CA1047133A - Coil for magnetic field generation - Google Patents
Coil for magnetic field generationInfo
- Publication number
- CA1047133A CA1047133A CA236,151A CA236151A CA1047133A CA 1047133 A CA1047133 A CA 1047133A CA 236151 A CA236151 A CA 236151A CA 1047133 A CA1047133 A CA 1047133A
- Authority
- CA
- Canada
- Prior art keywords
- coil
- conductors
- leg portion
- stripe line
- conductor
- 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
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F27/00—Details of transformers or inductances, in general
- H01F27/28—Coils; Windings; Conductive connections
- H01F27/2847—Sheets; Strips
- H01F2027/2861—Coil formed by folding a blank
Landscapes
- Coils Or Transformers For Communication (AREA)
- Manufacturing Cores, Coils, And Magnets (AREA)
Abstract
A COIL FOR MAGNETIC FIELD GENERATION
Abstract of the Disclosure An improved coil for magnetic field generation in bubble memory devices. A stripe line coil pattern having varying widths of conductors is etched from a conductive film supported on a polyamide film. The stripe line layer is wrapped around a coil form and the outer ends of the conductors are electrically connected in an offset fashion to form a field coil having a single closed loop. The stripe line coil is arranged in a multiple layer structure having the conductors with varying widths aligned in series along the layer direction rather than in parallel, thereby providing improved magnetic field uniformity and minimizing high frequency loss in a uniform, easily wound coil configuration. A stripe line coil having reduced resistance and correspondingly minimized power loss is achieved by substantially increasing the ratio of stripe line conductor area to insulation area. This is accomplished by forming the coil from a single sided stripe line with a double thick conductor film, in one preferred embodiment of the invention, or, from a double sided stripe line, in another preferred embodiment.
Abstract of the Disclosure An improved coil for magnetic field generation in bubble memory devices. A stripe line coil pattern having varying widths of conductors is etched from a conductive film supported on a polyamide film. The stripe line layer is wrapped around a coil form and the outer ends of the conductors are electrically connected in an offset fashion to form a field coil having a single closed loop. The stripe line coil is arranged in a multiple layer structure having the conductors with varying widths aligned in series along the layer direction rather than in parallel, thereby providing improved magnetic field uniformity and minimizing high frequency loss in a uniform, easily wound coil configuration. A stripe line coil having reduced resistance and correspondingly minimized power loss is achieved by substantially increasing the ratio of stripe line conductor area to insulation area. This is accomplished by forming the coil from a single sided stripe line with a double thick conductor film, in one preferred embodiment of the invention, or, from a double sided stripe line, in another preferred embodiment.
Description
1047~3~
--,Background of the Invention 1. Field of the Invention This invention relates to magnetic field coils for and, more particularly, to a printed circuit coil which may be used for devices requiring a large area of uniform ma~net-ic field, such as field acGess bubble memory devices.
--,Background of the Invention 1. Field of the Invention This invention relates to magnetic field coils for and, more particularly, to a printed circuit coil which may be used for devices requiring a large area of uniform ma~net-ic field, such as field acGess bubble memory devices.
2. Description of Prior Art The field access type bubble domain devices require an in-plane rotating field.for device operation. This in-plane rotating field is generally provided by a coil winding.Ideally, the coil should generate a uniform field, exhibit low elec-tronic power loss, and be relatively easy to wind repeatable to the same geometry. Unfor~unately, the wire wound coils presently used do not consistently meet these requirements.
In the wire wound coil, current density along the coil axis is uniform, which causes the magnetic field strength to peak at the coil center with gradual fall off toward both ends of the coil. The magnetic field uniformity 2a can be improved by adding additional turns near both ends of the coil. This arrangement of additional turns of course causes the coil to have an ocld shape configuration and also increases the coil size, both of which are undesirable features.
Also, skin and proximity effects are inherent in wire wound coils. These effects are primarily due to coupling between the closely wound wire turns and result in a high frequency loss. A prior art means of eliminating the high ~requency loss is to use a Litz wire, i.e., a conductor consisting of several individual insulated wires.
