Microgapping process for magnetic cores

Abstract

 A magnetic device is assembled by first applying an adhesive to the end surface of a leg of one core portion, slipping a bobbin onto one of the legs (preferably a different leg) of the core portion, and mating the two core portions together. Then while observing the inductance of the coil, the two core portions are ground toward each other, gradually narrowing the adhesive-induced gap between the mating surfaces, until the desired inductance is achieved. The adhesive is then cured. Preferably the adhesive includes particulate matter to help resist the narrowing of the gap during the grinding process. Alternatively, the particulate matter can be applied to the mating surface without adhesive, and the resulting assembly can be clamped together.

Description

BACKGROUND

1. Field of the Invention

[0001] The invention relates to the field of magnetic core assemblies, and more particularly to a process for assembling cores for transformers, inductors and other magnetic devices with small but controllable gap spacing.

2. Description of Related Art

[0002] Transformers and inductors are often designed as one or more wire coils wound around a core. The core defines a magnetic flux loop passing through the centerhole of the coil and closing outside the coil. Because of the difficulty in winding a wire around one side of a closed loop core structure, devices using closed loop cores are typically manufactured using two core portions that are mated together during assembly. Each core portion is itself open, so that a coil can be wound on one or more legs of the core before the core portions are mated together. Typically the coil or coils are pre-wound onto a non-magnetic bobbin, which is simply slipped onto the desired leg of one core portion before the core portions are mated together.

[0003] Cores can have many different shapes. U-cores, for example, are assembled from two U-shaped core portions, each with two legs protruding toward the opposite core portion. One or more coils can be wound around one or both legs of the core portion before the core portions are mated together, the end surfaces of the legs of one core portion being placed into face-to-face contact with the end surfaces of the legs of the other core portion. E-cores are assembled from two E-shaped core portions, each with three legs protruding toward the opposite core portion. Cylindrically shaped cores are assembled from two cylindrical core portions, each having a center post protruding toward the other core portion. The coil(s) are typically wound around the center post before mating. Numerous other shapes exist. It will be appreciated that the two core portions that make up a complete core need not be symmetrical, although they often are.

[0004] Cores intended for operation above about 100 kHz are often fabricated from one of a number of ferrite materials. Certain ferrites advantageously have very high permeability (µ), for example µ>10,000, allowing for very high inductance devices. In order to use this high permeability in mated core portions, the mating surfaces are ground to a high polish and the core portions are clamped together. The operation is delicate because even a fingerprint can degrade the permeability. More recently a very thin layer of interfacial epoxy adhesive has been used between the mating surfaces of the core portions to hold them in place.

[0005] The effective permeability of magnetic devices with mated cores is very difficult to control during the manufacturing process. And since the inductance of a coil encircling the core is a function of the core permeability, the inductance of such a coil is also very difficult to control. Typically the inductance can be controlled only to within a tolerance of ±25% or so. In addition, the mating process itself degrades controllability even further, perhaps by yet another ±5%. One way to control the permeability more precisely is to introduce an air gap within one leg of the core, typically the leg passing through the coil. Machinery currently exists which can grind this leg down on one of the mating core portions to within a much tighter tolerance. However, the introduction of an air gap also typically reduces the nominal permeability of the core by 10 or more. Core permeability can alternatively be controlled by the simple process of testing and rejecting those cores that are not within the required tolerance specification. This process is expensive and wasteful, however, especially since it cannot be performed until after the core has already been assembled.

[0006] Accordingly, there i$ a great need in the industry for a process for manufacturing magnetic devices using mated core portions which permits precise control of the resulting effective core permeability.

SUMMARY OF THE INVENTION

[0007] According to the invention, roughly described, a magnetic device is assembled by first applying an adhesive to the end surface of a leg of one core portion, slipping a bobbin onto one of the legs (preferably a different leg) of the core portion, and mating the two core portions together. Then while observing the inductance of the coil, the two core portions are ground toward each other, gradually narrowing the adhesive-induced gap between the mating surfaces, until the desired inductance is achieved. The adhesive is then cured. Preferably the adhesive includes particulate matter to help resist the narrowing of the gap during the grinding process. The result is a "microgapped" core in which the effective permeability has been controlled to within a very tight tolerance. The improvement in precision achieved due to the assembly process described herein is not limited to a reduction of the tolerance degradation that takes place during a conventional assembly process, but can also correct for permeability imprecision that might have existed in the unmated core portions themselves, prior to assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The invention will be described with respect to specific embodiments thereof, and reference will be made to the drawings, in which:

Fig. 1 is a perspective diagram illustrating components of a transformer that can be assembled in accordance with features of the invention.

