U.S. patent application number 15/079239 was filed with the patent office on 2017-09-28 for separator layer for flow battery.
The applicant listed for this patent is United Technologies Corporation. Invention is credited to Scott Alan Eastman, Michael L. Perry, Wei Xie.
Application Number | 20170279130 15/079239 |
Document ID | / |
Family ID | 58387726 |
Filed Date | 2017-09-28 |
United States Patent
Application |
20170279130 |
Kind Code |
A1 |
Eastman; Scott Alan ; et
al. |
September 28, 2017 |
SEPARATOR LAYER FOR FLOW BATTERY
Abstract
A flow battery includes an electrochemical cell that has a first
electrode, a second electrode spaced apart from the first
electrode, and a separator layer arranged between the first
electrode and the second electrode. The separator layer is formed
of a polymer that has a polymer backbone with cyclic groups that
are free of unsaturated nitrogen and one or more polar groups
bonded between the cyclic groups.
Inventors: |
Eastman; Scott Alan;
(Glastonbury, CT) ; Xie; Wei; (East Hartford,
CT) ; Perry; Michael L.; (Glastonbury, CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
United Technologies Corporation |
Farmington |
CT |
US |
|
|
Family ID: |
58387726 |
Appl. No.: |
15/079239 |
Filed: |
March 24, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 4/96 20130101; H01M
8/188 20130101; H01M 2250/10 20130101; H01M 8/0213 20130101; H01M
8/1032 20130101; H01M 8/103 20130101; H01M 8/20 20130101; H01M
8/0221 20130101; H01M 8/1025 20130101; Y02B 90/10 20130101; H01M
2/1653 20130101; H01M 8/1027 20130101; H01M 4/8605 20130101; Y02E
60/50 20130101; Y02E 60/10 20130101 |
International
Class: |
H01M 8/0221 20060101
H01M008/0221; H01M 8/0213 20060101 H01M008/0213; H01M 4/86 20060101
H01M004/86; H01M 4/96 20060101 H01M004/96; H01M 8/18 20060101
H01M008/18; H01M 8/20 20060101 H01M008/20 |
Claims
1. A flow battery comprising: an electrochemical cell including a
first electrode, a second electrode spaced apart from the first
electrode, and a separator layer arranged between the first
electrode and the second electrode, wherein the separator layer is
formed of a polymer having a polymer backbone with aromatic groups
that are free of unsaturated nitrogen and one or more polar groups
bonded in the polymer backbone.
2. The flow battery as recited in claim 1, wherein the one or more
polar groups includes an atom selected from the group consisting of
sulfur, oxygen, nitrogen, and combinations thereof.
3. The flow battery as recited in claim 1, wherein the aromatic
groups include nitrogen heterocycles.
4. The flow battery as recited in claim 1, wherein the polymer
backbone is free of unsaturated nitrogen.
5. The flow battery as recited in claim 1, wherein the polymer
includes at least one of adsorbed acid groups or aqueous
electrolyte that is non-covalently bonded to the one or more polar
groups.
6. The flow battery as recited in claim 1, wherein the polymer
includes polyetherimide (PEI).
7. The flow battery as recited in claim 1, wherein the polymer
includes polyamide-imide (PAI).
8. The flow battery as recited in claim 1, wherein the polymer
includes polyetheretherketone (PEEK).
9. The flow battery as recited in claim 1, wherein the polymer
includes polysulfone (PSF).
10. The flow battery as recited in claim 1, wherein the polymer
includes polyphenylene sulfide (PPS).
11. The flow battery as recited in claim 1, wherein the polymer is
selected from the group consisting of polyetherimide (PEI),
polyamide-imide (PAI), polyetheretherketone (PEEK), polysulfone
(PSF), polyphenylene sulfide (PPS), and combinations thereof.
12. The flow battery as recited in claim 1, further comprising a
supply/storage system external of the electrochemical cell, the
supply/storage system including first and second vessels, first and
second liquid electrolytes in, respectively, the first and second
vessels, fluid lines connecting the first and second vessels to,
respectively, the first electrode and the second electrode, and a
plurality of pumps operable to circulate the first and second
liquid electrolytes via the fluid lines between the first and
second vessels and the electrochemical cell.
13. The flow battery as recited in claim 1, wherein the separator
layer has an area specific resistance of less than approximately
425 m.OMEGA.*cm.sup.2.