Unfortuna.tely, as may be appreciated, this approach is very ~ - 2 -"`` 3L047~33 ; --expensive.
In summary, the existing known methods of coil winding do not generate a uniform field, are cumbersome to produce and the improvements required to correct these undesirable features are not economically feasible. The ~ 2a ~
...~.....
~esent invention, which uses a conductor stripe type coil winding etched on a conductor foil supported on an insulating film, provides the desired characteristics using conductors of varied widths and arranging the stripe line patterns in a multiple layer stripe structure having the conductors aligned in series along the layer direction rather than in parallel.
SUMMARY
A printed circuit magnetic field coil is produced on a flexible L-shaped conductor substrate by etching a desired stripe line pattern having conductors with varying widths on a conductor foil supported on an insulating film (for example, cold rolled copper on a polyamide film); wrapping this stripe line film pattern around a fixed coil form; connecting the outer ends in an offset manner, i.e., displaced by one row of conductors to electrically connect all the stripe lines as a continuous single loop; and arranging a multiple layer structure with the conductors seried along the layer direction rather than in the axial direction. The conductor length, width and spacing are controlled by the etched pa~tern. The controlled geometry and seried connections provides improved coil parameters such as impedance, field uniformity, dissipation factor, size and shape, and high frequency operation.
More specifically, the invention consists of a coil for magnetic field generation, comprising a flexible substrate having a planar L-shaped configuration, a conductive layer formed on a first side of the substrate, the conductive layer having formed therein a plurality of conductors, each of the conductors having respective first and second ends, said conductive layer including first and second leg portions, said first leg portion having first and second ends and being substantially longer than said second leg portion, said second leg portion positioned . .~
~g~47133 `~~`\adjacent to the second end of said ~irst leg portion whereby the respective conductors formed in the conductive layer of said first and second leg portions are disposed at substan-tially right angles with respect to one another, said second end of said first leg portion wound at least once in a direction towards said first end of said first leg portion, said second leg portion wound around said first leg portion in a direction substantially perpendicular to the direction in which said first leg portion is wound, and said second leg portion folded back upon itself at an angle of substantially 45, whereby the conductors in said first end of said first leg portion are electrically interconnected to said conductors in said second leg portion to form a continuous closed loop.
Brief Description of the Drawings Fig. 1 is a plan view of the stripe line coil pattern prior to be wrapped into a field coil;
Fig. 2 is a fragmentary, sectional view of the stripe line coil pattern taken on the B side along line 2-2 of Figure l;
Fig. 3 is a perspective view of a completed stripe line coil winding of the instant invention;
Fig. 3a is a partial top plan view of Figure 3;
Fig. 4 is a cross-section of a stripe line coil with variable stripe width;
Fig. 5a is a fragmentary, sectional view of a single sided stripe line with a double thick conductor formed in accordance with the instant invention;
Fig~ 5b is a fragmentary, sectional view of a double sided conductor stripe line formed in accordance with 3Q the instant invention;
Fig. 6a is an end view of a multilayer stripe . __....
~47~33 line coil formed from the double sided conductor stripeline of Fig. 5b; and ~ Fig. 6b is a sectional view taken along lines 6b-6b of Fig. 6a.
Detailed Description of the Preferred Embodiment Referring concurrently to Figs. 1 and 2, there is shown an L-shaped stripe line composite 10 comprising an etched conductor foil 11 (Fig. 2) supported on an insulating film substrate 12 ~Fig. 2). Preferably the conductor layer 11 is copper on a polyamide film 12. One method of forming the stripe line pattern of the conductor layer is by known photolithographic techniques, i.e., by coating the copper surface with a thin layer of light sensitive photoresist, exposing the coated surface to light through a photomaster having the desired stripe line design and developing and etching the conductor material to produce the pattern (e.g., such as the parallel conductor pattern shown in Fig. 1).
