A highly tunable and sensitive radio-frequency (RF) sensor is presented for the measurement of aqueous-solution dielectric properties. Two quadrature hybrids are utilized to achieve destructive interference that eliminates the probing signals at both measurement ports. As a result, weak signals of material-under-test (MUT) are elevated for high sensitivity detections at different frequencies. The sensor is demonstrated through measuring 2-propanol-water solution permittivity at 0.01 mole fraction concentration level from ~ 4 GHz to ~ 12 GHz. De-ionized water and methanol-water solution are used to calibrate the sensor for quantitative MUT analysis through our proposed model. Micro-meter coplanar waveguides (CPW) are fabricated as RF sensing electrodes. A polydimethylsiloxane (PDMS) microfluidic channel is employed to introduce 250 nL liquid, of which ~ 1 nL is effectively the MUT. The permittivity and the relaxation time of 2-propanol-water solution are obtained. Compared with our power divider based sensors, the differential reflection coefficients in this work provide additional information that complements the transmission coefficient methods.

中文翻译：

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用于检测和分析水溶液的基于正交的可调谐射频传感器

提出了一种高度可调且灵敏的射频 (RF) 传感器，用于测量水溶液介电特性。两个正交混合器用于实现消除两个测量端口的探测信号的破坏性干扰。因此，被测材料 (MUT) 的微弱信号被提升，以在不同频率进行高灵敏度检测。该传感器是通过测量 0.01 摩尔分数浓度水平的 2-丙醇-水溶液介电常数来证明的，从~4 GHz 到~12 GHz。通过我们提出的模型，去离子水和甲醇水溶液用于校准传感器以进行定量 MUT 分析。微米共面波导 (CPW) 被制造为 RF 传感电极。采用聚二甲基硅氧烷 (PDMS) 微流体通道引入 250 nL 液体，其中~ 1 nL 是有效的 MUT。得到2-丙醇-水溶液的介电常数和弛豫时间。与我们基于功率分配器的传感器相比，这项工作中的差分反射系数提供了补充传输系数方法的附加信息。