# US 2013/0240718 A1 · Method for measuring the deformation of a specimen usting a fiber optic extensometer

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- Number: US 2013/0240718 A1
- Document ID: US20130240718A1
- Status: Published application
- Kind: A1
- Application number: 13/611,159
- Filed: 2012-09-12
- Published: 2013-09-19
- Earliest claimed: 2009-08-20
- Assignees: Polytechnic Institute of New York University
- Inventors: Nikhil Gupta; Nguyen Quang Nguyen
- Web page: https://patentgrep.com/patent/US20130240718A1

## CPC

- G01B 11/16: for measuring the deformation in a solid, e.g. optical strain gauge
- G01L 1/243: {using means for applying force perpendicular to the fibre axis}
- G01M 5/0033: {by determining damage, crack or wear}
- G01M 5/0091: {by using electromagnetic excitation or detection}
- Y02B 10/30: Wind power
- G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01L: MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE (weighing G01G)
- G01M: TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- Y02B: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS

## Abstract

A method for measuring the deformation of a specimen using an extensometer having a loop of a single-mode optical fiber. At least two points of the loop are attached to desired locations on a specimen. Light is transmitted through the loop and the transmitted optical power is measured by a photodetector. The deformation of the specimen causes the size and shape of the loop to change, which changes the transmitted optical power. The change in optical power is related to extension or compression using calibration curves. The sensor works on the principle of transmitted power modulation through the curved section.

## Claims

### Claim 1

A method for measuring the deformation of a specimen comprising the steps of:
a) attaching a fiber-optic extensometer to a specimen of interest, wherein the fiber-optic extensometer comprises
i) a loop of a single-mode optical fiber;
ii) a light source attached to a first end of the loop for transmitting light having an optical power through the loop; and
iii) a photodetector attached to a second end of the loop for detecting the light transmitted through the loop,
b) transmitting the light supplied by the light source through the loop; and
c) using the photodetector to detect any change in optical power of the light passing through the loop.

### Claim 2 (depends on 1)

The method as claimed in claim 1, further comprising the step of the deformation of the specimen while the light is being transmitted through the loop.

### Claim 3 (depends on 2)

The method as claimed in claim 2, wherein the deformation of the loop changes the optical power of the light being transmitted through the loop.

### Claim 4 (depends on 3)

The method as claimed in claim 3, wherein the change in the optical power of the light being transmitted through the loop is related to the deformation of the loop using calibration curves.

### Claim 5 (depends on 4)

The method as claimed in claim 4, further comprising coupling the photodetector to a computer having a database of the calibration curves relating the change in the optical power to the deformation of the loop.

### Claim 6 (depends on 1)

The method as claimed in claim 1, wherein the loop is attached to the specimen at at least two points.

### Claim 7 (depends on 6)

The method as claimed in claim 6, wherein the two points are diametrically opposite each other.

### Claim 8 (depends on 1)

The method as claimed in claim 1, wherein the extensometer is bonded to a surface of the specimen.

### Claim 9 (depends on 1)

The method as claimed in claim 1, wherein the extensometer is embedded inside the specimen.

### Claim 10 (depends on 1)

The method as claimed in claim 1, wherein the extensometer is used in a large measurement range with a lower measurement sensitivity and in a small measurement range of one intermediate peak at high sensitivity.