Referring to Figure 2, a fixed size field coil can be formed by first wrapping the stripe line pattern composite 10 (Fig. 1) around a coil form (not shown). The inner end B' of the leg 14 of the composite 10 is wrapped over the coil form and wound a convenient number of times towards the inner end B in Figure 1, while the shorter leg extends outwardly from the inside of the winding. The flap end A of shorter leg 16 is next wrapped around the coil and folded back upon itself at an angle of about 45 so that the parallel conductors in the flap end A are aligned with the parallel conductors in the inner end B. As will be under-stood by those skilled in the ar~, to prevent shorting ofthe conductors in leg 14 during the wrapping of leg 16 around ~ _ 5 _ ~47~33 the coil, the conductors in leg 16 may be sprayed with an insulating film or covered with an insulating tape (e.g., Mylar*, Kapton* or the like). Thereafter, in one preferred embodiment, the conductors in end A are electrically interconnected by suitable means (e.g., soldering) in an offset fashion (e.g., by the width of one conductor) to *Trade Marks ~ - 5a .
~047133 r-spective conductors in end B, as shown in Figures 3 and 3a, thereby forming a single closed loop, Thus, the current carried by the offset parallel conduct~rs travels in a continuous current path around the closed loop. The conductor length, width and spacing are cont.rolled by the accuracy attained in the etched pattern. Therefore, consistent accuracy is attained in the coil parameters such as impedance, f:Leld uniformity, dissipation factor, size and shape.
~ 5b ~ L7~L33 .
One o~ the problems encountered in the con~entional wire wound coil is the closeness o~ the wire turns, which results in interwire coupling and high frequency loss. The multiple layer stripe line coil 13 structure of the instant invention, shown in Figure 4, substantially reduces the high frequency loss in two fashions. First, the spacing between layers or columns 17 of conductors can be easily controlled by patterns generated in the photomaster, so that a sufficient spacing can be provided as required between conductors to reduce the aforementioned adverse effects o~
the interwire coupling. Secondly, when the winding in this coil is connected in series, the sequence of the current flow is illustrated in Fig. 4. That is, the current flows in series through adjacent vertical arrays or columns 17 of conductors. The current 10ws in a single series loop from conductor 1 to 2 to 3 (the first vertical array or column 17) then from conductor 3 to conductor 4 to 5 to 6 (the next column 17) and from conductor 6 to conductor 7 to 8 to 9 (the next column 17) and so on. This winding arrangement minimizes the potential differences between neighboring turns thereby minimizing high frequency loss due to interwire coupling. This arrangement also helps minimize the unequal current distribution at high frequencies which occurs in coils having parallel wound layer~. The effective turns in this winding scheme can be controlled by varying the conductor width. That is, by increasing the conductor width the number of effective turns in the winding is decreased.
In wire wound coils, the magnetic field streng~h peaks at the coil center then gradually tapers off towards both ends of the coil. This field deficiency at the coil ` ~47~33 - ends can be improved by winding additional turns of wire - close to both coil ends. However, this winding arrangement results in an Qdd shape configuration for the coil and also increases the coil size. This invention controls the field deficiency at the ends of the coil by varying the conductor width as shown in Figure 4. That is, the conductor width is decreased as required at both ends along the coil axis, causing the field density to increase at the ends to thereby more evenly distribute a uniform magnetic field alon~ the coil axis. Since the stripes are photolithographically etched, the stripe width variations can be accurately controlled.
The total power dissipation of a stripe line coil is dependent upon its overall electrical resistance. With conventional stripe line wound coil configurations, the power dissipation is higher than with the corresponding wire wound coil having the same relative dimensions. Conventional polyamide film has ~.nown conductor thickness of .001-.004 inches and an insulator thickness of .001-.002 inches. Thus, conventional stripe line wound coil configurations are relatively inefficient because of the low ratio between conductor area and the winding cross section area. What is more, a stripe line conauctor (e.g., commonly, plated copper) frequently has a higher resistivity than that of the solid conductor wire. Although the conductor film can be plated to several thousandths of an inch in thickness, a thick conductor film cannot be wrapped so as to have a small wound radius, because stress induced in the coil winding will cause cracking in the conductor and thereby increase both 3Q the electrical resistance and, correspondingly, the power dissipation of the coil. Moreover, a stripe line pattern 47~33 as to be etched in the conductor film. A thick con~uctor film will make etching mo~e difficult because of the etch depth-to-width ratio, ~hus increasing the etch loss in the stripe pattern and, therefore, increasing the power loss of the coil.
