Bulk amorphous metal inductive device

[0002] 1. Field of the Invention

[0003] This invention relates to an inductive device, and more particularly, to a high efficiency, low core loss inductive device having a core assembled from a plurality of bulk amorphous metal magnetic components.

[0004] 2. Description of the Prior Art

[0005] Inductive devices are essential components of a wide variety of modern electrical and electronic equipment, most commonly including transformers and inductors. Most of these devices employ a core comprising a soft ferromagnetic material and one or more electrical windings that encircle the core. Inductors generally employ a single winding with two terminals, and serve as filters and energy storage devices. Transformers generally have two or more windings. They transform voltages from one level to at least one other desired level, and electrically isolate different portions of an overall electric circuit. Inductive devices are available in widely varying sizes with correspondingly varying power capacities. Different types of inductive devices are optimized for operation at frequencies over a very wide range, from DC to GHz. Virtually every known type of soft magnetic material finds application in the construction of inductive devices. Selection of a particular soft magnetic material depends on the combination of properties needed, the availability of the material in a form that lends itself to efficient manufacture, and the volume and cost required to serve a given market. In general, a desirable soft ferromagnetic core material has high saturation induction B_satto minimize core size, and low coercivity H_c, high magnetic permeability μ, and low core loss to maximize efficiency.

[0006] Components such as motors and small to moderate size inductors and transformers for electrical and electronic devices often are constructed using laminations punched from various grades of magnetic steel supplied in sheets having thickness as low as 100 μm. The laminations arc generally stacked and secured and subsequently wound with the requisite one or more electrical windings that typically comprise high conductivity copper or aluminum wire. These laminations are commonly employed in cores with a variety of known shapes.

[0007] Many of the shapes used for inductors and transformers are assembled from constituent components which have the general form of certain block letters, such as “C,” “U,” “E,” and “I,”, by which the components are often identified. The assembled shape may further be denoted by the letters reflecting the constituent components; for example, an “E-I” shape would be made by assembling an “E” component with an “I” component. Other widely used assembled shapes include “E-E,” “C-I,” and “C-C.” Constituent components for prior art cores of these shapes have been constructed both of laminated sheets of conventional crystalline ferromagnetic metal and of machined bulk soft ferrite blocks.

[0008] Although many amorphous metals offer superior magnetic performance when compared to other common soft ferromagnetic materials, certain of their physical properties make conventional fabrication techniques difficult or impossible. Amorphous metal is typically supplied as a thin, continuous ribbon having a uniform ribbon width. However, amorphous metals are thinner and harder than virtually all conventional metallic soft magnetic alloys, so conventional stamping or punching of laminations causes excessive wear on fabrication tools and dies, leading to rapid failure. The resulting increase in the tooling and manufacturing costs makes fabricating bulk amorphous metal magnetic components using such conventional techniques commercially impractical. The thinness of amorphous metals also translates into an increased number of laminations needed to form a component with a given cross-section and thickness, further increasing the total cost of an amorphous metal magnetic component. Machining techniques used for shaping ferrite blocks are also not generally suited for processing amorphous metals.

[0009] The properties of amorphous metal are often optimized by an annealing treatment. However, the annealing generally renders the amorphous metal very brittle, further complicating conventional manufacturing processes. As a result of the aforementioned difficulties, techniques that are widely and readily used to form shaped laminations of silicon steel and other similar metallic sheet-form FeNi- and FeCo-based crystalline materials, have not been found suitable for manufacturing amorphous metal devices and components. Amorphous metals thus have not been accepted in the marketplace for many devices; this is so, notwithstanding the great potential for improvements in size, weight, and energy efficiency that in principle would be realized from the use of a high induction, low loss material.

[0010] For electronic applications such as saturable reactors and some chokes, amorphous metal has been employed in the form of spirally wound, round toroidal cores. Devices in this form are available commercially with diameters typically ranging from a few millimeters to a few centimeters and are commonly used in switch-mode power supplies providing up to several hundred volt-amperes (VA). This core configuration affords a completely closed magnetic circuit, with negligible demagnetizing factor. However, in order to achieve a desired energy storage capability, many inductors include a magnetic circuit with a discrete air gap. The presence of the gap results in a non-negligible demagnetizing factor and an associated shape anisotropy that are manifested in a sheared magnetization (B-H) loop. The shape anisotropy may be much higher than the possible induced magnetic anisotropy, increasing the energy storage capacity proportionately. Toroidal cores with discrete air gaps and conventional material have been proposed for such energy storage applications. However, the gapped toroidal geometry affords only minimal design flexibility. It is generally difficult or impossible for a device user to adjust the gap so as to select a desired degree of shearing and energy storage. In addition, the equipment needed to apply windings to a toroidal core is more complicated, expensive, and difficult to operate than comparable winding equipment for laminated cores. Oftentimes a core of toroidal geometry cannot be used in a high current application, because the heavy gage wire dictated by the rated current cannot be bent to the extent needed in the winding of a toroid. In addition, toroidal designs have only a single magnetic circuit. As a result, they are not well suited and are difficult to adapt for polyphase transformers and inductors, including especially common three-phase devices. Other configurations more amenable to easy manufacture and application are thus sought.

[0011] Moreover, the stresses inherent in a strip-wound toroidal core give rise to certain problems. The winding inherently places the outside surface of the strip in tension and the inside in compression. Additional stress is contributed by the linear tension needed to insure smooth winding. As a consequence of magnetostriction, a wound toroid typically exhibits magnetic properties that are inferior to those of the same strip measured in a flat strip configuration. Annealing in general is able to relieve only a portion of the stress, so only a part of the degradation is eliminated. In addition, gapping a wound toroid frequently causes additional problems. Any residual hoop stress in the wound structure is at least partially removed on gapping. In practice the net hoop stress is not predictable and may be either compressive or tensile. Therefore the actual gap tends to close or open in the respective cases by an unpredictable amount as required to establish a new stress equilibrium. Therefore, the final gap is generally different from the intended gap, absent corrective measures. Since the magnetic reluctance of the core is determined largely by the gap, the magnetic properties of finished cores are often difficult to reproduce on a consistent basis in the course of high-volume production.

[0012] Amorphous metals have also been used in transformers for much higher power devices, such as distribution transformers for the electric power grid that have nameplate ratings of 10 kVA to 1 MVA or more. The cores for these transformers are often formed in a step-lap wound, generally rectangular configuration. In one common construction method, the rectangular core is first formed and annealed. The core is then unlaced to allow pre-formed windings to be slipped over the long legs of the core. Following incorporation of the pre-formed windings, the layers are relaced and secured. A typical process for constructing a distribution transformer in this manner is set forth in U.S. Pat. No. 4,734,975 to Ballard et al. Such a process understandably entails significant manual labor and manipulation steps involving brittle annealed amorphous metal ribbons. These steps are especially tedious and difficult to accomplish with cores smaller than 10 kVA. Furthermore, in this configuration, the cores are not readily susceptible to controllable introduction of an air gap, which is needed for many inductor applications.

[0013] Another difficulty associated with the use of ferromagnetic amorphous metals arises from the phenomenon of magnetostriction. Certain magnetic properties of any magnetostrictive material change in response to imposed mechanical stress. For example, the magnetic permeability of a component containing amorphous materials typically is reduced, and its core losses are increased, when the component is subjected to stress. The degradation of soft magnetic properties of the amorphous metal device due to the magnetostriction phenomenon may be caused by stresses resulting from any combination of sources, including deformation during core fabrication, mechanical stresses resulting from mechanical clamping or otherwise fixing the amorphous metal in place and internal stresses caused by the thermal expansion and/or expansion due to magnetic saturation of the amorphous metal material. As an amorphous metal magnetic device is stressed, the efficiency at which it directs or focuses magnetic flux is reduced, resulting in higher magnetic losses, reduced efficiency, increased heat production, and reduced power. The extent of this degradation is oftentimes considerable. It depends upon the particular amorphous metal material and the actual intensity of the stresses, as indicated by U.S. Pat. No. 5,731,649.

[0014] Amorphous metals have far lower anisotropy energies than many other conventional soft magnetic materials, including common electrical steels. Stress levels that would not have a deleterious effect on the magnetic properties of these conventional metals have a severe impact on magnetic properties such as permeability and core loss, which are important for inductive components. For example, the '649 patent teaches that forming amorphous metal cores by rolling amorphous metal into a coil, with lamination using an epoxy, detrimentally restricts the thermal and magnetic saturation expansion of the coil of material. High internal stresses and magnetostriction are thereby produced, which reduce the efficiency of a motor or generator incorporating such a core. In order to avoid stress-induced degradation of magnetic properties, the '649 patent discloses a magnetic component comprising a plurality of stacked or coiled sections of amorphous metal carefully mounted or contained in a dielectric enclosure without the use of adhesive bonding.

