Patent Description:
Unless otherwise indicated, the foregoing is not admitted to be prior art to the claims recited herein and should not be construed as such.

Wireless power transfer is becoming increasingly popular in portable electronic devices, such as mobile phones, computer tablets, etc. Such devices typically require long battery life and low battery weight. The ability to power an electronic device without the use of wires is an attractive solution for users of portable electronic devices. Wireless power transfer gives manufacturers an option for developing solutions to problems due to limited choices for power sources in consumer electronic devices.

Wireless power transfer capability can improve the user's charging experience. In a multiple device charging situation, for example, wireless power transfer may reduce overall cost (for both the user and the manufacturer) because conventional charging hardware such as power adapters and charging chords can be eliminated. There is flexibility in having different coil sizes and shapes on the transmitter and/or the receiver in terms of industrial design and support for a wide range of devices from mobile handheld devices to computer laptops. <CIT> describes wireless charging of an electronic watch device. <CIT> discloses an apparatus for wireless power reception.

Aspects of the invention are disclosed in independent claims <NUM> and <NUM>. The invention is set out in the set of appended claims.

The following detailed description and accompanying drawings provide a better understanding of the nature and advantages of the present disclosure.

With respect to the discussion to follow and in particular to the drawings, it is stressed that the particulars shown represent examples for purposes of illustrative discussion, and are presented in the cause of providing a description of principles and conceptual aspects of the present disclosure. In this regard, no attempt is made to show implementation details beyond what is needed for a fundamental understanding of the present disclosure. The discussion to follow, in conjunction with the drawings, makes apparent to those of skill in the art how embodiments in accordance with the present disclosure may be practiced. In the accompanying drawings:.

Wireless power transfer may refer to transferring any form of energy associated with electric fields, magnetic fields, electromagnetic fields, or otherwise from a transmitter to a receiver without the use of physical electrical conductors (e.g., power may be transferred through free space). The power output into a wireless field (e.g., a magnetic field or an electromagnetic field) may be received, captured by, or coupled by a "power receiving element" to achieve power transfer.

<FIG> is a functional block diagram of a wireless power transfer system <NUM>, in accordance with an illustrative embodiment. Input power <NUM> may be provided to a transmitter <NUM> from a power source (not shown in this figure) to generate a wireless (e.g., magnetic or electromagnetic) field <NUM> for performing energy transfer. A receiver <NUM> may couple to the wireless field <NUM> and generate output power <NUM> for storing or consumption by a device (not shown in this figure) coupled to the output power <NUM>. The transmitter <NUM> and the receiver <NUM> may be separated by a distance <NUM>. The transmitter <NUM> may include a power transmitting element <NUM> for transmitting/coupling energy to the receiver <NUM>. The receiver <NUM> may include a power receiving element <NUM> for receiving or capturing/coupling energy transmitted from the transmitter <NUM>.

In one illustrative embodiment, the transmitter <NUM> and the receiver <NUM> may be configured according to a mutual resonant relationship. When the resonant frequency of the receiver <NUM> and the resonant frequency of the transmitter <NUM> are substantially the same or very close, transmission losses between the transmitter <NUM> and the receiver <NUM> are reduced. As such, wireless power transfer may be provided over larger distances. Resonant inductive coupling techniques may thus allow for improved efficiency and power transfer over various distances and with a variety of inductive power transmitting and receiving element configurations.

In certain embodiments, the wireless field <NUM> may correspond to the "near field" of the transmitter <NUM>. The near-field may correspond to a region in which there are strong reactive fields resulting from the currents and charges in the power transmitting element <NUM> that minimally radiate power away from the power transmitting element <NUM>. The near-field may correspond to a region that is within about one wavelength (or a fraction thereof) of the power transmitting element <NUM>.

In certain embodiments, efficient energy transfer may occur by coupling a large portion of the energy in the wireless field <NUM> to the power receiving element <NUM> rather than propagating most of the energy in an electromagnetic wave to the far field.

In certain implementations, the transmitter <NUM> may output a time varying magnetic (or electromagnetic) field <NUM> with a frequency corresponding to the resonant frequency of the power transmitting element <NUM>. When the receiver <NUM> is within the wireless field <NUM>, the time varying magnetic (or electromagnetic) field may induce a current in the power receiving element <NUM>. As described above, if the power receiving element <NUM> is configured as a resonant circuit to resonate at the frequency of the power transmitting element <NUM>, energy may be efficiently transferred. An alternating current (AC) signal induced in the power receiving element <NUM> may be rectified to produce a direct current (DC) signal that may be provided to charge or to power a load.

<FIG> is a functional block diagram of a wireless power transfer system <NUM>, in accordance with another illustrative embodiment. The system <NUM> may include a transmitter <NUM> and a receiver <NUM>. The transmitter <NUM> (also referred to herein as power transfer unit, PTU) may include transmit circuitry <NUM> that may include an oscillator <NUM>, a driver circuit <NUM>, and a front-end circuit <NUM>. The oscillator <NUM> may be configured to generate an oscillator signal at a desired frequency that may adjust in response to a frequency control signal <NUM>. The oscillator <NUM> may provide the oscillator signal to the driver circuit <NUM>. The driver circuit <NUM> may be configured to drive the power transmitting element <NUM> at, for example, a resonant frequency of the power transmitting element <NUM> based on an input voltage signal (VD) <NUM>. The driver circuit <NUM> may be a switching amplifier configured to receive a square wave from the oscillator <NUM> and output a sine wave.