14. A separator layer for use in a flow battery, the separator
layer being formed of a polymer having a polymer backbone with
aromatic groups that are free of unsaturated nitrogen, wherein the
separator layer has an area specific resistance of less than
approximately 425 m.OMEGA.*cm.sup.2.
15. The separator layer as recited in claim 14, wherein the
separator layer has an area specific resistance of less than
approximately 300 m.OMEGA.*cm.sup.2.
16. The separator layer as recited in claim 14, wherein the polymer
is selected from the group consisting of polyetherimide (PEI),
polyamide-imide (PAI), polyetheretherketone (PEEK), polysulfone
(PSF), polyphenylene sulfide (PPS), polystyrene (PS) and
combinations thereof.
17. A flow battery comprising: an electrochemical cell including a
first electrode, a second electrode spaced apart from the first
electrode, and a separator layer arranged between the first
electrode and the second electrode, and the first electrode and the
second electrode are configured to operate at a current density of
greater than or equal to approximately 100 mA/cm.sup.2; and a
supply/storage system external of the electrochemical cell, the
supply/storage system including first and second vessels, first and
second liquid electrolytes in, respectively, the first and second
vessels, fluid lines connecting the first and second vessels to,
respectively, the first electrode and the second electrode, and a
plurality of pumps operable to circulate the first and second
liquid electrolytes via the fluid lines between the first and
second vessels and the electrochemical cell, wherein the separator
layer is formed of a polymer having a polymer backbone with
aromatic groups that are free of unsaturated nitrogen and one or
more polar groups bonded in the polymer backbone.
18. A flow battery comprising: an electrochemical cell including a
first electrode, a second electrode spaced apart from the first
electrode, and a separator layer arranged between the first
electrode and the second electrode, wherein the separator layer is
formed of a polymer having a polymer backbone with triazine
groups.
19. The flow battery as recited in claim 18, wherein the polymer
backbone includes one or more polar groups bonded in the polymer
backbone
20. The flow battery as recited in claim 19, wherein the one or
more polar groups includes an atom selected from the group
consisting of sulfur, oxygen, nitrogen, and combinations thereof.
Description
BACKGROUND
[0001] Flow batteries, also known as redox flow batteries or redox
flow cells, are designed to convert electrical energy into chemical
energy that can be stored and later released when there is demand.
As an example, a flow battery may be used with a renewable energy
system, such as a wind-powered system, to store energy that exceeds
consumer demand and later release that energy when there is greater
demand.
[0002] A typical flow battery includes a redox flow cell that has a
negative electrode and a positive electrode separated by an
ion-exchange membrane. A negative fluid electrolyte (sometimes
referred to as the anolyte) is delivered to the negative electrode
and a positive fluid electrolyte (sometimes referred to as the
catholyte) is delivered to the positive electrode to drive
electrochemically reversible redox reactions. Upon charging, the
electrical energy supplied causes a chemical reduction reaction in
one electrolyte and an oxidation reaction in the other electrolyte.
The separator prevents the electrolytes from freely and rapidly
mixing but permits selected ions to pass through to complete the
redox reactions. Upon discharge, the chemical energy contained in
the liquid electrolytes is released in the reverse reactions and
electrical energy can be drawn from the electrodes. Flow batteries
are distinguished from other electrochemical devices by, inter
alia, the use of externally-supplied, fluid electrolyte solutions
that include reactants that participate in reversible
electrochemical reactions.
SUMMARY
[0003] A flow battery according to an example of the present
disclosure includes an electrochemical cell that has a first
electrode, a second electrode spaced apart from the first
electrode, and a separator layer arranged between the first
electrode and the second electrode. The separator layer is formed
of a polymer having a polymer backbone with aromatic groups that
are free of unsaturated nitrogen and one or more polar groups
bonded in the polymer backbone.
[0004] In a further embodiment of any of the foregoing embodiments,
the one or more polar groups includes an atom selected from the
group consisting of sulfur, oxygen, nitrogen, and combinations
thereof.
[0005] In a further embodiment of any of the foregoing embodiments,
the aromatic groups include nitrogen heterocycles.
[0006] In a further embodiment of any of the foregoing embodiments,
the polymer backbone is free of unsaturated nitrogen.
[0007] In a further embodiment of any of the foregoing embodiments,
the polymer includes at least one of adsorbed acid groups or
aqueous electrolyte that is non-covalently bonded to the one or
more polar groups.
