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

• US 7,288,945 B2
• Filed: 08/11/2005
• Issued: 10/30/2007
• Est. Priority Date: 08/18/2004
• Status: Active Grant

• Current Assignee: Southwest Research Institute
• Original Assignee: Southwest Research Institute
• Inventors: Cerwin, Stephen A., Martinez, Robert E., Goyen, Todd H.
• Primary Examiner(s): Benson; Walter
• Assistant Examiner(s): Dole; Timothy J
• Application Number:
  US11/201,753
• Publication Number:
  US 20060076985A1
• Time in Patent Office: 810 Days
• Field of Search: 324/663, 324/683, 324/686, 324/688, 324/672, 324/679
• US Class Current: 324/663
• 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 sensor electrode;

a signal generator;

a first op-amp comprising;

a first inverting node coupled to the sensor electrode and a first non-inverting node coupled to the signal generator, where the sensor electrode is indirectly driven by the first op-amp and where the first op-amp provides a floating ground to the sensor electrode;

a counter-electrode in proximity to the sensor electrode;

a second op-amp comprising a second inverting node coupled to the counter-electrode and a second non-inverting node coupled to the signal generator, where the counter-electrode is indirectly driven by the second op-amp and where the second op-amp provides another floating ground to the counter-electrode; and

a third op-amp comprising a third inverting node coupled to the output of the first op-amp and a third non-inverting node coupled to the output of the second op-amp, the third op-amp providing a differential signal between the sensor electrode and the counter-electrode.

2. The system of claim 1, further comprising:

a guard electrode coupled to the signal generator and to the second non-inverting node of the second op-amp, the guard electrode providing shielding from stray electric fields to the sensor electrode and the counter-electrode.

3. The system of claim 2, where the guard electrode surrounds the counter-electrode.

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

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

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

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

8. 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 1, further comprising a buffer amplifier coupled to the output of the first op-amp.

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

11. The system of claim 1,

where the counter-electrode surrounds the sensor electrode.