Abstract:
An electron emitter assembly includes a plurality of electron emitters, and a removable structure connected to, and fixing a positional relationship among, individual ones of the plurality of electron emitters. A method of assembling an electron emitter assembly includes connecting individual ones of a plurality of electron emitters together with a removable structure, and fixing a positional relationship among the individual ones of the plurality of electron emitters.

Description:
FIELD 
       [0001]    The disclosed exemplary embodiments relate generally to X-ray generation, and more particularly to one or more X-ray emitter structures for an X-ray tube. 
       BACKGROUND 
       [0002]    In non-invasive imaging systems, X-ray tubes are used in various X-ray systems and computed tomography (CT) systems as a source of X-ray radiation. Typically, an X-ray tube includes a cathode and an anode. An emitter within the cathode may emit a stream of electrons in response to heat resulting from an applied electrical current. The electron stream may be guided toward the anode by one or more electrical or magnetic fields positioned along the electron stream. The anode generally includes a target that is impacted by the stream of electrons. The target may, as a result of impact by the electron beam, produce X-ray radiation that is emitted from the X-ray tube. 
         [0003]    In typical imaging applications, the radiation passes through a subject of interest, such as a patient, baggage, or an article of manufacture, and a portion of the radiation impacts a detector or photographic plate where the image data is collected. The detector produces signals representative of an amount or intensity of radiation impacting discrete elements of the detector. The signals may then be processed to generate an image that may be displayed for review. In CT systems, a detector array, including a series of detector elements, produces similar signals through various positions as a gantry is rotated about a patient. In other systems, such as systems for oncological radiation treatment, the X-ray tube may produce ionizing radiation directed toward a target tissue. 
         [0004]    The cathode of an X-ray tube may include one or more emitters having various configurations. However, as emitters are generally becoming larger, the first resonant frequency is being driven lower and lower. This modal frequency eventually arrives within the range of other structurally relevant frequencies of the X-ray tube, such as the anode rotor operational frequency. When this modal frequency exists at, or below the other operational frequencies of the X-ray tube, energy may be deposited into this mode, introducing emitter deformation and encouraging additional failure modes. Furthermore, the larger emitters may have less structural rigidity resulting in challenges during fabrication, assembly, shipment, and operation. In addition, multiple emitters may be used, compounding placement accuracy problems, in particular when placing them in close proximity to each other or any external geometry. 
         [0005]    It would be advantageous to provide methods for fabrication and stiffening that overcome these and other disadvantages. 
       SUMMARY 
       [0006]    In at least one aspect of the disclosed embodiments, an electron emitter assembly includes a plurality of electron emitters, and a removable structure connected to, and fixing a positional relationship among, individual ones of the plurality of electron emitters. 
         [0007]    The removable structure may include one or more ligaments connected among the individual ones of the plurality of electron emitters. 
         [0008]    The removable structure may include a substrate supporting the individual ones of the plurality of electron emitters. 
         [0009]    At least a portion of the removable structure may be removable by an ablation process. 
         [0010]    At least a portion of the removable structure may be removable by a separation process. 
         [0011]    At least a portion of the removable structure may be retained to provide modal stiffness for the individual ones of the plurality of electron emitters. 
         [0012]    The positional relationship among the individual ones of the plurality of electron emitters may be planar. 
         [0013]    The positional relationship may be an out of plane relationship among the individual ones of the plurality of electron emitters. 
         [0014]    The out of plane relationship among the individual ones of the plurality of electron emitters may be effected by a bend applied to the removable structure. 
         [0015]    At least a portion of the removable structure may be retained to provide a current path among the individual ones of the plurality of electron emitters. 
         [0016]    In one or more aspects of the disclosed embodiments, a method of assembling an electron emitter assembly includes connecting individual ones of a plurality of electron emitters together with a removable structure, and fixing a positional relationship among the individual ones of the plurality of electron emitters. 
         [0017]    The removable structure may include one or more ligaments connected among the individual ones of the plurality of electron emitters. 
