Determining an environmental condition of an RFID tag
A method begins by a radio frequency identification (RFID) reader transmitting a first and second radio frequency (RF) signal of a plurality of RF signals, which each include a unique carrier frequency and an instruction to an RFID tag to respond with a received power level indication. The method continues by the RFID reader receiving, in response to the first and second signals sent at a first and second carrier frequency, a first and second response from the RFID tag that includes a first and second received power level indication. The method continues by the RFID reader determining an estimated resonant frequency of the RFID tag based on the first and second received power level indications and the first and second carrier frequencies. The method continues by the RFID reader determining an environmental condition based on the estimated resonant frequency.
1. A method comprises:
transmitting, by a radio frequency identification (RFID) reader, a first radio frequency (RF) signal of a plurality of RF signals, wherein each RF signal of the plurality of RF signals includes a unique carrier frequency and further includes an instruction to an RFID tag to respond with a received power level indication;
receiving, by the RFID reader, a first response from the RFID tag in response to a first RF signal of the plurality of RF signals, wherein the first response includes a first received power level indication, and wherein the first RF signal has a first carrier frequency;
transmitting, by the RFID reader, a second RF signal of the plurality of RF signals;
receiving, by the RFID reader, a second response from the RFID tag in response to the second RF signal of the plurality of RF signals, wherein the second response includes a second received power level indication, and wherein the second RF signal has a second carrier frequency;
determining, by the RFID reader, an estimated resonant frequency of the RFID tag based on the first and second received power level indications and the first and second carrier frequencies; and
determining, by the RFID reader, an environmental condition based on the estimated resonant frequency.
2. The method of claim 1 , wherein the instruction comprises:
a request for the RFID tag to respond with a unique identifier that identifies the RFID tag.
3. The method of claim 1 further comprises:
transmitting the first RF signal of the plurality of RF signals at a third carrier frequency of the plurality of carrier frequencies, wherein the third carrier frequency is based on a frequency within a range of frequencies that correspond to a known calibrated condition; and
transmitting the second RF signal of the plurality of RF signals at a fourth carrier frequency of the plurality of carrier frequencies wherein the fourth carrier frequency is based on a second frequency within the range of frequencies that correspond to the known calibrated condition.
4. The method of claim 1 , wherein the transmitting the plurality of RF signals comprises:
transmitting the plurality of RF signals in one of a plurality of patterns, wherein a pattern of the plurality of patterns include one of:
a low carrier frequency to a high carrier frequency pattern;
a high carrier frequency to a low carrier frequency pattern; and
a random carrier frequency pattern.
5. The method of claim 1 further comprises:
transmitting, by the RFID reader, the plurality of RF signals, wherein each RF signal of the plurality of RF signals includes the unique carrier frequency and further includes the instruction to the RFID tag to respond with the received power level indication;
receiving, by the RFID reader, the first response from the RFID tag in response to the first RF signal of the plurality of RF signals, wherein the first response includes the first received power level indication, wherein the first RF signal has the first carrier frequency, and wherein the first RF signal of the plurality of signals is based on a known environmental condition;
receiving, by the RFID reader, the second response from the RFID tag in response to the second RF signal of the plurality of RF signals, wherein the second response includes the second received power level indication, wherein the second RF signal has a second carrier frequency, and wherein the second RF signal of the plurality of signals is based on the known environmental condition; and
determining, by the RFID reader, an estimated calibrated resonant frequency of the RFID tag based on the first and second received power level indications and the first and second carrier frequencies.
6. The method of claim 5 further comprises:
receiving, by the RFID reader, a third response from the RFID tag in response to a third RF signal of the plurality of RF signals, wherein the third response includes a third received power level indication, wherein the third RF signal has a third carrier frequency, and wherein the third RF signal of the plurality of signals is based on an unknown environmental condition;
receiving, by the RFID reader, a fourth response from the RFID tag in response to a fourth RF signal of the plurality of RF signals, wherein the fourth response includes a fourth received power level indication, wherein the fourth RF signal has a fourth carrier frequency, and wherein the fourth RF signal of the plurality of signals is based on the unknown environmental condition;
determining, by the RFID reader, the estimated resonant frequency of the RFID tag based on the third and fourth received power level indications and the third and fourth carrier frequencies; and
determining, by the RFID reader, the environmental condition based on a difference between the estimated resonant frequency and the estimated calibrated resonant frequency.
