One of the most important characteristics of planar microwave resonator-based sensors is their sensitivity. Since their measuring parameter is resonance frequency shift, the sensitivity could be described as the shift in the resonance frequency of the microwave resonators versus variation in the dielectric constant of the material under the test. Although label-free microwave resonator-based sensors are capable of providing moderate levels of sensitivity sufficient for enabling numerous applications, detection of material variations in sub-percent or ppm (part per million) range is not easily possible with these structures. This paper investigates the reasons behind the limited sensitivity of planar microwave resonator-based sensors and suggests a measurement structure capable of measuring extremely low concentrations of water contamination in mineral oil samples. Simulation and experimental results verify the capability of the presented sensing structure in the detection of as low water concentrations as 50 ppm in mineral oil samples expressing extremely high sensitivity for the presented sensor with 30 kHz in the frequency shift of the resonator.

中文翻译：

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用于高精度检测矿物油中水污染的高灵敏度微波传感器

基于平面微波谐振器的传感器最重要的特性之一是它们的灵敏度。由于它们的测量参数是谐振频率偏移，因此灵敏度可以描述为微波谐振器的谐振频率的偏移与被测材料的介电常数的变化之间的关系。尽管基于无标记微波谐振器的传感器能​​够提供足以实现众多应用的中等灵敏度水平，但使用这些结构并不容易检测亚百分比或 ppm（百万分之一）范围内的材料变化。本文研究了基于平面微波谐振器的传感器灵敏度有限的原因，并提出了一种能够测量矿物油样品中极低浓度水污染的测量结构。仿真和实验结果验证了所提出的传感结构在检测矿物油样品中低至 50 ppm 的水浓度方面的能力，这表明所提出的传感器在谐振器频移为 30 kHz 时具有极高的灵敏度。