CA1306767C - Electrical heating device - Google Patents
Electrical heating deviceInfo
- Publication number
- CA1306767C CA1306767C CA000587166A CA587166A CA1306767C CA 1306767 C CA1306767 C CA 1306767C CA 000587166 A CA000587166 A CA 000587166A CA 587166 A CA587166 A CA 587166A CA 1306767 C CA1306767 C CA 1306767C
- Authority
- CA
- Canada
- Prior art keywords
- voids
- semi
- pattern
- adjacent
- conductive material
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
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Classifications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/20—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater
- H05B3/22—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater non-flexible
- H05B3/26—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater non-flexible heating conductor mounted on insulating base
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/10—Heater elements characterised by the composition or nature of the materials or by the arrangement of the conductor
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/20—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater
- H05B3/34—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater flexible, e.g. heating nets or webs
- H05B3/36—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater flexible, e.g. heating nets or webs heating conductor embedded in insulating material
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B2203/00—Aspects relating to Ohmic resistive heating covered by group H05B3/00
- H05B2203/011—Heaters using laterally extending conductive material as connecting means
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B2203/00—Aspects relating to Ohmic resistive heating covered by group H05B3/00
- H05B2203/013—Heaters using resistive films or coatings
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B2203/00—Aspects relating to Ohmic resistive heating covered by group H05B3/00
- H05B2203/017—Manufacturing methods or apparatus for heaters
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B2203/00—Aspects relating to Ohmic resistive heating covered by group H05B3/00
- H05B2203/037—Heaters with zones of different power density
Landscapes
- Surface Heating Bodies (AREA)
Abstract
ELECTRICAL HEATING DEVICE
Abstract Heating devices, in which a conductive pattern is carried on an insulating surface and a pair of spaced apart electrodes are electrically connected to the conductive pattern, are characterized in that the conductive pattern in at least one heating area of the device defines a two-dimensional array of areas that are devoid of conductive material ("voids") within a continuous "mesh" of conductive material. In preferred embodiments in which the conductive pattern comprises either a printed conductive graphite ink layer or a vacuum-deposited metal layer, the centers of the adjacent voids are at the corners of equilateral triangles and each void is a hexagon.
Abstract Heating devices, in which a conductive pattern is carried on an insulating surface and a pair of spaced apart electrodes are electrically connected to the conductive pattern, are characterized in that the conductive pattern in at least one heating area of the device defines a two-dimensional array of areas that are devoid of conductive material ("voids") within a continuous "mesh" of conductive material. In preferred embodiments in which the conductive pattern comprises either a printed conductive graphite ink layer or a vacuum-deposited metal layer, the centers of the adjacent voids are at the corners of equilateral triangles and each void is a hexagon.
Description
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ELECTRICAL HEATING DEVICE
Field of Invention This invention relates to electrical heating devices and, more particularly, to devices including a pattern of conductive material carried on an insulat-ing surface.
Background of Invention U. S. Patent No. 4,485,297 discloses an electri-cal heatlng device in which a semi-conductor pattern is printed on an insulating substrate. The pattern includes a pair of parallel longltudinal stripes and a plurality of bars extending obliquely between the stripes. The heating device is designed to produce a unlform watt density over the heated area, and the patent teaches that the watt density may be varied by changing the oblique angle between the bars and stripes.
U. S. Patent No. 4,633,068, dlscloses a heating device, particularly suited for use as an infrared imaging target, which similarly includes a semi-conductor pattern including a plurality of bars extending between a pair of longitudinally-extending stripes. Different areas of the device there disclosed have different watt densities, the variation in watt density between the different areas being ac-complished by varying the width of selected bars along their length.
U. S. Patent No. 4,542,285 discloses conductors useful for connection to semi-conductor pattern of devices such as those in the above-referenced patent ': ' ;
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~3~67~'7 - 2 ~ 69675-53 and application. The conduc-tor comprises a conductiYe me~al s~rip having a pair of tr~nsversely-spaced, longitudinally-extendiny strip portions and, therebetween, a central portion -that includes a plurality of longitudinally-spaced openings~ As disclosed, one of the conductor's strip portions overlies a stripe of the semi-conductor pattern, and an overlying insulating layer is sealed to the layer carrying the semi-conductor pattern through the openings in the central portion and along the inner and outer edges o~ the conductor.
The prior art also includes a number of different types of electrical devices made b~ depositing a thin film of conductive metal, for example, nickel or silver, on an insulating substrate, e.g., paper or organic plastic. The resistivity (ohms per square) of such a layer depends, of course, on the volume resistivity (ohm-centimeters) of the metal and the thickness of the layer.
Using vacuum deposition procedures, it is possible to deposit a metal layer as thin as, perhaps, 35 to 40 Angstrom. A nickel layer of such a thickness has a resistivity of about 20 ohms per square.
~0 Summary of Inventlon The present invention provides a conductive pattern that, using a thin, essentially uni-form layer of conductive mater-ial (e.g., a semi-conductive ink printed, or a conductive metal film vacuum deposited, at a uniform thickness) makes it possible to produce areas of varying size and shape which have significant-ly different resistivities (ohms per square); and thereby makes it possible to make, for '`; ~
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example, heating devices in which different heating areas of the same size or configuration have different watt densit:ies, or in which the same watt density is produced in different heating areas of very different size or configuration. The invention also makes it possiDle to produce a heater that is highly resistant to tearing and delamination; and to produce anti-static devices.
According to the present invention, heating devices, e.g., of the type in which a conductive pat-tern is carried on an insulating surface and a pair of spaced apart electrodes are electrically connected to the conductive pattern, are characterized in that the conductive pattern in at least one heating area of the device defines a two-dimensional array of areas that are devoid of conductive material ("voids") within a continuous "mesh" of conductive material.
In heating devices in which the conductive mate-rial is a semi-conductive ink of the type discussed in the aforementioned UOS. Patents, another heating area of the device is connected in series with the first area and comprises an area, printed with the same ink at the same thickness as in the first area, either (i) substantially all of which is covered with semi-conductive material or (ii) which contains a mesh-void pattern different from that in the ~irst area. In the heating areas in which the semi-conductive pattern is arranged in a mesh-void pattern, the voids cover not more than about 90% of the heating area and are preferably arranged in a regular, typically rectilinear, array (e.g., the centers of adjacent voids form triangles, squares, parallelograms or diamonds). Each void has an area not more than that of a circle about 1/2 inch in diameter, and the minimum distance between adjacent voids (i.e., the 4 ~3~676~ 6~675~53 minimum width of the seml-~onductive material mesh) is about 0.015 to 0.020 inch. In most preferred embodiments, the centers of the adjacent voids are at the corners of equilateral triangles and each void is a hexagon having an inscribed circle diameter of not more khan about 1~4 inch; and an insulating cover sheet is bonded to the substxate through the voids.
In electric resistance devices comprising a thin metal layer on an insula~ing substrate, the resistivity of the device is increased to substantiaIly more than the resistivity o~ the layer itself by removing spaced portions of the deposited metal. The remaining metal defines a regular array of metal-free voids ~preferably hexagonal and arranged with the centers of sets of three adjacent voids at the corners of equilateral triangles and with the edges of adjacent voids parallel to each other) within the metal mesh.
In accordance with the present invention, there is provided an electrical heating device including a layer o~ semi~
conductive material carried on an insulating surface and defininy a semi-conductive pattern, and a paix o~ spaced-apart conductors electrically connected to said semi-conductive pat-tern, said device being characterized ln that a first heating portion of said semi-conductive pat~ern intermediate said conduckors includes a two-dimensional array of areas devoid of semi-conductive material l"voids") within a mesh of semi-conduc~ive material, said voids being arranged such that the centers of the voids foxming sets of three adjacent voids are positioned ak the corners of equilateral triangles.
~3~
4a 69675-53 In accordance wlth the invention ~here is Eurther provided an electrical heating device including a layer of semi-conductive material carried on an insulating surface and defininy a semi-conductive pattern, and a pair of spaced-apart conductors electrically connecked to said semi-conductive pattern, said device beiny characterized in that a first heating portlon of said semi-conductive pattern intermediate said conductors in~ludes a two-dimensional array of areas devoid of semi-conductive material ("voids") within a mesh of semi-conductive material, and said conductors and said voids being arranged such that the centers of the voids forming sets of three adjacent voids are positioned at the corners of trianyles, and the overall direction of current flow between said conductors ls not parallel to the sides of said triangles.
In accordance with the invention, there is further provided an electrical heating device including a layer of semi-conductive material arried on an insulating surface and defininy a semi-conductive pattern, and a pair oE spaced-apart conductors eleetrically connected to said ~semi-conductive pattern, said device bein~ characterized in that a Eirst heating portion of said semi-conductive pattern intermediate said conductors includes a two-dimensional array of areas devoid o~ semi-conductive material ("voids") within a mesh of semi-conductive material, said voids being hexayons arranged such that the centers o~ the voids forminy sets of four adjacent hexagons are positioned a~ the corners of parallelograms.
In accordance with the invention, there is provided an . ~ ~, , .
~3~\~i7~7 ~b 69675~53 electrical heating device including a layer of semi-conductive material carried on an insulating surface and defining a semi-conductive pattern, and a pair of spaced-apart conductors electrically connected to said semi-conductive pattern, said device being characterized in that first and second heatlng portions of said semi-conductive pattern intermediate said conductors each include a respective regular two-dimensional array of areas devoid of semi-conductive material ("voids") within a mesh of semi-conductive material, and said second heating portion of said semi-conductor pattern is con~iguous ~o said first heating portion and has a resistivity (ohms per square) different from that of said first portion.
In accordance with the invention there is provided an electrical heating device comprising: a substrate;
a layer of semi-conductor material carried on an insulating surface of said substrate and defining a semi-conductor pattern includiny a pair of spaced~apart conductor contact portions and at least one heating portion; and a pair of spaced-apart electrical conductors each of whlch electrically engayes one of saicl conductor contact portions o:E said semi-conductor pattern;
said device beiny characterized in tha~, sald heating port.ion comprlses a regular two-dimensional array of areas devoid of semi conductor material ~"voids") within a continuous mesh of semi-conductor material, said voids being circles or polygons and being arranged such that the centers of the voids forming se~ o~ three adjacent voids are positioned at the corners of equila~eral triangles.
