The present invention generally relates to magnetic flux concentrators and methods of manufacturing magnetic flux concentrators.
Magnetic flux concentrators, sometimes referred to as flux guides, flux focusers, flux intensifiers, flux diverters, flux controllers, flux reflectors and other names, are generally known and have been used in inductive heating and inductive power transfer applications. Flux concentrators intensify the magnetic field in certain areas and can assist in increasing efficiency in power or heat transfer. Without a concentrator, the magnetic field is more likely to spread around and intersect with any electrically conductive surroundings. In some circumstances, a magnetic flux shield can be a type of magnetic flux concentrator.
Soft magnetic materials, that is materials that are magnetized when an external magnetic field is applied, are sometimes used in manufacturing flux concentrators. Soft magnetic materials have magnetic domains that are randomly arranged. The magnetic domains can be temporarily arranged by applying an external magnetic field.
One of the most common soft magnetic materials used in manufacturing flux concentrators is ferrite. Ferrite flux concentrators are dense structures typically made by mixing iron oxide with oxides or carbonates of one or more metals such as nickel, zinc, or manganese. The variety of “ferrites” is extremely diverse, because of the numerous combinations of metal oxides, including some that contain no iron. Typically, they are pressed, then sintered in a kiln at high temperature and machined to suit the coil geometry. Ferrites generally have very high magnetic permeability (typically over μr=2000) and low saturation flux density (typically between 3000 to 4000 Gauss). The main drawbacks of ferrite flux concentrators are that they are often brittle and tend to warp when manufactured in thin cross sections. Ferrites also typically have a low saturation flux density and therefore become saturated easily and thus are no longer significantly more permeable to magnetic fields than air in the presence of other magnetic fields, which may be undesirable in some applications. Ferrite flux concentrators are sometimes made thicker to compensate for the brittleness and poor saturation flux density. Ferrite flux concentrators may be machined thinner, though the hardness can make it difficult. However, machining thin components will not resolve the saturation issues or volume manufacturability. Further, machining components can make mass production expensive and difficult.
Another soft magnetic material sometimes used in manufacturing flux concentrators is magnetodielectric materials (MDM). These materials are made from soft magnetic material and dielectric material, which serves as a binder and electric insulator of the particles. MDM flux concentrators come in two forms: formable and solid. Formable MDM is putty-like and is intended to be molded to fit the geometry of the coil. Solid MDM is produced by pressing a metal powder and a binder with subsequent thermal treatment. The characteristics of an MDM flux concentrator vary based on, among other things, binder percentage. Typically, the less binder the higher the permeability. However, in conventional arrangements, less binder translates to more metal on metal contact, and therefore more eddy currents forming during use of the flux concentrator. Although MDM flux concentrators may be manufactured with a thin profile, it is difficult to manufacture an MDM flux concentrator with all of the desired magnetic and thermal characteristics due to the competing effects of varying the binder percentage.
Consumer electronics, such as cell phones, mp3 players, and PDA's, are trending toward slimmer profiles. Simultaneously, there is increasing demand for portable devices to be capable of receiving wireless power. Current flux concentrators suitable for use with wireless charging systems are generally too thick and therefore can noticeably increase the profile of consumer devices. Accordingly, there is a desire for a method of manufacturing a thin flux concentrator that has the desired magnetic and thermal characteristics suitable for use with a wireless power transfer system.
The present invention provides flux concentrator and a method for manufacturing a flux concentrator. In one embodiment, the method includes the following steps: 1) combining a powdered soft magnetic material, a binder, a solvent, and one or more lubricants; 2) mixing at least the powdered soft magnetic material, the binder, and the solvent for a sufficient time to dissolve the binder in the solvent to create a mixture; 3) evaporating the solvent from the mixture; 4) molding the mixture to form a flux concentrator; and 5) curing the flux concentrator. Utilizing the appropriate types and amounts of materials the resultant magnetic flux concentrator can be manufactured with magnetic and thermal characteristics suitable for use with a wireless power transfer system. In addition, the resultant magnetic flux concentrator can be reliably manufactured with dimensions appropriate for a wireless power transfer system. For example, in one embodiment a magnetic flux concentrator can be manufactured with a saturation induction greater than or equal to about 500 mT and have a minimum width to thickness dimension ratio or a minimum height to thickness dimension ratio of about 25 to 1. These results are achievable, at least in part, due to particle or agglomeration sizes being kept within a particular range. In some embodiments, prior to molding, the mixture may be sieved to control the size of the particles or agglomerations to be molded. In one embodiment the powdered soft magnetic material is agglomerated and sieved to between about 75 and 430 microns. In an alternative embodiment, the powdered soft magnetic material particle size is naturally between about 75 and 430 microns, so no agglomerations need be formed and no sieving is necessary.
