Patent Publication Number: US-10790708-B2

Title: Wireless charging apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 14/812,536, filed Jul. 29, 2015, now U.S. Pat. No. 9,973,026, issued May 15, 2018, which claims the benefit under 35 U.S.C. § 119 of Korean Patent Application No. 10-2014-0096641, filed Jul. 29, 2014, all of which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     Field of the Invention 
     The present invention relates to a wireless charging apparatus. 
     Discussion of Related Art 
     Ferrous soft magnetic alloys used in magnetic cores include iron-silicon (Fe—Si) alloys, amorphous alloys, nanocrystalline alloys, and so on. Here, the Fe—Si alloys have low resistivity and are rarely applied to shield members of wireless power transceiving systems using a high-frequency band, and the amorphous alloys and the nanocrystalline alloys can be applied to the shield members of the wireless power transceiving systems, but make it difficult to reduce thicknesses of the shield members and to increase a power transmission capacity due to a low saturation magnetic flux density. Further, the ferrous soft magnetic alloys have a low glass forming ability, and thus crystalline phases such as Fe 2 B, Fe 23 B 6 , etc. are generated according to a solidification rate to increase a coercive force. The ferrous soft magnetic alloys have a high content of a metalloid, and thus are rarely processed into a flake form. 
     BRIEF SUMMARY 
     The present invention is directed to a wireless charging apparatus constituting a wireless charging system. 
     According to an aspect of the present invention, there is provided a wireless charging apparatus which includes: a soft magnetic material; and a coil disposed on the soft magnetic material. The soft magnetic material includes a soft magnetic alloy that has a chemical formula expressed as Fe 100−x−y Cu x B y  (where x ranges from 0.1 at % to 1.7 at % and y ranges from 2.3 at % to 9.6 at %) and grains with a size from 10 nm to 99 nm. 
     Here, the soft magnetic alloy may have a flake form. 
     Further, the soft magnetic alloy may be processed into the flake form through a ball milling process. 
     Also, the soft magnetic alloy may be subjected to a heat treatment process in the flake form to remove residual stress. 
     Here, the heat treatment process may be performed at a temperature of 250° C. to 450° C. Further, the flake form may have an aspect ratio of 10 or more. 
     Meanwhile, the soft magnetic alloy may have a saturation magnetic flux density of 1.7 T or more and a coercive force of 40 Oe or less. 
     Further, the grains may be formed in an amorphous matrix made by solidifying the Fe—Cu—B alloy in a molten state using a water quenching method. 
     Here, the Fe—Cu—B alloy for the grains may be heated to a temperature of 1700° C. or more for the molten state. 
     Further, the grains may each be formed in such a manner that Fe and B are bonded to Cu acting as a crystalline nucleus. 
     Also, saturation magnetization of the soft magnetic alloy may have an absolute value of at least 190 emu/g. 
     Further, the wireless charging apparatus may further include: a wireless power transmitter that includes a soft magnetic core containing the soft magnetic alloy and a transmission coil; and a wireless power receiver that includes a soft magnetic sheet containing the soft magnetic alloy and a reception coil. 
     Further, a permanent magnet may be disposed on the soft magnetic core. 
     In addition, a near field communication (NFC) antenna may be disposed is disposed on the soft magnetic sheet. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the accompanying drawings, in which: 
         FIG. 1  is a view showing a wireless charging system according to an embodiment; 
         FIG. 2  is a view showing the wireless power transmitter according to the embodiment; 
         FIG. 3  is a view showing the wireless power receiver according to the embodiment 
         FIG. 4  is a view showing a process of forming grains of the soft magnetic alloy according to the embodiment; 
         FIG. 5  is a graph showing a change in magnetization according to a strength of a magnetic field applied to the soft magnetic alloy according to the embodiment; 
         FIG. 6  is a flow chart showing a method of manufacturing the soft magnetic alloy according to the embodiment; and 
         FIGS. 7 and 8  are electron microscope photographs of the soft magnetic alloy according to the embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Exemplary embodiments of the present invention will be described in detail below with reference to the accompanying drawings. While the present invention is shown and described in connection with exemplary embodiments thereof, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention. 
     Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meanings as those generally understood by those with ordinary knowledge in the field of art to which the invention belongs. Such terms as those defined in a generally used dictionary are to be interpreted to have the meanings equal to the contextual meanings in the relevant field of art, and are not to be interpreted to have ideal or excessively formal meanings unless clearly defined in the present application. 
     It will be understood that, when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements, components, and/or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or combinations thereof. 
