An aircraft transparency has a heatable member to remove fog, ice and snow from the outer surface of the transparency. The heatable member includes a pair of spaced parallel bus bars with the ends of the bus bars offset from one another, and a coating including a plurality of spaced segments of an electrically conductive coating electrically connecting the bus bars. The ratio of the major diagonal to the minor diagonal is in the range of greater than 1 to 1.25 to more uniformly heat the coating and the outer surface of the transparency.

FIELD OF THE INVENTION

This invention relates to a heatable transparency, e.g. a vehicle transparency, and in particular to a heatable aerospace, e.g. an airplane windshield.

DISCUSSION OF THE TECHNOLOGY

Heatable transparencies, e.g. windshields for vehicles, e.g. airplanes and automobiles, are disclosed, among other places, in U.S. Pat. Nos. 3,789,191; 3,789,192; 3,790,752; 3,794,809; 4,543,466; 4,820,902; 5,213,828 and 7,132,625, which patents in their entirety are hereby incorporated by reference. In general a pair of spaced bus bars is applied to a surface of a glass or plastic sheet and an electrically conductive member is applied onto the surface between and in electrical contact with the bus bars. Thereafter, the glass or plastic sheet having the heatable member is laminated to another glass or plastic sheet by a plastic interlayer. The conductive member is usually an evaporated, sputtered, or pyrolytic electrically conductive coating, e.g. of the type sold by PPG Industries, inc. under the registered trademarks NESATRON and NESA.

Usually, the aircraft and automotive windshield has a generally trapezoidal peripheral shape, and the outer major surface of the windshield as mounted in the aircraft or automobile is convex with the upper portion of the windshield having the shorter length. Usually, the conductive member follows the peripheral outline of the windshield and is spaced from the peripheral edges of the sheet on which it is applied. Because of the peripheral shape of the windshield, the electrically conductive coating is either between and connected to a pair of spaced bus bars of different lengths having the ends of the smaller bus bar within the boundaries set by the ends of the longer bus bar, or the coating is between and connected to a pair of spaced bus bars having the ends of the bus bars offset from one another with only one end of a bus bar within the boundary defined by the ends of the other bus bar.

The problems associated with the above type of heating arrangements are non-uniform heating of the windshield surfaces and reduced efficiency in the removal of condensation and/or ice that forms outside the boundaries of the smaller bus bar. The problems associated with the coating between a pair of spaced bus bars of different lengths having the ends of the smaller bus bar within the boundaries set by the ends of the longer bus bar are discussed, and solutions to solve the problems presented, in U.S. Pat. No. 7,132,625.

The problems associated with having a conductive coating between and connected to spaced bus bars where the spaced bus bars are of equal length, or unequal length, and have the ends of the bus bars offset from one another with only one end of a bus bar within the boundary defined by the ends of the other bus bar are not discussed in the art, nor is a solution to the problem provided in the art. In view of the foregoing, it can now be appreciated by those skilled in the art that it would be advantageous to provide a heatable member, e.g. a heatable transparency, e.g. an aircraft windshield having a conductive coating between and connected to a pair of spaced bus bars where the ends of the spaced bus bars are offset from one another with only one end of a bus bar within the boundaries defined by the ends of the other bus bar that provides uniform heating of the conductive coating to remove condensation and/or ice that would otherwise not be removed from areas along the top and bottom surface of the windshield.

SUMMARY OF THE INVENTION

This invention relates to an improved heatable member of the type having a dielectric substrate having a major surface having a first bus bar and a spaced second bus bar, and an electrically conductive coating between and in electrical contact with the bus bars, the first bus bar having a first end and an opposite second end, and the second bus bar having a first end and an opposite second end, wherein the first and the second ends of the first bus bar are offset from the first and the second ends of the second bus bar and the coating is a continuous electrically conductive coating. The improvement of the invention includes, among other things, the coating having, among other things, a plurality of electrically conductive segments, each of the segments comprising a first end and an opposite second end, wherein the first end of each of the segments is in electrical contact the first bus bar, the second end of each of the segments is in electrical contact with the second bus bar, and portions of each of the segments between the first bus bar and the second bus bar in spaced relationship to one another to prevent electrical contact between adjacent ones of the segments between the bus bars, wherein a ratio of a major diagonal to a minor diagonal is greater than 1.