[0015] A significant trend in recent technology has been the design of power supplies, converters, and related circuits using switch-mode circuit topologies. The increased capabilities of available power semiconductor switching devices have allowed switch-mode devices to operate at increasingly high frequencies. Many devices that formerly were designed with linear regulation and operation at line frequencies (generally 50-60 Hz on the power grid or 400 Hz in military applications) are now based on switch-mode regulation at frequencies that are often 5-200 kHz, and sometimes as much as 1 MHz. A principal driving force for the increase in frequency is the concomitant reduction in the size of the required magnetic components, such as transformers and inductors. However, the increase in frequency also markedly increases the magnetic losses of these components. There thus exists a significant need to lower these losses.

[0016] The limitations of magnetic components made using existing materials entail substantial and undesirable design compromises. In many applications, the core losses of the common electrical steels are prohibitive. In such cases a designer may be forced to use a permalloy alloy or a ferrite as an alternative. However, the attendant reduction in saturation induction (e.g. 0.6-0.9T or less for various permalloy alloys and 0.3-0.4 T for ferrites, versus 1.8-2.0T for ordinary electrical steels) necessitates an increase in the size of the resulting magnetic components. Furthermore, the desirable soft magnetic properties of the permalloys are adversely and irreversibly affected by plastic deformation which can occur at relatively low stress levels. Such stresses may occur either during manufacture or operation of the permalloy component. While soft ferrites often have attractively low losses, their low induction values result in impractically large devices for many applications wherein space is an important consideration. Moreover, the increased size of the core undesirably necessitates a longer electrical winding, so ohmic losses increase.

[0017] Notwithstanding the advances represented by the above disclosures, there remains a need in the art for improved inductive devices that exhibit a combination of excellent magnetic and physical properties needed for current requirements. Construction methods are also sought that use amorphous metal efficiently and can be implemented for high volume production of devices of various types.

[0018] The present invention provides a high efficiency inductive device comprising a plurality of low-loss bulk amorphous metal magnetic components. Such components are assembled in juxtaposed relationship to form a magnetic core having at least one magnetic circuit. They are secured in position by a securing means. At least one electrical winding encircles at least a portion of the magnetic core. Each of the components comprises a plurality of substantially similarly shaped, planar layers of amorphous metal strips bonded together with an adhesive agent to form a generally polyhedrally shaped part having a plurality of mating faces. The thickness of each component is substantially equal. Components are assembled with the layers of amorphous metal in each component arranged in substantially parallel planes. Each mating face is proximate to a mating face of another component of the device.

[0019] Advantageously the device of the invention has a low core loss. More specifically, the inductive device has a core loss less than about 12 W/kg when operated at an excitation frequency “f” of 5 kHz to a peak induction level “B_max” of 0.3 T. In another aspect, the device has a core loss less than “L” wherein L is given by the formula L=0.0074 f (B_max)^{1 3}+0.000282 f^{1 5}(B_max)^{2 4}, the core loss, excitation frequency, and peak induction level being measured in watts per kilogram, hertz, and teslas, respectively.

[0020] The inductive device of the invention finds use in a variety of circuit applications. It may serve as a transformer, autotransformer, saturable reactor, or inductor. The component is especially useful in the construction of power conditioning electronic devices that employ various switch mode circuit topologies. The present device is useful in both single and polyphase applications, and especially in three-phase applications.

[0021] Advantageously the bulk amorphous metal magnetic components are readily assembled to form the one or more magnetic circuits of the finished inductive device. In some aspects, the mating faces of the components are brought into intimate contact to produce a device having low reluctance and a relatively square B-H loop. However, by assembling the device with air gaps interposed between the mating faces, the reluctance is increased, providing a device with enhanced energy storage capacity useful in many inductor applications. The air gaps are optionally filled with non-magnetic spacers. It is a further advantage that a limited number of standardized sizes and shapes of components may be assembled in a number of different ways to provide devices with a wide range of electrical characteristics.

[0022] Preferably, the components used in constructing the present device have shapes generally similar to those of certain block letters such as “C,” “U,” “E,” and “I” by which they are identified. Each of the components has at least two mating faces that are brought proximate and parallel to a like number of complementary mating faces on other components. In some aspects of the invention, components having mitered mating faces are advantageously employed. The flexibility of size and shape of the components permits a designer wide latitude in suitably optimizing both the overall core and the one or more winding windows therein. As a result, the overall size of the device is minimized, along with the volume of both core and winding materials required. The combination of flexible device design and the high saturation induction of the core material is beneficial in designing electronic circuit devices having compact size and high efficiency. Compared to conventional inductive devices using lower saturation induction core material, transformers and inductors of given power and energy storage ratings generally are smaller and more efficient. As a result of its very low core losses under periodic magnetic excitation, the magnetic device of the invention is operable at frequencies ranging from DC to as much as 200 kHz or more. It exhibits improved performance characteristics when compared to conventional silicon-steel magnetic devices operated over the same frequency range. These and other desirable attributes render the present device easily customized for specialized magnetic applications, e.g. for use as a transformer or inductor in power conditioning electronic circuitry employing switch-mode circuit topologies and switching frequencies ranging from 1 kHz to 200 kHz or more.

[0023] The present device is readily provided with one or more electrical windings. Advantageously, the windings may be formed in a separate operation, either in a self-supporting assembly or wound onto a bobbin coil form, and slid onto one or more of the components. The windings may also be wound directly onto one or more of the components. The difficulty and complication of providing windings on prior art toroidal magnetic cores is thereby eliminated.

[0024] The present invention also provides a method for constructing a highly efficient inductive device incorporating a plurality of bulk amorphous metal magnetic components. An implementation of the method includes the steps of: (i) encircling at least one of the magnetic components with an electrical winding; (ii) positioning said components in juxtaposed relationship to form said core having at least one magnetic circuit, the layers of each component lying in substantially parallel planes; and (iii) securing the components in the juxtaposed relationship. The assembly of the device advantageously does not impart excessive stress that would unacceptably degrade the soft magnetic properties of the components and the device in which they are incorporated.

[0025] The invention will be more fully understood and further advantages will become apparent when reference is had to the following detailed description of the preferred embodiments of the invention and the accompanying drawings, wherein like reference numerals denote similar elements throughout the several views, and in which:

[0026] FIG. 1 is a perspective view depicting an inductive device of the invention having a “C-I” shape, assembled using bulk amorphous metal magnetic components having “C” and “I” shapes;

[0027] FIG. 2A is a plan view illustrating an inductive device of the invention having a “C-I” shape wherein the “C” and “I” shaped bulk amorphous metal magnetic components are in mating contact and the C-shaped component bears an electrical winding on each of its legs;

[0028] FIG. 2B is a plan view showing an inductive device of the invention having a “C-I” shape wherein the “C” and “I” shaped bulk amorphous metal magnetic components are separated by spacers and the I-shaped component bears an electrical winding;

[0029] FIG. 2C is a plan view depicting an inductive device of the invention that has a “C-I” shape and comprises bulk amorphous metal magnetic components that have mitered mating faces;

[0030] FIG. 3 is a perspective view showing a bobbin bearing electrical windings and adapted to be placed on a bulk amorphous metal magnetic component comprised in the inductive device of the invention;

[0031] FIG. 4 is a perspective view depicting an inductive device of the invention having an “E-I” shape assembled using bulk amorphous metal magnetic components having “E” and “I” shapes and a winding disposed on each of the legs of the “E” shape;

[0032] FIG. 5 is a cross-section view illustrating a portion of the device shown in FIG. 4;

[0033] FIG. 6 is a plan view showing an “E-I” shaped inductive device of the invention comprising “E” and “I” shaped bulk amorphous metal magnetic components assembled with air gaps and spacers between the mating faces of the respective components;

[0034] FIG. 7 is a plan view showing an “E-I” shaped inductive device of the invention wherein each of the mating faces of the bulk amorphous metal magnetic components is mitered;

[0035] FIG. 8 is plan view depicting a generally “E-I” shaped device of the invention assembled from five “I”-shaped bulk amorphous metal magnetic components, the three leg components being of one size and the two back components being of another size;

[0036] FIG. 9 is a plan view depicting a square inductive device of the invention assembled from four substantially identical “I”-shaped bulk amorphous metal magnetic components;

[0037] FIG. 10 is a perspective view depicting a generally rectangular prism-shaped bulk amorphous metal magnetic component used in constructing the inductive device of the invention;

[0038] FIG. 11 is a perspective view depicting an arcuate bulk amorphous metal magnetic component used in constructing the device of the invention;

[0039] FIG. 12 is a schematic depiction of an apparatus and process for forming a rectangular bar of laminated strips of amorphous metal ribbon from which one or more bulk amorphous metal magnetic components of the invention are cut;

[0040] FIG. 13 is a perspective view depicting a bar of laminated strips of amorphous metal ribbon appointed to be cut to form trapezoidal bulk amorphous metal magnetic components used in constructing the inductive device of the invention;

[0041] FIG. 14 is a plan view of an inductive device of the invention having a quadrilateral shape and assembled from four trapezoidal bulk amorphous metal magnetic components;

[0042] FIG. 15 is a schematic depiction of an apparatus and process for forming a rectangular toroidal core of laminated strips of amorphous metal ribbon from which one or more bulk amorphous metal magnetic components of the invention are cut; and.

