U.S. patent application number 11/139124 was filed with the patent office on 2007-02-15 for optical fiber substrate useful as a sensor or illumination device component.
Invention is credited to Philbrick Allen, W. Randolph Hursey, Randolph S. Kohlman, John G. Lever.
Application Number | 20070037462 11/139124 |
Document ID | / |
Family ID | 37743110 |
Filed Date | 2007-02-15 |
United States Patent
Application |
20070037462 |
Kind Code |
A1 |
Allen; Philbrick ; et
al. |
February 15, 2007 |
Optical fiber substrate useful as a sensor or illumination device
component
Abstract
This disclosure generally pertains to a method for manufacturing
a distributed optical fiber scrim comprising a functional optical
fiber, the functional optical fiber scrim thus manufactured, and
composites in which an optical fiber scrim is incorporated. The
present disclosure describes a variety of textile scrims,
particularly adhesively bonded nonwoven scrim materials, each
comprising at least one optical fiber with a continuous path across
at least the length or width of the fabric. Such optical fiber
scrims may be useful as sensor components (for example, as a
detector of breakage, strain, pressure, or torque), as illumination
components (for example, in a variety of light-providing
applications), or as data-distribution components, either alone or
in combination with other materials, such as fabrics, films, foams,
and the like.
Inventors: |
Allen; Philbrick; (US)
; Kohlman; Randolph S.; (US) ; Hursey; W.
Randolph; (US) ; Lever; John G.; (US) |
Correspondence
Address: |
Legal Department, M-495
PO Box 1926
Spartanburg
SC
29304
US
|
Family ID: |
37743110 |
Appl. No.: |
11/139124 |
Filed: |
May 27, 2005 |
Current U.S.
Class: |
442/5 ;
442/2 |
Current CPC
Class: |
D10B 2403/0243 20130101;
D10B 2403/02412 20130101; D10B 2101/08 20130101; D10B 2331/02
20130101; G02B 6/0011 20130101; D10B 2101/06 20130101; D03D 15/00
20130101; D04B 21/165 20130101; D10B 2505/02 20130101; G01M 11/086
20130101; D10B 2321/02 20130101; D10B 2101/12 20130101; D10B
2101/20 20130101; D04H 3/04 20130101; D10B 2401/20 20130101; D10B
2331/021 20130101; D10B 2211/02 20130101; Y10T 442/107 20150401;
D10B 2201/02 20130101; D10B 2331/04 20130101; G02B 6/0005 20130101;
D03D 15/47 20210101; Y10T 442/102 20150401 |
Class at
Publication: |
442/005 ;
442/002 |
International
Class: |
D04H 1/00 20060101
D04H001/00; D03D 15/00 20060101 D03D015/00; D03D 19/00 20060101
D03D019/00; D03D 9/00 20060101 D03D009/00 |
Claims
1. A scrim fabric comprising (a) at least one warp yarn set having
at least two yarns and (b) at least one yarn that crosses said warp
yarn set, wherein at least one of said yarns is comprised of an
optical fiber.
2. The scrim fabric of claim 1, wherein said scrim has a
construction selected from the group consisting of an adhesively
bonded laid scrim, a thermally bonded laid scrim, a woven scrim, a
weft-inserted warp knit scrim, a multi-axial knit scrim, a
stitch-bonded scrim, and a cross-plied scrim.
3. The scrim of claim 1, wherein said warp yarn set has yarns that
are present in an amount of between about 1 yarn per every 60
inches and about 25 yarns per inch.
4. The scrim of claim 3, wherein said warp yarn set has yarns that
are present in an amount of between about 1 yarn per 30 inches and
about 12 yarns per inch.
5. The scrim fabric of claim 1, wherein said optical fiber has a
core made of a material selected from the group consisting of glass
and polymers.
6. The scrim of claim 1, wherein said optical fiber has a change in
light transmission characteristics when exposed to one or more
sources selected from the group consisting of mechanical agents,
chemical agents, moisture, temperature, pH changes, biological
sources, neutrons, and ionizing radiation.
7. The scrim fabric of claim 1, wherein said at least one optical
fiber is of a type selected from the group consisting of single
mode fibers, multi-mode fibers, light pipes, photosensitive fibers,
polarization-maintaining fibers, multiple step-indexed fibers,
graded index fibers, reduced cladding fibers, high index fibers,
wave-guiding films, and photonic lattice fibers.
8. The scrim fabric of claim 7, wherein said optical fiber is a
single-mode fiber.
9. The scrim of claim 1, wherein said at least one optical fiber
comprises a compressible sheath.
10. The scrim fabric of claim 1, wherein said warp yarn set
comprises at least one optical fiber.
11. The scrim fabric of claim 1, wherein at least one optical fiber
crosses said warp yarn set.
12. The scrim fabric of claim 11, wherein more than one optical
fiber crosses said warp yarn set.
13. The scrim fabric of claim 11, wherein said yarn that crosses
said warp yarn set further comprises yarns selected from the group
consisting of polyesters, polyamides, polyolefins, ceramics,
fiberglass, aramids, cotton, wool, metal, carbon, and combinations
thereof.
14. The scrim fabric of claim 11, wherein said warp yarn set
comprises yarns selected from the group consisting of polyesters,
polyamides, polyolefins, ceramics, fiberglass, aramids, cotton,
wool, metal, carbon, optical fibers, and combinations thereof.
15. The scrim fabric of claim 14, wherein said warp yarn set
further comprises at least one optical fiber.
16. The scrim fabric of claim 11, wherein said at least one optical
fiber is positioned in a sinuous path across said warp yarn
set.
17. The scrim fabric of claim 16, wherein said scrim construction
has a square pattern.
18. The scrim fabric of claim 16, wherein the smallest radius of
curvature of said optical fiber within said sinuous path is greater
than about 0.1 inches.
19. The scrim fabric of claim 18, wherein the smallest radius of
curvature of said optical fiber within said sinuous path is greater
than about 0.5 inches.
20. The scrim fabric of claim 11, wherein said scrim construction
has a tri-axial pattern.
21. The scrim fabric of claim 20, wherein said triaxial scrim has a
construction in which said crossing yarns are present in an amount
of between about 1 of said crossing yarns per 6 inches and about 4
of said crossing yarns per inch in an upward diagonal direction and
a downward diagonal direction.
22. The scrim fabric of claim 11, wherein said scrim is an
adhesively bonded scrim.
23. The scrim fabric of claim 22, wherein said at least one yarn
that crosses said warp yarn set is positioned between two warp yarn
sets.
24. The scrim fabric of claim 22, wherein said warp yarn set
contains yarns that are present only at selvage areas of said scrim
fabric and wherein said scrim fabric is attached to a flexible
carrier sheet, said carrier sheet being selected from the group
consisting of films, foils, nonwoven fabrics, woven fabrics, and
knit fabrics.
25. The scrim fabric of claim 1, wherein said scrim fabric
comprises more than one type of said optical fiber.
26. A method of making a fiber optic scrim, said method comprising
manufacturing a scrim fabric by a process selected from the group
consisting of adhesively bonding, thermally bonding, projectile
weaving, weft-insert warp knitting, multi-axial warp knitting,
stitch-bonding, and cross-plying, wherein said scrim fabric
comprises (a) at least one warp yarn set having at least two yarns
and (b) at least one yarn that crosses said warp yarn set, wherein
at least one of said yarns is comprised of an optical fiber.
27. The method of claim 26, wherein said scrim is manufactured by
adhesive bonding.
28. The method of claim 26, wherein said at least one optical fiber
is positioned in a sinuous path across said warp yarn set.
29. The method of claim 26, wherein said at least one optical fiber
is laid in a substantially crimp-free manner.
30. The method of claim 26, wherein said scrim is attached to a
flexible carrier during manufacturing.
31. A composite having multiple components, wherein a first of said
components is a scrim comprising (a) at least one warp yarn set
having at least two yarns and (b) at least one yarn that crosses
said warp yarn set, wherein at least one of said yarns is comprised
of an optical fiber and wherein a second of said components is an
energy-absorbing component selected from the group consisting of an
open cell foam, a closed cell foam, a nonwoven, rubber, a gel
material, and a spacer fabric.
32. The composite of claim 30, wherein said composite has a
symmetrical construction comprising said scrim layer centrally
positioned in said composite, an energy-absorbing layer in contact
with each side of said scrim layer, and a stress-distributing layer
in contact with each of said energy-absorbing layers, said
stress-distributing layer selected from the group consisting of
rigid and semi-rigid materials.
