Radio frequency identification (RFID) moisture tag(s) and sensors with extended sensing via capillaries

A radio frequency identification (RFID) sensor comprises:

• an antenna;
• and
• an RFID tag, wherein the RFID tag includes:
• an antenna port coupled to the antenna;
• a power harvesting circuit operably coupled to the antenna port, wherein, when the antenna is electromagnetically receiving a radio frequency (RF) signal, the power harvesting circuit is operable to generate at least a minimum power for the RFID tag from the RF signal;
• a self-tuning circuit operably coupled to the antenna port, wherein, when the power harvesting circuit is generating the at least a minimum power, the self-tuning circuit is operable to adjust impedance of the RFID sensor by adjusting capacitance of the RFID sensor such that a resonant frequency of the RFID sensor approximately matches a resonant frequency of the RF signal;
• memory operable to store a unique identification number of the RFID tag, wherein, when the RFID sensor is associated with an asset, the asset is identifiable based on the unique identification number;
• a processing module operably coupled to the self-tuning circuit and to the memory, wherein the processing module is operable to generate a first transmit signal that includes the unique identification number, wherein the processing module is further operable to:
• generate an adjustment signal in response to a change in an impedance of the antenna;
• generate a digital value representative of the adjustment signal;
• and
• generate a second transmit signal that includes the digital value;
• and
• a wireless communication circuit operably coupled to the antenna port to transmit the first transmit signal and the second transmit signal.