[0043] FIG. 16 is a perspective view of a generally rectangular core of laminated amorphous metal ribbon appointed to be cut to form bulk amorphous metal magnetic components used in constructing the inductive device of the invention.

[0044] The present invention is directed to high efficiency inductive devices such as inductors and transformers. The devices employ a magnetic core comprising a plurality of low-loss bulk ferromagnetic amorphous metal components assembled to form at least one magnetic circuit. Generally polyhedrally shaped bulk amorphous metal components constructed in accordance with the present invention can have various geometrical shapes, including rectangular, square, and trapezoidal prisms, and the like. In addition, any of the previously mentioned geometric shapes may include at least one arcuate surface, and preferably two oppositely disposed arcuate surfaces, to form a generally curved or arcuate bulk amorphous metal component. The inductive device further comprises at least one electrically conductive winding.

[0045] The device of the invention preferably is assembled from constituent components having overall shapes generally similar to those of certain block letters such as “C,” “U,” “E,” and “I” by which they are identified. The finished device frequently is denoted by the letters indicating the shapes of the two or more constituent components. For example, “C-I,” “E-I,” “E-E,” “C-C”, and “C-I-C” devices are conveniently formed with the components of the invention. Each of the components, in turn, comprises a plurality of planar layers of amorphous metal having substantially similar shape. The layers are stacked to substantially the same height and packing density and are bonded together to form the component. The device is assembled by securing the components in adjacent relationship with a securing means, thereby forming at least one magnetic circuit. In the assembled configuration the layers of amorphous metal strip in each of the components lie in substantially parallel planes. Each of the components has at least two mating faces that are brought proximate and parallel to a like number of complementary mating faces on other components. Some of the shapes, e.g. C, U, and E shapes, terminate in mating faces that are generally substantially co-planar. The I (or rectangular prismatic) may have two parallel mating faces at its opposite ends or one or more mating faces on its long sides. Preferably the mating faces are perpendicular to the planes of the constituent ribbons in the component to minimize core loss. Some embodiments of the invention further comprise bulk magnetic components having mating faces that are mitered relative to the elongated direction of features of the component.

[0046] In some aspects of the invention two magnetic components, each having two mating faces, are used when forming the inductive device with a single magnetic circuit. In other aspects the components have more than two mating faces or the devices have more than two components; accordingly, some of these embodiments also provide more than one magnetic circuit. As used herein, the term magnetic circuit denotes a path along which continuous lines of magnetic flux are caused to flow by imposition of a magnetomotive force generated by a current-carrying winding encircling at least a part of the magnetic circuit. A closed magnetic circuit is one in which flux lies exclusively within a core of magnetic material, while in an open circuit part of the flux path lies outside the core material, for example traversing an air gap or a non-magnetic spacer between portions of the core. The magnetic circuit of the device of the invention is preferably relatively closed, the flux path lying predominantly within the magnetic layers of the components of the device but also crossing at least two air gaps between the proximate mating faces of the respective components. The openness of the circuit may be specified by the fraction of the total magnetic reluctance contributed by the air gaps and by the magnetically permeable core material. Preferably, the magnetic circuit of the present device has a reluctance to which the gap contribution is at most ten times that of the permeable components.

[0047] Referring in detail to FIG. 1, there is depicted generally one form of a “C-I” shaped inductive device 1 of the invention comprising a “C”-shaped magnetic component 2 and an “I”-shaped magnetic component 3. “C” component 2 further includes first side leg 10 and second side leg 14, each extending perpendicularly from a common side of back portion 4 and terminating distally in a first rectangular mating face 11 and a second rectangular mating face 15, respectively. The mating faces are generally substantially coplanar. Side legs 10, 14 depend from opposite ends of the side of back portion 4. “I” component 3 is a rectangular prism having a first rectangular mating face 12 and a second rectangular mating face 16, both of which are located on a common side of component 3. The mating faces 12, 16 have a size and spacing therebetween complementary to that of the respective mating faces 11, 15 at the ends of legs 10, 14 of component 2. Each of the side legs 10, 14, back portion 4 between the side legs, and I component 3 has a generally rectangular geometric cross-section, all of which preferably have substantially the same height, width, and effective magnetic area. By effective magnetic area is meant the area within the geometric cross-section occupied by magnetic material, which is equal to the total geometric area times the lamination fraction.

[0048] In one aspect of the invention best visualized in FIG. 2A, the complementary mating faces 11, 12 and 15, 16, respectively, are brought into intimate contact during assembly of the C-I device 1. This disposition provides a low reluctance for device 1 and concomitantly a relatively square B-H magnetization loop. In another aspect, seen in FIG. 2B, optional spacers 13, 17 are interposed between the respective mating faces of components 2, 3 to provide gaps between the components in the magnetic circuit, the gaps also being known as air gaps. Spacers 13, 17 preferably are composed of a non-conductive, non-magnetic material having sufficient heat resistance to prevent degradation or deformation upon exposure to the temperatures encountered in the assembly and operation of device 1. Suitable spacer materials include ceramics and polymeric and plastic materials such as polyimide film and kraft paper. The width of the gap is preferably set by the thickness of spacers 13, 17 and is selected to achieve a desired reluctance and demagnetizing factor and the associated degree of shearing of the B-H loop of device 1 needed for application in a given electrical circuit.

[0049] The “C-I” device 1 further comprises at least one electrical winding. In the aspect depicted by FIGS. 1 and 2A, there are provided a first electrical winding 25 and a second electrical winding 27 encircling the respective legs 10, 14. A current passing in the positive sense, entering at terminal 25a and exiting at terminal 25burges a flux generally along a path 22 and having the indicated sense 23 in accordance with the right-hand rule. C-I device 1 may be operated as an inductor using either one of windings 25, 27 or with both connected in series aiding to increase inductance. Alternatively C-I device 1 may be operated as a transformer, e.g. with winding 25 connected as the primary and winding 27 connected as the secondary, in a manner well known in the art of electrical transformers. The number of turns in each winding is selected in accordance with known principles of transformer or inductor design. FIG. 2B further depicts an alternative inductor configuration having a single winding 28 disposed on I component 3.

[0050] The at least one electrical winding of device 1 may be located at any place on either of the components 2, 3 although the windings preferably do not impinge on any of the air gaps. One convenient means of providing the winding is to wind turns of conductive wire, usually copper or aluminum, onto a bobbin having a hollow interior volume dimensioned to allow it to be slipped over one of legs 10, 14 or onto I component 3. FIG. 3 depicts one form of bobbin 150 having a body section 152, end flanges 154, and an interior aperture 156 dimensioned to permit bobbin 150 to be slipped over the requisite magnetic component. One or more windings 158 encircle body section 152. Advantageously wire may be wound on bobbin 150 in a separate operation using simple winding equipment, prior to assembly of the inductive device. Bobbin 150, preferably composed of a non-conductive plastic such as polyethylene terephthalate resin, provides added electrical insulation between the windings and the core. Furthermore, the bobbin affords mechanical protection for the core and windings during fabrication and use of the device. Alternatively turns of wire may be wound directly over a portion of one of the components 2, 3. Any known form of wire, including round, rectangular, and tape forms, may be used.

