Compact DDS-based system for contactless interrogation of resonant sensors based on time-gated technique

A compact system is presented for contactless interrogation of a piezoelectric resonant sensor via the electromagnetic coupling between two coils connected to the interrogation and sensor units, respectively, exploiting a time-gated technique which excites the resonator in a time window and detects the decaying oscillations. Direct Digital Synthesis (DDS)-based signal generators are adopted to set the resonator into vibrations during the excitation phase and to generate a reference signal for heterodyne demodulation (frequency mixing) during the detection phase. Subsequently, an autocorrelation analysis technique allows to estimate both the sensor damped angular resonant frequency ω_dm and quality factor Q. The system has been experimentally validated on Quartz Crystal Resonator (QCR) sensors as representative devices obtaining an excellent agreement between the estimated values of resonant frequency and quality factor and the reference values taken with an impedance analyzer.