This paper presents a sensitive microwave near-field sensor based on utilizing a three-dimensional capacitor within a planar split-ring resonator. The planar resonator is etched in the ground plane of a microstrip line, where the resonator’s length is relatively smaller than the guided wavelength. The sensor was fabricated utilizing PCB technology and used to detect the presence of dielectric fluids. The numerical analysis shows that the three-dimensional capacitor significantly enhances the electric field in the sensing area (free space) leading to an increase in the sensitivity. The electric field enhancement was quantitatively investigated using numerical analysis. The analysis shows that a loaded-quality factor of 1556 can be achieved using a three-dimensional capacitor with a length of 29 mm, which is significantly higher than what can be achieved by using planar resonators working in the same range of frequency. In addition, the utilization of the high-dielectric substrate can enhance coupling to the resonator. The proposed sensor was experimentally tested on two fluids, chloroform and dichloromethane with the relative permittivity of 4.81 and 8.93, respectively. The proposed sensor shows higher sensitivity of 700% and 374.5% in detecting the presence of chloroform and dichloromethane, respectively. Furthermore, the proposed sensor was utilized to detect the changes in fluid levels.

中文翻译：

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基于三维开口环谐振器的流体检测传感器

本文提出了一种敏感的微波近场传感器，该传感器基于在平面开口环谐振器内利用三维电容器的功能。平面谐振器蚀刻在微带线的接地平面中，其中谐振器的长度相对小于引导波长。该传感器采用PCB技术制造，用于检测介电液的存在。数值分析表明，三维电容器显着增强了感应区域（自由空间）中的电场，从而导致了灵敏度的提高。使用数值分析定量研究了电场增强。分析表明，使用长度为29 mm的三维电容器可以达到1556的负载质量因数，这比使用在相同频率范围内工作的平面谐振器所能达到的要高得多。另外，高介电基板的利用可以增强与谐振器的耦合。所提议的传感器在两种液体（氯仿和二氯甲烷）上进行了实验测试，相对介电常数分别为4.81和8.93。所提出的传感器在检测氯仿和二氯甲烷的存在方面分别显示出700％和374.5％的更高灵敏度。此外，所提出的传感器用于检测液位的变化。氯仿和二氯甲烷的相对介电常数分别为4.81和8.93。所提出的传感器在检测氯仿和二氯甲烷的存在方面分别显示出700％和374.5％的更高灵敏度。此外，所提出的传感器用于检测液位的变化。氯仿和二氯甲烷的相对介电常数分别为4.81和8.93。所提出的传感器在检测氯仿和二氯甲烷的存在方面分别显示出700％和374.5％的更高灵敏度。此外，所提出的传感器用于检测液位的变化。