[0051] The assembly of C-I device 1 is secured to provide mechanical integrity to the finished device and to maintain the relative positioning of the constituent components 2, 3, the electrical windings 25, 27, the gap spacers 13, 17 if present, and ancillary hardware. The securing may comprise any combination of mechanical banding, clamping, adhesives, potting, or the like. Device 1 may further comprise an insulative coating on at least a portion of the external surfaces of the components 2, 3. Such a coating preferably is not present on any of mating surfaces 11, 12, 15, 16 in aspects wherein the lowest possible reluctance and intimate contact of the components is desired. The coating is especially helpful if windings are applied directly to components 2, 3, since abrasion, shorting, or other damage to the insulation of the wire windings may otherwise occur. The coating may comprise epoxy resins, or paper- or polymer-backed tape, or other known insulative materials wound around the surface of either component.

[0052] Another implementation of a C-I core of the invention is depicted by FIG. 2C. In this aspect, core 51 comprises C-shaped component 52 and trapezoidal component 53. The distal ends of legs 10, 14 of C-component 52 are mitered at an inwardly sloping angle, preferably 45°, and terminate in mitered mating faces 33, 36. C-component 52 also has radiused outside and inside vertices 42, 43 at each of its corners. Such radiused vertices may be present in many components used in the implementation of this invention. Trapezoidal component 53 terminates in mitered mating faces 34, 37. The mitering of component 53 is at an angle complementary to that of C-component 52, and is preferably also 45°. With this arrangement of the miter angles, components 52, 53 can be juxtaposed so that their respective mating faces either make intimate contact, or as depicted by FIG. 2C, are slightly separated to form an air gap in which spacers 33, 38 are optionally interposed.

[0053] FIGS. 4-6 depict aspects of the invention that provide an “E-I” device 100 including constituent components having “E” and “I” shapes. E component 102 comprises a plurality of layers prepared from ferromagnetic metal strip. Each layer has a substantially identical E-shape. The layers are bonded together to form E component 102 substantially uniform in thickness and having a back portion 104 and a central leg 106, a first side leg 110, and a second side leg 114. Each of central leg 106 and side legs 110, 114 extends perpendicularly from a common side of back portion 104 and terminates distally in a rectangular face 107, 111, 115, respectively. Central leg 106 depends from the center of back portion 104, while side legs 110, 114 depend respectively from opposite ends of the same side of back portion 104. The lengths of central leg 106 and side legs 110, 114 are generally substantially identical so that the respective faces 107, 111, 115 are substantially co-planar. As depicted by FIG. 5, the cross-section A—A of the back portion 104 between central leg 104 and either of side legs 110, 114 is substantially rectangular with a thickness defined by the height of the stacked layers and a width defined by the width of each layer. Preferably the width of back portion 104 in cross-section A—A is chosen to be at least as wide as any of the faces 107, 111, 115.

[0054] I component 101 has a rectangular prismatic shape and comprises a plurality of layers prepared using the same ferromagnetic metal strip as the layers in E component 102. The layers are bonded together to form I component 101 with a substantially uniform thickness. I component 101 has a thickness and a width which are substantially equal to the thickness and width of back portion 104 at section A—A and a length substantially identical to the length of E component 102 measured between the outside surfaces of the side legs 110, 114. On one side of I component 101 at its center is provided a central mating face 108, while a first end mating face 112 and a second end mating face 116 are located at opposite ends of the same side of component 101. Each of mating faces 107, 111, 115 is substantially identical in size to the complementary faces 108, 112, 116, respectively.

[0055] As further depicted by FIGS. 4 and 6, the assembly of device 100 comprises (i) providing one or more electrical windings, such as windings 120, 121, 122, encircling one or more portions of components 102 or 101; (ii) aligning E component 102 and I component 101 in close proximity and with all the layers therein being in substantially parallel planes; and (iii) mechanically securing components 101 and 102 in juxtaposed relationship. Components 102 and 101 are aligned such that faces 107 and 108, 111 and 112, and 115 and 116, respectively, are in proximity. The spaces between the respective faces define three air gaps with substantially identical thickness. Spacers 109, 113, and 117 are optionally placed in these gaps to increase the reluctance and the energy storage capacity of each of the magnetic circuits in device 100. Alternatively, the respective faces may be brought into intimate mating contact to minimize the air gaps and increase the initial inductance.

[0056] The “E-I” device 100 may be incorporated in a single phase transformer having a primary winding and a secondary winding. In one such implementation winding 122 serves as the primary and windings 120 and 121 connected in series-aiding serve as the secondary. In this implementation it is preferred that the width of each of side legs 110 and 114 be at least half the width of center leg 106.

[0057] The implementations in FIGS. 4-6 provide three magnetic circuits schematically having paths 130, 131, and 132 in “E-I” device 100. As a result, device 100 may be used as a three-phase inductor, with each of the three legs bearing a winding for one of the three phases. In still another implementation “E-I” device 100 may be used as a three-phase transformer, with each leg bearing both the primary and secondary windings for one of the phases. In most implementations of an E-I device intended for use in a three-phase circuit it is preferred that the legs 106, 110, and 114 be of equal width to balance the three phases better. In certain specialized designs, the different legs may have different cross-sections, different gaps, or different numbers of turns. Other forms suitable for various polyphase applications will be apparent to those having ordinary skill in the art.

[0058] FIG. 7 depicts another E-I implementation wherein E-I device 180 comprises mitered E component 182 and mitered I component 181. The distal end of center leg 106 of component 182 is mitered with a symmetric taper on each of its sides to form mating faces 140a, 140band with and an inwardly sloping miter at the distal end of outside legs 110, 114 to form mitered mating faces 144, 147. I component 181 is mitered at its ends at angles complementary to the miter of legs 110, 114 to form mitered end mating faces 145, 148 and at its center with a generally V-shaped notch forming mating faces 141a, 141bcomplementary to the mitering of leg 106. Preferably each of the faces is mitered at a 4520 angle relative to the long direction of the respective portion of the component on which it is located. The lengths of legs 106, 110, 114 are chosen to permit components 181, 182 to be brought into juxtaposition with the corresponding mating faces either in intimate contact or spaced with a gap in which optional spacers 142, 146, and 149 are placed. The mitering of the mating faces depicted by FIGS. 2C and 7 advantageously increases the area of the mating face and reduces leakage flux and localized excess eddy current losses.

[0059] Components having an I-shape are especially convenient for the practice of the invention, insofar as magnetic devices having a wide variety of configurations may be assembled from a few standard I-components. Using such components, a designer may easily choose a configuration to produce a device having requisite electrical characteristics for a given circuit application. For example, many applications for which the E-I device 100 depicted by FIG. 4 is suited generally may also be satisfied using a device 200 having an arrangement of five rectangular prismatic magnetic components as depicted by FIG. 8. The components comprise a first back component 210 and a second back component 211 which are of substantially identical size; and a center leg component 240, a first end leg component 250 and a second end leg component 251 of substantially identical size. Each of the five components 210, 211, 240, 250, and 251 comprises layers of ferromagnetic strip laminated to produce components of substantially the same stack height, but the back components and the leg components are generally of different respective lengths and widths. The components are disposed with all the layers of amorphous metal therein lying in parallel planes. Suitable choice of the dimensions of the components provides windows to accommodate electrical windings optimized using art-recognized principles. The windings are preferably disposed on legs 240, 250, and 251 in a manner similar to the configuration in device 100. Alternatively or additionally, windings may be placed on either or both of the back components 210, 211 between the legs. Spacers are optionally placed in the gaps between the components of device 200 to adjust the reluctance of the magnetic circuits of device 200 in the manner discussed hereinabove in connection with device 100. Mitered joints similar to those depicted by FIGS. 2C and 7 are in some instances advantageous.

[0060] In FIG. 9 there is depicted an embodiment of the invention wherein four substantially identical rectangular prismatic components 301 are assembled in a generally square configuration. The device 300, which is thereby formed, may be used in some applications as an alternative to the “C-I” device shown in FIG. 1. Other configurations employing rectangular shaped components of one or more sizes are useful when constructing the inductive devices of the invention. These configurations and ways for constructing inductive devices will be apparent to those skilled in the art, and are within the scope of the present invention.

[0061] As previously noted, the device of the invention utilizes a plurality of polyhedrally shaped components. As used herein, the term polyhedron means a multi-faced or sided solid. It includes, but is not limited to, three-dimensional rectangular and square prisms having mutually orthogonal sides and other shapes, such as trapezoidal prisms, having some non-orthogonal sides. In addition, any of the previously mentioned geometric shapes may include at least one, and preferably two, arcuate surfaces or sides that are disposed opposite each other to form a generally arcuately shaped component. Referring now to FIG. 10, there is depicted one form of magnetic component 56 used in constructing the device of the invention and having the shape of a rectangular prism. The component 56 is comprised of a plurality of substantially similarly shaped, generally planar layers 57 of amorphous metal strip material that are bonded together. In one aspect of the invention, the layers are annealed and then laminated by impregnation with an adhesive agent 58, preferably a low viscosity epoxy.

