Abstract:
An electromagnetic missile launcher is disclosed that provides greater flexibility for use with a variety of missile types and also provides potentially higher performance and efficiency as compared to prior-art electromagnetic missile launchers.

Description:
FIELD OF THE INVENTION 
   The present invention relates to missilery in general, and, more particularly, to missile launchers. 
   BACKGROUND OF THE INVENTION 
   During launch of a missile that contains a chemical booster, a thrust-providing plume of exhaust gas is generated. The exhaust gas is extremely hot (in excess of 5000° F.) and very erosive due to the presence of metallic particulates. Booster-assisted launch, which is typically referred to as “hot launch,” has a number of drawbacks, including:
         heating of the launch platform, which creates a readily-identifiable thermal signature;   obscuring the visibility and/or temporarily blinding missile-launch personnel;   impairing radar systems in the vicinity of the launch platform due to the presence of the metallic particulates in the missile exhaust; and   the difficulty of adequately venting the exhaust gas from relatively larger missiles, which, in comparison with smaller missiles, is relatively hotter and more voluminous.       

   To address these problems, “cold launch” technologies are being developed. One promising cold-launch technology is the electromagnetic missile launcher. In current electromagnetic missile launchers, plural, independently-addressable, preformed coils are stacked around a cylindrical launch tube. During a typical electromagnetic launch, electric current is sequenced through these coils to accelerate an armature that is located within the launch tube. The moving armature propels a missile to launch velocity. 
   Although prior-art electromagnetic launchers effectively address the problems of hot launch, they suffer from other drawbacks. In particular, prior-art electromagnetic launchers have relatively low propulsion efficiency. Furthermore, some prior-art electromagnetic missile launchers are relatively inflexible in that they have essentially no ability to accommodate missiles that vary from a design diameter. In addition, the weight, size, reliability, and complexity of prior-art electromagnetic launchers are negatively impacted by the manner in which they are fabricated. 
   SUMMARY OF THE INVENTION 
   The present invention enables the electromagnetic launch of a missile without some of the costs and disadvantages for doing so in the prior art. 
   Embodiments of the present invention, like the prior art, use a plurality of propulsion coils arrayed along the length of a tube to eject a missile from the tube with sufficient velocity for flight. In some prior art electromagnetic launchers, the propulsion coils are equally-sized, stackable coils that each act as an independent unit during launch. As a result, these prior-art electromagnetic launchers are limited in their ability to: 1) vary the dimensional properties of their propulsion coils, and 2) reduce the minimum separation between the propulsion coils and an armature that propels the missile within the tube. In addition, the minimum separation between the propulsion coils and the armature in prior-art electromagnetic launchers includes extra space, which is required to facilitate their assembly. The increased separation distance reduces the efficiency of prior-art electromagnetic launchers. 
   In contrast to the prior art, the present invention comprises propulsion coils that are formed directly onto the outer surface of the tube. As a result, embodiments of missile launchers in accordance with the present invention can have readily varied coil sizes, coil diameters, coil spacings, and coil wire sizes, as a function of the tube size. In addition, embodiments in accordance with the present invention can have a smaller minimum spacing between the propulsion coils and the armature. 
   Embodiments of the present invention derive any one or more of the following advantages over the prior art:
         1) improved performance;   2) greater efficiency;   3) less complexity;   4) reduced launcher size and/or weight;   5) increased flexibility for use with different missile types; and   6) improved reliability.       

   Like prior-art electromagnetic missile launchers, embodiments of the present invention eject a missile from a tube by accelerating an armature. The armature is accelerated by a force that arises due to mutual inductance between the armature and a plurality of propulsion coils that carry electric current. The flow of electric current in each propulsion coil is controlled and sequenced by a power system that is electrically-connected to the propulsion coils. But the efficiency with which the propulsion coils of launchers disclosed herein propel the armature is improved over prior-art electromagnetic missile launchers. A reason for this is that the minimum separation between the propulsion coils and the armature of the present launcher is less than for prior-art launchers. 
   An embodiment of the present invention comprises:
         a tube for encircling an armature, wherein the tube has an outer surface;   a first coil for conducting electric current, wherein the first coil is substantially immovable with respect to the tube, and wherein a portion of the first coil is physically-coupled to the outer surface of the tube;   a second coil for conducting electric current, wherein the second coil is substantially immovable with respect to the tube, and wherein a portion of the second coil is physically-coupled to the outer surface of the tube; and   the armature, wherein the armature comprises a third coil for conducting electric current, and wherein the third coil is substantially immovable with respect to the armature;   wherein the flow of electric current in at least one of the first coil and the second coil induces the armature to move with respect to the tube.       

