Abstract:
The disclosure features wireless power receiver modules for computing systems. The wireless power receiver modules can include a receiver resonator that can include an inductor formed substantially in a first plane. The receiver resonator can be configured to capture oscillating magnetic flux. The modules can include a planar piece of metallic material formed in a second plane. The planar piece of metallic material can define an aperture in which the inductor of the receiver resonator is disposed. The planar piece of metallic material can define first and second breaks extending from an outer edge of the planar piece of metallic material to the aperture to form first and second portions of the planar piece of metallic material.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application incorporates herein by reference and claim priority to U.S. Provisional Patent Application No. 62/133,089 filed Mar. 13, 2015 and entitled “WIRELESS POWER TRANSFER FOR MOBILE DEVICES.” 
     
    
     FIELD 
       [0002]    The field of this invention relates to wireless power transfer. 
       BACKGROUND 
       [0003]    Energy can be transferred from a power source to receiving device using a variety of known techniques such as radiative (far-field) techniques. For example, radiative techniques using low-directionality antennas can transfer a small portion of the supplied radiated power, namely, that portion in the direction of, and overlapping with, the receiving device used for pick up. In this example, most of the energy is radiated away in all the other directions than the direction of the receiving device, and typically the transferred energy is insufficient to power or charge the receiving device. In another example of radiative techniques, directional antennas are used to confine and preferentially direct the radiated energy towards the receiving device. In this case, an uninterruptible line-of-sight and potentially complicated tracking and steering mechanisms are used. 
         [0004]    Another approach is to use non-radiative (near-field) techniques. For example, techniques known as traditional induction schemes do not (intentionally) radiate power, but uses an oscillating current passing through a primary coil, to generate an oscillating magnetic near-field that induces currents in a near-by receiving or secondary coil. Traditional induction schemes can transfer modest to large amounts of power over very short distances. In these schemes, the offset tolerance offset tolerances between the power source and the receiving device are very small. Electric transformers and proximity chargers are examples using the traditional induction schemes. 
       SUMMARY 
       [0005]    In a first aspect, the disclosure features wireless power receiver modules for computing systems. The wireless power receiver modules can include a receiver resonator that includes an inductor formed substantially in a first plane and is configured to capture oscillating magnetic flux and a planar piece of metallic material formed in a second plane. The planar piece of metallic material defines an aperture in which the inductor of the receiver resonator is disposed and the planar piece of metallic material defines first and second breaks extending from an outer edge of the planar piece of metallic material to the aperture to form first and second portions of the planar piece of metallic material. 
         [0006]    Embodiments of the modules can include any one or more of the following features. The metallic material can include copper. The planar piece of metallic material can define a third break from the outer edge to the aperture. The planar piece of metallic material can define a fourth break from the outer edge to the aperture. The wireless power receiver modules can include a layer of magnetic material disposed between a surface of the inductor and the computing system. The layer of magnetic material can extend beyond an outer perimeter of the inductor. The layer of magnetic material can extend to the outer edge of the planar piece of metallic material. The computing systems can be a laptop, notebook computer, tablet, or mobile phone. The planar piece of metallic material can form a back cover of the computing system. 
         [0007]    The aperture can be rectangular with four edges with four midpoints and the breaks in the planar piece of metallic material can be formed at the four midpoints. The breaks in the planar piece of metallic material can be formed at an angle to the aperture. The planar piece of metallic material can enhance coupling between the receiver resonator and a source resonator configured to generate an oscillating magnetic field when the receiver resonator is positioned over the source resonator. The thermal interface material can be positioned in the breaks of the planar piece of metallic material. The first plane and second plane can be coplanar. 
         [0008]    The breaks in the planar piece of metallic material can have a width equal to or greater than 0.05 mm. The first portion can confine a first eddy current and the second portion can confine a second eddy current when the module is positioned near a wireless power source. 