Fig. 2 is a flow chart illustrating the significant steps performed in the assembly of the transformer of Fig. 1.

Fig. 3 schematically illustrates a test setup that can be used during the permeability observation step of Fig. 2.

Fig. 4 is a perspective view of a magnetic device incorporating features of the invention.

DETAILED DESCRIPTION

[0009] Fig. 1 is a perspective diagram illustrating components of a transformer that can be assembled in accordance with features of the invention. The components include first and second core portions 110 and 112, a bobbin 114, and a spring clamp 116. The core 110/112 (collectively, 118) in the example of Fig. 1 has airindustry-standard shape known as EP-13. In this example the two core portions are symmetrical, so only core portion 112 will be described. Referring to Fig. 1, core portion 112 includes a center post, or leg, 120, about which the bobbin 114 will be placed during assembly. Partially surrounding the center post 120 is a wall 122, partially cylindrical in shape, and spaced from the outer surface of the center post 120 sufficiently to permit insertion of the bobbin 114. Like the center post 120, the outer wall 122 protrudes from an outer surface 124 of the core portion 112, toward the first core portion 110. The end surface 126 of the center post 120, which will mate with a corresponding end surface 128 of center post 130 on the first core portion 110, is substantially co-planar with the end surface 132 of the wall 122 which will mate with the corresponding end surface 134 of the wall 136 of the first core portion 110. The core portions 110 and 112 in the example of Fig. 1 each have unitary construction, and are made from a high-permeability ferrite material such as Nippon Ceramics NC-10 or TDK H5C2. These materials have a permeability of µ = 10,000, but they are specified only with a tolerance of ±30%.

[0010] The EP-13 core in the example of Fig. 1 is an example of a partially cylindrical core. As used herein, a "leg" of a core portion refers to any member of the core portion that protrudes toward the mating portion. A "leg" need not be post-like, such as the center posts 120 and 130. For example, as used herein, the walls 122 and 136 of the core portions 110 and 112 also constitute "legs" of such core portions. In addition, as used herein, a "rim" of a core portion refers to any mating member of the core portion other than a member that is encircled by the coil. A "rim" member does not have to be circular in shape, or partially circular in shape such as the walls 122 and 136 of the core portions 110 and 112, nor must it even surround a central leg to any extent. For example, in an E-core, in which the coil encircles the central leg, each of the outer legs constitute "rim" members as that term is used herein.

[0011] The bobbin 114 includes a central tube 138 having a centerhole 140 into which the center posts 120 and 130 can be inserted from opposite ends. Coils of wire (not shown) are wound around the tube 138. To help manage the winding, end stops 142 and 144 are disposed on opposite ends of the tube 138. In the particular example of Fig. 1, coils will be wound around the bobbin 114 so as to create a transformer having a single primary and two secondaries. Electrical connections are made via surface mount pins 148 on the bobbin 114. The shape of the bobbin 114 is an industry-standard shape known as SEP-13, and it is made of a non-magnetic material such as phenolic.

[0012] After the two core portions 110 and 112 are mated around the bobbin 114, they are held in place by a spring clamp 116 in a well-known manner. Spring clamp 116 may be made, for example, from a nickel silver material.

[0013] Fig. 2 is a flow chart illustrating the significant steps performed in the assembly of the transformer of Fig. 1. In step 210, a coil or coils are wound onto the bobbin in a manner desired for the electrical purposes of the device. In the embodiment of Fig. 1, three coils are wound: one primary and two secondaries. The step 210 can be performed either at the same location as the following steps, or at some other location and some earlier time.

