Radio frequency identification (RFID) moisture tag(s) and sensors with extended sensing via capillaries
A radio frequency identification (RFID) tag includes a power harvesting circuit that operates generate power for the RFID tag from a continuous wave of a radio frequency (RF) signal. The RFID tag further includes a self-tuning circuit that is tuned based on a capacitance setting, where the capacitance setting is indicative of a power level of the power. The RFID tag further includes a processing module operably coupled to the tuning circuit, where the processing module operates to generate the capacitance setting to obtain a desired power level for the power. In an example, the processing module further generates an adjustment signal in response to a change in an impedance of an antenna coupled to the RFID tag, and generates a digital value representative of the adjustment signal.
1 . A radio frequency identification (RFID) tag comprises:
an antenna port;
a power harvesting circuit operably coupled to the antenna port, wherein, when an antenna is operably coupled to the antenna port and 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 input impedance of the RFID tag by adjusting capacitance of the RFID tag such that a resonant frequency of the RFID tag, when coupled to the antenna, 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 tag 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 transmit, via the antenna port, the first transmit signal and the second transmit signal.
2 . The RFID tag of claim 1 , wherein the self-tuning circuit is further operable to adjust the impedance of the RFID tag in accordance with the adjustment signal.
3 . The RFID tag of claim 2 further comprises:
the processing module is further operable to generate the adjustment signal as a capacitance setting; and
the self-tuning circuit includes a variable capacitance circuit, wherein capacitance of the variable capacitance circuit is set in accordance with the capacitance setting.
4 . The RFID tag of claim 1 , wherein the wireless communication circuit transmits the first transmit signal and the second transmit signal for reception by an RFID reader.
5 . The RFID tag of claim 1 , wherein the memory is further operable to store the digital value representative of the adjustment signal.
6 . 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.
7 . The RFID sensor of claim 6 , wherein the self-tuning circuit is further operable to adjust the impedance of the RFID tag in accordance with the adjustment signal.
8 . The RFID sensor of claim 7 further comprises:
the processing module is further operable to generate the adjustment signal as a capacitance setting; and
the self-tuning circuit includes a variable capacitance circuit, wherein capacitance of the variable capacitance circuit is set in accordance with the capacitance setting.
9 . The RFID sensor of claim 6 , wherein the wireless communication circuit transmits the first transmit signal and the second transmit signal for reception by an RFID reader.
10 . The RFID sensor of claim 6 , wherein the memory is further operable to store the digital value representative of the adjustment signal.
11 . The RFID sensor of claim 6 further comprises:
an environmental sensor positioned proximal to the antenna, wherein, when the environmental sensor is exposed to an environmental condition, the impedance of the antenna is effected, and wherein the adjustment signal is representative of the environmental condition.
12 . The RFID sensor of claim 11 , wherein the environmental sensor comprises:
a collecting section; and
a transporting section operably coupled to the collection section, wherein the transporting section is positioned proximal to the antenna and wherein the collecting section is within an area of the asset that is suspectable to moisture.