The invention further relates to an aircraft window having a first major surface and an opposite second major surface and a heatable member between the first and the second major surfaces. The heatable member includes, among other things, a first bus bar and a spaced second bus bar, and an electrically conductive coating between and in electrical contact with the bus bars, the first bus bar having a first end and an opposite second end, and the second bus bar having a first end and an opposite second end, wherein the first and the second ends of the first bus bar are offset from the first and the second ends of the second bus bar. A coating includes, among other things, a plurality of electrically conductive segments, each of the segments comprising a first end and an opposite second end, wherein the first end of each of the segments is in electrical contact the first bus bar, the second end of each of the segments is in electrical contact with the second bus bar, and portions of each of the segments between the first bus bar and the second bus bar in spaced relationship to one another to prevent electrical contact between adjacent ones of the segments between the bus bars, wherein a ratio of a major diagonal to a minor diagonal is greater than 1.

DETAILED DISCUSSION OF THE INVENTION

As used herein, spatial or directional terms such as “inner”, “outer”, “left”, “right”, “up”, “down”, “horizontal”, “vertical”, and the like, relate to the invention as it is shown in the drawing on the figures. However, it is to be understood that the invention can assume various alternative orientations and, accordingly, such terms are not to be considered as limiting. Further, all numbers expressing dimensions, physical characteristics, and so forth, used in the specification and claims are to be understood as being modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical values set forth in the following specification and claims can vary depending upon the property desired and/or sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Moreover, all ranges disclosed herein are to be understood to encompass any and all subranges subsumed therein. For example, a stated range of “1 to 10” should be considered to include any and all subranges between and inclusive of the minimum value of 1 and the maximum value of 10; that is, all subranges beginning with a minimum value of 1 or more and ending with a maximum value of 10 or less, e.g., 1 to 6.7, or 3.2 to 8.1, or 5.5 to 10. Also, as used herein, the term “positioned over” or “mounted over” means positioned on or mounted over but not necessarily in surface contact with. For example, one article or component of an article “mounted over′ or positioned over” another article or component of an article does not preclude the presence of materials between the articles, or between components of the article, respectively.

Before discussing several non-limiting embodiments of the invention, it is understood that the invention is not limited in its application to the details of the particular non-limiting embodiments shown and discussed herein since the invention is capable of other embodiments. Further, the terminology used herein to discuss the invention is for the purpose of description and is not of limitation. Still further, unless indicated otherwise, in the following discussion like numbers refer to like elements.

Non-limiting embodiments of the invention will be directed to aircraft laminated transparencies, and in particular, to an aircraft windshield. The invention, however, is not limited to any particular type of aircraft and/or aircraft transparency, and the invention can be practiced on any type of aircraft and/or aircraft transparency having a heatable member to heat a surface, usually the outer surface of the transparency. Further, the invention can be practiced on commercial and residential windows, e.g. but not limited to the type disclosed in U.S. Pat. No. 5,675,944, which patent in its entirety is hereby incorporated by reference; a window for any type of land vehicle; a canopy, cabin window and windshield for any type of air and space vehicle, a window for any above or below water vessel, and a window for a viewing side or door for any type of containers, for example but not limited to a refrigerator, cabinet and/or oven door. Still further, the invention is not limited to the material of the layers or sheets of the aircraft window, and the layers or sheets can be made of, but not limited to, cured and uncured plastic sheets; annealed, heat strengthened, and heat and chemically strengthened, clear, colored, coated and uncoated glass sheets.

Shown inFIG. 1is an aircraft18having a non-limiting embodiment of an aircraft transparency20of the invention. With reference toFIG. 2, the windshield20includes a first transparent sheet22secured to a second transparent sheet24by a first vinyl-interlayer26; the second sheet24secured to a second vinyl-interlayer28by a first urethane interlayer30, and the second vinyl-interlayer28secured to a heatable member32(seeFIG. 3) incorporating features of the invention by a second urethane interlayer34. An edge member or moisture barrier36of the type used in the art, e.g. but not limited to a silicone rubber or other flexible durable moisture resistant material is secured to (1) peripheral edge38of the windshield20, i.e. the peripheral edge38of the first and second sheets22,24; of the first and second vinyl-interlayers26,28, and the first and second urethane interlayers30,34and of the heatable member32; (2) margins or marginal edges40of inner surface42of the windshield20, i.e. the margins40of the outer surface42of the first glass sheet22of the windshield20, and (3) margins or marginal edges44of outer surface46of the windshield20, i.e. margins of the outer surface46of the heatable member32.

