U.S. patent application number 13/951026 was filed with the patent office on 2013-11-21 for multi-gap interferometric sensors.
This patent application is currently assigned to BAKER HUGHES INCORPORATED. The applicant listed for this patent is Lance A. Beckner, Brooks A. Childers, Robert M. Harman, Daniel S. Homa. Invention is credited to Lance A. Beckner, Brooks A. Childers, Robert M. Harman, Daniel S. Homa.
Application Number | 20130311095 13/951026 |
Document ID | / |
Family ID | 44904563 |
Filed Date | 2013-11-21 |
United States Patent
Application |
20130311095 |
Kind Code |
A1 |
Childers; Brooks A. ; et
al. |
November 21, 2013 |
MULTI-GAP INTERFEROMETRIC SENSORS
Abstract
An apparatus for estimating a property includes a hollow core
tube and an input light guide disposed at least partially within
hollow core tube. The apparatus also includes a second gap disposed
within the hollow core tube and separated from the input light
guide by an air gap width. The second gap is formed of a first
solid material and has a second gap width. The apparatus also
includes a third gap disposed at least partially within the hollow
core tube and being further from the input light guide than the
second gap. The third gap is formed of a second solid material and
has a third gap width.
Inventors: |
Childers; Brooks A.;
(Christiansburg, VA) ; Harman; Robert M.;
(Troutville, VA) ; Homa; Daniel S.; (Blacksburg,
VA) ; Beckner; Lance A.; (Roanoke, VA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Childers; Brooks A.
Harman; Robert M.
Homa; Daniel S.
Beckner; Lance A. |
Christiansburg
Troutville
Blacksburg
Roanoke |
VA
VA
VA
VA |
US
US
US
US |
|
|
Assignee: |
BAKER HUGHES INCORPORATED
Houston
TX
|
Family ID: |
44904563 |
Appl. No.: |
13/951026 |
Filed: |
July 25, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12772253 |
May 3, 2010 |
|
|
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13951026 |
|
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61294240 |
Jan 12, 2010 |
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Current U.S.
Class: |
702/8 |
Current CPC
Class: |
G01B 9/02025 20130101;
G01B 2290/25 20130101; G01K 5/48 20130101; G01K 11/3206 20130101;
G01D 5/268 20130101; G01B 9/02023 20130101; G01V 8/02 20130101 |
Class at
Publication: |
702/8 |
International
Class: |
G01V 8/02 20060101
G01V008/02 |
Claims
1. A computer based method for estimating a property, the method
comprising: receiving at a computing device a series of data values
based on an amplitude of reflected light from a sensor that
includes an air gap, a second gap and a third gap; providing an
estimate of a width of the air gap, an estimate of a width of the
second gap, and an estimate of a width of the third gap to a curve
fitting algorithm on the computing device; receiving intermediate
gap widths for the second and third gaps; verifying the
intermediate gap width for the third gap to create a verified third
gap width; and providing a revised estimate of the width of the air
gap to the curve fitting algorithm, the revised estimate being
based on the verified third gap.
2. The method of claim 1, wherein verifying includes: in the event
that the intermediate gap width for the third gap is within a
predefined range, setting the verified third gap equal to the
intermediate gap width for the third gap; otherwise, adding or
subtracting a preset value to the intermediate gap width until the
intermediate gap width is within the predefined range and then
setting the verified third gap equal to the intermediate gap width
for the third gap.
3. The method of claim 2, wherein the predefined range is less than
a fringe order of the light applied to sensor.
4. The method of claim 2, wherein the preset value is less than
half of the mean wave length of the light applied to the
sensor.
5. The method of claim 1, wherein the estimates of the second gap
width and the third gap width is not based on a spectral analysis
of the data values.
6. The method claim 1, where the estimates of the second gap width
and the third gap width are within a range of possible widths based
on the materials forming the second gap and the third gap.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS AND PRIORITY CLAIM
[0001] This application is a divisional of Non-provisional
Application Ser. No. 12/772,253, entitled "MULTI-GAP
INTERFEROMETRIC SENSORS", which claims the benefit of U.S.
Provisional Application Ser. No. 61/29,240, entitled "IMPROVED EFPI
SENSOR", filed Jan. 12, 2010, under 35 U.S.C. .sctn.119(e), and
which is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an improved Extrinsic
Fabry-Perot Interferometer (EFPI) sensor. More particularly, the
EFPI sensor is configured to be disposed in a borehole penetrating
the earth.
