EP4736199A1 - Magnetically permeable core and transformer including the same - Google Patents

Abstract

A magnetically permeable core includes an integral multilayer film continuously extending along a length between opposing first and second longitudinal ends of the multilayer film and wound to form a plurality of substantially concentric coil loops. The plurality of substantially concentric coil loops has an average height H1 in a height direction of the core and a largest lateral dimension D1 in an in-plane direction of the core, wherein D1/H1 ≥ 2. The multilayer film includes a plurality of substantially co-extensive layers including at least one magnetically permeable layer and at least one adhesive layer bonding the concentric coil loops to each other. For at least one pair of inner and outer coils in the plurality of substantially concentric coil loops, the inner and outer coils have relative magnetic permeabilities different by at least 10% at a same frequency in a range from about 10 kilohertz to about 10 megahertz.

Description

MAGNETICALLY PERMEABLE CORE AND TRANSFORMER INCLUDING THE SAME

Technical Field

The present disclosure relates to a magnetically permeable core for use in a transformer and a transformer including the magnetically permeable core.

Background

A transformer includes a magnetic core and conductor wires wound around the magnetic core. When a current flows in the conductor wires, a magnetic flux is generated and is confined in the magnetic core. However, the magnetic flux may have a different distribution within the magnetic core. Due to this phenomenon, there may be a non-uniform distribution of the magnetic flux. The non-uniform distribution of the magnetic flux may cause localized magnetic saturation at a localized area. Furthermore, the non-uniform distribution of the magnetic flux may create excessive heat in the localized area.

Summary

In a first aspect, the present disclosure provides a magnetically permeable core for use in a transformer. The magnetically permeable core includes an integral multilayer film continuously extending along a length of the multilayer film between opposing first and second longitudinal ends of the multilayer film. The multilayer film is wound to form a plurality of substantially concentric coil loops. The plurality of substantially concentric coil loops numbers at least 50 in total and, in combination, has an average height Hl in a height direction of the core and a largest lateral dimension DI in an in-plane direction of the core, wherein Dl/Hl > 2. The coil loops include an innermost coil loop including the first longitudinal end of the multilayer film and an outermost coil loop including the second longitudinal end of the multilayer film. The multilayer film includes a plurality of substantially co-extensive layers including at least one magnetically permeable layer and at least one adhesive layer bonding the concentric coil loops to each other. For at least one pair of inner and outer coils in the plurality of substantially concentric coil loops, the inner and outer coils have relative magnetic permeabilities different by at least 10% at a same frequency in a range from about 10 kilohertz (kHz) to about 10 megahertz (MHz).

In a second aspect, the present disclosure provides a transformer including the magnetically permeable core of the first aspect. The transformer further includes first and second wire windings wound around the magnetically permeable core to form respective primary and secondary windings of the transformer.

In a third aspect, the present disclosure provides a magnetically permeable core including at least one magnetically permeable layer wound to form a plurality of substantially concentric magnetically permeable loops numbering at least 50 in total. A relative magnetic permeability of the at least one magnetically permeable layer is modulated along a length thereof so that average relative magnetic permeabilities of at least one pair of inner and outer loops in the plurality of magnetically permeable loops are different by at least 10%.

In a fourth aspect, the present disclosure provides a transformer including a substantially planar magnetically permeable core, and first and second wire windings wound around the magnetically permeable core to form respective primary and secondary windings of the transformer. The substantially planar magnetically permeable core has an average height Hl and a largest lateral dimension DI, wherein DI /Hl > 5, such that when energized, the primary winding generates a magnetic flux within the substantially planar magnetically permeable core that varies by less than about 50% along a radial direction of the core.

Brief Description of Drawings

Exemplary embodiments disclosed herein are more completely understood in consideration of the following detailed description in connection with the following figures. The figures are not necessarily drawn to scale. Like numbers used in the figures refer to like components. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labelled with the same number.

FIG. 1A is a schematic top perspective view of a transformer, according to an embodiment of the present disclosure.

FIG. IB is a schematic side view of the transformer of FIG. 1A, according to an embodiment of the present disclosure.

FIG. 2A is a photograph illustrating a plan top view of a magnetically permeable core of the transformer, according to an embodiment of the present disclosure;

FIG. 2B is a schematic side view of the magnetically permeable core of FIG. 2A, according to an embodiment of the present disclosure;

FIG. 3A is a schematic perspective view of a multilayer film of the magnetically permeable core of FIG. 2 A, according to an embodiment of the present disclosure; FIG. 3B is a schematic plan top view of the multilayer film of FIG. 3 A, according to an embodiment of the present disclosure;

FIG. 3C is a schematic cross-sectional view of a portion of the magnetically permeable core taken along a line 1-1 of FIG. 2 A, according to an embodiment of the present disclosure;

FIG. 4A is a schematic top view of an innermost coil loop of the magnetically permeable core, according to an embodiment of the present disclosure;

FIG. 4B is a schematic top view of an outermost coil loop of the magnetically permeable core, according to an embodiment of the present disclosure;

FIG. 5A illustrates a method for making the multilayer film, according to an embodiment of the present disclosure;

FIG. 5B schematically illustrates a method for making the multilayer film, according to another embodiment of the present disclosure;

FIG. 6A is a photograph illustrating a perspective view of the transformer, according to an embodiment of the present disclosure;

FIG. 6B is a photograph illustrating a perspective view of the magnetically permeable core, according to an embodiment of the present disclosure;

FIG. 6C illustrates a schematic sectional side view of the transformer, according to an embodiment of the present disclosure;

FIG. 7 is a magnified portion of the photograph of the transformer shown in FIG. 6A illustrating the magnetically permeable core, according to an embodiment of the present disclosure;

FIGS. 8A-8D schematically illustrate steps of a method for making the magnetically permeable core, according to an embodiment of the present disclosure;

FIG. 9A is a photograph illustrating a magnetic flux generated by a primary winding of a transformer including a comparative core; and

FIG. 9B is a photograph illustrating a magnetic flux generated by a primary winding of the transformer including the magnetically permeable core, according to an embodiment of the present disclosure.

Detailed Description

In the following description, reference is made to the accompanying figures that form a part thereof and in which various embodiments are shown by way of illustration. It is to be understood that other embodiments are contemplated and are made without departing from the scope or spirit of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense.

In the following disclosure, the following definitions are adopted.

As used herein, “a,” “an,” “the,” “at least one,” and “one or more” are used interchangeably.