         [0009]    Embodiments of the modules can also include any of the other features disclosed herein, including features disclosed in connection with different embodiments, in any combination as appropriate. 
         [0010]    In another aspect, the disclosure features methods including forming a first break and a second break in a planar piece of metallic material such that the first and second breaks extend from an outer edge of the planar piece of metallic material to an aperture defined in the planar piece of metallic material. The planar piece of metallic material can be in a first plane and the first and second breaks form a first portion and a second portion of the planar piece of metallic material. The methods can include disposing an inductor of a receiver resonator in the aperture in a second plane. 
         [0011]    Embodiments of the methods can include any one or more of the following features. 
         [0012]    The methods can include forming a third break in the planar piece of metallic material such that the third break extends from the outer edge to the aperture. The methods can include forming a fourth break in the planar piece of metallic material such that the fourth break extends from the outer edge to the aperture. The first portion can confine a first eddy current and the second portion can confine a second eddy current when the module is positioned near a wireless power source. 
         [0013]    As used herein, a “break” in a metallic material means a break in the continuity of the metallic material and can be formed, for example, by placing two pieces of metallic material next to one another with a gap in between. 
         [0014]    Embodiments of the methods can also include any of the other features disclosed herein, including features disclosed in connection with different embodiments, in any combination as appropriate. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0015]      FIG. 1A  shows an diagram of an exemplary embodiment of a wireless power transfer system for a computing device.  FIG. 1B  shows an exemplary embodiment of a wirelessly powered computing device on a wireless power source. 
           [0016]      FIG. 2A  shows a model of an exemplary embodiment of a back cover of a computing device without any breaks.  FIG. 2B  shows a model of an exemplary embodiment of a back cover of a computing device with two breaks. 
           [0017]      FIG. 3  shows a model of an exemplary embodiment of a wireless power system for a computing device. 
           [0018]      FIGS. 4A-4B  show simulations of an exemplary embodiment of a source and back cover without breaks. 
           [0019]      FIGS. 5A-5B  show simulations of an exemplary embodiment of a source and back cover with breaks. 
           [0020]      FIGS. 6A-6D  show models of exemplary embodiments of back covers for a computing device. 
           [0021]      FIGS. 7A-7B  show models of exemplary embodiments of back covers for a computing device. 
           [0022]      FIGS. 8A-8C  show cross-sectional views of exemplary embodiments of wirelessly charged computing devices. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    Various aspects of wireless power transfer systems are disclosed, for example, in commonly owned U.S. Patent Application Publication No. 2012/0119569 A1, U.S. Patent Application Publication No. 2013/0200721 A1, and U.S. Patent Application Publication 2013/0033118 A1, U.S. Patent Application Publication 2013/0057364 A1, the entire contents of which are incorporated by reference herein. 
         [0024]      FIG. 1A  shows an diagram of an exemplary embodiment of a wireless power transfer system for a computing device, such as a laptop. A wireless power transfer system may transfer power to directly power a computing device or to charge a battery of the computing device. A computing device may be a laptop, notebook computer, tablet, phablet, mobile phone, smartphone, and the like. A wireless power transfer system may include a source that draws power from a power supply such as AC mains, battery, solar cell, and the like. The source may include electronics to convert power from the power supply, an amplifier, an impedance matching network, and one or more controllers that may interface with any component of the source-side system. The source also includes a source resonator that includes an inductor and a capacitance that is driven by the source electronics to generate an oscillating magnetic field by which to transfer energy to a device. In embodiments, the source resonator may be a high-Q resonator. In embodiments, the quality factor of the high-Q resonator may be greater than 100. A current may be generated in the device resonator, which also includes an inductor and a capacitance. The energy received via the device resonator can be transferred to a load. For example, the load can be the computing device itself or a battery of the computing device. The device electronics may include a matching network, rectifier, one or more controllers, and the like. In exemplary embodiments, the device resonator may be a high-Q resonator. In embodiments, the high-Q resonator may have a quality factor of greater than 100. In exemplary embodiments, the source may include multiple source resonators. In exemplary embodiments, the device may include multiple device resonators.  FIG. 1B  shows an exemplary embodiment of a wirelessly powered computing system, for example a laptop  102 , on a wireless power source  104 . The laptop may be positioned on, over, near, or next to a source  104 . In exemplary embodiments, the source may in the form of a pad on a surface, such as a table, or under a surface. The end-to-end efficiency can be greater than 30%, 50%, 70%, 75%, 80%, 90%, or 95%. In embodiments, the device can provide 1 W, 2.5 W, 5 W, 10 W, 20 W, 30 W, 50 W, or more to the load (for example, battery of a mobile phone or laptop). For example, a source may be able to transmit at least 20W of power to a laptop battery with at least 70% end-to-end efficiency. In another example, a source may be able to transmit at least 5W of power to a phone battery with at least 60% end-to-end efficiency. In embodiments, the operating frequency of wireless power transmission is 50 to 300 kHz, 6.78 MHz, or any Industrial, Scientific, Medical (ISM) band frequency. 