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  depicts a schematic of the salient components of a launch system according to an illustrative embodiment of the present invention. 
       FIG. 2  depicts a perspective drawing of a prior-art launch tube. 
       FIG. 3  depicts a side view of prior-art stackable coil launch tube  218 . 
       FIG. 4  depicts a cross-sectional view of the coil arrangement of prior-art stackable coil launch tube  218  in a pre-launch state. 
       FIG. 5  depicts a perspective view of a launch tube in accordance with an illustrative embodiment of the present invention. 
       FIG. 6  depicts a side view of unitary barrel launch tube  518  in accordance with the illustrative embodiment of the present invention. 
       FIG. 7  depicts a cross-sectional view of a region of unitary barrel launch tube  518  in accordance with the illustrative embodiment of the present invention. 
       FIG. 8  depicts the salient operations for assembling a unitary barrel launch tube in accordance with the illustrative embodiment of the present invention 
   

   DETAILED DESCRIPTION 
     FIG. 1  depicts a schematic of the salient components of a launch system according to an illustrative embodiment of the present invention. Launch system  100  comprises electromagnetic missile launcher  108 , weapons control system  102 , launch controller  104 , power system  106 , propulsion current bus  112 , signal line  114 , and data bus  116 . Launch system  100  is described in U.S. patent application Ser. No. 10/899,234, filed Sep. 26, 2004, which is incorporated by reference herein. 
   Electromagnetic missile launcher  108  (hereinafter “launcher  108 ”) is a system that has the capability to house and expel a conventional missile upon command. A conventional missile typically comprises an explosive warhead and a chemical-propellant engine. Launcher  108  comprises launch tube  118 . Launcher  108  expels a missile from launch tube  118  using an electromagnetic catapult and without the aid of the missile&#39;s chemical-propulsion engine. This is advantageous because it enables the missile to clear the launch platform before engine start, which mitigates the aforementioned problems of hot launch. 
   Weapons control system  102  provides targeting and flight information and firing authority to launch controller  104  prior to and during a launch sequence. 
   Launch controller  104  provides the targeting and flight information to a missile prior to launch and also provides the directive to launch to power system  106 . 
   Power system  106  comprises circuitry that conditions and manages the storage and delivery of power to launcher  108  in response to signals from launch controller  104 . Power system  106  controls power generation, storage, and delivery prior to, during, and after each launch. 
   Propulsion current bus  112  carries power from power system  106  to launcher  108 . 
   Signal line  114  connects launch controller  104  to power system  106  and carries the commands that direct power system  106  to initiate and control the launch of a missile. Data bus  116  carries the targeting information from launch controller  104  to launcher  108 . 
     FIG. 2  depicts a perspective drawing of a prior-art launch tube. Stackable coil launch tube  218  comprises tube  202 , three stackable coils  204 - 1  through  204 - 3 , and clamps  206 . For clarity, the interconnection of stackable coil launch tube  218  and propulsion current bus  112  is not shown. 
   Tube  202  is a cylindrical tube that has sufficient interior diameter to accommodate missile  208  and sufficient strength to withstand the forces exerted on tube  202  during a missile launch. 
   Stackable coils  204 - 1  through  204 - 3  (referred to collectively as stackable coils  204 ) are described in detail below and with reference to  FIG. 4 . Stackable coils  204  are the propulsion coils for stackable coil launch tube  218 . 
   Clamp  206  is a metal clamp which holds stackable coils  204  together prior to, during, and after a missile launch. 
   Missile  208  is a conventional missile which comprises an explosive warhead and a chemical-propellant engine. Missile  208  resides within tube  202  and is attached to armature  304  (described below and with respect to  FIG. 3 ) via missile restraint bolts. 
   Stackable coil launch tube  218  is assembled by sliding each of equal size stackable coils  204 - 1 ,  204 - 2 , and  204 - 3  over tube  202 , thereby stacking them. Stackable coils  204  surround the outer diameter of tube  202 . Each of the stackable coils has an interior diameter large enough to accommodate tube  202 , plus additional clearance to facilitate assembly. Once stackable coils  204  are stacked around tube  202 , they are clamped together by clamps  206 . Clamps  206  impede motion of stackable coils  204  in response to forces to which each is subjected during a missile launch. 