For minimum coil size and power loss, a stripe line composite having maximum conductor thickness and minimum insulator thickness is required. Figs. 5a and 5b illustrate preferred embodiments of the instant invention wherein a stripe line coil having minimized power loss may be fabricated in order to generate an in-plane magnetic field for a magnetic bubble memory device. Magnetic field uniformity within a stripe line coil is maximized by increasing the surface area of conductor material which forms the stripe pattern with respect to the areas of insulation. In accordance with the instant invention, the conductor-to-insulator ratio may be maximized by forming a single sided stripe line composite 20 comprised of an etched double thick (relative to conventional single sided stripe line configurations) conductor (copper) foil 21 supported on an insulating ~polyamide) film 22, as shown in Fig. 5a. An efficient low loss stripe line coil (not shown) having minimized power losses can be fabricated with the single sided stripe line 20 of Fig. 5a by utilizing a conductor with an optimum thickness that is twice the conductor skin depth at the operating frequency.
For moderate frequencies of operation, ~he conductor film layer has to be relatively thick (e.g., .007 inches for 500 kHz), because the square root of conductor skin depth is generally inversely proportional to the optimum frequency of operation. A thick conductor polyamide )47~33 film is difficult to make, as the copper tends to crack during the coil winding operation. Additionally, a thick conductor pattern is difficult to define in the chemical etching process. Fig. 5b illustrates a double sided stripe line composite 23 having a maximized conductor-to-insulator ratio, suitable for use at moderate frequencies of operation. The double sided stripe line 23 is comprised of conductor ~oils 24a and 24b supported by the front and back sides, respectively, of an insulating film 26. The stripe line pattern is etched on both sides of the insulating film 26, as shown.
Fig. 6a illustrates an end view of a multiple layer stripe line coil structure 28 utilizing the double sided conductor stripe line configuration 23 of Fig. 5b.
Reference numerals 30 and 32 correspond to convenient electrically conducting securing means (e.g., solder joints) to properly align the front and back conductor stripe patterns 24a an~ 24b with respect to one another between layers of insulating film 26 (best shown in Fig. 6b) and to maintain the adjacent conductor layers which are in close contact with one another at the same electrical potential. Reference numerals 34 and 36 correspond to coil end terminals to which electrical components (not shown) may be suitably connected.
Fig. 6b is a cross sectional view taken along lines 6~-6b of Fig. 6a, showing the multiple layer conductor stripe alignment of front and back conductor foils 24a and 24b with respect to one another. When a stripe line composite is assembled into the coil configuration 28 of Fig. 6a, a bottom conductor stripe 24b is positioned immediately adjacent a top conductor stripe 24a and between _ g _ . _.. .
1g34~7133 --a pair of film insulating layers 26, as sho~n. Thus, adjacent bottom and top conductor stripes 24b and 24a, respectively, are electrically connected in parallel during coil winding so as to form a thick conductor film which will have less susceptibility to stripe line cracking than conventional conductor stripe line windings which have relatively large conductor areas.
With a configuration as shown in Fig. 6b, no electrical insulation is required between adjacent bottom and top conductor stripe lines 24b and 24a, thus maximizing the stripe line conductor area and reducing the amount of insulatlng film (i.e., by half) that would be required by conventional single sided stripe line coil configuration.
Therefore, the equivalent resistance and the corresponding resulting power loss and the etch loss (or undercutting) in individual conducting foils within a stripe line coil formed in accordance with the instant inventïon is substantially reduced. What is more, difficulties encountered during the winding of a coil pattern, particularly multilayer patterns, clre minimized by virtue of the instant invention, as compared to conventional stripe line coil configurations.
It will be apparent that while a preferred embodi-ment of the invention has been shown and described, vaxious modifications may be made without departing from the spirit and scope of the invention. For example, although various materials have been disclosed for forming the stripe line composite of the instant invention, these materials are for exemplary purposes only. It is to be understood that any other suitable materials may be utilized. Additionally, although the disclosed method for forming the stripe line patterns in the conducting foil layers of the instant stripe ~line composite is by photolithographic techniques, any ~ other suitable technique may be employed.