33. The composite of claim 31, wherein said composite comprises an
adhesively bonded scrim, a foam layer in contact with each side of
said scrim, and a rigid thermoplastic material in contact with each
of said foam layers.
34. A composite having multiple components, wherein a first of said
components is a scrim comprising (a) at least one warp yarn set
having at least two yarns and (b) at least one yarn that crosses
said warp yarn set, wherein at least one of said yarns is comprised
of an optical fiber and wherein a second of said components is an
stress-distributing material selected from the group consisting of
metal sheets, metal panels, composites, plywood, oriented strand
board, gypsum panels, cementitious panels, ceramic panels,
thermoplastic panels, and thermosetting panels.
35. A composite comprising a flexible carrier sheet to which is
attached at least one optical fiber, wherein said optical fiber is
positioned in a sinuous path across said flexible carrier sheet,
said flexible carrier sheet being of a material selected from the
group consisting of films, foils, papers, nonwoven fabrics, woven
fabrics, and knit fabrics.
Description
TECHNICAL FIELD
[0001] This disclosure generally pertains to a method for
manufacturing a distributed optical fiber scrim comprising a
functional optical fiber, the functional optical fiber scrim thus
manufactured, and composites in which an optical fiber scrim is
incorporated. Such optical fiber scrims may be useful as sensor
components (for example, as a detector of breakage, strain,
pressure, or torque), as illumination components (for example, in a
variety of light-providing applications), or as data-distribution
components. The present disclosure describes a variety of textile
scrims, particularly adhesively bonded nonwoven scrim materials,
each comprising at least one optical fiber with a continuous path
across at least the length or width of the fabric.
BACKGROUND
[0002] Historically, optical fibers have been added to textile
structures, laminates, or composites to take advantage of the
functional attributes of these fibers, such as the ability to
transmit light, and data encoded in the light, over extended
distances. In addition, modifications to the fiber--such as
mechanical notches in the coating and/or fiber, small radius bends
in the fiber, or chemical modifications of the cladding or
protective layers of the optical fiber--can result in light leakage
from the fiber and a decreased light transmission. If the decreased
light transmission is due to interaction with an external stimulus,
then the light leakage may be used to provide sensing properties.
Changes in the polarization of the light signal input or in the
propagation mode, interference effects, or other pertinent optical
parameter changes may also be manipulated to obtain a desired
effect on, for instance, the sensing functionality of the textile
substrate. Alternately, the light leakage from the fiber optics may
provide intentional illumination effects to the textile
product.
Approaches Using Fiber Optics to Produce Illumination
[0003] In some applications, the light-carrying and
light-distributing functions of optical fibers are used to provide
lighting effects or directed illumination capacity to a fabric.
[0004] U.S. Pat. No. 4,234,907, for instance, discloses the use of
optical fibers to replace some of the traditional yarns in a woven
fabric. The optical fiber surfaces are intentionally scratched so
that light can escape from the fibers and provide an overall
illumination to the woven fabric. There are many parallel optical
fibers in this application, which are necessarily grouped together
at their ends to allow light to be coupled into the whole array,
thereby illuminating the whole fabric panel. Incorporation of the
optical fiber into a woven structure results in the fibers being
exposed to crimp, or small radius bends. The optical fiber is
incorporated either in the warp direction or the fill direction. In
the fill direction, a special machine is used that leaves fiber
optic "tails" on only one selvage.
[0005] U.S. Pat. No. 4,652,981 takes advantage of the
light-carrying capability of optical fibers to create an
illuminated belt. In this application, the optical fibers are not
integrated into a textile but loosely bundled into a tube.
[0006] U.S. Pat. No. 4,727,603 describes feeding multiple
side-emitting optical fibers through a fabric and attaching them to
an aesthetic side of the fabric for lighted aesthetics on that
surface. The fibers are bundled on the non-aesthetic side of the
fabric to introduce the light into them. This manner of
incorporating optical fibers typically is a more labor-intensive
way to distribute fiber optics on a surface, because the fibers
were added to the textile after the textile was manufactured,
rather than being integrated during fabric formation.
[0007] U.S. Pat. No. 4,875,144 is a variation of the '603 patent,
in which the optical fibers are grouped into bundles so that
different colors of light can be transmitted into different
bundles. U.S. Pat. No. 6,217,188 is another variant of the previous
approaches, which uses color-changeable light-emitting diodes and a
brightness control to produce a more eye-catching visual display
featuring the fiber optics. In U.S. Pat. No. 5,424,922, a similar
construction is applied to create illuminated safety apparel. In
U.S. Pat. No. 5,722,757, a light emitting diode and a non-uniformly
side-emitting optical fiber are incorporated onto a soft object to
provide illumination to, for instance, a shoe.
[0008] U.S. Pat. No. 4,754,372 discloses a floor or wall covering
composite with a fibrous face from which the optical fibers project
to provide lighting effects. In this approach, multiple parallel
optical fibers are grouped to bundle light into them. The optical
fibers are incorporated into a composite structure but the fibers
themselves are not integral in any single textile component. U.S.
Pat. No. 6,709,142 discloses a glove with optical fiber ribbons
disposed between an inner and outer layer of the glove, such that
light can leak out from the glove to provide illumination for the
user.
Approaches Using Fiber Optics as Sensor Components
[0009] In other textile applications, manufacturers took advantage
of the sensitivity of the optical fiber to its state of mechanical
flexure, twist, elongation, breakage, or the chemical state in
which the fiber exists and the accompanying optical index of
refraction changes of the fiber optical system (which result in
changes in how the light propagates through the optical fiber).
[0010] For example, in U.S. Pat. No. 5,567,932, multiple parallel
optical fibers are incorporated into a waste containment
geo-membrane. They are described as being laminated into the
structure or integral to the textile. They are incorporated in
parallel in the longitudinal direction. The optical fibers are
bundled to input light. Transmission of light through the optical
fibers is monitored to look for breaches, slope creep, subsidence,
leachate levels, fires, and types of material present and leaking
from the site. The patent does not provide details as to how the
fiber is incorporated into the textile. Laying the optical fiber
into the composite involves additional processes and labor compared
with incorporating it directly into the textile.
[0011] In U.S. Pat. No. 6,145,551, a woven product is disclosed
that incorporates optical fibers as data transmission lines or
sensing lines. U.S. Pat. No. 6,381,482 further broadens this
concept to include tubular, flat woven, or knitted products with
incorporated optical and electrical fibers for sensing. The fabric
must be comfortable as well as functional, since it is to be worn
close to a person's skin for monitoring their vital signs. U.S.
Pat. No. 6,687,523 discloses using the above article with a means
for communicating to an external device, and a means for ensuring a
snug fit, to make a garment to monitor the vital signs of an infant
(for instance, to prevent sudden infant death syndrome). These
textiles, which are designed to be comfortable and durable for use
in apparel, are also highly constructed.
[0012] Another example of a wearable textile with integrated
optical fibers is disclosed in U.S. Pat. No. 6,727,197. The optical
fiber is used in a data or power transmission cable that is woven,
knitted, or braided. The fabric is easy to manufacture, washable,
corrosion resistant, and has high fatigue strength. Because the
fabric is designed to be worn, it also has a very full-faced
textile construction typical of apparel fabrics.
[0013] In U.S. Pat. No. 6,299,104, a set of optical fibers is
attached to a parachute, along with light sources and detectors,
for monitoring the loads exerted on a parachute during deployment.
The optical fiber detection system is attached to the parachute
after it is created and, therefore, it is not integral to the
textile. Additionally, there are significant labor issues involved
in putting the system together.
[0014] In US Published Patent Application 2004/0240776A1, the use
of optical fibers in a textile for a seat occupation sensor is
disclosed. The optical fiber-based sensor detects microbends or
modifications of the Bragg wavelength caused by loads positioned on
the seat. The optical fiber can be woven into the cover of the seat
or into the cushion.
[0015] Hence, there have been many textile-based products that
utilize optical fibers integrated into the textile, attached to the
textile, or incorporated into a composite with a textile for
lighting or sensing. However, the articles disclosed use multiple
parallel optical fibers and do not include a single optical fiber
disposed in a sinuous manner along the textile. Use of a single
fiber that is distributed over the whole width and/or length of the
textile article can simplify an optical circuit, such as is
necessary for a sensing or light-emitting device, since only a
single light source and, optionally, a single detector are
needed.