The method of manufacturing a flux concentrator may include adding an external lubricant and an internal lubricant. In embodiments including both external and internal lubricant, the external lubricant tends to bloom to the outside surface of the agglomerated mixture and lubricate the flow of the mixture as it fills the mold. The external lubricant may also help during the compression of the mixture. The internal lubricant tends to lubricate the individual soft magnetic particles, which reduces particle-to-particle contact as pressure is applied during the molding process, resulting in fewer eddy currents forming during use of the flux concentrator. The manufacturing process may be used to cost effectively mass produce flux concentrators that contain small amounts of binder and exhibit suitable magnetic and thermal characteristics. Further, a thin flux concentrator profile is readily achievable with this method. In alternative embodiments, a single lubricant may be utilized.
In one embodiment, the raw materials of the flux concentrator includes a range of 0.001-2.0 percentage of external lubricant by weight, a range of 0.005-3.0 percentage of internal lubricant by weight, a range of 0.5-3.0 percentage of binder by weight, and a balance of soft magnetic material. In embodiments where a solvent is used, the amount of solvent depends on the binder and the solvent selected. In the current embodiment, between 10-20 times as much solvent as binder is used. In one embodiment, during manufacture, a plurality of agglomerations made up lubricants, soft magnetic particles, and binder particles may be created. In embodiments where solvent is added, substantially all of the solvent can be evaporated during manufacture. The method of manufacture produces a mixture with agglomerations 700 microns and below. The mixture may be sieved to a narrower particle size range to help with uniformity of the material during the compaction process. In the current embodiment, the act of sieving separates the size of the agglomerations to between about 75 and 430 microns. In one embodiment, the flux concentrator has the following magnetic, thermal, and physical characteristics: permeability greater than 15 times the permeability of free space, saturation greater than 30 mT, conductivity less than 1 S/m, and thickness less than 1 mm. Such a flux concentrator may be manufactured using an embodiment of a method for manufacturing a flux concentrator of the present invention. In alternative embodiments, the flux concentrator may be manufactured to achieve different magnetic, thermal, and physical characteristics, depending on the application.
The flux concentrator may be laminated and broken into multiple pieces, which make the flux concentrator more flexible. Breaking the flux concentrator does not significantly affect the magnetic properties. Since the permeability of the binder is very similar to that of air, adding tiny air gaps between the fractions is not significantly different than adding more binder.
These and other features of the invention will be more fully understood and appreciated by reference to the description of the embodiments and the drawings.
A flowchart for a method for manufacturing a flux concentrator in accordance with an embodiment of the present invention is illustrated in
The flux concentrator may be manufactured using essentially any soft magnetic material. In the current embodiment, iron powder is used because it has desirable magnetic characteristics in a frequency range used in connection with inductive power transfer systems. Two examples of suitable iron powder are Ancorsteel 1000C and carbonyl iron powder. Ancorsteel 1000C, and carbonyl iron powder both have relatively high permeability, relatively high saturation, and relatively low magnetic losses in the frequency range of 50 kHz to 500 kHz when insulated or used with a binder. Ancorsteel 1000C is available from Hoeganaes Corporation and carbonyl iron powder is available from BASF Corporation. The particle size of the soft magnetic material may vary depending on the application. In embodiments that utilize carbonyl iron powder, the carbonyl iron powder particles typically range from 0.5 to 500 microns. In embodiments that utilize Ancorsteel 1000C, the Ancorsteel 1000C particles typically range from 75 and 430 microns. Other types of iron powder or combinations of different types of iron powder may be used in different embodiments for cost reasons or to achieve certain desired properties of the flux concentrator.
In alternative embodiments, other soft magnetic materials may be used, such as soft magnetic alloys, insulated metal particles, or powdered ferrites. Specific examples of soft magnetic alloys that may be used include Moly Permalloy Powder, Permalloy, and Sendust. Use of soft magnetic alloys may enable use of a higher binder percentage without degrading the performance of the flux concentrator. An example of an insulated metal is phosphate coated iron. The insulation may reduce eddy currents and corrosion. It may be appropriate to modify the curing process to avoid inadvertently eliminating the insulation, which may be vulnerable to temperatures used during curing.
The particle distribution may be customized based on the particular application. In the current embodiment, a single type of soft magnetic material and binder is utilized, but in alternative embodiments, bimodal or other customized particle distributions may be utilized. For example, a combination of ferrite powder and carbonyl iron powder may be used to manufacture a flux concentrator with desired characteristics for a specific application. In alternative embodiments, blends of other powdered materials may be suitable, for example a combination of high permeability, soft magnetic powders.