[0004] 2. Description of the Related Art
[0005] In exploration and production of hydrocarbons, it is often
necessary to drill a borehole into the earth to gain access to the
hydrocarbons. Equipment and structures, such as borehole casings
for example, are generally disposed into a borehole as part of the
exploration and production. Unfortunately, the environment
presented deep into the borehole can place extreme demands upon the
equipment and structures disposed therein. For example, the
equipment and structures can be exposed to high temperatures and
pressures that can effect their operation and longevity.
[0006] Because optical fibers can withstand the harsh downhole
environment, sensors using optical fibers are often selected for
downhole applications. One type of sensor using optical fibers is
the Extrinsic Fabry-Perot Interferometer (EFPI) sensor. The EFPI
sensor can measure pressure or temperature for example by measuring
a displacement of one optical fiber in relation to another optical
fiber.
[0007] An example of a prior art EFPI sensor 10 is illustrated in
FIG. 1. The EFPI sensor 10 includes a capillary tube 11. Disposed
within the capillary tube 11 at one end is a single-mode optical
fiber 12. Disposed at the other end of the hollow core fiber 11 is
a multimode optical fiber 13. A Fabry-Perot (FP) cavity is formed
between the ends of the optical fibers 12 and 13 within the
capillary tube 11. The single mode optical fiber 12 provides input
light to the FP cavity and receives light reflections from the FP
cavity. The multimode optical fiber 13 acts as a reflector. The
capillary tube 11 is configured to guide the optical fibers 12 and
13 to and from each other based on the application of an external
force while maintaining their alignment.
[0008] The input light enters the single mode optical fiber 12 and
is partially reflected by a first glass-to-air interface 14 to
produce first reflected output light 15. The input light not
reflected by the first glass-to-air interface 14 travels through
the FP cavity and is reflected by a second glass-to-air interface
16 to produce second reflected output light 17. The first
reflection output light 15 interferes with the second reflection
output light 17 to create an interference pattern or interferogram
that depends on a difference in the optical path lengths traveled
by the reflection output light 15 and 17. The intensity of total
output light due to the interference pattern is related to the
difference between the two optical paths. By measuring the
intensity of the total light output the displacement of the single
mode optical fiber 12 with respect to the multimode optical fiber
13 can be measured. Hence, a property such as temperature or
pressure can be estimated by measuring a change in intensity of the
total light output.
BRIEF SUMMARY OF THE INVENTION
[0009] Disclosed is an apparatus for estimating a property. The
apparatus includes a hollow core tube and an input light guide
disposed at least partially within hollow core tube. The apparatus
also includes a second gap disposed within the hollow core tube and
separated from the input light guide by an air gap width. The
second gap is formed of a first solid material and has a second gap
width. The apparatus also includes a third gap disposed at least
partially within the hollow core tube and being further from the
input light guide than the second gap. The third gap is formed of a
second solid material and has a third gap width.
[0010] Also disclosed is a system for estimating a property that
includes a hollow core tube and an input light guide disposed at
least partially within hollow core tube. The system also includes a
second gap disposed within the hollow core tube and separated from
the input light guide by an air gap width. The second gap is formed
of a first solid material and has a second gap width. The system
also includes a third gap disposed at least partially within the
hollow core tube and being further from the input fiber than the
second gap. The third gap is formed of a second solid material and
has a third gap width. In addition, the system includes a light
source in optical communication with the input light guide and
configured to transmit an input light signal and a light detector
in optical communication with the input fiber and configured to
detect light reflections of the input light signal wherein the
light reflections are related to the air gap, the second gap and
the third gap.
[0011] Further disclosed is a computer based method for estimating
a property that includes: receiving at a computing device a series
of data values based on an amplitude of reflected light from a
sensor that includes an air gap, a second gap and a third gap;
providing an estimate of a width of the air gap, an estimate of a
width of the second gap, and an estimate of a width of the third
gap to a curve fitting algorithm on the computing device; receiving
intermediate gap widths for the second and third gaps; verifying
the intermediate gap width for the third gap to create a verified
third gap width; and providing a revised estimate of the width of
the air gap to the curve fitting algorithm, the revised estimate
being based on the verified third gap.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The subject matter, which is regarded as the invention, is
particularly pointed out and distinctly claimed in the claims at
the conclusion of the specification. The foregoing and other
features and advantages of the invention are apparent from the
following detailed description taken in conjunction with the
accompanying drawings, wherein like elements are numbered alike, in
which:
[0013] FIG. 1 illustrates a prior art EFPI sensor;
[0014] FIG. 2 illustrates an exemplary embodiment of an EFPI sensor
system with the sensor disposed in a borehole penetrating the
earth;
[0015] FIG. 3 illustrates an example of an EFPI sensor according to
one embodiment;
[0016] FIG. 4 shows a gap region of the sensor shown in FIG. 3;
and
[0017] FIG. 5 is a flow diagram of a method according to one
embodiment.