   Stackable coil launch tube  218  is assembled using a stackable coil assembly approach. The use of this approach, however, can lead to any of several undesirable consequences. For example, space must be added to some components to accommodate assembly. As explained below, these gaps increase the separation between the propulsion coils and the armature, which in turn leads to a reduction of the propulsion efficiency. In addition, the use of uniformly-sized stackable coils limits the flexibility of the launcher. This, in turn, limits the limits the utility of the stackable coil approach for missiles of various types and sizes. Further, misalignment between coils stacked around the tube degrades the efficiency of the launcher. Finally, since each stackable coil is an independent unit, the propulsive force generated during a launch can act to drive the stackable coils apart. Banding and/or clamps, such as clamp  206 , are therefore required to keep the stackable coils from separating during launch. The addition of banding and/or clamps undesirably increases the weight, size, and/or complexity of prior-art electromagnetic missile launchers. 
     FIG. 3  depicts a side view of prior-art stackable coil launch tube  218 . Armature  304 , which is included in stackable coil launch tube  218  but can not be seen in  FIG. 2 , comprises a rigid platform and an armature coil. Armature  304  is described in more detail below and with reference to  FIG. 4 . 
   During the launch of missile  208 , power system  106  energizes stackable coil  204 - 1  with electric current via propulsion current bus  112 . The flow of electric current in stackable coil  204 - 1  causes a mutual inductance between stackable coil  204 - 1  and the armature coil in armature  304 . The mutual inductance between the propulsion coils and the armature coil results in a force that accelerates armature  304  toward the muzzle end of stackable coil launch tube  218 . As armature  304  moves, power system  106  sequences the flow of electric current from stackable coil  204 - 1  to stackable coil  204 - 2  and then to stackable coil  204 - 3 . The sequencing of the flow of electric current serves to maintain the acceleration of armature  304  and missile  208  so as to impart sufficient velocity to the missile for it to achieve aerodynamic flight. Once missile  208  has attained sufficient velocity, armature  304  decelerates and the missile restraint bolts (not shown) that hold it to armature  304  are broken. Missile  208  is thereby thrown free of launcher  108 . Once sufficient separation between missile  208  and launcher  108  is achieved, the chemical-propellant engine of missile  208  ignites and the missile continues its flight toward its target. 
   The efficiency with which stackable coil launch tube  218  accelerates missile  208  is inversely proportional to the separation between the electrical conductors in stackable coils  204  and armature  304  (specifically, the armature coil included in armature  304 ). It is desirable, therefore, to keep this separation as small as possible, as a more efficient launcher can be smaller, lighter, and less expensive. Unfortunately, the use of a stackable coil approach for fabrication of stackable coil launch tube  218  results in a larger separation between the propulsion and armature coils. This is described in more detail below and with respect to  FIG. 4 . 
     FIG. 4  shows a cross-section of region A-A of  FIG. 3 , which depicts prior-art stackable coil  204 - 1  and armature  304  in a pre-launch state. Stackable coil  204 - 1  comprises coil  402 - 1 , coil form  404 - 1 , and coil lid  408 - 1 . Stackable coil  204 - 1  is representative of each of stackable coils  204 , which are substantially identical. Armature  304  comprises armature coil  410  and sled  412 . 
   Sled  412  is a rigid platform suitable for holding missile  208  and locating armature coil  410 . 
   Armature coil  410  is a length of electrical conductor that is suitable for developing a mutual inductance with energized coils  402 . Armature coil  410  is substantially immovable with respect to sled  412 . 
   Coil  402 - 1  is a length of electrical conductor that is suitable for carrying sufficient electric current to accelerate armature  304 . Coil  402 - 1  is representative of each of coils  402 . The propulsive force provided by coil  402 - 1  to armature  304  is a function of the number of turns in coil  402 - 1 , the current carried by coil  402 - 1 , and the separation between coil  402 - 1  and the armature coil in armature  304 . 
   Coil form  404 - 1  is a hollow annulus of fiber-reinforced epoxy with an opening appropriate for locating coil  402 - 1 . Coil form  404 - 1  is representative of each of coil forms  404 . The opening in coil form  404 - 1  is defined by an inner hub, which has a hub wall thickness of t 1 , a bottom, which has a bottom thickness of t 2 , and an outer hub. The opening in coil form  404 - 1  is slightly larger than the relevant dimensions of coil  402 - 1  so that coil  402 - 1  can be inserted into it. 