[0008] In a further embodiment of any of the foregoing embodiments,
the polymer includes polyetherimide (PEI).
[0009] In a further embodiment of any of the foregoing embodiments,
the polymer includes polyamide-imide (PAI).
[0010] In a further embodiment of any of the foregoing embodiments,
the polymer includes polyetheretherketone (PEEK).
[0011] In a further embodiment of any of the foregoing embodiments,
the polymer includes polysulfone (PSF).
[0012] In a further embodiment of any of the foregoing embodiments,
the polymer includes polyphenylene sulfide (PPS).
[0013] In a further embodiment of any of the foregoing embodiments,
the polymer is selected from the group consisting of polyetherimide
(PEI), polyamide-imide (PAI), polyetheretherketone (PEEK),
polysulfone (PSF), polyphenylene sulfide (PPS), and combinations
thereof.
[0014] A further embodiment of any of the foregoing embodiments
includes a supply/storage system external of the electrochemical
cell. The supply/storage system includes first and second vessels,
first and second liquid electrolytes in, respectively, the first
and second vessels, fluid lines connecting the first and second
vessels to, respectively, the first electrode and the second
electrode, and a plurality of pumps operable to circulate the first
and second liquid electrolytes via the fluid lines between the
first and second vessels and the electrochemical cell.
[0015] In a further embodiment of any of the foregoing embodiments,
the separator layer has an area specific resistance of less than
approximately 425 m.OMEGA.*cm2.
[0016] A separator layer for use in a flow battery, the separator
layer being formed of a polymer having a polymer backbone with
aromatic groups that are free of unsaturated nitrogen, wherein the
separator layer has an area specific resistance of less than
approximately 425 m.OMEGA.*cm2.
[0017] In a further embodiment of any of the foregoing embodiments,
the separator layer has an area specific resistance of less than
approximately 300 m.OMEGA.*cm2.
[0018] In a further embodiment of any of the foregoing embodiments,
the polymer is selected from the group consisting of polyetherimide
(PEI), polyamide-imide (PAI), polyetheretherketone (PEEK),
polysulfone (PSF), polyphenylene sulfide (PPS), polystyrene (PS)
and combinations thereof.
[0019] A flow battery according to an example of the present
disclosure includes an electrochemical cell that has a first
electrode, a second electrode spaced apart from the first
electrode, and a separator layer arranged between the first
electrode and the second electrode. The first electrode and the
second electrode are configured to operate at a current density of
greater than or equal to approximately 100 mA/cm2 and a
supply/storage system external of the electrochemical cell. The
supply/storage system includes first and second vessels, first and
second liquid electrolytes in, respectively, the first and second
vessels, fluid lines connecting the first and second vessels to,
respectively, the first electrode and the second electrode, and a
plurality of pumps operable to circulate the first and second
liquid electrolytes via the fluid lines between the first and
second vessels and the electrochemical cell. The separator layer is
formed of a polymer having a polymer backbone with aromatic groups
that are free of unsaturated nitrogen and one or more polar groups
bonded in the polymer backbone.
[0020] A flow battery according to an example of the present
disclosure includes an electrochemical cell that has a first
electrode, a second electrode spaced apart from the first
electrode, and a separator layer arranged between the first
electrode and the second electrode. The separator layer is formed
of a polymer having a polymer backbone with triazine groups.
[0021] In a further embodiment of any of the foregoing embodiments,
the polymer backbone includes one or more polar groups bonded in
the polymer backbone
[0022] In a further embodiment of any of the foregoing embodiments,
the one or more polar groups includes an atom selected from the
group consisting of sulfur, oxygen, nitrogen, and combinations
thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The various features and advantages of the present
disclosure will become apparent to those skilled in the art from
the following detailed description. The drawings that accompany the
detailed description can be briefly described as follows.
[0024] FIG. 1 illustrates an example flow battery.
DETAILED DESCRIPTION
[0025] FIG. 1 schematically shows portions of an example flow
battery 20 for selectively storing and discharging electrical
energy. As an example, the flow battery 20 can be used to convert
electrical energy generated in a renewable energy system to
chemical energy that is stored until a later time when there is
greater demand, at which time the flow battery 20 then converts the
chemical energy back into electrical energy. The flow battery 20
can supply the electric energy to an electric grid, for
example.