[0062] FIG. 11 depicts another form of component 80 useful in constructing the inductive device of the invention. Arcuate component 80 comprises a plurality of arcuately shaped lamination layers 81, each of which is preferably a section of an annulus. The layers 81 are bonded together, thereby forming a polyhedrally shaped component having outside arcuate surface 83, inside arcuate surface 84, and end mating surfaces 85 and 86. Preferably, component 80 is impregnated with an adhesive agent 82 allowed to infiltrate the space between adjacent layers. Preferably, mating surfaces 85 and 86 are substantially equal in size and perpendicular to the planes of the strip layers 81.

[0063] “U”-shaped arcuate components 80 wherein surfaces 85 and 86 are coplanar are especially preferred. Also preferred are arcuate components wherein surfaces 85, 86 are at angles of 120° or 90° to each other. Two, three, or four such components, respectively, are readily assembled to form an annular core which is a substantially closed magnetic circuit.

[0064] An inductive device constructed from bulk amorphous metal magnetic components in accordance with the present invention advantageously exhibits low core loss. As is known in the magnetic materials art, core loss of a device is a function of the excitation frequency “f” and the peak induction level “B_max” to which the device is excited. In one aspect, the magnetic device has (i) a core-loss of less than or approximately equal to 1 watt-per-kilogram of amorphous metal material when operated at a frequency of approximately 60 Hz and at a flux density of approximately 1.4 Tesla (T); (ii) a core-loss of less than or approximately equal to 20 watts-per-kilogram of amorphous metal material when operated at a frequency of approximately 1000 Hz and at a flux density of approximately 1.4 T, or (iii) a core-loss of less than or approximately equal to 70 watt-per-kilogram of amorphous metal material when operated at a frequency of approximately 20,000 Hz and at a lo flux density of approximately 0.30T. In accordance with another aspect, a device excited at an excitation frequency “f” to a peak induction level “B_max” may have a core loss at room temperature less than “L” wherein L is given by the formula L=0.0074 f (B_max)^{1 3}+0.000282 f^{1 5}(B_max)^2.4, the core loss, the excitation frequency and the peak induction level being measured in watts per kilogram, hertz, and teslas, respectively.

[0065] The component of the invention advantageously exhibits low core loss when the component or any portion thereof is magnetically excited along any direction substantially within the plane of the amorphous metal pieces comprised therein. The inductive device of the invention, in turn, is rendered highly efficient by the low core losses of its constituent magnetic components. The resulting low values of core loss of the device make it especially suited for use as an inductor or transformer intended for high frequency operation, e.g., for magnetic excitation at a frequency of at least about 1 kHz. The core losses of conventional steels at high frequency generally render them unsuitable for use in such inductive devices. These core loss performance values apply to the various embodiments of the present invention, regardless of the specific geometry of the bulk amorphous metal components used in constructing the inductive device.

[0066] There is further provided a method of constructing the bulk amorphous metal components used in the device of the present invention. In one implementation shown in FIG. 12, a continuous strip 22 of ferromagnetic amorphous metal strip material is fed from roll 30 through cutting blades 32, which cut a plurality of strips 92 having the same shape and size. The strips 92 are stacked to form a bar 90 of stacked amorphous metal strip material. Bar 90 is annealed and the layers 92 adhered to one another with an adhesive agent that is activated and cured. Preferably the bar is impregnated with an adhesive agent, such as a low viscosity, thermally activated epoxy resin. The bar is cut to produce one or more generally three-dimensional parts having a desired shape, for example a generally rectangular, square or trapezoidal prism shape. In one aspect of the invention bar 90 is cut along the cut lines 98, depicted in FIG. 13, to produce a plurality of trapezoidally shaped components 96 bonded by impregnation with epoxy resin 94. Cut lines 98 preferably are oriented at alternating 45° angles with respect to the parallel long sides of bar 90. In one aspect this cutting process is used to form two pairs of components, the members of each pair having substantially the same dimensions. The two pairs may be assembled as depicted by FIG. 14 by mating the 45° faces to form a quadrilateral rectangular configuration 99 having mitered corner joints and the pairs on opposite sides of the quadrilateral. Advantageously, the mitered joints enlarge the contact area at the respective joints and reduce the deleterious effects of flux leakage and increased core loss.

[0067] In another aspect of the method of the present invention, shown in FIGS. 15 and 16, a rectangular prismatic bulk amorphous metal magnetic component is formed by winding a single ferromagnetic amorphous metal strip 22 or a group of ferromagnetic amorphous metal strips 22 around a generally rectangular mandrel 60 to form a generally rectangular wound core 70. The core 70 is annealed and the layers adhered to each other, preferably by impregnation with an adhesive agent that is activated and cured. A low viscosity, thermally activated epoxy resin is preferred. Two rectangular components may be formed by cutting the short sides 74, leaving the radiused corners 76 connected to the long sides 78aand 78b. Additional magnetic components may be formed by removing the radiused corners 76 from the long sides 78aand 78b, and cutting the long sides 78aand 78bat one or more locations, such as those indicated by the dashed lines 72. In the example illustrated in FIG. 16, the cuts form a bulk amorphous metal component having a generally three-dimensional rectangular shape, although other three-dimensional shapes are contemplated by the present invention such as, for example, shapes having at least one trapezoidal or square face.

[0068] Adhesive means are used in the practice of this invention to adhere a plurality of pieces or laminations of amorphous metal strip material in suitable registry to each other, thereby providing a bulk, three-dimensional object. This bonding affords sufficient structural integrity that permits the present component to be handled and incorporated into a larger structure, without concomitantly producing excessive stress that would result in high core loss or other unacceptable degradation of magnetic properties. A variety of adhesive agents may be suitable, including those composed of epoxies, varnishes, anaerobic adhesives, cyanoacrylates, and room-temperature-vulcanized (RTV) silicone materials. Adhesives desirably have low viscosity, low shrinkage, low elastic modulus, high peel strength, and high dielectric strength. The adhesive may cover any fraction of the surface area of each lamination sufficient to effect adequate bonding of adjacent laminations to each other and thereby impart sufficient strength to give the finished component mechanical integrity. The adhesive may cover up to substantially all the surface area. Epoxies may be either multi-part whose curing is chemically activated or single-part whose curing is activated thermally or by exposure to ultra-violet radiation. Preferably, the adhesive has a viscosity of less than 1000 cps and a thermal expansion coefficient approximately equal to that of the metal, or about 10 ppm.

[0069] Suitable methods for applying the adhesive include dipping, spraying, brushing, and electrostatic deposition. In strip or ribbon form amorphous metal may also be coated by passing it over rods or rollers which transfer adhesive to the amorphous metal. Rollers or rods having a textured surface, such as gravure or wire-wrapped rollers, are especially effective in transferring a uniform coating of adhesive onto the amorphous metal. The adhesive may be applied to an individual layer of amorphous metal at a time, either to strip material prior to cutting or to laminations after cutting. Alternatively, the adhesive means may be applied to the laminations collectively after they are stacked. Preferably, the stack is impregnated by capillary flow of the adhesive between the laminations. The impregnation step may be carried out at ambient temperature and pressure. Alternatively, the stack is placed either in vacuum or under hydrostatic pressure to effect more complete filling, yet minimize the total volume of adhesive added. This procedure assures high stacking factor and is therefore preferred. A low-viscosity adhesive agent, such as an epoxy or cyanoacrylate is preferably used. Mild heat may also be used to decrease the viscosity of the adhesive, thereby enhancing its penetration between the lamination layers. The adhesive is activated as needed to promote its bonding. After the adhesive has received any needed activation and curing, the component may be finished to accomplish at least one of removing any excess adhesive, giving it a suitable surface finish, and giving it the final component dimensions. If carried out at a temperature of at least about 175° C., the activation or curing of the adhesive may also serve to affect magnetic properties as discussed in greater detail hereinbelow.