Having thus set forth a preferred embodiment of the instant invention, what is claimed is:
In the wire wound coil, current density along the coil axis is uniform, which causes the magnetic field strength to peak at the coil center with gradual fall off toward both ends of the coil. The magnetic field uniformity 2a can be improved by adding additional turns near both ends of the coil. This arrangement of additional turns of course causes the coil to have an ocld shape configuration and also increases the coil size, both of which are undesirable features.
Also, skin and proximity effects are inherent in wire wound coils. These effects are primarily due to coupling between the closely wound wire turns and result in a high frequency loss. A prior art means of eliminating the high ~requency loss is to use a Litz wire, i.e., a conductor consisting of several individual insulated wires.
Unfortuna.tely, as may be appreciated, this approach is very ~ - 2 -"`` 3L047~33 ; --expensive.
In summary, the existing known methods of coil winding do not generate a uniform field, are cumbersome to produce and the improvements required to correct these undesirable features are not economically feasible. The ~ 2a ~
...~.....
~esent invention, which uses a conductor stripe type coil winding etched on a conductor foil supported on an insulating film, provides the desired characteristics using conductors of varied widths and arranging the stripe line patterns in a multiple layer stripe structure having the conductors aligned in series along the layer direction rather than in parallel.
SUMMARY
A printed circuit magnetic field coil is produced on a flexible L-shaped conductor substrate by etching a desired stripe line pattern having conductors with varying widths on a conductor foil supported on an insulating film (for example, cold rolled copper on a polyamide film); wrapping this stripe line film pattern around a fixed coil form; connecting the outer ends in an offset manner, i.e., displaced by one row of conductors to electrically connect all the stripe lines as a continuous single loop; and arranging a multiple layer structure with the conductors seried along the layer direction rather than in the axial direction. The conductor length, width and spacing are controlled by the etched pa~tern. The controlled geometry and seried connections provides improved coil parameters such as impedance, field uniformity, dissipation factor, size and shape, and high frequency operation.
More specifically, the invention consists of a coil for magnetic field generation, comprising a flexible substrate having a planar L-shaped configuration, a conductive layer formed on a first side of the substrate, the conductive layer having formed therein a plurality of conductors, each of the conductors having respective first and second ends, said conductive layer including first and second leg portions, said first leg portion having first and second ends and being substantially longer than said second leg portion, said second leg portion positioned . .~
~g~47133 `~~`\adjacent to the second end of said ~irst leg portion whereby the respective conductors formed in the conductive layer of said first and second leg portions are disposed at substan-tially right angles with respect to one another, said second end of said first leg portion wound at least once in a direction towards said first end of said first leg portion, said second leg portion wound around said first leg portion in a direction substantially perpendicular to the direction in which said first leg portion is wound, and said second leg portion folded back upon itself at an angle of substantially 45, whereby the conductors in said first end of said first leg portion are electrically interconnected to said conductors in said second leg portion to form a continuous closed loop.
Brief Description of the Drawings Fig. 1 is a plan view of the stripe line coil pattern prior to be wrapped into a field coil;
Fig. 2 is a fragmentary, sectional view of the stripe line coil pattern taken on the B side along line 2-2 of Figure l;
Fig. 3 is a perspective view of a completed stripe line coil winding of the instant invention;
Fig. 3a is a partial top plan view of Figure 3;
Fig. 4 is a cross-section of a stripe line coil with variable stripe width;
Fig. 5a is a fragmentary, sectional view of a single sided stripe line with a double thick conductor formed in accordance with the instant invention;
Fig~ 5b is a fragmentary, sectional view of a double sided conductor stripe line formed in accordance with 3Q the instant invention;
Fig. 6a is an end view of a multilayer stripe . __....
~47~33 line coil formed from the double sided conductor stripeline of Fig. 5b; and ~ Fig. 6b is a sectional view taken along lines 6b-6b of Fig. 6a.
