FIBER OPTICAL ANCHOR FOR LOCALLY DISTRIBUTED MEASUREMENT IN BRISTUL MEDIA

Abstract

A fiber optic cable system designed for distributed measurement in a brittle installation medium, the fiber optic cable system comprising a fiber optic cable and a plurality of anchors. The fiber optic cable contains a fiber core, a buffer layer, a reinforcement element, and a jacket. These components are interconnected at numerous anchor points along the fiber optic cable such that they are connected at the anchor points and separated from each other between the anchor points. The anchors are attached to the fiber optic cable at the anchor points and are designed to engage with the brittle installation medium to secure the fiber optic cable to the brittle installation medium at the anchor points.

Description

STATE INTERESTS

[0001] This invention was made with government support under Contract No. 75D30120C09233, awarded by the National Institute for Occupational Safety and Health. The government has certain rights in the invention. BACKGROUND

[0002] Fiber optic cables typically consist of a fiber core for data transmission and sensing, a buffer layer, a strength member made of aramid yarn or other loose material, and an outer jacket. Fiber optic cables with loose inner layers are not very suitable for locally distributed strain measurements, as the loose inner layers can slip within the jacket, leading to erroneous strain measurements. Conversely, fiber optic cables with tight-fitting inner layers are commercially available for strain measurement purposes, but when used in installation media such as cement in a borehole or sand in a trench, the fiber optic cable can slip relative to the installation media upon stretching, resulting in erroneous measurements.

[0003] The spatial resolution of a fiber optic distributed measurement system is a function of the light pulse duration and the maximum measurement range. If the length of the portion of the fiber optic cable subject to strain is less than the spatial resolution of the distributed measurement system used, a lower strain value than expected will be measured, or in extreme cases, no measurement will be possible. SUMMARY

[0004] The present invention solves the above and other problems and represents a significant advance in the field of distributed measurement.

[0005] A fiber optic cable system according to an embodiment of the invention comprises a fiber optic cable and a plurality of anchors.

[0006] The fiber optic cable contains multiple fiber cores, multiple buffer layers, a strength member, and a jacket. The fiber optic cable is elastically flexible and configured to be communicatively connected to (and part of) a distributed measurement system.

[0007] The fiber cores are designed to transmit an optical signal and can be made of glass, plastic, or other suitable material. Although the two-core design is shown, other designs with multiple cores or a single core can also be used.

[0008] The buffer layers mechanically protect and support the fiber cores. These buffer layers are coatings made of polymers or similar materials that form small tubes surrounding the fiber cores.

[0009] The strength element surrounds the fiber cores and buffer layers and can contain yarn (e.g., aramid yarn), fiberglass-epoxy rods, synthetic fibers (e.g., nylon), steel wire, or similar materials. The strength element provides the fiber optic cable with strength and durability while remaining at least partially flexible.

[0010] The sheath surrounds the fiber cores, buffer layers, and strength element. The sheath is made of a plenum plastic or other suitable material that protects the fiber cores, buffer layers, and strength element from environmental influences.

[0011] The fiber cores, the buffer layers, the strength element and the sheath are attached to a plurality of anchor points which are spaced apart from each other by an interval length, so that the fiber cores, the buffer layers, the strength element and the sheath are connected to each other at the anchor points and are detached from each other between the anchor points.

[0012] Each anchor may have opposing ends and a structure designed to engage the brittle installation medium. In one embodiment, the structure may include a plurality of ribs defining an infiltration space.

[0013] The ribs comprise four orthogonally spaced ribs that extend between opposite ends and merge into one another. The ribs project radially from a longitudinal axis of the armature.

[0014] The infiltration space accommodates the brittle installation medium when the brittle installation medium is at least in a semi-liquid state (e.g., wet cement). For this purpose, the infiltration space is a large central cavity between the ribs to ensure that the brittle installation medium completely fills the area around the ribs.

[0015] The manufacture of the fiber optic cable and the construction of the fiber optic cable system involves attaching the fiber cores, buffer layers, strength member, and jacket together at multiple anchor points spaced apart by an interval length, such that these components are bonded together at the anchor points and released from each other between the anchor points. This may involve melting the jacket at the anchor points using a heating element such as a heat-shrink gun.