DETAILED DESCRIPTION OF THE INVENTION
[0018] Reference may now be had to FIG. 2. FIG. 2 illustrates an
exemplary embodiment of an EFPI sensor system 20. The EFPI sensor
system 20 includes an EFPI sensor 21 configured to be disposed in a
borehole 2 penetrating the earth 3. Being configured for operation
in the borehole 2 includes being operable at the high temperatures
and pressures encountered downhole.
[0019] Still referring to FIG. 2, the EFPI sensor 21 is coupled to
surface optoelectronics by way of a communication optical fiber 22.
In an alterative embodiment, some or all of the optoelectronics can
be disposed downhole. The surface optoelectronics include a light
source 23, such as a laser diode, and a light detector 24. The
light source 23 is configured to transmit input light to the EFPI
sensor 21 while the light detector 24 is configured to receive and
measure light reflections from the sensor 21. An optical coupler 25
is configured to couple the light source 23 and the light detector
24 to the communications optical fiber 22. A computer processing
system 26 may be coupled to the light source 23 and the light
detector 24 and configured to operate the EFPI sensor system 20. In
addition, the computer processing system 26 may process
interference patterns generated by light reflections from the EFPI
sensor 21 to estimate a property being measured.
[0020] As discussed above, EFPI sensors may produce sinusoidal
interference patterns where the phase is dependent on a parameter
of interest that modulates the optical path length, e.g. physical
length or refractive index. Due to the periodic nature of the
sinusoidal pattern, the values of the parameters recovered by
current algorithms and current sensors can have discrete errors
based on mis-interpretation of the interferometric fringe order. A
zero order fringe represents zero optical path difference and a
first order fringe represents an optical path difference of one
mean wavelength of the light source. These fringe order
misinterpretations are colloquially termed "solution jumps" and may
be a source of errors. Also, due to the possibility of solution
jumps, such sensors cannot be properly classified as absolute
sensors since once the fringe misinterpretation exists it can
persist requiring additional information to get back on the right
fringe order.
[0021] Embodiments presented herein may provide a multi-gap sensor
and method that reduces or eliminates the above-described problems.
In one embodiment, the sensor includes at least three "gaps." A
"gap," as the term is used herein, refers to a width of a material
or air disposed between two reflection surfaces. The reflections
may be caused, for example, by a transition from a solid to air or
vice versa, a reflective material displaced in the optical path, or
a change in material forming the optical path.
[0022] FIG. 3 shows a cut-away side view of an EFPI sensor 30
according to one embodiment. In more detail, the EFPI sensor
("sensor") includes input light guide 31. The input light guide 31
may include an optical waveguide core 32 in one embodiment. Of
course, the waveguide core 32 could be omitted in one embodiment.
The optical waveguide core 32 may be a single mode optical fiber
that provides input light to the sensor and receives light
reflections from the multiple gaps of the sensor 30. The input
light guide 31 may have an internal portion 33 disposed within the
hollow core tube 34. The hollow core tube 34 may have a circular
cross-section in one embodiment. Of course, the hollow core tube 34
could have other cross-sections. In one embodiment, the hollow core
tube 34 is formed of a glass material. In one embodiment, the
internal portion 33 has a smaller outer diameter than the hollow
core tube 34. In such an embodiment, the outer diameter of the
internal portion may be smaller than an inner diameter of the
hollow core tube 34 such that a compression gap 36 exists there
between. The compression gap 36 protects the internal portion 33
from compression when the sensor 30 is exposed to pressure.