As is appreciated by those skilled in the art and not limiting to the invention, the first and second glass sheets22,24; the first and second vinyl-interlayers26,28and the first urethane interlayer30form the structural part, or inner segment, of the windshield20, and the outer surface42of the glass sheet22of the windshield20faces the interior of the aircraft18(hereinafter the outer surface42of the glass sheet22is also referred to as the inner surface42of the windshield20), and the second urethane layer34and the heatable member32form the non-structural part, or outer segment, of the windshield20, and the surface46of the heatable member32of the windshield20faces the exterior of the aircraft18. The heatable member32provides heat to prevent fog from forming on, to remove fog from, to prevent ice from forming on, and/or to melt ice on, the outer surface46of the heatable member32of the windshield20(hereinafter the outer surface46of the heatable member32is also referred to as the outer surface46of the windshield20) in a manner discussed below.

As can be appreciated, the invention is not limited to the construction of the windshield20and any of the constructions of aircraft windshields used in the art can be used in the practice of the invention. For example and not limiting to the invention, the windshield20can include a construction wherein the second vinyl interlayer28and the first urethane interlayer30are omitted, and/or the sheets22and24are glass or plastic sheets. Generally the sheets22and24of the windshield20are clear chemically strengthened glass sheets; however, the invention is not limited thereto, and the glass sheets22and24can be heat strengthened or heat tempered glass sheets. Further as is appreciated by those skilled in the art, the invention is not limited to the number of glass sheets, vinyl interlayers, or urethane interlayers that make up the windshield20, and the windshield20can have any number of sheets and/or interlayers and any combinations thereof.

With reference toFIG. 4, there is shown a prior art heatable member48(heatable member48of the prior art is replaced by the heatable member32(seeFIG. 3) of the invention). The heatable member48includes a glass sheet50having a conductive coating52applied to surface54of the glass sheet50, and a pair of spaced bus bars66,68in electrical contact with the conductive coating52. Each of the bus bars66and68are connected by a wire70and71, respectively, to an electrical power source72, e.g. a direct current battery and/or an alternating current electric generator of the airplane18to pass current through the bus bars66and68, and the conductive coating62to heat the conductive coating52and the sheet50to prevent the formation of fog and/or ice on, and to remove ice and/or fog from, the outer surface of the windshield, e.g. the surface46of the windshield20.

An on-off switch and a rheostat or variable transformer73is connected to one of the wires, e.g. the wire71to position the on-off switch and the rheostat or variable transformer73between the power source72and the bus bar68to vary or regulate the current flow through the bus bars68and66, and the conductive coating52to control the temperature of the heatable member48. Preferably the ends75and76of the bus bar66, ends78and79of the bus bar68and the conductive coating52are spaced from adjacent sides81-84of the glass sheet50to prevent arcing of the bus bars66and68with metal body cover85of the aircraft18(seeFIG. 1).

With continued reference toFIG. 4, the bus bars66and68have the same length, as measured between the ends75and76of the bus bar66and as measured between the ends78and79of the bus bar68, and the bus bars66and68are parallel to one another. For purpose of discussion and not limiting to the invention, the bus bar66is designated as the top bus bar, and the bus bar68is designated as the bottom bus bar, as the heatable member48is mounted in the airplane18. The ends75and76of the top bus bar66are offset from the ends78and79of the bus bar68, and only one end of a bus bar, e.g. the end78of the bus bar68is between the boundaries set by the ends of the other bus bar, e.g. the ends75and76of the bus bar66. The boundary of an end of a bus bar is set by an imaginary line (dotted lines112and114) generally normal to the longitudinal axis of the bus bar and extending from the end of the bus bar to the other bus bar. The longitudinal axis of the bus bar is defined as a straight line drawn from the midpoint of one end, e.g. the end74of the bus bar68or the end75of the bus bar66, to the midpoint of the other end, e.g. the end79of the bus bar68, or the end76of the bus bar66, respectively. Stated another way, the ends of the bus bars are offset from one another when the ends of two bus bars are not vertically aligned.