[0026] The flow battery 20 includes a fluid electrolyte 22 that has
an electrochemically active species 24 that functions in a redox
pair with regard to an additional fluid electrolyte 26 that has an
electrochemically active species 28. The electrochemically active
species 24/28 include ions of elements that have multiple,
reversible oxidation states in a selected liquid solution, such as
but not limited to, aqueous solutions or dilute aqueous acids, such
as 1-5M sulfuric acid. In some examples, the multiple oxidation
states are non-zero oxidation states, such as for transition metals
including but not limited to vanadium, iron, manganese, chromium,
zinc, molybdenum and combinations thereof, and other elements
including but not limited to sulfur, cerium, lead, tin, titanium,
germanium and combinations thereof. In some examples, the multiple
oxidation states can include the zero oxidation state if the
element is readily soluble in the selected liquid solution in the
zero oxidation state. Such elements can include the halogens, such
as bromine, chlorine, and combinations thereof. The
electrochemically active species 24/28 could also be organic
molecules that contain groups that undergo electrochemically
reversible reactions, such as quinones.
[0027] The first fluid electrolyte 22 (e.g., the negative
electrolyte) and the second fluid electrolyte 26 (e.g., the
positive electrolyte) are contained in a supply/storage system 30
that includes first and second vessels 32/34 and pumps 35. The
fluid electrolytes 22/26 are delivered using the pumps 35 to at
least one electrochemical cell 36 of the flow battery 20 through
respective feed lines 38 and are returned from the cell 36 to the
vessels 32/34 via return lines 40. The feed lines 38 and the return
lines 40 connect the vessels 32/34 with first and second electrodes
42/44. Multiple cells 36 can be provided as a stack.
[0028] The cell 36 includes the first electrode 42, the second
electrode 44 spaced apart from the first electrode 42, and a
separator layer 46 arranged between the first electrode 42 and the
second electrode 44. For example, the electrodes 42/44 are porous
carbon structures, such as carbon paper or felt. The electrodes
42/44 may each be configured for operation at relatively high
current densities, such as but not limited to, current density
greater than or equal to approximately 100 mA/cm.sup.2.
[0029] In general, the cell or cells 36 can include bipolar plates,
manifolds and the like for delivering the fluid electrolytes 22/26
through flow field channels to the electrodes 42/44. The bipolar
plates can be carbon plates, for example. It is to be understood
however, that other configurations can be used. For example, the
cell or cells 36 can alternatively be configured for flow-through
operation where the fluid electrolytes 22/26 are pumped directly
into the electrodes 42/44 without the use of flow field
channels.
[0030] The fluid electrolytes 22/26 are delivered to the cell 36 to
either convert electrical energy into chemical energy or, in the
reverse reaction, convert chemical energy into electrical energy
that can be discharged. The electrical energy is transmitted to and
from the cell 36 through an electric circuit 48 that is
electrically coupled with the electrodes 42/44.
[0031] The separator layer 46 prevents the fluid electrolytes 22/26
from freely and rapidly mixing but permits selected ions to pass
through to complete the redox reactions while electrically
isolating the electrodes 42/44. In this regard, the fluid
electrolytes 22/26 are generally isolated from each other during
normal operation, such as in charge, discharge and shutdown
states.
[0032] In particular, due to the highly oxidative and acidic
environment in flow batteries in comparison to gaseous fuel cells,
there are only a few materials (e.g., perfluorosulfonic acid) that
are useful as a separator layer or ion exchange membrane. Materials
that may be effective in the less severe environment of a gaseous
fuel cell are degraded by the oxidative and acidic environment in
flow batteries and suffer from inadequate ion conductivity (e.g.,
proton conductivity) and/or ion selectivity (e.g., blocking
permeation of vanadium or other electrochemically active ion
species that can reduce energy efficiency). In this regard, as
discussed further below, the disclosed separator layer 46 is formed
of a polymer that may be stable in the oxidative and acidic
environment in the flow battery 20 and that may have good ion
conductivity and ion selectivity, among other properties.