         [0018]    The removable structure may include a substrate supporting the individual ones of the plurality of electron emitters. 
         [0019]    The method of assembling an electron emitter assembly may include removing at least a portion of the removable structure by an ablation process. 
         [0020]    The method of assembling an electron emitter assembly may include removing at least a portion of the removable structure by a separation process. 
         [0021]    The method of assembling an electron emitter assembly may include retaining at least a portion of the removable structure to provide modal stiffness for the individual ones of the plurality of electron emitters. 
         [0022]    The positional relationship among the individual ones of the plurality of electron emitters may be planar. 
         [0023]    The positional relationship may be an out of plane relationship among the individual ones of the plurality of electron emitters. 
         [0024]    The method of assembling an electron emitter assembly may include forming the out of plane relationship among the individual ones of the plurality of electron emitters by applying a bend to the removable structure. 
         [0025]    The method of assembling an electron emitter assembly may include retaining at least a portion of the removable structure to provide a current path among the individual ones of the plurality of electron emitters. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    The foregoing and other aspects of the disclosed embodiments are made more evident in the following Detailed Description, when read in conjunction with the attached Drawing Figures, wherein: 
           [0027]      FIG. 1  shows a diagram of an imaging system incorporating one or more of the disclosed embodiments; 
           [0028]      FIG. 2  shows a block diagram of the imaging system of  FIG. 1 ; 
           [0029]      FIG. 3  is a schematic diagram of an X-ray tube according to the disclosed embodiments; 
           [0030]      FIGS. 4A-4C  show an exemplary set of emitters fabricated with ligaments according to the disclosed embodiments; 
           [0031]      FIGS. 5A-5C  show an exemplary set of emitters fabricated on a substrate according to the disclosed embodiments; 
           [0032]      FIGS. 6A-6C  show an exemplary set of emitters fabricated with ligaments on a substrate according to the disclosed embodiments; 
           [0033]      FIGS. 7A-7D  show exemplary sets of emitters fabricated with ligaments having a bend according to the disclosed embodiments; 
           [0034]      FIGS. 8A-8D  show exemplary sets of emitters fabricated on a substrate having a bend according to the disclosed embodiments; 
           [0035]      FIGS. 9A-9E  show exemplary sets of emitters fabricated with ligaments on a substrate having a bend according to the disclosed embodiments; 
           [0036]      FIGS. 10A-10C and 11A-11C  illustrate emitter sets with ligaments positioned at ends of the emitter sets according to the disclosed embodiments; 
           [0037]      FIGS. 12A-12D  illustrate emitters fabricated with stiffness and rigidity features according to the disclosed embodiments; and 
           [0038]      FIGS. 13, 14, 15A, and 15B  illustrate the use of ligaments emitters to compensate for cold spots and defects according to the disclosed embodiments; 
       
    
    
     DETAILED DESCRIPTION 
       [0039]      FIG. 1  shows an exemplary computed tomography (CT) imaging system  10  in which the disclosed embodiments may be utilized. The imaging system  10  includes a gantry  12  with an X-ray source or tube  14  and a detector assembly  18 . The X-ray tube  14  may project a beam of X-rays  16  toward the detector assembly  18  which may be located on an opposite side of the gantry  12 . The detector assembly  18  may include a plurality of detectors  20  ( FIG. 2 ) and a data acquisition system  32 . The plurality of detectors  20  may sense the projected X-rays that pass through a subject of interest  22 , for example a medical patient, and the data acquisition system  32  may convert signals from the detectors  20  to digital data for subsequent processing. Each detector  20  may produce an electrical signal that represents an intensity of an attenuated beam as it passes through the subject of interest  22 . During a scan to acquire X-ray projection data, the gantry  12  and the components mounted thereon may rotate about a center of rotation  24  ( FIG. 2 ). 
