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

Currently, the reader based on frequency modulated continuous wave (FMCW) radar used to dynamically interrogate the chipless 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 paper introduces a low-cost FMCW reader for 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 analyzed theoretically, followed by verification through simulations performed in Advanced Design System (ADS). Hilbert-based algorithms are presented for restoring the amplitude and phase variations of sampled signal in 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 vector network analyzer (VNA), demonstrating the accuracy and reliability of the reader. Combined with 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).