As used herein as a modifier to a property or attribute, the term “generally”, unless otherwise specifically defined, means that the property or attribute would be readily recognizable by a person of ordinary skill but without requiring absolute precision or a perfect match (e.g., within +/- 20 % for quantifiable properties).

The term “substantially”, unless otherwise specifically defined, means to a high degree of approximation (e.g., within +/- 10% for quantifiable properties) but again without requiring absolute precision or a perfect match.

As used herein, all numbers should be considered modified by the term “about”. The term “about”, unless otherwise specifically defined, means to a high degree of approximation (e.g., within +/- 5% for quantifiable properties) but again without requiring absolute precision or a perfect match.

As used herein, the terms “first” and “second” are used as identifiers. Therefore, such terms should not be construed as limiting of this disclosure. The terms “first” and “second” when used in conjunction with a feature or an element can be interchanged throughout the embodiments of this disclosure.

As used herein, when a first material is termed as “similar” to a second material, at least 90 weight % of the first and second materials are identical and any variation between the first and second materials comprises less than about 10 weight % of each of the first and second materials.

As used herein, “at least one of A and B” should be understood to mean “only A, only B, or both A and B”.

As used herein, the term “film” generally refers to a material with a very high ratio of length or width to thickness. A film has two major surfaces defined by a length and width. Films typically have good flexibility and can be used for a wide variety of applications, including displays. Films may also be of thickness or material composition, such that they are semi-rigid or rigid. Films described in the present disclosure may be composed of various polymeric materials. Films may be monolayer, multilayer, or blend of different polymers.

As used herein, the term “layer” generally refers to a thickness of material within a film that has a relatively consistent chemical composition. Layers may be of any type of material including polymeric, cellulosic, metallic, or a blend thereof. A given polymeric layer may include a single polymer- type or a blend of polymers and may be accompanied by additives. A given layer may be combined or connected to other layers to form films. A layer may be either partially or fully continuous as compared to adjacent layers or the film. A given layer may be partially or fully coextensive with adjacent layers. A layer may contain sub-layers.

As used herein, the term “between about”, unless otherwise specifically defined, generally refers to an inclusive or a closed range. For example, if a parameter X is between about A and B, then A < X < B.

Substantially concentric loops of a coil or a core may have a same or close center, e.g., centered to within 20%, or within 10%, or within 5% of a largest lateral dimension (e.g., diameter of an outermost loop). Substantially concentric loops can have a substantially circular, elliptical, or rounded rectangular shape, for example.

As used herein, the term “relative magnetic permeability” refers to a ratio of the magnetic permeability p of a substance to a magnetic permeability pO of the vacuum.

A transformer includes a magnetic core and conductor wires wound around the magnetic core. When a current flows in the conductor wires, a magnetic flux is generated and is confined in the magnetic core. In some cases, the magnetic flux confined in the magnetic core may have a different distribution within the magnetic core. Specifically, a strong magnetic flux may pass through an inner perimeter of the magnetic core while a relatively weak magnetic flux may pass through an outer perimeter of the magnetic core. Due to this phenomenon, there may be a non-uniform distribution of the magnetic flux. The non-uniform distribution of the magnetic flux may cause localized magnetic saturation at a localized area. Furthermore, the non-uniform distribution of the magnetic flux may create excessive heat in the localized area.

In an aspect, the present disclosure provides a magnetically permeable core for use in a transformer. The magnetically permeable core includes an integral multilayer film continuously extending along a length of the multilayer film between opposing first and second longitudinal ends of the multilayer film. The multilayer film is wound to form a plurality of substantially concentric coil loops. The plurality of substantially concentric coil loops numbers at least 50 in total and, in combination, has an average height Hl in a height direction of the core and a largest lateral dimension DI in an in-plane direction of the core, wherein Dl/Hl > 2. The coil loops include an innermost coil loop including the first longitudinal end of the multilayer film and an outermost coil loop including the second longitudinal end of the multilayer film. The multilayer film includes a plurality of substantially co-extensive layers including at least one magnetically permeable layer and at least one adhesive layer bonding the concentric coil loops to each other. For at least one pair of inner and outer coils in the plurality of substantially concentric coil loops, the inner and outer coils have relative magnetic permeabilities different by at least 10% at a same frequency in a range from about 10 kilohertz (kHz) to about 10 megahertz (MHz).

Since the inner and outer coils have relative magnetic permeabilities different by at least 10% at the same frequency in the range from about 10 kHz to about 10 MHz, the magnetically permeable core of the present disclosure may provide a substantially uniformly distributed magnetic flux within the magnetically permeable core. The substantially uniformly distributed magnetic flux may prevent localized magnetic saturation at the localized area which may otherwise lead to generation of excessive heat in the localized area.

Referring now to figures, FIG. 1A illustrates a schematic top perspective view of a transformer 300, according to an embodiment of the present disclosure. FIG. IB illustrates a schematic side view of the transformer 300 of FIG. 1A, according to an embodiment of the present disclosure.

Referring to FIGS. 1A and IB, the transformer 300 defines mutually orthogonal x-, y-, and z-axes. The x- and y-axes correspond to in-plane axes of the transformer 300, while the z- axis is a transverse axis disposed along a thickness direction of the transformer 300. In other words, the x- and y- axes are disposed along a plane (i.e., the x-y plane) of the transformer 300, and the z-axis is disposed perpendicular to the plane of the transformer 300.

The transformer 300 includes a magnetically permeable core 200. The magnetically permeable core 200 may be interchangeably referred to as “the core 200”. In the illustrated embodiment of FIGS. 1A and IB, the transformer 300 includes a substantially planar magnetically permeable core 200. In such embodiments, the magnetically permeable core 200 may be interchangeably referred to as “the substantially planar magnetically permeable core 200”.

The transformer 300 further includes a first wire winding 310a and a second wire winding 310b. The first wire winding 310a and the second wire winding 310b are wound around the magnetically permeable core 200 to form respective primary and secondary windings of the transformer 300.

FIG. 2A is a photograph illustrating a plan top view of the magnetically permeable core 200, according to an embodiment of the present disclosure. FIG. 2B illustrates a schematic side view of the magnetically permeable core 200 of FIG. 2A, according to an embodiment of the present disclosure.

Referring to FIGS. 1A to 2B, the magnetically permeable core 200 for use in the transformer 300 includes an integral multilayer film 10 (also shown in FIG. 3A). In other words, the substantially planar magnetically permeable core 200 includes an elongated multilayer film 10. The integral multilayer film 10 may be interchangeably referred to as “the multilayer film 10”.

