HIGH FREQUENCY POWER INDUCTOR MATERIAL

Abstract

High frequency power inductor material having first and second opposed major surfaces, comprising a thermosetting binder and a plurality of multilayered flakes dispersed in the high temperature binder, the multilayered flakes comprising at least two layer pairs, wherein each layer pair comprises a ferromagnetic layer and a dielectric electrical isolation layer so that the ferromagnetic layers are electrically isolated from each other by dielectric layers, and wherein the multilayered flakes are substantially aligned parallel to the first and second major surfaces such that they do not provide an electrically continuous path over a range of greater than 0.5 mm. Exemplary high frequency power inductor materials described herein are useful, for example, as a power inductor in Point of Load converters, low profile inductors for inductivecapacitive (LC) filters (e.g., for global system for mobile communication (GSM) pulse noise suppression in cellular phone speakers), or other applications wherein compact, inductive elements are required on a circuit board.

Claims

1. A high frequency power inductor material having first and second opposed major surfaces, comprising: a thermosetting binder; and a plurality of multilayered flakes dispersed in the high temperature binder, the multilayered flakes comprising at least two layer pairs, wherein each layer pair comprises a ferromagnetic layer and a dielectric electrical isolation layer so that the ferromagnetic layers are electrically isolated from each other by dielectric layers, and wherein the multilayered flakes are substantially aligned parallel to the first and second major surfaces such that they do not provide an electrically continuous path over a range of greater than 0.5 millimeters.

2. The high frequency power inductor material of claim 1, wherein the multilayered flakes each have a thickness up to 10 micrometers.

3. The high frequency power inductor material of claim 1, wherein at least 50 percent by number of each ferromagnetic material layer comprises at least 50 percent by volume ferromagnetic material, based on the total volume of the respective ferromagnetic material layer.

4. The high frequency power inductor material of claim 3, wherein the ferromagnetic material is in the form of granules dispersed in an electrically insulating material.

5. The high frequency power inductor material of claim 4, wherein the granules have particle sizes in a range from 1 nanometer to 30 nanometers.

6. The high frequency power inductor material of claim 4, wherein the electrically insulating material comprises, on a theoretical basis, at least one of Al.sub.2O.sub.3, HfO.sub.2, SiO, SiO.sub.2, Y.sub.2O.sub.3, ZnO, ZrO.sub.2, Si.sub.3N.sub.4, B.sub.2O.sub.3, or MgF.sub.2.

7. The high frequency power inductor material of claim 4, wherein the electrically insulating material is at least one of Al.sub.2O.sub.3, HfO.sub.2, SiO, SiO.sub.2, Y.sub.2O.sub.3, ZnO, ZrO.sub.2, Si.sub.3N.sub.4, B.sub.2O.sub.3, or MgF.sub.2.

8. The high frequency power inductor material of claim 7, wherein the ferromagnetic material is at least one of Co, Fe, or Ni.

9. The high frequency power inductor material of claim 1, wherein the electrically insulating layer comprises, on a theoretical basis, at least one of Al.sub.2O.sub.3, HfO.sub.2, SiO, SiO.sub.2, Y.sub.2O.sub.3, ZnO, ZrO.sub.2, Si.sub.3N.sub.4, B.sub.2O.sub.3, or MgF.sub.2.

10. The high frequency power inductor material of claim 1, wherein the ferromagnetic material layers each have a thickness up to 1000 nanometers.

11. The high frequency power inductor material of claim 1, wherein the electrically insolating layers each have a thickness of at least 5 nanometers.

12. The high frequency power inductor material of claim 1, wherein the multilayered flakes are present in an amount of at least 10 percent by volume of the high frequency power inductor material.

13. The high frequency power inductor material of claim 1, wherein the ferromagnetic material comprises ferromagnetic metal.

14. The high frequency power inductor material of claim 1, wherein the ferromagnetic material comprises crystalline ferromagnetic material.

15. The high frequency power inductor material of claim 14, wherein the ferromagnetic material is a NiFe soft magnetic alloy.

