Flexible, stretchable, and distributed strain sensors

• US 8,250,927 B2
• Filed: 03/17/2010
• Issued: 08/28/2012
• Est. Priority Date: 03/17/2010
• Status: Expired due to Fees

• Current Assignee: Indian Institute of Science
• Original Assignee: Indian Institute of Science
• Inventors: Anand, Sandeep Venkit, Mahapatra, Debiprosad Roy
• Primary Examiner(s): Caputo, Lisa
• Assistant Examiner(s): DUNLAP, JONATHAN M
• Application Number:
  US12/726,091
• Publication Number:
  US 20110226066A1
• Time in Patent Office: 895 Days
• Field of Search: 737/63, 737/65, 737/66, 737/68, 73774-777
• US Class Current: 73/777
• CPC Class Codes: G01B 7/18 using change in resistance
• CPC Class Codes: G01B 7/20 formed by printed-circuit technique

Abstract

Methods and systems for sensing strain are disclosed. A thin film sensor includes a thin film polymer matrix that has two electrical terminals, conductive nanoparticles dispersed within the polymer matrix, and carbon nanotubes dispersed within the polymer matrix. The thin film sensor has a resistivity across the two electrical terminals that varies with a magnitude of strain applied to the thin film sensor. Strain may be sensed by applying a voltage to the thin film sensor, and an electrical response of the thin film sensor may be detected due to a strain present across the sensor. A magnitude of the strain can be determined based on the electrical response. Methods and systems for a memristor are also disclosed. The memristor has a resistivity that varies with a time-varying voltage input and with a time-varying strain input.

Claims

1. A composite comprising:

an electrically resistant material, wherein the electrically resistant material comprises epoxy resin;

conductive nanoparticles dispersed substantially throughout the electrically resistant material; and

conductive nano-structures dispersed substantially throughout the electrically resistant material, wherein a weight of the conductive nano-structures is less than about 5% of a total weight of the composite, wherein a gauge factor of the composite is greater than about 4.

2. The composite of claim 1, wherein a volume of the conductive nanoparticles is approximately 33% of a total volume of the composite.

3. The composite of claim 1, wherein the conductive nanoparticles comprise amorphous carbon.

4. The composite of claim 3, wherein the amorphous carbon comprises carbon black.

5. The composite of claim 1, wherein the conductive nanoparticles are of at least one of the following types:

platinum, silver, copper, and polyanylene.

6. The composite of claim 1, wherein the conductive nano-structures comprises carbon nanotubes.

7. The composite of claim 6, wherein the carbon nanotubes include at least about 99% carbon and less than about 1% impurities.

8. A thin film sensor comprising:

a thin film polymer matrix having two electrical terminals;

conductive nanoparticles dispersed within the thin film polymer matrix; and

carbon nanotubes dispersed within the thin film polymer matrix, wherein the thin film sensor has a resistivity across the two electrical terminals that varies with a magnitude of strain applied to the thin film sensor;

wherein the thin film sensor has two operational modes, wherein a first operational mode is a resistive-type strain sensing mode and wherein a second operational mode is a semiconductor-type strain sensing mode, and wherein a bias voltage applied across the thin film sensor determines the operational mode.

9. The thin film sensor of claim 8, wherein the conductive nanoparticles have a volume of approximately 33% of a total volume of the thin film sensor, and wherein the carbon nanotubes have a weight that is less than about 5% of a total weight of the thin film sensor.

10. The thin film sensor of claim 8, wherein the conductive nanoparticles comprise carbon black, and wherein the thin film polymer matrix comprises epoxy resin.

11. The thin film sensor of claim 8, wherein a range of resistivity values are mapped onto a range of magnitude of applied strain values, such that a measured resistivity corresponds to a value of the magnitude of applied strain.

12. The thin film sensor of claim 8, wherein the carbon nanotubes are randomly aligned.

13. A method for sensing strain comprising:

applying a voltage to a flexible thin film strain sensor that is applied to a sensing area, wherein the flexible thin film strain sensor comprises an electrically resistant material, conductive nanoparticles dispersed substantially throughout the electrically resistant material, and conductive nano-structures dispersed substantially throughout the electrically resistant material, wherein the flexible thin film strain sensor has a resistivity that varies with a magnitude of strain applied to the thin film sensor, and wherein a strain is present across the sensing area;

applying a bias voltage across the flexible thin film strain sensor;

detecting an electrical response of the flexible thin film strain sensor in response to the strain present across the sensing area; and

determining a magnitude of the strain based on the electrical response and the bias voltage.

14. The method of claim 13, further comprising measuring a temperature of the flexible thin film strain sensor, and wherein determining the magnitude of the strain comprises determining the magnitude of the strain based on the electrical response and on the temperature.

15. The method of claim 13, further comprising ascertaining a residual strain of the flexible thin film strain sensor, and wherein determining the magnitude of the strain comprises determining the magnitude of the strain based on the electrical response and on the residual strain.