U.S. Pat. No. 7,132,625 relates to heatable windshields having a pair of spaced bus bars with the ends of the shorter bus bar within the boundaries set by the ends of the longer bus bar. Further, U.S. Pat. No. 7,132,625 discloses in column 6, line 38 to column 7, line 15, that the watt density of a conductive coating at a longer bus bar is different than the watt density of the coating at an opposite shorter bus bar. The forging is correct when the ends of the shorter bus bar are with the boundaries set by the ends of the longer bus bar, however, the forgoing is not considered correct when the bus bars are offset from one another with only one end of one bus bar within the boundaries set by the ends of the other or opposite bus bar. More particularly, if the forgoing was correct for the situation when the bus bars are offset from one another with only one end of one bus bar within the boundaries set by the ends of the other bus bar, It would be expected that the conductive coating52(seeFIG. 4) will be uniformly heated between the bus bars66and68because the watt density of the conductive coating52at the top bus bar66is equal to the watt density at the bottom bus bar68.

It has been observed, however, that center portion115of the coating52of the heatable member48outlined by the imaginary lines112and114between the bus bars66and68, the portion of the bus bar66(identified by the number116) between the end76of the bus bar66and the imaginary line112, and the portion of the bus bar68(identified by the number118) between the end78and the imaginary line114is uniformly heated, and the portions of the coating outside of the center portion115are heated to a temperature less than the temperature of the center portion115and that the end76and the end78of the upper and lower bus bars66and68, respectively, draw all of the current from the areas outside of center portion115. The result is presence of fog, snow and ice, (depending on the weather condition) at portions of the window20outside of the center portion115, which reduces the area of visibility of the window20to the center portion115of the conductive coating52and a very high concentration of heat at the end76and the end78of the bus bars66and68, respectively, which can result in overheating of the interlayer adjacent to the heatable member32(seeFIG. 2).

It was concluded that the non-uniform heating problem was the result of the electric current taking the path of least resistance, which in this case is the current path with the shortest length. With continued reference toFIG. 4, the current paths having the shortest distance are within the center portion115of the coating52which is a rectangle defined by the sides112,114116and118. The side116of the center portion110has a length measured from the end76of the bus bar66to a position120on the bus bar66spaced from the end75of the bus bar66and at the intersection point of the imaginary line112and the bus bar66. The side118of the center portion110has a length measured from the end78of the bus bar68to a position122on the bus bar68spaced from the end79of the bus bar68and at the intersection point of the imaginary line114and the bus bar68. In one non-limiting embodiment of the invention, the imaginary lines112and114are normal to the longitudinal axis of the bus bar66and68such that the corners of the center portion115are each 90 degrees.

With reference toFIG. 3, there is shown a non-limiting embodiment of a heatable member32of the invention. The heatable member32of the invention includes a glass sheet130having a segmented electrically conductive coating132on surface134of the glass sheet130between, and in electrical contact, with the pair of spaced bus bars66,68. The surface134of the glass sheet is opposite to surface136, and in this embodiment of the invention is also the outer surface46of the windshield20(seeFIG. 2). Each of the bus bars66and68are connected by the wire70and71, respectively, to the electrical power source72(seeFIG. 4), to flow current through the bus bars66and68, and segments137A-137F of the segmented conductive coating130to heat the segmented conductive coating132, and the sheet130to prevent the formation of fog and/or ice on, and to remove ice and/or fog from, the outer surface, e.g. the surface136of the windshield20(seeFIGS. 2 and 3).

The invention is not limited to the design and/or construction of the bus bars66and68, and any of the types of bus bars used in the art can be used in the practice of the invention. Examples of bus bars that can be used in the practice of the invention, include, but are not limited to, the types disclosed in U.S. Pat. Nos. 4,623,389; 4,894,513; 4,994,650, and 4,902875, which patents in their entirety are hereby incorporated by reference. In the preferred practice of the invention, the bus bars are fired on silver ceramic glass frit, e.g. of the type disclosed in U.S. Pat. No. 4,623,389.