         [0040]      FIG. 2  shows a block diagram of the imaging system of  FIG. 1 . A control mechanism  26  may control rotation of the gantry  12  and the operation of the X-ray tube  14 . The control mechanism  26  may include an X-ray controller  28  that provides power and timing signals to the X-ray tube  14  and a gantry motor controller  30  that controls a rotational speed and position of gantry  12 . An image reconstructor  34  may receive sampled and digitized X-ray data from the data acquisition system  32  and may perform an image reconstruction. The reconstructed image may be applied as an input to a computer  36  that stores the image in a mass storage device  38 . 
         [0041]    The computer  36  may also receive commands and scanning parameters from an operator via a console  40  that may have a user interface, for example, a keyboard, mouse, voice activated controller, or any other suitable input apparatus. An associated display  42  may allow a user to observe the reconstructed image and other data from the computer  36 . User supplied commands and parameters may be used by the computer  36  to provide control signals and information to the data acquisition system  32 , the X-ray controller  28 , and the gantry motor controller  30 . In addition, the computer  36  may operate a table motor controller  44  that controls a motorized table  46  to position the subject of interest  22  and the gantry  12 . The table  46  may move the subject of interest  22  partly or wholly through a gantry opening  48  ( FIG. 1 ). 
         [0042]      FIG. 3  shows a diagram of the exemplary X-ray tube  14  according to the disclosed embodiments. The X-ray tube  14  may include a cathode assembly  50  and an anode assembly  52  encased in a housing  54 . The anode assembly  52  may include a rotor  56  configured to turn a rotating anode disc  58  also referred to as a target. When struck by an electron current  60  from the cathode assembly  50 , the anode  58  emits an X-ray beam  62 . 
         [0043]    The cathode assembly  50  and the anode assembly  52  may be supported within a housing  54  defining an area of relatively low pressure (e.g., a vacuum). The housing  54  may be constructed of various materials including, for example, glass, ceramic, stainless steel, or other suitable materials. The target  58  may be manufactured of any metal or composite, for example, tungsten, molybdenum, copper, or any material that contributes to generating radiation when bombarded with electrons. The target&#39;s surface material is typically selected to have a relatively high thermal diffusivity to withstand the heat generated by electrons impacting the target  58 . The space between the cathode assembly  50  and the target  58  may be evacuated to minimize electron collisions with other atoms and to increase high voltage stability. Moreover, such evacuation may advantageously allow a magnetic flux to quickly interact with (i.e., steer or focus) the electron beam  62 . Electrostatic potential differences are created between the cathode assembly  50  and the anode  58 , causing electrons emitted by the cathode assembly  50  to accelerate towards the anode  58 . 
         [0044]    The cathode assembly  50  may include one or more emitters  66  mounted on a support  64 . The support  64  may provide a mounting surface for the one or more emitters  66 . In some embodiments the support  64  may include a focusing cup or focusing head that may at least partially circumscribe the one or more emitters  66 . In one or more embodiments, the support  64  may contact the emitters  66  along one or more edges. In some embodiments, the support may  64  include one or more posts on which the one or more emitters  66  may be mounted. A power supply  68  may provide drive current to heat the one or more emitters  66  to promote electron emission. The emitters  66  may include suitable materials to facilitate electron emission, including, for example, various anisotropic polycrystalline materials such as tungsten, tungsten alloy, tantalum, or hafnium carbide. 
         [0045]      FIG. 4A  shows an exemplary set of emitters  70 . According to the disclosed embodiments, the emitter set  70  may be fabricated with a support structure to facilitate installation in an X-ray tube. In some embodiments, a portion of the support structure may be removed after installation. For example, the emitter set  70  may be fabricated from a sheet of emitter material, for example, by laser cutting a tungsten sheet, to yield two emitters  72 ,  74  connected by one or more ligaments  76 . 