,~9, -4c ~ 6~7 ~ 9675-5~
In accordance with th~ invention there is provided in ~n electrical device comprising: a substrate having an insulating surface; and a layer of conductive material carried on said insulating surface of said substrate and defining a conductive pattern, that improvement wherein said pattern comprises a regular two-dimensional array of areas devoid of conductive material ~"voids") within a continuous mesh o conductive material, said voids being circles or regular polygons and being arranged such that the centers of the voids forming sets of three adjacent voids are positioned at the corners of equilateral triangles.
In accordance with ~he invention there is also provided in the me~hod of making an electric resistance device in which a thin layer or film of metal is uniformly deposited on an insulating substrate, that improvement comprising the steps of thereafter selectively removing portions of the metal so deposited such that in a selected area of said device the remaining metal defines a conductive metal pattern comprising a two-dimensional regular array of areas devoid of conductive material ("voids") within a mesh of conductive material, said voids beiny arran~ed such that the centers of the voids forming a set of three adjacent voids are positioned at the corners of an equilateral triangle.
In accordance with the invention there is also provided in the me~hod of making an electric resistance device in which a thin layer or film of metal is uniformly deposited on an insulating substrate, that improvement comprising the steps of thereaf~er selectively removing portions of the metal deposited such that in a selected area of said device the remaining metal .., " . ~
~ ' ~
4d 13~676~ 6g675 s~
defines a conductlve metal pattern comprising a two-dim~nsional array of areas devoid of conductive material ~"voids"~ within a mesh of conductive material, said voids being reyularly spaced hexagons arranged such that the sides of adjacent hexagons are parallel to each other.
In accordance with the invention there is also provided in the method of making an electric resistance device in which a thin layer of film of metal is uniformly deposited on an insulating substrate, that improvement comprising the steps of thereafter selectively removing portions of the metal so deposited such that in a selected area of said device the remalning ~etal defines a conductive metal pattern comprising a two-dimensional regular array of areas devoid of conductive material ~"voids") within a mesh of conductive material, said voids being arranged such that the centers of the voids forming a set of three adjacent voids are positioned at the corners of a trianyle ancl the overall direction of current flow in said device is not parallel to any of the sides of said triangle.
In accordance with the invention there is provided an electrical resistance device inaludlng a conductive metal pattern carried on an insulatlng surface, said device being characterized in that a portion of said conductive metal pa~tern includes a two-di~ensional array of substantially identical areas of said substrate devoid oi conductive material on said substrate, said voids being arranged such that the centers of sets of three adjacent voids are positioned at the corners of the triangles and the overall direction of current flow in said dev.ice is genexally ,, , 4 ~3~76~ 69575-53 not parallel to sides of said triangles.
DescriPtion of Dr~
Figure 1 is a plan view of an electrical heating device constructed in accord wi~h the pre~ent invention, with the top insulating layer and metal conductors of the device removed for purposes of clarity.
Figure 2 is a sectional view taken at line 2-2 of Figure 1, with the top insulating layer and metal condu~tors of the device in place.
Figure 3 is an enlarged view of a por~ion of the semi-conductor pa~tern of the device of Figure 1.
Figure 4 is a diagram illustrating aspects of the semi-conductor pattern shown in Figure 1.
Figures 5-7 illustrate other semi-conductor mesh-void plan view of another electrical heating device, embodying the inven~ion.
Figure 8 is a schema-tic plan view of another heater embodyiny the invention.
, . ., :
.
~3~ 7 Figure 9 is a plan view of an electrical resistance device embodying the present invention.
Figure lO is a section taken at line lO-10 of Figure 9.
Figure ll is an enlarged plan view of a portion of the device of Figure 9, more clearly illustrating the mesh-void pattern.
Detailed De cription of Preferred Embodiment Referring now to Figures 1-4, there is shown an electrical sheet heter, generally designated lO, comprising an electrically-insulating plastic substrate 12 on which is printed a semi-conductor pat-tern 14 of colloidal graphite. In the embodiment shown, the heater is intended for use as an infrared imaging target, and the semi-conductor pattern is designed to produce a thermal image similar to that produced by a human being.
As shown, substrate 12 is 0.004 inch thick polyester ~"Mylar"), and the relative size of the substrate 12 and semi-conductor pattern 14 are such as to provide an uncoated side boundary area 8, between the outer edges of the semi-conductor pattern 14 and the edges of the substrate. Area 8 has a minimum width of l/2 inch along the sides 9 of the target and of 1 1/4 inch along the target bottom 11. The semi-conductor pattern provides a watt density of about 12-15 watts per square foot over its surface when the heater is connected to a llO volt power source.
For connecting the target to a power source, the semi-conductor pattern 14 includes a pair of connect-ing portions 16, each about 5/32 inch wide, extending generally across the target bottom. As shown, the connecting portions are aligned with each other, with an about 1/4 inch wide space 18 (i.e., an insulating * rr~A4'~
- 6 - ~ 34Jl6 ~ ~'7 area free of semi-conducting material) between their adjacent ends. A series of small rectangles 20, each about 1/4 inch high and 1/8 inch wide are spaced along the length of each connecting portion 16, with the lower edge of each rectangle 20 about 5/32 inch from the bottom edge of the connecting portion. The distance between adjacent rectangles 20 is 1/4 inch.
A pair of electrodes 22, each comprising a tinned copper strip 1 inch wide and 0.003 inch thick, extend across the bottom of the target. Each electrode 22 partially overlies and electrically engages a respec-tive one of connecting portions 16. As shown most clearly in above-referenced U. S. Patent No.
4,542,285, each electrode includes two transversely-spaced longitudinally-extending rows of spaced square holes 24, with solid copper strips 26, 28 and 30 being provided along the inner and outer edges of the electrode and between the two rows of holes.
A thin electrically insulating plastic cover sheet 32, shown in Figure 2 and comprising an es-sentially transparent co-lamination of an 0.005 cm.
(0.002 in.) thick polyester ("Mylar") and an 0.007 cm (0.003 in.) thick adhesive binder, e.g., polyethylene, overlies substrate 12, semi-conductor pattern 14, and conductors 22. The conductors 22 are not themselves bonded to the underlying substrate or semi--conductor material. However, the cover sheet 32 ~which is coextensive with the entire substrate 12) bonds tightly to the uncoated (with semi-conductor material) areas 8 of substrate 12 (along the marginal areas where the two sheets are in face-to-face engagement and through the holes 24 in conductors 22), and also to the uncoated rectangular areas 40 spaced along the inside edges of conductor strips 26. In the areas in _ 7 _ ~3~76~
which (as discussed hereinafter) the conductive mate-rial is printed in a mesh-void pattern, the cover sheet 32 bonds to the substrate 12 in the voids also.
Typically, substrate 12 and cover sheet 32 are essentially transparent. In military target applica-tions, cover sheet 32 may be painted the color of, e.g., a tank.
The portions of semi-conductor pattern 14 which produce the desired thermal image include three gener-ally "U" shaped "heating" portions, designated 50, 51and 52, respectively, which form the "head" of the target; a pair of generally trapezoidal "heating" por-tions, designated 60 and 61, respectively, which form the "shoulders" of the target; and a pair of rectangular "heating" portions, designated 70 and 71, respectively, which form the rest of the body.
In all three areas, the semi-conductor ink is printed at essentially the same thickness, e.g., about 0.0005 in.; and the resistivity (ohms per s~uare) of the areas actually covered by ink, is essentially the same throughout. As will become apparent, however, the resistivities of the three areas on a lager scale (e.g., on a scale including both the areas covered by ink and, in the shoulder and body portions, the array of "voids") differ. As shown, U-shaped semi-conductor-free insulating areas 80 are provided between the adjacent "head" portions 50, 51 and 52, and another semi-conductor-free insulating area 81 is provided between the adjacent "body" portion~ 70 and 71 and between the adjacent "shoulder" portions 60 and 61. The heating portions 5Q, 51 and 52 which form the head are connected (in parallel with each other) electrically in series with "shoulder" portions 60 and 61, and each of "body" portions 70 and 71 is connected electrically in series between a respective one of - 8 - ~ 3~ 6t76~
"shoulder' portions 60, 61 and a respective one of connecting portions 16.
In each of "head" portions 50, 51, and 52, the semi-conductor colloidal graphite material is printed over the entire area, covering the entire area at a uniform thickness, typically in the range of 0.3 to l.~ mil. In connecting portions 16, the semi-conductor material similarly covers the entire area of the connecting portions, except for the rectangular openings 40 that provide for bondiny of the top sheet 32 to substrate 14 and hold conductors 22 in place.
In the "shoulder" portions 60, 61, and in the "body" portions 70, 71, the resistivity (ohms per square) required to produce the desired watt density typically cannot be obtained by printing the semi-conductor colloidal graphite material over the entire area at the same thickness at which it is printed over the "head" portions 50, 51 and connecting portions 16.
In each of portions 60, 61, 70, and 71, the semi-conductor rnaterial is printed over the area in an openmesh pattern, i.e., a regular array of small areas which are devoid of semi-conductor material ("voids") within a continuous semi-conductor "mesh" that sur-rounds the "voids" and covers the rest of the respec tive portion. Although the resistivity of the ink layer itself remains constant, the resistivity (ohms per s~uare) and resulting watt density of a portion including voids depends on, and varies according to, the void configuration and pattern (e.g., the arrange ment and spacing of, and the percentage of the overall area that is covered by the voids). An area in which the "voids" cover 50 percent of the entire area typically will have greater resistivity than will an area in which the "voids" cover only 25 percent of the area; and the least resistivity typically will be - g - ~L3~6'~7 found in an area in which the percentage of "voids" is zero, i.e., in an area, such as "head" portions 50, 51, 52, all of which i9 coated or printed with semi-conductor material.