The flux concentrator may be manufactured using essentially any binder capable of binding together the soft magnetic material to form a flux concentrator. A binder is a material used to bind together materials in a mixture. Examples of binders suitable for use in the present invention include thermoset polymers, thermoplastic polymers, silicone polymers, inorganic materials such as alumina, silica, or silicates, or any other binder capable of binding together the soft magnetic material to form a flux concentrator. Examples of thermoset polymers include epoxide (sometimes referred to as epoxy), Bakelite, and Formica. Epoxy is the binder used in the current embodiment. Epoxy is formed from reaction of an epoxide resin with a polyamine. The current embodiment uses a latent cure epoxy. It is a solid at room temperature, when the two monomers are combined, but do not cure to a crosslinked resin until heated. The resin and catalyst may be pre-combined or combined at the same time with the other materials before mixing, as in the current embodiment.
A solvent may be utilized as a carrier to disperse the binder within the soft magnetic powder. In the current embodiment, acetone is used as a solvent in order to dissolve the epoxy binder. In alternative embodiments, a different solvent may be utilized to disperse the binder. In the current embodiment, once the binder is dissolved in the solvent and mixed in the process, the solvent is evaporated.
Mixing a small percentage of binder with the powdered soft magnetic material can cause agglomerations to form in the mixture. Fine powders do not flow well and when poured into a mold cavity the fine particles tend to trap air. Relative to fine powders agglomerates can have better fill and flow characteristics. Depending on the makeup of the mixture, the size of agglomerations may be within a desired range, for example between from 75 and 430 microns. Depending on the makeup of the mixture, it can be beneficial to sieve the mixture to remove the smaller agglomerates and/or smaller particles and further improve fill and flow characteristics. For example, sieving may be utilized to achieve agglomeration sizes between 75 and 430 microns. In addition, certain agglomerates can provide certain magnetic, thermal, and mechanical properties to the resultant flux concentrator.
In embodiments that utilize external lubricants, the external lubricant can provide lubrication between the agglomerated particles, which allows the mixture to flow more quickly and fill the mold cavity with more uniformity. The external lubricant blooms to the outside surface of the agglomerations as the solvent evaporates and provides lubrication, thereby increasing the flow of the mixture and converting it into a free flowing powder.
The external lubricant can be selected to have limited compatibility with some or all of the soft magnetic material, binder, and solvent. In one embodiment, the external lubricant may be combined with the soft magnetic material, binder, and solvent before or during mixing. In alternative embodiments, the external lubricant may be added after mixing, but before the molding step. Polydimethylsiloxane may be used as an external lubricant and can be combined with the other materials before the mixing step. In alternative embodiments, a different external lubricant may be utilized, for example mineral oils or vegetable oils.
In embodiments that utilize internal lubricants the internal lubricant can reduce soft magnetic particle-to-particle conductivity in the finished flux concentrator and provide lubrication between the metal or ferrite particles during the molding operation. That is, the internal lubricant can reduce the eddy currents that form in the flux concentrator. Examples of suitable internal lubricants include metal soaps such as zinc stearate, and powdered waxes. The internal lubricant does not bloom to the outside of the agglomerations. Instead, the internal lubricant penetrates the agglomeration and gets in-between the soft magnetic powder particles, which decrease the opportunities for the particles to collide, which could result in additional electrical losses.
The lubricants used during the manufacturing process, both the internal and external, may enable less binder to be utilized while providing similar or improved magnetic and thermal characteristics.
The materials may be mixed in a conventional mixer and essentially any mixing technique may be utilized that mixes thoroughly enough and for a sufficient time to dissolve the binder in the solvent. Materials may be added in different orders and at different time throughout the mixing process.
A variety of evaporation techniques may be used in order to evaporate the solvent. In the current embodiment, the mixer includes a jacket where hot water or steam may be passed to heat the material in the mixer. The mixer of the current embodiment also includes a pump to obtain a vacuum within the mixer. As the solvent evaporates, the mixture dries into a powder, where there may be agglomerations of binder particles and soft magnetic material particles.
The powder may be directly poured into a cavity for molding or sieved to control the particle and/or agglomerate size. In one embodiment, powder is processed until a sufficient amount of solvent is evaporated such that the powder is dry and may be sieved. In an alternative embodiment, the sieving step is skipped and a less refined powder may be poured into the mold.