The multilayer film 10 continuously extends along a length L (shown in FIG. 3 A) of the multilayer film 10 between opposing first and second longitudinal ends 11, 12 of the multilayer film 10. The first longitudinal end 11 may be one longitudinal end of the multilayer film 10, and the second longitudinal end 12 may be the other longitudinal end of the multilayer film 10.

The multilayer film 10 is wound to form a plurality of substantially concentric coil loops 20. As illustrated in FIG. 2A, the multilayer film 10 is wound along a winding direction 205 to form the plurality of substantially concentric coil loops 20. The plurality of substantially concentric coil loops 20 may be interchangeably referred to as “the concentric coil loops 20” “the substantially concentric magnetically permeable loops 20” or “the coil loops 20”. Each of the coil loops 20 may include the multilayer film 10 wound to form the coil loops 20.

The multilayer film 10 is wound to form the plurality of substantially concentric coil loops 20 numbering at least 50 in total. In some embodiments, the multilayer film 10 is wound to form the plurality of substantially concentric coil loops 20 numbering at least 75, at least 100, at least 150, at least 200, at least 250, at least 300, at least 350, or at least 400 in total.

The core 200 includes opposing top and bottom major surfaces 200a, 200b. Specifically, the multilayer film 10 may form the top major surface 200a and the bottom major surface 200b opposite to the top major surface 200a of the core 200.

The substantially planar magnetically permeable core 200 includes substantially planar opposing top and bottom major surfaces 200a, 200b. Specifically, the multilayer film 10 may form the top major surface 200a that is substantially planar and the bottom major surface 200b that is substantially planar and opposite to the top major surface 200a of the core 200.

The substantially planar magnetically permeable core 200 has an average height Hl in a height direction of the core 200. The term “average height” as used herein refers to an average of height measured at multiple points along a plane (i.e., the x-y plane) of the substantially planar magnetically permeable core 200. The height direction of the substantially planar magnetically permeable core 200 is along the z-axis. The substantially planar magnetically permeable core 200 may have the average height Hl defined between the substantially planar opposing top and bottom major surfaces 200a, 200b along the thickness direction (i.e., the z- axis).

The substantially planar magnetically permeable core 200 has a largest lateral dimension DI in an in-plane direction of the core 200. Specifically, the largest lateral dimension DI of the core 200 is along the x-y plane of the transformer 300. The largest lateral dimension DI is shown along the x-axis in FIGS. IB and 2B.

In some embodiments, the plurality of substantially concentric coil loops 20, in combination, has the average height Hl in the height direction of the core 200 and has the largest lateral dimension DI in the in-plane direction of the core 200.

In some embodiments, a ratio of the largest lateral dimension DI to the average height Hl is greater than or equal to about 2, i.e., Dl/Hl > 2. In some embodiments, Dl/Hl > 3, Dl/Hl > 4, Dl/Hl > 5, Dl/Hl > 10, Dl/Hl > 15, or Dl/Hl > 20.

In some embodiments, the ratio of the largest lateral dimension DI to the average height Hl is greater than or equal to about 5, i.e., Dl/Hl > 5. In some embodiments, Dl/Hl > 10, Dl/Hl > 15, Dl/Hl > 20, Dl/Hl > 30, Dl/Hl > 40, Dl/Hl > 50, or Dl/Hl > 100.

In some embodiments, the magnetically permeable core 200 has a shape of a disc, a toroid, a doughnut, an ellipsoid, or a coil. In some embodiments, when viewed along the height direction (i.e., along the z-axis), the magnetically permeable core 200 has an oval, a circular, a square, or a rectangular shape. In the illustrated embodiment of FIGS. 1A to 2B, the magnetically permeable core 200 has the shape of the disc. Further, the disc-shaped core 200 has a central through-opening 230.

The coil loops 20 include an innermost coil loop 20a and an outermost coil loop 20b. The innermost coil loop 20a includes the first longitudinal end 11 of the multilayer film 10 and the outermost coil loop 20b includes the second longitudinal end 12 of the multilayer film 10. The core 200 further defines the central through-opening 230 defined by the innermost coil loop 20a.

FIG. 3A illustrates a schematic perspective sectional view of the multilayer film 10, according to an embodiment of the present disclosure. FIG. 3B illustrates a schematic plan top view of the multilayer film 10, according to an embodiment of the present disclosure. FIG. 3C illustrates a schematic cross-sectional view of a portion of the core 200 taken along a line 1-1 of FIG. 2A, according to an embodiment of the present disclosure.

Referring to FIGS. 3A-3C, the multilayer film 10 includes a plurality of substantially co-extensive layers. The multilayer film 10 defines mutually orthogonal xl-, yl-, and zl-axes. The xl- and yl-axes correspond to in-plane axes of the multilayer film 10, while the zl-axis is a transverse axis disposed along a thickness direction of the multilayer film 10. In other words, the xl- and yl- axes are disposed along a plane (i.e., the xl-yl plane) of the multilayer film 10, and the zl-axis is disposed perpendicular to the plane of the multilayer film 10. The xl-axis of the multilayer film 10 may correspond to the winding direction 205 (shown in FIG. 1A) of the core 200 and the yl-axis of the multilayer film 10 may correspond to the thickness direction (i.e., the z-axis) of the core 200.

As discussed above, the multilayer film 10 continuously extends along the length L between the opposing first and second longitudinal ends 11, 12. Therefore, the plurality of substantially co-extensive layers of the multilayer film 10 also continuously extends along the length L between the opposing first and second longitudinal ends 11, 12. The length L extends along a length direction of the multilayer film 10. The length direction of the multilayer film 10 is along the xl-axis.

In some embodiments, the substantially co-extensive layers in the multilayer film 10 are stacked along the thickness direction of the multilayer film 10 orthogonal to the length direction of the multilayer film 10. As discussed above, the thickness direction of the multilayer film 10 is along the zl-axis. In some embodiments, the multilayer film 10 has an average thickness T1 along the thickness direction of the multilayer film 10. In some embodiments, the multilayer film 10 has a width W1 along a width direction of the multilayer film 10 orthogonal to the thickness and length directions of the multilayer film 10. Specifically, the width direction of the multilayer film 10 is along the yl-axis. Since the yl-axis of the multilayer film 10 may correspond to the thickness direction (i.e., the z-axis) of the core 200, the width W1 may correspond to the average height Hl of the core 200.