In the embodiment of Figs. 1-4, the voids are hexagonal and are arranged in a regular rectilinear array in which the centers of adjacent voids form equilateral triangles. Figure 3 is an enlarged view of part of "bodyl' portion 70 illustrating the hexagonal voids 80 and semi-conductor material mesh 82, and Figure 4 is a diagram further illustrating the geometry of the Fig. 3 void-mesh pattern. In Figure 4, the distance between the centers of adjacent hexagonal voids 80 is designated "D", the distance from the center to each corner of a void (and hence the radius of a circle tangent to the inside of and subscribed by the void) is desiynated "R", and the width of the semi-conductor material mesh strips 81 between adjacent voids is designated "P". As will be apparent, the relationship between these three distances i5:
P = D - 2R.
It has been found that "P" should not be less than about 0.015 inches, preferably not less than about 0.020 inches, and that R should not be less than l/64 inch~ preerably not less than about l/32 inch.
To provide even heating over the entire area, it also has been found desirable that the individual voids should not be too large, e.g., R typically should not exceed about l/4 inch.
In the hexagonal void pattern of Figure 4, the width of the semi-conductor mesh strip 81 between each pair of adjacent voids 80 essentially constant, and the overall mesh pattern consists of a series of constant width strips 81 joined at their ends - 1 o - ~L3~ 7 (adjacent the corners of the hexagonal voids) by equilateral triangular portions 83 each side of which is equal in length to the strip width. It also will be noted that the percentage of an overall heating portion that is covered by semi-conductor material depends on spacing between voids and the ~idth of the mesh strips between adjacent hexagonal voids;
theoretically, it may vary from 0% (P = o; each hexagon is so large that the adjacent voids abut each other) to 100% (P = D; the entire area is covered with semi conductor material; each hexagon has an area of zero). In a typical arrangement in which the distance D between void centers is 0.375 in., if P is 0.015 in.
voids will cover about 90% of the overall area, and lS the semi-conductor mesh will cover the remaining about 10%. It will be noted that the percentage covered by the voids may be somewhat increased by increasing center-to-center spacing of the voids while maintain-ing or (if printing will permit) decreasing P; and that the percentage of void coverage can be decreased as desired by reducing the voids size ~R) or by maintaining the void size while increasing "D".
In the heater of Fig. 1, the hexagonal voids in the "shoulder" portions 60, 61 and "body" portion 70, 71 are arranged so that the distance between adjacent voids is 0.375". In "shoulder portions" 60, 61, the voids are sized (R = 0.10 in.) so that the voids in the mesh-void pattern cover about 20% of the area of the shoulder portions. In body portions 70, 71 the voids are larger (R - 0.14 in.), and the voids cover about 40% of the overall area.
The resistivity (ohms per square) of an area comprising a mesh-void pattern is greater than that of an area completely covered by the same semi-conductor ~3~;~t~7 material printed at the same thickness. Using a mesh-void pattern in which the shape and center-to-center again of the voids remains the same, the resistivity of an area generally can be increased by using larger voids, and decreased if the voids are made smaller.
With reference to the heater of Figs. 1-4, it thus will be seen that the resistivity (ohms per square) in the head portions 50, 51, 52 (which are entirely covered with semi-conductive material) is less than that in any of the other portions of the semi-conductor pattern (which are mesh-void patterns).
Similarly, the resistance (ohms per square) in the shoulder portions 60, 61 ~in which the voids cover about 20~ of the total area) is less than that in body portions 70, 71 (in which the voids cover about 40% oE
the area). In the illustrated embodiment, the resistance in the "shoulder" portions 60, 61 is about 130% of that in head portions 50, 51, 52; and that in body portions 70, 71 is about 180% of that in the head portions. However, the overall sizes and shapes of the various portions are such that the watt densities produced by each of the "body" and "shoulder" portions (which represent portions of a human's body that ~ill be clothed and thus should appear to an infrared imag-ing device to be slightly cooler than an unclothedhead) are about th~ same, and are slightly less than the watt density produced by the head portions.
It will be noted that, in each of "shoulder" por-tions 60, 61 and "body" portions 70, 71, the direction of current flow is generally vertical. In areas that include a mesh-void pattern, it normally is desirable that the lines connecting the centers of adjacent voids not be parallel to the overall direction of cur-rent flow. Thus, the mesh-void patterns in the shoulder and body portions are oriented such that the - 12 ~ 7 sides of the equilateral triangles connecting adjacent voids are either perpendicular or at a 30 angle to the generally vertical current flow direction.
Similarly, if the void centers were arranged in a square pattern, it would normally be desirable to ori-ent the pattern so that the sides of the squares form 45 angles to the current flow direction.
Alternative mesh-void patterns, in which the voids are circular, are shown in Figures 5 and 6.
In the Figure 5 pattern, the circular voids 180 are arranged so that the centers of three adjacent voids form equilateral triangles, the distance between the centers of adjacent void9 beinq designated D', the radius of each void being designated R', and the width of the semi-conductor material mesh between adjacent voids being designated P'. The minimum width of the semi-conductor mesh strips 181 between each pair of voids 180 is located on the line connecting the centers of the voids and is equal to D'-2R'.
The circular voids 280 in the Figure 6 pattern are arranged with the centers of four adjacent voids located at the corners of a square. The distance between the centers of two adjacent voids, i.e., the length of each side of each square, is D", the radius of each void 280 is R", and the minimum width 8" of the semi-conductor strip 281 between two adjacent voids 281 ~which again is located on the line connect-ing the void centers) is D'l-2R".
In the circular void patterns of Figures 5 and 6, the semi-conductor mesh strips 181, 281 between adjacent pairs of voids 180, 280 vary in width. In each, the minimum width is on the line connecting the center of adjacent pairs of voids and the width of the end portions of each strip is considerably greater.
Thus, and unlike in the hexagonal void pattern of - 13 ~ 7 Figure 4, there is considerable variation in resistance along the length of each mesh strip 1~1, 281. It also will be noted that circular void pat-terns should not be used when it is desirable for the voids to cover a large percentage of the overall heat-ing area. For example, in the Figure 5 pattern in which the centers of the circular voids are located at the corners of equilateral triangles, the maximum theoretical percentage of the overall heating portion areas covered by voids ~i.e., the percentage covered when R is almost as large as P/2 and adjacent voids are almost tangent to each other) is about 90%; in the Figure 6 pattern, in which the void centers are located at the corners of squares, the maximum theoretical percentage that can be covered by voids is about 20%. As a practical matter, the requirement that P be not less than about 0.015 in. means that the maximum void coverage that can be obtained using circular void patterns is considerably less than the theoretical maximum (e.g., about 80% equilateral triangle corner pattern; and about 60~ using a square corner pattern) and to insure good printing and even heating, circular void patterns typically will not be employed in circumstances in which it is desirable for the voids to cover more than about 2/3 of the heating area.
In other embodiments, other void shapes and pat-terns may be employed. For example, the voids need not be circular or hexagonal in shape, e.g., squares, ovals, triangles or irre~ular shapes could be used; in some circumstances the centers of the voids may not be arranged in a regular, rectilinear array; and in some circumstances it may be desirable to create the mesh-void pattern by printing over an entire area and then 3s "punching-out" the voids.
.
3L3~6~ 7 Figure 7, for example, illustrates, enlarged, a void-mesh semi-conductor pattern of the present inven-tion in which the "voids" 380 are in the shape of diamonds so arranged that diamond centers are located on the corners of parallelograms the sides of which are about 0.4 in. long. The mesh 382 between voids comprises interconnected stripes 381 about 0.020 inO
wide.
Fig. 8 illustrates a special purpose heater 410 in which a serpentine semi-conductor pattern 414 of varying overall width is printed on a paper substrate 412. The pattern 414 includes a solid conductor contract portion 416 at each end of the pattern, and a number of serially-connected heating portions designated 420, 422, 424, 426, 428, 430, 432 therebetween. Heating portions 420, 424, 428 and 432 are "solid" (i.e., the semi-conductor material covers the entire area of each). Heating portions 422, 426 and 4~8 are printed in a mesh-void pattern. In por-tions 422 and 428, the mesh-void pattern comprises hexagonal voids aligned in an equilateral triangle portion with D = 0.375 in. and R = 0.0625 in. In portion 426, the mesh void pattern comprises hexagons of the same size arranged in an equilateral triangle pattern in which D - 0.250 in. Circular tinned copper conductors 450 are held in face-to-face electrical contact with each of conductor contact areas 416 by, e.g., a conductive adhesive.
In the above-described embodiments, and in those described in the aforementioned U.S. Patents, the material forming the semi-conductor pattern typically has (if printed uniformly over an area at a thickness of 0.0005 in.) a resistivity of about 80 ohms per square. By way of contract the resistivity of a metal te.g., nickel) film having the same thickness will be IL3~767 using much less. ~he resistivity of such a metal layer may be increased somewhat by making the film very thin; but on a commercial basis it is extremely difficult, if not impossible, to deposit unirorm metal films at thicknesses significantly less than about 35 Angstroms, (at which thickness the resistivity of a nickel layer is about 20 ohm per square) and it heretofore has not been feasible to produce uniform metal layers having a resistivity much greater than that of a uniform 35 Angstrom layer.
Figures 9-11 show an electrical resistance device, generally designated 110, comprising a metal pattern 112 deposited at essentially uniform thickness (i.e., about 35 Angstroms) on an organic plastic (e.g., polyester) substrate 114. Along the opposite side edges of device 110, metal pattern 112 comprises continuous conductor contact strips 116 about one-half inch wide. A tinned copper conductor 118 overlies and is adhesively attached (e.g., with a conventional conductive adhesive) to each conductor contact strip 14. In other embodiments, the conductor contact strips may be deposited at a greater thickness than the remaining portion of the metal pattern, often in lieu of providing separate conductors.