[0014] In step 212, an adhesive 150 (Fig. 1) is applied to one of the mating surfaces of one of the core portions 112. The adhesive 150 preferably, but not necessarily, includes some hard particulate matter to improve controllability of the grinding process described below with respect to step 218. An example adhesive is Zymet 517F, which is a thixotropic epoxy containing 3% by weight of 10 micron silica particles. Zymet 517F is available in premixed syringes for application.

[0015] In step 214, the two core portions 110 and 112 are mated together around and through the coils and bobbin 114 (Fig. 1), and clamped together with the spring clamp 116. At this point, the rim surface 132 of core portion 112 is "mated" with the corresponding rim surface 134 of core portion 110, as that term is used herein, although a very narrow gap spacing remains between the two surfaces due to the adhesive 150. Similarly, since the end surface 126 of the center post 120 is co-planar with the rim surface 132 of the wall 122 of core portion 112, and the end surface 128 of the center post 130 of the core portion 110 is co-planar with the rim surface 134 of the wall 136 of core portion 110, the two end surfaces 126 and 128 also remain spaced by a narrow gap. These two surfaces are nevertheless considered "mated", as the term is used herein, inside the bobbin tube 138.

[0016] In step 216, the effective permeability of the core 118 is observed. As used herein, observation of a characteristic such as permeability includes indirect observation of that characteristic, such as by observing an effect that is dependent upon the characteristic. Permeability, for example, can be "observed", as the term is used herein, by observing the inductance of a coil which is in sufficient proximity to the core to be affected by the effective permeability of the core. Similarly, the term "observing the inductance", as used herein, includes indirect observation of the inductance, such as by observing an effect that is dependent upon the inductance. In the embodiment of Fig. 2, the effective permeability of the core 118 is observed by observing the inductance of the two secondary windings connected in series.

[0017] Fig. 3 schematically illustrates the test setup. The transformer 310 includes a primary winding 312 having terminals 314 and 316. The first secondary winding 318 has terminals 320 and 322, and the second secondary winding 324 has terminals 326 and 328. For purposes of the test setup, terminals 322 and 326 are connected together and an inductance meter 330 is connected across terminals 320 and 328. Since the inductance of any one of the windings 312, 318 and 324 is mathematically related to the effective permeability of the core 118, observation of the inductance of any one of the coils, or any two of the coils connected in parallel or series, or all three of the coils connected in various non-canceling ways, will effectively constitute observation of the effective permeability of the core 118. In addition, although the coil whose inductance is observed in step 216 encircles the core 118, it will be appreciated that in another embodiment, the coil might instead be merely in sufficient proximity to the core so as to be affected measurably by the core permeability. It will also be appreciated that observation of an inductance is a particularly advantageous method of observing the effective core permeability, because usually it is the inductance, not the effective permeability of the core, which is specified in electronic circuits.

[0018] Returning to Fig. 2, in step 216, it is determined whether the effective permeability of the core 118 is within the desired tolerance. For the test setup of Fig. 3, this determination is made by determining whether the inductance read from inductance meter 330 is within a desired tolerance of a nominal inductance value. If it is not, then in step 218, the gap spacing is adjusted and the effective permeability of the core 118 is again observed (step 216). The process continues until the effective permeability of the core 118 is within the desired tolerance. In one embodiment, the observation step 216 and the adjustment step 218 are performed simultaneously and continuously until a desired permeability is reached, whereas in another embodiment, the two steps are performed in alternating manner.

[0019] The adjustment of gap spacing in step 218 can be performed in any of a number of ways. In one embodiment, the two core portions 110 and 112 are held tightly by apparatus which mechanically moves the cores toward or away from each other in sufficiently fine increments. In another embodiment, the two core portions 110 and 112 are simply ground toward each other. For example, with the spring clip 116 urging the two core portions toward each other, and the adhesive 150 resisting a narrower gap spacing, the two core portions 110 and 112 are either rotated relative to each other or translated relative to each other, or both, in a plane parallel to their mating surfaces. This motion effectively "grinds" the two core portions toward each other. The rotation and/or translation can be uni-directional, bi-directional or vibratory, and can be performed manually or by machine. In this connection, it will be appreciated that the particulates in the adhesive 150 help resist the collapse of the adhesive structure, thereby slowing the narrowing of the gap spacing and improving controllability during the grinding process. When particulates are used, they should preferably be of a non-magnetic material such as silica, so they do not saturate magnetically during circuit operation.

