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.
In this study, the graphene-protected Si anode with an optimized graphene size demonstrates a superior life cycle and a high-power performance attributed to abundant ion channels, stable LiF-rich SEI formation, and swelling control.
The integration of silicon (Si) anode into lithium-ion batteries (LIBs) holds great promise for energy storage, but challenges arise from unstable electrochemical reactions and volume changes during cycling. This study investigates the influence of reduced graphene oxide (rGO) size on the performance of rGO-protected Si composite (Si@rGO) anodes. Two sizes of graphene oxide (GO(L) and GO(S)) are used to synthesize Si@rGO composites with a core-shell structure by spray drying and thermal reduction. Electrochemical evaluations show the advantages of Si@rGO(S) anode with improved cycle life and cycling efficiency over Si@rGO(L) and pure Si. The Si@rGO(S) anode facilitates the formation of a stable LiF-rich solid electrolyte interface (SEI) after cycling, ensuring enhanced capacity retention and swelling control. Rate capability tests also demonstrate the superior high-power performance of Si@rGO(S) with low and stable resistances in Si@rGO(S) over extended cycles. This study provides critical insights into the tailoring of graphene-protected Si composites, highlighting the critical role of rGO size in shaping structural and electrochemical properties. The Si material wrapped by graphene with an optimal lateral size of graphene emerges as a promising candidate for high-performance LIB anodes, thereby advancing electrochemical energy storage technologies.
