Pressure based wireless sensor and applications thereof
A radio frequency identification (RFID) tag includes an antenna, an analog front end, a processing circuit, and memory. The analog front end includes a power circuit, a tuning circuit, a transmitter, and a receiver. The power circuit is operably coupled to convert a radio frequency (RF) signal into a power supply voltage. The tuning circuit, when enabled, adjusts an RF characteristic of the analog front end to tune power harvesting from the RF signal. The transmitter is operably coupled to transmit a response signal to the RFID reader via the antenna. The receiver is operably coupled to receive a command signal from the RFID reader, wherein the command signal is contained within a portion of the RF signal. The processing circuit is operable to interpret the command signal and generate the response signal.
1. A circuit of use in a wireless sensor comprises:
a tuning circuit;
a pressure sensing circuit operably coupled to the tuning circuit, wherein the tuning circuit and the pressure sensing circuit collectively have one or more radio frequency (RF) characteristics and wherein the pressure sensing circuit causes the one or more RF characteristics to vary with varying sensed pressures;
a processing module operable to:
detect a variance of the one or more RF characteristics from a desired value of the one or more RF characteristics;
in response to the detecting of the variance, adjust the tuning circuit to substantially re-establish the desired value of the one or more RF characteristics; and
generate a message regarding the adjusting of the tuning circuit, wherein a level of the adjusting of the tuning circuit is representative of a variance of pressure sensed by the pressure sensing circuit; and
a transmitter operably coupled to transmit the message.
2. The circuit of claim 1 , wherein the pressure sensing circuit comprises:
a variable capacitance circuit that includes a first plate, a second plate, and a diaphragm, wherein, as a result of pressure variations on the diaphragm, causes a change in capacitance of the variable capacitance circuit.
3. The circuit sensor of claim 1 , wherein the pressure sensing circuit comprises:
a variable capacitance circuit that includes a first plate, a second plate, and a diaphragm puck, wherein, as a result of pressure variations on the diaphragm puck, causes a change in capacitance of the variable capacitance circuit.
4. The circuit of claim 1 , wherein the pressure sensing circuit comprises:
a variable inductance circuit that includes a tuning loop and a diaphragm that, as a result of pressure variations, causes an inductance change of the tuning loop.
5. The circuit of claim 1 , wherein the pressure sensing circuit comprises:
a variable inductance circuit that includes a tuning loop and a diaphragm puck that, as a result of pressure variations, causes an inductance change of the tuning loop.
6. The circuit of claim 1 , wherein an RF characteristic of the one or more RF characteristics comprises:
an impedance at a frequency;
a resonant frequency;
a quality factor; or
a gain.
7. The circuit of claim 1 , wherein the processing module is further operable to:
in response to a calibration request at a known pressure, adjust the tuning circuit to establish the desired value of the one or more RF characteristics; and
record a level of the adjusting of the tuning circuit to represent a pressure calibration of the wireless sensor.
8. The circuit of claim 1 further comprises:
a power harvesting operably coupled to convert a received radio frequency (RF) signal into a power supply voltage.
9. The circuit of claim 1 further comprises:
a temperature sensor operably coupled to the processing module, wherein the temperature sensor senses a temperature of an environment proximal to the wireless sensor, and wherein the processing module includes a sensed temperature within the message.