Abstract:
Provided is a display apparatus that improves luminous efficiency and reduces a driving voltage. The display apparatus includes: a first electrode and a second electrode separated from each other; an electron accelerating layer interposed between the first and second electrodes and accelerating and emitting electrons when a voltage is applied between the first and second electrodes; and a light emitting layer interposed between the second electrode and the electron accelerating layer and producing visible rays by the electrons emitted from the electron accelerating layer.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims the priority of Korean Patent Application No. 10-2005-0103435, filed on Oct. 31, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present embodiments relate to a display apparatus having a new structure in which luminous efficiency is high and a driving voltage is low. 
   2. Description of the Related Art 
   Apparatuses using an inorganic electroluminescence device as apparatuses for displaying an image have been studied in various ways. A traditional structure of such an inorganic electroluminescence device is disclosed in U.S. Pat. Nos. 5,543,237 and 5,648,181. The inorganic electroluminescence device has a structure shown in  FIG. 1 . A transparent indium tin oxide (ITO) electrode  2  is formed on a substrate  1 , and a first dielectric layer  3  is formed on the ITO electrode  2 . An inorganic light emitting layer  4  in which electroluminescence occurs is formed on the first dielectric layer  2 . A second dielectric layer  5  and a back electrode  6  are sequentially stacked on the inorganic light emitting layer  4 . This stacked structure is isolated from the outside by a protective layer (not shown) to be formed on the back electrode  6 . The inorganic electroluminescence device is driven by an alternating current (AC). An inorganic light emitting body collides with electrons accelerated by a high electric field, is excited and then stabilized, thereby producing visible rays for realizing an image. Thus, in order to achieve high efficiency, a large amount of electrons are accelerated with high energy so that a driving voltage is increased. 
   In addition, since a plasma display panel (PDP) requires high energy to ionize a discharge gas, the driving voltage is large and luminous efficiency is lowered. 
   SUMMARY OF THE INVENTION 
   The present embodiments provide a plasma display panel (PDP) having a new structure in which luminous efficiency is high and a driving voltage is low. 
   According to an aspect of the present embodiments, there is provided a display apparatus, the display apparatus including: a first electrode and a second electrode separated from each other; an electron accelerating layer interposed between the first and second electrodes and accelerating and emitting electrons when a voltage is applied between the first and second electrodes; and a light emitting layer interposed between the second electrode and the electron accelerating layer and producing visible rays by the electrons emitted from the electron accelerating layer. 
   According to another aspect of the present embodiments, there is provided a display apparatus, the display apparatus including: a first electrode and a second electrode separated from each other; an electron accelerating layer interposed between the first and second electrodes and accelerating and emitting electrons when a voltage is applied between the first and second electrodes; and a light emitting layer formed outside the second electrode and producing visible rays by the electrons emitted from the electron accelerating layer. 
   According to another aspect of the present embodiments, there is provided a display apparatus, the display apparatus including: a first substrate and a second substrate opposing each other; a first electrode and a second electrode formed between the first substrate opposing the second substrate and the second substrate to be separated from each other; a first electron accelerating layer and a second electron accelerating layer formed on the first and second electrodes, respectively, and accelerating and emitting electrons when a voltage is applied between the first and second electrodes; and a light emitting layer interposed between the first and second accelerating layers and producing visible rays by the electrons emitted from the first and second electron accelerating layers. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other aspects and advantages of the present embodiments will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
       FIG. 1  is a schematic cross-sectional view of a conventional inorganic electroluminescence device; 
       FIG. 2  is a schematic cross-sectional view of a display apparatus according to an embodiment; 
       FIG. 3  is a schematic view of quantum dots; 
       FIG. 4  is a schematic cross-sectional view of a display apparatus according to another embodiment; 
       FIG. 5  is a schematic cross-sectional view of a display apparatus according to another embodiment; 
       FIG. 6  is a schematic cross-sectional view of a display apparatus according to another embodiment; 
       FIG. 7  is a schematic cross-sectional view of a display apparatus according to another embodiment; 
       FIG. 8  is a schematic cross-sectional view of a display apparatus according to another embodiment; and 
       FIG. 9  is a schematic cross-sectional view of a display apparatus according to another embodiment. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present embodiments will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments are shown. Like reference numerals denote like elements. 
