Carbon nanotube-based sensor and method for detection of crack growth in a structure

• US 7,278,324 B2
• Filed: 06/15/2005
• Issued: 10/09/2007
• Est. Priority Date: 06/15/2005
• Status: Expired due to Fees

• Current Assignee: The Government of The US As Represented By The Secretary of The Navy, United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Original Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Inventors: Wincheski, Russell A., Watkins, Anthony N., Ingram, JoAnne L., Moore, Thomas C., Smits, Jan M., Williams, Phillip A., Kite, Marlen T.
• Primary Examiner(s): Cygan; Michael
• Assistant Examiner(s): ROY, PUNAM P
• Application Number:
  US11/155,923
• Publication Number:
  US 20060283262A1
• Time in Patent Office: 846 Days
• Field of Search: 737/99, 737/74, 737/88, 737/62, 737/63, 977/742
• US Class Current: 73/799
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: G01N 2203/0062 Crack or flaws
• CPC Class Codes: G01N 2203/0617 Electrical or magnetic indicating, recording or sensing means
• CPC Class Codes: G01N 27/041 of a solid body
• CPC Class Codes: Y10S 977/742 Carbon nanotubes, CNTs

Abstract

A sensor has a plurality of carbon nanotube (CNT)-based conductors operatively positioned on a substrate. The conductors are arranged side-by-side, such as in a substantially parallel relationship to one another. At least one pair of spaced-apart electrodes is coupled to opposing ends of the conductors. A portion of each of the conductors spanning between each pair of electrodes comprises a plurality of carbon nanotubes arranged end-to-end and substantially aligned along an axis. Because a direct correlation exists between the resistance of a carbon nanotube and its strain, changes experienced by the portion of the structure to which the sensor is coupled induce a corresponding change in the electrical properties of the conductors, thereby enabling detection of crack growth in the structure.

Claims

1. A method of detecting crack growth experienced by a structure, said method comprising the steps of:

positioning a plurality of carbon nanotube (CNT)-based sensors into a close grouping on a portion of the structure, each said sensor comprising (i) a substrate adapted to be coupled to the portion of the structure, said substrate being flexible such that strain experienced by the portion of the structure causes relative strain in said substrate, (ii) a plurality of carbon nanotube (CNT)-based conductors operatively positioned on said substrate and arranged side-by-side to one another, said plurality of CNT-based conductors being coated with a gas-impermeable membrane to reduce pressure sensitivity of said plurality of CNT-based conductors, and (iii) at least one pair of spaced-apart electrodes electrically coupled to opposing ends of said plurality of CNT-based conductors with a portion of each of said plurality of CNT-based conductors spanning between each pair of said spaced-apart electrodes comprising a plurality of carbon nanotubes arranged end-to-end and substantially aligned along an axis;

monitoring electrical properties of said plurality of CNT-based sensors when the portion of the structure is experiencing baseline levels of the parameter of strain to establish a baseline response; and

continually monitoring the electrical properties over time to identify any change in the electrical properties from the baseline response, wherein a change in the electrical properties of said plurality of CNT-based sensors is indicative of crack growth experienced by the portion of the structure.

2. A method according to claim 1 wherein said step of positioning comprises the step of coupling said plurality of CNT-based sensors to a surface of the structure.

3. A method according to claim 1 wherein each of said plurality of carbon nanotubes is a single-wall carbon nanotube.

4. A method of detecting crack growth experienced by a structure, said method comprising the steps of:

embedding a plurality of carbon nanotube (CNT)-based sensors into a close grouping in a portion of the structure, each said sensor comprising (i) a substrate adapted to be coupled to the portion of the structure, said substrate being flexible such that strain experienced by the portion of the structure causes relative strain in said substrate, (ii) a plurality of carbon nanotube (CNT)-based conductors operatively positioned on said substrate and arranged side-by-side to one another, said plurality of CNT-based conductors being coated with a gas-impermeable membrane to reduce pressure sensitivity of said plurality of CNT-based conductors, and (iii) at least one pair of spaced-apart electrodes electrically coupled to opposing ends of said plurality of CNT-based conductors with a portion of each of said plurality of CNT-based conductors spanning between each pair of said spaced-apart electrodes comprising a plurality of carbon nanotubes arranged end-to-end and substantially aligned along an axis;