16. The high frequency power inductor material of claim 14, wherein the ferromagnetic material is at least one of NiFe, FeCoNi, or FeCo soft magnetic alloy.

17. The high frequency power inductor material of claim 1, wherein the ferromagnetic material comprises amorphous ferromagnetic metal.

18. The high frequency power inductor material of claim 17, wherein the ferromagnetic material is a soft magnetic alloy of at least one of FeCoB or TLTE, where TL is at least one of Fe, Co, or Ni, and TE is at least one of Zr, Ta, Nb, or Hf.

19. The high frequency power inductor material of claim 1, wherein each electrically insulating layer comprises at least one of a nitride, fluoride, or oxide.

20. The high frequency power inductor material of claim 1, wherein the high temperature binder is a diglycidyl ether of at least one of polyhydric phenols, acrylates, benzoxazines, cyanate ester, polyimide, polyamide, polyester, polyurethanes, or epoxy resins.

21-26. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 is schematic of an exemplary high frequency power inductor material described herein.

[0017] FIG. 2 is schematic of another exemplary high frequency power inductor material described herein.

[0018] FIG. 3 shows the frequency dependence of permeability in Example 1.

[0019] FIG. 4 shows the frequency dependence of permeability in Example 2.

DETAILED DESCRIPTION

[0020] Referring to FIG. 1, high frequency power inductor material 100 has first and second opposed major surfaces 101, 102, high temperature binder 104, and plurality of multilayered flakes 106 dispersed in high temperature binder 104. Multilayered flakes 106 comprise at least two layer pairs 110. Each pair 110 comprises ferromagnetic material layer 111 and adjacent thereto electrically insulating dielectric layer 112 (comprised of electrically insulating material). Multilayered flakes 106 are substantially aligned parallel to first and second major surfaces 101, 102 such that they do not provide an electrically continuous path over a range of greater than 0.5 mm (i.e., multilayered flakes 106 are electrically isolated from each other). For example, the sheet resistance between two vias through the inductor material layer for some embodiments is greater than 10 /square, while for others it may be greater than 1 k/square, and yet for some it may be greater than 1 M/square.

[0021] Referring to FIG. 2, high frequency power inductor material 200 has first and second opposed major surfaces 201, 202, high temperature binder 204, and plurality of multilayered flakes 206 dispersed in high temperature binder 204. Multilayered flakes 206 comprise at least two layer pairs 210. Each pair 210 comprises ferromagnetic material layer 211 and adjacent thereto electrically insulating layer 212 (of electrically insulating material). Ferromagnetic material layer 211 comprises granules 220 of ferromagnetic material dispersed in electrically insulating material 221. Multilayered flakes 206 are electrically isolated from each other. Multilayered flakes 206 are substantially aligned parallel to first and second major surfaces 201, 202 such that they do not provide an electrically continuous path over a range of greater than 0.5 mm.

[0022] Exemplary electrically insulating materials comprise, on a theoretical basis, at least one of a nitride (e.g., Si.sub.3N.sub.4,), fluoride (e.g., MgF.sub.2), or oxide (e.g., Al.sub.2O.sub.3, HfO.sub.2, SiO, SiO.sub.2, Y.sub.2O.sub.3, ZnO, B.sub.2O.sub.3, and ZrO.sub.2). Sources of electrically insulating materials include those available from Zhongnuo Advanced Material, Beijing, China; EM Industries, Hawthorn, N.Y.; Materion, Milwaukee, Wis.; and RD Mathis, Long Beach, Calif. Other exemplary electrically insulating materials include high temperature (i.e., with a glass transition temperature, T.sub.g, exceeding 250 C. and decomposition temperatures exceeding 350 C.) polymeric materials (e.g., polyimides).