The plurality of substantially co-extensive layers of the multilayer film 10 is substantially co-extensive in the length L generally along the length direction, i.e., along the xl- axis of the multilayer film 10, and in the width W 1 generally along the width direction, i.e., along the yl- axis of the multilayer film 10.

In some embodiments, W 1 and T1 are within 50% of each other. In some embodiments, W1 and T1 are within 45%, within 40%, within 35%, within 30%, within 25%, within 20%, within 15%, within 10%, or within 5% of each other.

The multilayer film 10 includes at least one magnetically permeable layer 30a, 30b, 30c, 30d and at least one adhesive layer 40a bonding the concentric coil loops 20 to each other. Specifically, the at least one adhesive layer 40a bonds adjacent loops to each other. The at least one magnetically permeable layer 30a, 30b, 30c, 30d is wound to form the plurality of substantially concentric magnetically permeable loops 20.

In some embodiments, the multilayer film 10 includes the plurality of substantially coextensive layers including at least two magnetically permeable layers 30a, 30b, 30c, 30d bonded to each other by one or more adhesive layers 40c, 40d, 40e. In some embodiments, the multilayer film 10 includes the plurality of substantially co-extensive layers including at least three or at least four magnetically permeable layers 30a, 30b, 30c, 30d bonded to each other by the one or more adhesive layers 40c, 40d, 40e.

In the illustrated embodiment of FIG. 3 A, the multilayer film 10 includes four magnetically permeable layers 30a, 30b, 30c, 30d and one adhesive layer 40a bonding the concentric coil loops 20 to each other. Further, the four magnetically permeable layers 30a, 30b, 30c, 30d are bonded to each other by the one or more adhesive layers 40c, 40d, 40e. Specifically, the magnetically permeable layer 30a is bonded to the magnetically permeable layer 30b by the adhesive layer 40c, the magnetically permeable layer 30b is bonded to the magnetically permeable layer 30c by the adhesive layer 40d, and the magnetically permeable layer 30c is bonded to the magnetically permeable layer 30d by the adhesive layer 40e.

In some embodiments, the plurality of substantially co-extensive layers further includes at least one non-adhesive electrically insulative layer 50a, 50b bonded to another layer in the plurality of substantially co-extensive layers by one or more adhesive layers 40b, 40e. In some embodiments, an electrical resistivity of the at least one non-adhesive electrically insulative layer 50a, 50b is at least 100 ohm meters (Qm). In some embodiments, the electrical resistivity of the at least one non-adhesive electrically insulative layer 50a, 50b is greater than 100 Qm, greater than 200 Qm, greater than 500 Qm, or greater than 1000 Qm.

In the illustrated embodiment of FIG. 3A, the plurality of substantially co-extensive layers includes two non-adhesive electrically insulative layers 50a, 50b bonded to another layer in the plurality of substantially co-extensive layers by one or more adhesive layers 40b, 40e. Specifically, the non-adhesive electrically insulative layer 50a is bonded to the magnetically permeable layer 30a by the adhesive layer 40b and the non-adhesive electrically insulative layer 50b is bonded to the magnetically permeable layer 30c by the adhesive layer 40e.

In some embodiments, the at least one magnetically permeable layer 30a, 30b, 30c, 30d includes one or more of magnetically conductive ferrite, soft magnet, metal, crystalline alloy, nanocrystalline alloy, amorphous alloy, and composite.

In some embodiments, the magnetically conductive ferrite includes one or more of a manganese-zinc ferrite, and a nickel-zinc ferrite.

In some embodiments, the magnetically conductive metal includes a magnetically conductive alloy including iron. In some embodiments, the magnetically conductive alloy further includes one or more of silicon, aluminum, boron, niobium, copper, cobalt, nickel, and molybdenum. In some embodiments, the magnetically conductive alloy further includes one or more of silicon, boron, niobium, and copper.

In some embodiments, the magnetically conductive crystalline alloy includes two or more of iron, cobalt, and nickel. In some embodiments, the magnetically conductive nanocrystalline alloy includes iron, silicon, boron, niobium, and copper.

In some embodiments, the magnetically conductive amorphous alloy includes cobalt or iron, and one or more of silicon and boron.

In some embodiments, the magnetically conductive composite includes particles dispersed in a binder. In some embodiments, the particles include metallic particles. In some embodiments, the metallic particles include an iron-aluminum-silicon alloy.

In some embodiments, the adhesive layers 40a, 40b, 40c, 40d, 40e may include any suitable adhesive, such as adhesives including silicone, polyurethane, acrylic, polylactide, polyhydroxybutyrate, and blends thereof. In some embodiments, the adhesive layers 40a, 40b, 40c, 40d, 40e may include one or more of thermoset adhesives or epoxies.

In some embodiments, each of the at least one magnetically permeable layer 30a, 30b, 30c, 30d has an average thickness T2 of between about 0.5 microns and about 50 microns. In some embodiments, each of the at least one magnetically permeable layer 30a, 30b, 30c, 30d has the average thickness T2 of greater than or equal to about 1 micron, greater than or equal to about 1.5 microns, greater than or equal to about 2 microns, greater than or equal to about 2.5 microns, or greater than or equal to about 3 microns. In some embodiments, each of the at least one magnetically permeable layer 30a, 30b, 30c, 30d has the average thickness T2 of less than or equal to about 45 microns, less than or equal to about 40 microns, less than or equal to about 35 microns, or less than or equal to about 30 microns.

In some embodiments, each of the at least one adhesive layer 40a has an average thickness T3 of between about 0.5 microns and about 20 microns. In some embodiments, each of the at least one adhesive layer 40a has the average thickness T3 of greater than or equal to about 1 micron, greater than or equal to about 1.5 microns, or greater than or equal to about 2 microns. In some embodiments, each of the at least one adhesive layer 40a has the average thickness T3 of less than or equal to about 15 microns or less than or equal to about 10 microns.

In some embodiments, the maximum and minimum relative magnetic permeabilities of the multilayer film 10 are between about 100 to about 2000.

In some embodiments, between the opposing first and second longitudinal ends 11, 12 of the multilayer film 10, a maximum relative magnetic permeability of the multilayer film 10 is greater than about 500 and a minimum relative magnetic permeability of the multilayer film is less than about 400.

In some embodiments, between the opposing first and second longitudinal ends 11, 12 of the multilayer film 10, the maximum relative magnetic permeability of the multilayer film 10 is greater than about 600, greater than about 750, greater than about 1000, greater than about 1250, greater than about 1500, or greater than about 1750. In some embodiments, between the opposing first and second longitudinal ends 11, 12 of the multilayer film 10, the minimum relative magnetic permeability of the multilayer film is less than about 350, less than about 300, less than about 250, less than about 200, less than about 150, or less than about 100.

