Abstract:
According to one exemplary embodiment, a wide temperature range dielectric absorber includes a dielectric absorber comprising a blend of lanthanum oxide, strontium oxide, and cobalt oxide, and is represented by (1−z)[La 1−x Sr x CoO 3±y ]+z[La 2−x Sr x CoO 4±y ]. The dielectric absorber includes a first crystalline structure existing independently from a second crystalline structure causing the dielectric absorption composition to have a wide temperature range of electromagnetic radiation absorption. In one embodiment, the first crystalline structure is a perovskite crystalline structure and the second crystalline structure is a potassium nickel fluoride crystalline structure.

Description:
The present application claims the benefit of and priority to a pending provisional patent application entitled “High Temperature Dielectric Absorber,” Ser. No. 60/811,919 filed on Jun. 8, 2006. The disclosure in that pending provisional application is hereby incorporated fully by reference into the present application. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to the field of dielectric absorbers. More specifically, the invention relates to dielectric absorbers of electromagnetic radiation. 
   2. Background Art 
   In many applications, such as aviation applications, it can be desirable for a structure to be “invisible” to or undetectable. For example, aircraft invisible to electromagnetic radiation is less likely to be spotted on a radar system, which can be desirable in some applications. Conventional approaches have utilized oxide or dielectric absorbent coatings comprising ferromagnetic materials to reduce reflection of electromagnetic waves. However, a ferromagnetic material loses its characteristic ferromagnetic ability at temperatures above the Curie temperature for that material, causing the net magnetization of the ferromagnetic material to be zero. 
   In applications subjected to a broad temperature range including very high temperatures, such as up to 1100° C., it has proven very difficult to provide a dielectric absorber capable of uniformly absorbing electromagnetic radiation. For example, one conventional method for shielding an aircraft from electromagnetic radiation utilizes a single material dielectric absorber coated on the aircraft. However, many components of an aircraft can reach temperatures in excess of the effective electromagnetic absorption temperature, causing the absorber coating to be ineffective at absorbing electromagnetic radiation at that temperature. Furthermore, in applications subjected to a very broad temperature range, a single material dielectric absorber is ineffective at providing uniform electromagnetic radiation absorption over the entire temperature range. 
   Thus there is a need in the art for a high temperature dielectric absorber with a wider temperature range of electromagnetic absorption. 
   SUMMARY OF THE INVENTION 
   A wide temperature range dielectric absorber, substantially as shown in and/or described in connection with at least one of the figures, and as set forth more completely in the claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a ternary phase diagram of dielectric absorbers in accordance with one embodiment of the present invention. 
       FIG. 2  is a plot displaying the absorption characteristics of dielectric absorbers in accordance with one embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention is directed to a wide temperature range dielectric absorber. Although the invention is described with respect to specific embodiments, the principles of the invention, as defined by the claims appended herein, can obviously be applied beyond the specifically described embodiments of the invention described herein. Moreover, in the description of the present invention, certain details have been left out in order to not obscure the inventive aspects of the invention. The details left out are within the knowledge of a person of ordinary skill in the art. 
   The drawings in the present application and their accompanying detailed description are directed to merely exemplary embodiments of the invention. To maintain brevity, other embodiments of the invention which use the principles of the present invention are not specifically described in the present application and are not specifically illustrated by the present drawings. 
     FIG. 1  represents ternary phase diagram  100  at 1100° C. in air of a ternary system including a primary component group of lanthanum oxide, strontium oxide, and cobalt oxide, in accordance with one embodiment of the present invention. Ternary phase diagram  100  further includes trapezoidal dielectric region  108 , which is bounded by points  110 ,  112 ,  114 , and  116 . In the present embodiment, line  118  extends from point  112  to point  114 , line  120  extends from point  110  to point  116 , line  122  extends along line  124  from point  114  to point  116 , and line  126  extends from point  112  to point  110 . 
   Line  118  represents the upper bound of trapezoidal dielectric region  108 , and extends from point  112  to point  114 . The chemical formula of the composition along line  118  is La 1−x Sr x CoO 3±y  where “x” can have a value ranging from 0 to 0.9. The value of “x” is one factor in determining the value of “y,” which is largely based on the oxidation state of the cobalt. In the present embodiment, the composition along line  118  has the perovskite crystalline structure. The chemical formula of the composition at point  112  is known to be LaCoO 3 , and does not contain any strontium oxide because it lies on the line between lanthanum oxide vertex  102  and cobalt oxide vertex  106 . Moving from point  112  towards point  114  along line  118  changes the chemical composition of the ternary system by increasing the mole percent of strontium oxide in the composition and decreasing the mole percent of lanthanum oxide in the composition. The mole percent of cobalt oxide in the composition remains constant along line  118 . 
   Line  120  represents the lower bound of trapezoidal dielectric region  108 , and extends from point  110  to point  116 . The chemical formula of the composition along line  120  is La 2−x Sr x CoO 4±y , where “x” can have a value ranging from 0 to 0.9. The value of “x” is one factor in determining the value of “y,” which is largely based on the oxidation state of the cobalt. In the present embodiment, the composition along line  120  has the potassium nickel fluoride crystalline structure. The chemical formula of the composition at point  110  is known to be La 2 CoO 4 , and does not contain any strontium oxide because it lies on the line between lanthanum oxide vertex  102  and cobalt oxide vertex  106 . Moving from point  110  towards point  116  along line  120  changes the chemical composition of the ternary system by increasing the mole percent of strontium oxide in the composition and decreasing the mole percent of lanthanum oxide in the composition. The mole percent of cobalt oxide in the composition remains constant along line  120 . 