Detailed Description of the Preferred Embodiment Referring concurrently to Figs. 1 and 2, there is shown an L-shaped stripe line composite 10 comprising an etched conductor foil 11 (Fig. 2) supported on an insulating film substrate 12 ~Fig. 2). Preferably the conductor layer 11 is copper on a polyamide film 12. One method of forming the stripe line pattern of the conductor layer is by known photolithographic techniques, i.e., by coating the copper surface with a thin layer of light sensitive photoresist, exposing the coated surface to light through a photomaster having the desired stripe line design and developing and etching the conductor material to produce the pattern (e.g., such as the parallel conductor pattern shown in Fig. 1).
Referring to Figure 2, a fixed size field coil can be formed by first wrapping the stripe line pattern composite 10 (Fig. 1) around a coil form (not shown). The inner end B' of the leg 14 of the composite 10 is wrapped over the coil form and wound a convenient number of times towards the inner end B in Figure 1, while the shorter leg extends outwardly from the inside of the winding. The flap end A of shorter leg 16 is next wrapped around the coil and folded back upon itself at an angle of about 45 so that the parallel conductors in the flap end A are aligned with the parallel conductors in the inner end B. As will be under-stood by those skilled in the ar~, to prevent shorting ofthe conductors in leg 14 during the wrapping of leg 16 around ~ _ 5 _ ~47~33 the coil, the conductors in leg 16 may be sprayed with an insulating film or covered with an insulating tape (e.g., Mylar*, Kapton* or the like). Thereafter, in one preferred embodiment, the conductors in end A are electrically interconnected by suitable means (e.g., soldering) in an offset fashion (e.g., by the width of one conductor) to *Trade Marks ~ - 5a .
~047133 r-spective conductors in end B, as shown in Figures 3 and 3a, thereby forming a single closed loop, Thus, the current carried by the offset parallel conduct~rs travels in a continuous current path around the closed loop. The conductor length, width and spacing are cont.rolled by the accuracy attained in the etched pattern. Therefore, consistent accuracy is attained in the coil parameters such as impedance, f:Leld uniformity, dissipation factor, size and shape.
~ 5b ~ L7~L33 .
One o~ the problems encountered in the con~entional wire wound coil is the closeness o~ the wire turns, which results in interwire coupling and high frequency loss. The multiple layer stripe line coil 13 structure of the instant invention, shown in Figure 4, substantially reduces the high frequency loss in two fashions. First, the spacing between layers or columns 17 of conductors can be easily controlled by patterns generated in the photomaster, so that a sufficient spacing can be provided as required between conductors to reduce the aforementioned adverse effects o~
the interwire coupling. Secondly, when the winding in this coil is connected in series, the sequence of the current flow is illustrated in Fig. 4. That is, the current flows in series through adjacent vertical arrays or columns 17 of conductors. The current 10ws in a single series loop from conductor 1 to 2 to 3 (the first vertical array or column 17) then from conductor 3 to conductor 4 to 5 to 6 (the next column 17) and from conductor 6 to conductor 7 to 8 to 9 (the next column 17) and so on. This winding arrangement minimizes the potential differences between neighboring turns thereby minimizing high frequency loss due to interwire coupling. This arrangement also helps minimize the unequal current distribution at high frequencies which occurs in coils having parallel wound layer~. The effective turns in this winding scheme can be controlled by varying the conductor width. That is, by increasing the conductor width the number of effective turns in the winding is decreased.
In wire wound coils, the magnetic field streng~h peaks at the coil center then gradually tapers off towards both ends of the coil. This field deficiency at the coil ` ~47~33 - ends can be improved by winding additional turns of wire - close to both coil ends. However, this winding arrangement results in an Qdd shape configuration for the coil and also increases the coil size. This invention controls the field deficiency at the ends of the coil by varying the conductor width as shown in Figure 4. That is, the conductor width is decreased as required at both ends along the coil axis, causing the field density to increase at the ends to thereby more evenly distribute a uniform magnetic field alon~ the coil axis. Since the stripes are photolithographically etched, the stripe width variations can be accurately controlled.