     Exemplary embodiments of the present invention will be described in detail below with reference to the accompanying drawings, and description of the known configuration irrelevant to the gist of the present invention will be omitted, Note that, in giving reference numerals or symbols to the components in the drawings, the same reference numerals or symbols are given to the same components even among the different drawings as far as possible. 
       FIG. 1  is a view showing a wireless charging system according to an embodiment. 
     Referring to  FIG. 1 , a wireless charging system according to an embodiment includes a power supply  100 , a wireless power transmitter  200 , a wireless power receiver  300 , and a load  400 . The wireless power transmitter  200  includes a transmission coil  210 , and the wireless power receiver  300  includes a reception coil  310  and a rectifier  330 . 
     The power supply  100  supplies the wireless power transmitter  200  with alternating current (AC) power having a predetermined frequency. The wireless power transmitter  200  wirelessly transmits the AC power to the wireless power receiver  300  using a magnetic induction or resonance system. Here, the magnetic induction system is a wireless power transmission system that uses an AC magnetic field of 110 kHz to 205 kHz as an energy transfer medium, and the magnetic resonance system is a wireless power transmission system that uses an AC magnetic field of 6.78 MHz. 
     In the magnetic induction system, when an electric current is applied to the transmission coil  210  of the wireless power transmitter  200 , the AC magnetic field is generated. Due to this AC magnetic field, a change in voltage is induced at the reception coil  310  of the wireless power receiver  300  that is magnetically coupled with the transmission coil  210 , is converted into a direct current (DC) voltage by the rectifier  330 . The DC voltage is supplied to the load  400 . Here, the load  400  may be a battery or a device in which such a battery is mounted. The wireless power receiver  300  and the load  400  may be included in a single device. 
     For example, the wireless power receiver  300  and the load  400  of the wireless charging system according to the embodiment may be included in a smart phone, a feature phone, a tablet personal computer (PC), a portable computer, a personal digital assistant (PDA), or a phablet that is a smart phone having a function of a tablet. Further, the wireless power transmitter  200  of the wireless charging system according to the embodiment may be configured in the form of a pad on which a mobile device can be placed, but the present invention is not limited thereto. The power supply  100  and the wireless power transmitter  200  may be included in a single device. 
     Meanwhile, in the magnetic resonance system, each of the transmission coil  210  of the wireless power transmitter  200  and the reception coil  310  of the wireless power receiver  300  may be made up of an induction coil and a resonance coil. Here, an impedance and an LC resonance frequency of the resonance coil of the wireless power transmitter  200  should be matched with those of the resonance coil of the wireless power receiver  300 , respectively. 
       FIG. 2  is a view showing the wireless power transmitter according to the embodiment. 
     Referring to  FIG. 2 , the wireless power transmitter  200  according to the embodiment includes the transmission coil  210  and a soft magnetic core  220 . The transmission coil  210  is disposed on the soft magnetic core  220 . Although not shown in the figure, a permanent magnet may be further disposed on the soft magnetic core  220 . This permanent magnet may be enclosed by the transmission coil  210 . 
     Especially, the soft magnetic core  220  includes a soft magnetic alloy according to an embodiment of the present invention, i.e., a soft magnetic alloy having a chemical formula expressed as Fe 100−x−y Cu x B y  (where x ranges from 0.1 at % to 1.7 at % and y ranges from 2.3 at % to 9.6 at %). The soft magnetic alloy has a saturation magnetic flux density of 1.7 T or more, a coercive force of 40 Oe or less, grains having sizes of tens of nanometers, and a flake form. 
       FIG. 3  is a view showing the wireless power receiver according to the embodiment. 
     Referring to  FIG. 3 , the wireless power receiver  300  according to the embodiment includes a reception coil  310  and a soft magnetic sheet  320 . The reception coil  310  is disposed on the soft magnetic sheet  320 . Although not shown in the figure, a near field communication (NFC) antenna for short range communication may be further disposed on the soft magnetic sheet  320 . This permanent magnet may be enclosed by the transmission coil  210 . 
     Especially, the soft magnetic sheet  320  includes a soft magnetic alloy according to an embodiment of the present invention, i.e., a soft magnetic alloy having a chemical formula expressed as Fe 100−x−y Cu x B y  (where x ranges from 0.1 at % to 1.7 at % and y ranges from 2.3 at % to 9.6 at %). The soft magnetic alloy has a saturation magnetic flux density of 1.7 T or more, a coercive force of 40 Oe or less, grains having sizes of tens of nanometers, and a flake form. 
     Tables 1 to 4 show compositions (at %), saturation magnetization (emu/g), saturation magnetic flux densities (T), coercive forces (Oe), and pass/fail (P/F) of the soft magnetic alloys according to Comparative Examples and Examples. 
     