In some embodiments, a relative magnetic permeability of the multilayer film 10 varies by at least 10% between the opposing first and second longitudinal ends 11, 12 of the multilayer film 10. In some embodiments, the relative magnetic permeability of the multilayer film 10 varies by at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, or at least 50% between the opposing first and second longitudinal ends 11, 12 of the multilayer film 10. In other words, the relative magnetic permeability of the multilayer film 10 varies along the length L (i.e., along the x-axis) of the multilayer film 10.

In some embodiments, a relative magnetic permeability of the at least one magnetically permeable layer 30a, 30b, 30c, 30d is modulated along the length L thereof so that average relative magnetic permeabilities of at least one pair of inner and outer loops (interchangeably referred to as “the inner and outer loops”, “the inner and outer coils”, and “the inner and outer coil loops”) in the plurality of magnetically permeable loops are different by at least 10%. In some embodiments, the relative magnetic permeability of the at least one magnetically permeable layer 30a, 30b, 30c, 30d is modulated along the length L thereof so that the average relative magnetic permeabilities of the at least one pair of inner and outer loops in the plurality of magnetically permeable loops are different by at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, or at least 50%.

In some embodiments, the relative magnetic permeability of the at least one magnetically permeable layer 30a, 30b, 30c, 30d is modulated along the length L thereof by intentionally cracking the at least one magnetically permeable layer 30a, 30b, 30c, 30d.

Further, for the at least one pair of inner and outer coils in the plurality of substantially concentric coil loops 20, the inner and outer coils have the relative magnetic permeabilities different by at least 10% at a same frequency in a range from about 10 kilohertz (kHz) to about 10 megahertz (MHz). In some embodiments, for the at least one pair of inner and outer coils in the plurality of substantially concentric coil loops 20, the inner and outer coils have relative magnetic permeabilities different by at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, or at least 50% at a same frequency in the range from about 10 kHz to about 10 MHz.

In some embodiments, each of the inner and outer coils in the at least one pair of inner and outer coils includes ion implants affecting the relative magnetic permeability of the corresponding coil. In some embodiments, average ion densities of the ion implants in the inner and outer coils are different by at least 10%. In some embodiments, the average ion densities of the ion implants in the inner and outer coils are different by at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, or at least 50%. Ion density refers to a number of ion implants per unit volume in the inner or outer coils.

In some embodiments, the inner coil may be the innermost coil loop 20a and the outer coil may be the outermost coil loop 20b. However, the at least one pair of inner coil and the outer coil may include any pair of coils in the plurality of substantially concentric coil loops 20. Specifically, the inner coil of the at least one pair of inner and outer coils may be relatively closer to the innermost coil loop 20a than the outer coil of the at least one pair of inner and outer coils. In other words, the inner coil of the at least one pair of inner and outer coils may be relatively closer to the first longitudinal end 11 of the multilayer film 10 than the outer coil of the at least one pair of inner and outer coils.

In some embodiments, for each pair of the inner and outer coils in the plurality of substantially concentric coil loops 20, the inner and outer coils have respective relative magnetic permeabilities l and p2. Specifically, for each pair of the inner and outer coils in the plurality of substantially concentric coil loops 20, the inner coil has the relative magnetic permeability l and outer coil has relative magnetic permeability p2. The relative magnetic permeability pl is less than or equal to the relative magnetic permeability p2, i.e., pl < p2. In other words, the relative magnetic permeability pl of the inner coil of the pair of inner and outer coils in the plurality of substantially concentric coil loops 20 is less than or equal to the relative magnetic permeability p2 of the outer coil of the pair of inner and outer coils in the plurality of substantially concentric coil loops 20.

Since, the inner and outer coils have the respective relative magnetic permeabilities different by at least 10%, specifically, the relative magnetic permeability pl of the inner coil is less than or equal to the relative magnetic permeability p2 of the outer coil, the magnetically permeable core 200 may provide a substantially uniformly distributed magnetic flux within the magnetically permeable core 200. The substantially uniformly distributed magnetic flux may prevent localized magnetic saturation at a localized area which may otherwise lead to generation of excessive heat in the localized area.

FIG. 4A illustrates a schematic top view of the innermost coil loop 20a, according to an embodiment of the present disclosure. FIG. 4B illustrates a schematic top view of the outermost coil loop 20b, according to an embodiment of the present disclosure.

Referring to FIGS. 1 to 4A-4B, in some embodiments, at least one same magnetically permeable layer 30a, 30b, 30c, 30d in the at least one magnetically permeable layer 30a, 30b, 30c, 30d is intentionally cracked in each of the at least one pair of inner and outer coil loops in the plurality of substantially concentric coil loops 20 to form a plurality of interconnected cracks 31a, 31b defining a plurality of magnetically permeable islands 32a, 32b. In other words, the at least one same magnetically permeable layer 30a, 30b, 30c, 30d in the at least one magnetically permeable layer 30a, 30b, 30c, 30d is intentionally cracked in the inner coil loop in the plurality of substantially concentric coil loops 20 to form the plurality of interconnected cracks 31a defining the plurality of magnetically permeable islands 32a and the at least one same magnetically permeable layer 30a, 30b, 30c, 30d in the at least one magnetically permeable layer 30a, 30b, 30c, 30d is intentionally cracked in the outer coil loop in the plurality of substantially concentric coil loops 20 to form the plurality of interconnected cracks 31b defining the plurality of magnetically permeable islands 32b.

Specifically, the at least one same magnetically permeable layer 30a, 30b, 30c, 30d in the at least one magnetically permeable layer 30a, 30b, 30c, 30d in each of the inner and outer coils in the at least one pair of inner and outer coils is intentionally cracked across substantially an entirety of the corresponding coil to form the plurality of interconnected cracks 31a, 31b defining the plurality of magnetically permeable islands 32a, 32b.

In the illustrated example of FIGS. 4 A and 4B, the inner and outer coil loops in the at least one pair of inner and outer coils are the innermost coil loop 20a and the outermost coil loop 20b, respectively. Further, the at least one same magnetically permeable layer 30a, 30b, 30c, 30d is the magnetically permeable layer 30d which is intentionally cracked across substantially the entirety of the corresponding coil (the innermost coil 20a or the outermost coil 20b) to form the plurality of interconnected cracks 31a, 31b defining the plurality of magnetically permeable islands 32a, 32b.