[0016] Further, having the optical fiber directly integrated into
the textile structure allows ease of incorporation of the
associated textile into composites, for instance, and insures
repeatable placement of the optical fiber. Many of the existing
articles described above require post-production attachment of the
optical fiber system into the article (that is, the fiber optics
are secured to the textile after the textile is manufactured). The
present disclosure provides a fiber optic fabric, in which the
optical fibers are integrated into the fabric construction.
[0017] In a few instances, the optical fiber is directly
incorporated into a woven, knit, or braided fabric to produce a
fabric with high durability to abrasion, flex, washing, and the
like. In these embodiments, a high degree of small radius bends, or
crimp, may be imparted to the optical fiber during fabric
production, resulting in substantial inability to transmit light
without loss. In applications where the optical fiber path is very
long, this light loss due to optical fiber crimp may be
unacceptable. The present disclosure addresses this problem by
providing a family of scrim fabrics, where an optical fiber is
integrated in a manner substantially free of small radius bends.
Optionally, a continuous length of a single fiber can be extended
throughout the fabric.
[0018] Because the economics of optical fiber typically dictates
sparing use of the fiber, a textile utilizing an optical fiber as a
component may preferably be embodied as an open construction, such
as a scrim, where there is substantial open space between adjacent
yarns. The present disclosure provides a variety of scrim fabrics
in which an optical fiber is integrated. Due to its open
construction, such an article may be more easily incorporated into
a variety of composites including resin impregnated composites
(thermosetting or thermoplastic), textile composites, cementitious
composites, laminates with various flexible, rigid, and semi-rigid
substrates such as wood, metal sheets, foils, multi-ply lay ups,
and the like. It is to be understood that there is no requirement
that the composite itself have an open construction, rather only
that the scrim fabric have such a construction.
[0019] Other objects and advantages of the present approach are
described herein.
OBJECTS OF THE PRESENT DISCLOSURE
[0020] It is an object of the current disclosure to provide a
textile substrate with an open construction, commonly referred to
as a scrim, in which the scrim possesses at least one integrated
optical fiber for providing sensing properties, illumination
properties, or data transmission properties.
[0021] It is a further object to provide a textile scrim where at
least a single optical fiber can be distributed over the whole
surface of the textile, preferably in a sinuous path across its
width, thereby providing uniform sensitivity or illumination over
the surface of the textile. Optionally, or additionally, one or
more optical fibers may be extended in substantially parallel paths
throughout the length (machine direction) of the textile scrim.
[0022] It is another object of this disclosure to provide a textile
scrim in which the optical fiber is incorporated with minimal
crimp, so that unwanted loss of light from the fiber can be
minimized.
[0023] It is yet another object of the present disclosure to
provide a textile scrim with either a square or angled pattern for
the optical fiber as it is distributed over the surface of the
textile.
[0024] It is a further object of the disclosure to provide a
textile substrate that, due to its open construction, may be easily
incorporated into a variety of composites including
resin-impregnated composites, textile composites, cementitious
composites, laminates with various flexible, rigid, and semi-rigid
substrates such as wood, metal sheets, foils, multiply lay ups, and
the like.
[0025] It is another object of the disclosure to provide a scrim
that provides the functionality of the optical fiber, as well as
reinforcing or tensile properties attributable to the remaining
yarns in the scrim.
[0026] It is yet another object of the present disclosure to
provide a readily manufacturable optical fiber configuration, or
optical circuit, which can be incorporated into illumination,
sensing, or data-distribution products.
[0027] It is in addition an object of the current disclosure to be
able to provide a distributed network of optical fibers for
monitoring conditions over a distributed surface, such as, for
example, stress in a structural composite part like an aircraft
hull or bridge or environmental conditions in a reactor, where the
stress may be indicated, for instance, by breaks in the optical
fiber.
SUMMARY
[0028] The present disclosure is directed to a textile scrim
material in which at least a single continuous optical fiber is
preferably incorporated in the cross-machine direction, the machine
direction, or both. The resulting functional material may be used
as a sensing element, as a light-providing element, or as a
data-distributing element, either alone or in combination with
other materials. The scrim material may be an adhesively bonded
laid scrim, a thermally bonded laid scrim, a weft-inserted warp
knit scrim, a multi-axial knit scrim, a woven scrim, a cross-plied
scrim, or a stitch-bonded scrim. In one embodiment, manufacturing
of the scrim and the ultimate functional composite is simplified
because a single optical fiber is distributed in a sinuous path
along the length of the textile.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 is a plan view of a textile scrim material, in which
a continuous optical fiber, laid in a sinuous path, comprises the
weft;
[0030] FIG. 2 is a plan view of a textile scrim material, in which
optical fibers comprise the warp and weft;
[0031] FIG. 3 is a plan view of a textile scrim material, in which
multiple optical fibers, laid in sinuous paths, comprise the
weft;
[0032] FIG. 4 is a plan view of a tri-axial textile scrim fabric,
in which optical fibers, laid in a sinuous path, comprise the
weft;
[0033] FIG. 5A is a plan view of a composite, in which an optical
fiber scrim is combined with a layer of film or fabric;
[0034] FIG. 5B is a plan view of a composite, in which an optical
fiber scrim with only selvage yarns is combined with a layer of
film or fabric;
[0035] FIG. 6 is a plan view of a weft-inserted warp knit fabric,
in which an optical fiber, laid in a sinuous path, comprises the
weft;
[0036] FIG. 7 is a plan view of a stitch-bonded fabric that has
been stitched to a nonwoven sheet, wherein an optical fiber, laid
in a sinuous path, comprises the weft of the stitch-bonded
fabric;
[0037] FIG. 8 is a plan view of a woven scrim fabric in which an
optical fiber, incorporated in a sinuous path, comprises the
fill;
[0038] FIG. 9A is a cross-sectional view of a composite material,
including an optical fiber scrim as its central layer; and
[0039] FIG. 9B is a cross-sectional view of an alternate composite
material, including an optical fiber scrim as its central
layer.
DETAILED DESCRIPTION
Types of optical fiber
[0040] Optical fiber is commonly used, for instance, in the
telecommunications industry, to transmit signals over a long
distance using light pulses with very little loss of signal.
Optical fibers typically have at least three parts: a core, a
cladding, and a buffer coating.
[0041] The core, where the light travels, is typically made of
glass (such as silica), which has been engineered to minimize
absorptive or scattering loss. Alternately, the core may also be
made of a polymer, such as polymethylmethacrylate (PMMA) or
polystyrene, though these cores tend to attenuate light more. The
core typically has a cylindrical shape and is the center of the
optical fiber.
[0042] The cladding is an outer material that surrounds the core
and that has a lower optical index of refraction than the core.
This index of refraction mismatch at the boundary between the core
and cladding causes light that impinges on the cladding layer from
the core to reflect back into the core, assuming the angle of
impingement is less than a critical angle. This reflection is
called "total internal reflection," and is the basic principal by
which optic fibers are able to transmit light with low loss over
long distances. For angles larger than the critical angle, light
may leak out from the core and result in signal attenuation.
[0043] One of the advantages of optical fiber is that it can
transmit light even if the optical fiber is bent, twisted, or
otherwise mechanically deformed. However, if the optical fiber is
exposed to a bending radius beneath a critical bend radius, the
transmission of light through the fiber may be dramatically
reduced. Typical glass-core optical fibers have a minimum bend
radius of about 1 inch, while polymer-core optical fibers have a
minimum bend radius of about 0.125 cm.
[0044] The buffer coating is typically a plastic coating over the
core and cladding that protects them from moisture and damage. In
some embodiments, the buffer coating may not be present. In some
potentially preferred embodiments, the buffer coating is made of a
material (such as PVC) that is readily compressible, thereby
reducing the likelihood of the fiber optic from being crimped or
fractured from incidental contact. Additional layers may be added
to the basic layers above, depending on the requirements of the
product.
[0045] Optical fibers are offered either as single-mode or
multi-mode fibers. The single-mode fibers tend to have smaller
diameter cores (on the order of about 10 microns) and transmit
infrared light at specific wavelengths with low attenuation. The
light travels only in a single path through this fiber, creating a
well-defined optical profile, which depends on the geometry of the
fiber, the index of refraction profile, and the wavelength of light
propagated. These single-mode fibers provide high
information-carrying capacity and low attenuation.
