Systems and methods for detection of dielectric change in material and structure

• US 20060076985A1
• Filed: 08/11/2005
• Published: 04/13/2006
• Est. Priority Date: 08/18/2004
• Status: Active Grant

• Current Assignee: Southwest Research Institute
• Original Assignee: Southwest Research Institute
• Inventors: Cerwin, Stephen A., Goyen, Todd H., Martinez, Robert E.
• Granted Patent: US 7,288,945 B2
• Time in Patent Office: Days
• US Class Current: 327/110
• CPC Class Codes: G01V 3/088 operating with electric fields G01V3/082 takes precedence
• CPC Class Codes: H03K 17/955 using a capacitive detector

Abstract

Methods and systems are described for efficiently detecting an object. The system includes at least one electrode for measuring a displacement current. The at least one electrode is coupled to a floating ground configuration provided by an op-amp, where the inverting node of the op-amp is coupled to electrode and the non-inverting node is coupled to a signal generator. The system may include a single capacitance sensor for detecting an object. Systems may include a plurality of capacitance sensors in an array configuration for detecting an object.

Claims

1. A system comprising:

a first electrode;

a signal generator;

an op-amp coupled to the signal generator, the op-amp comprising;

an inverting node coupled to the first electrode; and

a non-inverting node coupled to the signal generator;

where the first electrode is indirectly driven by the op-amp and where the op-amp provides a floating ground.

2. The system of claim 1, the first electrode comprising a sensor electrode.

3. The system of claim 1, the signal generator operating above 1 Hz.

4. The system of claim 1, the signal generator operating at a peak-to-peak amplitude of about less than or equal to 50 volts.

5. The system of claim 1, the signal generator providing a continuous AC signal.

6. The system of claim 1, further comprising a feedback connection between an output of the op-amp and the inverting node.

8. The system of claim 1, further comprising a buffer amplifier coupled to an output of the op-amp.

10. The system of claim 1, further comprising a second electrode in proximity to the first electrode, the second electrode indirectly driving a second op-amp, the second op amp comprising:

a second inverting node coupled to the second electrode; and

a second non-inverting node coupled to the signal generator;

where the second electrode is driven by the second op-amp.

7. The system of claim 7, the feedback connection comprising a resistor network configured for achieving a current-to-voltage gain of approximately 10⁸ Ohms.

9. The system of claim 9, the buffer amplifier comprising a differential amplifier for subtracting an AC drive from the output of the op-amp.

11. A system comprising:

a plurality of capacitance sensors configured for measuring displacement currents and detecting an object, each of the plurality of capacitance sensors comprising a sensor electrode; and

a floating ground circuitry coupled to each sensor electrode.

12. The system of claim 12, where each sensor of the plurality of capacitance sensors measures displacement currents with a detection sensitivity of less than 1 picoamp.

13. The system of claim 12, where each sensor of the plurality of capacitance sensors measures stray capacitance between about 10⁻

18 to about 10<sup>−

20</sup> farads.

14. The system of claim 12, where the plurality of capacitance sensors are arranged in an array configuration.

15. The system of claim 12, further comprising a guard electrode in proximity to the plurality of capacitance sensors configured for shielding the plurality of capacitance sensors from stray electric fields.

17. The system of claim 12, the floating ground circuitry comprising an operational amplifier including an inverting node coupled to the sensor electrode and a non-inverting node coupled to a signal generator.

22. The system of claim 12, where each of the sensor electrodes has a substantially equal potential.

16. The system of claim 16, where the guard electrode is further configured to shield the floating ground circuitry from stray electric fields.

18. The system of claim 18, the floating ground circuitry further comprising a buffer amplifier coupled to an output of the op-amp, the buffer amplifier configured for subtracting an AC drive from an output of the op-amp.

19. The system of claim 19, where the buffer amplifier references the output of each sensor electrode of the plurality of capacitance sensors to a true circuit ground.

20. The system of claim 19, the buffer amplifier comprising a differential amplifier.

21. The system of claim 19, the buffer amplifier comprising an isolation amplifier.

23. A method comprising:

determining displacement currents from each pixel of a plurality of pixels;

determining an average displacement current from the displacement currents;

comparing the average displacement current with any one of the displacement currents; and

detecting an object using the comparison between the average displacement current and any one of the displacement currents.

25. The method of claim 25, further comprising providing the displacement currents to a multiplexer.

24. The method of claim 25, where each pixel comprises an electrode and where the step of determining a displacement current comprises measuring the displacement current with the electrode.

28. The method of claim 28, further comprising providing the result of the comparing step to adjusting circuitry configured for adjusting the amplitude and phase of the result.

26. The method of claim 27, the step of comparing the average displacement current further comprising selecting a displacement current from the multiplexer.

27. The method of claim 28, the step of comparing the average displacement current further comprising subtracting the average current from the selected displacement current.

29. A method comprising:

providing a reference signal;

comparing a displacement current to the reference signal;

determining a difference between the reference signal and the displacement current;

adjusting the phase and gain of the displacement current to nullify the difference;

using the difference between the reference signal and the displacement signal to detect an object.

31. The method of claim 31, where comparing a displacement further comprises comparing a displacement current from each pixel in an array of pixel.

30. The method of claim 31, where the reference signal may be an average displacement current of a plurality of displacement currents.

32. The method of claim 31, where providing a reference signal comprises generating the reference signal by sensing current across a reference capacitor.

36. The method of claim 31, where the reference signal is generated by sensing current across a reference capacitor.

33. A method comprising:

receiving a displacement signal;

determining the voltage of the displacement signal;

setting a voltage of a reference signal to a range similar to the voltage of the displacement signal;

determining a difference between the reference signal and the displacement current;

amplifying the difference; and

using the difference between the reference signal and the displacement signal to detect an object.

34. The method of claim 34, where the voltage of the reference signal is greater than the voltage of the displacement signal.

35. The method of claim 34, where the voltage of the reference signal is less than the voltage of the displacement signal.