   Coil lid  408 - 1  is a lid of fiber-reinforced epoxy for enclosing coil  402 - 1  in the opening of coil form  404 - 1 . Coil lid has a coil lid thickness of t 3 . 
   Stackable coil  204 - 1  is formed by first winding coil  402 - 1  on a winding tool. Once wound, coil  402 - 1  is removed from the winding tool and placed in coil form  404 - 1 . Often, the packing density of the windings in coil  402 - 1  degrades while it is physically moved from the winding tool to coil form  404 - 1 . A reduction in the packing density of its windings reduces the propulsion efficiency of a propulsion coil. After coil  402 - 1  is inserted into coil form  404 - 1 , lid  408 - 1  is then fixed onto coil form  404 - 1 . In order to facilitate coil insertion into the coil form, the inner diameter of coil  402 - 1  is made slightly larger than the outer diameter of the hub portion of coil form  404 - 1 . As a result, clearance gap g 1  is present between coil  402 - 1  and the hub wall of coil form  404 - 1 . After coil lid  408 - 1  is secured to coil form  404 - 1 , the assembly is completed by injecting encapsulant  406  into the coil form to pot coil  402 - 1 . These steps are representative of the process used to form each of stackable coils  204 . 
   Once they are fabricated, stackable coils  204  are placed on top of one another around tube  202 . In order to facilitate the placement of the stackable coils around tube  202 , the inner diameter of coil forms  404  are made slightly larger than the outer diameter of tube  202 . As a result, coil form clearance gap g 2  is present between stackable coil  402 - 1  and tube wall  302 . 
   The use of the stackable coil approach, therefore, results in a minimum separation between stackable coil  402 - 1  and armature coil  410  that is the total of coil clearance gap g 1 , hub wall thickness t 1 , coil form clearance gap g 2 , tube wall thickness t 4 , gap g 3 , and armature coil gap g 4  (i.e., the distance between armature coil  410  and the edge of armature  304 ). 
     FIG. 5  depicts a perspective view of a launch tube in accordance with an illustrative embodiment of the present invention. Unitary barrel launch tube  518  comprises tube  202 , flanges  502 - 1  through  502 - 4 , and coils  504 - 1  through  504 - 3 . For clarity, the outer structure of launch tube  500  (e.g., encapsulation and outer jacket), as well as the interconnection between unitary barrel launch tube  518  and power system  106  are not shown. Although the illustrative embodiment comprises four flanges and three coils, it will be clear to those skilled in the art, after reading this specification, how to make and use alternative embodiments of the present invention that comprise any number of flanges and/or any number of coils. 
   Although in the illustrative embodiment tube  202  has a circular cross-section, it will be clear to those skilled in the art, after reading this specification, how to make and use alternative embodiments wherein tube  202  has a non-circular cross-section such as square, rectangular, or elliptical. 
   Each of flanges  502 - 1  through  502 - 4  (collectively “flanges  502 ”) is an annulus of fiber-reinforced epoxy resin that has an inner diameter slightly larger than the outer diameter of tube  202 . The inner diameter of flanges  502 , therefore, is suitable for accommodating the insertion of tube  202  into flanges  502 . During launcher assembly, flanges  502  are slid onto tube  202  and fixed in their desired positions on tube  202 . Flanges  502  are arranged on tube  202  to form spaces between them that are suitable for defining each of coils  504 - 1  through  504 - 3 . Each of flanges  502  has a thickness suitable for providing adequate physical separation between two coils as shown. Although in the illustrative embodiment each of flanges  502  has substantially the same thickness, it will be clear to those skilled in the art, after reading this specification, how to make and use alternative embodiments in which flanges  502  are not all of the same thickness. 
   Each of coils  504 - 1  through  504 - 3  (collectively “coils  504 ”) comprises a length of electrical conductor that is suitable for carrying sufficient electric current to generate a desired propulsive force on armature  304 . Coils  504  are the propulsion coils in unitary barrel launch tube  518 . Coils  504  are discussed in more detail below in with respect to  FIG. 7 . 