The heating area 119 of device 110 (i.e., the portion between the spaced apart conductors 118 and conductor contact strips 116) comprises a regular rectilinear array of hexagonal voids 120 (i.e., hexagonally shaped areas that are free of metal or other conductive material) in a metal mesh pattern 121. The voids 120 are arranged on 0.375 in. centers, with the centers of strips of three adjacent voids at the corners of equilateral triangles (each leg of each triangle being 0.375 in. long). The triangles are arranged so that their sides are perpendicular to or ~3~
form 30 angles with the direction of current ~low, i.e., with a line extending transversely of device 110. The adjacent side edges of adjacent hexagonal voids are parallel to each other, and the size of the voids is such that the metal strip 122 between adjacent voids is about 0.005 inches wide (i.e., the size of each hexagon is such that the diameter of a circle within and tangent to the sides of the triangle is 0.370 in.).
The exact resistivity tohms per square) of the heating area 118 should be determined empirically. To a close approximation, the resistivlty (R) is given by the following formula:
1.732rD/W
where r is the resistivity (ohms per square) of the metal layer, and D and W are, respectively, the diameter of a circle inscribed within and tangent to hexagonal voids 20 and W is the width of the strip 22 between adjacent voids. Using the formula, it will be seen that resistivity (R) of the heating area 19 of device 10 is about 74r. If, as in the illustrated embodiment, the metal layer is nickel about 35A thic!c, r is about 20.5 ohms per square and R is about 1525 ohms per square.
In practice, the electrical device 110 of Figures 9-11 is made as follows:
a. Deposit a continuous metal layer of the desired thickness on substrate 114. In preferred practice the layer is deposited using a conventional vacuum deposition or metallization procedure.
b. Deposit an acid resist pattern over the continuous metal layer. The acid resist pattern ls deposited such that resist material covers all the metal that is not to be removed (i.e., it covers conductor contact strips 116 and the metal mesh in 1~ 7~7 heating area ll9). The acid resist pattern may be deposited using any of a number of conventional techniques. For example, screen printing, roto-graveure or flexo-graveure. Alternatively, a solid layer of acid resist may be deposited over the entire metal layer, and the pattern then produced by selectively removing portions of the resist using a conventional photoresist technique. Materials useful in forming the resist pattern include Blake Acid Resist from Cudner & O'Connor, Dychem (Type M or AX) film photoresist and Dupont (#4113) film photo resist.
c. Pass the device (with the resist plan pattern thereon) through an acid bath to remove all the metal layer that is not protected (i.e., covered) by the acid resist pattern (the remaining metal provides conductor contact strips 116 and mesh 121.
d. Remove the resist pattern.
e. Adhesively attach conductors 118.
As with the conductive graphite embodiments discussed above, metal mesh devices also may include a number of different heating areas of different resistivity. For example, such a device may include one area in which the array of hexagonal voids is as just discussed with respect to Figures 9~11, and in a secondary the hexagonal voids may be arranged on dif~
ferent (e.g., .250 inch centers) and the width of the metal strips between adjacent voids may be different also (e.g., a width as small as about 0.001 in. may be produced using a photoresist process). The two heat-ing areas have different resistivities. The firstwill have a resistivity 74 times greater than that of the metal layer; in the second, the resistivity will be about 250 times that of the metal layer.
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~L3~ 6'7 Similarly, other conductive materials (e.g., either metals such as silver or gold or other conduc-tive compositions or dispersions) may be used in lieu of nickel, and different mesh-void patterns (e.g., those described in our above-referenced and incorporated application) may be used.
These and other embodiments will be within the scope of the foIlowing claims.
What is claimed is:
;
~. ~, .. . . .. .
ELECTRICAL HEATING DEVICE
Field of Invention This invention relates to electrical heating devices and, more particularly, to devices including a pattern of conductive material carried on an insulat-ing surface.
Background of Invention U. S. Patent No. 4,485,297 discloses an electri-cal heatlng device in which a semi-conductor pattern is printed on an insulating substrate. The pattern includes a pair of parallel longltudinal stripes and a plurality of bars extending obliquely between the stripes. The heating device is designed to produce a unlform watt density over the heated area, and the patent teaches that the watt density may be varied by changing the oblique angle between the bars and stripes.
U. S. Patent No. 4,633,068, dlscloses a heating device, particularly suited for use as an infrared imaging target, which similarly includes a semi-conductor pattern including a plurality of bars extending between a pair of longitudinally-extending stripes. Different areas of the device there disclosed have different watt densities, the variation in watt density between the different areas being ac-complished by varying the width of selected bars along their length.
U. S. Patent No. 4,542,285 discloses conductors useful for connection to semi-conductor pattern of devices such as those in the above-referenced patent ': ' ;
,;'' .,~
~3~67~'7 - 2 ~ 69675-53 and application. The conduc-tor comprises a conductiYe me~al s~rip having a pair of tr~nsversely-spaced, longitudinally-extendiny strip portions and, therebetween, a central portion -that includes a plurality of longitudinally-spaced openings~ As disclosed, one of the conductor's strip portions overlies a stripe of the semi-conductor pattern, and an overlying insulating layer is sealed to the layer carrying the semi-conductor pattern through the openings in the central portion and along the inner and outer edges o~ the conductor.
The prior art also includes a number of different types of electrical devices made b~ depositing a thin film of conductive metal, for example, nickel or silver, on an insulating substrate, e.g., paper or organic plastic. The resistivity (ohms per square) of such a layer depends, of course, on the volume resistivity (ohm-centimeters) of the metal and the thickness of the layer.
Using vacuum deposition procedures, it is possible to deposit a metal layer as thin as, perhaps, 35 to 40 Angstrom. A nickel layer of such a thickness has a resistivity of about 20 ohms per square.
~0 Summary of Inventlon The present invention provides a conductive pattern that, using a thin, essentially uni-form layer of conductive mater-ial (e.g., a semi-conductive ink printed, or a conductive metal film vacuum deposited, at a uniform thickness) makes it possible to produce areas of varying size and shape which have significant-ly different resistivities (ohms per square); and thereby makes it possible to make, for '`; ~
`` ~3~7~
example, heating devices in which different heating areas of the same size or configuration have different watt densit:ies, or in which the same watt density is produced in different heating areas of very different size or configuration. The invention also makes it possiDle to produce a heater that is highly resistant to tearing and delamination; and to produce anti-static devices.
According to the present invention, heating devices, e.g., of the type in which a conductive pat-tern is carried on an insulating surface and a pair of spaced apart electrodes are electrically connected to the conductive pattern, are characterized in that the conductive pattern in at least one heating area of the device defines a two-dimensional array of areas that are devoid of conductive material ("voids") within a continuous "mesh" of conductive material.
In heating devices in which the conductive mate-rial is a semi-conductive ink of the type discussed in the aforementioned UOS. Patents, another heating area of the device is connected in series with the first area and comprises an area, printed with the same ink at the same thickness as in the first area, either (i) substantially all of which is covered with semi-conductive material or (ii) which contains a mesh-void pattern different from that in the ~irst area. In the heating areas in which the semi-conductive pattern is arranged in a mesh-void pattern, the voids cover not more than about 90% of the heating area and are preferably arranged in a regular, typically rectilinear, array (e.g., the centers of adjacent voids form triangles, squares, parallelograms or diamonds). Each void has an area not more than that of a circle about 1/2 inch in diameter, and the minimum distance between adjacent voids (i.e., the 4 ~3~676~ 6~675~53 minimum width of the seml-~onductive material mesh) is about 0.015 to 0.020 inch. In most preferred embodiments, the centers of the adjacent voids are at the corners of equilateral triangles and each void is a hexagon having an inscribed circle diameter of not more khan about 1~4 inch; and an insulating cover sheet is bonded to the substxate through the voids.
In electric resistance devices comprising a thin metal layer on an insula~ing substrate, the resistivity of the device is increased to substantiaIly more than the resistivity o~ the layer itself by removing spaced portions of the deposited metal. The remaining metal defines a regular array of metal-free voids ~preferably hexagonal and arranged with the centers of sets of three adjacent voids at the corners of equilateral triangles and with the edges of adjacent voids parallel to each other) within the metal mesh.
In accordance with the present invention, there is provided an electrical heating device including a layer o~ semi~
conductive material carried on an insulating surface and defininy a semi-conductive pattern, and a paix o~ spaced-apart conductors electrically connected to said semi-conductive pat-tern, said device being characterized ln that a first heating portion of said semi-conductive pat~ern intermediate said conduckors includes a two-dimensional array of areas devoid of semi-conductive material l"voids") within a mesh of semi-conduc~ive material, said voids being arranged such that the centers of the voids foxming sets of three adjacent voids are positioned ak the corners of equilateral triangles.
~3~
4a 69675-53 In accordance wlth the invention ~here is Eurther provided an electrical heating device including a layer of semi-conductive material carried on an insulating surface and defininy a semi-conductive pattern, and a pair of spaced-apart conductors electrically connecked to said semi-conductive pattern, said device beiny characterized in that a first heating portlon of said semi-conductive pattern intermediate said conductors in~ludes a two-dimensional array of areas devoid of semi-conductive material ("voids") within a mesh of semi-conductive material, and said conductors and said voids being arranged such that the centers of the voids forming sets of three adjacent voids are positioned at the corners of trianyles, and the overall direction of current flow between said conductors ls not parallel to the sides of said triangles.
In accordance with the invention, there is further provided an electrical heating device including a layer of semi-conductive material arried on an insulating surface and defininy a semi-conductive pattern, and a pair oE spaced-apart conductors eleetrically connected to said ~semi-conductive pattern, said device bein~ characterized in that a Eirst heating portion of said semi-conductive pattern intermediate said conductors includes a two-dimensional array of areas devoid o~ semi-conductive material ("voids") within a mesh of semi-conductive material, said voids being hexayons arranged such that the centers o~ the voids forminy sets of four adjacent hexagons are positioned a~ the corners of parallelograms.
In accordance with the invention, there is provided an . ~ ~, , .