A flowchart of another embodiment of a method for manufacturing a flux concentrator is illustrated in
The mixture may be sieved to remove particles or agglomerates that are larger than a threshold, smaller than a threshold, or both. Narrow particle distributions will typically fill the mold more consistently and reliably. In one embodiment, the powder particles and agglomerates that are below a designated threshold are removed. Removal of fine particles leads to a better increased uniformity in filling the mold. Air can be trapped more easily by the smaller particles, so removing them from the mixture can be beneficial to the mold filling operation.
In one embodiment, if needed, large particles and agglomerates are removed with a 40 mesh US Standard Sieve (430 microns) and fine particles are removed with a 200 mesh US Standard Sieve (75 microns). Large agglomerates may be ground or crushed and added to the mixture and the smaller particles can be recycled back into future batches. In alternative embodiments, different size meshes or other sieving devices may be used to achieve different size particles in the mixture.
A variety of different techniques may be used to mold the mixture to form the flux concentrator. In the current embodiment, the mixture is compression molded. An exemplary press 300 for compression molding is illustrated in
During the compression, pressure is applied to the agglomerations and the soft magnetic material particles within the agglomerations. In embodiments that utilize an internal lubricant, the internal lubricant helps the individual particles of soft magnetic material move as they are compressed. This can help produce parts of increased density and compressibility, decreased deformation and induced stress in the finished parts. The resultant flux concentrator can provide better performance characteristics than those produced using prior art techniques.
Although the current method is implemented using compression molding, alternatives to compression molding may be used. For example, extrusion techniques (such as ram extrusion), impact molding, or Ragan Technologies Inc. High-shear compaction are all examples of techniques that may be used instead of compression molding.
Once the compression molding is complete, the flux concentrator may be ejected from the mold. The flux concentrator may be cured or have other post treatment processes applied, before or after ejection. A number of post treatments may be appropriate to finalize the flux concentrator. In the current embodiment, temperature of about 350 degrees Fahrenheit is applied to the flux concentrator in order to cure the binder. In alternative embodiments, the part may be partially cured through a heated mold and then receive a final cure after ejection from the mold. There may be other post treatments, such as heat activation, low temperature curing, drying, moisture curing, UV curing, radiation curing, or resin impregnation. Resin impregnation is a process where the flux concentrator is dipped or coated with a binder resin dissolved in a solvent, if appropriate. The porous parts of the flux concentrator are they filled with the binder resin. The solvent is evaporated, leaving the resin to give additional strength to the flux concentrator. Depending on the binder resin, a heat process may be used to cure the binder. Resin impregnation may be useful to increase the strength of the flux concentrator or reduce the amount of metal corrosion that occurs over time.
As shown in
In the current embodiment, the embedded coil is a two layer stamped coil. A stamped coil is a coil that is sheared from a sheet of metal. A multi-layer stamped coil may be created by layering multiple stamped coils together with a dielectric in-between Vias or another type of connection can be utilized to connect the layers together. Although the stamped coil is two layers in the illustrated embodiment, in alternative embodiments the stamped coil may include additional or fewer layers. In alternative embodiments, the embedded coil may be a wire wound coil instead of a stamped coil and the coil may be a single layer or more than two layers.
As shown in
Terminals 1806 may be stamped to conform to the edges of the flux concentrator. Connection to other circuit components may be touch-contact or soldered. The terminals might be straight to allow for Molex connectors. Also, straight terminal would facilitate direct soldering to a PCBA. Hole 1808, molded around/under the stamped copper facilitates the punching out of the traces. Punch-out location 1810 in copper stamping. After molding, this area is punched-out to break the circuit between the two traces.
The stamped copper traces embedded in compression molded flux concentrator can enhance the strength of the part, reduces overall assembly stack height because the trace required for the center wire is embedded in the magnetic flux concentrator, and enhance electrical connection of coil-flux concentrator assembly by allowing various termination types.
As shown in
The permanent magnet or magnetic attractor may be configured so that it is exposed on the surface intended for magnetic attraction. Alternatively, the permanent magnet or magnetic attractor may be buried below the surface, but still capable of providing sufficient magnetic attraction for alignment of a remote device in a wireless power transfer system.
The permanent magnet or magnetic attractor may extend through the entire flux concentrator as illustrated in
As shown in
As shown in
As shown in
The laminated flux concentrator may be separated or broken into multiple pieces in order to form air gaps between different pieces of concentrator. The air gaps created by separating the flux concentrator into multiple pieces in conjunction with the lamination allows the flux concentrator to become more flexible. In addition, the additional air gaps in the flux concentrator do not significantly affect the properties of the flux concentrator. For example, in some embodiments there are already air gaps in the flux concentrator due to the polymeric materials included during its construction. Breaking the flux concentrator described above will generally increase the amount of air gaps, but not in a manner that significantly affects the properties of the flux concentrator relative to breaking up a prior art ferrite shield.