     FIG. 2  is a schematic cross-sectional view of a display apparatus  100  according to an embodiment. Referring to  FIG. 2 , a first electrode  131  is formed on a substrate  110 . The substrate  110  may be, for example, a glass substrate having a high visible-rays transmission ratio and may also be colored for bright room contrast improvement. In addition, the substrate  110  can be formed of plastics and thus may have a flexible structure. 
   The first electrode  131  may be formed of a transparent conductive material, such as indium tin oxide (ITO) having a high visible-rays transmission ratio. 
   An electron accelerating layer  140  is formed on the first electrode  131 . The electron accelerating layer  140  may be formed of a material that accelerates electrons, for example, oxidized porous silicon. Examples of the oxidized porous silicon include oxidized porous polysilicon and oxidized porous amorphous silicon. In addition, the electron accelerating layer  140  may include carbon nanotubes (CNTs) or boron nitride bamboo shoot (BNBS). Here, BNBS is the name of an sp 3  combination 5H-BN which has been developed by Japanese national institute for material science (NIMS) and published on March 2004 (29a-YC-5, Extended Abstract of Spring meeting of Japan Society of Applied Physics). It is well-known that this BNBS is very stable and has extreme hardness similar to the hardness of diamond. In addition, BNBS has a transparent property in the range of wavelength of about 380 to about 780 nm which is the visible rays region and has negative electron affinity and thus has a very excellent electron emission property. 
   A light emitting layer  115  is formed on the electron accelerating layer  140 . The light emitting layer  115  is a material layer that produces visible rays by collision with electrons, and a detailed description thereof will be described later. The light emitting layer  115  may be formed of an inorganic material. However, the present embodiments are not limited to this and the light emitting layer  115  may include quantum dots. Characteristics of the quantum dots will now be described. 
   Since atoms are aggregated in a solid emission material, an energy band is formed. In this case, in the solid emission material, electrons excited by an energy received from the outside are stabilized from a conduction band to a valence band so that visible rays corresponding to a difference between the conduction band and the valence band are produced. In the quantum dots, there is no interference between the atoms. Thus, if an energy is received from the outside, electrons excited at an atom energy level are stabilized and visible rays are produced. Thus, theoretical quantum efficiency of the quantum dots can be improved up to 100% and electrons can be excited even at a low voltage so that luminous efficiency can be improved. In addition, since a light emitting layer can be formed using a printing process, it is advantageous to make a display apparatus bigger. An example of a quantum dot is illustrated in  FIG. 3 . Referring to  FIG. 3 , a quantum dot  80  includes a core  81 , a shell  82 , and caps  83 . CdSe can be used for the core  81 . The shell  82  can be formed of ZnS and surrounds the core  81 . The caps  83  can be formed of trioctylphosphine oxide (TOPO) and support the core  81  and the shell  82 . The core  81 , the shell  82 , and the caps  83  can have a single layer structure or a multi-layer structure but may have a single layer structure for luminous efficiency. 
   Referring to  FIG. 2 , a second electrode  132  is formed on the light emitting layer  115 . The second electrode  132  may extend to be parallel to the first electrode  131  or to cross it. The second electrode  132  may be formed of ITO or metal having high conductivity, such as copper. In addition, since the second electrode  132  has no direct relation with a visible-rays transmission ratio, the thickness of the second electrode  132  can be large and thus it is advantageous for an increased lifetime of the display apparatus. 
   The operation of the display apparatus  100  having the above structure will now be described. The case where the light emitting layer  115  is formed of an inorganic material will now be described. 
   Voltages having various shapes can be applied to the first electrode  131  and the second electrode  132 . If voltages applied to the first electrode  131  and the second electrode  132  are V 1  and V 2 , respectively, a predetermined voltage is applied to each of the first and second electrodes  131  and  132  so as to satisfy V 1 &lt;V 2 . The voltages applied to the first electrode  131  and the second electrode  132  can be direct current (DC) voltages or alternating current (AC) voltages. If the voltages are applied to the display apparatus  100  and a strong electric field of more than 1MV/cm is formed due to the voltages applied to the first electrode  131  and the second electrode  132 , electrons trapped at an interface level between the electron accelerating layer  140  and the light emitting layer  115  are emitted so that electrons are tunneled into the conduction band of the light emitting layer  115 . In particular, according to the current embodiment, since the electrons are accelerated by the electron accelerating layer  140  and tunneled into the light emitting layer  115  with a large initial incident energy, luminous efficiency can be improved and the driving voltages applied to the first electrode  131  and the second electrode  132  can be reduced. 