         [0046]    It should be understood that the emitter set  70  may be fabricated to yield any suitable number of emitters. The emitters may have meander conduction paths  78  or may have any other suitable conduction path configuration. The ligaments  76  may operate to fix a positional relationship between the two emitters  72 ,  74  to facilitate installation. For example, rather than attempting to precisely locate two or more emitters relative to each other and relative to other structures within the cathode assembly, the ligaments may simplify operations by allowing the placement of a single object or structure within the cathode assembly. The emitter set  70  may be fabricated as a substantially flat sheet of material.  FIG. 4B  shows an embodiment of the emitters  72 ,  74  as installed in the cathode assembly  50  where the positional relationship among the emitters  72 ,  74  is planar, that is the emitters  72 ,  74  are substantially in the same plane. 
         [0047]    The emitters  72 ,  74  may be installed by bonding, welding, brazing, or any suitable attachment method for attaching the emitters  72 ,  74  to support structures in the cathode assembly. The support structures may include mounting posts or other structures. 
         [0048]    In this embodiment, one or more of the ligaments  76  may be left in place to provide modal stiffness and other ligaments may be removed, for example, by an ablation process, a separation process, for example, a chemical separation process or heat separation process, or some other suitable removal process. In some embodiments, all the ligaments  76  may be left in place. Ligaments  76  remaining connected to the emitters  72 ,  74  may be altered to achieve specific current flows through the emitters  72 ,  74  as will be described below.  FIG. 4C  shows another embodiment of the emitters  72 ,  74  as installed in the cathode assembly  50  where all of the ligaments are removed. 
         [0049]      FIG. 5A  shows another exemplary set of emitters  80 . The emitter set  80  may be fabricated by depositing emitter material onto a substrate  82  to yield a plurality of emitters, for example, emitters  84 ,  86 . 
         [0050]    The emitters  84 ,  86  may have meander conduction paths or may have any other suitable conduction path configuration. In this embodiment, the substrate  82  may be flat and may operate to fix a positional relationship between the two emitters  84 ,  86  to facilitate installation in the cathode assembly  50 .  FIG. 5B  shows an embodiment of the emitters  84 ,  86  as installed. In this embodiment, one or more portions  88  of the substrate  82  itself may be retained or left in place to provide modal stiffness and other portions of the substrate  82  may be removed, for example, by a suitable removal process as mentioned above. In some embodiments, the entire substrate  82  may be left in place.  FIG. 5C  shows another embodiment of the emitters  84 ,  86  as installed where the substrate  82  has been completely removed after installation. 
         [0051]      FIG. 6A  shows yet another exemplary set of emitters  90 . The emitter set  90  may be fabricated by depositing emitter material onto a substrate  92  to yield a plurality of emitters  94 ,  96  and structural ligaments  98  connecting the emitters  94 ,  96  together. Similar to other embodiments, the emitters  94 ,  96  may have meander conduction paths or may have any other suitable conduction path configuration, and the substrate  92  may be flat and may operate to fix a positional relationship between the two emitters  94 ,  96  to facilitate installation.  FIG. 6B  shows an embodiment of the emitters  94 ,  96  as installed where the substrate  92  has been removed. In some embodiments, the substrate  92  may be removed before the emitter set  90  is installed in the cathode assembly  50 . One or more ligaments  98  may be removed for example, by a suitable removal process as mentioned above, and one or more ligaments  98  may be left in place to provide modal stiffness. In some embodiments, all the ligaments  98  may be left in place. The ligaments  98  remaining connected to the emitters  94 ,  96  may be adapted to achieve specific current flows through the emitters  94 ,  96  as will be described below.  FIG. 6C  shows another embodiment of the emitters  94 ,  96  where all of the ligaments are removed after installation. 