[0070] One preferred adhesive is a thermally activated epoxy sold under the tradename Epoxylite 8899 by the P. D. George Co. The device of the invention is preferably bonded by impregnation with this epoxy, diluted 1:5 by volume with acetone to reduce its viscosity and enhance its penetration between the layers of the ribbon. The epoxy may be activated and cured by exposure to an elevated temperature, e.g. a temperature ranging from about 170 to 180° C. for a time ranging from about 2 to 3 h. Another adhesive found to be preferable is a methyl cyanoacrylate sold under the trade name Permabond 910FS by the National Starch and Chemical Company. The device of the invention is preferably bonded by applying this adhesive such that it will penetrate between the layers of the ribbon by capillary action. Permabond 910FS is a single part, low viscosity liquid that will cure at room temperature in the presence of moisture in 5 seconds.

[0071] The present invention further provides a method of assembling a plurality of bulk amorphous metal magnetic components to form an inductive device having a magnetic core. The method comprises the steps of: (i) encircling at least one of the components with an electrical winding; (ii) positioning the components in juxtaposed relationship to form the core which has at least one magnetic circuit, and wherein the layers of each component lie in substantially parallel planes; and (iii) securing the components in juxtaposed relationship.

[0072] The arrangement of the components assembled in the device of the invention is secured by any suitable securing means. Preferably the securing means does not impart high stress to the constituent components that would result in degradation of magnetic properties such as permeability and core loss. The components are preferably banded with an encircling band, strip, tape, or sheet made of metal, polymer, or fabric. In another embodiment of the invention the securing means comprises a relatively rigid housing or frame, preferably made of a plastic or polymer material, having one or more cavities into which the constituent components are fitted. Suitable materials for the housing include nylon and glass-filled nylon. More preferable materials include polyethylene terephthalate and polybutylene terephthalate, which are available commercially from DuPont under the tradename Rynite PET thermoplastic polyester. The shape and placement of the cavities secures the components in the requisite alignment. In still another embodiment, the securing means comprises a rigid or semi-rigid external dielectric coating or potting. The constituent components are disposed in the requisite alignment. Coating or potting is then applied to at least a portion of the external surface of the device and suitably activated and cured to secure the components. In some implementations one or more windings are applied prior to application of the coating or potting. Various coatings and methods are suitable, including epoxy resins. If required, the finishing operation may include removal of any excess coating. An external coating beneficially protects the insulation of electrical windings on components from abrasion at sharp metal edges and acts to trap any flakes or other material which might tend to come off the component or otherwise become lodged inappropriately in the device or other nearby structure.

[0073] Optionally the fabrication of the component further comprises the step of preparing mating faces on the component, the faces being substantially planar and perpendicular to the constituent layers. If necessary, preparing the faces may comprise a planing operation to refine the mating faces and remove any asperities or non-planarity. The planing preferably comprises at least one of milling, surface grinding, cutting, polishing, chemical etching, and electro-chemical etching, or similar operation, to provide a planar mating surface. The planing step is especially preferred for mating faces located on the side of a component to counter any effects of imperfect registration of the amorphous metal layers.

[0074] The various securing techniques may be practiced in combination to provide additional strength against externally imposed mechanical forces and magnetic forces attendant to the excitation of the component during operation.

[0075] The cutting of bulk amorphous metal magnetic components of the present invention from bars 50 of stacked amorphous metal strip or cores 70 of wound amorphous metal strip may be accomplished using numerous cutting technologies. Suitable methods include, but are not limited to, use of an abrasive cutting blade or wheel, mechanical grinding, diamond wire cutting, high-speed milling performed in either horizontal or vertical orientation, abrasive water jet milling, electric discharge machining by wire or plunge, electrochemical grinding, electrochemical machining, and laser cutting. It is preferred that the cutting method not produce any appreciable damage at or near a cut surface. Such damage may result, for example, from excessive cutting speeds that locally heat the amorphous metal above its crystallization temperature or even melt the material at or near the edge. The adverse results may include increased stress and core loss in the vicinity of the edge, interlaminar shorting, or degradation of mechanical properties. Components having relatively simple shapes without inside vertices, such as rectangular prism-shaped or trapezoidal components, are preferably cut from the bar 50 or core 70 using a cutting blade or wheel. Other shapes that have inside vertices, such as C- and E-components, are more readily cut from bars 50 or cores 70 by techniques such as mechanical grinding, diamond wire cutting, high-speed milling performed in either horizontal or vertical orientation, abrasive water jet milling, electric discharge machining by wire or plunge, electrochemical grinding, electrochemical machining, and laser cutting.

[0076] Inductive devices incorporating bulk amorphous metal magnetic components constructed in accordance with the present invention are especially suited as inductors and transformers for a wide variety of electronic circuit devices, notably including power conditioning circuit devices such as power supplies, voltage converters, and similar power conditioning devices operating using switch-mode techniques at switching frequencies of 1 kHz or more. The low losses of the present inductive device advantageously improves the efficiency of such electronic circuit devices. Magnetic component manufacturing is simplified and manufacturing time is reduced. Stresses otherwise encountered during the construction of bulk amorphous metal components are minimized. Magnetic performance of the finished devices is optimized.

[0077] The bulk amorphous metal magnetic components used in the practice of the present invention can be manufactured using numerous amorphous metal alloys. Generally stated, the alloys suitable for use in constructing the component of the present invention are defined by the formula: M_70-85Y_5-20Z_0-20, subscripts in atom percent, where “M” is at least one of Fe, Ni and Co, “Y” is at least one of B, C and P, and “Z” is at least one of Si, Al and Ge; with the proviso that (i) up to ten (10) atom percent of component “M” can be replaced with at least one of the metallic species Ti, V, Cr, Mn, Cu, Zr, Nb, Mo, Ta and W, and (ii) up to ten (10) atom percent of components (Y+Z) can be replaced by at least one of the non-metallic species In, Sn, Sb and Pb. As used herein, the term “amorphous metallic alloy” means a metallic alloy that substantially lacks any long range order and is characterized by X-ray diffraction intensity maxima which are qualitatively similar to those observed for liquids or inorganic oxide glasses.

[0078] Amorphous metal alloys suitable as feedstock in the practice of the invention are commercially available, generally in the form of continuous thin strip or ribbon in widths up to 20 cm or more and in thicknesses of approximately 20-25 μm. These alloys are formed with a substantially fully glassy microstructure (e.g., at least about 80% by volume of material having a non-crystalline structure). Preferably the alloys are formed with essentially 100% of the material having a non-crystalline structure. Volume fraction of non-crystalline structure may be determined by methods known in the art such as x-ray, neutron, or electron diffraction, transmission electron microscopy, or differential scanning calorimetry. Highest induction values at low cost are achieved for alloys wherein “M,” “Y,” and “Z” are at least predominantly iron, boron, and silicon, respectively. Accordingly, it is preferred that the alloy contain at least 70 atom percent Fe, at least 5 atom percent B, and at least 5 atom percent Si, with the proviso that the total content of B and Si be at least 15 atom percent. Amorphous metal strip composed of an iron-boron-silicon alloy is also preferred. Most preferred is amorphous metal strip having a composition consisting essentially of about 11 atom percent boron and about 9 atom percent silicon, the balance being iron and incidental impurities. This strip, having a saturation induction of about 1.56 T and a resistivity of about 137 μΩ-cm, is sold by Honeywell International Inc. under the trade designation METGLAS® alloy 2605SA-1. Another suitable amorphous metal strip has a composition consisting essentially of about 13.5 atom percent boron, about 4.5 atom percent silicon, and about 2 atom percent carbon, the balance being iron and incidental impurities. This strip, having a saturation induction of about 1.59 T and a resistivity of about 137 μΩ-cm, is sold by Honeywell International Inc. under the trade designation METGLAS® alloy 2605SC. For applications in which even higher saturation induction is desired, strip having a composition consisting essentially of iron, along with about 18 atom percent Co, about 16 atom percent boron, and about 1 atom percent silicon, the balance being iron and incidental impurities, is suitable. Such strip is sold by Honeywell International Inc. under the trade designation METGLAS® alloy 2605 CO. However, losses of a component constructed with this material tend to be slightly higher than those using METGLAS 2605SA-1.

[0079] As is known in the art, a ferromagnetic material may be characterized by its saturation induction or equivalently, by its saturation flux density or magnetization. An alloy suitable for use in the present invention preferably has a saturation induction of at least about 1.2 tesla (T) and, more preferably, a saturation induction of at least about 1.5 T. The alloy also has high electrical resistivity, preferably at least about 100 μΩ-cm, and most preferably at least about 130 μΩ-cm.

