Patent Publication Number: US-11024449-B2

Title: Multipole elastomeric magnet with magnetic-field shunt

Description:
This application claims the benefit of provisional patent application No. 62/515,904, filed Jun. 6, 2017, which is hereby incorporated by reference herein in its entirety. 
    
    
     FIELD 
     This relates generally to magnets, and, more particularly, to magnets formed from magnetic particles in polymers such as molded elastomers. 
     BACKGROUND 
     Magnets may be used as closures in bags, as clasps in watch bands, and in other items where it is desirable to hold structures together. If care is not taken, magnetic structures may be overly rigid, may not provide desired performance during engagement and disengagement, may not be integrable into desired products, or may be bulky and weak. 
     SUMMARY 
     A multipole permanent magnet may be provided with a magnetic-field shunt. The multipole magnet and magnetic-field shunt may be used in forming clasps for wrist bands and closures for electronic devices, cases, enclosures, and other items. 
     The multipole permanent magnet may be formed from compression-molded elastomeric polymer with magnetic particles such as magnetically anisotropic rare-earth particle. A magnetic field may be applied to the magnet during molding to align the rare-earth particles. A matrix of electromagnets may be used to magnetize the magnet and thereby create a desired pattern of poles. 
     The magnetic-field shunt may be formed from magnetic members in a polymer binder or from magnetic particles in a polymer binder. The magnetic particles in the polymer binder may be ferrite particles or other magnetic particles. The polymer binder may be formed from an elastomeric material and may be integral with the elastomeric polymer of the multipole permanent magnet or separated from the elastomeric polymer of the multipole permanent magnet by a polymer separator layer. 
     Conductive particles may be formed in polymer such as the elastomeric polymer with the magnetic particles. The conductive particles may be configured to form electrical connector contacts and other signal paths. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an illustrative magnetic system having a pair of magnets in accordance with an embodiment. 
         FIG. 2  is side view of an illustrative device with upper and lower housing portions that rotate about a hinge and that are coupled by magnets in accordance with an embodiment. 
         FIG. 3  is a cross-sectional view of an illustrative electronic device and associated cover with magnets in accordance with an embodiment. 
         FIG. 4  is a side view of an illustrative watch having a watch band with magnets in accordance with an embodiment. 
         FIG. 5  is a cross-sectional side view of an enclosure having a hinge and having magnets in accordance with an embodiment. 
         FIG. 6  is a top view of an illustrative electronic device having an electrical connector with magnets and a corresponding cable having a mating electrical connector with magnets in accordance with an embodiment. 
         FIG. 7  is a cross-sectional side view of an illustrative magnet being formed by molding polymer material and magnetic particles, applying a magnetic field to orient the magnetic particles, and applying a pattern of magnetic fields to create a desired pattern of poles in the magnet in accordance with an embodiment. 
         FIG. 8  is a cross-sectional side view of an illustrative multipole magnet in accordance with an embodiment. 
         FIG. 9  is a top view of a portion of a structure such as a watch band having a multipole magnetic in accordance with an embodiment. 
         FIG. 10  is a cross-sectional side view of an illustrative magnet with an integral magnetic-field shunt in accordance with an embodiment. 
         FIG. 11  is a cross-sectional side view of an illustrative magnet with an internal separation layer separating a layer of permanent magnetic elements from a magnetic-field shunt layer in accordance with an embodiment. 
         FIG. 12  is a cross-sectional side view of an illustrative magnet with a layer of permanent magnet elements and a magnetic-field shunt layer in accordance with an embodiment. 
         FIG. 13  is a cross-sectional side view of an illustrative magnet with a layer of permanent magnet elements and a magnetic-field shunt layer formed from discrete members of magnetic material in accordance with an embodiment. 
         FIG. 14  is a cross-sectional side view of an illustrative connector having molded magnets and conductive regions forming signal paths in accordance with an embodiment. 
         FIG. 15  is a top view of an illustrative elastomeric layer having integral conductive regions in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Magnets may be used in forming magnetic systems such as clasps for watchbands, may be used in forming closures for bags, cases, and other enclosures, and may be incorporated into other items in which magnetic attraction and/or repulsion between structures is desired. An illustrative magnetic system is shown in  FIG. 1 . As shown in  FIG. 1 , magnetic system  14  may include magnets  10 . Each magnet  10  may have one or more permanent magnetic elements  12  (sometimes referred to as magnetic domains). The poles of elements  12  in magnets  10  may be arranged so that magnets  10  attract each other in directions  15 . When desired, a user may separate magnets  10  by pulling magnets  10  apart. 