   The electrons emitted into the conduction band of the light emitting layer  115  obtain a sufficient energy to be accelerated by an external electric field and to excite a light emitting center and then collide with the outermost electrons of the light emitting center, and the light emitting center is excited. At this time, the electrons in an excited state are stabilized to the base state from an excited state and visible rays are emitted due to the energy difference. In addition, part of the electrons with a high energy collide with a light emitting body and are ionized, thereby emitting secondary electrons. These electrons lose energy when colliding with the light emitting center. The primary electrons and secondary electrons which do not collide with the light emitting center move into a high energy state, and then excite a material of the light emitting center and are trapped at an interface level of the second electrode  132 . 
   Even when the light emitting layer  115  includes quantum dots, the electrons accelerated and emitted from the electron accelerating layer  140  and having a high energy collide with the quantum dots so that the electrons of the quantum dots can be effectively excited. The excited electrons are stabilized and visible rays are produced. Thus, due to characteristics of the electron accelerating layer  140  and the quantum dots, luminous efficiency can be improved and the driving voltages applied to the first electrode  131  and the second electrode  132  can be reduced. 
     FIG. 4  is a schematic partially cross-sectional view of a display apparatus  200  according to another embodiment. Referring to  FIG. 4 , a first electrode  231  is formed on a substrate  210 . The first electrode  231  may be formed of a transparent conductive material, such as ITO having a high visible-rays transmission ratio. 
   A first dielectric layer  251  is formed on the first electrode  231 . In addition, an electron accelerating layer  240  is formed on the first electrode  231 . The electron accelerating layer  240  may include oxidized porous silicon. Examples of the oxidized porous silicon include oxidized porous polysilicon and oxidized porous amorphous silicon. In addition, the electron accelerating layer  240  may include carbon nanotubes (CNTs) or boron nitride bamboo shoot (BNBS). 
   A light emitting layer  215  is formed on the electron accelerating layer  240 . The light emitting layer  215  may be formed of an inorganic material or a material including quantum dots. 
   A second dielectric layer  252  is formed on the light emitting layer  215 . In addition, a second electrode  232  is formed on the second dielectric layer  252 . The second electrode  232  may extend to be parallel to the first electrode  231  or to cross it. The second electrode  232  may be formed of ITO or metal having high conductivity, such as copper. 
   Voltages having various shapes can be applied to the first electrode  231  and the second electrode  232 . If voltages applied to the first electrode  231  and the second electrode  232  are V 1  and V 2 , respectively, a predetermined voltage is applied to each of the first and second electrodes  231  and  232  so as to satisfy V 1 &lt;V 2 . The voltages applied to the first electrode  231  and the second electrode  232  can be direct current (DC) voltages or alternating current (AC) voltages. If the voltages are applied to the display apparatus  200  and a strong electric field of more than 1 MV/cm is formed due to the voltages applied to the first electrode  231  and the second electrode  232 , electrons are accelerated inside the electron accelerating layer  240  and incident on the light emitting layer  215 . The electrons excite the light emitting layer  215  and the light emitting layer  215  is stabilized so that visible rays are produced. At this time, since due to the electron accelerating layer  240 , the energy level of the electrons incident on the light emitting layer  215  is high, luminous efficiency can be improved and the driving voltages applied to the first electrode  231  and the second electrode  232  can be reduced. In particular, when the second electrode  232  is in a grounded state, the electrons which transmit the light emitting layer  215  and the second dielectric layer  252  can be emitted. 
     FIG. 5  is a schematic partially cross-sectional view of a display apparatus  300  according to another embodiment. Referring to  FIG. 5 , a first electrode  331  is formed on a substrate  310 . The first electrode  331  may be formed of a transparent conductive material, such as ITO having a high visible-rays transmission ratio. 
