System and method for the wireless sensing of physical properties

• US 6,111,520 A
• Filed: 04/02/1998
• Issued: 08/29/2000
• Est. Priority Date: 04/18/1997
• Status: Expired due to Term

• Current Assignee: Georgia Tech Research Corporation (University System of Georgia)
• Original Assignee: Georgia Tech Research Corporation (University System of Georgia)
• Inventors: Allen, Mark G., English, Jennifer M.
• Primary Examiner(s): Lee, Benjamin C.
• Application Number:
  US09/054,011
• Time in Patent Office: 880 Days
• Field of Search: 340/825.54, 340/870.11, 340/870.16, 340/870.17, 340/870.28, 340/447, 340/870.31, 340/870.32, 340/870.37, 340/870.38, 340/879.4 , 340/690, 340/572, 340/448, 340/442, 340/449, 340/451, 340/584, 340/665, 340/521, 340/531, 374/120, 374/154, 374/163, 374/183, 374/184, 422/82.02, 331/66, 331/141, 724/655
• US Class Current: 340/870.16
• CPC Class Codes: B60C 23/0408 transmitting the signals by non-mechanical means from the wheel or tyre to a vehicle body mounted receiver
• CPC Class Codes: G01D 5/48 using wave or particle radiation means G01D5/26 takes precedence
• CPC Class Codes: G01L 9/0073 using a semiconductive diaphragm

Abstract

Several sensors are provided for determining one of a number of physical properties including pressure, temperature, and other physical conditions. In general, the sensors feature a resonant circuit with an inductor coil which is electromagnetically coupled to a transmitting antenna. When an excitation signal is applied to the antenna, a current is induced in the sensor circuit. This current oscillates at the resonant frequency of the sensor circuit. The resonant frequency and bandwidth of the sensor circuit is determined using an impedance analyzer, a transmitting and receiving antenna system, or a chirp interrogation system. The resonant frequency may further be determined using a simple analog circuit with a transmitter. The sensors are constructed so that either the resonant frequency or bandwidth of the sensor circuit, or both, are made to depend upon the physical properties such as pressure, temperature, presence of a chemical species, or other condition of a specific environment. The physical properties are calculated from the resonant frequency and bandwidth determined.

Claims

1. A sensor for wirelessly determining physical properties of a medium, comprising:

a self-contained resonant circuit comprising a capacitor, a resistor, and an inductor;

the resistor being variable in response to the temperature of the medium

the capacitor being variable in response to pressure of the medium; and

,

the inductor being adapted to allow inducement of a current in the resonant circuit when the sensor is subjected to a time-varying electromagnetic field.

2. A sensor for wirelessly determining physical properties of a medium, comprising:

a first layer on which is disposed a first plate and an inductor coil;

a second layer having a hole;

a third layer on which is disposed a second plate, the first plate facing the second plate through the hole in the second layer, the first and second plates forming a capacitor, the inductor coil being electrically coupled between the first plate and the second plate; and

,

the capacitor and the inductor forming a self-contained resonant circuit, the capacitor being variable in response to pressure of the medium, and, the inductor being adapted to allow inducement of a current in the resonant circuit when the sensor is subjected to a time-varying electromagnetic field.

3. A sensor for wirelessly determining physical properties of a medium, comprising:

a first end layer having a first plate;

at least one middle layer having a hole and a conductive loop surrounding the hole, the conductive loops being electrically coupled thereby forming an inductive coil;

a second end layer having a second plate, the first and second plates facing each other through the hole in said at least one middle layer forming a capacitor, the first and second plates being electrically coupled at opposite ends of the inductor coil; and

the capacitor and the inductive coil forming a self-contained resonant circuit, the capacitor being variable in response to pressure of the medium, and, the inductor being adapted to allow inducement of a current in the resonant circuit when the sensor is subjected to a time-varying electromagnetic field.

4. A sensor for wirelessly determining physical properties of a medium, comprising:

a self-contained resonant circuit comprising a capacitor, an inductor, and a resistor;

the resistor being variable in response to the presence of a chemical species in a medium; and

the inductor being adapted to allow the inducement of a current in the resonant circuit from a transmitted electromagnetic field.

5. A sensor for wirelessly determining physical properties of a medium, comprising:

a self-contained resonant circuit comprising a capacitor, an inductor, and a resistor;

the resistor being variable in response to the temperature of the medium, wherein a bandwidth of the resonant circuit varies with the resistance of the resistor; and

the inductor being adapted to allow the inducement of a current in the resonant circuit when the sensor is subjected to a time-varying electromagnetic field.

6. A sensor having a resonant circuit for wirelessly determining physical properties of a medium, comprising:

means for providing a capacitance in the resonant circuit which is variable in response to the ambient pressure of the medium;

means for providing an inductance in the resonant circuit;

means for providing a resistance in the resonant circuit;

means for providing a resistance in the resonant circuit which is variable in response to the temperature of the medium; and

means for inducing a current in the resonant circuit when the sensor is subjected to a time-varying electromagnetic field.

7. A sensor having a resonant circuit for wirelessly determining physical properties of a medium, comprising:

means for providing a capacitance in the resonant circuit;

means for providing an inductance in the resonant circuit;

means for providing a resistance in the resonant circuit, the resistance being variable in response to the temperature of the medium, wherein a bandwidth of the resonant circuit varies with the resistance; and

means for inducing a current in the resonant circuit when the sensor is subjected to a time-varying electromagnetic field.