       
         
           
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Fe 100−x−y Cu x B y   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                   
                 Saturation 
                   
                   
               
               
                   
                   
                 Saturation 
                 magnetic 
               
               
                   
                 Composition 
                 magnetization 
                 flux density 
                 Coercive force 
               
               
                   
                 (at %) 
                 (emu/g) 
                 (T) 
                 (Oe) 
                 Pass/Fail (P/F) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Comparative 
                 x = 0, y = 9.6 
                 192.4 
                 1.88 
                 43.1 
                 F 
               
               
                 Example 1 
               
               
                 Comparative 
                 x = 2.4, y = 9.6 
                 173.8 
                 1.70 
                 45.9 
                 F 
               
               
                 Example 2 
               
               
                 Comparative 
                 x = 3.3, y = 9.6 
                 168.9 
                 1.65 
                 49.0 
                 F 
               
               
                 Example 3 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 Fe 100−x−y Cu x B y   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 Saturation 
                 Saturation 
                   
                   
               
               
                   
                 Composition 
                 magnetization 
                 magnetic flux 
                 Coercive force 
               
               
                   
                 (at %) 
                 (emu/g) 
                 density (T) 
                 (Oe) 
                 Pass/Fail (P/F) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Example 1 
                 x = 0.1, y = 9.6 
                 190.4 
                 1.86 
                 37.8 
                 P 
               
               
                 Example 2 
                 x = 0.8, y = 9.6 
                 187.4 
                 1.83 
                 35.2 
                 P 
               
               
                 Example 3 
                 x = 1.2, y = 9.6 
                 183.7 
                 1.80 
                 32.3 
                 P 
               
               
                 Example 4 
                 x = 1.7, y = 9.6 
                 181.5 
                 1.77 
                 38.8 
                 P 
               
               
                   
               
            
           
         
       
     
     Referring to Tables 1 and 2, Comparative Examples 1 to 3 and Examples 1 to 4 show results of a test in which a content of boron (B) was fixed at 9.6 at % and a content of copper (Cu) was changed from 0 at % to 3.3 at %. Here, it can be found that, as the content of copper acting as a seed creating a nucleus due to a greater atomic radius than iron (Fe) is increased, the saturation magnetization of the soft magnetic alloy containing Cu and the saturation magnetic flux density proportional to the saturation magnetization are reduced. Further, the coercive force that is a magnetic characteristic representative of soft magnetism is preferably as low as possible. In detail, an alloy whose coercive force exceeds 40 Oe is unfit for use as a soft magnetic member. Therefore, in the soft magnetic alloy having the chemical formula expressed as Fe 100−x−y Cu x B y , the content of Cu is preferably limited to a range from 0.1 at % to 1.7 at %. 
     