[0023] In some embodiments, the ferromagnetic material comprises at least one of Co, Fe, or Ni. In some embodiments, the ferromagnetic material comprises at least two of Co, Fe, or Ni (e.g., soft magnetic alloys of FeCo, NiFe, or FeCoNi). In some embodiments, the ferromagnetic material further comprises at least one of Mo, Cr, Cu, V, Si, or Al as additional alloying elements (e.g., soft magnetic alloys of FeSiAl (also commonly referred to as sendust) or NiFeMo (commonly referred to as supermalloy)). In some embodiments, the ferromagnetic material comprises crystalline ferromagnetic material (e.g., soft magnetic alloys of FeSiAl, NiFe, NiFeMo, FeCo, or FeCoNi). In some embodiments, the ferromagnetic material comprises amorphous ferromagnetic metal (e.g., soft magnetic alloys of FeCoB, or TLTE, where TL is at least one of Fe, Co, or Ni, and TE is at least one of Zr, Ta, Nb, or Hf).

[0024] The use of ferromagnetic metal material layers or metal based granular material layers provides high magnetic saturation induction. Variation in the aspect ratio of the two-dimensional flake can be used to control for higher permeability, or higher ferromagnetic resonance frequency (i.e., less loss coming from resonance). A higher ratio of flake diameter to flake thickness tends to increase permeability. Further, the spaces between flakes form natural air gaps leading to slow saturation.

[0025] In some embodiments, the ferromagnetic material layers each have a thickness up to 1000 (in some embodiments, up to 750, 500, 250, 200, or even up to 150) nm. It is generally desirable for the thickness of a ferromagnetic material layer to be less than (in some embodiments, less than ) of the skin depth of the layer, wherein the skin depth is calculated from the formula

505*sqrt(/f),

where is the resistivity (-m) of the ferromagnetic layer, is the relative permeability of the layer itself, and f is frequency (Hz) of the electrical excitation interacting with the inductor.

[0026] In some embodiments, at least 50 (in some embodiments, at least 55, 60, 65, 70, 75, 80, 85, 90, 95, 96, 97, 98, 99, 99.5, or even 100) percent by number of each ferromagnetic material layer comprises at least 50 (in some embodiments, at least 55, 60, 65, 70, 75, 80, 85, 90, 95, 96, 97, 98, 99, 99.5, or even 100) percent by volume ferromagnetic material, based on the total volume of the respective ferromagnetic material layer.

[0027] In some embodiments, the ferromagnetic material is in the form of granules dispersed in a second electrically insulating material (see, e.g., FIG. 2). In some embodiments, the granules have particle sizes in a range from 1 nm to 30 nm (in some embodiments, 2 nm to 15 nm).

[0028] The ferromagnetic material, in the form of granules dispersed in a second electrically insulating material, can be provided, for example, by co-sputtering from two cathodes, one has a ferromagnetic metal target, and the other has an insulator target.

[0029] In some embodiments, the electrically insulating material comprising the insulating layer and the electrically insulating material, in which the granules are dispersed, are the same material (i.e., the same composition). In some embodiments, the electrically insulating material comprising the insulating layer and the electrically insulating material, in which the granules are dispersed, are different materials (i.e., different compositions).

[0030] In some embodiments, the electrically insulating layers each have a thickness of at least 5 (in some embodiments, up to 10, 15, 20, 25, 30, 35, 40, 50, 75, 100, 125, or even up to 150; in some embodiments, in a range from 5 to 150, 50 to 100, or even 10 to 150) nm. Typically, it is desirable for an electrically insulating layer to be as thin as possible while still ensuring adequate magnetic and electrical isolation of the ferromagnetic metal layers.

[0031] In some embodiments, the multilayered flakes each have a thickness up to 10 (in some embodiments, up to 9, 8, 7, 6, 5, 4, 3, 2, or even up to 1) micrometers.

[0032] In some embodiments, the multilayered flakes are present in an amount of at least 10 (in some embodiments, at least 20, 30, 40, 50, 60, or even 70; in some embodiments, in the range from 30 to 60) percent by volume of the high frequency power inductor material.