   Line  122  represents the right-hand bound of trapezoidal dielectric region  108 , and extends from point  114  to point  116  along line  124 . Line  124  is created by drawing a line from the cobalt oxide vertex  106  through the 90 mole percent marker on the line between lanthanum oxide vertex  102  and strontium oxide vertex  104 . Line  124  intersects line  118  at point  114 , and intersects line  120  at point  116 . 
   Line  126  represents the left-hand bound of trapezoidal dielectric region  108 , and extends from point  112  to point  110  along the line between lanthanum oxide vertex  102  and cobalt oxide vertex  106 . Line  126  intersects line  118  at point  112 , and intersects line  120  at point  110 . The composition represented by line  126  contains only lanthanum oxide and cobalt oxide. 
   In the present embodiment, any point within the portion of trapezoidal dielectric region  108  that is below line  118  and above line  120  represents a composition that includes either the perovskite crystalline structure or the potassium nickel fluoride crystalline structure, or both. The chemistry of the composition represented by trapezoidal dielectric region  108  is unique in that two independent phases (i.e., the perovskite crystalline structure and the potassium nickel fluoride crystalline structure) co-exist together in a single composition. The mole percent of the individual oxides (i.e., lanthanum oxide, strontium oxide, and cobalt oxide) in the composition depends on the specific location selected within trapezoidal dielectric region  108 . For example, the mole percent of cobalt oxide in the composition increases towards line  118  and decreases towards line  120 . Similarly, moving from line  126  towards line  122  increases the mole percent of strontium oxide in the composition and decreases the mole percent of lanthanum oxide in the composition. The formula (1−z)[La 1−x Sr x CoO 3±y ]+z[La 2−x Sr x CoO 4±y ] represents the chemical composition of any point within trapezoidal dielectric region  108 . In this formula, “x” can have a value ranging from 0 to 0.9, and “z” can have a value ranging from 0 to 1. The value of “x” is one factor in determining the value of “y,” which is largely based on the oxidation state of the cobalt. 
   In the embodiment of the present invention in  FIG. 1 , ternary phase diagram  100  represents a composition of lanthanum oxide, strontium oxide, and cobalt oxide. The portion of ternary phase diagram  100  found within trapezoidal dielectric region  108  represents a stable composition of these oxides and forms either the perovskite or the potassium nickel fluoride crystalline structure, or both. Each individual phase contains two different valence states of cobalt allowing for different absorption mechanisms. In addition, by combining these chemically compatible materials that have different temperature-dependent properties for absorption of light or other electromagnetic waves, such as those generated and used in the radar technology, the embodiment of the invention in  FIG. 1  advantageously creates a two-phase oxide dielectric absorber (i.e. a two-phase oxide material or coating) with a flatter curve for absorption of electromagnetic waves or light over a wider range of temperatures. This is called a two-phase oxide dielectric absorber because two atomic arrangements exist in the composition (i.e., both the perovskite and potassium nickel fluoride crystalline structures). Because the two arrangements are chemically compatible throughout the entire temperature range (i.e. up to 1100° C.), they are able to co-exist together and do not react to form a third phase. 
     FIG. 2  shows plot  200  displaying the absorption characteristics of dielectric absorbers, in accordance with one embodiment of the present invention. Plot  200  displays the percentage of absorption of electromagnetic radiation as temperature increases for single-phase dielectric absorption material  202 , single-phase dielectric absorption material  204 , and two-phase dielectric absorption material  206 . 
   As shown in  FIG. 2 , single-phase dielectric absorption material  202  absorbs a high percentage of electromagnetic radiation from temperature  208  to temperature  210 . For example, single-phase dielectric absorption material  202  might effectively absorb electromagnetic radiation from 700° C. to 900° C. As shown in  FIG. 2 , once the temperature increases beyond temperature  210 , single-phase dielectric absorption material  202  does not effectively absorb electromagnetic radiation, as the absorption curve tapers off. Similarly, single-phase dielectric absorption material  204  displays a high percentage of electromagnetic absorption from temperature  210  to temperature  212 . For example, single-phase dielectric absorption material  204  might effectively absorb electromagnetic radiation from 900° C. to 1100° C. As shown in  FIG. 2 , once the temperature increases beyond temperature  212 , single-phase dielectric absorption material  204  does not effectively absorb electromagnetic radiation, as the absorption curve tapers off. 
   An embodiment of the present invention, as shown in  FIG. 2 , effectively combines two single-phase dielectric absorption materials, such as single-phase dielectric absorption materials  202  and  204 , to form two-phase dielectric absorption material  206  with a very broad temperature range of absorption. For example, by combining single-phase dielectric absorption materials  202  and  204  to form two-phase dielectric absorption material  206 , the temperature range of absorption can be expanded to 700° C. to 1100° C. Since two-phase dielectric absorption material  206  provides uniform absorption of electromagnetic radiation across a broader temperature range, the present invention advantageously provides for more effective electromagnetic absorption in high temperature applications. Two-phase dielectric absorption material  206  includes both the perovskite crystalline structure and the potassium nickel fluoride crystalline structure, so two atomic arrangements exist in two-phase dielectric absorption material  206 . Because the two arrangements are chemically compatible throughout the entire temperature range (i.e. up to 1100° C.), they are able to co-exist together and do not react to form a third phase. 
   From the above description of the invention it is manifest that various techniques can be used for implementing the concepts of the present invention without departing from its scope. Moreover, while the invention has been described with specific reference to certain embodiments, a person of ordinary skill in the art would appreciate that changes can be made in form and detail without departing from the spirit and the scope of the invention. Thus, the described embodiments are to be considered in all respects as illustrative and not restrictive. It should also be understood that the invention is not limited to the particular embodiments described herein but is capable of many rearrangements, modifications, and substitutions without departing from the scope of the invention. 
   Thus, wide temperature range dielectric absorber has been described.