         [0052]      FIGS. 7A-11B  show exemplary embodiments of fabricated emitter sets with out of plane emitters.  FIG. 7A  shows a side view of an emitter set  100  formed from a sheet of material with two emitters  102 ,  104  joined by one or more ligaments  106 . A bend may be applied to the emitter set  100  by applying heat to the emitter set  100  until the emitter material is ductile and applying a bending force to, for example the ligament portion  106 . Heat may be applied from a separate heat source or may be applied by passing a current through the emitter set  100 . The bending force may be applied using a die, tooling, or other suitable bending technique to achieve a V bend  108 , as shown in  FIG. 7B , a rounded bend  110 , as shown in  FIG. 7C , or any suitable bend. The bends  108 ,  110  may include any number of angles to achieve a desired out of plane relationship between the emitters  102 ,  104 . A suitable bend may be applied to achieve a particular orientation between the emitters  102 ,  104 , such as an angular orientation, a positional orientation, or both. After installation, one or more of the ligaments  106  may be removed by a suitable removal process as mentioned above, and one or more ligaments  106  may be left in place to provide modal stiffness. In some embodiments, all the ligaments  106  may be left in place. Ligaments  106  left in place may be modified to achieve specific current flows through the emitters  102 ,  104  as will be described below. As shown in  FIG. 7D , in some embodiments, all of the ligaments may be removed after installation. 
         [0053]      FIG. 8A  shows a side view of an exemplary initial assembly for an out of plane emitter set  120  formed by depositing emitter material onto a substrate  122 . In this example, a plurality of emitters  124 , 126  may be formed on an initially flat substrate  122  and a bend may be applied to the substrate  122  by hot forming, cold forming, or any suitable process. A V bend  128 , as shown in  FIG. 8B , a rounded bend  130 , as shown in  FIG. 8C , or any suitable bend may be applied to the substrate  122 . The bends  128 ,  130  may include any number of angles to achieve a desired out of plane relationship between the emitters  124 ,  126 . A suitable bend may be applied to achieve a particular orientation between the emitters  124 ,  126 , such as an angular orientation, a positional orientation, or both. In one or more embodiments, the substrate  122  may be bent and the plurality of emitters may be formed on the substrate  122  after bending. One or more portions of the substrate  122  may be removed by a suitable removal process, and one or more portions may be left in place to provide modal stiffness. In some embodiments, the substrate  122  may be left in place. As shown in  FIG. 8D , in some embodiments, substantially all of the substrate may be removed after installation. 
         [0054]      FIG. 9A  shows a side view of yet another exemplary initial assembly for an out of plane emitter set  140 . Similar to other embodiments, a plurality of emitters  144 ,  146  may be formed by depositing emitter material onto a substrate  142 . A plurality of ligaments  148  connecting the emitters  144 ,  146  may also be formed as part of the deposition process. A bend may be applied to the initially flat substrate  142  by hot forming, cold forming, or any suitable process. A “V” bend  150 , as shown in  FIG. 9B , a rounded bend  152 , as shown in  FIG. 9C , or any suitable bend may be applied to the substrate  142 . The bends  150 ,  152  may include any number of angles to achieve a desired out of plane relationship between the emitters  144 ,  146 . A suitable bend may be applied to achieve a particular orientation between the emitters  144 ,  146 , such as an angular orientation, a positional orientation, or both. In one or more embodiments, the substrate  142  may be bent and the plurality of emitters may be formed on the substrate  142  after bending. In some embodiments, the substrate  142  may be removed before the emitter set  140  is installed in the cathode assembly  50  as shown in  FIG. 9D . One or more ligaments may be removed for example, by a suitable removal process as mentioned above, and one or more ligaments  148  may be left in place to provide modal stiffness. In some embodiments, all the ligaments  148  may be left in place. Remaining ligaments  148  may be adapted to achieve specific current flows through the emitters  144 ,  146  as will be described below.  FIG. 9E  shows another embodiment of the emitters  144 ,  146  where all of the ligaments are removed after installation. 