[0016] The sheath can then be compressed around the fiber cores at the anchorage points. This can be achieved by shrinking the sheath due to heating or melting the sheath. Alternatively, or additionally, the sheath can be crimped, which flattens the sheath and possibly the strength element and buffer layers.

[0017] The jacket can then be cooled, which results in the jacket being bonded to the fiber cores via the buffer layers and the strength member. In other words, the various layers and components of the fiber optic cable are bonded together and cannot slip or move relative to each other at the multiple anchor points. Cooling can be achieved actively via a cooling system or mechanism, or passively via the ambient temperature.

[0018] The above steps may be performed at each of the plurality of anchoring locations simultaneously or nearly simultaneously, or the above steps may be performed at each of the plurality of anchoring locations sequentially or in any combination thereof.

[0019] The cladding and fiber cores are not bonded between the anchor points, so the fiber cores may move relative to the cladding, particularly when the fiber optic cable is under shear or tension between nearby anchor points.

[0020] The anchors are then positioned along the fiber optic cable at the anchoring points so that the connected sections of the fiber optic cable lie at least partially within the infiltration spaces defined by the anchors. The anchors are then secured to the fiber optic cable with cable ties or similar fasteners.

[0021] The fiber optic cable system and method described above offers several advantages. For example, the fiber optic cable is anchored to anchor points spaced at known distances, preferably equal to or greater than the spatial resolution of the measurement system used. The fiber cores are released from the installation medium between the anchor points, enabling significantly improved monitoring of shear and tensile deformations within the installation medium. It also enables crack detection with a spatial resolution equivalent to that of the measurement system used.

[0022] This summary is intended to introduce, in simplified form, a selection of concepts described further below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to limit the scope of the claimed subject matter. Other aspects and advantages of the present invention will become apparent from the following detailed description of the embodiments and the accompanying drawings. SHORT DESCRIPTION OF THE DRAWING FIGURES

[0023] Embodiments of the present invention will be described in detail below with reference to the accompanying drawing figures, in which: Fig. 1 is a partial view of a fiber optic cable system constructed in accordance with an embodiment of the invention; Fig. 2a an enlarged partial view of a part of the fiber optic cable system of Fig. 1 is; Fig. 2b is an enlarged partial view of a part of the fiber optic cable system of Fig. 1 is; Fig. 3 a partial sectional view of a fiber optic cable of the fiber optic cable system of Fig. 1 is; Fig. 4 is a partial sectional view of a fiber optic cable system constructed in accordance with an embodiment of the invention; Fig. 5 is a partial sectional view of a fiber optic cable system constructed in accordance with an embodiment of the invention; and Fig. 6 is a flowchart of certain steps of a method of manufacturing a fiber optic cable system according to an embodiment of the invention.

[0024] The drawings do not limit the present invention to the specific embodiments disclosed and described herein. The drawings are not necessarily to scale. Rather, the emphasis is placed upon clearly illustrating the principles of the invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The following detailed description of the invention refers to the accompanying drawings, which illustrate certain embodiments of the invention. The embodiments are intended to describe aspects of the invention in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized, and changes may be made, without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense. The scope of the present invention is defined only by the appended claims, along with the full scope of equivalents to which such claims are entitled.

[0026] In this description, references to "an embodiment," "an embodiment," or "embodiments" mean that the referenced feature or features are included in at least one embodiment of the technology. Separate references to "an embodiment," "an embodiment," or "embodiments" in this description do not necessarily refer to the same embodiment, nor are they mutually exclusive, unless expressly stated and / or readily apparent to one skilled in the art from the description. For example, a feature, structure, act, etc. described in one embodiment may, but is not necessarily, included in other embodiments.Therefore, the present technology may include a variety of combinations and / or integrations of the embodiments described herein.

[0027] In the drawings, especially in the Fig. 1 to 5, a fiber optic cable system 100 is illustrated according to one embodiment of the invention. The fiber optic cable system 100 is configured for distributed sensing in a brittle installation medium, such as a brittle installation medium 200, and essentially comprises a fiber optic cable 102 and a plurality of anchors 104.