In some embodiments, the cracks 31a, 31b in the interconnected cracks 31a, 31b extend across an entire thickness (e.g., the average thickness T2 along the thickness direction of the multilayer film 10) of the at least one same magnetically permeable layer 30a, 30b, 30c, 30d isolating the islands 32a, 32b from each other.

In some embodiments, the islands 32a, 32b in the inner and outer coil loops (e.g., in the innermost coil loop 20a and the outermost coil loop 20b, respectively) have respective average largest lateral dimensions SI and S2. Specifically, the islands 32a in the inner coil loop (e.g., the innermost coil loop 20a) have the average largest lateral dimension SI and the islands 32b in the outer coil loop (e.g., the outermost coil loop 20b) have the average largest lateral dimension S2.

The average largest lateral dimension S 1 is an average of the largest lateral dimensions measured for each of the islands 32a in the inner coil loop. Similarly, the average largest lateral dimension S2 is an average of the largest lateral dimensions measured for each of the islands 32b in the outer coil loop.

As is apparent from FIGS. 4A and 4B, the average largest lateral dimension SI is less than the average largest lateral dimension S2, i.e., SI < S2. In some embodiments, S2 is greater than SI by at least 10%. In some embodiments, S2 is greater than SI by at least 20%, at least 30%, at least 40%, at least 50%, at least 100%, at least 150%, at least 200%, or at least 3000%.

Further, in some embodiments, the cracks 31a, 31b in the inner and outer coil loops (e.g., the innermost coil loop 20a and the outermost coil loop 20b, respectively) have respective average crack densities Cl and C2 per square millimeter. Specifically, the cracks 31a in the inner coil loop (e.g., the innermost coil loop 20a) have the average crack density Cl and the cracks 31b in the outer coil loop (e.g., the outermost coil loop 20b) have the average crack density C2.

The average crack density Cl is an average of the crack densities per square millimeter measured for the inner coil loop. Similarly, the average crack density C2 is an average of the crack densities per square millimeter measured for the outer coil loop.

The average crack density Cl is greater than the average crack density C2, i.e., Cl > C2. In some embodiments, Cl is greater than C2 by at least 10%. In some embodiments, Cl is greater than C2 by at least 20%, at least 30%, at least 40%, at least 50%, at least 100%, at least 150%, at least 200%, or at least 3000%.

FIG. 5 A schematically illustrates a method 100 for making the multilayer film 10, according to an embodiment of the present disclosure. FIG. 5B schematically illustrates a method 150 for making the multilayer film 10, according to another embodiment of the present disclosure. Specifically, FIG. 5 A schematically illustrates the method 100 for controlling the relative permeability the multilayer film 10 along the length (i.e., the length L) of the multilayer film 10 and FIG. 5B schematically illustrates the method 150 for controlling the relative permeability the multilayer film 10 along the length of the multilayer film 10.

The method 100 illustrated in FIG. 5 A is a cracking process for making the multilayer film 10. The cracking process includes controlling cracking pressures differently along the length of the multilayer film 10 to control the relative permeability the multilayer film 10 along the length of the multilayer film 10.

In FIG. 5 A, a plurality of set of rollers 110, 120 are shown. The plurality of set of rollers 110, 120 may be used to apply different cracking pressures along the length of the multilayer film 10 in order to modulate the relative permeability the multilayer film 10 along the length of the multilayer film 10. In the illustrated embodiment of FIG. 5 A, two sets of rollers 110, 120 are shown. However, the method 100 may use any number of sets of rollers as per desired application attributes.

As is shown in FIG. 5 A, the multilayer film 10 includes a first portion 10a, a second portion 10b, and a third portion 10c. In some embodiments, the first portion 10a may correspond to the inner loop (e.g., the innermost coil loop 20a shown in FIG. 4A) having the average largest lateral dimension SI and the average crack density Cl. In some embodiments, the third portion 10c may correspond to the outer loop (e.g., the outermost coil loop 20b shown in FIG. 4B) having the average largest lateral dimension S2 and the average crack density C2.

In FIG. 5B, a temperature-controlled chamber 160 is shown. The temperature- controlled chamber 160 is used to apply different annealing temperatures along the length of the multilayer film 10 in order to modulate the relative permeability of the multilayer film 10 along the length of the multilayer film 10. In some embodiments, the temperature-controlled chamber 160 is a continuous furnace.

As is shown in FIG. 5B, the multilayer film 10 also includes the first portion 10a, the second portion 10b, and the third portion 10c. In some embodiments, the first portion 10a may correspond to the inner loop and the third portion 10c may correspond to the outer loop, such that the average relative magnetic permeabilities of the inner and outer loops are different by at least 10%.

In some embodiments, the at least one adhesive layer 40a may be heat-sensitive. In such cases, only the at least one magnetically permeable layer (e.g., the magnetically permeable layer 30d) of the multilayer film 10 is provided to the temperature-controlled chamber 160 to modulate the relative permeability of the at least one magnetically permeable layer along the length of the at least one magnetically permeable layer.

Referring to FIGS. 5A and 5B, in some embodiments, the methods 100, 150 may be combined to achieve a target distribution of relative permeability along the length of the multilayer film 10 as per desired application attributes.

Specifically, the plurality of set of rollers 110, 120 that are used to apply the different cracking pressures along the length of the multilayer film 10 in order to modulate the relative permeability the multilayer film 10 along the length of the multilayer film 10 may be provided in the temperature-controlled chamber 160 that is used to apply the different annealing temperatures along the length of the multilayer film 10 in order to modulate the relative permeability the multilayer film 10 along the length of the multilayer film 10.

FIG. 6A is a photograph illustrating a perspective view of the transformer 300, according to an embodiment of the present disclosure. FIG. 6B is a photograph illustrating a perspective view of the magnetically permeable core 200, according to an embodiment of the present disclosure. FIG. 6C illustrates a schematic sectional side view of the transformer 300, according to an embodiment of the present disclosure.

Referring to FIGS. 6A to 6C, in some embodiments, the magnetically permeable core 200 is at least partially embedded in an electrically insulative and magnetically non-permeable substrate 60. In some embodiments, the substrate 60 includes a Flame Retardant 4 (FR4) substrate. In some embodiments, the FR4 substrate may prevent a hazardous condition in case of any defect or fault in the transformer 300.