         [0055]      FIG. 10A  illustrates a front view of an emitter set embodiment with ligaments  162 ,  164  at ends of the emitter set  160 . In this example, the emitter set  160  may be fabricated from a sheet of emitter material cut to produce emitters  166 ,  168  between the ligaments  162 ,  164 . The emitter set  160  may initially be fabricated as a substantially flat sheet of material.  FIG. 10B  shows a side view of the emitter set  160  where a bend may be applied to the ligaments  162 ,  164  by hot forming, cold forming, or any suitable process. While a round bend is shown in  FIG. 10B , a “V” bend or any suitable bend may be applied to the ligaments  162 ,  164  at any number of angles. As shown in  FIG. 100 , one or more of ligaments  162 ,  164  may be fabricated with one or more grooves  184  to facilitate bending. A suitable bend is applied to achieve a particular orientation between the emitters  166 ,  168 , such as an angular orientation, a positional orientation, or both. A suitable bend may be applied to achieve a particular orientation between the emitters  162 ,  164 , such as an angular orientation, a positional orientation, or both. One or more of the ligaments  162 ,  164  may be removed after installation, in some embodiments the ligaments  162 ,  164  may be left in place, and in other embodiments all the ligaments  162 ,  164  may be removed. Any of the ligaments  162 ,  164  remaining may be modified to achieve specific current flows through the emitters  72 ,  74  as will be described below. 
         [0056]      FIG. 11A  shows a front view of another embodiment of an emitter set  170  with ligaments  172 ,  174  at ends of the emitter set  170 . In this embodiment, the emitter set  170  may be formed by depositing emitter material onto a substrate  176  to form emitters  178 ,  180  along with ligaments  172 ,  174 . The emitter set  170  may initially be deposited on a substantially flat substrate.  FIG. 11B  shows a side view of the emitter set  170  where a bend  182  may be applied to the ligaments  172 ,  174  by hot forming, cold forming, or any suitable process. While a round bend is shown in  FIG. 11B , a “V” bend or any suitable bend may be applied to the ligaments  172 ,  174  at any number of angles to achieve a desired out of plane relationship between the emitters  178 ,  180 . A suitable bend may be applied to achieve a particular orientation between the emitters  178 ,  180 , such as an angular orientation, a positional orientation, or both. In one or more embodiments, the substrate  176  may be bent and the plurality of emitters may be formed on the substrate  176  after bending. Alternately, one or more of the ligaments  172 ,  174  may be removed before bending the substrate, for example, to relieve strain that may be encountered when bending the ligament material. As shown in  FIG. 110 , one or more of ligaments  172 ,  174  may be fabricated with one or more grooves  186  to facilitate bending. In some embodiments, the substrate  176  may be removed before the emitter set  170  is installed, while in other embodiments, the substrate  176  may be left in place during and subsequent to installation. In still further embodiments, the substrate  176  may be left in place during installation and then may be removed. One or more of the ligaments  172 ,  174  may be removed after installation, while in some embodiments the ligaments  172 ,  174  may be left in place, and in other embodiments all the ligaments  172 ,  174  may be removed. Any of the ligaments  172 ,  174  remaining may be modified to achieve specific current flows through the emitters  178 ,  180  as will be described below. 
         [0057]    Other techniques may also be utilized to provide emitters themselves with stiffness and rigidity. For example, as shown in  FIGS. 12A and 12B , an emitter  190 ,  192  may be fabricated with a bend, or a bend may be applied to an emitter after fabrication. In one or more embodiments, the emitters  190 ,  192  may be formed by depositing emitter material onto a substrate  194 ,  196 . The substrate  194  may have a round bend  198  as shown in  FIG. 12A , while the substrate  196  may have a “V” bend  200  as shown in  FIG. 12B . It should be understood that the substrates  194 ,  196  may include any bend suitable for adding rigidity to the emitters  190 ,  192 . In other embodiments, emitters  190 ,  192  may be fabricated from an emitter material sheet to which one or more bends may be applied by hot forming, cold forming, or any suitable process. The emitters may have meander conduction paths or any other suitable conduction path configuration.  FIG. 12C  shows an exemplary embodiment of an emitter  202  with a round bend  204  fabricated with ligaments  206 . The ligaments  206  may operate to fix a positional relationship between portions of the emitter  202  and may also be adapted to effect specific current paths through the portions of the emitter  202 .  FIG. 12D  illustrates an exemplary emitter  208  with a “V” bend  210  and fabricated with ligaments  212  which may also operate to fix a positional relationship between portions of the emitter  208  and may be adapted to effect specific current paths through the portions of the emitter  208 . Fabricating the emitters  190 ,  192 ,  202 ,  208  with a bend or applying a bend subsequent to fabrication may provide the emitters  190 ,  192 ,  202 ,  208  with a focused output. For example, an emitter installed in an X-ray tube with a convex or protruding side of a bend facing the anode may produce a divergent electron beam, while an emitter installed with a concave or indented side of a bend facing the anode may produce a convergent electron beam. 