   A disadvantage associated with some prior-art electromagnetic missile launchers that are assembled using the stackable coil approach is an inability to customize the characteristics of the propulsion coils, such as coil width, coil spacing, coil cross-section, and/or coil wire gauge, for a specific application. Although in the illustrative embodiment flanges  502  are arranged on tube  202  with substantially uniform spacing between them, it will be clear to those skilled in the art, after reading this specification, how to make and use alternative embodiments of the present invention wherein the spacing between flanges  502  is not uniform. In addition, it will be clear to those skilled in the art, after reading this specification, how to make and use alternative embodiments wherein the thickness and/or diameter of each of flanges  502  is not uniform. 
   In contrast to prior-art electromagnetic missile launchers, therefore, the present invention provides a means to customize:
         i. coil cross-section; or   ii. coil diameter; or   iii. coil spacing; or   iv. coil wire gauge; or   v. the coil to armature gap; or   vi. any combination of i, ii, iii, iv, and v.       

   A customized design regarding one or more of the above parameters i through v facilitates an improvement in some of the design and/or performance parameters of unitary barrel launch tube  518 , such as the transient acceleration profile of armature  304  during launch, length of the propulsion system, weight of the propulsion system, reliability, efficiency, and performance. 
     FIG. 6  depicts a side view of unitary barrel launch tube  518  in accordance with the illustrative embodiment of the present invention. Unitary barrel launch tube  518  comprises tube  202 , armature  304 , missile  208 , flanges  502 , coils  504 , encapsulant  602 , and outer jacket  604 . 
   Encapsulant  602  is a flowable epoxy suitable for potting electrical windings. It will be clear to those skilled in the art how to make and use encapsulant  602 . 
   Outer jacket  604  is a fiber wound coating that is added to unitary barrel launch tube  500  after coils  504  have been potted in encapsulant  602 . The addition of encapsulant  602  and outer jacket  604  to launcher  108  reduces the need for clamp  206 , described above and with respect to  FIG. 2 , since encapsulant  602  and outer jacket  604  serve to bond tube  202 , flanges  502 , and coils  504  together as a single physical unit. As a result, coils  504  are less likely to separate due to the forces to which they are subjected during a missile launch. 
   In similar fashion to the prior-art stackable coil approach described above and with respect to  FIGS. 2-4 , the propulsive force provided to armature  304  is generated by the flow of electric current in coils  502 - 1  through  502 - 3 . The flow of electric current through coils  502  is controlled and sequenced by power system  106 , which is connected to coils  504  through propulsion current bus  112 . 
   Although the illustrative embodiment comprises a launcher for throwing a missile, it will be clear to those skilled in the art, after reading this specification, how to make and use alternative embodiments of the present invention that throw munitions that do not comprise a chemical-propellant engine, such as mortars or other projectiles. 
     FIG. 7  depicts a cross-sectional view of a region of unitary barrel launch tube  518  in accordance with the illustrative embodiment of the present invention. 
   Region B-B depicts an enlarged view of a portion of propulsion coil  504 - 1  and some of its surrounding region. Coil  504 - 1  is representative of each of coils  504 . Coil  504 - 1  comprises a length of coil wire  702 . Coil wire  702  is an electrical conductor that is coated with a layer of electrical insulation. Coil wire  702  is suitable for carrying sufficient electric current to generate a desired propulsive force on armature  304 . Coil  504 - 1  is formed of a plurality of radial layers  704 , at least one of which is physically-coupled to the outer surface of tube  202 . For the purposes of this specification, including the appended claims, the term “physically-coupled” means direct, physical contact between two objects (e.g., two surfaces that abut one another, etc.). 
   Layer  706  is a layer of permeable fabric. Layer  706  separates each radial layer  704  of coil  504 - 1  from its neighboring layers without significantly perturbing the magnetic field developed by coil  504 - 1  when coil  504 - 1  is energized by electric current. During electromagnetic missile launch, the propulsion coils and/or coil windings may exhibit mechanical movement due to such factors as thermal expansion or electromagnetic force. Over time, this mechanical motion may erode the insulation coating on coil wire  702 . Layer  706  provides a protective barrier between radial layers  704  to protect the coil wire insulation and improve launcher reliability. 
   Just as in prior-art electromagnetic missile launchers, the propulsive force on armature  304  generated by each of the propulsion coils (i.e., coils  504 ) is a function of: the number of turns the propulsion coil contains; the electric current it carries; and the separation between the propulsion coil and the armature within tube  202 . In the prior-art stackable coil approach, the efficiency of a launcher is reduced by the structural aspects inherent to the use of separate stackable coils. Specifically, as discussed above and with respect to  FIG. 4 , prior-art launcher performance is degraded by the need for assembly clearances such as those between coils  402  and coil forms  404  (i.e., coil clearance gap, g 1 ), and those between coil forms  404  and the outer surface of tube  202  (i.e., coil form clearance gap, g 2 ). 