[0023] In another embodiment, the input fiber 31 includes a taper
from the first portion 31 to an end of the internal portion 33 to
prevent contact between each of the input fiber and the hollow core
tube 34. The taper may isolate the inner surface of the hollow core
tube 34 for 360 degrees about the longitudinal axis of from the
first fiber 31. Hence, the internal portion 33 in FIG. 3 may be
described as being "perimetrically" (i.e., related to the
perimeter) isolated from the hollow core tube 34. In one
embodiment, a solution of hydrofluoric acid can be used to etch the
optical fiber 31 to produce the taper.
[0024] The sensor 30 may also include a gap region 35. The gap
region 35 may include an air gap 37. The air gap 37 separates the
first fiber from two or more materials which cause two or more
reflections. As shown in FIG. 3, the two materials, first material
38 and second material 39 form the second and third gaps described
below and cause three reflections. The reflections are shown in
greater-detail below.
[0025] The two materials 38 and 39 are typically fused or otherwise
joined together or are formed of the same material with a reflector
disposed between them. In one embodiment, the second material 39 is
fused or otherwise joined to the hollow core tube 34. In one
embodiment, the hollow core tube 34 and one or both of the first
material 38 and second material 39 are formed of a glass or glass
like material.
[0026] When the sensor 30 is subjected to changes in pressure
(e.g., a hydrostatic pressure), the size of the entire sensor 30
may vary. In particular, the hollow core tube 34 may compress as
pressure increases. In addition, the second material 39 may
compress as pressure increases as well. However, in one embodiment,
due to the compression gap 36, the internal portion 33 and the
first material 38 may not compress as pressure increases. In
addition, due to the compression of the hollow core tube 34, the
width of the air gap 37 may become smaller.
[0027] Typical prior art EFPI sensor had only one or two optical
path lengths. The path lengths were demodulated to recover
temperature and some other parameter, such as pressure. To
alleviate the solution jumps mentioned above, in one embodiment,
the gap region 35 may include three or more gaps. In one
embodiment, the gap region 35 includes only three gaps.
[0028] In one embodiment, the hollow core tube 34 has an outer
diameter of about two millimeters. Accordingly, when the outer
diameter of the hollow core tube 34 is two millimeters, the optical
fibers disposed within the tube 34 will have outer diameters less
than one millimeter taking into account the wall thickness of the
tube 34.
[0029] In one embodiment, the EFPI sensor 30 is fabricated as a
micro-electromechanical system (MEMS) using techniques used for
fabricating semiconductor devices. Exemplary embodiments of these
techniques include photolithography, etching and
micromachining.
[0030] FIG. 4 shows a detailed view of the gap region 35 shown in
FIG. 3. The gap region 35 includes an air gap 37 having a gap width
of Wg1, a second gap having a width of Wg2 and formed by the first
material 38 and a third gap having a width of Wg3 and formed by the
second material 39. As discussed above, the compression (or
expansion) of the air gap 37 and the second material 39 due to
pressure variations will cause variations in their respective gap
widths. The transitions between the internal portion 33 and the air
gap 37, the air gap 37 and the second material 38, and the second
material 38 and the third material 39 define three reflection
surfaces, a first reflection surface 50, a second reflection
surface 51 and a third reflection surface 52, respectively. A
fourth reflection surface 53 is formed by the transition from the
third material 39 and air or some other material.
[0031] In more detail, the air gap 37 exists between the internal
second portion 33 and the first material 39 and has a width of Wg1.
Stated differently, the air gap 37 has a width Wg1 defined as the
distance between the first reflection surface 50 and the second
reflection surface 51. The first reflection surface 50 causes a
first reflection 43 and the second reflection surface 51 causes the
second reflection 44. The first reflection 43 interferes with the
second reflection 44 to create an interference pattern or
interferogram that depends on a difference in the optical path
lengths traveled by the first reflection 43. This difference is
equal to Wg1.
[0032] Similarly, the junction between the first material 38 and
the second material 39 at third reflection surface 52 causes a
third reflection 45. This third reflection 45 also causes
interference that can be utilized to determine the Wg2. For ease of
discussion, the second material 38 may also be referred to as the
second gap.
[0033] Finally, the junction between the second material 39 and the
external environment at the fourth refection surface 53 causes a
fourth reflection 46. This fourth reflection 46 also causes
interference that can be utilized to determine the Wg3. For ease of
discussion, the second material 39 may also be referred to as the
third gap.
[0034] In one embodiment, the divider 40 is an optical reflector.