monitoring electrical properties of said plurality of CNT-based sensors when the portion of the structure is experiencing baseline levels of the parameter of strain to establish a baseline response; and

continually monitoring the electrical properties over time to identify any change in the electrical properties from the baseline response, wherein a change in the electrical properties of said plurality of CNT-based sensors is indicative of crack growth experienced by the portion of the structure.

5. A method according to claim 4 wherein said step of embedding further comprises the steps of:

embedding a portion of said plurality of CNT-based sensors in the structure; and

coupling a remainder of said plurality of CNT-based sensors to a surface of the structure.

6. A method of detecting crack growth experienced by a structure, said method comprising the steps of:

positioning a plurality of carbon nanotube (CNT)-based sensors into a close grouping on a portion of the structure, including arranging said plurality of CNT-based sensors such that the axis of sensitivity associated with each one of said CNT-based sensors is at an orientation unique to the axis of sensitivity of each of the other of said CNT-based sensors within the close grouping of CNT-based sensors, each said sensor comprising (i) a substrate adapted to be coupled to the portion of the structure, said substrate being flexible such that strain experienced by the portion of the structure causes relative strain in said substrate, (ii) a plurality of carbon nanotube (CNT)-based conductors operatively positioned on said substrate and arranged side-by-side to one another, said plurality of CNT-based conductors being coated with a gas-impermeable membrane to reduce pressure sensitivity of said plurality of CNT-based conductors, and (iii) at least one pair of spaced-apart electrodes electrically coupled to opposing ends of said plurality of CNT-based conductors with a portion of each of said plurality of CNT-based conductors spanning between each pair of said spaced-apart electrodes comprising a plurality of carbon nanotubes arranged end-to-end and substantially aligned along an axis;

monitoring electrical properties of said plurality of CNT-based sensors when the portion of the structure is experiencing baseline levels of the parameter of strain to establish a baseline response; and

continually monitoring the electrical properties over time to identify any change in the electrical properties from the baseline response, wherein a change in the electrical properties of said plurality of CNT-based sensors is indicative of crack growth experienced by the portion of the structure.

7. A method according to claim 6 wherein said step of continually monitoring the electrical properties comprises individually addressing each of said close groupings of CNT-based sensors in an ordered matrix.

8. A method of detecting crack growth experienced by a structure, said method comprising the steps of:

positioning a plurality of carbon nanotube (CNT)-based sensors into a close grouping on a portion of the structure, each said sensor comprising (i) a substrate adapted to be coupled to the portion of the structure, said substrate being flexible such that strain experienced by the portion of the structure causes relative strain in said substrate, (ii) a plurality of carbon nanotube (CNT)-based conductors operatively positioned on said substrate and arranged side-by-side to one another, said plurality of CNT-based conductors being coated with a gas-impermeable membrane to reduce pressure sensitivity of said plurality of CNT-based conductors, and (iii) at least one pair of spaced-apart electrodes electrically coupled to opposing ends of said plurality of CNT-based conductors with a portion of each of said plurality of CNT-based conductors spanning between each pair of said spaced-apart electrodes comprising a plurality of carbon nanotubes arranged end-to-end and substantially aligned along an axis;

monitoring elcetrical properties of said plurality of CNT-based sensors when the portion of the structure is experiencing baseline levels of the parameter of strain to establish a baseline response; and

continually monitoring the electrical properties over time, including individually addressing each one of said CNT-based sensors in an ordered matrix, to identify any change in the electrical properties from the baseline response, wherein a change in the electrical properties of said plurality of CNT-based sensors is indicative of crack growth experienced by the portion of the structure.