In some embodiments, the substrate 60 includes at least one ground layer 61a, 61b (shown in FIG. 6C) embedded therein. Specifically, in some embodiments, the transformer 300 includes the at least one ground layer 61a, 61b embedded in the substrate 60. In the illustrated embodiment of FIG. 6C, the substrate 60 includes two ground layers 61a, 61b embedded therein. Specifically, the transformer 300 includes the two ground layers 61a, 61b embedded in the substrate 60.

FIG. 7 is a magnified portion 201 of the photograph of the transformer 300 shown in FIG. 6A illustrating the magnetically permeable core 200, according to an embodiment of the present disclosure.

Referring to FIGS. 6A-6C and 7, in some embodiments, at least one of the opposing top and bottom major surfaces 200a, 200b of the core 200 includes a regular pattern 210. In some embodiments, the top major surface 200a of the core 200 includes the regular pattern 210. In some embodiments, the bottom major surface 200b of the core 200 includes the regular pattern 210. In some embodiments, each of the opposing top and bottom major surfaces 200a, 200b of the core 200 includes the regular pattern 210.

In some embodiments, the regular pattern 210 includes a plurality of substantially parallel features 220 across the corresponding major surface 200a, 200b. In some embodiments, the regular pattern 210 includes the plurality of substantially parallel features 220 across the top major surface 200a. In some embodiments, the regular pattern 210 includes the plurality of substantially parallel features 220 across the bottom major surface 200b. In some embodiments, the regular pattern 210 includes the plurality of substantially parallel features 220 across each of the top and bottom major surfaces 200a, 200b. In some embodiments, at least one of the parallel features 220 is a groove.

FIGS. 8A-8D schematically illustrate steps of a method for making the magnetically permeable core 200 shown in FIG. 7, according to an embodiment of the present disclosure.

A rod 410 and an uncut multilayer film 420 are shown. In some embodiments, an end 434 of the uncut multilayer film 420 sticks to the rod 410 via the at least one adhesive layer 40a shown in FIG. 3 A. Specifically, the innermost coil loop 20a (shown in FIG. 1A) includes the end 434 of the uncut multilayer film 420 which sticks to the rod 410 via the at least one adhesive layer 40a.

In some embodiments, the end 434 of the uncut multilayer film 420 sticks to the rod 410 as schematically illustrated in FIG. 8 A and the uncut multilayer film 420 is wound around the rod 410 as schematically illustrated in FIG. 8B for a plurality of turns to form an assembly 401 schematically illustrated in FIG.8C. The uncut multilayer film 420 can be wound around the rod 410 by turning the rod 410, for example. Tension can be provided along an edge 436 while turning the rod 410. The uncut multilayer film 420 can be wound around the rod 410 in either orientation.

In some embodiments, the method further includes cutting the assembly 401 into sections having a desired width (i.e., the average height Hl of the core 200 shown in FIG. 2B) for the core 200. In some embodiments, a length L2 of the rod 410 is greater than a lateral width W2 of the uncut multilayer film 420. In some embodiments, the rod 410 extends beyond at least one lateral edge 421 of the uncut multilayer film 420. In some embodiments, the uncut multilayer film 420 having the lateral width W2 is cut to obtain the multilayer film 10 having the width W1 shown in FIGS. 3 A and 3B. FIG. 8D schematically illustrates cutting substantially laterally (e.g., in a plane 6496 having a normal making an angle with an axis of the rod 410 of less than 45 degrees, less than 30 degrees, less than 20 degrees, less than 10 degrees, or less than 5 degrees) through the assembly 401 to form a separated portion of the assembly 401 which includes the core 200. In some embodiments, the separated portion has the width W1 or the height Hl (e.g., variations in the width W1 less than 20%, less than 10%, or less than 5%). In some embodiments, the separated portion of the assembly 401 has a substantially uniform width substantially equal to the widths of the plurality of substantially co-extensive layers of the multilayer film 10.

In some embodiments, the cutting step includes cutting or slicing substantially laterally through the assembly 401 using a diamond wire saw. In some embodiments, cutting substantially laterally through the assembly 401 includes using a plurality of spaced apart cutting wires to form a plurality of separated portions of the assembly 401 where each separated portion of the assembly includes the core 200.

Referring to FIGS. 7 and 8A to 8D, in some embodiments, the cutting or slicing step creates at least one of the opposing top and bottom major surfaces 200a, 200b of the core 200. As discussed above, the at least one of the opposing top and bottom major surfaces 200a, 200b of the core 200 includes the regular pattern 210. In some embodiments, the cutting step creates each of the opposing top and bottom major surfaces 200a, 200b of the core 200. In some embodiments, each of the opposing top and bottom major surfaces 200a, 200b of the core 200 includes the regular pattern 210.

In some embodiments, the regular pattern 210 extends substantially along a same first direction and across substantially the entire core 200. In some embodiments, the regular pattern 210 includes a pattern of substantially parallel grooves extending across the adjacent coil loops 20 (shown in FIG. 2 A) of the multilayer film 10 (shown in FIG. 2 A) of the core 200. In some embodiments, the regular pattern 210 has a first average pitch in a first region of the core 200 and a different second average pitch in a different second region of the core 200. In some embodiments, in at least one first region of the core 200, the core 200 includes a regular optical and topographical pattern along a first direction, and a regular optical, but not topographical, pattern along an orthogonal second direction.

In some embodiments, a wire saw 6494 is used to cut or slice through the assembly 401. In some embodiments, the wire saw 6494 includes a plurality of spaced apart cutting wires 6495 to form a plurality of separated portions (i.e., the cores 200) of the assembly 401. In some embodiments, the cutting wires 6495 used to slice through the assembly are diamond wire(s). Diamond cutting wires can include a wire impregnated with diamond dust and have been used for slicing ceramics, for example.

FIG. 9A is a photograph illustrating a magnetic flux 80 generated by a primary winding of a transformer including a comparative core 500. FIG. 9B is a photograph illustrating a magnetic flux 85 generated by the primary winding of the transformer 300 (shown in FIG. 1 A) including the magnetically permeable core 200, according to an embodiment of the present disclosure. In other words, FIG. 9B depicts the photograph of the magnetic flux 85 generated by the first wire winding 310a (shown in FIG. 1A) wound around the magnetically permeable core 200, according to an embodiment of the present disclosure.

As is apparent from FIG. 9A, when energized, the primary winding of the comparative core 500 generates the magnetic flux 80 that varies by greater than about 50% within the comparative core 500. Specifically, a strong magnetic flux 80 passes through an inner perimeter of the comparative core 500 while a relatively weak magnetic flux 80 passes through an outer perimeter of the comparative core 500. Due to this phenomenon, there may be a non- uniform distribution of the magnetic flux 80. The non-uniform distribution of the magnetic flux 80 may cause localized magnetic saturation at a localized area. Furthermore, the non- uniform distribution of the magnetic flux 80 may create excessive heat in the localized area.