[0033] In some embodiments, the high temperature binder is at least one of a diglycidyl ether of at least one of polyhydric phenols, acrylates, benzoxazines, cyanate ester, polyimide, polyamide, polyester, polyurethanes, or epoxy resins (e.g., epoxy novolac resins).

[0034] In some embodiments, the high frequency power inductor materials described herein have a relative permeability of at least 20 (in some embodiments, at least 30, 40, 50, 75, 100, 150, 200, or even up to 250).

[0035] In some embodiments, the high frequency power inductor materials described herein have a saturation magnetic induction, B.sub.s, of at least 0.2 (in some embodiments, at least 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or even at least 1) T.

[0036] In some embodiments, the high frequency power inductor materials described herein have a magnetic resonance frequency in a range from 50 to 1500 (in some embodiments, 800 to 1400, or even 1000 to 5000) megahertz.

[0037] In some embodiments, the high frequency power inductor materials described herein have a magnetic coercivity, H.sub.c, not greater than 10 (in some embodiments, not greater than 5) Oe.

[0038] In some embodiments, the flakes have an aspect ratio of up to 100:1 (in some embodiments, at least 75:1, 50:1, 25:1, or even up to 10:1; in some embodiments, in a range from 10:1 to 100:1).

[0039] Exemplary high frequency power inductor materials described herein are useful, for example, as a power inductor in Point of Load (POL) converters, low profile inductors for inductive-capacitive (LC) filters (e.g., for global system mobile communication (GSM) pulse noise suppression in cellular phone speakers), or other applications wherein compact, inductive elements are required on a circuit board.

Exemplary Embodiments

[0040] 1A. A high frequency (i.e., 5 MHz to 150 MHz) power inductor material having first and second opposed major surfaces, comprising:

[0041] a high temperature binder; and

[0042] a plurality of multilayered flakes dispersed in the high temperature binder, the multilayered flakes comprising at least two (in some embodiments, at least 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 75, 80, 85, 90, 95, or even at least 100; in some embodiments, in a range from 2 to 100, 5 to 50, or even 20 to 40) layer pairs, wherein each layer pair comprises a ferromagnetic layer and a dielectric electrical isolation layer so that the ferromagnetic layers are electrically isolated from each other by dielectric layers, and wherein the multilayered flakes are substantially aligned parallel to the first and second major surfaces such that they do not provide an electrically continuous path over a range of greater than 0.5 mm. [0043] 2A. The high frequency power inductor material of Exemplary Embodiment 1A, wherein the multilayered flakes each have a thickness up to 10 (in some embodiments, up to 9, 8, 7, 6, 5, 4, 3, 2, or even up to 1) micrometers. [0044] 3A. The high frequency power inductor material of any preceding A Exemplary Embodiment, wherein at least 50 (in some embodiments, at least 55, 60, 65, 70, 75, 80, 85, 90, 95, 96, 97, 98, 99, 99.5, or even 100) percent by number of each ferromagnetic material layer comprises at least 50 (in some embodiments, at least 55, 60, 65, 70, 75, 80, 85, 90, 95, 96, 97, 98, 99, 99.5, or even 100) percent by volume ferromagnetic material, based on the total volume of the respective ferromagnetic material layer.

[0045] 4A. The high frequency power inductor material of Exemplary Embodiment 3A, wherein the ferromagnetic material is in the form of granules dispersed in an electrically insulating material. [0046] 5A. The high frequency power inductor material of Exemplary Embodiment 4A, wherein the granules have particle sizes in a range from 1 nm to 30 nm (in some embodiments, 2 nm to 15 nm). [0047] 6A. The high frequency power inductor material of either Exemplary Embodiment 4A or 5A, wherein the electrically insulating material comprises, on a theoretical basis, at least one of Al.sub.2O.sub.3, HfO.sub.2, SiO, SiO.sub.2, Y.sub.2O.sub.3, ZnO, ZrO.sub.2, Si.sub.3N.sub.4, B.sub.2O.sub.3, or MgF.sub.2. [0048] 7A. The high frequency power inductor material of either Exemplary Embodiment 4A or 5A, wherein the electrically insulating material is at least one of Al.sub.2O.sub.3, HfO.sub.2, SiO, SiO.sub.2, Y.sub.2O.sub.3, ZnO, ZrO.sub.2, Si.sub.3N.sub.4, B.sub.2O.sub.3, or MgF.sub.2.