   An electron accelerating layer  340  is formed on the first electrode  331 . The electron accelerating layer  340  may be an insulating layer. A third electrode  333  is formed on the electron accelerating layer  340 . The third electrode  333  may be formed of a transparent conductive material, such as ITO having a high visible-rays transmission ratio. The first electrode  331 , the electron accelerating layer  340 , and the third electrode  333  constitute a metal-insulator-metal (MIM) structure. 
   A light emitting layer  315  is formed on the electron accelerating layer  340 . The light emitting layer  315  may be formed of an inorganic material or a material including quantum dots. 
   A second electrode  332  is formed on the light emitting layer  315 . The second electrode  332  may extend to be parallel to the first electrode  331  or to cross it. The second electrode  332  may be formed of ITO or metal having high conductivity, such as copper. 
   Voltages having various shapes can be applied to the first electrode  331 , the second electrode  332 , and the third electrode  333 . If voltages applied to the first electrode  331 , the second electrode  332 , and the third electrode  333  are V 1 , V 2 , and V 3 , respectively, a predetermined voltage is applied to each of the first, second, and third electrodes  331 ,  332 , and  333  so as to satisfy V 1 &lt;V 3 ≦V 2 . The voltages applied to the first electrode  331 , the second electrode  332 , and the third electrode  333  can be direct current (DC) voltages or alternating current (AC) voltages. If the voltages are applied to the display apparatus  300 , electrons starting from the first electrode  331  tunnel the electron accelerating layer  340  and are accelerated and then pass through the third electrode  333  and are incident on the light emitting layer  315 . The electrons excite the light emitting layer  315  and the light emitting layer  315  is stabilized so that visible rays are produced. At this time, since due to the electron accelerating layer  340 , the energy level of the electrons incident on the light emitting layer  315  is high, luminous efficiency can be improved and the driving voltages applied to the first electrode  331 , the second electrode  332 , and the third electrode  333  can be reduced. In particular, when the second electrode  332  is in a grounded state, the electrons which transmit the light emitting layer  315  can be emitted. 
     FIG. 6  is a schematic partially cross-sectional view of a display apparatus  400  according to another embodiment. Referring to  FIG. 6 , a first electrode  431  is formed on a substrate  410 . The first electrode  431  may be formed may be formed of a transparent conductive material, such as ITO having a high visible-rays transmission ratio. 
   An electron accelerating layer  440  is formed on the first electrode  431 . The electron accelerating layer  440  may include oxidized porous silicon. Examples of oxidized porous silicon include oxidized porous poly silicon and oxidized porous amorphous silicon. In addition, the electron accelerating layer  440  may include carbon nanotubes (CNTs) or boron nitride bamboo shoot (BNBS). 
   A second electrode  432  is formed on the electron accelerating layer  440 . The second electrode  432  may extend to be parallel to the first electrode  431  or to cross it. When the electron accelerating layer  440  is an insulating layer, the first electrode  431 , the electron accelerating layer  440 , and the second electrode  432  constitute an MIM structure. 
   A light emitting layer  415  is formed on the second electrode  432 . The light emitting layer  415  may be formed of an inorganic material or a material including quantum dots. 
   Voltages having various shapes can be applied to the first electrode  431  and the second electrode  432 . If voltages applied to the first electrode  431  and the second electrode  432  are V 1  and V 2 , respectively, a predetermined voltage is applied to each of the first and second electrodes  431  and  432  so as to satisfy V 1 &lt;V 2 . The voltages applied to the first electrode  431  and the second electrode  432  can be direct current (DC) voltages or alternating current (AC) voltages. If the voltages are applied to the display apparatus  400 , due to the voltages applied to the first electrode  431  and the second electrode  432 , electrons are accelerated inside the electron accelerating layer  440  and incident on the light emitting layer  415 . The electrons excite the light emitting layer  415  and the light emitting layer  415  is stabilized so that visible rays are produced. At this time, since due to the electron accelerating layer  440 , the energy level of the electrons incident on the light emitting layer  415  is high, luminous efficiency can be improved and the driving voltages applied to the first electrode  431  and the second electrode  432  can be reduced. 