Referring to FIG. 9B, in some embodiments, when energized, the primary winding generates the magnetic flux 85 within the magnetically permeable core 200 that varies by less than about 50% within the core 200. In some embodiments, when energized, the primary winding generates the magnetic flux 85 within the magnetically permeable core 200 that varies by less than about 45%, less than about 40%, less than about 35%, less than about 30%, less than about 25%, less than about 20%, less than about 15%, less than about 10%, or less than about 5% within the core 200.

In some embodiments, when energized, the primary winding generates the magnetic flux 85 within the substantially planar magnetically permeable core 200 that varies by less than about 50% along a radial direction (i.e., along the x-axis or along the y-axis) of the core 200. In some embodiments, when energized, the primary winding generates the magnetic flux 85 within the substantially planar magnetically permeable core 200 that varies by less than about 45%, less than about 40%, less than about 35%, less than about 30%, less than about 25%, less than about 20%, less than about 15%, less than about 10%, or less than about 5% along the radial direction of the core 200.

Therefore, the magnetic flux 85 may be substantially uniformly distributed along the radial direction of the core 200. The substantially uniformly distributed magnetic flux 85 may prevent localized magnetic saturation at a localized area which may otherwise lead to generation of excessive heat in the localized area.

Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified by the term “about”. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein.

Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations can be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.

Claims

1. A magnetically permeable core for use in a transformer and comprising an integral multilayer film continuously extending along a length of the multilayer film between opposing first and second longitudinal ends of the multilayer film and wound to form a plurality of substantially concentric coil loops numbering at least 50 in total and, in combination, having an average height Hl in a height direction of the core, and a largest lateral dimension DI in an in-plane direction of the core, Dl/Hl > 2, the coil loops comprising an innermost coil loop comprising the first longitudinal end of the multilayer film and an outermost coil loop comprising the second longitudinal end of the multilayer film, the multilayer film comprising a plurality of substantially co-extensive layers comprising at least one magnetically permeable layer and at least one adhesive layer bonding the concentric coil loops to each other, wherein for at least one pair of inner and outer coils in the plurality of substantially concentric coil loops, the inner and outer coils have relative magnetic permeabilities different by at least 10% at a same frequency in a range from about 10 kHz to about 10 MHz.

2. The magnetically permeable core of claim 1, wherein at least one same magnetically permeable layer in the at least one magnetically permeable layer in each of the inner and outer coils in the at least one pair of inner and outer coils is intentionally cracked across substantially an entirety of the corresponding coil to form a plurality of interconnected cracks defining a plurality of magnetically permeable islands, wherein the islands in the inner and outer coils have respective average largest lateral dimensions SI and S2, SI < S2.

3. The magnetically permeable core of claim 2, wherein the cracks in the interconnected cracks extend across an entire thickness of the at least one same magnetically permeable layer isolating the islands from each other.

4. The magnetically permeable core of claim 1 , wherein for each pair of inner and outer coils in the plurality of substantially concentric coil loops, the inner and outer coils have respective relative magnetic permeabilities pl and p2, wherein l < p2.

5. The magnetically permeable core of claim 1, wherein a relative magnetic permeability of the multilayer film varies by at least 10% between the opposing first and second longitudinal ends of the multilayer film.

6. The magnetically permeable core of claim 1, wherein between the opposing first and second longitudinal ends of the multilayer film, a maximum relative magnetic permeability of the multilayer film is greater than about 500 and a minimum relative magnetic permeability of the multilayer film is less than about 400.

7. The magnetically permeable core of claim 1, wherein each of the inner and outer coils in the at least one pair of inner and outer coils comprises ion implants affecting a relative magnetic permeability of the coil, wherein average ion densities of the ion implants in the inner and outer coils are different by at least 10%.

8. The magnetically permeable core of claim 1, wherein at least one same magnetically permeable layer in the at least one magnetically permeable layer in each of the inner and outer coils in the at least one pair of inner and outer coils is intentionally cracked across substantially an entirety of the corresponding coil to form a plurality of interconnected cracks defining a plurality of magnetically permeable islands, wherein the cracks in the inner and outer coils have respective average crack densities Cl and C2 per square millimeter, Cl > C2.

9. The magnetically permeable core of claim 1, wherein at least one of opposing top and bottom major surfaces of the core comprises a regular pattern comprising a plurality of substantially parallel features across the corresponding major surface.

10. A magnetically permeable core comprising at least one magnetically permeable layer wound to form a plurality of substantially concentric magnetically permeable loops numbering at least 50 in total, a relative magnetic permeability of the at least one magnetically permeable layer modulated along a length thereof so that average relative magnetic permeabilities of at least one pair of inner and outer loops in the plurality of magnetically permeable loops are different by at least 10%.

11. The magnetically permeable core of claim 10, wherein the relative magnetic permeability of the at least one magnetically permeable layer is modulated along the length thereof by intentionally cracking the at least one magnetically permeable layer.

12. A transformer comprising a substantially planar magnetically permeable core, and first and second wire windings wound around the magnetically permeable core to form respective primary and secondary windings of the transformer, the substantially planar magnetically permeable core having an average height Hl and a largest lateral dimension DI, Dl/Hl > 5, such that when energized, the primary winding generates a magnetic flux within the substantially planar magnetically permeable core that varies by less than about 50% along a radial direction of the core.

13. The transformer of claim 12, wherein the substantially planar magnetically permeable core comprising an elongated multilayer film wound to form a plurality of substantially concentric coil loops numbering at least 50 in total, the multilayer film comprising a plurality of substantially co-extensive layers comprising at least one magnetically permeable layer and at least one adhesive layer bonding the concentric coil loops to each other.

14. The transformer of claim 13, wherein at least one same magnetically permeable layer in the at least one magnetically permeable layer is intentionally cracked in each of at least one pair of inner and outer coil loops in the plurality of substantially concentric coil loops to form a plurality of interconnected cracks defining a plurality of magnetically permeable islands, wherein the islands in the inner and outer coil loops have respective average largest lateral dimensions SI and S2, SI < S2.

15. The transformer of claim 12, wherein the substantially planar magnetically permeable core is at least partially embedded in an electrically insulative and magnetically non-permeable substrate.