8. A system for sensing physical properties of a medium, comprising:

a transmitter adapted to transmit an excitation signal;

a sensor adapted to be placed in the medium, the sensor having a resonant circuit which is capable of being electromagnetically coupled to the transmitter, the resonant circuit having a natural frequency which varies with an ambient pressure of the medium and a bandwidth which varies in response to a temperature of the medium;

a receiver adapted to receive a modified excitation signal which results from the electromagnetic coupling of the resonant circuit to the transmitter; and

a logical circuit electrically coupled to the receiver, the logical circuit being adapted to determine the ambient pressure of the medium based on the natural frequency of the resonant circuit manifested in the modified excitation signal, and the logical circuit being adapted to determine the temperature of the medium based upon a bandwidth of the resonant circuit manifested in the modified excitation signal.

9. The system of claim 8, wherein the resonant circuit further comprises a resistance which varies in response to the temperature of the medium, thereby altering the bandwidth of the resonant circuit.

10. The system of claim 8, further comprising:

the resonant circuit having an inductance, a capacitance which varies in response to the ambient pressure of the medium, thereby altering the natural frequency of the resonant circuit, and a resistance disposed in the resonant circuit which varies in response to the temperature of the medium, thereby altering a bandwidth of the resonant circuit.

11. A system for sensing physical properties of a medium, comprising:

means for transmitting an excitation signal;

a sensor adapted to be placed in the medium, the sensor having a resonant circuit which is capable of being electromagnetically coupled to the transmitter, the resonant circuit having a natural frequency which varies with an ambient pressure of the medium, and a bandwidth which varies in response to the temperature of the medium;

means for receiving a modified excitation signal which results from the electromagnetic coupling of the resonant circuit to the transmitter; and

means for determining the ambient pressure of the medium based on the natural frequency of the resonant circuit, the resonant frequency being determined from the modified excitation signal; and

means for determining the temperature of the medium based upon the bandwidth of the resonant circuit, the bandwidth being determined from the modified excitation signal.

12. The system of claim 11, wherein the resonant circuit further comprises a resistance which varies in response to the temperature of the medium, thereby altering the bandwidth of the resonant circuit.

13. A system for sensing physical properties of a medium, comprising:

means for transmitting an excitation signal;

a sensor adapted to be placed in the medium, the sensor having a resonant circuit which is capable of being electromagnetically coupled to the transmitter, the resonant circuit having a natural frequency which varies with an ambient pressure of the medium, and a bandwidth which varies with a temperature of the medium;

means for receiving a modified excitation signal which results from the electromagnetic coupling of the resonant circuit to the transmitter; and

means for determining the ambient pressure of the medium based on the natural frequency of the resonant circuit, the resonant frequency being determined from the modified excitation signal;

means for determining the temperature of the medium based upon the bandwidth of the resonant circuit, the bandwidth being determined from the modified excitation signal;

the resonant circuit further comprising

a predetermined inductance;

a capacitance which varies in response to the ambient pressure of the medium, thereby altering the natural frequency of the resonant circuit; and

a resistance disposed in the resonant circuit which varies in response to the temperature of the medium, thereby altering the bandwidth of the resonant circuit.

14. A method for sensing physical properties of a medium, comprising the steps of:

transmitting an excitation signal;

inducing a current in a coil inductor of a resonant circuit with the transmitted excitation signal;

resonating the current at the natural frequency of the resonant circuit;

varying the natural frequency of the resonant circuit with a pressure of the medium in which the resonant circuit is placed;

varying a bandwidth of the resonant circuit in response to a temperature of the medium;

receiving a modified excitation signal which results from the inducement of the current in the coil inductor;

determining the pressure of the medium from the natural frequency of the resonant circuit; and

determining the temperature of the medium based upon the bandwidth of the resonant circuit.

15. The method of claim 14, wherein the step of varying a bandwidth of the resonant circuit in response to the temperature of the medium further comprises the step of varying a resistance disposed in the resonant circuit in response to the temperature of the medium.

16. The method of claim 15, further comprising the step of determining the temperature of the medium based upon the bandwidth of the resonant circuit.

17. A method for sensing physical properties of a medium, comprising the steps of:

transmitting an excitation signal;

inducing a current in a coil inductor of a resonant circuit with the transmitted excitation signal;

resonating the current at the natural frequency of the resonant circuit;

varying a resistance in the resonant circuit in response to a temperature of the medium in which the resonant circuit is placed, thereby proportionally varying a bandwidth of the resonant circuit;

receiving a modified excitation signal which results from the inducement of the current in the coil inductor; and

determining the temperature of the medium from the bandwidth of the resonant circuit.

18. A system for sensing physical properties of a medium, comprising:

a transmitting antenna configured to transmit a time-varying electromagnetic field into the medium;

an impedance analyzer coupled to the transmitting antenna, the impedance analyzer determining an impedance of the transmitting antenna over a predetermined range of frequencies;

a sensor adapted to be placed in the medium, the sensor having a resonant circuit which is capable of being electromagnetically coupled to the transmitting antenna, the resonant circuit having a bandwidth which varies with the presence of a chemical element in the medium; and

a logical circuit electrically coupled to the impedance analyzer, the logical circuit being adapted to determine the presence of the chemical element in the medium based on the bandwidth of the resonant circuit as determined by the impedance analyzer.

19. A system for sensing physical properties of a medium, comprising:

a transmitting means for transmitting a time-varying electromagnetic field into the medium;

an analyzer means for determining an impedance of the transmitting means over a predetermined range of frequencies, the analyzer means being coupled to the transmitting means;

a sensor adapted to be placed in the medium, the sensor having a resonant circuit which is capable of being electromagnetically coupled to the transmitting means, the resonant circuit having a bandwidth which varies with the presence of a chemical element in the medium; and

means for determining the presence of a chemical element in the medium based on the bandwidth of the resonant circuit as determined by the analyzer means.