Our new paper in IEEE Sensors Letters "A Zero-Power Harmonic Tag for Real-Time Wireless Food Quality Monitoring"
This letter proposes a compact, low-profile, and battery-free wireless sensor, capable of continuously monitoring spoilage gases, such as ammonia (NH3), in meat and seafood products. The wireless sensor consists of a high-Q microstrip antenna loaded with a varactor diode, whose capacitance is reconfigured by an electrochemical ammonia (NH3) sensor such that the resonance frequency of antenna can be tuned by ammonia levels. This (receiving) antenna sensor operating at the fundamental frequency f0 is connected to a passive frequency doubler and a wideband monopole (transmitting) antenna operating at the second harmonic 2f0, within a compact tag. By receiving and re-transmitting radio waves with orthogonal frequencies under the frequency hopping spread spectrum (FHSS) framework, electromagnetic interferences caused by clutters and jamming can be filtered out, thus ensuring robust wireless food sensing with absolute accuracy in noisy environments. The effectiveness and robustness of the proposed sensor are demonstrated through remote monitoring of the spoilage process of packaged fish within two days. Results show that the ammonia concentration can be sensed by tracking the peak frequency of the received strength signal indicator (RSSI) at harmonic frequencies. This passive RFID sensor, with minimal footprint, complexity, and low cost, may be readily placed into the food package/container, enabling real-time assessment and forecasting of food quality and safety.
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