         [0058]    The ligaments between the emitters disclosed herein may be adapted to achieve specific current flows through the emitters. The specific current flows may be used for various purposes including, for example, to compensate for cold spots and defects in the emitters.  FIG. 13  shows an exemplary emitter set  214  with electrical connectors  216 ,  218 ,  220 ,  222  for connecting the emitters  224 ,  226  to power supply  68 . Power from power supply  68  may be used to heat the emitters  224 ,  226  to stimulate electron emission. The emitter set  214  may have been initially fabricated with a number of ligaments which may have been removed after the emitters  224 ,  226  were installed. The emitter set  214  may be installed on a post to maintain structural rigidity, however, the post may cause a cold spot  229  when the emitter set  214  is heated. In at least one embodiment, a ligament  228  may be provided to supply a current path through the cold spot  229  to generate heat to compensate for the temperature difference at the cold spot. Additional ligaments may be utilized to provide heat for other cold spots. 
         [0059]    One or more ligaments may provide additional current paths to compensate for defects in emitters.  FIG. 14  shows emitters exemplary  230 ,  232 , each with a defect  234 ,  236 . Ligaments  238  and  240  may be utilized to provide a current path around defect  234 , and ligaments  242  and  244  may be utilized to provide a current path around defect  236 , thus providing viability even when more than one defect may occur. Current in the vicinity of the defects  234 ,  236  may be reduced and emitter life may be improved because the current is diverted over a limited length. 
         [0060]    Use of an emitter set instead of a single emitter may also provide additional current connection capabilities. As shown in  FIG. 15A , emitters  250 ,  252  may be connected in series resulting in a constant current through a defect  254 . As shown in  FIG. 15B , emitters  256 ,  258  may be connected in parallel resulting in a reduced current through a defect  260  and a longer emitter life. 
         [0061]    While the disclosed emitter sets have been described in terms of two emitters, it should be understood that any number of emitters may be utilized as part of any of the disclosed embodiments. 
         [0062]    While the disclosed substrates have been described and shown as a relatively flat rectangular prism or cuboid, it should be understood that the substrates may have any suitable shape or structure, for example, a cylindrical or polyhedron structure, and may be embodied as a rod with any suitable shape. Furthermore, it should be understood that while the emitters are shown as being deposited or otherwise placed on a top side of the substrates, the emitters may be placed on any side or surface of the substrates. 
         [0063]    Various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings. However, all such and similar modifications of the teachings of the disclosed embodiments will still fall within the scope of the disclosed embodiments. 
         [0064]    While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. Furthermore, the skilled artisan will recognize the interchangeability of various features among different embodiments and that various aspects of different embodiments may be combined together. Similarly, the various method steps and features described, as well as other known equivalents for each such methods and feature, can be mixed and matched by one of ordinary skill in this art to construct additional assemblies and techniques in accordance with principles of this disclosure. In addition, many modifications may be made to adapt a particular 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. 
         [0065]    Furthermore, some of the features of the exemplary embodiments could be used to advantage without the corresponding use of other features. As such, the foregoing description should be considered as merely illustrative of the principles of the disclosed embodiments and not in limitation thereof.