In such an embodiment, the first material 38 and second material 39
may be formed of the same material. The divider 40 may include
gold, titanium oxide or silicon nitride to cause reflections at the
junction of the second and third materials, 38 and 39,
respectively, resulting in the third reflection 45. The divider 40
could also be one of a class of broadband multilayer dielectric
reflectors.
[0035] In another embodiment, the first material 38 has a different
refractive index than the second material 39. The difference in
indicies causes the third reflection 45. In such an embodiment, the
divider 40 may be omitted. In one embodiment, the first material 38
and the second material 39 are both a glass or glass-like material.
For example, both the first material 38 and the second material 39
may be formed of silica. In another embodiment, the first material
38 could be a non-glass amorphous or crystalline material such as,
for example, silicon.
[0036] In operation, pressure is applied to outside of the sensor
30 (FIG. 3). This pressure may cause compression of the tube 34 and
to the third gap 39. The first material (second gap) 38, however,
is not directly coupled to a pressure. Accordingly, the width Wg2
of the second material 38 may be utilized as a temperature gauge.
Both the air gap 37 and the second material (third gap) 39 may be
utilized as pressure gauges. In one embodiment, the third gap gives
a rough estimate of the pressure and the air gap 37, based on the
rough estimate, is utilized for more precise pressure
measurements.
[0037] It shall be understood that the configuration shown in FIG.
4 is illustrative only. For example, the dispersion of the light
beams from the core 32 and the angle and position of the
reflections is not meant to be limiting. In addition, in one
embodiment, the core 32 may be omitted in the event that collimated
light is provided to the sensor 30.
[0038] In operation, in order to determine the values of W.sub.g1,
W.sub.g2, and W.sub.g3, actual data points are collected and then
curve-fitting techniques may be employed. In one embodiment,
non-linear least squares fitting technique may be employed.
[0039] As one of ordinary skill will realize, non-linear curve
fitting techniques require initial estimates for the unknown
variables. In addition, the temperature is typically required to
perform a temperature compensation step. To achieve the precision
desired, the gap width changes typically are many multiples of the
source mean wavelength span and covers many fringe orders. If the
first and second materials are configured (i.e., sized) such that
their widths may only change by less than one fringe order over any
expected temperature or pressure variation, the recovered gap
widths determined in a first stage of the algorithm described below
may be used to seed a second stage of the algorithm with sufficient
accuracy to guarantee both a unique solution and the desired
precision. To this end, the widths of the second and third gaps,
W.sub.g2 and W.sub.g3, respectively, may be selected such that over
any expected temperature or pressure change, these widths will not
vary more than one fringe order.
[0040] In one embodiment, the sensor 30 may be formed such that the
air gap 37 has a width of about 160 um, the first material 38 has a
width of about 300 um, and the second material 39 has a width of
about 700 um. Of course, these values could change based on the
material being used and the expected external conditions the sensor
30 may experience.
[0041] According to one embodiment, a two-stage method of
determining the widths of the gaps is utilized. In the first stage,
an initial solution is found for all the gaps W.sub.g1, W.sub.g2
and W.sub.g3. Given that the width of the first and second
materials cannot vary by more than a single fringe order, the
initial solutions for those values (Wg2 and Wg3) may e corrected by
adding or subtracting an integer multiple of half the mean
wavelength of the source to place the gap values W.sub.g2 and
W.sub.g3 in the correct physical range. The algorithm is repeated
and all the resulting gap values recovered are on the correct
absolute fringe order allowing accurate and high precision values
to be obtained.
[0042] In the prior art when only two gaps (an air gap for pressure
and a solid gap for temperature) were used, a Fourier transform of
the output signal may have been utilized to determine its frequency
content. From the frequency content, an estimate of the gap widths
was created. These estimates were then used in the curve fitting
technique as a starting point. The result of the curve fitting gave
solutions for gap widths and, thus, the measurement of the physical
property interest. However, as described above, the variation of
the gaps may be greater than a fringe length. As such, these
results could include solution jumps.
[0043] FIG. 5 shows a flow chart of a method according to the
present invention. At a block 52 a series of data values are
collected. These data values may be based, for example, on
measurements of the output as the frequency of the input light is
varied. In the prior art, it was from these values that the
spectral content was gathered and thus, from which the initial
estimates for the gaps was made for curve fitting. In one
embodiment, the data values are received from a sensor having at
least three gaps. In one embodiment, the sensor has one air gap and
two gaps (second and third gaps) formed by solid materials.