     In each magnet  10 , elements  12  may be arranged so that the poles of different elements have potentially different orientations. For example, in a magnet with four elements  12 , one element  12  may have its north pole pointing upwards (in the +Z direction of  FIG. 1 ) and three elements  12  may have their north poles pointing downwards (e.g., in the −Z direction). The opposing magnet in a pair of magnets in a closure or clasp may have a corresponding set of magnet elements arranged in a complementary pattern so that magnets  16  are attracted to each other. Systems of the type shown in  FIG. 1  in which magnets  10  each have multiple elements with potentially different pole arrangements (e.g., multiple different poles pointing in different respective directions) may sometimes be referred to as multipole magnet systems. Elements  12  of a multipole magnet such as magnet  10  can maintain their magnetization permanently and are therefore sometimes referred to as permanent magnetic elements. If desired, one of the magnets in a pair of multipole magnets  10  in system  14  may be replaced by a magnetic structure formed from a magnetic material (e.g., a bar of unmagnetized iron). In this type of arrangement, the magnetic material will be attracted to the permanent magnetic elements in the magnet. Arrangements in which system  14  is formed from a pair of multipole permanent magnets each having multiple permanent magnetic elements  12  are sometimes described herein as examples. 
     Magnetic system  14  may be incorporated into wearable items such as wristwatches, health bands, clothes, accessories such as earbuds, power cords, enclosures, electronic devices such as laptop computers, and/or other electronic equipment. An illustrative configuration in which magnets  10  of system  14  have been incorporated into a foldable portable electronic device is shown in  FIG. 2 . In this type of arrangement, item  16  may be an electronic device such as a laptop computer or other foldable device. As shown in  FIG. 2 , item  16  has a lower housing  18  (e.g., a housing with a keyboard, track pad, and/or portion of a display) and an upper housing  20  (e.g., a housing with a display, etc.). Magnets  10  may be mounted in housing portions  18  and  20  so that magnets  10  mate with each other when housing portion  20  is rotated into a closed position relative to housing portion  18  using hinge  22 . 
     In the example of  FIG. 3 , item  16  is a cover (case) for a tablet computer or other portable device such as device  24 . Item  16  may have a lower portion such as portion  28  and an upper portion  26  that are coupled by a flexible portion of item  16  (e.g., a flexible fabric, a flexible polymer structure, a metal hinge, etc.). Magnets  10  may be incorporated into portion  26  of cover  16  and a mating portion of device  24  and/or magnets  10  may be mounted on mating regions in portions  26  and  28 . 
       FIG. 4  shows how item  16  may be a wrist band such as a watch band for a watch. Item  16  may have a main watch unit such as unit  30  that is formed from metal, glass, etc. and that has a display, controller, battery, and other circuitry. Magnets  10  of  FIG. 4  may be located on item  16  so that magnets  10  mate with each other when wrist band  16  is placed around the wrist of a user. Wrist band (strap)  16  may be formed from materials such as fabric, polymer, leather, metal, and other materials. Magnets  10  may be attached to one or more layers of these materials, may be embedded within the layer(s) of materials forming band  16 , etc. 
       FIG. 5  shows how item  16  may be an enclosure (e.g., a bag, case, cover, etc.) in which enclosure walls  34  can be rotated relative to each other about hinge  32  or a flexible portion of enclosure walls  32 . Magnets  10  may form a closure for item  16 . 
       FIG. 6  shows how item  16  may include a connector system. For example, item  16 A may be an electrical connector at the end of cable  36 . Item  16 B may be a corresponding electrical connector in electronic device  38 . Magnets  10  may be incorporated into items  16 A and  16 B so that item  16 A mates with item  16 B and is held in place on item  16 B magnetically after item  16 A is moved in direction  40  to engage with item  16 B. Item  16 A may include signal paths for forming contacts and carrying data signals and/or power signals. 
     Magnets  10  may be formed by molding. For example, magnets  10  may be formed by compression molding magnetic particles such as neodymium particles or other rare earth magnetic particles in a polymer. The polymer may be, for example, an elastomeric polymer such as silicone or urethane. Illustrative configurations in which silicone is used in forming magnets  10  may sometimes be described herein as examples. In general, any suitable polymers (e.g., flexible polymers, polymers formed from a mixture of one or more polymeric substances, etc.) may be used in forming magnets  10 . 