~3~\~i7~7 ~b 69675~53 electrical heating device including a layer of semi-conductive material carried on an insulating surface and defining a semi-conductive pattern, and a pair of spaced-apart conductors electrically connected to said semi-conductive pattern, said device being characterized in that first and second heatlng portions of said semi-conductive pattern intermediate said conductors each include a respective regular two-dimensional array of areas devoid of semi-conductive material ("voids") within a mesh of semi-conductive material, and said second heating portion of said semi-conductor pattern is con~iguous ~o said first heating portion and has a resistivity (ohms per square) different from that of said first portion.
In accordance with the invention there is provided an electrical heating device comprising: a substrate;
a layer of semi-conductor material carried on an insulating surface of said substrate and defining a semi-conductor pattern includiny a pair of spaced~apart conductor contact portions and at least one heating portion; and a pair of spaced-apart electrical conductors each of whlch electrically engayes one of saicl conductor contact portions o:E said semi-conductor pattern;
said device beiny characterized in tha~, sald heating port.ion comprlses a regular two-dimensional array of areas devoid of semi conductor material ~"voids") within a continuous mesh of semi-conductor material, said voids being circles or polygons and being arranged such that the centers of the voids forming se~ o~ three adjacent voids are positioned at the corners of equila~eral triangles.
,~9, -4c ~ 6~7 ~ 9675-5~
In accordance with th~ invention there is provided in ~n electrical device comprising: a substrate having an insulating surface; and a layer of conductive material carried on said insulating surface of said substrate and defining a conductive pattern, that improvement wherein said pattern comprises a regular two-dimensional array of areas devoid of conductive material ~"voids") within a continuous mesh o conductive material, said voids being circles or regular polygons and being arranged such that the centers of the voids forming sets of three adjacent voids are positioned at the corners of equilateral triangles.
In accordance with ~he invention there is also provided in the me~hod of making an electric resistance device in which a thin layer or film of metal is uniformly deposited on an insulating substrate, that improvement comprising the steps of thereafter selectively removing portions of the metal so deposited such that in a selected area of said device the remaining metal defines a conductive metal pattern comprising a two-dimensional regular array of areas devoid of conductive material ("voids") within a mesh of conductive material, said voids beiny arran~ed such that the centers of the voids forming a set of three adjacent voids are positioned at the corners of an equilateral triangle.
In accordance with the invention there is also provided in the me~hod of making an electric resistance device in which a thin layer or film of metal is uniformly deposited on an insulating substrate, that improvement comprising the steps of thereaf~er selectively removing portions of the metal deposited such that in a selected area of said device the remaining metal .., " . ~
~ ' ~
4d 13~676~ 6g675 s~
defines a conductlve metal pattern comprising a two-dim~nsional array of areas devoid of conductive material ~"voids"~ within a mesh of conductive material, said voids being reyularly spaced hexagons arranged such that the sides of adjacent hexagons are parallel to each other.
In accordance with the invention there is also provided in the method of making an electric resistance device in which a thin layer of film of metal is uniformly deposited on an insulating substrate, that improvement comprising the steps of thereafter selectively removing portions of the metal so deposited such that in a selected area of said device the remalning ~etal defines a conductive metal pattern comprising a two-dimensional regular array of areas devoid of conductive material ~"voids") within a mesh of conductive material, said voids being arranged such that the centers of the voids forming a set of three adjacent voids are positioned at the corners of a trianyle ancl the overall direction of current flow in said device is not parallel to any of the sides of said triangle.
In accordance with the invention there is provided an electrical resistance device inaludlng a conductive metal pattern carried on an insulatlng surface, said device being characterized in that a portion of said conductive metal pa~tern includes a two-di~ensional array of substantially identical areas of said substrate devoid oi conductive material on said substrate, said voids being arranged such that the centers of sets of three adjacent voids are positioned at the corners of the triangles and the overall direction of current flow in said dev.ice is genexally ,, , 4 ~3~76~ 69575-53 not parallel to sides of said triangles.
DescriPtion of Dr~
Figure 1 is a plan view of an electrical heating device constructed in accord wi~h the pre~ent invention, with the top insulating layer and metal conductors of the device removed for purposes of clarity.
Figure 2 is a sectional view taken at line 2-2 of Figure 1, with the top insulating layer and metal condu~tors of the device in place.
Figure 3 is an enlarged view of a por~ion of the semi-conductor pa~tern of the device of Figure 1.
Figure 4 is a diagram illustrating aspects of the semi-conductor pattern shown in Figure 1.
Figures 5-7 illustrate other semi-conductor mesh-void plan view of another electrical heating device, embodying the inven~ion.
Figure 8 is a schema-tic plan view of another heater embodyiny the invention.
, . ., :
.
~3~ 7 Figure 9 is a plan view of an electrical resistance device embodying the present invention.
Figure lO is a section taken at line lO-10 of Figure 9.
Figure ll is an enlarged plan view of a portion of the device of Figure 9, more clearly illustrating the mesh-void pattern.
Detailed De cription of Preferred Embodiment Referring now to Figures 1-4, there is shown an electrical sheet heter, generally designated lO, comprising an electrically-insulating plastic substrate 12 on which is printed a semi-conductor pat-tern 14 of colloidal graphite. In the embodiment shown, the heater is intended for use as an infrared imaging target, and the semi-conductor pattern is designed to produce a thermal image similar to that produced by a human being.
As shown, substrate 12 is 0.004 inch thick polyester ~"Mylar"), and the relative size of the substrate 12 and semi-conductor pattern 14 are such as to provide an uncoated side boundary area 8, between the outer edges of the semi-conductor pattern 14 and the edges of the substrate. Area 8 has a minimum width of l/2 inch along the sides 9 of the target and of 1 1/4 inch along the target bottom 11. The semi-conductor pattern provides a watt density of about 12-15 watts per square foot over its surface when the heater is connected to a llO volt power source.
For connecting the target to a power source, the semi-conductor pattern 14 includes a pair of connect-ing portions 16, each about 5/32 inch wide, extending generally across the target bottom. As shown, the connecting portions are aligned with each other, with an about 1/4 inch wide space 18 (i.e., an insulating * rr~A4'~
- 6 - ~ 34Jl6 ~ ~'7 area free of semi-conducting material) between their adjacent ends. A series of small rectangles 20, each about 1/4 inch high and 1/8 inch wide are spaced along the length of each connecting portion 16, with the lower edge of each rectangle 20 about 5/32 inch from the bottom edge of the connecting portion. The distance between adjacent rectangles 20 is 1/4 inch.
A pair of electrodes 22, each comprising a tinned copper strip 1 inch wide and 0.003 inch thick, extend across the bottom of the target. Each electrode 22 partially overlies and electrically engages a respec-tive one of connecting portions 16. As shown most clearly in above-referenced U. S. Patent No.
4,542,285, each electrode includes two transversely-spaced longitudinally-extending rows of spaced square holes 24, with solid copper strips 26, 28 and 30 being provided along the inner and outer edges of the electrode and between the two rows of holes.
A thin electrically insulating plastic cover sheet 32, shown in Figure 2 and comprising an es-sentially transparent co-lamination of an 0.005 cm.
(0.002 in.) thick polyester ("Mylar") and an 0.007 cm (0.003 in.) thick adhesive binder, e.g., polyethylene, overlies substrate 12, semi-conductor pattern 14, and conductors 22. The conductors 22 are not themselves bonded to the underlying substrate or semi--conductor material. However, the cover sheet 32 ~which is coextensive with the entire substrate 12) bonds tightly to the uncoated (with semi-conductor material) areas 8 of substrate 12 (along the marginal areas where the two sheets are in face-to-face engagement and through the holes 24 in conductors 22), and also to the uncoated rectangular areas 40 spaced along the inside edges of conductor strips 26. In the areas in _ 7 _ ~3~76~
which (as discussed hereinafter) the conductive mate-rial is printed in a mesh-void pattern, the cover sheet 32 bonds to the substrate 12 in the voids also.
Typically, substrate 12 and cover sheet 32 are essentially transparent. In military target applica-tions, cover sheet 32 may be painted the color of, e.g., a tank.
The portions of semi-conductor pattern 14 which produce the desired thermal image include three gener-ally "U" shaped "heating" portions, designated 50, 51and 52, respectively, which form the "head" of the target; a pair of generally trapezoidal "heating" por-tions, designated 60 and 61, respectively, which form the "shoulders" of the target; and a pair of rectangular "heating" portions, designated 70 and 71, respectively, which form the rest of the body.
In all three areas, the semi-conductor ink is printed at essentially the same thickness, e.g., about 0.0005 in.; and the resistivity (ohms per s~uare) of the areas actually covered by ink, is essentially the same throughout. As will become apparent, however, the resistivities of the three areas on a lager scale (e.g., on a scale including both the areas covered by ink and, in the shoulder and body portions, the array of "voids") differ. As shown, U-shaped semi-conductor-free insulating areas 80 are provided between the adjacent "head" portions 50, 51 and 52, and another semi-conductor-free insulating area 81 is provided between the adjacent "body" portion~ 70 and 71 and between the adjacent "shoulder" portions 60 and 61. The heating portions 5Q, 51 and 52 which form the head are connected (in parallel with each other) electrically in series with "shoulder" portions 60 and 61, and each of "body" portions 70 and 71 is connected electrically in series between a respective one of - 8 - ~ 3~ 6t76~
"shoulder' portions 60, 61 and a respective one of connecting portions 16.
In each of "head" portions 50, 51, and 52, the semi-conductor colloidal graphite material is printed over the entire area, covering the entire area at a uniform thickness, typically in the range of 0.3 to l.~ mil. In connecting portions 16, the semi-conductor material similarly covers the entire area of the connecting portions, except for the rectangular openings 40 that provide for bondiny of the top sheet 32 to substrate 14 and hold conductors 22 in place.
In the "shoulder" portions 60, 61, and in the "body" portions 70, 71, the resistivity (ohms per square) required to produce the desired watt density typically cannot be obtained by printing the semi-conductor colloidal graphite material over the entire area at the same thickness at which it is printed over the "head" portions 50, 51 and connecting portions 16.