[0046] Multi-mode fibers, in contrast, tend to have larger diameter
cores (on the order of about 60 microns), which allow a broader
range of infrared light to be transmitted. However, multi-mode
fibers also exhibit a higher attenuation than single-mode fibers.
The light transmitted through a multi-mode fiber travels over more
paths, resulting in a less well-defined optical profile.
[0047] Either single-mode or multi-mode fibers may be used for many
applications. For applications in which less attenuation is.
desirable (e.g., in many sensing applications), use of a
single-mode fiber may be preferred.
[0048] Increasingly, in addition to those described above, other
types of optical fibers--such as light pipes, photosensitive
fibers, polarization maintaining fibers, multiple step-indexed
fibers, graded index fibers, reduced cladding fibers, high index
fibers, wave-guiding films, and photonic lattice fibers--are
available. All of these variations of optical fiber could be
incorporated into the present optical fiber substrate for use in
different applications. These different types of optical fiber are
generally well described in technical and product literature and
information regarding these can be readily found on the Internet
(for instances, at manufacturers' websites).
[0049] As has been described, optical fibers are currently deployed
in a wide variety of applications. They can be employed in data
transmission, for instance as land lines for the telecommunications
industry to transmit high-density signals. They have been employed
as light-guiding elements or light pipes, either to provide
aesthetic or functional illumination or to transmit light to remote
locations where it is inconvenient to incorporate separate light
sources. One example of this approach is the use of optical fibers
to bring concentrated laser light into the body during minimally
invasive surgeries. Optical fibers are also used to transmit images
from difficult-to-reach locations to locations where they can be
more usefully analyzed or captured. The area of distributed
lighting is becoming increasingly of interest. A high intensity
light at one location is capable of providing light to a variety of
locations by distribution through collections of light pipes.
[0050] Because transmission of light through optical fibers is
affected by the geometry of the fiber as well as the
chemical/optical characteristics of the parts of the fiber, there
are many aspects of the fiber that allow it to be used as a sensor.
For instance, dramatic changes to the fiber (such as breaking it)
can effect transmission of light, but also more subtle
effects--like bending the fiber, mechanically elongating or
straining the fiber, exposing it to chemicals that change the index
of refraction of the core or cladding layers, exposing it to
temperature or humidity changes, or exposing it to ionizing
radiation that affects the absorptive losses of the core--may
affect the fiber's ability to transmit light.
Uses of optical fiber for sensing
[0051] The use of optical fibers for sensing purposes is
well-documented in the technical literature, representative
examples of which are included in the following list. [0052]
Luminescent optical fibers in sensing. Grattan, K. T. V.; Zhang, Z.
Y.; Sun, T. Department of Electrical, Electronic & Information
Engineering, City University, London, UK. Optical Fiber Sensor
Technology (1999), 4, 205-247. [0053] Sensing system using plastic
optical fiber. Muto, Shinzo; Morisawa, Masayuki. Grad.
[0054] Sch. Med. Eng., Univ. Yamanashi, Kofu, Japan. Oyo Butsuri
(2004), 73(11), 1423-1427. [0055] Non-linear distributed
optical-fiber sensing. Rogers, A. J. Dep. Electron. Electr. Eng.,
King's Coll. London, London, UK. Proceedings of SPIE--The
International Society for Optical Engineering (1993), 1797
(Distributed and Multiplexed Fiber Optic Sensors II), 50-62. [0056]
Distributed optical-fiber sensing. Rogers, A. J. Dep. Electron.
Electr. Eng., King's Coll., London, UK. Proceedings of SPIE-The
International Society for Optical Engineering (1991), 1504
(Fiber-Opt. Metrol. Stand.), 2-24. [0057] Status of fiber-optic
sensing. Davis, Charles M. Opt. Technol., Inc., Herndon, Va., USA.
Proceedings of SPIE--The International Society for Optical
Engineering (1988),959 (Optomech. Electro-Opt. Des. Ind. Syst.),
60-65. [0058] Novel optical fibers for sensing applications.
Gambling, W. A. Dep. Electron. Comp. Sci., Univ. Southampton,
Southampton, UK. Journal of Physics E: Scientific Instruments
(1987), 20(9), 1091-96.
[0059] Optical fibers are increasingly being used to provide
sensing functionality either into systems or composite structures,
by choosing cladding materials for the optical fiber whose index of
refraction changes upon exposure to chemical agents, moisture, pH
changes, or biological sources. The chemicals that can be sensed
include hydrocarbons, such as are used for fuels, or dangerous
process chemicals, as might be employed in manufacturing
operations. In addition, optical fibers can be made sensitive to
neutrons and ionizing radiation from nuclear materials.
Examples of technical literature related to optical fibers with
sensitivity to the stimuli listed above include:
Sensitivity to Chemicals
[0060] Sensing ammonia with ferrocene-based polymer coated tapered
optical fibers. Shadaram, Mehdi; Martinez, Juan; Garcia, Fernando;
Tavares, David. Department Electrical Computer Engineering,
University Texas-El Paso, El Paso, Tex., USA. Fiber and Integrated
Optics (1997), 16(1), 115-122. [0061] Chemical sensing by surface
plasmon resonance in a multimode optical fiber. Trouillet, A.;
Ronot-Trioli, C.; Veillas, C.; Gagnaire, H. Laboratoire Traitement
du Signal et Instrumentation, CNRS-URA, Fr. Pure and Applied Optics
(1996), 5(2), 227-237. [0062] Phase-sensitive polarimetric sensing
in the evanescent field of single-mode fibers. Lehmann, H.;
Lippitsch, M. E.; Ecke, W.; Haubenreisser, W.; Willsch, R.; Raabe,
D. Institut fuer Physikalische Hochtechnologie, Helmholtzweg 4,
Jena, Germany. Sensors and Actuators, B: Chemical (1995), B29(1-3),
410-15. [0063] Optical fiber chemical sensor. Minami, Shigeo. Fac.
Eng., Osaka Univ., Suita, Japan. Oyo Butsuri (1986), 55(1), 56-62.
Sensitivity to pH Changes [0064] Optical sensing of pH in low ionic
strength waters. Swindlehurst, Ben R.; Narayanaswamy, Ramaier.
Department of Instrumentation and Analytical Science, UMIST,
Manchester, UK. Springer Series on Chemical Sensors and Biosensors
(2004), 1(Optical Sensors), 281-308. [0065] Recent progress in
fiber optic pH sensing. Baldini, Francesco. Ist. Ric. Onde
Electromagn., CNR, Florence, Italy. Proceedings of SPIE--The
International Society for Optical Engineering (1991), 1368 (Chem.,
Biochem., Environ. Fiber Sens. 2), 184-90. Sensitivity to
Biological Sources [0066] Evanescent sensing of biomolecules and
cells. Haddock, Hong S.; Shankar, P. M.; Mutharasan, R. Department
of Chemical Engineering, Drexel University, Philadelphia, PA, USA.
Sensors and Actuators, B: Chemical (2003), B88(1), 67-74.
Sensitivity to Nuclear Materials [0067] Application of an optical
fiber-sensing technique for nuclear power plant monitoring. Eiji,
Takada; Nakazawa, Masaharu. Study Applying Optical Fiber Sensing
Technique Nuclear Plant Monitoring, Fac. Eng., Univ. Tokyo, Tokyo,
Japan. Hoshasen (1997), 23(3), 51-61. [0068] Neutron-sensing
scintillating glass optical fiber detectors. Bliss, M.; Reeder, P.
L.; Craig, R. A. Pacific Northwest Laboratory, Richland, Wash.,
USA. Nuclear Materials Management (1994), 23, 583-588. [0069]
Conception of an ionizing radiation detection scheme based on
controlled light induced annealing of silica fibers. Vassilopoulos,
C.; Kourtis, A.; Mantakas, C. Natl. Cent. Sci. Res., Inst. Inf.
Telecommunicat., Athens, Greece. IEE Proceedings--J:
Optoelectronics (1993), 140(4), 267-72.
[0070] Optical fibers may also be used to sense a variety of
mechanical changes to a system, such as breakage, strain, pressure,
torsion, torque, acceleration, and rotation. Such sensing can be
particularly useful for smart monitoring systems for structural
composites, such as bridges or airplane hulls, to sense impending
failures. Other optical fiber systems can be useful for making
temperature measurements over a wide range of temperatures with
spatial resolution. Such temperature measurements could be useful
in manufacturing process reactors, in buildings for internal
temperature control, and the like.
