Passive wireless gastroesophageal sensor

1. A passive wireless gastroesophageal sensor comprising:

an LC (inductor capacitor) resonance circuit;

one or more electrodes configured to measure an impedance within a gastroesophageal tract; and

a passive batteryless Radio Frequency Identification (RFID) circuit connected to the LC resonance circuit and the one or more electrodes, wherein the passive batteryless RFID circuit comprises a voltage regulator, a voltage multiplier connected to the voltage regulator, a transistor switch connected in parallel between the LC resonance circuit and the voltage multiplier, and an impedance to frequency converter connected to the electrodes and the voltage regulator, wherein the impedance to frequency converter controls the transistor switch, and wherein the switching frequency of the transistor switch varies with the measured impedance such that the RFID circuit transmits a frequency modulated signal using the LC resonance circuit, the frequency modulation of the transmitted signal varying between a first frequency corresponding to a non-reflux condition and a second frequency corresponding to a reflux condition, based on the measured impedance, in response to a signal received from a detector; and

wherein the sensor is adapted to be attached to the gastroesophageal tract.

2. The sensor as recited in claim 1 , wherein:

the non-reflux condition comprises a substance before the substance has entered a stomach disposed on or between the electrodes; and

the reflux condition comprises a stomach acid or stomach contents disposed on or between the electrodes.

3. The sensor as recited in claim 1 , wherein:

the first frequency comprises a measured frequency of between 6 k Hz and 11 kHz; and the second frequency comprises a measured frequency greater than 11 kHz.

4. The sensor as recited in claim 1 , wherein:

the LC circuit comprises a parallel connected antenna and a capacitor.

5. The sensor as recited in claim 1 , wherein the voltage multiplier includes a series of diodes and capacitors for energy harvesting, the impedance-to-frequency convertor converts the impedance of the electrodes to frequency-varying signals, and the sensor further comprises a modulation circuit.

6. The sensor as recited in claim 1 , wherein the sensor is configured as a capsule, a tag or an implant having an overall size equal to or less than 0.5×l×3 cm 3 .

7. The sensor as recited in claim 3 , wherein the antenna comprises at least one wire coil surrounding the electrodes.

8. The sensor as recited in claim 7 , wherein the wire coil comprises at least 15 turns of a conductor having a width of 200 μm and a spacing of 50 μm in each turn.

9. The sensor as recited in claim 1 , wherein the electrodes comprise at least 10 interdigitated fingers that are about 0.4 mm wide and about 5 mm long with about 0.1 mm spacing there between.

10. The sensor as recited in claim 1 , wherein the passive batteryless RFID circuit uses a frequency shift keying modulation to reduce noise.

11. The sensor as recited in claim 1 , wherein the electrodes are fabricated by a process comprising the steps of:

evaporating a first conductive material on a flexible polyimide substrate;

patterning a photoresist layer on selected portions of the first conductive material;

electroplating the first conductive material;

removing the photoresist layer and etching the first conductive material to form the electrodes;

patterning an epoxy based negative resist layer; and

electroplating a second conductive material on the electrodes.

12. A system for detecting Gastroesophageal Reflux Disease (GERD) in an animal comprising:

a detector comprising:

an external resonance circuit formed from an external coil,

a power amplifier connected to the external resonance circuit,

a radio frequency source connected to the power amplifier,

an envelope detector connected to the power amplifier, and

a band pass filter connected to the envelope detector; and

one or more passive wireless gastroesophageal sensors, each sensor comprising:

an LC (inductor capacitor) resonance circuit;

one or more electrodes configured to measure an impedance within a gastroesophageal tract; and

a passive batteryless Radio Frequency Identification (RFID) circuit connected to the LC resonance circuit and the one or more electrodes, wherein the passive batteryless RFID circuit comprises a voltage regulator, a voltage multiplier connected to the voltage regulator, a transistor switch connected in parallel between the LC resonance circuit and the voltage multiplier, and an impedance to frequency converter connected to the electrodes and the voltage regulator, wherein the impedance to frequency converter controls the transistor switch, and wherein the switching frequency of the transistor switch varies with the measured impedances such that the RFID circuit transmits a frequency modulated signal using the LC resonance circuit, the frequency modulation of the transmitted signal varying between a first frequency corresponding to a non-reflux condition and a second frequency corresponding to a reflux condition based on the measured impedance in response to a signal received from a detector; and

wherein the sensor is adapted to be attached to the gastroesophageal tract.

13. The system as recited in claim 12 , wherein the power amplifier is a class-E power amplifier and the envelope detector includes a diode, RC networks, and an op-amp buffer.

14. The system as recited in claim 12 , wherein: the first frequency comprises a measured frequency of between 6 kHz and 11 kHz; and the second frequency comprises a measured frequency greater than 11 kHz.

15. The system as recited in claim 12 , wherein:

the LC resonance circuit comprises a parallel connected antenna and a capacitor.

16. The system as recited in claim 12 , wherein the one or more sensors comprise multiple sensors implanted to detect a refluxate in multiple areas of the gastroesophageal tract of the animal.

17. The system as recited in claim 12 , wherein the electrodes are fabricated by a process comprising the steps of:

evaporating a first conductive material on a flexible polyimide substrate;

patterning a photoresist layer on selected portions of the first conductive material;

electroplating the first conductive material;

removing the photoresist layer and etching the first conductive material to form the electrodes;

patterning an epoxy based negative resist layer; and

electroplating a second conductive material on the electrodes.

18. The system as recited in claim 12 , wherein the external resonance circuit is uniquely coupled to each sensor.

19. The system as recited in claim 12 , wherein the external resonance circuit is uniquely coupled to more than one of the sensors.