In each of portions 60, 61, 70, and 71, the semi-conductor rnaterial is printed over the area in an openmesh pattern, i.e., a regular array of small areas which are devoid of semi-conductor material ("voids") within a continuous semi-conductor "mesh" that sur-rounds the "voids" and covers the rest of the respec tive portion. Although the resistivity of the ink layer itself remains constant, the resistivity (ohms per s~uare) and resulting watt density of a portion including voids depends on, and varies according to, the void configuration and pattern (e.g., the arrange ment and spacing of, and the percentage of the overall area that is covered by the voids). An area in which the "voids" cover 50 percent of the entire area typically will have greater resistivity than will an area in which the "voids" cover only 25 percent of the area; and the least resistivity typically will be - g - ~L3~6'~7 found in an area in which the percentage of "voids" is zero, i.e., in an area, such as "head" portions 50, 51, 52, all of which i9 coated or printed with semi-conductor material.
In the embodiment of Figs. 1-4, the voids are hexagonal and are arranged in a regular rectilinear array in which the centers of adjacent voids form equilateral triangles. Figure 3 is an enlarged view of part of "bodyl' portion 70 illustrating the hexagonal voids 80 and semi-conductor material mesh 82, and Figure 4 is a diagram further illustrating the geometry of the Fig. 3 void-mesh pattern. In Figure 4, the distance between the centers of adjacent hexagonal voids 80 is designated "D", the distance from the center to each corner of a void (and hence the radius of a circle tangent to the inside of and subscribed by the void) is desiynated "R", and the width of the semi-conductor material mesh strips 81 between adjacent voids is designated "P". As will be apparent, the relationship between these three distances i5:
P = D - 2R.
It has been found that "P" should not be less than about 0.015 inches, preferably not less than about 0.020 inches, and that R should not be less than l/64 inch~ preerably not less than about l/32 inch.
To provide even heating over the entire area, it also has been found desirable that the individual voids should not be too large, e.g., R typically should not exceed about l/4 inch.
In the hexagonal void pattern of Figure 4, the width of the semi-conductor mesh strip 81 between each pair of adjacent voids 80 essentially constant, and the overall mesh pattern consists of a series of constant width strips 81 joined at their ends - 1 o - ~L3~ 7 (adjacent the corners of the hexagonal voids) by equilateral triangular portions 83 each side of which is equal in length to the strip width. It also will be noted that the percentage of an overall heating portion that is covered by semi-conductor material depends on spacing between voids and the ~idth of the mesh strips between adjacent hexagonal voids;
theoretically, it may vary from 0% (P = o; each hexagon is so large that the adjacent voids abut each other) to 100% (P = D; the entire area is covered with semi conductor material; each hexagon has an area of zero). In a typical arrangement in which the distance D between void centers is 0.375 in., if P is 0.015 in.
voids will cover about 90% of the overall area, and lS the semi-conductor mesh will cover the remaining about 10%. It will be noted that the percentage covered by the voids may be somewhat increased by increasing center-to-center spacing of the voids while maintain-ing or (if printing will permit) decreasing P; and that the percentage of void coverage can be decreased as desired by reducing the voids size ~R) or by maintaining the void size while increasing "D".
In the heater of Fig. 1, the hexagonal voids in the "shoulder" portions 60, 61 and "body" portion 70, 71 are arranged so that the distance between adjacent voids is 0.375". In "shoulder portions" 60, 61, the voids are sized (R = 0.10 in.) so that the voids in the mesh-void pattern cover about 20% of the area of the shoulder portions. In body portions 70, 71 the voids are larger (R - 0.14 in.), and the voids cover about 40% of the overall area.
The resistivity (ohms per square) of an area comprising a mesh-void pattern is greater than that of an area completely covered by the same semi-conductor ~3~;~t~7 material printed at the same thickness. Using a mesh-void pattern in which the shape and center-to-center again of the voids remains the same, the resistivity of an area generally can be increased by using larger voids, and decreased if the voids are made smaller.
With reference to the heater of Figs. 1-4, it thus will be seen that the resistivity (ohms per square) in the head portions 50, 51, 52 (which are entirely covered with semi-conductive material) is less than that in any of the other portions of the semi-conductor pattern (which are mesh-void patterns).
Similarly, the resistance (ohms per square) in the shoulder portions 60, 61 ~in which the voids cover about 20~ of the total area) is less than that in body portions 70, 71 (in which the voids cover about 40% oE
the area). In the illustrated embodiment, the resistance in the "shoulder" portions 60, 61 is about 130% of that in head portions 50, 51, 52; and that in body portions 70, 71 is about 180% of that in the head portions. However, the overall sizes and shapes of the various portions are such that the watt densities produced by each of the "body" and "shoulder" portions (which represent portions of a human's body that ~ill be clothed and thus should appear to an infrared imag-ing device to be slightly cooler than an unclothedhead) are about th~ same, and are slightly less than the watt density produced by the head portions.
It will be noted that, in each of "shoulder" por-tions 60, 61 and "body" portions 70, 71, the direction of current flow is generally vertical. In areas that include a mesh-void pattern, it normally is desirable that the lines connecting the centers of adjacent voids not be parallel to the overall direction of cur-rent flow. Thus, the mesh-void patterns in the shoulder and body portions are oriented such that the - 12 ~ 7 sides of the equilateral triangles connecting adjacent voids are either perpendicular or at a 30 angle to the generally vertical current flow direction.
Similarly, if the void centers were arranged in a square pattern, it would normally be desirable to ori-ent the pattern so that the sides of the squares form 45 angles to the current flow direction.
Alternative mesh-void patterns, in which the voids are circular, are shown in Figures 5 and 6.
In the Figure 5 pattern, the circular voids 180 are arranged so that the centers of three adjacent voids form equilateral triangles, the distance between the centers of adjacent void9 beinq designated D', the radius of each void being designated R', and the width of the semi-conductor material mesh between adjacent voids being designated P'. The minimum width of the semi-conductor mesh strips 181 between each pair of voids 180 is located on the line connecting the centers of the voids and is equal to D'-2R'.
The circular voids 280 in the Figure 6 pattern are arranged with the centers of four adjacent voids located at the corners of a square. The distance between the centers of two adjacent voids, i.e., the length of each side of each square, is D", the radius of each void 280 is R", and the minimum width 8" of the semi-conductor strip 281 between two adjacent voids 281 ~which again is located on the line connect-ing the void centers) is D'l-2R".
In the circular void patterns of Figures 5 and 6, the semi-conductor mesh strips 181, 281 between adjacent pairs of voids 180, 280 vary in width. In each, the minimum width is on the line connecting the center of adjacent pairs of voids and the width of the end portions of each strip is considerably greater.
Thus, and unlike in the hexagonal void pattern of - 13 ~ 7 Figure 4, there is considerable variation in resistance along the length of each mesh strip 1~1, 281. It also will be noted that circular void pat-terns should not be used when it is desirable for the voids to cover a large percentage of the overall heat-ing area. For example, in the Figure 5 pattern in which the centers of the circular voids are located at the corners of equilateral triangles, the maximum theoretical percentage of the overall heating portion areas covered by voids ~i.e., the percentage covered when R is almost as large as P/2 and adjacent voids are almost tangent to each other) is about 90%; in the Figure 6 pattern, in which the void centers are located at the corners of squares, the maximum theoretical percentage that can be covered by voids is about 20%. As a practical matter, the requirement that P be not less than about 0.015 in. means that the maximum void coverage that can be obtained using circular void patterns is considerably less than the theoretical maximum (e.g., about 80% equilateral triangle corner pattern; and about 60~ using a square corner pattern) and to insure good printing and even heating, circular void patterns typically will not be employed in circumstances in which it is desirable for the voids to cover more than about 2/3 of the heating area.
In other embodiments, other void shapes and pat-terns may be employed. For example, the voids need not be circular or hexagonal in shape, e.g., squares, ovals, triangles or irre~ular shapes could be used; in some circumstances the centers of the voids may not be arranged in a regular, rectilinear array; and in some circumstances it may be desirable to create the mesh-void pattern by printing over an entire area and then 3s "punching-out" the voids.
.
3L3~6~ 7 Figure 7, for example, illustrates, enlarged, a void-mesh semi-conductor pattern of the present inven-tion in which the "voids" 380 are in the shape of diamonds so arranged that diamond centers are located on the corners of parallelograms the sides of which are about 0.4 in. long. The mesh 382 between voids comprises interconnected stripes 381 about 0.020 inO
wide.
Fig. 8 illustrates a special purpose heater 410 in which a serpentine semi-conductor pattern 414 of varying overall width is printed on a paper substrate 412. The pattern 414 includes a solid conductor contract portion 416 at each end of the pattern, and a number of serially-connected heating portions designated 420, 422, 424, 426, 428, 430, 432 therebetween. Heating portions 420, 424, 428 and 432 are "solid" (i.e., the semi-conductor material covers the entire area of each). Heating portions 422, 426 and 4~8 are printed in a mesh-void pattern. In por-tions 422 and 428, the mesh-void pattern comprises hexagonal voids aligned in an equilateral triangle portion with D = 0.375 in. and R = 0.0625 in. In portion 426, the mesh void pattern comprises hexagons of the same size arranged in an equilateral triangle pattern in which D - 0.250 in. Circular tinned copper conductors 450 are held in face-to-face electrical contact with each of conductor contact areas 416 by, e.g., a conductive adhesive.
In the above-described embodiments, and in those described in the aforementioned U.S. Patents, the material forming the semi-conductor pattern typically has (if printed uniformly over an area at a thickness of 0.0005 in.) a resistivity of about 80 ohms per square. By way of contract the resistivity of a metal te.g., nickel) film having the same thickness will be IL3~767 using much less. ~he resistivity of such a metal layer may be increased somewhat by making the film very thin; but on a commercial basis it is extremely difficult, if not impossible, to deposit unirorm metal films at thicknesses significantly less than about 35 Angstroms, (at which thickness the resistivity of a nickel layer is about 20 ohm per square) and it heretofore has not been feasible to produce uniform metal layers having a resistivity much greater than that of a uniform 35 Angstrom layer.