     An illustrative compression molding tool for forming magnets  10  is shown in  FIG. 7 . Magnet  10  may be compression molded in mold  44  of molding tool  42  under heat and pressure. As shown in  FIG. 7 , magnet  10  may be formed from magnetic particles  54  (e.g., neodymium particles or other rare earth magnetic particles) embedded in a polymer such as elastomeric polymer  52 . During molding, elastomeric polymer  52  may be cured (e.g., from an initial uncured liquid state to a final cured solid state). Magnetic fields may be applied by electromagnets  46  and  48  while polymer  52  has a sufficiently low viscosity to allow particles  54  to be reoriented. 
     Particles  54  preferably are magnetically anisotropic, so the poles of particles  54  become aligned along a common dimension when electromagnets  46  and  48  apply a magnetic field to magnet  10  (e.g., a magnetic field aligned along the Z dimension). After the particles  54  are aligned, curing can be completed so that polymer  52  becomes sufficiently solid to hold particles  54  in their desired orientation. Magnets  46  and  48  (or other suitable magnets) may then be used to magnetize particles  54  to form permanent magnetic elements  12  in a desired pattern. To form a multipole magnet, a pattern of magnetizing magnetic fields may be applied to magnets  10  (e.g., using matrices of individually adjustable electromagnets in electromagnets  46  and  48 , as illustrated by individually adjustable electromagnet  50 ). 
       FIG. 8  is a cross-sectional side view of an illustrative multipole magnet following compression molding of an elastomeric polymer with embedded magnetically anisotropic rare earth particles, magnetic alignment of the particles, and magnetization using a matrix of electromagnets to form a desired pattern of permanent magnetic elements. In the example of  FIG. 8 , elements  12 A,  12 B, and  12 D have their north poles pointing upwards in direction Z and have their south poles pointing downwards in direction −Z, whereas element  12 C has its north pole pointing in the −Z direction and its south pole pointing in the Z direction. Other patterns of magnetic polarity may be used in forming magnetic elements for magnet  10 , if desired. 
     By forming multiple magnetic poles in magnet  10 , magnet  10  may exhibit desired alignment and attraction properties. Consider, as an example, item  16  of  FIG. 9 . Illustrative item  16  of  FIG. 9  may be, for example, a watch band. Magnet  10  may be formed so that rows of elements  12  have alternating polarity and so that the edges of each row have magnetic polarities that help align the two mating halves of the band. For example, odd rows R 1  and R 3  may have central portions with exposed south poles, whereas alternating even rows R 2  and R 4  may have central portions with exposed north poles. By alternating polarity in alternating rows, slippage along the length of the band may be minimized, but other patterns of magnetic elements may be used, if desired. 
     The flanking magnetic elements at the edges of each row in the example of  FIG. 9  may have a polarity that is opposite to the polarity of the elements in the center of that row. For example, the edges of row R 1  may have elements  12  with exposed north poles, whereas the central element in row R 1  have exposed south poles. The mating magnet in band  16  in this illustrative scenario has edges with elements  12  having exposed south poles and a central region with exposed north poles. This type of pattern helps avoid lateral slippage of the band halves (e.g., slippage along the lengths of the rows is minimized). In general, any suitable multipole magnetic pattern may be used in forming magnets  10  and item  16 . The configuration of  FIG. 9  is merely illustrative. 
     In some configurations, magnets  10  may have integrated magnetic-field shunts. Shunts may be formed from magnetic particles such as ferrite particles in a polymer binder (e.g., an elastomeric polymer such as silicone). Shunts that are formed from magnetic members such as ferrite members may also be used. 
     Consider, as an example, magnet  10  of  FIG. 10 . As shown in  FIG. 10 , magnet  10  may have one or more permanent magnet portions such as multipole permanent magnet layer  60 . Layer  60 , which may sometimes be referred to as a permanent magnetic layer or layer of permanent magnetic elements, may have multiple magnetic elements  12  formed by compression molding, magnetic alignment of magnetically anisotropic rare-earth particles, and magnetization of the elastomeric material with embedded rare earth magnetic particles, as described in connection with  FIGS. 7 and 8 . Magnetic  10  may also have one or more magnetic-field shunt portions such as magnetic-field shunt layer  62 . Shunt layer  62  may be formed from ferrite particles embedded in a polymer binder such as a compression molded silicone layer or other magnetic structures and may serve to shunt magnetic field B between adjacent poles of opposite polarity (e.g., magnetic field B may be shunted through layer  62  from the south pole in the leftmost element  12  of  FIG. 10  to the north pole in the rightmost element  12  of  FIG. 10  rather than being emitted out of the lower surface of magnet  10 ). The presence of shunt layer  62  may improve the performance of magnet  10  by concentrating magnetic fields. 