[0020] After the gap spacing has been adjusted to provide the core 118 with the desired effective permeability, in step 220, the adhesive is cured while the gap spacing is maintained. Curing is performed according to the instructions of the adhesive manufacturer, and may involve, for example, placing the assembly in a 170°C oven for 10 to 15 minutes, or applying RF heating. Preferably, virtually no curing takes place during the steps 216 and 218 of observing and adjusting, but in another embodiment, partial curing during these steps can be accommodated. The curing process typically increases the permeability of the core 118 by approximately 10%, but the curing step does not significantly impact the precision of the device manufacturing process because the permeability increase during cure is predictable. Instead, the desired effective permeability targeted in steps 216 and 218 is merely reduced by the known percentage increase that will take place during the curing step 220.

[0021] In step 222, the process is complete. It will be appreciated that not only has the process overcome the tolerance degradation that takes place during a conventional assembly process, but has also corrected for imprecision in the permeability of the raw core portions 110 and 112 as originally manufactured. The process permits magnetic devices to be tuned over a wide range, the upper limit being essentially the same permeability as that which the core 118 would exhibit when tightly clamped together without adhesive.

[0022] As mentioned above, in the embodiment of Fig. 1, the adhesive 150 is applied only to the rim surface 132 of one of the core portions 112. As used herein, application of adhesive to one mating surface can be performed either directly or indirectly, for example by depositing adhesive onto the corresponding mating surface of the opposite core portion and then mating the two together. Advantageously (but not necessarily), no adhesive is applied to any mating surface that comes into close proximity with the coil or bobbin 114, so as to prevent any accidental bonding between the core 118 and the coil or bobbin 114. Otherwise the temperature coefficient of expansion of the combined structure might be indeterminate, thereby introducing an uncertainty into the circuit which may not be desired. Instead, one end 142 or 144 of the bobbin 114 can be adhesive bonded if desired to the inside end section of the corresponding core portion 110 or 112. Of course if the device is simply an inductor having a single central core member (i.e. the core has only one "leg"), then the leg supporting the adhesive is the same as the leg encircled by the coil.

[0023] Although the specific EP-13 core shape is illustrated in the example of Fig. 1, it will be appreciated that the invention can be used with a wide variety of symmetric and asymmetric core shapes. For E-cores, for example, if the bobbin is placed on the center leg, then the adhesive can be applied to the end surfaces of the two outer legs. For E-cores, cylindrical cores and the EP-13 core illustrated in Fig. 1, the surface(s) supporting the adhesive exists on opposite sides of the leg that is encircled by the coil. The substantially equal resistance exerted by the adhesive on both sides of the central leg therefore maintains the two mating surfaces of the central leg in substantially parallel planes. It is desirable, but not essential, that these two planes remain substantially parallel to avoid local saturation of part of the core. In some embodiments this may be difficult but not impossible to achieve during the grinding process. For example, a U-core, which has two legs on each core portion, may receive the adhesive on the end surface of one leg and receive the bobbin on the other leg. In this case, the mating surfaces inside the bobbin tube can be maintained in substantially parallel planes by applying the grinding force to the two core portions substantially co-axially with the legs supporting the adhesive. Other accommodations will be apparent for other kinds of core shapes.

[0024] It will also be appreciated that the invention can be used even where not all of the mating surfaces are co-planar with each other. In the EP-13 core illustrated in Fig. 1, for example, the invention can still be used even if the center post 120 or 130 of one or both of the core portions 110 and 112 has been shortened to create an intentional air gap between them. As previously mentioned, equipment currently exists to achieve very small permeability tolerance in this situation, but the permeability tolerance can be improved even further through the use of the invention.

[0025] Fig. 4 is a perspective view of a magnetic device illustrating another aspect of the invention. It comprises first and second core portions 410 and 412, held together in an assembly 418 by a clamp 414. The coil is internal to the assembly of Fig. 4, wound on a bobbin supported on a central leg similarly to the arrangement shown unassembled in Fig. 1. A microgap spacing 416 between the mated surfaces of the core assembly 418 is maintained by particulate matter disposed in the gap 416. Unlike Fig. 1, however, there is no adhesive in the gap 416. Instead, the gap spacing is fixed by the particulate matter resisting against sustained force provided by the clamp 414, urging the two core portions 410 and 412 toward each other.

