Optical waveguides – Optical fiber waveguide with cladding – Utilizing multiple core or cladding
Reexamination Certificate
2000-06-30
2001-06-26
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
Optical fiber waveguide with cladding
Utilizing multiple core or cladding
C385S012000, C385S013000, C385S147000
Reexamination Certificate
active
06253014
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains generally to the location of fiber optic sensors embedded in a material and more specifically to the location of embedded fiber optic sensors by the use of radiographic inspection.
2. Description of the Related Art
The purpose of embedding fiber optic sensors in materials is to accurately measure a specific material property at a specific location in the composite specimen. To accomplish this, the fiber optic sensor (FOS) must be placed precisely in the desired location (including depth or layer), and ingress of the optical fiber leads must be accomplished with a minimum of risk to the optical fiber and host composite part. The position of the sensor must be determined accurately within the finished product.
Optical fiber sensor systems come in many configurations and have the ability to measure a wide range of material properties and environmental conditions. Fiber optic sensors may be multiplexed (many sensors on a single fiber optic cable), and the sensor length may vary from microns to kilometers, a factor which is wholly dependent on the application and measureand of interest. Fiber optic sensors may be of intrinsic or extrinsic design. Intrinsic fiber optic sensors, or all-fiber fiber optic sensors, are sensors whose light throughput properties are modulated by an external environmental condition.
Intrinsic sensors often are indistinguishable from the parent fiber; i.e., it is impossible to tell where the sensor begins and ends on the fiber optic cable. Visual indicators, such as ink marks, may be used to locate the sensor bodies during fabrication, but these become useless once the fiber sensor strand is embedded in a composite part. It is of great importance to be able to locate the position of these sensors with high accuracy. For example, knowledge of sensor position within the part is critical for true knowledge of the strain distribution within the structure, and for correlation of measured strain with an analytical model of the structure.
Ideally, the optical fiber should be disturbed as little as possible by the cure and post cure operations on the part. However, the optical fiber may actually shift within the composite part during curing as the matrix resin liquefies and flows. In thin composite laminates, the position of the optical fiber can sometimes be detected on the surface of the part either tactiley or visually after cure. This allows for avoidance of the optical fiber strand during machining operations. However, the fiber optic sensor is undetectable from the surface of the specimen. This problem is compounded in thicker laminates as there are absolutely no visual indications of the optical fiber position, and one is clueless as to sensor position.
Previous methods for locating intrinsic fiber optic sensors were a “tap test” where the operator taps around on the component with the edge of a coin while watching the sensor output. The method is time consuming, inaccurate, and does not produce a direct record of the sensor location for future reference. There is also no way to determine the orientation of the sensor (at what angle the sensor may be to some reference edge, or surface) or what depth the sensor is within the part.
A second method used for sensors sensitive to temperature is to touch the part with a warm finger, or in the case of thick parts, a soldering iron while watching the sensor output. Again, the method is time consuming, inaccurate, and does not produce a direct record of the sensor location for future reference. As before, there is also no way to determine the orientation of the sensor (at what angle to some reference edge, or surface) or at what depth the sensor is within the part.
BRIEF SUMMARY OF THE INVENTION
The object of this invention is to provide a process whereby embedded fiber optic sensors may be accurately located within a composite material as to position, orientation and depth.
Another objective of this invention is to provide a process for accurately locating embedded fiber optic sensors in composite material that is inexpensive, improves quality control on embedded sensor systems, and does not require any new or unusual non-destructive inspection methods.
These and other objectives are achieved by coating a fiber optic sensor with an X-ray opaque epoxy, or other similar material compatible with the components found within a composite material , prior to embedding the sensor in the composite material and then mapping the composite material using radiographic techniques to establish the location of the embedded sensors in position, orientation and depth. The radiographic films provide permanent record of the exact placement of the sensors that may be referenced during machining operations, correlation of test results, and accurate mapping of the structure.
REFERENCES:
patent: 6141480 (2000-10-01), Simon et al.
Pogue, III William R.
Simon Wayne R.
Karasek John J.
Palmer Phan T. H.
Stockstill Charles J.
The United States of America as represented by the Secretary of
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