration, in which syringe pumps are employed to deliver liquids through a fluidic channel. This enables dynamic monitoring of dielectric property changes in flowing liquid samples. To validate the feasibility of the proposed sensing architecture, a prototype sensor was fabricated using high-frequency-stable Rogers RO4350B substrate. Scattering parameters were measured using a vector network analyzer to analyze the actual sensing response. A comparison between simulation and experimental results confirms that the designed structure exhibits excellent dual-port response characteristics and resonance sensitivity. The designed device exhibits a resonance frequency of 5.0792 GHz, with a maximum electric field intensity reaching 1012.49 kV/m. The sensitivity to dielectric constant changes achieves 4.23 MHz/Δε, demonstrating the potential of the branched coupled-line structure for non-planar sensing applications. In the glucose solution sensing experiment, a sensitivity of 382.82 kHz/(mg/dL) was achieved, while ethanol–water mixtures obtain a sensitivity of 2.30 MHz/%. These results demonstrate the feasibility and advantages of the proposed three-dimensional energy distribution design in high-sensitivity dielectric sensing of liquids. The structure also shows promising potential for future applications in multi-channel sensing.