[0026] The device of Fig. 4 can be made by the same process as that set forth in the flow chart of Fig. 2, except that the particulate matter is applied to the mating surface in step 212 without adhesive, and the step 220 of curing the adhesive is replaced by a step of clamping the two core portions together to apply sustained force urging the two core portions toward each other.

[0027] As used herein, a given signal, event or value is "responsive" to a predecessor signal, event or value if the predecessor signal, event or value influenced the given signal, event or value. If there is an intervening processing element, step or time period, the given signal, event or value can still be "responsive" to the predecessor signal, event or value. If the intervening processing element or step combines more than one signal, event or value, the signal output of the processing element or step is considered "responsive" to each of the signal, event or value inputs. If the given signal, event or value is the same as the predecessor signal, event or value, this is merely a degenerate case in which the given signal, event or value is still considered to be "responsive" to the predecessor signal, event or value. "Dependency" of a given signal, event or value upon another signal, event or value is defined similarly.

[0028] Also as used herein, movement of two components "relative" to each other, and movement of one component "relative" to another, does not imply any restrictions about which component is moving relative to any absolute. In other words, a statement that component A moves relative to component B is intended to include all of the following possibilities and to not select among them: that component A is stationary and component B is moves; that component B is stationary and component A moves; and that component A moves and component B move differently from component A.

[0029] The foregoing description of preferred embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in this art. For example, whereas the embodiments described above involve ferrite cores, it will be appreciated that cores made of other materials, even amorphous materials, can also benefit from the invention. Nor must the core material have high permeability; low permeability cores can be used as well. In addition, whereas the above-described embodiments use only two core portions to assemble an entire core, in another embodiment, three or more core portions can be used. In such an embodiment the adhesive can be applied in between any one or more of any pair of the mating surfaces of any of the core portions, depending on requirements. Furthermore, and without limitation, any and all variations described or suggested in the Background section of this patent application are specifically incorporated by reference into the description herein of embodiments of the invention. The embodiments described herein were chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.

Claims

1. A method for assembling a magnetic device having first and second core portions, the first the core portion having at least a first mating surface that mates with a corresponding surface of the second core portion, comprising the steps of:

applying an adhesive to the first mating surface;

mating the first and second core portions to form a core assembly having the adhesive between the first mating surface and the corresponding surface of the second core portion, the core assembly having a gap spacing between a surface of the first core portion and a surface of the second core portion;

observing the effective permeability of the core assembly; and

adjusting the gap spacing until the effective permeability achieves a desired value.

2. A method according to claim 1, wherein the gap spacing is disposed between a second mating surface of the first core portion and a corresponding surface of the second core portion, the second mating surface of the first core portion being different from the first mating surface of the first core portion.

3. A method according to claim 1, wherein the adhesive includes non-adhesive particulates.

4. A method according to claim 1, wherein the step of observing the effective permeability of the core assembly comprises the step of observing the inductance of an inductor that is in sufficient proximity to the core assembly such that the inductance varies in dependence upon the gap spacing,
   and wherein the step of adjusting the gap spacing until the effective permeability achieves a desired value comprises the step of adjusting the gap spacing until the inductance achieves a desired value.

5. A method according to claim 4, further comprising the step of encircling a leg of the first core portion with the inductor prior to the step of observing the inductance of an inductor.

6. A method according to claim 5, wherein the steps of mating and encircling collectively comprise the step of mating the first and second core portions such that the leg of the first core portion mates with a leg of the second core portion and the inductor encircles the mated legs in combination.

7. A method according to claim 4, wherein the step of mating comprise the step of mating the first and second core portions such that a leg of the first core portion mates with a leg of the second core portion through a bobbin which supports the inductor.

8. A method according to claim 7, wherein the legs of the first and second core portions have respective mating end surfaces, and wherein the end surfaces are different from the first mating surface of the first core portion.

9. A method according to claim 8, wherein neither of the end surfaces receive adhesive before or during the step of adjusting.