Figures 9-11 show an electrical resistance device, generally designated 110, comprising a metal pattern 112 deposited at essentially uniform thickness (i.e., about 35 Angstroms) on an organic plastic (e.g., polyester) substrate 114. Along the opposite side edges of device 110, metal pattern 112 comprises continuous conductor contact strips 116 about one-half inch wide. A tinned copper conductor 118 overlies and is adhesively attached (e.g., with a conventional conductive adhesive) to each conductor contact strip 14. In other embodiments, the conductor contact strips may be deposited at a greater thickness than the remaining portion of the metal pattern, often in lieu of providing separate conductors.
The heating area 119 of device 110 (i.e., the portion between the spaced apart conductors 118 and conductor contact strips 116) comprises a regular rectilinear array of hexagonal voids 120 (i.e., hexagonally shaped areas that are free of metal or other conductive material) in a metal mesh pattern 121. The voids 120 are arranged on 0.375 in. centers, with the centers of strips of three adjacent voids at the corners of equilateral triangles (each leg of each triangle being 0.375 in. long). The triangles are arranged so that their sides are perpendicular to or ~3~
form 30 angles with the direction of current ~low, i.e., with a line extending transversely of device 110. The adjacent side edges of adjacent hexagonal voids are parallel to each other, and the size of the voids is such that the metal strip 122 between adjacent voids is about 0.005 inches wide (i.e., the size of each hexagon is such that the diameter of a circle within and tangent to the sides of the triangle is 0.370 in.).
The exact resistivity tohms per square) of the heating area 118 should be determined empirically. To a close approximation, the resistivlty (R) is given by the following formula:
1.732rD/W
where r is the resistivity (ohms per square) of the metal layer, and D and W are, respectively, the diameter of a circle inscribed within and tangent to hexagonal voids 20 and W is the width of the strip 22 between adjacent voids. Using the formula, it will be seen that resistivity (R) of the heating area 19 of device 10 is about 74r. If, as in the illustrated embodiment, the metal layer is nickel about 35A thic!c, r is about 20.5 ohms per square and R is about 1525 ohms per square.
In practice, the electrical device 110 of Figures 9-11 is made as follows:
a. Deposit a continuous metal layer of the desired thickness on substrate 114. In preferred practice the layer is deposited using a conventional vacuum deposition or metallization procedure.
b. Deposit an acid resist pattern over the continuous metal layer. The acid resist pattern ls deposited such that resist material covers all the metal that is not to be removed (i.e., it covers conductor contact strips 116 and the metal mesh in 1~ 7~7 heating area ll9). The acid resist pattern may be deposited using any of a number of conventional techniques. For example, screen printing, roto-graveure or flexo-graveure. Alternatively, a solid layer of acid resist may be deposited over the entire metal layer, and the pattern then produced by selectively removing portions of the resist using a conventional photoresist technique. Materials useful in forming the resist pattern include Blake Acid Resist from Cudner & O'Connor, Dychem (Type M or AX) film photoresist and Dupont (#4113) film photo resist.
c. Pass the device (with the resist plan pattern thereon) through an acid bath to remove all the metal layer that is not protected (i.e., covered) by the acid resist pattern (the remaining metal provides conductor contact strips 116 and mesh 121.
d. Remove the resist pattern.
e. Adhesively attach conductors 118.
As with the conductive graphite embodiments discussed above, metal mesh devices also may include a number of different heating areas of different resistivity. For example, such a device may include one area in which the array of hexagonal voids is as just discussed with respect to Figures 9~11, and in a secondary the hexagonal voids may be arranged on dif~
ferent (e.g., .250 inch centers) and the width of the metal strips between adjacent voids may be different also (e.g., a width as small as about 0.001 in. may be produced using a photoresist process). The two heat-ing areas have different resistivities. The firstwill have a resistivity 74 times greater than that of the metal layer; in the second, the resistivity will be about 250 times that of the metal layer.
~q clc rnar tC
~L3~ 6'7 Similarly, other conductive materials (e.g., either metals such as silver or gold or other conduc-tive compositions or dispersions) may be used in lieu of nickel, and different mesh-void patterns (e.g., those described in our above-referenced and incorporated application) may be used.
These and other embodiments will be within the scope of the foIlowing claims.
What is claimed is:
;
~. ~, .. . . .. .
Claims (49)
1. An electrical heating device including a layer of semi-conductive material carried on an insulating surface and defining a semi-conductive pattern, and a pair of spaced-apart conductors electrically connected to said semi-conductive pattern, said device being characterized in that a first heating portion of said semi-conductive pattern intermediate said conductors includes a two-dimensional array of areas devoid of semi-conductive material ("voids") within a mesh of semi-conductive material, said voids being arranged such that the centers of the voids forming sets of three adjacent voids are positioned at the corners of equilateral triangles.
2. The heating device of claim 1 further characterized in that said voids are circles or regular polygons.
3. The device of claim 1 wherein said voids are hexagons and are arranged such that the overall direction of current flow between said conductors is not parallel to the sides of said triangles.
4. An electrical heating device including a layer of semi-conductive material carried on an insulating surface and defining a semi conductive pattern, and a pair of spaced-apart conductors electrically connected to said semi-conductive pattern, said device being characterized in that a first heating portion of said semi-conductive pattern intermediate said conductors includes a two-dimensional array of areas devoid of semi-conductive material ("voids") within a mesh of semi-conductive material, and said conductors and said voids being arranged such that the centers of the voids forming sets of three adjacent voids are positioned at the corners of triangles, and the overall direction of current flow between said conductors is not parallel to the sides of said triangles.
5. The heating device of claim 1 further characterized in that said voids are hexagons, that the centers of sets of four adjacent hexagons are positioned at the corners of parallelograms, and that sides of adjacent hexagons are parallel to each other.
6. The device of claim 4 wherein said voids are hexagons and are regularly arranged with sides of adjacent hexagons parallel to each other.
7. An electrical heating device including a layer of semi-conductive material carried on an insulating surface and defining a semi-conductive pattern, and a pair of spaced-apart conductors electrically connected to said semi-conductive pattern, said device being characterized in that a first heating portion of said semi conductive pattern intermediate said conductors includes a two-dimensional array of areas devoid of semi-conductive material, ("voids") within a mesh of semi-conductive material, said voids being hexagons arranged such that the centers of the voids forming sets of four adjacent hexagons are positioned at the corners of parallelograms.
8. The heating device of claim 1 further characterized in that the minimum width of semi-conductive material of said mesh intermediate adjacent ones of said voids is not less than about 0.015 in.
9. An electrical heating device including a layer of semi-conductive material carried on an insulating surface and defining a semi-conductive pattern, and a pair of spaced-apart conductors electrically connected to said semi-conductive pattern, said device being characterized in that first and second heating portions of said semi-conductive pattern intermediate said conductors each include a respective regular two-dimensional array of areas devoid of semi-conductive material ("voids") within a mesh of semi-conductive material, and said second heating portion of said semi-conductor pattern is contiguous to said first heating portion and has a resistivity (ohms per square) different from that of said first portion.
10. The heating device of claim 9 wherein said first heating portion and said second heating portion each comprises a respective regular two-dimensional array of hexagonal voids.
11. The heating device of claim 9 wherein the distance between the centers of the voids in said first and second heating portions are the same, and the size of the voids in said first portion is greater than the size of the voids in said second portion.
12. The heating device of claim 9 wherein the percentage of said first portion covered by semi-conductor material is greater than the percentage of said second portion covered by semi-conductor material.
13. The heating device of claim 9, wherein at least one of the configuration, center-to-center-spacing and size of the voids of said first portion is different from the respective one characteristic of the voids of the second portion.
14. The heating device of claim 1 further characterized in that the area of each of said voids is not more than that of a circle about 1/2 in. in diameter.
15. The heating device of claim 14 where said voids are regularly spaced circles or polygons and the minimum width of the semi-conductor mesh between adjacent voids is not less than about 0.015 inch.
16. The heating device of claim 15 wherein the percentage of said first heating portion covered by said voids is between 10 and 90.
17. An electrical heating device comprising:
a substrate;
a layer of semi-conductor material carried on an insulating surface of said substrate and defining a semi-conductor pattern including a pair of spaced-apart conductor contact portions and at least one heating portion; and a pair of spaced-apart electrical conductor each of which electrically engages one of said conductor contact portions of said semi-conductor pattern;
said device being characterized in that:
said heating portion comprises a regular two-dimensional array of areas devoid of semi-conductor material ("voids") within a continuous mesh of semi-conductor material, said voids being circles or polygons and being arranged such that the centers of the voids forming sets of three adjacent voids are positioned at the corners of equilateral triangles.
a substrate;
a layer of semi-conductor material carried on an insulating surface of said substrate and defining a semi-conductor pattern including a pair of spaced-apart conductor contact portions and at least one heating portion; and a pair of spaced-apart electrical conductor each of which electrically engages one of said conductor contact portions of said semi-conductor pattern;
said device being characterized in that:
said heating portion comprises a regular two-dimensional array of areas devoid of semi-conductor material ("voids") within a continuous mesh of semi-conductor material, said voids being circles or polygons and being arranged such that the centers of the voids forming sets of three adjacent voids are positioned at the corners of equilateral triangles.
18. The device of claim 17 wherein the minimum distance between the adjacent edges of adjacent ones of said voids being not less than about 0.015 in.
19. The device of claim 18 wherein said voids are hexagons, and are arranged such that the centers of sets of four adjacent hexagons are positioned at the corners of a parallelogram having sides of substantially equal length and an included angle of about 60°.