9. A sensor for detecting crack growth in a structure, comprising:

a flexible substrate adapted to be coupled to a portion of the structure;

a plurality of carbon nanotube (CNT)-based conductors operatively positioned on said substrate and arranged side-by-side to one another, said plurality of CNT-based conductors being coated with a gas-impermeable membrane to reduce pressure sensitivity of said plurality of CNT-based conductors; and

,

at least one pair of spaced-apart electrodes, each of said at least one pair of spaced-apart electrodes being coupled to opposing ends of at least one CNT-based conductor, said at least one CNT-based conductor electrically coupling such spaced-apart electrodes to one another;

a portion of each of said plurality of CNT-based conductors spanning between each pair of said spaced-apart electrodes comprising a plurality of carbon nanotubes arranged end-to-end and substantially aligned along an axis, wherein growth of a crack line experienced by the portion of the structure induces a change in electrical properties of said plurality of CNT-based conductors.

10. A sensor as in claim 9 wherein at least one of said pair of spaced-apart electrodes comprises two spaced-apart electrode strips positioned on said substrate, with said plurality of CNT-based conductors being positioned on said two spaced-apart electrode strips at the opposing ends of each CNT-based conductor.

11. A sensor as in claim 9 wherein at least one of said pair of spaced-apart electrodes comprises two spaced-apart electrode strips positioned on the opposing ends of each of said plurality of CNT-based conductors.

12. A sensor as in claim 9 wherein at least one of said pair of spaced-apart electrodes comprises:

a first pair of spaced-apart electrode strips positioned on said substrate, with said plurality of CNT-based conductors being positioned on said first pair of spaced-apart electrode strips at the opposing ends of each CNT-based conductor; and

a second pair of spaced-apart electrode strips positioned on the opposing ends of each of said plurality of CNT-based conductors.

13. A sensor as in claim 9 wherein each of said plurality of carbon nanotubes is a single-wall carbon nanotube.

14. A sensor as in claim 9 wherein each of said pair of spaced-apart electrodes comprises parallel electrode strips.

15. A sensor as in claim 9 wherein the CNT-based conductors are arranged substantially parallel to one another.

16. A sensor as in claim 9 further comprising a CNT attraction material deposited on said substrate among at least one of said pairs of said spaced-apart electrodes.

17. A sensor assembly for detecting crack growth experienced by a structure, comprising:

a plurality of carbon nanotube (CNT)-based sensors positioned into a close grouping on a portion of the structure, each of said CNT-based sensors comprising (i) a substrate adapted to be coupled to the portion of the structure, said substrate being flexible such that strain experienced by the portion of the structure causes relative strain in said substrate, (ii) a plurality of carbon nanotube (CNT)-based conductors operatively positioned on said substrate and arranged side-by-side to one another, said plurality of CNT-based conductors being coated with a aas-imnermeable membrane to reduce pressure sensitivity of said plurality of CNT-based conductors, and (iii) at least one pair of spaced-apart electrodes electrically coupled to opposing ends of said plurality of CNT-based conductors with a portion of each of said plurality of CNT-based conductors spanning between each pair of said spaced-apart electrodes comprising a plurality of carbon nanotubes arranged end-to-end and substantially aligned along an axis; and

means for monitoring the electrical properties of said plurality of CNT-based sensors over time so as to establish a baseline response when the portion of the structure is experiencing baseline levels of the parameter of strain and to identify any change in the electrical properties from the baseline response, wherein a change in the electrical properties of said plurality of CNT-based sensors is indicative of crack growth experienced by the portion of the structure.