10. A method according to claim 7, wherein the bobbin further supports a second inductor.

11. A method according to claim 10, wherein the first and second inductors form a transformer.

12. A method according to claim 1, wherein the step of adjusting the gap spacing comprises the step of grinding the first mating surface against the corresponding surface of the second core portion while urging the first core portion toward the second core portion.

13. A method according to claim 1, wherein the step of adjusting the gap spacing comprises the step of rotating the first mating surface relative to the corresponding surface of the second core portion, in a plane parallel to the first mating surface, while urging the first core portion toward the second core portion.

14. A method according to claim 1, wherein the step of adjusting the gap spacing comprises the step of translating the first mating surface relative to the corresponding surface of the second core portion, in a plane parallel to the first mating surface, while urging the first core portion toward the second core portion.

15. A method according to claim 1, wherein the step of adjusting the gap spacing comprises the step of vibrating the first and second core portions relative to each other while urging the first core and second core portions toward each other.

16. A method according to claim 1, wherein the step of adjusting the gap spacing until the effective permeability achieves a desired value comprises the step of adjusting the gap spacing until the effective permeability is within a desired range.

17. A method according to claim 1, further comprising the step of curing the adhesive.

18. A method according to claim 17, wherein the step of curing is performed after the step of adjusting.

19. A product made by the process of any of claims 1, 3, 4, 5, 12 and 17.

20. A method for assembling a magnetic device having first and second core portions, comprising the steps of:

applying an adhesive to a rim surface of the first core portion, the first core portion further having a coil support leg having a leg end surface;

mating the first and second core portions to form a core assembly having the rim surface of the first core portion mating with a corresponding surface of the second core portion, the adhesive being disposed between the rim surface of the first core portion and the corresponding surface of the second core portion, the core assembly further having the coil support leg end surface of the first core portion mating with a corresponding surface of the second core portion but spaced therefrom by a gap spacing, the step of mating including the step of encircling the coil support leg with an inductor having an inductance;

observing the inductance of the inductor; and

adjusting the gap spacing until the inductance achieves a desired value.

21. A method according to claim 20, wherein the step of encircling the coil support leg with an inductor comprises the step of inserting the coil support leg into a centerhole of a bobbin which supports the inductor.

22. A method according to claim 20, wherein the step of mating further comprises the step of encircling the coil support leg with a second inductor.

23. A method according to claim 20, wherein the adhesive includes particulates.

24. A method according to claim 23, wherein the step of adjusting the gap spacing comprises the step of grinding the first and second core portions toward each other until the inductance achieves the desired value.

25. A method according to claim 24, wherein the step of-grinding comprises the step of rotating the first and second core portions relative to each other in a plane parallel to the rim surface of the first core portion, while urging the first core and second core portions toward each other.

26. A method according to claim 24, wherein the step of grinding comprises the step of translating the first and second core portions relative to each other in a plane parallel to the rim surface of the first core portion, while urging the first core and second core portions toward each other.

27. A method according to claim 24, wherein the step of grinding comprises the step of vibrating the first and second core portions relative to each other while urging the first core and second core portions toward each other.

28. A method according to claim 20, further comprising the step of curing the adhesive after the step of adjusting.

29. A method according to claim 20, wherein neither the coil support leg end surface nor the surface of the second core portion corresponding to the coil support leg end surface receives adhesive.

30. A product made by the process of any of claims 20, 21, 23, 24 and 28.

31. A method for assembling a magnetic device having first and second core portions, comprising the steps of:

applying an adhesive to a rim surface of the first core portion, but not to an end surface of a coil support leg of the first core portion, the adhesive containing particulate matter;

mating the first and second core portions to form a core assembly having the rim surface of the first core portion mating with a first corresponding surface of the second core portion, the adhesive being disposed between the rim surface of the first core portion and the first corresponding surface of the second core portion, the core assembly further having the end surface of the coil support leg mating with a second corresponding surface of the second core portion but spaced therefrom by a gap spacing, the step of mating including the step of encircling the coil support leg with a bobbin supporting at least a first coil having an inductance;

observing the inductance of the coil;

grinding the first and second core portions toward each other until the inductance achieves a desired value; and subsequently

curing the adhesive.

32. A method according to claim 31, wherein the step of grinding comprises the step of vibrating the first and second core portions relative to each other while urging the first core and second core portions toward each other.