[0049] 8A. The high frequency power inductor material of Exemplary Embodiment 7A, wherein the ferromagnetic material comprises at least one of Co, Fe, or Ni.

[0050] 9A. The high frequency power inductor material of Exemplary Embodiment 7A, wherein the ferromagnetic material comprises at least two of Co, Fe, or Ni.

[0051] 10A. The high frequency power inductor material of either Exemplary Embodiment 8A or 9A, wherein the ferromagnetic material further comprises at least one of Mo, Cr, Cu, V, Si, or Al.

[0052] 11A. The high frequency power inductor material of Exemplary Embodiment 7A, wherein the ferromagnetic material is a soft magnetic alloy of at least one of FeCo, NiFe, or FeCoNi.

[0053] 12A. The high frequency power inductor material of any preceding A Exemplary Embodiment, wherein the electrically insulating layer comprises, on a theoretical basis, at least one of Al.sub.2O.sub.3, HfO.sub.2, SiO, SiO.sub.2, Y.sub.2O.sub.3, ZnO, ZrO.sub.2, Si.sub.3N.sub.4, B.sub.2O.sub.3, or MgF.sub.2.

[0054] 13A. The high frequency power inductor material of any preceding A Exemplary Embodiment, wherein the ferromagnetic material layers each have a thickness up to 1000 (in some embodiments, up to 750, 500, 250, 200, or even up to 150) nm. [0055] 14A. The high frequency power inductor material of any preceding A Exemplary Embodiment, wherein the electrically insolating layers each have a thickness of at least 5 (in some embodiments, up to 10, 15, 20, 25, 30, 35, 40, 50, 75, 100, 125, or even up to 150; in some embodiments, in a range from 5 to 150, or even 10 to 150) nm.

[0056] 15A. The high frequency power inductor material of any preceding A Exemplary Embodiment, wherein the multilayered flakes are present in an amount of at least 10 (in some embodiments, at least 20, 30, 40, 50, 60, or even 70; in some embodiments, in the range from 30 to 60) percent by volume of the high frequency power inductor material.

[0057] 16A. The high frequency power inductor material of any preceding A Exemplary Embodiment, wherein the ferromagnetic material comprises ferromagnetic metal.

[0058] 17A. The high frequency power inductor material of any preceding A Exemplary Embodiment, wherein the ferromagnetic material comprises crystalline ferromagnetic material.

[0059] 18A. The high frequency power inductor material of Exemplary Embodiment 17A, wherein the ferromagnetic material is a NiFe soft magnetic alloy.

[0060] 19A. The high frequency power inductor material of Exemplary Embodiment 17A, wherein the ferromagnetic material is a soft magnetic alloy of at least one of FeCo, NiFe, or FeCoNi.

[0061] 20A. The high frequency power inductor material of any preceding A Exemplary Embodiment, wherein the ferromagnetic material comprises amorphous ferromagnetic metal.

[0062] 21A. The high frequency power inductor material of Exemplary Embodiment 20A, wherein the ferromagnetic material is a soft magnetic alloy of at least one of FeCoB or TLTE, where TL is at least one of Fe, Co, or Ni, and TE is at least one of Zr, Ta, Nb, or Hf.

[0063] 22A. The high frequency power inductor material of any preceding A Exemplary Embodiment, wherein each electrically insulating layer comprises at least one of a nitride, fluoride, or oxide. [0064] 23A. The high frequency power inductor material of any preceding A Exemplary Embodiment, wherein the high temperature binder is a diglycidyl ether of at least one of polyhydric phenols, acrylates, benzoxazines, cyanate ester, polyimide, polyamide, polyester, polyurethanes, or epoxy resins (e.g., epoxy novolac resins).