[0028] The fiber optic cable 102 may include fiber cores 106 A, B, buffer layers 108 A, B, a strength member 110, and a jacket 112. The fiber optic cable 102 may be resiliently flexible and configured to be communicatively connected to (and part of) a distributed measurement system.

[0029] The fiber cores 106A, B may be configured to transmit an optical signal and may be made of glass, plastic, or other suitable material. Although the two-core design is shown, other designs with multiple cores or a single core may also be used.

[0030] The buffer layers 108 A, B mechanically protect and support the fiber cores 106 A, B. The buffer layers 108 A, B may be coatings made of polymer or similar material that form small tubes surrounding the fiber cores 106 A, B.

[0031] The strength member 110 may enclose the fiber cores 106 A, B and the buffer layers 108 A, B and may include yarn (e.g., aramid yarn), fiberglass-epoxy rods, synthetic fibers (e.g., nylon), steel wire, or the like. The strength member 110 provides strength and durability to the fiber optic cable 102 while being at least partially flexible.

[0032] The jacket 112 may enclose the fiber cores 106 A, B, the buffer layers 108 A, B, and the strength member 110. The jacket 112 may be made of a plenum plastic or other suitable material to protect the fiber cores 106 A, B, the buffer layers 108 A, B, and the strength member 110 from environmental influences. For this purpose, the jacket 112 may be waterproof or water-resistant, UV-resistant, and abrasion- and crack-resistant.

[0033] As explained in more detail below, the fiber cores 106 A, B, the buffer layers 108 A, B, the strength member 110 and the jacket 112 can be secured together at a plurality of anchor points 124 spaced apart by an interval length (see spacings in Fig. 4 and Fig. 5 by vertical dimensional arrows), such that the fiber cores 106 A, B, the buffer layers 108 A, B, the strength element 110 and the sheath 112 are connected to one another at the plurality of anchoring points 124 and are detached from one another between the plurality of anchoring points 124.

[0034] The plurality of anchors 104 may be substantially similar, so only one anchor 104 will be described in detail. The anchor 104 may have opposite ends 114 A, B and a structure configured to engage the brittle installation medium 200. In one embodiment, the structure may include a plurality of ribs 116 AD defining an infiltration space 118. The anchor 104 may be made of any suitable rigid or semi-rigid material. For simplicity, the anchors 104 in the Fig. represented as blocks.

[0035] In one embodiment, the ribs 116 AD may include four orthogonally spaced ribs 116 AD extending between and merging with each other at the opposite ends 114 A, B. The ribs 116 AD may extend radially from a longitudinal axis of the armature 104. The ribs 116 AD are illustrated with an arcuate curvature, however, other configurations and shapes, such as cantilevered ribs, may be used.

[0036] The ribs 116 AD may define a plurality of mounting openings 120 and mounting guides 122 for receiving securing fasteners such as cable ties, as shown in Fig. 2a. In one embodiment, the first two opposing ribs 116A,C include mounting openings near one end and mounting guides near their other end. Two second opposing ribs 116B,D have mounting openings near one end aligned with the mounting guides of the first two opposing ribs, and mounting guides near the other end aligned with the mounting openings of the first two opposing ribs. In this manner, a toggle fastener can be alternately mounted in two fastener openings and fastener guides near the ends of the ribs 116AD.

[0037] The infiltration space 118 may accommodate a portion of the brittle installation medium 200 when the brittle installation medium 200 is in at least a semi-liquid state (e.g., wet cement). To this end, the infiltration space 118 may be a large central cavity between the plurality of ribs 116 to ensure that the brittle installation medium 200 completely fills the area around the ribs 116. The anchor 104 may further include smaller spaces, channels, tunnels, openings, porous features, jagged or irregular geometries, guides, protrusions, or the like to ensure that the anchor 104 is embedded in and mechanically secured to the brittle installation medium 200.