33. A product made by the process of claim 31.

34. A method for assembling a magnetic device having first and second core portions, the first the core portion having at least a first mating surface that mates with a corresponding surface of the second core portion, comprising the steps of:

applying particulate matter to the first mating surface;

mating the first and second core portions to form a core assembly having the particulate matter between the first mating surface and the corresponding surface of the second core portion, the core assembly having a gap spacing between a surface of the first core portion and a surface of the second core portion;

observing the effective permeability of the core assembly;

adjusting the gap spacing until the effective permeability achieves a desired value; and

fixing the gap spacing resulting from the step of adjusting.

35. A method according to claim 34, wherein the step of fixing comprises the step of clamping core assembly so as to provide sustained force urging the first and second core portions toward each other.

36. A method according to claim 34, wherein the step of applying particulate matter to the first mating surface comprises the step of applying an adhesive to the first mating surface, the adhesive containing the particulate matter,
   and wherein the step of fixing comprises the step of curing the adhesive.

37. A method according to claim 34, wherein the step of observing the effective permeability of the core assembly comprises the step of observing the inductance of an inductor encircling a leg of the first core portion,
   and wherein the step of adjusting the gap spacing until the effective permeability achieves a desired value comprises the step of adjusting the gap spacing until the inductance achieves a desired value.

38. A method according to claim 34, wherein the step of adjusting the gap spacing comprises the step of rotating the first mating surface relative to the corresponding surface of the second core portion, in a plane parallel to the first mating surface, while urging the first core portion toward the second core portion.

39. A method according to claim 34, wherein the step of adjusting the gap spacing comprises the step of translating the first mating surface relative to the corresponding surface of the second core portion, in a plane parallel to the first mating surface, while urging the first core portion toward the second core portion.

40. A product made by the process of either of claims 34 and 35.

41. A method for assembling a magnetic device having first and second core portions, comprising the steps of:

applying an particulate matter to a rim surface of the first core portion, the first core portion further having a coil support leg having a leg end surface;

mating the first and second core portions to form a core assembly having the rim surface of the first core portion mating with a corresponding surface of the second core portion, the particulate matter being disposed between the rim surface of the first core portion and the corresponding surface of the second core portion, the core assembly further having the coil support leg end surface of the first core portion mating with a corresponding surface of the second core portion but spaced therefrom by a gap spacing, the step of mating including the step of encircling the coil support leg with an inductor having an inductance;

observing the inductance of the inductor

adjusting the gap spacing until the inductance achieves a desired value; and

fixing the gap spacing resulting from the step of adjusting.

42. A method according to claim 41, wherein the step of fixing comprises the step of clamping core assembly so as to provide sustained force urging the first and second core portions toward each other.

43. A method according to claim 41, wherein the step of applying particulate matter to the first mating surface comprises the step of applying an adhesive to the first mating surface, the adhesive containing the particulate matter,
   and wherein the step of fixing comprises the step of curing the adhesive.

44. A product made by the process of either of claims 41 and 42.

45. A magnetic device comprising:

a first core portion having a first mating surface mated with a second core portion having a second mating surface, the first mating surface being spaced from the second mating surface by particulate matter; and

means fixing the spacing between the first and second mating surfaces.

46. A device according to claim 45, wherein the first core portion includes a leg protruding toward the second core portion,
   further comprising a coil at least partially encircling the leg.

47. A magnetic device comprising:

a first core portion having a first mating surface mated with a second core portion having a second mating surface, the first mating surface being spaced from the second mating surface by particulate matter; and

an adhesive between the first and second mating surfaces fixing the spacing between the first and second mating surfaces.

48. A device according to claim 47, wherein the first core portion includes a leg protruding toward the second core portion,
   further comprising a coil at least partially encircling the leg.

49. A magnetic device comprising:

a first core portion having a first mating surface mated with a second core portion having a second mating surface, the first mating surface being spaced from the second mating surface by particulate matter; and

a clamp providing sustained force urging the first and second mating surfaces toward each other.

50. A device according to claim 49, wherein the first core portion includes a leg protruding toward the second core portion,
   further comprising a coil at least partially encircling the leg.

Drawing