[0065] 24A. The high frequency power inductor material of any preceding A Exemplary Embodiment having a relative permeability of at least 20 (in some embodiments, at least 30, 40, 50, 75, 100, 150, 200, or even up to 250).

[0066] 25A. The high frequency power inductor material of any preceding A Exemplary Embodiment having a saturation magnetic induction, B.sub.s, of at least 0.2 (in some embodiments, at least 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or even at least 1) T.

[0067] 26A. The high frequency power inductor material of any preceding A Exemplary Embodiment having a magnetic resonance frequency in a range from 50 to 1500 (in some embodiments, 800 to 1400, or even 1000 to 5000) megahertz.

[0068] 27A. The high frequency power inductor material of any preceding A Exemplary Embodiment having a magnetic coercivity, H.sub.c, not greater than 10 (in some embodiments, not greater than 5) Oe.

[0069] 28A. The high frequency power inductor material of any preceding A Exemplary Embodiment, wherein the flakes have an aspect ratio of up to 100:1 (in some embodiments, at least 75:1, 50:1, 25:1, or even up to 10:1; in some embodiments, in a range from 10:1 to 100:1).

[0070] 29A. The high frequency power inductor material of any preceding A Exemplary Embodiment having a skin depth, wherein the magnetic layer thickness is less than (in some embodiments, not greater than , (in some embodiments, less than ) of the skin depth.

[0071] Advantages and embodiments of this invention are further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this invention. All parts and percentages are by weight unless otherwise indicated.

EXAMPLES

Core Loss Measurement Test Method

[0072] The core loss was measured as described in D. Hou et. al., New high-frequency core loss measurement method with partial cancellation concept, pp. 2987-2994, IEEE Transactions on Power Electronics, Vol. 32, No. 4, (2017), the disclosure of which is incorporated herein by reference.

Permeability Spectrum Measurement Test Method

[0073] Permeability spectrum from 1 MHz to 100 MHz is measured using an impedance analyzer (obtained under the trade designation KEYSIGHT E4990A Keysight Technologies Inc., Santa Rosa, Calif.) and a terminal adapter (obtained under the trade designation 42942A from Keysight Technologies Inc.).

Example 1

(EX-1)

[0074] Permeable multi-layered NiFe/insulator particulate material consisting of multiple sub-skin-depth magnetic layers alternated with dielectric spacer layers (FFDM) particles (permeable multi-layered NiFe/insulator particulate material of multiple sub-skin-depth magnetic layers alternated with dielectric spacer layers) (obtained under the trade designation 3M FLUX FIELD DIRECTIONAL MATERIALS PARTICLE EM05EC from 3M Company, St. Paul, Minn.) were in the form of flakes with total flake thickness of about 6 micrometers, and a lateral size less than 500 micrometers. Four grams of the selected particles were mixed with 2.5 grams of polyimide resin (PIR) (obtained under the trade designation UN1866 CP1 from NeXolve Corporation, Huntsville, Ala.) and 1 milliliter of diethylene glycol dimethyl ether (obtained from Alfa Aesar, Lancashire, United Kingdom) in a mixing jar (obtained under the trade designation FLACTEK 501 222PT-J Max 60 from FlackTek, Landrum, S.C.). After mixing with a mixer (obtained under the trade designation DAC 600 FVZ SPEEDMIXER from FlackTek), the slurry was coated onto a polyethylene terephthalate (PET) substrate (obtained under the trade designation MELINEX ST504 from Tekra, New Berlin, Wis.) using a film applicator (obtained under the trade designation MICROM II FILM APPLICATOR from Gardco, Pompano Beach, Fla.). The coated film was 180 micrometers thick after drying at 90 C. for 1 hour. The composite sheet was then peeled off the substrate backing.