         [0025]    In exemplary embodiments, it may be challenging to transfer power via a magnetic field to computing devices such as laptops, tablets, and mobile phones due to the use of metallic materials in the construction. Metallic materials can include metals, such as aluminum and copper, as well as metal alloys, such as magnesium alloys, steel, aluminum alloys, and the like. For example, a computing device may have a back cover that may be most exposed to a source&#39;s magnetic field (as shown in  FIG. 1B ). The back cover, if made of metallic materials, such as a magnesium allow, may be lossy due to the eddy currents that are induced. Losses in metallic materials will result in a lower efficiency of wireless power transfer. Eddy currents will form to oppose the magnetic field of the source. Thus, for a given time interval, the current of the source resonator and eddy current will flow in opposite directions. A given time internal may be an instantaneous “snapshot” of the oscillating magnetic field.  FIG. 2A  shows the net result of eddy currents flowing in a back cover of a computing device  208 . The net resulting eddy currents  210  will flow along the outer edge  202  of the back cover  208 . The outer edge  202  extends around the entire outer perimeter of the back cover  208 . Another example of this can be seen in  FIG. 2B , where the back cover of the computing device is broken into two continuous pieces. Here, instead of flowing on the overall outer edge of the back cover, the eddy currents  220 ,  222  will flow via the lower impedance path which is along the breaks  220  and  218  of back cover. Note that for a source magnetic field  226  pointing out of the page, the eddy currents will create a magnetic field  212  (into the page) to oppose. 
         [0026]      FIG. 2A - FIG. 2B  show models of exemplary embodiments of back covers of a wirelessly charged computing system. In both embodiments, the outer edge  202  of the back cover is shaped to follow the form factor of a bottom surface of a laptop, tablet, mobile phone, and the like. The inner edge  204  of the back cover is shaped to form a hole or aperture for the shape  206  of a device resonator coil  206  to fit into.  FIG. 2A  shows a back cover made of a continuous piece  208  of magnesium alloy. When a source (not shown) generates a magnetic field, both a current in the device resonator coil and eddy currents  210  in the back cover  208  are induced. The eddy currents  210  shown are generally concentrated at the outer edge of the back cover and, for a given time interval, may flow in the clockwise fashion to oppose the source&#39;s magnetic field (B-field) pointing into the page  212 .  FIG. 2B  shows a back cover made of two continuous pieces  214  and  216  of magnesium alloy. Breaks  218  and  220  form these two continuous pieces  214 ,  216  that define a hole or aperture for the shape  206  of a device resonator coil to fit into. In exemplary embodiments, the breaks in the back cover may be equal to or greater than 0.05 mm, 0.1 mm, 0.5 mm, 1 mm or greater. In embodiments, the breaks  218  and  220  can be formed at various locations along the outer edge and inner edge. The eddy currents  220 ,  222  that form in the two continuous pieces  214  and  216  are generally concentrated at the outer edge of each of the two pieces. Due to the shapes of the two pieces forming the aperture in which the resonator coil is placed, the eddy currents flow opposite to one another. In other words, eddy currents  220  flow opposite in direction to eddy currents  222 . This creates an overall effect of eddy currents flowing in the shape shown in dotted lines  224 . An advantage of this created effect is that the coupling between the source resonator and device resonator is enhanced. 
