A Wireless Paper Humidity Sensor Based on Copper-Graphene Composite for Plant Transpiration Monitoring

In this paper, a passive, wireless humidity sensor based on polyimide (PI) paper and a copper-graphene composite was presented. The innovative use of laser-induced graphene and electrochemical deposition (LIG-ECD) enables the fabrication of highly conductive radio-frequency (RF) circuits on a PI paper substrate. The sensor achieves rapid response (30s) and recovery (61s) times across 20-90% RH and stable performance over 150 days. Its lightweight and flexible design ensures integration with plants for real-time transpiration monitoring.