     Layers  60  and  62  may be formed in one or more molding operations and/or may be fabricated using other techniques (lamination, etc.). 
     As shown in the illustrative configuration of  FIG. 11 , layer  62  may be formed from magnetic particles  66  (e.g., non-rare-earth magnetic particles such as ferrite particles) embedded in polymer binder  68  (e.g., silicone or other elastomeric material). Layer  64  (e.g., a flexible polymer layer such as a layer of silicone or other elastomeric polymer that serves as a separator layer) may be placed on top of liquid polymer precursor material for polymer  68  in mold tool  42  ( FIG. 7 ). Polymer  52  with embedded magnetic particles  54  may then be introduced in tool  42  on top of layer  64 . Due to the presence of layer  64 , magnetic particles  54  will not migrate to layer  62  and magnetic particles  66  will not migrate to layer  60  during compression molding operations to form magnet  10  in tool  42 . 
     In the illustrative configuration of  FIG. 12 , layer  64  has been omitted. In this type of arrangement, magnetic particles  66  and magnetic particles  54  may be incorporated into a common material (e.g., binder  52  and binder  68  may both be silicone or other elastomeric material). In the mold cavity in tool  42 , magnetic particles  66  may settle to the bottom of magnet  10 , so that layer  60  contains primarily magnetic particles  54  and so that layer  62  contains primarily magnetic particles  66 , thereby forming layers  60  and  62  as integral sublayers in a common layer of elastomeric material for magnet  10 . 
       FIG. 13  is a cross-sectional side view of magnet  10  in an illustrative configuration in which layer  62  contains multiple individual magnetic members  66 M embedded in elastomeric polymer  68 . Magnetic members  66 M serve as shunts and thereby form a magnetic-field shunt layer. Members  66 M may be formed from ferrite bars or other pieces of magnetic material. Layer  64  may optionally be used to separate polymer  68  and shunt members  66 M from layer  60  during compression molding of layers  62 ,  64 , and  60  in tool  42 . Gaps may be formed between adjacent members  66 M to ensure that magnet  10  is flexible. 
     If desired, other arrangements may be used for forming flexible magnets  10  (e.g., by laminating a flexible multipole permanent magnet layer with a flexible shunt layer after forming these parts separately). The configurations of  FIGS. 11, 12, and 13  are illustrative. 
     In some arrangements, conductive particles are incorporated into compression molded elastomeric structures in addition to or instead of magnetic particles. Consider, as an example, illustrative electrical connector  16 A of  FIG. 14 . As shown in  FIG. 14 , connector  16 A may include conductive paths such as contacts  72 . Contacts  72  may be used to carry signals from wires in cable  36  of  FIG. 6  to mating contacts in electrical connector  16 B of device  38  when connectors  16 A and  16 B are coupled together. Contacts  72  may be formed from conductive particles  70  embedded in polymer  74 . Conductive particles  70  may be metal particles such as copper particles, nickel particles, or particles in conductive powders formed from other materials (e.g., cobalt, beryllium, titanium, tantalum, tungsten, etc.). Polymer  74  may be an elastomeric polymer such as silicone and may be the same as the material used in forming polymer binder  52  and/or  68  or may be a different polymeric material. To help attract connector  16 A to connector  16 B, connector  16 A may be provided with a multipole magnet formed from flexible permanent magnetic elements  12  having poles arranged in a complementary pattern to the arrangement of magnetic element poles in a mating multipole magnet in connector  16 B. Shunt layer  62  may optionally be included in connector adjacent to layer  60 . 
     As shown in the top view of illustrative item  16  of  FIG. 15 , conductive signal paths such as paths  76  may be formed in item  16 . Paths  76  may be formed from conductive particles  70  ( FIG. 14 ) embedded in polymer  74  ( FIG. 14 ). Other portions of item  16  of  FIG. 15  may be formed from flexible polymer such as polymer  78  (e.g., an elastomeric polymer such as silicone, etc.). Polymer  78  and the polymer of paths  76  may be formed from the same material or different materials. During molding operations (e.g., compression molding of polymer  78  and the polymer of paths  76  or other suitable molding operations), desired layouts may be implemented for paths  76  (e.g., to route power signals between electrical components in item  16 , to form data lines that carry analog and/or digital signals in item  16 , to form a ground structure, to form an electromagnetic interference shield, etc.). Item  16  of  FIG. 15  may be, as an example, a wrist band for a watch, a stand-alone wrist band device such as a health band, etc. 
     The foregoing is merely illustrative and various modifications can be made to the described embodiments. The foregoing embodiments may be implemented individually or in any combination.