       
         
           
               
               
             
               
                   
                 TABLE 3 
               
             
            
               
                   
                   
               
               
                   
                 Fe 100−x−y Cu x B y   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 Saturation 
                 Saturation 
                   
                   
               
               
                   
                 Composition 
                 magnetization 
                 magnetic flux 
                 Coercive 
                 Pass/Fail 
               
               
                   
                 (at %) 
                 (emu/g) 
                 density (T) 
                 force (Oe) 
                 (P/F) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Comparative 
                 x = 1.2, 
                 195.3 
                 1.91 
                 41.9 
                 F 
               
               
                 Example 4 
                 y = 1.2 
               
               
                 Comparative 
                 x = 1.2, y = 13.8 
                 177.2 
                 1.74 
                 42.3 
                 F 
               
               
                 Example 5 
               
               
                 Comparative 
                 x = 1.2, y = 18.5 
                 170.2 
                 1.67 
                 48.3 
                 F 
               
               
                 Example 6 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
             
               
                   
                 TABLE 4 
               
             
            
               
                   
                   
               
               
                   
                 Fe 100−x−y Cu x B y   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 Saturation 
                 Saturation 
                   
                   
               
               
                   
                 Composition 
                 magnetization 
                 magnetic flux 
                 Coercive force 
               
               
                   
                 (at %) 
                 (emu/g) 
                 density (T) 
                 (Oe) 
                 Pass/Fail (P/F) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Example 5 
                 x = 1.2, y = 2.3 
                 195.1 
                 1.91 
                 36.9 
                 P 
               
               
                 Example 6 
                 x = 1.2, y = 4.5 
                 190.4 
                 1.86 
                 31.0 
                 P 
               
               
                 Example 7 
                 x = 1.2, y = 9.6 
                 183.7 
                 1.80 
                 29.1 
                 P 
               
               
                   
               
            
           
         
       
     