The flux concentrator may be broken or separated into uniform or non-uniform pieces. In some embodiments, the flux concentrator is separated into generally uniform sized portions, such as the generally uniformly sized squares shown in the flux concentrator 800 of
There are a number of different techniques for breaking or separating the flux concentrator. Some of the possible techniques include 1) laminating and punching; 2) laminating and rolling; 3) scoring, laminating, and breaking; and 4) molding, laminating, and breaking.
Laminating and punching includes laminating the flux concentrator and then applying force onto a patterned die 1000 to punch the laminated flux concentrator 900 and break it into multiple pieces corresponding to the patterned die. Utilizing this technique, the flexible flux concentrator of
Laminating and rolling includes laminating the flux concentrator and running the flux concentrator 11000 through a roller system 1102 to break the flux concentrator into multiple pieces. As shown in
A method of scoring, laminating, and breaking is illustrated in
The flux concentrator may be molded with a pattern in order to facilitate breaking it into multiple pieces. A representative drawing of this technique is illustrated in
In some embodiments, the breaks may be designed to allow the flux concentrator to be shaped in a particular manner. For example, in some embodiments, the chunks of flux concentrator may be sufficiently small that the flux concentrator can be flexed about a curved surface. In other embodiments, the flux concentrator may include different size or shaped pieces. For example, as shown in
The above configurations may help enhance the desired magnetic, thermal, or mechanical properties of the magnetic flux concentrator. One or more of the configurations may be used in combination with the flux concentrator.
The wireless power module provides a simple package for manufacturers to integrate wireless power into a product. The wireless power module includes all of the components and circuitry necessary to either transmit or receive wireless power.
In the current embodiment, the wireless power semiconductor and support components 2104 includes a rectifier and microcontroller. The rectifier converts the AC power received from the coil into DC. The microcontroller can perform a variety of different functions. For example, the microcontroller may be capable of communicating with an inductive power supply, or regulating the amount of power provided by the wireless power module.
The configuration loops 2109 may be utilized to manually change the characteristics of the coil in the wireless power module. In one configuration, each configuration loop includes a high conductive path, and by breaking the loop, additional resistance may be added to the circuit. This technique is discussed in more detail in application No. 61/322,056 entitled Product Monitoring Devices, Systems, and Methods application.
The alignment element 2110 in the current configuration is a magnet. In alternative embodiments, a different alignment element may be used or eliminated altogether. The magnet cooperates with a magnet associated with the primary coil in order to line up the coils and provide efficient power transfer.
The wireless power module 2100 can be manufactured by placing any components to be embedded in the flux concentrator in a mold cavity and compression molding the flux concentrator so as to embed those components. In the embodiment shown in
A multi-layer coil array assembly 2012 for embedding in a flux concentrator can be created by positioning coils 2014 in a desired pattern and securing them in place. PCB or other non-conductive material 2016 may be utilized to protect the flux concentrator from covering the mixture during molding. During manufacture, the entire multi-layer coil array assembly 2012 can be placed in the mold cavity, soft magnetic powder mixture can be poured on the multi-layer coil array and be compression molded in order to embed the entire array in the flux concentrator. When the flux concentrator is ejected from the mold, some of the coils in the multi-layer coil array are exposed, and flush with a flux concentrator surface, other coils are embedded deeper in the flux concentrator and are not flush with the flux concentrator surface. However, a substantial portion of the coils that are embedded deeper in the flux concentrator are covered either by a coil that is flush with the flux concentrator surface or by the PCB or other non-conductive material 2016 that is part of the multi-layer coil array assembly. In some embodiments, such as the one shown in
Although the coil arrays of
In embodiments including a multi-layer coil array, the coils and leads from the multi-layer coil array can be aligned and routed utilizing one of the multi-layer shim assemblies described in U.S. Provisional Patent Appl. No. 61/376,909, entitled Wireless Power Supply System and Multi-layer Shim Assembly, filed on Aug. 25, 2010, which is herein incorporated by reference.
The above description is that of current embodiments of the invention. Various alterations and changes can be made without departing from the spirit and broader aspects of the invention as defined in the appended claims, which are to be interpreted in accordance with the principles of patent law including the doctrine of equivalents. Any reference to claim elements in the singular, for example, using the articles “a,” “an,” “the” or “said,” is not to be construed as limiting the element to the singular.
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Number | Date | Country | |
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20110050382 A1 | Mar 2011 | US |
Number | Date | Country | |
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61236732 | Aug 2009 | US | |
61267187 | Dec 2009 | US |