         [0027]      FIG. 3  shows a model of an exemplary embodiment of a wireless power transfer system for a computing device. The system is shown at an angle to be able to view the direction of the currents generated in the various components of the system for an instantaneous time interval. The source  302  includes a source resonator (not shown) having a current flowing in clockwise direction for an instantaneous time interval, generating a magnetic field with a dipole moment  304  out of the plane of the source  302 . As the device resonator sits in the magnetic field of the source, a current is generated in the device resonator. The current may be in a clockwise direction for the same instantaneous time interval. Also generated by the presence of the magnetic field are eddy currents in the back cover  306  of the computing system. The example of the configuration of the back cover  308  is that shown in  FIG. 2B . 
         [0028]      FIGS. 4A-4B  show simulations of an exemplary embodiment of a back cover near a source. The back cover shown in this example uses the properties of aluminum and is one continuous piece (similar to that shown in  FIG. 2A ).  FIG. 4B  shows a cross-sectional view of the back cover shown in  FIG. 4A . As shown in  FIG. 4B , due to the opposing eddy currents generated in the back cover  402 , the source magnetic field is opposed in the aperture  406 . Therefore, the source will not be able to efficiently transfer energy to the device resonator that may be positioned in that aperture  406 . 
         [0029]      FIGS. 5A-5B  show simulations of an exemplary embodiment of a back cover near a source. The back cover shown in this example also uses the properties of aluminum and is made of two continuous pieces (similar to that shown in  FIG. 2B ).  FIG. 5B  shows a cross-sectional view of the back cover shown in  FIG. 5A . In this case, due to the breaks  504  formed in the back cover  502 , the source&#39;s magnetic field  506  can reach the device resonator and is further enhanced due to the effect described in  FIG. 2B  and  FIG. 3 . In other words, compared to a source resonator transferring energy to a device resonator in free space, the back cover with breaks as shown in  FIG. 2B  enhances the magnetic field and acts as a repeater at the aperture  508  where the device resonator is to be positioned. 
         [0030]      FIGS. 6A-6D  show models of exemplary embodiments of back covers of a wirelessly charged computing system.  FIG. 6A  shows a back cover made of one continuous piece  602  of magnesium alloy. The continuous piece  602  has a single break  604  from the outer edge  606  of the back cover to the inner edge  608  of the back cover. This single break  604  is sufficient to “lead” or provide the lowest impedance path for the eddy current  610  to the inner edge  608  closest to the aperture in which the device resonator  612  resides. This forms the flow of eddy currents within the shape  614 . In exemplary embodiments, the aperture  608  may be off-center relative the overall shape of the back cover  606 .  FIG. 6B  shows a back cover made of two continuous pieces  616 ,  618  of magnesium alloy. Breaks  620 ,  622  form these two continuous pieces that form a hole or aperture in which resonator  612  resides. By creating these separate pieces around the resonator, the eddy currents are “led” to form around the aperture within the shape  624 .  FIG. 6C  shows a back cover made of four continuous pieces  626 ,  628 ,  630 , and  632  of magnesium alloy. Breaks  634 ,  636 ,  638 , and  640  form the four continuous pieces that form a hole or aperture in which resonator  612  resides. The breaks  634 ,  636 ,  638 , and  640  run fully from the outer edge of the back cover to the inner edge of the back cover. This leads eddy currents to flow within the shape  624  around the inner edge of the back cover. Similarly,  FIG. 6D  shows a back cover made of four continuous pieces  644 ,  646 ,  648 , and  650 . Breaks  652 ,  654 ,  656 , and  658  form the four continuous pieces. These breaks run from the outer edge to the inner edge of the back cover at an angle as compared to the breaks shown in  FIG. 6C . 