[0071] Based on analytical measurement techniques, optical fiber
sensors can be used as interferometric sensors, absorption
thermometers, heterodyne sensors, Bragg grating sensors,
backscatter systems, anti-Stokes thermometry, polarization optical
time domain reflectometry, and Raman, Brillouin, and optical Kerr
effect sensors, as well as simple break detectors.
Examples of technical literature related to optical fibers use to
sense mechanical changes, such as those listed above include:
Sensitivity to Strain
[0072] Distributed sensing of strain in synthetic fiber rope and
cable constructions using optical fiber sensors. Uttamchandani,
Deepak G.; Culshaw, Brian; Overington, M. S.; Parsey, M.; Facchini,
Massimo; Thevenaz, Luc. Dep. Electronic Electr. Eng., Univ. of
Strathclyde, Glasgow, UK. Proceedings of SPIE--The International
Society for Optical Engineering (1999), 3860(Fiber Optic Sensor
Technology and Applications), 273-275. Sensitivity to Torque [0073]
Novel fiber grating sensing technique based on the torsion beam.
Zhang, Weigang; Feng, Dejun; Ding, Lei; Zhang, Ying; Dong,
Xin-Yong; Zhao, Chunliu; Dong, Xiaoyi. Institute of Modern Optics,
Nankai Univ., Tianjin, Peop. Rep. China. Proceedings of SPIE--The
International Society for Optical Engineering (2000), 4082 (Optical
Sensing, Imaging, and Manipulation for Biological and Biomedical
Applications), 157-160. Sensitivity to Temperature [0074] A high
spatial resolution distributed optical fiber sensor for
high-temperature measurements. Feced, Ricardo; Farhadiroushan,
Mahmoud; Handerek, Vincent A.;
[0075] Rogers, Alan J. Department of Electronic and Electrical
Engineering, King's College London, Strand, London, UK. Review of
Scientific Instruments (1997), 68(10), 3772-3776. [0076]
Distributed sensing technique based on Brillouin optical-fiber
frequency-domain analysis. Garus, Dieter; Krebber, Katerina;
Schliep, Frank; Gogolla, Torsten. Ruhr-Universitaet Bochum, Bochum,
Germany. Optics Letters (1996), 21(17), 1402-1404. [0077]
Temperature sensing elements. Meijer, Gerard; Herwaarden, Sander
van; Kapsenberg, Theo; Venema, Adrian. Department Electrical
Engineering, Delft University Technology, Delft, Neth. Editor(s):
Meijer, Gerard C. M.; van Herwaarden, A. W. Therm. Sens. (1994),
90-133.
[0078] Optical fibers, in addition, have certain advantages over
electrical systems for sensing. Fiber optic strands do not corrode.
Since they do not carry a current, they are unlikely to induce
sparks or ignitions. They are not sensitive to electromagnetic
impulses, like electrical conductors. Therefore, the broad
applicability of optical fibers for sensing different stimuli, or
optionally providing illumination or carrying information, as well
as environmental stability make them of high value for
incorporation into functional products.
Optical Fiber Substrate Constructions
[0079] To provide a regular, manufacturable optical fiber circuit,
which can be handled and/or incorporated into functional products,
the optical fiber is preferably incorporated into a textile
scrim.
[0080] As used herein, the term "scrim" shall mean a fabric having
an open construction used as a base fabric or a reinforcing fabric,
which may be manufactured as an adhesively or thermally bonded laid
scrim, a woven scrim, a weft-inserted warp knit scrim, a
multi-axial knit scrim, a stitch-bonded scrim, or a cross-plied
scrim. These scrims may be attached to a carrier layer, such as a
film or a fabric web, during manufacture.
[0081] The open structure of a scrim fabric facilitates the ease
with which the scrim may be incorporated into a composite
structure. Particularly in those applications where an adhesive is
used to bond multiple layers, the openness of the scrim allows
adhesive flow-through, which results in a stronger bond between the
composite components.
[0082] Scrims, as described herein, contain at least one set of
warp yarns and at least one crossing yarn. Preferably, the warp
yarn set contains between about 1 yarn per 60 inches and about 25
yarns per inch; more preferably, the warp yarn set contains between
about 1 yarn per 30 inches and about 12 yarns per inch; and most
preferably, the warp yarn set contains between about 1 yarn per
inch and about 8 yarns per inch. The warp yarn density may be
determined by any of a number of factors, including, for instance,
the tensile requirements of the final product. Also, it is to be
understood that that scrims with a low warp yarn density (e.g., of
about 1 yarn per 60 inches) may be directly attached to a flexible
carrier sheet to provide additional mechanical stability.
[0083] Preferably, the crossing yarn is present at a spacing of
between about 1 yarn per 10 inches and 24 yarns per inch; more
preferably, the crossing yarn is present at between about 1 yarn
per 4 inches and 12 per inch; and most preferably, the crossing
yarn is present at between about 1 yarn per 2 inches and 8 per
inch. It should be understood that the crossing yarn spacing may be
achieved by positioning multiple fibers on the warp yarn set or by
positioning a single fiber, so that it curves back and forth across
the width of the fabric, as will be described further herein.
[0084] For purposes of this disclosure, the scrims of interest
allow for at least a single continuous path of optical fiber to be
laid or incorporated into the fabric. In a first embodiment, at
least one optical fiber is used in the warp direction, typically as
part of a warp yarn set in which a plurality of yarns extend in a
substantially straight path along the length of the fabric. In this
embodiment, the term "continuous" refers to the path of an
unbroken, or unsegmented, optical fiber in the warp direction.
[0085] In a second embodiment, where at least one optical fiber is
incorporated in the weft direction, the optical fiber(s) are
positioned in a sinuous path across the width of the scrim. The
term "sinuous" refers to a path of a single optical fiber, which
winds or curves back and forth, preferably across the width of the
scrim. Although a regular (i.e., symmetrical and sine-shaped) curve
may be preferred, it is not necessary. Similarly, although having
the sinuous optical fiber path extend substantially across the
width of the fabric may be preferred, this requirement is not
mandatory. It should also be noted that the sinuous path may
overlap itself, if, for instance, the optical fiber shifts between
the time the optical fiber is laid and the time it is secured by
adhesive, thermal bonding, stitching, or the like. Finally, it is
to be understood that multiple sinuous paths may be present in the
same scrim fabric.
[0086] In one preferred embodiment, the crossing yarn is an optical
fiber. When an optical fiber is used as the crossing yarn, the
spacing of the fiber is dictated by the minimum bending radius that
the optical fiber may realize without experiencing significant
attenuation. Optical fibers having cores made of glass typically
have a minimum bending radius of about 1 inch, while optical fibers
having polymer cores have minimum bending radii of as low as about
0.125 cm.
[0087] Optical fibers tend to act like monofilaments when the
optical fibers are incorporated into a textile fabric. As a result,
these optical fibers must be handled carefully during processing
and fabric formation to produce a functional fabric. Optical
fibers, like many other monofilaments, are typically packaged on a
spool with flanges on each end, where the flanges prevent the yarns
from being sloughed off (as might occur due to the low surface
friction of the yarn).
[0088] If the fiber begins to slough off the package, it may become
twisted or knotted with itself, causing it to break. At a minimum,
the knotted yarn results in a stoppage in the manufacturing process
and in defects in the scrim. Monofilament-like yarns also exhibit a
tendency to twist in any manufacturing process that involves
rotating the yarn continuously in the same direction. Such twisting
may cause the monofilament, such as an optical fiber, to kink
and/or break or at least to distort the geometry of the resulting
scrim. In addition, some optical fibers may have a very low tensile
strength, causing them to break when tension impulses are applied
to them, such as at startup.
[0089] To address these difficulties, the optical fiber may be fed
into the machine in several different ways. The optical fiber may
be placed in a barrel, or similar containment, with walls that
prevent the optical fiber from sloughing off of the package and
becoming twisted and then may be fed to the scrim formation machine
through an orifice in the barrel's lid. Another option is to use a
driven roll to feed the fiber optic into a scrim formation machine,
where the rate of the driven roll is optimized to avoid tension
impulses. Alternately, before the yarn is fed to the scrim
formation machine, a yarn accumulator can be used to protect the
yarn from tension impulses, as well as introduce some twist to the
yarn that may counterbalance the twist imposed during the scrim
formation process.
