Method and apparatus or sensing environmental conditions
A wireless sensor includes a radio frequency (RF) receiving circuit operable to receive an RF signal having a carrier frequency of a plurality of carrier frequencies. The RF receiving circuit further includes a variable impedance where impedance of the variable impedance is a factor in establishing a resonant frequency of the RF receiving circuit. The wireless sensor further includes a processing module that is operable to determine a first value for a first impedance of the variable impedance for a known temperature based on the resonant frequency and the carrier frequency, determine a second value a second impedance of the variable impedance for an unknown temperature based on the resonant frequency and the carrier frequency, and determine a difference between the first and second values that corresponds to a change between the known temperature and the unknown temperature.
1. A wireless sensor comprises:
a radio frequency (RF) receiving circuit operable to receive an RF signal having a carrier frequency, the RF receiving circuit includes a variable impedance, wherein impedance of the variable impedance is a factor in establishing a resonant frequency of the RF receiving circuit; and
a processing module operably coupled to the RF receiving circuit, wherein the processing module is operable to:
determine a first value for a first impedance of the variable impedance for a known temperature based on the resonant frequency and the carrier frequency;
determine a second value for a second impedance of the variable impedance for an unknown temperature based on the resonant frequency and the carrier frequency; and
determine a difference between the first and second values that corresponds to a change between the known temperature and the unknown temperature.
2. The wireless sensor of claim 1 , wherein the variable impedance comprises:
an antenna operable to receive the RF signal; and
a variable capacitor coupled to the antenna to form a tank circuit.
3. The wireless sensor of claim 2 , wherein the first impedance is established by
characteristics of the variable impedance.
4. The wireless sensor of claim 2 , wherein the second impedance is established by
adjusting characteristics of the variable impedance.
5. The wireless sensor of claim 1 , wherein the variable impedance comprises:
an antenna operable to receive the RF signal;
a variable capacitor; and
an inductor, wherein the variable capacitor and at least one of the antenna and the inductor are coupled to form a tank circuit.
6. The wireless sensor of claim 5 , wherein the first impedance is established by
characteristics of the variable impedance.
7. The wireless sensor of claim 5 , wherein the second impedance is established by
adjusting characteristics of the variable impedance.
8. The wireless sensor of claim 1 , wherein the processing module is further operable to determine the first value by:
for a range of values for the first impedance, determining power levels for the received RF signal; and
identifying a value of the range of values corresponding to a peak power level of the power levels as the first value.
9. The wireless sensor of claim 1 , wherein the processing module is further operable to determine the second value by:
for a range of values for the second impedance, determining power levels for the received RF signal; and
identifying a value of the range of values corresponding to a peak power level of the power levels as the second value.
10. A method for execution by a wireless sensor, the method comprises:
receiving a radio frequency (RF) signal having a carrier frequency, wherein an RF receiving circuit of the wireless sensor includes a variable impedance, wherein impedance of the variable impedance is a factor in establishing a resonant frequency of the RF receiving circuit;
determining a first value for a first impedance of the variable impedance for a known temperature based on the resonant frequency and the carrier frequency;
determining a second value for a second impedance of the variable impedance for an unknown temperature based on the resonant frequency and the carrier frequency; and
determining a difference between the first and second values that corresponds to a change between the known temperature and the unknown temperature.
11. The method of claim 10 , wherein the variable impedance comprises:
an antenna operable to receive the RF signal; and
a variable capacitor coupled to the antenna to form a tank circuit.
12. The method of claim 11 , wherein the first impedance is established by
characteristics of the variable impedance.
13. The method of claim 11 , wherein the second impedance is established by
adjusting characteristics of the variable impedance.
14. The method of claim 10 , wherein the variable impedance comprises:
an antenna operable to receive the RF signal;
a variable capacitor; and
an inductor, wherein the variable capacitor and at least one of the antenna and the inductor are coupled to form a tank circuit.
15. The method of claim 14 , wherein the first impedance is established by
characteristics of the variable impedance.
16. The method of claim 14 , wherein the second impedance is established by
adjusting characteristics of the variable impedance.
17. The method of claim 10 , wherein the determining the first value further comprises:
for a range of values for the first impedance, determining power levels for the received RF signal; and
identifying a value of the range of values corresponding to a peak power level of the power levels as the first value.
18. The method of claim 10 , wherein the determining the second value further comprises:
for a range of values for the second impedance, determining power levels for the received RF signal; and
identifying a value of the range of values corresponding to a peak power level of the power levels as the second value.