A Low-Cost FMCW Reader for High-Speed Interrogation of Chipless RFID Sensor

Currently, the reader based on the frequency modulated continuous wave (FMCW) radar used to dynamically interrogate the chipless radio frequency identification (RFID) sensor needs to collect the envelope of the echo signal through the oscilloscope, which entails expensive acquisition equipment and occupies a considerable amount of space. This article introduces a low-cost FMCW reader for the chipless RFID sensor’s dynamic interrogation. The reader mixes the received signal with the local oscillator signal and down-converts it into a low-frequency signal, which can be directly sampled by a low-cost analog to digital converter (ADC). Then, the sensor’s resonant frequency can be extracted from the amplitude and phase variation of the reader’s sampled signal, respectively within a single interrogation signal period. The working mechanism of the reader is analysed theoretically, followed by verification through the simulations performed in the advanced design system (ADS). Hilbert-based algorithms are presented for restoring the amplitude and phase variations of the sampled signal in the time domain. Then, the high-speed reader is employed to wirelessly query a crack sensor, and the measurement results acquired from the reader exhibit excellent concordance with those obtained from the vector network analyzer (VNA), demonstrating the accuracy and reliability of the reader. Combined with the other types of sensors, the reader can easily read information, such as acceleration, dynamic temperature, and humidity, providing massive dynamic data for structural health monitoring (SHM) and showing great potential in Internet of Things (IoT).