[0075] Subsequently, the composite sheet was cut and 4 pieces were stacked on top of one another for pressing. A heated press (obtained as Model 20-122TM2WCB from Wabash MPI, Wabash, Ind.) was used to densify the composite at 5 tons on a 4-inch (10-cm) diameter ram at 275 C. for 5 minutes, and then immediately cooled to room temperature under the same pressure for 3 minutes. A set of steel shims were used during pressing for setting composite thickness.

[0076] The static magnetic property of the EX-1 multilayer flake composite was tested with a vibrating sample magnetometer (obtained under the trade designation VSM; Model 7307 from Lake Shore Cryotronics, Westerville, Ohio). The coercivity of the EX-1 composite was found to be about 1.6 Oersted (Oe). The volume ratio between flakes and the composite was about 34%, and thickness of the sample was 0.53 millimeter.

[0077] The Permeability Spectrum Measurement Test Method was used to measure the permeability spectrum of the EX-1 composite. At 1 MHz, the real part of the permeability () was measured to be 96 and decreased slightly to 90 at 20 MHz, while the imaginary part of the permeability () remained less than 12 at 20 MHz (see FIG. 3). The magnetic loss tangent is defined as the ratio between the imaginary part and the real part of permeability. For EX-1, the loss tangent remained lower than 0.14 up to 20 MHz.

[0078] The Core Loss Measurement Test Method was used to measure the core loss of the composite EX-1. At 20 MHz, the EX-1 composite had a core loss density of 8400 kilowatt per meter cubed (kW/m.sup.3) with a maximum magnetic induction of 10 millitesla (mT) and a core loss density of 20500 kW/m.sup.3 with maximum magnetic induction of 15 mT.

Example 2

(EX-2)

[0079] FFDM particles (prepared as described in EX-1) were sieved to down select a lateral size larger than 120 micrometers. Three grams of the selected particles were mixed with 0.5 gram of high temperature epoxy (obtained under the trade designation DURALCO 4460 (316 C. (600 F.) low viscosity epoxy) from Cotronics, Brooklyn, N.Y.) in a mixing jar (FLACTEK 501 222PT-J MAX 60). After mixing with a spatula, the slurry was placed between two conventional polyethylene terephthalate (PET) sheets coated with a silicone release layer. A rubber roller was used to spread the slurry between the two PET sheets. The coated film was cured at 120 C. (250 F.) for 80 minutes. The composite sheet was then peeled off the substrate backing. The thickness of the composite sheet was about 0.5 mm.

[0080] Subsequently, the composite sheet was cut and 2 pieces were stacked on top of one another for pressing. The heated press (Model 20-122TM2WCB) was used to densify the composite at 4 tons on a 4-inch (10-cm) diameter ram at 120 C. for 1 hour, and then immediately cooled to room temperature under the same pressure for 3 minutes. A set of steel shims were used during pressing for setting composite thickness. The final sample thickness was 0.98 mm.

[0081] The static magnetic property of the EX-2 multilayer flake composite was tested with a vibrating sample magnetometer (VSM; Model 7307). The coercivity of the EX-2 composite was found to be about 1.4 Oersted (Oe). The volume ratio between flakes and the composite was about 32%.

[0082] The Permeability Spectrum Measurement Test Method was used to measure the permeability spectrum of the EX-2 composite. At 1 MHz, the real part of the permeability () was measured to be 81 and decreased slightly to 79 at 20 MHz, while the imaginary part of the permeability () remained less than 8 at 20 MHz (see FIG. 4). In this sample, the loss tangent remained lower than 0.1 up to 20 MHz.

[0083] The Core Loss Measurement Test Method was used to measure the core loss of the EX-2 composite. At 20 MHz, the EX-2 composite had a core loss density of 7400 kW/m3 with a maximum magnetic induction of 10 mT and a core loss density of 18900 kW/m3 with a maximum magnetic induction of 15 mT.

[0084] Foreseeable modifications and alterations of this disclosure will be apparent to those skilled in the art without departing from the scope and spirit of this invention. This invention should not be restricted to the embodiments that are set forth in this application for illustrative purposes.