The dielectric constant of cement will decrease with an increase of moisture content, resulting in an increasing fundamental resonant frequency of a covered patch antenna. Based on this principle, the authors utilized a patch-antenna sensor to determine the initial and final setting time of cement during hydration by sensing the variation of moisture content. The theory of an equivalent dielectric constant model was adopted to exhibit the relationship between the fundamental resonant frequency of a buried antenna sensor and a dielectric constant in the covering cement paste. The phenomenon is then verified by both simulation in a high frequency structure simulator (HFSS) and experiments. The initial setting time of cement is regarded as the moment when the moisture content starts to increase rapidly and the final setting time is taken as the maximum moisture content acceleration. The setting times measured by the patch antenna sensor are compared with the results of the penetration resistance method using a Vicat apparatus with a testing error of less than 10%. A moisture content detection experiment was further carried out after the paste's hydration assuming the specimen was soaked in water. The results indicate that the resonant frequency of the patch antenna sensor is sensitive to moisture content change as fine as 4‰ with respect to the paste volume after cement hardening. The buried antenna sensor can detect the setting time during cement hydration and serve as a leakage detection sensor in service.

中文翻译：

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使用贴片天线传感器检测水泥水化凝结时间

水泥的介电常数会随着水分含量的增加而降低，导致覆盖贴片天线的基波谐振频率增加。基于这一原理，作者利用贴片天线传感器通过感应水分含量的变化来确定水化过程中水泥的初凝和终凝时间。采用等效介电常数模型理论，展示了埋地天线传感器的基波谐振频率与覆盖水泥浆体中介电常数的关系。然后通过高频结构模拟器 (HFSS) 中的模拟和实验来验证该现象。水泥初凝时间为含水率开始快速增加的时刻，终凝时间为最大含水率加速度。将贴片天线传感器测量的设置时间与使用维卡仪的穿透阻力法的结果进行比较，测试误差小于 10%。假设样品浸泡在水中，在糊状物的水合之后进一步进行水分含量检测实验。结果表明，贴片天线传感器的谐振频率对水泥硬化后糊料体积的含水量变化敏感，细至4‰。埋地天线传感器可以检测水泥水化过程中的凝结时间，并在使用中作为泄漏检测传感器。