Further, the invention is not limited to the composition of the segmented conductive coating132, for example and not limiting to the invention, the conductive coating132can be made from any suitable electrically conductive material. Non-limiting embodiments of conductive coatings that can be used in the practice of the invention include, but are not limited to, a pyrolytic deposited fluorine doped tin oxide film of the type sold by PPG Industries, Inc. under the trademark NESA®; a magnetron sputter deposited tin doped indium oxide film of the type sold by PPG Industries, Inc under the trademark NESATRON®; a gold film deposited by the physical vapor deposition process, e.g. evaporation, and a coating made up of one or more magnetron sputter deposited films, the films including, but not limited to a metal film, e.g. silver between metal oxide films, e.g. zinc oxide and/or zinc stannate, each of which can be applied sequentially by magnetron sputtering, e.g. as disclosed in, but not limited to, U.S. Pat. Nos. 4,610,771; 4,806,220 and 5,821,001. The disclosures of U.S. Pat. Nos. 4,610,771; 4,806,220 and 5,821,001 in their entirety are hereby incorporated by reference.

The non-limiting embodiment of the invention shown inFIG. 3includes the bus bars66and68parallel to one another, having the same length and having the ends75and76of the bus bar66, and the ends78and79of the bus bar68offset from one another. As stated above, the boundaries of the ends of the bus bars are defined as an imaginary line extending from an end of a bus bar toward the other bus bar and normal to the longitudinal axis of the bus bar having the end. With this arrangement and as shown for the non-limiting embodiment of the invention shown inFIG. 3, the end75of the bus bar66is to the left of the end78of the bus bar68; the end78of the bus bar68is to the right of the end75of the bus bar66; the end76of the bus bar68is to the left of the end79of the bus bar68, and the end79of the bus bar68is to the right of the end76of the bus bar66.

The segmented electrically conductive coating132of the invention are separated by separation lines139in accordance to the invention uniformly heats the coating between the bus bars66and68by providing each of the segments137A-137E of the coating132with similar if not identical current path lengths. In this manner, there is uniform heating of the segments137A-137E and uniform heating of the segmented coating132. The invention is not limited to the number of coating segments137A-137E between the bus bars; however, in the preferred practice of the invention, the width of the segments137A-137E is selected such that there is no straight current path within the segments137A-137E that is equal to or shorter than the length of the imaginary line between the bus bars66and68. In other words, the straight current paths of each of the segments137A-137E are longer than the length of an imaginary line normal to the longitudinal axis of the bus bars, e.g. see imaginary lines112and114inFIG. 4.

More particularly, and with continued reference toFIG. 3, each segment137A-137E includes four sides140-143(only the sides of the segments137A and137B are marked inFIG. 3). The length of the sides140and142define the length of the segments, and the sides141and143define the width of the segments137A-137E. The width of each segment138A-137E is selected such that an imaginary line normal to the longitudinal axis of one of the bus bars, e.g. the bus bar68extends from one corner of one of the segments138A-138E of the coating132toward the opposite bus bar, e.g. the bus bar66and crosses over the side of an adjacent segment before extending to the opposite bus bar. More particularly and with reference toFIG. 5, in one non-limiting embodiment of the invention, the imaginary line112normal to the longitudinal axis of the bus bar68extends from the end78of the bus bar68, which is a corner of the segment137A between the sides140and141of the segment137A toward the bus bar66or opposite corner of the segment137A between the sides140and143of the segment137A. The imaginary line112crosses over the side140of the segment137A at crossing point147and optionally the side142of the segment137B at crossing point145before contacting the bus bar66.

In another non-limiting embodiment of the invention, the temperature difference between portions of the coating52outside of the center portion115(seeFIG. 4) are reduced to a lesser extent than by the preferred practice of the invention discussed above. In this non-limiting embodiment of the invention, the coating132is segmented to provide the segments137A-137E with a width such that an imaginary line normal to the longitudinal axis of one of the bus bars, e.g. the bus bar68extends from one corner of the bus bar to the opposite bus bar and stays within the sides of the segment. More particularly and with reference toFIG. 6, in this non-limiting embodiment of the invention, the imaginary line112is normal to the longitudinal axis of the bus bar68, extends from the end78of the bus bar68, which is the corner of the segment137A between the sides141and142of the segment137A toward the bus bar66or the opposite corner of the segment137A between the sides140and143of the segment137A, stays within the sides140-143of the segment137A and contacts the bus bar66or the side143of the segment137A. The measured distance from the corner between the sides142and143of the segment137A to the intersection of the side143of the segment137A and the imaginary line112in this non-limiting embodiment of the invention is in the range of 75 to 100% of the measured length of the side143of the segment137A, and preferably in the range of 85 to 100%.

