Optically Stimulated Differential Impedance Spectroscopy

• US 20120182025A1
• Filed: 12/02/2008
• Published: 07/19/2012
• Est. Priority Date: 12/02/2008
• Status: Active Grant

• Current Assignee: UT-Battelle LLC
• Original Assignee: UT-Battelle LLC
• Inventors: Maxey, Lonnie C., Lewis, Samuel A. Sr., Parks, James E. II, Partridge, William P Jr.
• Granted Patent: US 8,653,830 B2
• Time in Patent Office: Days
• US Class Current: 324/603
• CPC Class Codes: G01N 27/02 by investigating impedance

Abstract

Methods and apparatuses for evaluating a material are described. Embodiments typically involve use of an impedance measurement sensor to measure the impedance of a sample of the material under at least two different states of illumination. The states of illumination may include (a) substantially no optical stimulation, (b) substantial optical stimulation, (c) optical stimulation at a first wavelength of light, (d) optical stimulation at a second wavelength of light, (e) a first level of light intensity, and (f) a second level of light intensity. Typically a difference in impedance between the impedance of the sample at the two states of illumination is measured to determine a characteristic of the material.

Claims

1. A method of evaluating a material comprising:

measuring a first electrical impedance of the material under a first state of illumination;

measuring a second electrical impedance of the material under a second state of illumination that is different from the first state of illumination; and

evaluating the material based upon a difference between the first electrical impedance and the second electrical impedance.

2. The method of claim 1 wherein the first state of illumination is substantially no optical stimulation and the second state of illumination is substantial optical stimulation.

3. The method of claim 1 wherein the first state of illumination comprises optical stimulation at a first wavelength of light that causes an energy level excitation in the material.

4. The method of claim 1 wherein the first state of illumination comprises optical stimulation at a first wavelength of light and the second state of illumination comprises optical stimulation at a second wavelength of light that is different from the first wavelength of light.

5. The method of claim 1 wherein the first state of illumination comprises substantial optical stimulation at a first light intensity and the second state of illumination comprises substantial optical stimulation at a second light intensity that is different from the first light intensity.

6. The method of claim 1 wherein

the step of measuring a first electrical impedance comprises measuring a plurality of first electrical impedances over a frequency range,

the step of measuring a second electrical impedance comprises measuring a plurality of second electrical impedances over the frequency range, and

the step of evaluating the material comprises evaluating a plurality of differences between the measurements of the first electrical impedances over the frequency range and the measurements of the second electrical impedances over the frequency range.

7. The method of claim 1 wherein the step of evaluating the material based upon a difference between the first electrical impedance and the second electrical impedance comprises evaluating the first electrical impedance and the second electrical impedance as represented by an impedance of an electrical network comprising a parallel resistance/capacitance reactance circuit.

8. The method of claim 1 wherein the step of evaluating the material comprises comparing the difference between the first electrical impedance and the second electrical impedance with a reference impedance differential standard.

9. The method of claim 1 wherein the material comprises oil and wherein the step of evaluating the material comprises comparing the difference between the first electrical impedance and the second electrical impedance with a reference impedance differential standard to estimate the service life of the oil.

10. The method of claim 1 wherein the material comprises oil and first state of illumination comprises substantially no optical stimulation and the second state of illumination comprises substantial optical stimulation and the step of evaluating the material comprises analyzing the oil for the presence of fuel.

11. An apparatus for evaluating a material comprising:

an impedance sensor system configured to measure impedance of the composition of material;

a source of optical stimulation configured to expose the material to at least two different states of illumination; and

a control system configured to;

(1) switch the source of optical stimulation between the at least two different states of illumination, and

(2) trigger the impedance sensor system to measure the impedance of the material at each of the at least two different states of illumination.

12. The apparatus of claim 11 wherein the at least two different states of illumination comprise (1) substantially no optical stimulation and (2) substantial optical stimulation.

13. The apparatus of claim 11 wherein the at least two different states of illumination comprise optical stimulation at a wavelength of light that causes an energy level excitation in the composition of material.

14. The apparatus of claim 11 wherein the at least two different states of illumination comprise (1) optical stimulation at a first wavelength of light and (2) optical stimulation at a second wavelength of light.

15. The apparatus of claim 11 wherein the at least two different states of illumination comprise (1) optical stimulation at a first light intensity and (2) optical stimulation at a second light intensity.

16. The apparatus of claim 11 wherein the impedance sensor system comprises an interdigitated electrode.

17. The apparatus of claim 11 wherein the impedance sensor comprises a capacitive probe.

18. The apparatus of claim 11 wherein the source of optical stimulation comprises an optical fiber.

19. The apparatus of claim 11 wherein the source of optical stimulation comprises a light source for providing light at a wavelength and the at least two different states of optical stimulation comprise optical stimulation at the wavelength of light and the apparatus further comprises a test port window that is at least partially transparent to the light at the wavelength and that is disposed at least partially between at least a portion of the material and the light source.

20. The apparatus of claim 11 further comprising an analysis system to compare the impedance of the material at each of the at least two different states of optical stimulation and calculate a characteristic of the material based at least in part on the comparison.