[0090] Besides the tendency to twist, which can lead to breaks,
optical fibers have a unique problem associated with the bending of
the fiber. Optical fibers may be bent only to a certain critical
bending radius before light begins to leak out of the fiber and
increases the attenuation. This characteristic puts functional
limits on the radius bend that the fiber may experience in
application without severe attenuation losses, depending on the
type of fiber used. This sensitivity to bending radius is mitigated
by the open construction of a scrim. Because there is substantial
space between neighboring warp or weft yarns, the loops on the
selvage may be of sufficient radius that the optical fibers do not
begin to attenuate light.
Bonded Laid Scrims
[0091] There are a variety of fabric formation technologies that
can provide a scrim fabric with incorporated optical fiber. One
preferred method involves forming an adhesively bonded scrim, as
shown in FIG. 1. This method of forming an optical fiber substrate
10 involves forming two sets of warp yarns, an upper set 6 and a
lower set 6', between which a continuous cross-machine direction
yarn 4 (in this case, a continuous optical fiber) is laid in a
sinuous path.
[0092] The yarns of warp sets 6, 6' may be selected from any
commercially available yarn known in the art, including spun yarns,
multi-filament yarns, or monofilament yarns, which are made of
polyester, polyamides, polyolefin, ceramic, fiberglass, basalt,
carbon, aramid, metal, or combinations thereof. The warp yarns 6,
6' may additionally be twisted, covered, and/or plied. They
optionally may be single component or bi-component yarns, such as a
sheath-core fiber with a low-melt adhesive material in the sheath.
Preferably, warp yarns 6, 6' are either polyester or
fiberglass.
[0093] Also shown in FIG. 1 are selvage yarns 8, which secure the
desired dimensions of optical fiber substrate 10. Selvage yarns 8
preferably are chosen to have a higher strength than the remainder
of warp yarns 6, 6', so that more tension may be applied to selvage
yarns 8 to maintain the width of substrate 10 and the geometry of
the weft yarns. It is to be understood that the denier of the warp
yams 6, 6' determines the strength of substrate 10 and yarns 6, 6'
may be chosen to provide reinforcement to substrate 10. Therefore,
yarns of any denier may be used, as may meet the strength
requirements of the final product (i.e., either substrate 10 or a
composite containing substrate 10).
[0094] In one embodiment, cross-machine direction yarn 4
(preferably, the optical fiber) can be inserted between warp yarn
sets 6, 6', using a set of rotating screws on opposite ends of the
warp sheets and a single rotating arm that passes the yarn between
the two screws as it rotates. As the screws turn, they insert the
yarns extending between them into the warp sheets at a fixed number
per inch to provide the desired construction. This has the effect
of placing a single yarn in what is termed a "square pattern" into
the warp sheets, as shown in FIG. 1.
[0095] The square pattern includes a cross-direction yarn,
incorporated in a sinuous path, crossing the warp sheet at nearly a
right angle, forming a loop on the edge of the warp sheet, and
crossing the warp sheet again, nearly at a right angle, in the
opposite direction at some fixed spacing from the first yarn and so
on. The pitch between the flights on the screw determines the
spacing between the yarns. The spacing can be adjusted by changing
out the screw in the machinery. Because the cross-direction yarn is
not interlaced or looped around the majority of the other yarns at
close spacing, the cross-direction yarn is introduced into the
fabric with minimal yarn crimp (small radius bends in the yarn).
The yarns are held taut in their position to maintain the geometry
of the scrim by using the selvage yarns, which have a high tension
applied to them, around which the cross-directional yarns are
looped.
[0096] Depending on residual twist in the yarn, the
cross-directional (i.e., fiber optic) yarns may have a tendency to
move, so that the resulting scrim does not have a square pattern,
but one in which the optical fibers move on the warp sheet. To the
extent that the ability of the optical fiber to transmit light is
not impeded by this motion, this irregularly patterned scrim may be
perfectly acceptable for the applications of interest. In those
cases where the cross-directional yarns, preferably optical fibers,
move, the optical fibers may be constrained from moving by directly
attaching the scrim to a carrier substrate and adhesively bonding
the scrim in place.
[0097] In a preferred adhesively or thermally bonded scrim, where
the weft yarns are comprised of optical fibers, the warp yarns are
disposed at approximately 1 end per 2 inches to 25 ends per inch,
and the weft yarns comprised of optical fibers are disposed at
approximately 1 optical fiber per 10 inches up to 12 optical fibers
per inch. A more preferred fabric construction is from about 1 to
12 ends per inch in the warp and from about 1 optical fiber per 4
inches to 8 optical fibers per inch in the weft direction. A most
preferred construction is from about 1 to 8 warp ends per inch and
from about 1 optical fiber per 2 inches to about 4 optical fibers
per inch. As previously mentioned, if high light transmission for
the optical fiber is desired, the spacing for the optical fiber
(wefts per inch) will necessarily be dictated by the minimum
bending radius that the fiber can withstand before light begins to
leak at the bended regions.
[0098] In an alternate embodiment, separate optical fibers can be
placed into the fabric construction both in the machine direction
as well as in the cross-direction, as shown in FIG. 2. In this
embodiment, optical fibers are incorporated into warp yarn sets
4'and 4'', between which cross-machine directional yarn 4 (also an
optical fiber) is laid. The resulting optical fiber substrate 20
possesses multiple different sensing paths, illumination lines,
data-distribution lines, or combinations thereof, which provide
different geometrical pathways through substrate 20. Although
illustrated with all yarns being comprised of optical fibers, a
combination of optical fibers and non-optical fibers may be used
instead to provide mechanical strength to the scrim in addition to
optical functionality. FIG. 3 illustrates an adhesively bonded
nonwoven scrim material 30, in which a plurality of yarns 4, 12 are
laid in the cross-machine direction. Again, warp yarn set 6 is
positioned above cross-directional yarns 4, 12, while warp yarn set
6' is positioned below cross-directional yarns 4, 12. As shown,
yarns 4 are optical fibers. Yarn 12 is a fiber of a different type,
such as a polyester or fiberglass yarn, for example. Although three
cross-directional yarns are shown in FIG. 3, any number of yarns
may be used, limited only by the capabilities of the equipment.
Further, although FIG. 3 shows two optical fibers in the
cross-machine direction, all of the cross-machine direction yarns
may be optical fibers, as well as, or alternately, some or all of
the yarns in the warp yarn sets.
[0099] By incorporating multiple optical fibers in the same
textile, the possibility exists to include fibers with sensitivity
to different environmental sources (e.g., certain chemicals and
moisture). Alternately, for instance, optical fibers having sensing
capabilities may be used in combination with optical fibers
providing data distribution or illumination functionality. The
different optical fibers may also represent different data
distribution nodes.
[0100] In an alternate embodiment, multiple cross-directional yarns
may be laid between the warp sheets concurrently in an angled
configuration. For instance, up to 96 yarn spools may be attached
to a rotating shaft and fed into different flights of the screws
simultaneously. Using this approach, the fabric construction would
no longer exhibit a square pattern, but rather would exhibit what
is termed a "tri-axial" pattern as shown in FIG. 4. In a tri-axial
construction, plural weft yarns 4 having both an upward diagonal
slope and a downward diagonal slope are located between plural
longitudinal warp yarns 6, 6'that are located above and below weft
yarns 4 to create tri-axial scrim 40. In this case, one or more of
the cross-directional yarns 4 may be an optical fiber (as shown,
both cross-directional yams are optical fibers).
[0101] The preferred range of the fabric construction of tri-axial
optical fiber substrate is between approximately 25.times.4.times.4
(25 ends per inch in the warp direction, 4 ends per inch on the
upward diagonal slope in the weft direction, and 4 ends per inch on
the downward diagonal slope in the weft direction) and
2.times.1/6.times.1/6 (2 ends per inch in the warp direction and 1
end per every 6 inches on the upward diagonal slope in the weft
direction, and 1 end per every 6 inches on the downward diagonal
slope in the weft direction), and is most preferably
8.times.1/2.times.1/2 (8 ends per inch in the warp direction and 1
end per every 2 inches on the upward diagonal slope in the weft
direction, and 1 end per every 2 inches on the downward diagonal
slope in the weft direction). As has been previously mentioned, the
spacing of the optical fiber (wefts per inch) will necessarily be
dictated by the minimum bending radius that the fiber can withstand
before light begins to leak at the bend. The warp yarn density may
be determined, for instance, by tensile requirements of the final
product.
