介绍一种基于经典电路理论的无线、无源LC谐振传感器设计,并将其用于包装茶叶含水率的快速、无损检测。所提出的LC谐振传感器实质上是一个印刷在湿敏绝缘衬底上的单一平面电容和螺旋电感构成的谐振电路,通过将传感器放置在茶叶包装袋内,由于包装袋内湿度变化会引起平面电容的电容值变化,进而导致传感器的并联谐振频率变化,利用连接在包装袋外部含水率测量仪上的感应线圈远程检测传感器的谐振频率值,即可通过谐振频率的变化间接确定包装茶叶的含水率;实验结果表明了该检测方法合理可行,与国标方法相比较,测量结果无明显偏差,解决了包装茶叶含水率快速、准确、无损检测的难题。

The design of a wireless, passive LC resonant sensor based on classic circuit theory, and its application for quick, non-destructive measured of moisture content of packaged tea were described in this paper. The proposed LC resonant sensor is an inductive-capacitive resonant circuit, which is made of a single planar capacitor and spiral inductor printed on a humidity-sensitive insulating medium substrate. To measure the moisture content of packaged tea, the LC resonant sensor is embedded inside the tea package. As the variation of the humidity inside the tea package, the humidity-sensitive insulating medium substrate absorbs the water vapor, and the planar capacitor’s capacitance and the sensor’s resonant frequency were changed, which is remotely detected through a coil connected to the instrument for measuring moisture content outside the tea package. Therefore, the moisture content of packaged tea can be indirectly determined by measuring the change in sensor’s resonant frequency. The experiment results showed that the proposed method is reasonable, and is comprised with the GB method, no significant deviation is found between the measuring results. The difficult technological problem in how to quick, accurate and non-destructive measuring moisture content of packaged tea is solved.