     FIG. 7  is a schematic partially cross-sectional view of a display apparatus  500  according to another embodiment. Referring to  FIG. 7 , a first substrate  510  and a second substrate  520  are opposed to each other at predetermined intervals. A plurality of barrier ribs  513  are disposed between the first substrate  510  and the second substrate  520  and form a plurality of cells  514  by partitioning a space between the first substrate  510  and the second substrate  520 . 
   First electrodes  532  are disposed on the first substrate  510  that opposes the second substrate  520 . In addition, second electrodes  532  are disposed on the second substrate  520  that opposes the first substrate  510 . In  FIG. 7 , the first electrodes  531  extend to be parallel to the second electrodes  532 . However, the present embodiments are not limited to this and the first electrodes  531  may extend to cross the second electrodes  532 . 
   First electron accelerating layers  541  and second electron accelerating layers  542  are disposed on the first electrodes  531  and the second electrodes  532 , respectively. The first electron accelerating layers  541  and the second electron accelerating layers  542  may include oxidized porous silicon. Examples of oxidized porous silicon include oxidized porous poly silicon and oxidized porous amorphous silicon. In addition, the first electron accelerating layers  541  and the second electron accelerating layers  542  may include CNTs or BNBS. 
   Light emitting layers  515  are formed between the first electron accelerating layers  541  and the second electron accelerating layers  542 . The light emitting layers  515  may directly contact one of the first electron accelerating layers  541  or the second electron accelerating layers  542 . However, the light emitting layers  515  may closely contact the first electron accelerating layers  541  and the second electron accelerating layers  542  for luminous efficiency. The light emitting layers  515  may be formed of an inorganic material or a material including quantum dots. 
   In  FIG. 7 , both side surfaces of each of the first electrodes  531 , the second electrodes  532 , the first electron accelerating layers  541 , the second electron accelerating layers  542 , and the light emitting layers  515  contact the barrier ribs  513  but the present embodiments are not limited to this. 
   Voltages having various shapes can be applied to the first electrodes  531  and the second electrodes  532 . If voltages applied to the first electrodes  531  and the second electrodes  532  are V 1  and V 2 , respectively, AC power is applied to V 1  and V 2 . If the voltages are applied to the display apparatus  500 , due to the voltages applied to the first electrodes  531  and the second electrodes  532 , electrons are accelerated inside the first electron accelerating layers  541  and the second electron accelerating layers  542  and incident on the light emitting layers  515 . The electrons excite the light emitting layers  515  and the light emitting layers  515  are stabilized so that visible rays are produced. At this time, since due to the first electron accelerating layers  541  and the second electron accelerating layers  542 , the energy level of the electrons incident on the light emitting layers  515  is high, luminous efficiency can be improved and the driving voltages applied to the first electrode  531  and the second electrode  532  can be reduced. 
     FIG. 8  is a schematic partially cross-sectional view of a display apparatus  600  according to another embodiment. Referring to  FIG. 8 , a first substrate  610  and a second substrate  620  are opposed to each other at predetermined intervals. A plurality of barrier ribs  613  are disposed between the first substrate  610  and the second substrate  620  and form a plurality of cells  614  by partitioning a space between the first substrate  610  and the second substrate  620 . 
   First electrodes  631  are disposed on the first substrate  610  that opposes the second substrate  620 . In addition, second electrodes  632  are disposed on the second substrate  620  that opposes the first substrate  610 . In  FIG. 8 , the first electrodes  631  extend to be parallel to the second electrodes  632 . However, the present embodiments are not limited to this and the first electrodes  631  may extend to cross the second electrodes  632 . 
   First dielectric layers  633  and second dielectric layers  634  are disposed on the first electrodes  631  and the second electrodes  632 , respectively. In addition, first electron accelerating layers  641  and second electron accelerating layers  642  are disposed on the first dielectric layers  633  and the second dielectric layers  634 , respectively. The first electron accelerating layers  641  and the second electron accelerating layers  642  may include oxidized porous silicon. Examples of oxidized porous silicon include oxidized porous poly silicon and oxidized porous amorphous silicon. In addition, the first electron accelerating layers  641  and the second electron accelerating layers  642  may include CNTs or BNBS. 
