Passive Rf Sensors And Wireless Sensor Interrogation
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Recently, a new type of passive sensor called the antenna sensor has been developed. The antenna sensor incorporates a patch antenna as the sensing element as well as the data transmitting element. Physical factors such as strain and ground plane crack cause the patch antenna resonant frequency to change. By measuring the change in patch antenna resonant frequency these physical factors can be quantified.Conventional resonant frequency measurement methods require a wired connection to the antenna sensor. The wireless interrogation technique eliminates this requirement while offering all the advantages that a wireless sensor interface offers over a wired sensor interface. In this technique, a wideband interrogation signal is transmitted towards the antenna sensor. The backscatter signal, comprising of antenna mode and structure mode, is normalized to isolate the antenna mode backscatter from which antenna sensor resonant frequencies can be extracted.The concept of backscatter normalization, implementation of the normalization scheme and interrogation characteristics are described. In addition, preliminary study on using other microwave components, such as ring resonator, for crack and strain measurement is also presented.