Biodegradable Wireless Soil Urea Sensor Using Metamaterial Perfect Absorber for Distributed Deployment in Precision Agriculture

ABSTRACT This paper proposes a wirelessly operable soil urea sensor fabricated from biodegradable and low‐environmental‐impact materials, enabling low‐cost distributed installation over extensive farmland. The sensor consists of an alginate hydrogel containing immobilized urease and a metamaterial perfect absorber comprising a magnesium (Mg) film coated with a pH‐dependent soluble material. The sensor enables relative measurement of urea concentration by wirelessly detecting the structural degradation of the metamaterial perfect absorber induced by the urea present in the soil. In this study, wireless measurement using a metamaterial perfect absorber was shown to suppress electromagnetic reflections from the soil, enabling stable scanning of the sensor regardless of soil conditions. Furthermore, time‐transit changes in the electromagnetic response of the sensor placed on soils containing different urea concentrations demonstrated successful wireless detection of three urea levels (0, 40, and 80 m M ). These results indicate that the proposed sensor could be suited for soil monitoring in large‐scale agricultural fields.