[0038] The manufacture of the fiber optic cable 102 and the construction of the fiber optic cable system 100 will now be described with reference to Fig. 6. Significantly, the fiber cores 106 A, B, the buffer layers 108 A, B, the strength member 110, and the sheath 112 may be secured together at a plurality of anchor locations 124 spaced apart by an interval length, such that the fiber cores 106 A, B, the buffer layers 108 A, B, the strength member 110, and the sheath 112 are secured together at the plurality of anchor locations 124 and disengaged from each other between the plurality of anchor locations 124.

[0039] In one embodiment, securing the fiber cores 106 A, B, the buffer layers 108 A, B, the strength member 110, and the cladding 112 together at the plurality of anchor locations 124 may include melting the cladding 112 at the plurality of anchor locations, as shown in block 300. This may be accomplished using a heating element such as a shrink gun.

[0040] The jacket 112 may then be compressed around the fiber cores 106 A, B at the plurality of anchoring locations, as shown in block 302. This may be achieved by shrinking the jacket 112 as a result of heating or melting the jacket 112. Alternatively or additionally, the jacket 112 may be crimped, thereby flattening the jacket 112 and possibly the strength member 110 and the buffer layers 108 A, B.

[0041] The jacket 112 can then be cooled, resulting in the jacket 112 being bonded to the fiber cores 106 A, B via the buffer layers 108 A, B and the strength member 110, as shown in block 304. In other words, the various layers and components of the fiber optic cable 102 are thereby coupled together and cannot slip or move relative to each other at the plurality of anchor points. Cooling can be accomplished actively via a cooling system or mechanism, or passively via the ambient temperature.

[0042] The cladding 112 and the fiber cores 106 A, B may also be joined together in other ways. For example, adhesives, fasteners, interlocking components, or a combination thereof may be used.

[0043] The above steps may be performed at each of the plurality of anchoring locations simultaneously or nearly simultaneously, or the above steps may be performed at each of the plurality of anchoring locations sequentially or in any combination thereof.

[0044] The jacket 112 and the fiber cores 106 A, B may be unconnected between the plurality of anchor locations, so that the fiber cores 106 A, B may move relative to the jacket, particularly when the fiber optic cable 102 is in shear or tension between nearby anchor locations.

[0045] The anchors 104 can then be positioned along the fiber optic cable 102 at the plurality of anchoring locations such that the coupled portions of the fiber optic cable 102 lie at least partially within the infiltration spaces defined by the anchors 104. In one embodiment, the fiber optic cable 102 can be routed through the anchors 104.

[0046] After the anchors 104 are positioned, they can be attached to the fiber optic cable 102 using cable ties 126 or similar fasteners. In one embodiment, cable ties 126 can be threaded through the plurality of attachment openings and aligned within the plurality of attachment guides to pull the anchors 104 close to the fiber optic cable 102 and hold the anchors 104 in place.

[0047] Cemented epoxy resin 202 or a similar bonding material may then be applied to the anchors 104 and the fiber optic cable 102 to bond the anchors 104 to the fiber optic cable 102, as shown in Fig. 2b. In one embodiment, the binding material may be applied near the ends of the ribs 116 near the cable ties 126, where the fiber optic cable 102 is most rigidly connected to the anchors 104. The cable ties 126 may provide an additional binding interface for the binding material, while also preventing the cable ties 126 from loosening.

[0048] The fiber optic cable system 100 and method described above offers several advantages. For example, the fiber optic cable 102 can be anchored to anchor points spaced at known distances, preferably equal to or greater than the spatial resolution of the measurement system used. The fiber cores 106 A, B can be detached from the installation medium 200 between the anchor points while being protected from the harsh conditions of the installation by the strength member 110 and the jacket 112 (which is loose between the anchor points). This allows for significantly improved monitoring of shear and tensile deformations (see Fig. 4 and Fig. 5) within the installation medium 200. It also enables crack detection with a spatial resolution equivalent to that of the measurement system used.

[0049] Although the invention has been described with reference to the embodiments illustrated in the accompanying drawings, it is to be understood that equivalents and substitutions may be used without affecting the scope of the invention as set forth in the claims.