[0080] Mechanical and magnetic properties of the amorphous metal strip appointed for use in the component generally may be enhanced by thermal treatment at a temperature and for a time sufficient to provide the requisite enhancement without altering the substantially fully glassy microstructure of the strip. Generally, the temperature is selected to be about 100-175° C. below the alloy's crystallization temperature and the time ranges from about 0.25-8 h. The heat treatment comprises a heating portion, an optional soak portion and a cooling portion. A magnetic field may optionally be applied to the strip during at least a portion, such as during at least the cooling portion, of the heat treatment. Application of a field, preferably directed substantially along the direction in which flux lies during operation of the component, may in some cases further improve the magnetic properties and reduce the core loss of the component. Optionally, the heat treatment comprises more than one such heat cycle. Furthermore, the one or more heat treatment cycles may be carried out at different stages of the component manufacture. For example, discrete laminations may be treated or the lamination stack may be heat treated either before or after adhesive bonding. Preferably, the heat treatment is carried out before bonding, since many otherwise attractive adhesives will not withstand the requisite heat treatment temperatures.

[0081] The thermal treatment of the amorphous metal may employ any heating means which results in the metal experiencing the required thermal profile. Suitable heating means include infra-red heat sources, ovens, fluidized beds, thermal contact with a heat sink maintained at an elevated temperature, resistive heating effected by passage of electrical current through the strip, and inductive (RF) heating. The choice of heating means may depend on the ordering of the required processing steps enumerated above.

[0082] The magnetic properties of certain amorphous alloys suitable for use in the present component may be significantly improved by heat treating the alloy to form a nanocrystalline microstructure. This microstructure is characterized by the presence of a high density of grains having average size less than about 100 nm, preferably less than 50 nm, and more preferably about 10-20 nm. The grains preferably occupy at least 50% of the volume of the iron-base alloy. These preferred materials have low core loss and low magnetostriction. The latter property also renders the material less vulnerable to degradation of magnetic properties by stresses resulting from the fabrication and/or operation of a device comprising the component. The heat treatment needed to produce the nanocrystalline structure in a given alloy must be carried out at a higher temperature or for a longer time than would be needed for a heat treatment designed to preserve therein a substantially fully glassy microstructure. As used herein the terms amorphous metal and amorphous alloy further include a material initially formed with a substantially fully glassy microstructure and subsequently transformed by heat treatment or other processing to a material having a nanocrystalline microstructure. Amorphous alloys which may be heat treated to form a nanocrystalline microstructure are also often termed, simply, nanocrystalline alloys. The present method allows a nanocrystalline alloy to be formed into the requisite geometrical shape of the finished bulk magnetic component. Such formation is advantageously accomplished while the alloy is still in its as-cast, ductile, substantially non-crystalline form, before it is heat treated to form the nanocrystalline structure which generally renders it more brittle and more difficult to handle. Typically the nanocrystallization heat treatment is carried out at a temperature ranging from about 50° C. below the alloy's crystallization temperature to about 50° C. thereabove.

[0083] Two preferred classes of alloy having magnetic properties significantly enhanced by formation therein of a nanocrystalline microstructure are given by the following formulas in which the subscripts are in atom percent.

[0084] A first preferred class of nanocrystalline alloy is Fe_{100−u−x−y−z−w}R_uT_xQ_yB_zSi_w, wherein R is at least one of Ni and Co, T is at least one of Ti, Zr, Hf, V, Nb, Ta, Mo, and W, Q is at least one of Cu, Ag, Au, Pd, and Pt, u ranges from 0 to about 10, x ranges from about 3 to 12, y ranges from 0 to about 4, z ranges from about 5 to 12, and w ranges from 0 to less than about 8. After this alloy is heat treated to form a nanocrystalline microstructure therein, it has high saturation induction (e.g., at least about 1.5 T), low core loss, and low saturation magnetostriction (e.g. a magnetostriction having an absolute value less than 4×10⁻⁶). Such an alloy is especially preferred for applications wherein a device of minimum size is demanded.

[0085] A second preferred class of nanocrystalline alloy is Fe_{100−u−x−y−z−w}R_uT_xQ_yB_zSi_w, wherein R is at least one of Ni and Co, T is at least one of Ti, Zr, Hf, V, Nb, Ta, Mo, and W, Q is at least one of Cu, Ag, Au, Pd, and Pt, u ranges from 0 to about 10, x ranges from about 1 to 5, y ranges from 0 to about 3, z ranges from about 5 to 12, and w ranges from about 8 to 18. After this alloy is heat treated to form a nanocrystalline microstructure therein, it has a saturation induction of at least about 1.0T, an especially low core loss, and low saturation magnetostriction (e.g. a magnetostriction having an absolute value less than 4×10⁻⁶). Such an alloy is especially preferred for use in a device required to operate at very excitation frequency, e.g. 1000 Hz or more.

[0086] Bulk amorphous magnetic components will magnetize and demagnetize more efficiently than components made from other iron-base magnetic metals. When incorporated in an inductive device, the bulk amorphous metal component will generate less heat than a comparable component made from another iron-base magnetic metal when the two components are magnetized at identical induction and frequency. An inductive device using the bulk amorphous metal component can therefore be designed to operate: (i) at a lower operating temperature; (ii) at higher induction to achieve reduced size and weight and increased energy storage or transfer; or (iii) at higher frequency to achieve reduced size and weight, when compared to inductive devices incorporating components made from other iron-base magnetic metals.

[0087] As is known in the art, core loss is that dissipation of energy which occurs within a ferromagnetic material as the magnetization thereof is changed with time. The core loss of a given magnetic component is generally determined by cyclically exciting the component. A time-varying magnetic field is applied to the component to produce therein a corresponding time variation of the magnetic induction or flux density. For the sake of standardization of measurement the excitation is generally chosen such that the magnetic induction is homogeneous in the sample and varies sinusoidally with time at a frequency “f” and with a peak amplitude B_max. The core loss is then determined by known electrical measurement instrumentation and techniques. Loss is conventionally reported as watts per unit mass or volume of the magnetic material being excited. It is known in the art that loss increases monotonically with f and B_max. Most standard protocols for testing the core loss of soft magnetic materials used in inductive devices {e.g. ASTM Standards A912-93 and A927 (A927M-94)} call for a sample of such materials which is situated in a substantially closed magnetic circuit, i.e. a configuration in which closed magnetic flux lines are substantially contained within the volume of the sample and the magnetic material cross-section is substantially identical throughout the magnetic circuit. On the other hand, the magnetic circuit in an actual inductive device, especially a flyback transformer or an energy storage inductor, may be rendered relatively open by the presence of high-reluctance gaps that magnetic flux lines must traverse. Because of fringing field effects and non-uniformity of the field, a given material tested in an open circuit generally exhibits a higher core loss, i.e. a higher value of watts per unit mass or volume, than it would have in a closed-circuit measurement. The bulk magnetic component of the invention advantageously exhibits low core loss over a wide range of flux densities and frequencies even in a relatively open-circuit configuration.

[0088] Without being bound by any theory, it is believed that the total core loss of the low-loss bulk amorphous metal device of the invention is comprised of contributions from hysteresis losses and eddy current losses. Each of these two contributions is a function of the peak magnetic induction B_maxand of the excitation frequency f. Prior art analyses of core losses in amorphous metals (see, e.g., G. E. Fish, J. Appl. Phys. 57, 3569(1985) and G. E. Fish et al., J. Appl. Phys. 64, 5370(1988)) have generally been restricted to data obtained for material in a closed magnetic circuit.

[0089] The analysis of the total core loss L(B_max, f) per unit mass of the device of the invention is simplest in a configuration having a single magnetic circuit and a substantially identical effective magnetic material cross-sectional area. In that case, the loss may be generally be defined by a function having the form

[0090] L(B_max, f)=c₁f(B_max)ⁿ+c₂f^q(B_max)^m

[0091] wherein the coefficients c₁and c₂and the exponents n, m, and q must all be determined empirically, there being no known theory that precisely determines their values. Use of this formula allows the total core loss of the device of the invention to be determined at any required operating induction and excitation frequency. It is sometimes found that in the particular geometry of an inductive device the magnetic field therein is not spatially uniform, especially in implementations having a plurality of magnetic circuits and material cross-sections, such as are generally used for three-phase devices. Techniques such as finite element modeling are known in the art to provide an estimate of the spatial and temporal variation of the peak flux density that closely approximates the flux density distribution measured in an actual device. Using as input a suitable empirical formula giving the magnetic core loss of a given material under spatially uniform flux density, these techniques allow the corresponding actual core loss of a given component in its operating configuration to be predicted with reasonable accuracy by numerical integration over the device volume.