[0102] As has been mentioned, for both the bidirectional and
tri-directional scrims (as shown in FIGS. 1-4), an alternate
embodiment for which the optical fiber path extends in the machine
direction in parallel paths can be obtained by forming a warp beam
in which the optical fiber replaces one or many of the conventional
warp yarns at whatever spacing is desired. In this manner, optical
fibers can be made to traverse the length of the scrim. Again, the
optical fiber would be put into the scrim construction in a fairly
straight manner to minimize yarn crimp. In a variation of this
approach, the optical fiber may be used in combination with
non-optical fibers (e.g., fiberglass or polyester) to create a warp
yarn set, in which adjacent yarns may be of different types.
[0103] Whether the cross-directional yarns are inserted in either
the square or tri-axial fabric, as described above, they are
preferably permanently locked into place. This is typically
accomplished with an adhesive composition. During the initial part
of fabric formation, the yarns are held in place only by friction
between overlapping yarns. Typically, the construction is then
transported (a) over rollers directly into a chemical dip that
coats the fabric with an adhesive, (b) through a nip (or set of
squeeze rolls) to squeeze off excess adhesive, and (c) into an oven
or over a set of steam- or oil-heated cans to dry and cure the
adhesive. The buffer coating on the optical fiber is preferable for
protecting the fiber from manufacturing-induced attenuation caused
by pressure damage to the core or cladding at the nip roll.
[0104] The adhesive used to bind the warp yarns and
cross-directional yarns to one another may be chosen from materials
such as polyvinyl alcohol (PVOH), acrylic, polyvinyl acetate,
polyvinyl chloride, polyvinylidiene chloride, polyacrylate, acrylic
latex, styrene butadiene rubber (SBR), EVA, plastisol, or any other
suitable adhesive. Further, these yarns optionally could be
thermally bonded to form the optical fiber substrate if an
appropriate low-melt material is present as part of the yarn
system.
[0105] Alternate embodiments of the previously described scrims may
be obtained by modifying the set-up for producing these scrims.
Using additional rolls before the adhesive nip, a flexible carrier
sheet, such as a nonwoven (for example, a spun-bonded nonwoven, a
melt-blown nonwoven, or a carded nonwoven web), a woven or knitted
textile, a film, a paper roll, or a foil, may be introduced as the
scrim is formed. In this case, the carrier sheet, such as a
nonwoven, can provide structural support so that the amount of warp
yarn required to hold the scrim together can be drastically
reduced. This embodiment is shown in FIG. 5A, in which an optical
fiber substrate having warp yarn sets 6, 6', selvage yarns 8, and a
cross-machine yarn 4, preferably made of optical fiber, are
combined with a layer of material 16 to create a composite 50.
Although a thin layer of nonwoven fabric may be preferred in some
applications, layer 16 may be comprised instead of materials such
as a single or multi-layer film, a woven fabric layer, a foam
layer, a composite layer, and the like, depending on the properties
desired in the final product.
[0106] To reduce warp yarns to a minimum, illustrated in FIG. 5B,
selvage yarns 8 alone may be used to hold optical fiber 4 across
the fabric width, and all additional warp yarns can be removed.
This scrim (made of optical fiber 4 and selvage yarns 8) is laid
directly onto flexible layer 16 and passed through the adhesive or
thermal bonding zone to hold the optical yarns directly to the
flexible carrier substrate 16 and create a composite 52. A less
extreme example (not shown) may include, for instance, using only a
single sheet of the warp yarns while the scrim is formed.
[0107] In the most extreme example, the selvage yarns, as well as
the warp sheets, are removed and the optical fiber is laid in a
sinuous path directly onto the carrier sheet. By combining the
flexible carrier with the sinuous path of optical fiber attached
and a second flexible carrier with only uni-directional yarns
attached (for example, only warp yarns), a cross-plied scrim with
attached carrier layers may be formed. Using this approach, the
optical fibers could be used in the machine direction, in the
cross-machine direction, or both.
Weft-Inserted Warp Knit Scrims
[0108] Yet another means for forming a scrim with a continuous
optical fiber is to construct a fabric using a weft inserted warp
knit machine, as may be available from, for instance, Liba
Corporation or Mayer Corporation. Such machines are equipped with a
hook system at either side of the warp sheet, such that as the weft
carriage introduces the yarns as it moves back and forth, the weft
yarns loop around the hooks and, typically after indexing, may be
inserted continuously. In one embodiment, one or more optical
fibers are inserted. Optionally, one or more optical fibers, plus
additional yarns, which may provide additional weft direction
tensile strength to the scrim, are all inserted into the scrim. The
weft-inserted yams are attached to the warp sheet using a knit
stitch such as a tricot stitch, flat stitch, or some combination
thereof.
[0109] With this construction, an open scrim can be formed, in
which the optical fiber is inserted in a straight manner to
minimize yarn crimp.
[0110] One representative example of a weft-inserted warp knit
fabric is shown in FIG. 6. Optical fiber 4 is used as the weft of
optical fiber substrate 60. The warp yarns 66 are preferably
comprised of non-optical fibers of one or more types previously
provided. The stitch yarns 68, which are shown forming a tricot
stitch, are preferably the same fiber type as warp yarns 66, but
preferably are of a smaller denier (smaller diameter yarn) than
warp yarns 68. For instance, by way of example only, warp yarns 66
may be 1000 denier high tenacity polyester, while stitch yarns 68
are polyester with a size of between 70 and 150 denier. As shown,
more stitches than weft yarns may be used in optical substrate 60
(that is, stitch yarn 68 is connected to warp yarns 66 more often
than stitch yarn 68 connects warp yarns 66 to optical fiber 4). The
number of stitches between optical fiber weft inserts may vary,
depending on the machine set-up, the bending radius of the optical
fibers, and the desired construction. Tricot, flat, or combination
stitches may be used. The general construction ranges previously
mentioned for scrims apply to weft-inserted scrims as well.
[0111] Alternately, a multi-axial warp knit scrim could also be
manufactured so that the optical fiber could be laid in at an angle
similarly to tri-axial scrims.
Stitch-Bonded Scrims
[0112] As a further alternate embodiment, a stitch-bonded scrim can
be formed in a similar manner to a weft inserted warp knit fabric,
and so are subject to similar constraints. However, the scrim is
attached to an additional layer, such as a nonwoven. The attachment
is made by the knitting needles that directly stitch the scrim to
the nonwoven, as the scrim is being produced. Such a construction
is illustrated in FIG. 7.
[0113] In FIG. 7, optical fiber 4 comprises the weft of the
textile. In this embodiment, the warp yarns are optional (and are
not shown). A flexible rolled good 16, such as a nonwoven fabric or
film, is secured to the scrim as it is formed to form composite 70.
In this case, substrate 16 provides structural support so that the
warp yarns may be optional. Layer 16 may be comprised of a variety
of materials such as a nonwoven, a single or multi-layer film, a
woven or knit fabric layer (closed or open construction), a foam
layer, a foil, a paper layer, a composite layer, and the like,
depending on the properties desired in the final product. This
embodiment is similar to that shown in FIG. 5A, except that in FIG.
7 the scrim is a weft-inserted scrim rather than a nonwoven scrim.
Stitch yarns 68 secure the optical fiber 4 to layer 16.
[0114] With these fabric formation technologies (weft-inserted warp
knitting and stitch-bonding), twisting of the weft inserted yarn
and resulting kinks in the yarn may cause breakage of the yarns and
loss of optical continuity. As described previously, roll-off
mechanisms, or other means of controlling the twisting and
sloughing of the yarn, are preferably employed.
[0115] For both the weft inserted warp knit and stitch-bonded
scrims, an alternate embodiment for which the optical fiber path
extends in the machine direction in parallel paths can be obtained
by forming a warp beam in which the optical fiber replaces one or
many of the conventional warp yarns at whatever spacing is desired.
Using this approach, optical fibers can be made to traverse the
length of the scrim. Again, the optical fiber is preferably
incorporated into the scrim construction in a fairly straight
manner to minimize yarn crimp. As yet another alternate embodiment,
similar to that shown in FIG. 2, separate optical fibers can be
placed into the fabric construction both in the machine direction
as well as in the cross-direction.