[0033] In addition to ion conductivity and ion selectivity, the
separator layer 46 has properties such as ionic resistance, area
specific resistance, and electric conductivity and resistivity. The
ionic resistance is measured, in ohms (.OMEGA.), between the
opposed surfaces of the separator layer 46. The ionic resistance is
a function of the thickness of the separator layer 46, the
cross-sectional area, and the bulk resistivity. The (ionic) area
specific resistance is a function of the ionic resistance and
cross-sectional area. The area specific resistance can be
calculated, in units of amperes per area squared, by the equation
R.sub.AS=R*A, where R.sub.AS is the area specific resistance, R is
ionic resistance, and A is cross-sectional area.
[0034] As an example, the separator layer 46 is formed of a polymer
that has a polymer backbone with aromatic groups that are free of
(i.e., exclude) unsaturated nitrogen and that has one or more polar
groups that are bonded within the polymer backbone. Such polar
groups may be located between the cyclic groups, but are not
limited to such locations. The aromatic groups may provide the
separator layer 46 with good chemical stability in the oxidative
and acidic environment of the flow battery 20, while the polar
groups may provide permanent dipoles that are non-covalently bonded
to adsorbed acid groups and/or aqueous electrolyte that serve to
facilitate ion conductivity. As examples, the one or more polar
groups can include, but are not limited to, groups that have one or
more high electronegative atoms selected from sulfur, oxygen,
nitrogen, and combinations thereof. In further examples, the polar
groups include one or more of the chemical structures: C--O--C,
C.dbd.O, N--C.dbd.O, S.dbd.O, S.dbd.O.dbd.S, or C--S.
[0035] In further examples, the aromatic groups of the polymer
backbone include six-carbon atom rings and/or aromatic groups with
nitrogen heterocycles. Since the aromatic groups are free of
unsaturated nitrogen, the nitrogen heterocycles are also free of
unsaturated nitrogen. Although not limited, such nitrogen
heterocycles may include a five-atom ring that has one nitrogen
atom and four carbon atoms. As will be appreciated, other aromatic
groups and aromatic groups with nitrogen heterocycles according to
Huckel's rule may additionally or alternatively be used.
[0036] Furthermore, the flow battery 20 generally operates at much
lower temperatures (e.g., less than 100.degree. C., but typically
less 50.degree. C.) than some types of fuel cells (e.g., greater
than 200.degree. C.). Thus, the selected polymer need not have the
high temperature stability that is required in fuel cell membranes.
For instance, the glass transition temperature of the selected
polymer need only be greater than the expected operating
temperature of the flow battery 20 (greater than 50.degree. C. or
100.degree. C.).
[0037] In further examples, the polymer of the separator layer 46
is selected from polyetherimide (PEI), polyamide-imide (PAI),
polyetheretherketone (PEEK), polysulfone (PSF), polyphenylene
sulfide (PPS), or combinations thereof. It is to be understood that
the example polymers herein include the molecular formula of the
polymer and any isomers based upon the formula. Additionally, a
combination could be in the form of blends, alloys, and co-, ter-,
quatrenary- (etc.) polymers, where at least a portion of the
component is of the polymers listed subsequently. Shown below are
example structures of the polymer of the separator layer 46, with
adsorbed acid groups or aqueous electrolyte, represented at "A,"
that are non-covalently bonded to the one or more of the polar
groups:
[0038] Polyetherimide:
##STR00001##
[0039] Polyamide-Imide:
##STR00002##
[0040] Polyetheretherketone:
##STR00003##
[0041] Polysulfone:
##STR00004##
[0042] Polyphenylene Sulfide:
##STR00005##
[0043] In another example, the separator layer 46 is formed of a
polymer that has a polymer backbone with triazine groups. A
triazine group is a nitrogen heterocycle that includes three
nitrogen atoms in an aromatic ring. In further examples, the
polymer backbone may also include one or more polar groups as
discussed herein above that are bonded within the polymer backbone.
The triazine groups may provide the separator layer 46 with good
chemical stability in the oxidative and acidic environment of the
flow battery 20, while the polar groups may provide permanent
dipoles that are non-covalently bonded to adsorbed acid groups
and/or aqueous electrolyte that serve to facilitate ion
conductivity.