[0092] The measurement of the core loss of the magnetic device of the invention can be accomplished using various methods known in the art. Determination of the loss is especially straightforward in the case of a device with a single magnetic circuit and substantially constant cross-section. A suitable method comprises provision of a device with a primary and a secondary electrical winding, each encircling one or more components of the device. Magnetomotive force is applied by passing current through the primary winding. The resulting flux density is determined by Faraday's law from the voltage induced in the secondary winding. The applied magnetic field is determined by Ampère's law from the magnetomotive force. The core loss is then computed from the applied magnetic field and the resulting flux density by conventional methods.

[0093] The following examples are presented to provide a more complete understanding of the invention. The specific techniques, conditions, materials, proportions and reported data set forth to illustrate the principles and practice of the invention are exemplary and should not be construed as limiting the scope of the invention.

[0094] Fe₈₀B₁₁Si₉ferromagnetic amorphous metal ribbon, approximately 25 mm wide and 0.022 mm thick, is wrapped around a rectangular mandrel or bobbin having dimensions of approximately 25 mm by 60 mm. Approximately 1300 wraps of ferromagnetic amorphous metal ribbon are wound around the mandrel or bobbin producing a rectangular core form having inner dimensions of approximately 25 mm by 60 mm and a build thickness of approximately 30 mm. The core/bobbin assembly is annealed in a nitrogen atmosphere. The anneal consists of: 1) heating the assembly up to 365° C.; 2) holding the temperature at approximately 365° C. for approximately 2 hours; and, 3) cooling the assembly to ambient temperature. The rectangular, wound, amorphous metal core is removed from the core/bobbin assembly and then immersed in a low viscosity, heat-activated epoxy which is allowed to impregnate and infiltrate the spaces between adjacent laminations. The epoxy used is Epoxylite™ 8899 diluted 1:5 by volume with acetone to achieve a suitable viscosity. The bobbin is replaced, and the rebuilt, impregnated core/bobbin assembly is then exposed to a temperature of about 177° C. for approximately 2.5 hours to activate and cure the epoxy resin solution. When fully cured, the core is again removed from the core/bobbin assembly. The resulting rectangular, wound, epoxy bonded, amorphous metal core weighs approximately 1500 g.

[0095] One rectangular prism 30 mm long by 25 mm wide by 30 mm thick (approximately 1300 layers) is cut from approximately the center of each of the long sides of the epoxy bonded amorphous metal core with a 1.5 mm thick cutting blade. The cut surfaces of the rectangular prisms and the remaining sections of the core are etched in a nitric acid/water solution and cleaned in an ammonium hydroxide/water solution. The rectangular prisms and the remaining sections of the core are then reassembled into a full, cut core form, with the ribbon layers in the prisms in their original orientation. Primary and secondary electrical windings are fixed to the remaining sections of the core. The cut core form is electrically tested at 60 Hz, 1,000 Hz, 5,000 Hz and 20,000 Hz and compared to catalogue values for other ferromagnetic materials in similar test configurations (National-Arnold Magnetics, 17030 Muskrat Avenue, Adelanto, Calif. 92301 (1995)). The results are compiled below in Tables 1, 2, 3 and 4.

[0096] As shown by the data in Tables 3 and 4, the core loss is particularly low at excitation frequencies of 5000 Hz or more. Thus, the magnetic component of the invention is especially suited for use in constructing inductive devices of the present invention.

[0097] The core loss data taken in Example 1 above are analyzed using conventional non-linear regression methods. It is determined that the core loss of a low-loss bulk amorphous metal component comprised of Fe₈₀B₁₁Si₉amorphous metal ribbon can be essentially defined by a function having the form

[0098] L(B_max, f)=c₁f(B_max)ⁿ+c₂f^q(B_max)^m.

[0099] Suitable values of the coefficients c₁and c₂and the exponents n, m, and q are selected to define an upper bound to the magnetic losses of the bulk amorphous metal component. Table 5 recites the measured losses of the component in Example 1 and the losses predicted by the above formula, each measured in watts per kilogram. The predicted losses as a function of f (Hz) and B_max(Tesla) are calculated using the coefficients c₁=0.0074 and c₂=0.000282 and the exponents n=1.3, m=2.4, and q=1.5. The measured loss of the bulk amorphous metal component of Example 1 is less than the corresponding loss predicted by the formula.

[0100] Fe₈₀B₁₁Si₉ferromagnetic amorphous metal ribbon, approximately 25 mm wide and 0.022 mm thick, is cut into lengths of approximately 300 mm. Approximately 1,300 layers of the cut ferromagnetic amorphous metal ribbon are stacked to form a bar approximately 25 mm wide and 300 mm long, with a build thickness of approximately 30 mm. The bar is annealed in a nitrogen atmosphere. The anneal consists of: 1) heating the bar up to 365° C.; 2) holding the temperature at approximately 365° C. for approximately 2 hours; and, 3) cooling the bar to ambient temperature. The bar is vacuum impregnated with an epoxy resin solution and cured at 120° C. for approximately 4.5 hours. The resulting stacked, epoxy bonded, amorphous metal bar weighs approximately 1300 g.

[0101] The bar is cut with a 1.5 mm thick cutting blade to form four substantially identical trapezoidal prism components. The cuts are made with a 1.5 mm thick cutting blade at an angle mitered alternatingly at ±45° from the long axis of the strips comprising the starting laminated amorphous metal bar, thereby forming mating faces at each end of each prism. The mating faces are perpendicular to the plane of the ribbon layers in each prism and are approximately 35 mm wide and 30 mm thick, corresponding to the 1,300 layers of ribbon. The unequal side faces of each prism are parallel and approximately 100 mm and 150 mm long, respectively. The cut surfaces of each trapezoidal prism are etched in a nitric acid/water solution and cleaned in an ammonium hydroxide/water solution.

[0102] An electrical winding is wrapped around each of the four prisms, which are then assembled to form a transformer having square picture frame configuration with a square window. The respective windings on opposite components are connected in series aiding to form a primary and a secondary.

[0103] The core loss of the transformer is tested by driving the primary with a source of AC current and detecting the induced voltage in the secondary. The core loss of the transformer is determined using a Yokogawa Model 2532 conventional electronic wattmeter connected to the primary and secondary windings. With the core excited at a frequency of 5 kHz to a peak flux level of 0.3 T, a core loss of less than about 12 W/kg is observed.

[0104] A rectangular prism is prepared using amorphous metal ribbon approximately 25 mm wide and 0.018 mm thick and having a nominal composition of Fe_73.5Cu₁Nb₃B₉Si_13.5. Approximately 1,600 pieces of the strip 300 mm long are cut and stacked in registry in a fixture. The stack is heat treated to form a nanocrystalline microstructure in the amorphous metal. The anneal is carried out by performing the following steps: 1) heating the parts up to 580° C.; 2) holding the temperature at approximately 580° C. for approximately 1 hour; and 3) cooling the parts to ambient temperature. After heat treatment the stack is impregnated by immersion in a low viscosity epoxy resin. The resin is activated and cured at a temperature of about 177° C. for approximately 2.5 hours to form an epoxy impregnated, rectangular bar.

[0105] Four identical rectangular prisms 100 mm long and having end faces 25 mm wide and 30 mm high are formed by cutting the rectangular bar with an abrasive saw. The cut ends of two of the prisms are etched in a nitric acid/water solution and cleaned in an ammonium hydroxide/water solution to form mating faces. Mating faces are also prepared on a side of each of the remaining two bars. Each face region is lightly ground to form a flat surface of the requisite size. The face region is then etched in a nitric acid/water solution and cleaned in an ammonium hydroxide/water solution.

[0106] The four prisms are then assembled and secured to form an inductive device having rectangular picture-frame configuration. A primary electrical winding is applied encircling one of the prisms and a secondary winding is applied to the prism opposite. The windings are connected to a standard electronic wattmeter. The core loss of the device is then tested by passing an electrical current through the primary winding and detecting the induced voltage in the secondary winding. Core loss is determined with a Yokogawa 2532 wattmeter.

[0107] The nanocrystalline alloy inductive device has a core loss of less about 12 W/kg at 5,000 Hz and 0.3 T, rendering it suitable for use in a high efficiency inductor or transformer.

[0108] Having thus described the invention in rather full detail, it will be understood that such detail need not be strictly adhered to but that various changes and modifications may suggest themselves to one skilled in the art, all falling within the scope of the present invention as defined by the subjoined claims.