   The present invention provides an electromagnetic missile launcher capable of more efficient propulsion than some prior-art electromagnetic missile launchers. In contrast to the prior art, in the present invention, the propulsion coils are wound directly onto the outer surface of tube  202 . In the illustrative embodiment, the minimum separation between the propulsion coils and the armature coil is therefore reduced from that of the prior-art launcher depicted in  FIG. 4  by at least the sum of coil clearance gap g 1 , hub wall thickness t 1 , and coil form clearance gap g 2 . As a result, the separation between the propulsion coils (i.e., coils  504 ) and armature  304  includes only: 1) the thickness, t 4 , of tube wall  302 ; and 2) the clearance, g 4 , between armature  304  and the inner wall of tube  202 . 
   Although the illustrative embodiment comprises an armature that has an armature coil, it will be clear to those skilled in the art, after reading this specification, how to make and use alternative embodiments of the present invention that comprise an armature that does not have an armature coil. 
     FIG. 8  depicts the salient operations for assembling a unitary barrel launch tube in accordance with the illustrative embodiment of the present invention. 
   At operation  801 , flanges  502 - 1  through  502 - 4  are stacked around tube  202 . Each of flanges  502  is affixed into position along tube  202  so that the spaces between the flanges are suitable for the subsequent formation of coils  504 . In some alternative embodiments, reinforcing bars hold flanges  502  in place temporarily while they are being attached to tube  202 . 
   At operations  802  through  804 , each of coils  504 - 1  through  504 - 3  are formed in the spaces between flanges  502 . 
   For example, at operation  802 , coil  504 - 1  is formed by winding a first radial layer  704  of coil wire  702  onto the outer surface of tube  202 . Prior to winding a second radial layer  704  of coil wire  702  onto the first radial layer of coil wire, a layer of permeable fabric  706  is affixed around the outside of the first radial layer. After permeable fabric  706  is added, second radial layer  704  of coil wire  702  is added to coil  504 - 1 . Alternating layers of permeable fabric  706  and radial layers  704  of coil wire  702  are added until the desired diameter of coil  504 - 1  is achieved. Although in the illustrative embodiment, coil  504 - 1  comprises three radial layers  704  and two layers of permeable fabric  706 , it will be clear to those skilled in the art, after reading this specification, how to make and use alternative embodiments of the present invention that comprise a number of radial layers  704  other than three and/or a number of layers of permeable fabric  706  other than two. 
   At operation  803 , a first end of the coil wire that composes coil  504 - 1  is attached to terminal lug  708  that is attached to flange  502 - 1 . 
   At operation  804 , a second end of the coil wire that composes coil  504 - 1  is attached to terminal lug  708  that is attached to flange  502 - 2 . 
   Operations  802 ,  803 , and  804  are repeated for each of coils  504 - 1  through  504 - 3 . 
   At operation  805 , the assembly comprising flanges  502 - 1  through  502 - 4  and interposing coils  504 - 1  through  504 - 3  is potted in encapsulant  706  in well-known fashion. 
   At operation  806 , outer shell is formed around the outside of the assembly potted in operation  805 . 
   It is to be understood that the above-described embodiments are merely illustrative of the present invention and that many variations of the above-described embodiments can be devised by those skilled in the art without departing from the scope of the invention. For example, in this Specification, numerous specific details are provided in order to provide a thorough description and understanding of the illustrative embodiments of the present invention. Those skilled in the art will recognize, however, that the invention can be practiced without one or more of those details, or with other methods, materials, components, etc. 
   Furthermore, in some instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the illustrative embodiments. It is understood that the various embodiments shown in the Figures are illustrative, and are not necessarily drawn to scale. Reference throughout the specification to “one embodiment” or “an embodiment” or “some embodiments” means that a particular feature, structure, material, or characteristic described in connection with the embodiment(s) is included in at least one embodiment of the present invention, but not necessarily all embodiments. Consequently, the appearances of the phrase “in one embodiment,” “in an embodiment,” or “in some embodiments” in various places throughout the Specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments. It is therefore intended that such variations be included within the scope of the following claims and their equivalents.