18. A sensor assembly for detecting crack growth experienced by a structure, comprising:

a plurality of carbon nanotube (CNT)-based sensors positioned into a close grouping on a portion of the structure, each of said CNT-based sensors comprising (i) a substrate adapted to be coupled to the portion of the structure, said substrate being flexible such that strain experienced by the portion of the structure causes relative strain in said substrate, (ii) a plurality of carbon nanotube (CNT)-based conductors operatively positioned on said substrate and arranged side-by-side to one another, said plurality of CNT-based conductors being coated with a gas-impermeable membrane to reduce pressure sensitivity of said plurality of CNT-based conductors, and (iii) at least one pair of spaced-apart electrodes electrically coupled to opposing ends of said plurality of CNT-based conductors with a portion of each of said plurality of CNT-based conductors spanning between each pair of said spaced-apart electrodes comprising a plurality of carbon nanotubes arranged end-to-end and substantially aligned along an axis; and

means for monitoring the electrical properties of said plurality of CNT-based sensors over time so as to establish a baseline response when the portion of the structure is experiencing baseline levels of the parameter of strain and to identify any change in the electrical properties from the baseline response, wherein said means for monitoring includes individually addressing each one of said CNT-based sensors in an ordered matrix, and wherein a change in the electrical properties of said plurality of CNT-based sensors is indicative of crack growth experienced byte portion of the structure.

19. A sensor assembly for detecting crack growth experienced by a structure, comprising:

a plurality of carbon nanotube (CNT)-based sensors positioned into a close grouping on a portion of the structure, wherein said plurality of CNT-based sensors are positioned such that the axis of sensitivity associated with each one of said CNT-based sensors is at an orientation unique to the axis of sensitivity of each of the other of said CNT-based sensors for the close grouping of plurality of CNT-based sensors. each of said CNT-based sensors comprising (i) a substrate adapted to be coupled to the portion of the structure, said substrate being flexible such that strain experienced by the portion of the structure causes relative strain in said substrate, (ii) a plurality of carbon nanotube (CNT)-based conductors operatively positioned on said substrate and arranged side-by-side to one another, said plurality of CNT-based conductors being coated with a gas-impermeable membrane to reduce pressure sensitivity of said plurality of CNT-based conductors, and (iii) at least one pair of spaced-apart electrodes electrically coupled to opposing ends of said plurality of CNT-based conductors with a portion of each of said plurality of CNT-based conductors spanning between each pair of said spaced-apart electrodes comprising a plurality of carbon nanotubes arranged end-to-end and substantially aligned along an axis; and

means for monitoring the electrical properties of said plurality of CNT-based sensors over time so as to establish a baseline response when the portion of the structure is experiencing baseline levels of the parameter of strain and to identil$ any change in the electrical properties from the baseline response, wherein a change in the electrical properties of said plurality of CNT-based sensors is indicative of crack growth experienced by the portion of the structure.

20. A sensor assembly for detecting crack growth experienced by a structure, comprising:

multiple close groupings of a plurality of carbon nanotube (CNT)-based sensors positioned in a dense, ordered arrangement on a portion of the structure, each of said CNT-based sensors comprising (i) a substrate adapted to be coupled to the portion of the structure, said substrate being flexible such that strain experienced by the portion of the structure causes relative strain in said substrate, (ii) a plurality of carbon nanotube (CNT)-based conductors operatively positioned on said substrate and arranged side-by-side to one another, said plurality of CNT-based conductors being coated with a gas-impermeable membrane to reduce pressure sensitivity of said plurality of CNT-based conductors, and (iii) at least one pair of spaced-apart electrodes electrically coupled to opposing ends of said plurality of CNT-based conductors with a portion of each of said plurality of CNT-based conductors spanning between each pair of said spaced-apart electrodes comprising a plurality of carbon nanotubes arranged end-to-end and substantially aligned along an axis; and

means for monitoring the electrical properties of said plurality of CNT-based sensors over time so as to establish a baseline response when the portion of the structure is experiencing baseline levels of the parameter of strain and to identies any change in the electrical properties from the baseline response, wherein a change in the electrical properties of said plurality of CNT-based sensors is indicative of crack growth experienced by the portion of the structure.