         [0031]      FIGS. 7A-7B  show models of exemplary embodiments of back covers for a wirelessly charged computing system.  FIG. 7A  shows a back cover made of one continuous piece  702  that has a hole  704  on its outer edge that accommodates the size and shape of the resonator fixture  706 . The eddy currents  708  travel around three sides of the resonator fixture within the shape  710 . This may have a reduced “enhancing effect” than those eddy currents that travel on all four sides of the resonator.  FIG. 7B  shows a back cover made of two continuous pieces  712 ,  714  on either side of a resonator fixture  716 . This may be used to accommodate a larger resonator that takes up an entire dimension of a back cover as shown. This may have a reduced “enhancing effect” than those eddy currents that travel on all four sides of the resonator. Additionally, it may be important to consider the materials used on the sides of a computing device as the eddy currents may bypass the resonator fixture via the chassis of the computing device. This may result in greater losses. 
         [0032]      FIGS. 8A-8C  show cross-sectional views of exemplary embodiments of wirelessly charged computing devices (not to scale). The wirelessly charged computing device includes a chassis  802 , a device resonator  804 , the back cover  806 , and a layer of magnetic material  808 . In embodiments, the magnetic material may be ferrite. In embodiments, the device resonator  804  is flush or in plane with the back cover  806 . In  FIG. 8A , the magnetic material  808  is confined to the area directly behind resonator  804 . In  FIG. 8B , the magnetic material  810  is confined to the area behind the resonator  804  and to a portion of the area behind the back cover  806 . Thus, the magnetic material  808  overlaps both the back cover  806  and the resonator  804 . In  FIG. 8C , the magnetic material  812  covers the approximately the area behind the back cover  806  and resonator  804 . In exemplary embodiments, the configuration shown in  FIG. 8B  may be beneficial over the configuration shown in  FIG. 8A  so that losses in the gap  814  can be prevented. The gap  814  may be large enough such that losses are sustained in a metallic chassis  802  of the computing device. In exemplary embodiments, the configuration shown in  FIG. 8C  may be beneficial over the configurations shown in  FIG. 8A  and  FIG. 8B  so that losses can be further prevented. In embodiments, there may be additional material, such as plastic, acrylic, or polymer, which covers the coil  804  in a protective and/or aesthetic manner. The additional material can also cover the one or more pieces of the back cover  806 . 
         [0033]    In exemplary embodiments, it may be beneficial for the inductor of the device resonator to be as close as possible (without coming into direct contact) with the inner edge of the back cover so as to be better enhanced by the enhancing effect created by a back cover with breaks, such as that shown in  FIG. 2B  and  FIGS. 6A-6D . 
         [0034]    In exemplary embodiments, thermal interface material may be used if there are any “hot spots” that may pose a danger to the computing device&#39;s electronics and/or to the user. For example, thermal interface material or another type of material that will be thermally conductive but not electrically conductive may be used in the breaks of the back cover, between the back cover and the magnetic material, between the device resonator and the back cover, etc. 
         [0035]    While the disclosed techniques have been described in connection with certain preferred embodiments, other embodiments will be understood by one of ordinary skill in the art and are intended to fall within the scope of this disclosure. For example, designs, methods, configurations of components, etc. related to transmitting wireless power have been described above along with various specific applications and examples thereof. Those skilled in the art will appreciate where the designs, components, configurations or components described herein can be used in combination, or interchangeably, and that the above description does not limit such interchangeability or combination of components to only that which is described herein. 
         [0036]    All documents referenced herein are hereby incorporated by reference.