7. The method of claim 1 further comprises:
prior to the determining, by the RFID reader, the estimated resonant frequency:
receiving, by the RFID reader, a third response from the RFID tag in response to a third RF signal of the plurality of RF signals, wherein the third response includes a third received power level indication, and wherein the third RF signal has a third carrier frequency;
determining, by the RFID reader, the estimated resonant frequency of the RFID tag based on the first, second and third received power level indications and the first, second and third carrier frequencies.
8. A radio frequency identification (RFID) reader comprises:
memory;
a transmitter, wherein the transmitter is operable to:
transmit a first radio frequency (RF) signal of a plurality of RF signals, wherein each RF signal of the plurality of RF signals includes a unique carrier frequency and further includes an instruction to an RFID tag to respond with a received power level indication; and
transmit a second RF signal of the plurality of RF signals;
a receiver, wherein the receiver is operable to:
receive a first response from the RFID tag in response to the first RF signal of the plurality of RF signals, wherein the first response includes a first received power level indication, and wherein the first RF signal has a first carrier frequency; and
receive a second response from the RFID tag in response to the second RF signal of the plurality of RF signals, wherein the second response includes a second received power level indication, and wherein the second RF signal has a second carrier frequency; and
a processing module, wherein the processing module is operable to:
determine an estimated resonant frequency of the RFID tag based on the first and second received power level indications and the first and second carrier frequencies; and
determine an environmental condition based on the estimated resonant frequency.
9. The RFID reader of claim 8 , wherein the transmitter is further operable to:
transmit a request for the RFID tag to respond with a unique identifier that identifies the RFID tag.
10. The RFID reader of claim 8 , wherein the transmitter is further operable to transmit the plurality of RF signals by:
transmitting the first RF signal of the plurality of RF signals at a third carrier frequency of the plurality of carrier frequencies, wherein the third carrier frequency is based on a frequency within a range of frequencies that correspond to a known calibrated condition; and
transmitting the second RF signal of the plurality of RF signals at a fourth carrier frequency of the plurality of carrier frequencies wherein the fourth carrier frequency is based on a second frequency within the range of frequencies that correspond to the known calibrated condition.
11. The RFID reader of claim 8 , wherein the transmitter is further operable to transmit the plurality of RF signals by:
transmitting the plurality of RF signals in one of a plurality of patterns, wherein a pattern of the plurality of patterns include one of:
a low to high pattern;
a high to low pattern; and
a random pattern.
12. The RFID reader of claim 8 further comprises:
the transmitter is further operable to:
transmit the plurality of RF signals, wherein each RF signal of the plurality of RF signals includes the unique carrier frequency and further includes the instruction to the RFID tag to respond with the received power level indication;
the receiver is further operable to:
receive the first response from the RFID tag in response to the first RF signal of the plurality of RF signals, wherein the first response includes the first received power level indication, wherein the first RF signal has the first carrier frequency, and wherein the first RF signal of the plurality of signals is based on a known environmental condition; and
receive the second response from the RFID tag in response to the second RF signal of the plurality of RF signals, wherein the second response includes the second received power level indication, wherein the second RF signal has a second carrier frequency and wherein the second RF signal of the plurality of signals is based on the known environmental condition; and
the processing module is further operable to:
determine a calibrated resonant frequency of the RFID tag based on the first and second received power level indications and the first and second carrier frequencies.
13. The RFID reader of claim 12 further comprises:
the receiver is further operable to:
receive a third response from the RFID tag in response to a third RF signal of the plurality of RF signals, wherein the third response includes a third received power level indication, wherein the third RF signal has a third carrier frequency, and wherein the third RF signal of the plurality of signals is based on an unknown environmental condition; and
receive a fourth response from the RFID tag in response to a fourth RF signal of the plurality of RF signals, wherein the fourth response includes a fourth received power level indication, wherein the fourth RF signal has a fourth carrier frequency, and wherein the fourth RF signal of the plurality of signals is based on the unknown environmental condition;
the processing module is further operable to:
determine the estimated resonant frequency of the RFID tag based on the third and fourth received power level indications and the third and fourth carrier frequencies;
determine the environmental condition based on the estimated resonant frequency.
14. The RFID reader of claim 8 further comprises:
the receiver is further operable to, prior to the determining the estimated resonant frequency:
receive a third response from the RFID tag in response to a third RF signal of the plurality of RF signals, wherein the third response includes a third received power level indication, and wherein the third RF signal has a third carrier frequency;
the processing module is further operable to:
determine the estimated resonant frequency of the RFID tag based on the first, second and third received power level indications and the first, second and third carrier frequencies.