Radio frequency identification (RFID) moisture tag(s) and sensors with extended sensing via capillaries
Embodiments of the present invention provide a passive radio frequency identification (RFID) moisture sensor. This moisture sensor includes one or more antenna structures having a tail. The tail is operable to transport a disturbance such as, but not limited to fluid or moisture from a monitored location wherein the antenna has an impedance and varies with proximity to the disturbance. An integrated circuit couples to the antenna structure. This IC includes a power harvesting module operable to energize the integrated circuit, an impedance-matching engine coupled to the antenna, a memory module, and a wireless communication module. The impedance-matching engine may vary a reactive component to reduce a mismatch between the antenna impedance and the IC and produce an impedance value (sensor code) representative of the reactive component impedance. The memory module stores the impedance value (sensor code) until the wireless communication module communicates with an RFID reader and sends the impedance value/sensor code to the RFID reader. The RFID reader may then determine an environmental condition such as the presence of moisture or fluids at the tail of the RFID sensor. This sensor may deploy several antenna and/or tails sensitive to unique disturbances. These tails may be used to monitor different locations as well as different types of fluids. In one particular embodiment, the disturbance is a fluid or moisture within the gutter of a vehicle body.
1. A passive radio frequency identification (RFID) moisture sensor, comprising:
at least one antenna structure proximate to a mounting surface, the mounting surface comprising a super-absorbent polymer (SAP) having an effective dielectric constant, wherein the at least one antenna structure has an antenna impedance, the antenna impedance operable to vary with proximity to fluids within the SAP;
an integrated circuit (IC) coupled to the at least one antenna structure, the IC comprising:
a power harvesting module operable to power the IC;
an impedance matching engine coupled to the at least one antenna, the impedance matching engine operable to:
vary a reactive component impedance to reduce a mismatch between the antenna impedance and the IC;
produce at least one impedance value (sensor code) representative of the reactive component impedance;
a memory module operable to store the at least one impedance value (sensor code); and
a wireless communication module coupled to the memory module, the wireless communication module operable to:
communicate with an RFID reader, and
send the at least one impedance value (sensor code) to the RFID reader.
2. The passive RFID moisture sensor of claim 1 , wherein the antenna structure comprises a dual-mode dipole.
3. The passive RFID moisture sensor of claim 2 , wherein the antenna structure is offset from a surface to be sensed by an air-gap.
4. The passive RFID moisture sensor of claim 1 , wherein the impedance matching engine operates in a first mode proximate to the surface and in a second mode beyond a predetermined distance from the surface.
5. The passive RFID moisture sensor of claim 4 , wherein the IC produces substantially different impedance values (sensor codes) dependant on the impedance matching engine mode of operation.
6. The passive RFID moisture sensor of claim 1 , wherein the at least one antenna structure further comprises a capacitive pad.
7. The passive RFID moisture sensor of claim 1 , wherein the at least one antenna structure comprises a folded dipole.
8. The passive RFID moisture sensor of claim 1 , wherein the passive RFID moisture sensor is embedded within a diaper.
9. The passive RFID moisture sensor of claim 1 , wherein at least one impedance value (sensor code) vary with diaper wetness.
10. The passive RFID moisture sensor of claim 1 , wherein the super-absorbent polymer (SAP) is within a diaper.
11. The passive RFID moisture sensor of claim 1 , wherein the at least one antenna structure further comprises an interdigitated capacitor.
12. The passive RFID moisture sensor of claim 1 , wherein at least one passive RFID moisture sensor is inserted into a stack of materials.
13. The passive RFID moisture sensor of claim 1 , wherein moisture is wicked to the at least one antenna structure by a tail, the tail having a proximal end coupled to the at least one antenna structure and a distal end proximate to a location at which moisture is to be sensed.
14. A passive radio frequency identification (RFID) moisture sensor, comprising:
at least one antenna structure comprising a tail, the tail further comprising:
a sensing portion; and
a transport portion communicatively coupled to the sensing portion, the transport portion operable to transport a disturbance from a monitored location to the sensing portion, wherein the at least one antenna structure has an antenna impedance, the antenna impedance operable to vary with the disturbance transported from the monitored location to the sensing portion;
an integrated circuit (IC) coupled to the at least one antenna structure, the IC comprising:
a power harvesting module operable to power the IC;
an impedance matching engine coupled to the at least one antenna, the impedance matching engine operable to:
vary a reactive component impedance to reduce a mismatch between the antenna impedance and the IC;
produce at least one impedance value (sensor code) representative of the reactive component impedance;
a memory module operable to store the at least one impedance value (sensor code); and
a wireless communication module coupled to the memory module, the wireless communication module operable to:
communicate with an RFID reader, and
send the at least one impedance value (sensor code) to the RFID reader.
15. The passive RFID moisture sensor of claim 14 , wherein the disturbance comprises a fluid, wherein the fluid is wicked by the transport portion.
16. The passive RFID moisture sensor of claim 14 , wherein the monitored location comprises a mounting surface, the mounting surface selected from the group consisting of:
air (foam);
wood;
drywall;
Poly(methyl methacrylate) (PMMA);
Polyethylene terephthalate (PET);
Polytetrafluoroethylene (PTFE); and
glass.
17. A passive radio frequency identification (RFID) moisture sensor, comprising:
at least one antenna structure comprising at least one tail, the tail operable to transport a disturbance from a monitored location, wherein the at least one antenna structure has an antenna impedance, the antenna impedance operable to vary with proximity to the disturbance;
an integrated circuit (IC) coupled to the at least one antenna structure, the IC comprising:
a power harvesting module operable to power the IC;
an impedance matching engine coupled to the at least one antenna, the impedance matching engine operable to:
vary a reactive component impedance to reduce a mismatch between the antenna impedance and the IC;
produce at least one impedance value (sensor code) representative of the reactive component impedance;
a memory module operable to store the at least one impedance value (sensor code); and
a wireless communication module coupled to the memory module, the wireless communication module operable to:
communicate with an RFID reader, and
send the at least one impedance value (sensor code) to the RFID reader.
18. The passive RFID moisture sensor of claim 17 , wherein a plurality of tails and antenna structures are employed, wherein each tail is sensitive to a unique disturbance.
19. The passive RFID moisture sensor of claim 18 , wherein a plurality of tails and antenna structures are employed, wherein each tail monitors a different monitored location.
20. The passive RFID moisture sensor of claim 18 , the monitored location comprises a gutter within a vehicle body.
21. The passive RFID moisture sensor of claim 18 , the disturbance comprises a fluid/moisture.