As can now be appreciated, the discussion above regarding the sides141and143of the segment137A and the imaginary line112is applicable to the sides141and143of the segments137B-137F, unless indicated otherwise.

With reference toFIGS. 7 and 8, there is shown another preferred non-limiting embodiment of the invention. In this embodiment, heatable member160includes an electrically conductive coating162between and contacting a pair of spaced bus bars164and166applied to an acrylic sheet167. The bus bars164and166are offset from one another, non-parallel to one another and having different lengths. The electrically conductive coating162includes segments168A-168E. Each of the segments168A-168E have sides170-173and corners175-178(corners shown only for segments168A and168B, and shown only inFIG. 8). The sides170and172face one another, and the sides171and173face one another. A diagonal180extends from the corner175to the corner177, and a diagonal182extends from the corner176to the corner178. The longer diagonal of the segment e.g. the diagonal182is referred to as the major diagonal, and the smaller diagonal, e.g. the diagonal180of the segment is referred to as the minor diagonal.

Shown inFIG. 9is a coating segment190having a parallelogram shape having sides192-195and corners197-200. The opposite sides192and194, and193and195are parallel to one another. As can now be appreciated, the current moving between parallel sides of the segment190travels the same distance and has the same density, and uniformly heats the segment. The parallelogram can be defined by the ratio of the diagonals. More particularly, the ratio of the diagonals is 1. In the practice of this non-limiting embodiment of the invention, the ratio of the major diagonal to the minor diagonal is in the range of greater than 1 to less than 1.25, preferably in the range of greater than 1 to less than 1.15, more preferably in the range of greater than 1 to 1.05 and most preferably in the range of greater than 1 to 1.02. As can now be appreciated as the ratio of the major diagonal to the minor diagonal approach1the segments act as a segment having a parallelogram shape.

The invention is not limited to the manner of imposing separation lines139to electrically isolate the segments137A-137E and168A to168E from one another. More particularly, the separation lines139between the segments137A-137E and168A-168E can be provided by abrading the coating to impose a separation between the segments, using masks during the coating process to provide the separation between the segments. In the preferred practice of the invention a continuous coating, e.g. the coating132(seeFIG. 3) was applied to the surface134of the glass130, and a laser, e.g. of the type disclosed in U.S. Patent Application Publication No. 2010/0159251 A1, used to impose separation lines139to provide the segments of the invention. U.S. Patent Application Publication No. 2010/0159251 A1 in its entirety is hereby incorporated by reference.

With reference toFIGS. 5A and 6A, the invention contemplates removing the coating132(FIG. 3) or coating162(FIG. 7) on the bus bar, e.g. the bus bar68as shown inFIG. 5Ato completely separate the segments137A-137E along the adjacent sides140and142. The invention also contemplates leaving the coating on the bus bar as shown inFIG. 6A. Although not limiting to the invention, it is preferred in the practice of the invention to have the separation lines139extend over the bus bars as shown inFIG. 5A. In this manner each of the segments are completely separated from one another along the sides140and142(FIG. 3) and sides170and172(FIG. 7). Further, in the practice of the invention, it is preferred that the separation line139between the sides140and142of the segments137A to137F (FIG. 3), and the sides170and172of the segments168A to168E (FIG. 7) is large enough to prevent arcing between the segments. In the practice of the invention, it is preferred for the separation line139to have a length in the range of greater than 0 to less than 0.016 inch (0.04 centimeters), and preferably less than 0.002 inch (0.005 centimeters).

In one non-limiting embodiment of the invention, the invention was practiced on an aircraft windshield having a heatable member32having bus bars66and68. The bus bars each had a length of 17 inches; the end75was 14 inches to the left of the end78of the bus bar68, and the bus bars were parallel to one another and spaced 18 inches apart. A coating132of gold was applied on the surface134of an acrylic sheet130and a laser used to apply separation lines139to provide 28 segments between the bus bars. The coating on the bus bars was removed as shown inFIG. 5A. The length of each side140and142of the segments was 23 inches, and the length of each side141and143of the segments was 0.6 inches.

A voltage of 115 volts was applied between the bus bars66and68, and the coating132demonstrated a temperature uniformity within 10° F. across the entire heated area.

The invention is not limited to the embodiments of the invention presented and discussed above which are presented for illustration purposes only, and the scope of the invention is only limited by the scope of the following claims and any additional claims that are added to applications having direct or indirect linage to this application.