The total power dissipation of a stripe line coil is dependent upon its overall electrical resistance. With conventional stripe line wound coil configurations, the power dissipation is higher than with the corresponding wire wound coil having the same relative dimensions. Conventional polyamide film has ~.nown conductor thickness of .001-.004 inches and an insulator thickness of .001-.002 inches. Thus, conventional stripe line wound coil configurations are relatively inefficient because of the low ratio between conductor area and the winding cross section area. What is more, a stripe line conauctor (e.g., commonly, plated copper) frequently has a higher resistivity than that of the solid conductor wire. Although the conductor film can be plated to several thousandths of an inch in thickness, a thick conductor film cannot be wrapped so as to have a small wound radius, because stress induced in the coil winding will cause cracking in the conductor and thereby increase both 3Q the electrical resistance and, correspondingly, the power dissipation of the coil. Moreover, a stripe line pattern 47~33 as to be etched in the conductor film. A thick con~uctor film will make etching mo~e difficult because of the etch depth-to-width ratio, ~hus increasing the etch loss in the stripe pattern and, therefore, increasing the power loss of the coil.
For minimum coil size and power loss, a stripe line composite having maximum conductor thickness and minimum insulator thickness is required. Figs. 5a and 5b illustrate preferred embodiments of the instant invention wherein a stripe line coil having minimized power loss may be fabricated in order to generate an in-plane magnetic field for a magnetic bubble memory device. Magnetic field uniformity within a stripe line coil is maximized by increasing the surface area of conductor material which forms the stripe pattern with respect to the areas of insulation. In accordance with the instant invention, the conductor-to-insulator ratio may be maximized by forming a single sided stripe line composite 20 comprised of an etched double thick (relative to conventional single sided stripe line configurations) conductor (copper) foil 21 supported on an insulating ~polyamide) film 22, as shown in Fig. 5a. An efficient low loss stripe line coil (not shown) having minimized power losses can be fabricated with the single sided stripe line 20 of Fig. 5a by utilizing a conductor with an optimum thickness that is twice the conductor skin depth at the operating frequency.
For moderate frequencies of operation, ~he conductor film layer has to be relatively thick (e.g., .007 inches for 500 kHz), because the square root of conductor skin depth is generally inversely proportional to the optimum frequency of operation. A thick conductor polyamide )47~33 film is difficult to make, as the copper tends to crack during the coil winding operation. Additionally, a thick conductor pattern is difficult to define in the chemical etching process. Fig. 5b illustrates a double sided stripe line composite 23 having a maximized conductor-to-insulator ratio, suitable for use at moderate frequencies of operation. The double sided stripe line 23 is comprised of conductor ~oils 24a and 24b supported by the front and back sides, respectively, of an insulating film 26. The stripe line pattern is etched on both sides of the insulating film 26, as shown.
Fig. 6a illustrates an end view of a multiple layer stripe line coil structure 28 utilizing the double sided conductor stripe line configuration 23 of Fig. 5b.
Reference numerals 30 and 32 correspond to convenient electrically conducting securing means (e.g., solder joints) to properly align the front and back conductor stripe patterns 24a an~ 24b with respect to one another between layers of insulating film 26 (best shown in Fig. 6b) and to maintain the adjacent conductor layers which are in close contact with one another at the same electrical potential. Reference numerals 34 and 36 correspond to coil end terminals to which electrical components (not shown) may be suitably connected.
Fig. 6b is a cross sectional view taken along lines 6~-6b of Fig. 6a, showing the multiple layer conductor stripe alignment of front and back conductor foils 24a and 24b with respect to one another. When a stripe line composite is assembled into the coil configuration 28 of Fig. 6a, a bottom conductor stripe 24b is positioned immediately adjacent a top conductor stripe 24a and between _ g _ . _.. .
1g34~7133 --a pair of film insulating layers 26, as sho~n. Thus, adjacent bottom and top conductor stripes 24b and 24a, respectively, are electrically connected in parallel during coil winding so as to form a thick conductor film which will have less susceptibility to stripe line cracking than conventional conductor stripe line windings which have relatively large conductor areas.
With a configuration as shown in Fig. 6b, no electrical insulation is required between adjacent bottom and top conductor stripe lines 24b and 24a, thus maximizing the stripe line conductor area and reducing the amount of insulatlng film (i.e., by half) that would be required by conventional single sided stripe line coil configuration.