[0050] Having described various embodiments of the invention, the following is claimed as new and is to be protected by the patent:

Claims

[1] A fiber optic cable system designed for locally distributed sensing in a brittle installation medium, the fiber optic cable system comprising: a fiber optic cable with: a fiber core configured to transmit an optical signal; a buffer layer surrounding the fiber core; a strength element surrounding the buffer layer and the fiber core; and a sheath surrounding the fiber core, the buffer layer and the strength element, wherein the fiber core, the buffer layer, the strength member, and the cladding are secured to one another at a plurality of anchor locations along the fiber optic cable such that the fiber core, the buffer layer, the strength member, and the cladding are connected to one another at the plurality of anchor locations and are detached from one another between the plurality of anchor locations. [2] The fiber optic cable system of claim 1, further comprising: a plurality of anchors positioned at the plurality of anchoring locations, each of the plurality of anchors comprising: A structure configured to engage the brittle installation medium, the structure defining an infiltration space such that the brittle installation medium infiltrates the infiltration space when the brittle installation medium is in at least a semi-liquid state such that the structure is fixed in the brittle installation medium when the brittle installation medium is in a solid state. [3] The fiber optic cable system of claim 1 or 2, wherein the jacket is compressed over the strength member at the plurality of anchor points. [4] The fiber optic cable system of claim 1 or 2, wherein the plurality of anchor locations are spaced apart from each other by an interval length. [5] The fiber optic cable system of claim 2, wherein the structure includes a plurality of radially projecting ribs and the infiltration space is located between the plurality of radially projecting ribs. [6] The fiber optic cable system of claim 2, wherein the plurality of anchors each have opposite first and second ends and the plurality of radially projecting ribs merge into one another at the opposite first and second ends. [7] The fiber optic cable system of claim 2, wherein the plurality of anchors are either epoxy-attached to the fiber optic cable, clamped to the fiber optic cable, or integrated into the fiber optic cable. [8] A method of manufacturing a fiber optic cable, the method comprising a step of: Attaching a fiber core, a strength member, and a sheath together at a plurality of anchor locations spaced apart by an interval length such that the fiber core, the strength member, and the sheath are connected to each other at the plurality of anchor locations and are released from each other between the plurality of anchor locations. [9] The method of claim 8, wherein the securing step comprises a step of melting the shell at a plurality of anchoring locations. [10] The method of claim 8 or 9, wherein the securing step comprises a step of compressing the sheath around the fiber core at the plurality of anchoring locations. [11] The method of claim 9, wherein the securing step includes a step of cooling the shell. [12] The method of claim 8 or 9, wherein the securing step comprises a step of connecting the fiber core and the cladding at the plurality of anchoring locations. [13] The method of claim 8 or 9, wherein the securing step comprises a step of crimping the sheath at the plurality of anchoring locations. [14] An anchor for a fiber optic cable of a fiber optic cable system adapted for locally distributed sensing in a brittle installation medium, the anchor comprising: A structure configured to engage the brittle installation medium, the structure defining an infiltration space such that the brittle installation medium infiltrates the infiltration space when the brittle installation medium is in at least a semi-liquid state, such that the structure is fixed in the brittle installation medium when the brittle installation medium is in a solid state. [15] The anchor of claim 14, wherein the structure comprises a plurality of radially projecting ribs and the infiltration space is located between the plurality of radially projecting ribs. [16] The armature of claim 15, wherein the armature has opposite first and second ends and the plurality of radially projecting ribs merge into one another at the opposite first and second ends. [17] The anchor of claim 14, 15 or 16, wherein the structure includes a plurality of attachment openings configured to receive securing fasteners therethrough for securing the anchor to the fiber optic cable. [18] The anchor of claim 14, 15 or 16, wherein the structure further comprises a plurality of securing fasteners configured to receive portions of the securing fasteners. [19] The anchor according to claim 14, 15 or 16, wherein the anchor is attached to the optical fiber by means of epoxy resin or a clamping device or is integrated into the optical fiber. [20] The anchor of claim 14, wherein the anchor has opposite first and second ends, the structure comprising four radially projecting ribs that merge into one another at the opposite first and second ends, the four radially projecting ribs defining a plurality of attachment openings configured to receive securing fasteners therethrough and a plurality of attachment guides configured to receive portions of the securing fasteners to secure the anchor to the fiber optic cable, the infiltration space being between the plurality of radially projecting ribs.

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