     Referring to Tables 3 and 4, Comparative Examples 4 to 6 and Examples 5 to 7 show results of a test in which a content of Cu was fixed at 1.2 at % and a content of B was changed from 1.2 at % to 18.5 at %. Here, since B has a smaller atomic radius than Fe, it is possible to reduce a liquidus temperature of the alloy to increase a glass forming ability. However, if B is excessively added, crystalline phases such as Fe 2 B, Fe 23 B 6 , etc. are generated to be able to increase the coercive force. As the content of the non-magnetic alloying element increases, the saturation magnetic flux density is reduced. Therefore, in the soft magnetic alloy having the chemical formula expressed as Fe 100−x−y Cu x B y , the content of B is preferably limited to a range from 2.3 at % to 9.6 at %. 
     Consequently, in the soft magnetic alloy having the chemical formula expressed as Fe 100−x−y Cu x B y , when the content of Cu is preferably limited to a range from 0.1 at % to 1.7 at %, and when the content of B is preferably limited to a range from 2.3 at % to 9.6 at %, it is possible to increase the saturation magnetic flux density to 1.7 T or more while maintaining the coercive force below 40 Oe. 
       FIG. 4  is a view showing a process of forming grains of the soft magnetic alloy according to the embodiment. 
     Referring to  FIG. 4 , an existing ferrous soft magnetic alloy is generally manufactured to have a saturation magnetic flux density of about 1 T to 1.56 T by quenching a molten metal using a melt spinner to form an amorphous phase and then performing a post heat treatment to precipitate nanocrystalline phase nuclei or to grow nanocrystals. However, the soft magnetic alloy according to the embodiment of the present invention is solidified in a molten state by a water quenching method. Thereby, it is possible to obtain an amorphous matrix  500  and nanograins  520  without a post heat treatment process, and thus reduce a time and cost required to manufacture the soft magnetic alloy. 
     To be specific, in manufacturing a ternary alloy using Fe, Cu, and B without adding any expensive alloying element, the Fe—Cu—B ternary alloy is solidified in a molten state by a water quenching method, so that the matrix  500  can have an amorphous phase. In this process, Cu having a greater atomic radius than Fe can serve as a crystalline nucleus  510 , and Fe and B are bonded to Cu so that the nanograin  520  can be created. 
     Here, the nanograin  520  refers to a crystalline phase having a size of tens of nanometers, i.e. from 10 nm to 99 nm. The soft magnetic alloy according to the embodiment of the present invention can be subjected to plastic deformation because the content of a metalloid, i.e. B, is equal to or less than 10 at %, and be processed into a flake form. In this case, the flake form has an aspect ratio of 10 or more. When the soft magnetic alloy is processed in this way, there is an advantage in that permeability in a major axis direction is increased and shape magnetic anisotropy can be applied. Meanwhile, when the size of the nanograin  520  is beyond the range of tens of nanometers, that is, when the size of the nanograin  520  is merely several nanometers or reaches hundreds of nanometers, the magnetic characteristic is reduced. Especially, when the nanograin  520  grows to a micrograin  530  having a size above several micrometers, the magnetic characteristic may be greatly reduced. For this reason, it is possible to adjust a process time to prevent the nanograin  520  from growing excessively. 
       FIG. 5  is a graph showing a change in magnetization according to a strength of a magnetic field applied to the soft magnetic alloy according to the embodiment. 
     Referring to  FIG. 5 , when the strength of the magnetic field H applied to the soft magnetic alloy having the chemical formula expressed as Fe 100−x−y Cu x B y  (where x is 1.2 at % and y is 4.5 at %) is increased, a strength of magnetization M of the soft magnetic alloy is increased. However, if the strength of the magnetic field H exceeds about ±7500 Oe, the strength of magnetization M is maintained nearly constant. At this time, the strength of magnetization M is called saturation magnetization. It can be found in the graph that the saturation magnetization of the soft magnetic alloy is shown to be higher than at least ±190 emu/g. The soft magnetic alloy having high saturation magnetization in this way is appropriate for a material of the soft magnetic core of the wireless power transmitter or the soft magnetic sheet of the wireless power receiver. 
       FIG. 6  is a flow chart showing a method of manufacturing the soft magnetic alloy according to the embodiment, and  FIGS. 7 and 8  are electron microscope photographs of the soft magnetic alloy according to the embodiment. 
     Referring to  FIGS. 6 to 8 , Fe, Cu and B that are raw materials of the soft magnetic alloy according to the embodiment are heated to and melted at a temperature of, for instance, 1700° C. or more (S 110 ), and are solidified by a water quenching method (S 120 ). In this case, the soft magnetic alloy is processed into a spherical powder form using a gas atomizer (S 130 , see  FIG. 7 ), and the soft magnetic alloy of the spherical powder form is processed into a flake form, for instance, through a ball milling process (S 140 , see  FIG. 8 ). Meanwhile, to remove residual stress from the soft magnetic alloy, a process of performing a heat treatment at a temperature of 250° C. to 450° C., and preferably 350° C. may be further performed (S 150 ). 
     According to the embodiment of the present invention, without adding any expensive alloying element, only Fe, Cu, and B are used to obtain the nanocrystalline soft magnetic alloy that has the low coercive force and the high saturation magnetic flux density. The nanocrystalline soft magnetic alloy is applied to the wireless power transmitter and the wireless power receiver. Thereby, it is possible to make a shield member thin and increase a power transmission capacity. The soft magnetic alloy is easily processed into a flake form. The soft magnetic alloy processed in this way is applied to the shield member. Thereby, it is possible to increase permeability in a surface direction. 
     It will be apparent to those skilled in the art that various modifications can be made to the above-described exemplary embodiments of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention covers all such modifications provided they come within the scope of the appended claims and their equivalents.