Woven Scrims
[0116] Another, but less preferred, method of making an optical
fiber scrim is by weaving. A woven optical fiber scrim 80 is made
using a projectile weaving machine, which allows for a sinuous path
for optical fiber 4. Optical fiber 4 is fed over and under warp
yarns 26, which are preferably of a fiber type other than an
optical fiber. Alternately, as before, warp yarns 26 may be of a
single fiber type or of a combination of fiber types and may also
include an optical fiber as one component. This construction may be
less preferred for some applications, because of the crimp that is
induced into optical fiber 4 by weaving it through warp yarns 26.
For woven scrims, the general range of scrim constructions
mentioned previously apply.
Optical Fiber Scrim-Containing Composites
[0117] It is anticipated that any of the preceding reinforcement
fabrics could be attached to additional layers of material to form
a composite, as shown in representative form in FIGS. 9A and 9B.
Such composites may be engineered to provide shock absorption,
durability, structural support or load carrying ability, thermal
properties, impact resistance, abrasion resistance, chemical
encapsulation, selected chemical permeability, diffusion layers,
stiffness, and various other properties as may be desired.
[0118] The layers that optionally may be attached to the scrim with
incorporated optical fiber include substrates that are flexible
roll-goods, semi-flexible substrates, or rigid substrates. In the
final composite, there may be components represented from one, two,
or all of these groups.
[0119] Examples of flexible roll-goods include nonwovens, other
textile fabrics such as wovens, knits, or additional scrim layers,
films, foils, foams, paper, or other suitable materials. The
nonwovens, fabrics, and scrims may be made of polyolefin,
polyester, polyamide, fiberglass, or other materials known in the
art. Films may be made of thermoplastics, such as polyolefin,
polyester, polyamide, or others known in the art. Foils may be made
of metals of various sorts. Foams may be made of a variety of open
or closed cell foams, such as polyurethane, polystyrene,
polyisocyuranate, foam rubber, and others known in the art.
[0120] Some of these materials may be used to absorb impact
energies, thereby protecting the optical fiber scrim from
mechanical abuse. These materials are termed "energy-absorbing"
materials. This group of materials includes open and closed cell
foams, nonwovens, rubber and gel materials, and spacer fabrics
(three-dimensional textiles with yarns running in the compression
direction, typically monofilaments, that provide compression and
recovery).
[0121] To protect the optical fiber from mechanical abuse that is
concentrated in a small area, a stress-distributing material may be
included in the composite. These materials tend to be semi-rigid or
rigid materials that spread impact forces over a wider area.
Examples of semi-flexible substrates can include metal sheets,
composite lay-ups, and the like. Examples of rigid substrates can
include metal panels; wood products such as plywood, oriented
strand board, or the like; gypsum or cementitous panels; ceramic
panels; thermoplastic or thermosetting polymeric panels; and other
materials known in the art.
[0122] The additional layers may be used to provide a solid
structure with which to deploy the article, absorb impact to
protect the optical fiber substrate, provide electrical isolation,
provide requisite thermal properties, or provide other performance
properties as desired. Such structures are shown in FIGS. 9A and
9B, in which optical fiber substrate 10 is sandwiched between
layers of other materials to create composites 40 and 42. In FIG.
9A, optical fiber substrate 10 is positioned between opposing
layers 100 of a stress-distributing material. The layers may be
secured with an adhesive (not shown) or, optionally, thermally
bonded or welded. In FIG. 9B, optical fiber substrate 10 is
positioned between opposing layers 102 of an energy-absorbing
material. Layers 100 of stress-distributing material further
enclose the composite structure. Again, the layers are secured to
one another with an adhesive, thermal bonding, welding, or other
methods known to those of skill in the art.
[0123] As has been previously described, the layers 100, 102 may be
any of a number of different materials. Opposing layers may be of
the same material or of different materials, selected based on the
intended use of composite structure 40 or 42. Additionally,
although the structures illustrated are symmetrical, symmetry is
not a requirement (that is, there may be more layers below the
optical fiber substrate than above it, or vice versa). There also
is no requirement that another layer cover the optical fiber scrim.
Although composites 40 and 42 are illustrated with optical fiber
substrate 10 as the functional component, other optical fiber
substrates or fiber substrate composites (such as are shown in
FIGS. 2, 3A, and 3B) may also be used. In some instances, the use
of multiple optical fiber scrims may be desirable within the same
composite.
EXAMPLE
[0124] Using a single-arm machine, a bi-directional texile scrim
material was produced at a width of 49 inches. The warp yarn sets
each contained 120 500-denier polyester yarns. The selvage yarns
were 1500 denier polyester yarns, so that higher tension could be
applied to the selvage areas to hold the fiber optic fabric at the
appropriate width and position the fiber optic yarn properly within
the fabric construction. The cross-directional yarn, which was a
continuous PVC-coated optical fiber, available from Corning as Part
Number 001E41-31131-24, was delivered on a spool with flanges on
each end.
[0125] Single release screws were used to feed the optical fiber
between the warp yarn sets at a spacing of one fiber per inch. Care
was taken to minimize the amount of twist that was introduced into
the optical fiber. It was discovered that twisting often causes
kinks in the optical fibers, which may further lead to breakage. An
additional concern is that twisted yarns can become tangled in the
accumulator, causing the machine to shut down. To alleviate these
problems, the optical fiber was fed to the accumulator from the
spool, which was positioned inside a containment vessel with an
opening in its lid. This had the effect of keeping the optical
fiber from sloughing off the pack and twisting or kinking and
reduced impulse forces on the optical fiber. Based on the trial, it
was also contemplated that a driven roll-off would effectively
introduce the fiber optic into the accumulator, while minimizing
twisting and breakage.
[0126] Another problem encountered in manufacturing was the effect
of impulse forces on the optical fiber. Initial efforts to feed the
optical fiber into the warp yarn sets resulted in the optical fiber
being broken, simply from the force of pulling the fiber from the
spool. It was found that a yarn accumulator alleviated this problem
by buffering the impulse force to the fiber optic package. Finally,
twisted yarns tend to shift, sometimes significantly, during fabric
formation, resulting in a fabric with irregular yarn geometry (that
is, yarn straightness and pattern regularity).
[0127] The resulting fiber optic substrate was then dipped into a
chemical pad, containing a solution of polyvinyl alcohol adhesive.
The PVA was dried using a series of six steam cans operating at a
temperature of 300.degree. F. The adhesive successfully bonded the
PVC-coated optical fiber to the polyester (warp) yarns at a pick-up
rate of about 12-15% by weight.
TESTING
[0128] Initial lab testing of the optical fiber scrim of the
Example was conducted to determine whether the light transmission
capabilities of the fiber optic had been preserved throughout the
scrim manufacturing process. Using a laser diode (Thorlabs Model
CPS 180, 635 nm wavelength, 1 mW power output), a silicon detector
(Newport Model 883-SL), and some fiber optic couplings, an optical
circuit and sensor system was created, using an approximately
18-inch long piece of the adhesively bonded optical fiber
scrim.
[0129] The laser light was directed through the coupling and into
the optical fiber, which was incorporated through the scrim. The
laser light could be seen projecting out of the fiber optic at the
end opposite the laser. Thus, it was clear that the manufacturing
process was capable of producing a scrim fabric without damaging
the optical fiber.
[0130] To test the sensing properties of the optical fiber scrim,
the exit end of the fiber optic was mounted so that the light
emitted from the end of the fiber was directed into a power meter
(Newport Model 1815-C). The power attributable to laser light being
emitted from the fiber was measured at 2.4 nW. This measurement was
fairly stable over a period of time. Then, the optical fiber scrim
was flexed in various places, causing the power meter readings to
vary. At one point, the power measurement dropped to 1.4 nW. When
the pressure that caused the drop in power levels was released, the
power reading returned to the original level. This testing shows
that the fiber optic scrim was sensitive to even local bending or
flexing.
[0131] In conclusion, the present optical fiber scrims represent a
useful advancement over the prior art. Modifications and variations
to the products and processes described herein may be practiced by
those of ordinary skill in the art, without departing from the
spirit and scope of the present disclosure. Furthermore, those of
ordinary skill in the art will appreciate that the foregoing
description is by way of example only, and is not intended to limit
the scope of the appended claims.
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