   Light emitting layers  615  are formed between the first electron accelerating layers  641  and the second electron accelerating layers  642 . The light emitting layers  615  may directly contact one of the first electron accelerating layers  641  or the second electron accelerating layers  642 . However, the light emitting layers  615  may closely contact the first electron accelerating layers  641  and the second electron accelerating layers  642  for luminous efficiency. The light emitting layers  615  may be formed of an inorganic material or a material including quantum dots. 
   In  FIG. 8 , both side surfaces of each of the first electrodes  631 , the second electrodes  632 , the first dielectric layers  633 , the second dielectric layers  634 , the first electron accelerating layers  641 , the second electron accelerating layers  642 , and the light emitting layers  615  contact the barrier ribs  613  but the present embodiments are not limited to this. 
   Voltages having various shapes can be applied to the first electrodes  631  and the second electrodes  632 . If voltages applied to the first electrodes  631  and the second electrodes  632  are V 1  and V 2 , respectively, AC power is applied to V 1  and V 2 . If the voltages are applied to the display apparatus  500 , due to the voltages applied to the first electrodes  631  and the second electrodes  632 , electrons are accelerated inside the first electron accelerating layers  641  and the second electron accelerating layers  642  and incident on the light emitting layers  615 . The electrons excite the light emitting layers  615  and the light emitting layers  615  are stabilized so that visible rays are produced. At this time, since due to the first electron accelerating layers  641  and the second electron accelerating layers  642 , the energy level of the electrons incident on the light emitting layers  615  is high, luminous efficiency can be improved and the driving voltages applied to the first electrode  631  and the second electrode  632  can be reduced. 
     FIG. 9  is a schematic partially cross-sectional view of a display apparatus  700  according to another embodiment. Referring to  FIG. 9 , a first electrode  731  is formed on a substrate  710 . The first electrode  731  may be formed of one or various metals having high conductivity. 
   An electron accelerating layer  740  is formed on a side surface of the first electrode  731 . The electron accelerating layer  740  includes oxidized porous silicon. Examples of the oxidized porous silicon include oxidized porous poly silicon and oxidized porous amorphous silicon. In addition, the electron accelerating layer  740  may include CNTs or BNBS. 
   A light emitting layer  715  is formed on a side surface of the electron accelerating layer  740 . The light emitting layer  715  may be formed of an inorganic material or a material including quantum dots. 
   A second electrode  732  is formed on a side surface of the light emitting layer  715 . The second electrode  732  may extend to be parallel to the first electrode  731  or to cross it. The second electrode  732  may be formed of ITO and/or metal having high conductivity, such as copper. 
   Voltages having various shapes can be applied to the first electrode  731  and the second electrode  732 . If voltages applied to the first electrode  731  and the second electrode  732  are V 1  and V 2 , respectively, a predetermined voltage is applied to each of the first and second electrodes  731  and  732  so as to satisfy V 1 &lt;V 2 . The voltages applied to the first electrode  731  and the second electrode  732  can be direct current (DC) voltages or alternating current (AC) voltages. If the voltages are applied to the display apparatus  700 , due to the voltages applied to the first electrode  731  and the second electrode  732 , electrons are accelerated inside the electron accelerating layer  740  and incident on the light emitting layer  715 . The electrons excite the light emitting layer  715  and the light emitting layer  715  is stabilized so that visible rays are produced. At this time, since due to the electron accelerating layer  740 , the energy level of the electrons incident on the light emitting layer  715  is high, luminous efficiency can be improved and the driving voltages applied to the first electrode  731  and the second electrode  732  can be reduced. In particular, when the second electrode  732  is in a grounded state, the electrons which transmit the light emitting layer  715  can be emitted. 
   In the display apparatus  700  having the above structure, its thickness can be remarkably reduced. In addition, since the first electrode  731  and the second electrode  732  do not disturb a path of visible rays, they can also be formed of metal having high conductivity, such as copper, instead of ITO. 
   As described above, in the display apparatus according to the present embodiments, since electrons are accelerated by the electron accelerating layer and are incident on the light emitting layer, luminous efficiency can be improved and driving voltages can be reduced. In addition, since the display apparatus has a simple structure that can be easily made large, it can be applied to large display apparatuses or backlights. 
   While the present embodiments have been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present embodiments as defined by the following claims.