[0044] At a block 54 an estimate for the second and third gaps is
created. This estimate may be formed in many manners. In one
embodiment, Fourier analysis may be utilized in the estimate. In
another embodiment, in the event that the widths of the second and
third gaps are selected such that they cannot vary more than fringe
order, an estimate for these variables may be obtained by selecting
any value in the width variation range of the gap width. For
example, the estimate may be from the middle of the width variation
value. In one embodiment, a value in the middle of the air gap
variation range may be selected.
[0045] At a block 56, the gap width estimates are provided to a
curve fitting technique. Of course, other values, such as the
reflectivity of each of the surfaces and the mode field radius of
the input waveguide may be provided.
[0046] At a block 58 intermediate gap widths for the two solid
material gaps are received as a result of the curve fitting
technique. The air gap width may also be received but may be
ignored in one embodiment. At a block 60 it is determined if either
of the two solid material gap values are out of the possible range.
If so, half the mean wavelength of the input light is added or
subtracted until the values are within the possible ranges at a
block 62. Otherwise, processing proceeds to block 514. Blocks 60 to
62 may be referred to as "verifying" the gaps.
[0047] At block 64 the curve fitting technique is again applied. In
this iteration, the length of the third gap as finally determined
at either block 58 or 62 is converted to a corresponding air gap
width. The values for the second and third widths used in this
iteration are those determined in blocks 58 or 62.
[0048] At a block 66 the final air gap width is attained and may be
considered as an absolute solution.
[0049] In support of the teachings herein, various analysis
components may be used, including a digital and/or an analog
system. For example, and referring again to FIG. 2, the
optoelectronics such as the light source 23, the light detector 24,
or the computer processing system 25 may include the digital and/or
analog system. The system may have components such as a processor,
storage media, memory, input, output, communications link (wired,
wireless, pulsed mud, optical or other), user interfaces, software
programs, signal processors (digital or analog) and other such
components (such as resistors, capacitors, inductors and others) to
provide for operation and analyses of the apparatus and methods
disclosed herein in any of several manners well-appreciated in the
art. It is considered that these teachings may be, but need not be,
implemented in conjunction with a set of computer executable
instructions stored on a computer readable medium, including memory
(ROMs, RAMs), optical (CD-ROMs), or magnetic (disks, hard drives),
or any other type that when executed causes a computer to implement
the method of the present invention. These instructions may provide
for equipment operation, control, data collection and analysis and
other functions deemed relevant by a system designer, owner, user
or other such personnel, in addition to the functions described in
this disclosure.
[0050] Further, various other components may be included and called
upon for providing for aspects of the teachings herein. For
example, a power supply (e.g., at least one of a generator, a
remote supply and a battery), cooling component, heating component,
motive force (such as a translational force, propulsional force or
a rotational force), magnet, electromagnet, sensor, electrode,
transmitter, receiver, transceiver, antenna, controller, optical
unit, optical connector, optical splice, optical lens, electrical
unit or electromechanical unit may be included in support of the
various aspects discussed herein or in support of other functions
beyond this disclosure.
[0051] Elements of the embodiments have been introduced with either
the articles "a" or "an." The articles are intended to mean that
there are one or more of the elements. The terms "including" and
"having" are intended to be inclusive such that there may be
additional elements other than the elements listed. The conjunction
"or" when used with a list of at least two terms is intended to
mean any term or combination of terms. The terms "first" and
"second" are used to distinguish elements and are not used to
denote a particular order. The term "couple" relates to two devices
being either directly coupled or indirectly coupled via one or more
intermediate devices.
[0052] It will be recognized that the various components or
technologies may provide certain necessary or beneficial
functionality or features. Accordingly, these functions and
features as may be needed in support of the appended claims and
variations thereof, are recognized as being inherently included as
a part of the teachings herein and a part of the invention
disclosed.
[0053] While the invention has been described with reference to
exemplary embodiments, it will be understood that various changes
may be made and equivalents may be substituted for elements thereof
without departing from the scope of the invention. In addition,
many modifications will be appreciated to adapt a particular
instrument, situation or material to the teachings of the invention
without departing from the essential scope thereof. Therefore, it
is intended that the invention not be limited to the particular
embodiment disclosed as the best mode contemplated for carrying out
this invention, but that the invention will include all embodiments
falling within the scope of the appended claims.
* * * * *