Wireless LC Humidity Sensor with Distance-Insensitive Readout System

Ensuring the extended shelf life of packaged food and pharmaceutical products demands non-destructive, passive, and cost-effective moisture monitoring. This study presents the design and theoretical framework of a single-spiral Inductance–Capacitance (LC) sensor paired with a distance-insensitive readout system for humidity sensing. The LC resonant circuit, formed by the parasitic capacitance and inductance of the spiral coil, exhibits measurable shifts in resonant frequency in response to humidity changes. The sensor's performance is modeled and validated using Ansoft HFSS simulations, with results compared to empirical LC sensor data. For wireless interrogation, a readout coil is positioned near the sensor coil using a magnet, enabling passive and efficient humidity monitoring. This approach offers a promising solution for real-time, non-invasive quality control in perishable goods.