20. In an electrical device comprising:
a substrate having an insulating surface; and a layer of conductive material carried on said insulating surface of said substrate and defining a conductive pattern, that improvement wherein said pattern comprises a regular two-dimensional array of areas devoid of conductive material ("voids") within a continuous mesh of conductive material, said voids being circles or regular polygons and being arranged such that the centers of the voids forming sets of three adjacent voids are positioned at the corners of equilateral triangles.
a substrate having an insulating surface; and a layer of conductive material carried on said insulating surface of said substrate and defining a conductive pattern, that improvement wherein said pattern comprises a regular two-dimensional array of areas devoid of conductive material ("voids") within a continuous mesh of conductive material, said voids being circles or regular polygons and being arranged such that the centers of the voids forming sets of three adjacent voids are positioned at the corners of equilateral triangles.
21. The device of claim 20 wherein said voids are hexagons, the minimum distance between the adjacent edges of adjacent ones of said hexagons is not less than about 0.015 in., and said hexagons are arranged such that the centers of sets of four adjacent hexagons are positioned at the corners of a parallelogram having sides of substantially equal length and an included angle of about 60°.
22. The device of claim 21 including an electrically insulating sheet overlying said substrate and conductive pattern and adhesively attached to said voids.
23. The device of claim 20 wherein said voids are hexagons.
24. The device of claim 23 wherein said voids are regularly arranged with sides of adjacent hexagons parallel to each other.
25. The device of claim 17 wherein said voids are hexagons.
26. The device of claim 25 wherein said hexagons are arranged with the sides of adjacent hexagons parallel to each other and such that the overall direction of current flow between said conductors is not parallel to the sides of said triangles.
27. In the method of making an electric resistance device in which a thin layer or film of metal is uniformly deposited on an insulating substrate, that improvement comprising the steps of thereafter selectively removing portions of the metal so deposited such that in a selected area of said device the remaining metal defines a conductive metal pattern comprising a two-dimensional regular array of areas devoid of conductive material ("voids") within a mesh of conductive material, said voids being arranged such that the centers of the voids forming a set of three adjacent voids are positioned at the corners of an equilateral triangle.
28. In the method of making an electric resistance device in which a thin layer or film of metal is uniformly deposited on an insulating substrate, that improvement comprising the steps of thereafter selectively removing portions of the metal so deposited such that in a selected area of said device the remaining metal defines a conductive metal pattern comprising a two-dimensional array of areas devoid of conductive material ("voids") within a mesh of conductive material, said voids being regularly spaced hexagons arranged such that the sides of adjacent hexagons are parallel to each other.
29. The method of claim 28 wherein the distance between the sides of adjacent hexagons in not more than about 0.010 in.
30. The method of claim 28 including the steps of forming an acid resist pattern over said metal layer, said resist pattern covering the portions of said metal layer that are not to be selectively removed, and thereafter passing said device through an acid bath to remove the portions of said metal layer that are not covered by said resist pattern.
31. The method of claim 28 including the step of selectively removing metal in a second portion of said device to form in said second portion a mesh-void pattern different from that in said first portion.
32. In the method of making an electric resistance device in which a thin layer or film of metal is uniformly deposited on an insulating substrate, that improvement comprising the steps of thereafter selectively removing portions of the metal so deposited such that in a selected area of said device the remaining metal defines a conductive metal pattern comprising a two-dimensional regular array of areas devoid of conductive material ("voids") within a mesh of conductive material, said voids being arranged such that the centers of the voids forming a set of three adjacent voids are positioned at the corners of a triangle and the overall direction of current flow in said device is not parallel to any of the sides of said triangle.
33. The method of claim 28 wherein the centres of the voids forming a set of three adjacent voids are positioned at the corners of an equilateral triangle.
34. The method of claim 28 wherein said metal is silver or nickel deposited at a thickness less than about 100 Angstroms.
35. The method of claim 32 wherein said triangles are equilateral triangles.
36. The method of claim 27 wherein said voids are regular polygons.
37. An electrical resistance device including a conductive metal pattern carried on an insulating surface, said device being characterized in that a portion of said conductive metal pattern includes a two-dimensional array of substantially identical areas of said substrate devoid of conductive material ("voids") within a mesh of conductive material on said substrate, said voids being arranged such that the centers of sets of three adjacent voids are positioned at the corners of triangles and the overall direction of current flow in said device is generally not parallel to sides of said triangles.
38. The resistance device of claim 37 further characterized in that said voids are regular polygons.
39. The resistance device of claim 38 further characterized in that said voids are arranged such that the sides of adjacent voids are parallel to each other and said voids are regularly spaced.
40. The resistance device of claim 39 further characterized in that said voids are hexagons and that the centers of sets of three adjacent voids are positioned at the corners of equilateral triangles.
41. The resistance device of claim 40 further characterized in hexagons are arranged such that the overall direction of current flow in said device is not parallel to sides of said triangles.
42. The resistance device of claim 37 further characterized in that the width of conductive material of said mesh intermediate adjacent ones of said voids is not more than about 0.010 in.
43. The resistance device of claim 37 further characterized in that a second portion of said conductive pattern contiguous to said first mentioned portion has a resistivity (ohms per square) different from that of said first mentioned portion.
44. The resistance device of claim 43 wherein said first mentioned portion and said second portion each comprises a respective regular two-dimensional array of voids within a mesh of conductive material.
45. The resistance device of claim 44 wherein at least one of the distance between the centers of the voids and the size of the voids in said first portion is different than the distance between the center of the voids and the size of the voids in said second portion.
46. The resistance device of claim 45 wherein said voids are hexagons, and are arranged such that the sides of adjacent hexagons are parallel to each other.
47. The resistance device of claim 37 wherein said pattern comprises metal deposited on said substrate at substantially uniform thickness.
48. The resistance device of claim 47 wherein said thickness is less than about 100 Angstroms.
49. The resistance device of claim 47 wherein said metal is silver or nickel.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/138,857 US4892998A (en) | 1987-12-29 | 1987-12-29 | Semi-conductive electrical heating device with voids |
| US138,857 | 1988-01-11 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1306767C true CA1306767C (en) | 1992-08-25 |
Family
ID=22483973
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000587166A Expired - Fee Related CA1306767C (en) | 1987-12-29 | 1988-12-28 | Electrical heating device |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | US4892998A (en) |
| CA (1) | CA1306767C (en) |
Families Citing this family (20)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB9020400D0 (en) * | 1990-09-19 | 1990-10-31 | Raychem Sa Nv | Electrical heating tape |
| WO2000007197A2 (en) * | 1998-07-31 | 2000-02-10 | Oak-Mitsui Inc. | Composition and method for manufacturing integral resistors in printed circuit boards |
| US6180929B1 (en) | 1998-08-06 | 2001-01-30 | Clearpath, Inc. | Heating pad apparatus adapted for outdoor use |
| US6852956B2 (en) * | 1999-04-22 | 2005-02-08 | Malden Mills Industries, Inc. | Fabric with heated circuit printed on intermediate film |
| US6875963B2 (en) * | 1999-04-23 | 2005-04-05 | Malden Mills Industries, Inc. | Electric heating/warming fabric articles |
| US20080047955A1 (en) * | 2002-01-14 | 2008-02-28 | Malden Mills Industries, Inc. | Electric Heating/Warming Fabric Articles |
| US7202443B2 (en) * | 2002-01-14 | 2007-04-10 | Malden Mills Industries, Inc. | Electric heating/warming fabric articles |
| US7268320B2 (en) * | 2002-01-14 | 2007-09-11 | Mmi-Ipco, Llc | Electric heating/warming fabric articles |
| US7777156B2 (en) * | 2002-01-14 | 2010-08-17 | Mmi-Ipco, Llc | Electric heating/warming fabric articles |
| US7306283B2 (en) | 2002-11-21 | 2007-12-11 | W.E.T. Automotive Systems Ag | Heater for an automotive vehicle and method of forming same |
| JP2005197074A (en) * | 2004-01-07 | 2005-07-21 | Ngk Insulators Ltd | Resistance heating element and heater |
| US7763833B2 (en) * | 2004-03-12 | 2010-07-27 | Goodrich Corp. | Foil heating element for an electrothermal deicer |
| US7923668B2 (en) * | 2006-02-24 | 2011-04-12 | Rohr, Inc. | Acoustic nacelle inlet lip having composite construction and an integral electric ice protection heater disposed therein |
| US8702164B2 (en) * | 2010-05-27 | 2014-04-22 | W.E.T. Automotive Systems, Ltd. | Heater for an automotive vehicle and method of forming same |
| US9191997B2 (en) | 2010-10-19 | 2015-11-17 | Gentherm Gmbh | Electrical conductor |
| DE102012000977A1 (en) | 2011-04-06 | 2012-10-11 | W.E.T. Automotive Systems Ag | Heating device for complex shaped surfaces |
| DE202011109990U1 (en) | 2011-09-14 | 2012-12-17 | W.E.T. Automotive Systems Ag | Tempering device |
| US10201039B2 (en) | 2012-01-20 | 2019-02-05 | Gentherm Gmbh | Felt heater and method of making |
| DE102012017047A1 (en) | 2012-08-29 | 2014-03-06 | W.E.T. Automotive Systems Ag | Electric heater |
| DE102012024903A1 (en) | 2012-12-20 | 2014-06-26 | W.E.T. Automotive Systems Ag | Flat structure with electrical functional elements |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3287161A (en) * | 1962-10-01 | 1966-11-22 | Xerox Corp | Method for forming a thin film resistor |
| US3266005A (en) * | 1964-04-15 | 1966-08-09 | Western Electric Co | Apertured thin-film circuit components |
| AT310886B (en) * | 1969-11-04 | 1973-10-25 | Thermo Bauelement Ag | Underfloor heating with heat storage masses |
| US3664013A (en) * | 1970-03-06 | 1972-05-23 | Andrew Edward Macguire | Method of manufacturing electric heating panels |
| US4485297A (en) * | 1980-08-28 | 1984-11-27 | Flexwatt Corporation | Electrical resistance heater |
-
1987
- 1987-12-29 US US07/138,857 patent/US4892998A/en not_active Expired - Fee Related
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1988
- 1988-12-28 CA CA000587166A patent/CA1306767C/en not_active Expired - Fee Related
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| Publication number | Publication date |
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| US4892998A (en) | 1990-01-09 |
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