Therefore, the equivalent resistance and the corresponding resulting power loss and the etch loss (or undercutting) in individual conducting foils within a stripe line coil formed in accordance with the instant inventïon is substantially reduced. What is more, difficulties encountered during the winding of a coil pattern, particularly multilayer patterns, clre minimized by virtue of the instant invention, as compared to conventional stripe line coil configurations.
It will be apparent that while a preferred embodi-ment of the invention has been shown and described, vaxious modifications may be made without departing from the spirit and scope of the invention. For example, although various materials have been disclosed for forming the stripe line composite of the instant invention, these materials are for exemplary purposes only. It is to be understood that any other suitable materials may be utilized. Additionally, although the disclosed method for forming the stripe line patterns in the conducting foil layers of the instant stripe ~line composite is by photolithographic techniques, any ~ other suitable technique may be employed.
Having thus set forth a preferred embodiment of the instant invention, what is claimed is:
Claims (10)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A coil for magnetic field generation, comprising a flexible substrate having a planar L-shaped configuration, a conductive layer formed on a first side of the substrate, the conductive layer having formed therein a plurality of conductors, each of the conductors having respective first and second ends, said conductive layer including first and second leg portions, said first leg portion having first and second ends and being substantially longer than said second leg portion, said second leg portion positioned adjacent to the second end of said first leg portion whereby the respective conductors formed in the conductive layer of said first and second leg portions are disposed at substantially right angles with respect to one another, said second end of said first leg portion wound at least once in a direction towards said first end of said first leg portion, said second leg portion wound around said first leg portion in a direction substantially perpendicular to the direction in which said first leg portion is wound, and said second leg portion folded back upon itself at an angle of substantially 45°, whereby the conductors in said first end of said first leg portion are electrically interconnected to said conductors in said second leg portion to form a continuous closed loop.
2. The coil recited in claim 1, wherein said first and second plurality of conductor ends are interconnected in an offset relationship with respect to one another.
3. The coil recited in claim 2, wherein said first conductor ends which are electrically interconnected to said second conductor ends are offset with respect to one another by the width of one of said plurality of conductors.
4. The coil recited in claim 1, wherein each of said plurality of conductors are disposed in a parallel relationship with respect to one another in said at least one conductive layer.
5. The coil recited in claim 1, wherein the widths of said plurality of conductors are varied with respect to one another to control magnetic field strength and uniformity.
6. The coil recited in claim 5, wherein the widths of said plurality of conductors are progressively decreased with respect to a position at the center of said coil and outwardly along the axis around which said coil is wound to thereby progressively increase the magnetic field density outwardly and along said coil axis.
7. The coil recited in claim 1, wherein the thickness of at least some of said plurality of conductors is equal to approximately twice the skin depth thereof.
8. The coil recited in claim 1, including:
at least one second conductive layer formed on a second side of said substrate;
said second conductive layer having formed therein a plurality of conductors, each of said conductors having respective first and second ends; and means to electrically interconnect said first and second conductor ends of said second conductive layer so as to form said closed loop.
at least one second conductive layer formed on a second side of said substrate;
said second conductive layer having formed therein a plurality of conductors, each of said conductors having respective first and second ends; and means to electrically interconnect said first and second conductor ends of said second conductive layer so as to form said closed loop.
9. The coil recited in claim 8, wherein said coil is comprised of a plurality of said first and second conductive layers arranged so that some of said conductors in each of said first conductive layers are disposed immediately adjacent some of said conductors in each of said second conductive layers.
10. The coil recited in claim 8, wherein each of said plurality of conductors formed in said second conductive layer are electrically arranged in parallel with respect to one another.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US56648475A | 1975-04-09 | 1975-04-09 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1047133A true CA1047133A (en) | 1979-01-23 |
Family
ID=24263084
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA236,151A Expired CA1047133A (en) | 1975-04-09 | 1975-09-23 | Coil for magnetic field generation |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1047133A (en) |
-
1975
- 1975-09-23 CA CA236,151A patent/CA1047133A/en not_active Expired
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