[0044] In further examples, the separator layer 46 has a thickness
of less than approximately 125 micrometers or less than 100
micrometers, based on the flow battery 20 operating at an average
current density above approximately 100 mA/cm.sup.2 (e.g., greater
than 200 mA/cm.sup.2). In a further example, the area specific
resistance is less than approximately 425 m.OMEGA.*cm.sup.2, based
on the flow battery 20 operating at an average current density
above approximately 100 mA/cm.sup.2 (e.g., greater than 200
mA/cm.sup.2). In further examples, the separator layer 46 has an
area specific resistance of less than approximately 425
m.OMEGA.*cm.sup.2 and the polymer of the separator layer 46 is
selected from polyetherimide (PEI), polyamide-imide (PAI),
polyetheretherketone (PEEK), polysulfone (PSF), polyphenylene
sulfide (PPS), polystyrene, or combinations thereof.
[0045] In a further example, the area specific resistance of the
separator layer 46 is less than approximately 300
m.OMEGA.*cm.sup.2, based on the flow battery 20 operating at an
average current density above approximately 100 mA/cm.sup.2 (e.g.,
greater than 200 mA/cm.sup.2) and the use of aqueous electrolytes
22/26. In a further example, the ion conductivity of the separator
layer 46 is greater than or equal to 0.05 S/cm.
[0046] In an additional example, the separator layer 46 has an
electronic area specific resistance of greater than approximately
1.times.10.sup.4 .OMEGA.*cm.sup.2. Electronic area specific
resistance is similar to ionic area specific resistance but
utilizes electric resistance rather than ionic resistance in the
calculation. In a further example, the separator layer 46 has a
per-cycle selectivity of greater than 99.995% based on use of
dissimilar electrolytes 22/26. Per-cycle selectivity is defined as
the number of moles of desired ion passed over a full
charge/discharge cycle divided by the sum of the number of moles of
desired ion passed and the number of moles of reactant or other
species that can lead to degradation or a loss of current
efficiency per charge/discharge cycle.
[0047] The separator layer 46 can be fabricated using a technique
that is capable of producing a relatively uniform, thin layer of
the polymer. Example techniques may include, but are not limited
to, solution casting, blade coating, spin coating, dip molding,
melt pressing, extruding, and sol-gel processing.
[0048] In additional examples, the fabrication technique is adapted
to adjust a balance between ion conductivity and selectivity. For
example, where the polymer in an as-fabricated state has low ion
conductivity and high selectivity, the technique may be adapted to
sacrifice a portion of the selectivity in order to obtain better
conductivity. In this regard, the separator layer 46 can be
fabricated with a controlled porosity. The porosity permits greater
uptake of acid groups (e.g., acid electrolyte), which may
non-covalently bond at the permanent dipoles of the polar groups of
the polymer to increase ion conductivity. While such porosity
enhances conductivity, it may also decrease selectivity by
providing greater free volume through which electrochemically
active ions can migrate.
[0049] One example of an adapted fabrication technique includes
inclusion of a sacrificial additive, such as powder and/or liquid
additives, in a solution casting material. The sacrificial additive
is mixed into and dispersed through the solution casting material.
Upon casting and drying/curing, the additive remains in the
separator layer 46. However, the additive is active with regard to
the liquid electrolyte used in the flow battery 20 such that the
additive either dissolves or reacts once exposed to the liquid
electrolyte. The reaction or dissolution serves to remove the
additive from the separator layer 46, thereby leaving a controlled
porosity in the separator layer 46 for uptake of acid groups from
the electrolyte. As examples, the additive may include, but is not
limited to, oxalic acid, polyethylene glycol, or combinations
thereof. The separator layer 46 may this be fabricated in a "dry"
state without any adsorbed liquid electrolyte and subsequently
installed into the flow battery 20 in the dry state, which
facilitates greater toleration of stresses from handling and
compression during installation.
[0050] The reaction or dissolution of the powder may consume
protons from the liquid electrolyte; however, the effect on the
liquid electrolyte will be low and can be accounted for in
initially formulating the liquid electrolyte to have a higher
concentration of the active species that are affected.
[0051] Although a combination of features is shown in the
illustrated examples, not all of them need to be combined to
realize the benefits of various embodiments of this disclosure. In
other words, a system designed according to an embodiment of this
disclosure will not necessarily include all of the features shown
in any one of the FIGURES or all of the portions schematically
shown in the FIGURES. Moreover, selected features of one example
embodiment may be combined with selected features of other example
embodiments.
[0052] The preceding description is exemplary rather than limiting
in nature. Variations and modifications to the disclosed examples
may become apparent to those skilled in the art that do not
necessarily depart from this disclosure. The scope of legal
protection given to this disclosure can only be determined by
studying the following claims.
* * * * *