The front-end circuit <NUM> may include a filter circuit configured to filter out harmonics or other unwanted frequencies. The front-end circuit <NUM> may include a matching circuit configured to match the impedance of the transmitter <NUM> to the impedance of the power transmitting element <NUM>. As will be explained in more detail below, the front-end circuit <NUM> may include a tuning circuit to create a resonant circuit with the power transmitting element <NUM>. As a result of driving the power transmitting element <NUM>, the power transmitting element <NUM> may generate a wireless field <NUM> to wirelessly output power at a level sufficient for charging a battery <NUM>, or otherwise powering a load.

The transmitter <NUM> may further include a controller <NUM> operably coupled to the transmit circuitry <NUM> and configured to control one or more aspects of the transmit circuitry <NUM>, or accomplish other operations relevant to managing the transfer of power. The controller <NUM> may be a micro-controller or a processor. The controller <NUM> may be implemented as an application-specific integrated circuit (ASIC). The controller <NUM> may be operably connected, directly or indirectly, to each component of the transmit circuitry <NUM>. The controller <NUM> may be further configured to receive information from each of the components of the transmit circuitry <NUM> and perform calculations based on the received information. The controller <NUM> may be configured to generate control signals (e.g., signal <NUM>) for each of the components that may adjust the operation of that component. As such, the controller <NUM> may be configured to adjust or manage the power transfer based on a result of the operations performed by it. The transmitter <NUM> may further include a memory (not shown) configured to store data, for example, such as instructions for causing the controller <NUM> to perform particular functions, such as those related to management of wireless power transfer.

The receiver <NUM> (also referred to herein as power receiving unit, PRU) may include receive circuitry <NUM> that may include a front-end circuit <NUM> and a rectifier circuit <NUM>. The front-end circuit <NUM> may include matching circuitry configured to match the impedance of the receive circuitry <NUM> to the impedance of the power receiving element <NUM>. As will be explained below, the front-end circuit <NUM> may further include a tuning circuit to create a resonant circuit with the power receiving element <NUM>. The rectifier circuit <NUM> may generate a DC power output from an AC power input to charge the battery <NUM>, as shown in <FIG>. The receiver <NUM> and the transmitter <NUM> may additionally communicate on a separate communication channel <NUM> (e.g., Bluetooth, Zigbee, cellular, etc.). The receiver <NUM> and the transmitter <NUM> may alternatively communicate via in-band signaling using characteristics of the wireless field <NUM>.

The receiver <NUM> may be configured to determine whether an amount of power transmitted by the transmitter <NUM> and received by the receiver <NUM> is appropriate for charging the battery <NUM>. In certain embodiments, the transmitter <NUM> may be configured to generate a predominantly non-radiative field with a direct field coupling coefficient (k) for providing energy transfer. Receiver <NUM> may directly couple to the wireless field <NUM> and may generate an output power for storing or consumption by a battery (or load) <NUM> coupled to the output or receive circuitry <NUM>.

The receiver <NUM> may further include a controller <NUM> configured similarly to the transmit controller <NUM> as described above for managing one or more aspects of the wireless power receiver <NUM>. The receiver <NUM> may further include a memory (not shown) configured to store data, for example, such as instructions for causing the controller <NUM> to perform particular functions, such as those related to management of wireless power transfer.

As discussed above, transmitter <NUM> and receiver <NUM> may be separated by a distance and may be configured according to a mutual resonant relationship to minimize transmission losses between the transmitter <NUM> and the receiver <NUM>.

<FIG> is a schematic diagram of a portion of the transmit circuitry <NUM> or the receive circuitry <NUM> of <FIG>, in accordance with illustrative embodiments. As illustrated in <FIG>, transmit or receive circuitry <NUM> may include a power transmitting or receiving element <NUM> and a tuning circuit <NUM>. The power transmitting or receiving element <NUM> may also be referred to or be configured as an antenna or a "loop" antenna. The term "antenna" generally refers to a component that may wirelessly output or receive energy for coupling to another antenna. The power transmitting or receiving element <NUM> may also be referred to herein or be configured as a "magnetic" antenna, or an induction coil, a resonator, or a portion of a resonator. The power transmitting or receiving element <NUM> may also be referred to as a coil or resonator of a type that is configured to wirelessly output or receive power. As used herein, the power transmitting or receiving element <NUM> is an example of a "power transfer component" of a type that is configured to wirelessly output and/or receive power. The power transmitting or receiving element <NUM> may include an air core or a physical core such as a ferrite core (not shown in this figure).

When the power transmitting or receiving element <NUM> is configured as a resonant circuit or resonator with tuning circuit <NUM>, the resonant frequency of the power transmitting or receiving element <NUM> may be based on the inductance and capacitance. Inductance may be simply the inductance created by a coil and/or other inductor forming the power transmitting or receiving element <NUM>. Capacitance (e.g., a capacitor) may be provided by the tuning circuit <NUM> to create a resonant structure at a desired resonant frequency. As a non limiting example, the tuning circuit <NUM> may comprise a capacitor <NUM> and a capacitor <NUM>, which may be added to the transmit and/or receive circuitry <NUM> to create a resonant circuit.

The tuning circuit <NUM> may include other components to form a resonant circuit with the power transmitting or receiving element <NUM>. As another non limiting example, the tuning circuit <NUM> may include a capacitor (not shown) placed in parallel between the two terminals of the circuitry <NUM>. Still other designs are possible. In some embodiments, the tuning circuit in the front-end circuit <NUM> may have the same design (e.g., <NUM>) as the tuning circuit in front-end circuit <NUM>. In other embodiments, the front-end circuit <NUM> may use a tuning circuit design different than in the front-end circuit <NUM>.

For power transmitting elements, the signal <NUM>, with a frequency that substantially corresponds to the resonant frequency of the power transmitting or receiving element <NUM>, may be an input to the power transmitting or receiving element <NUM>. For power receiving elements, the signal <NUM>, with a frequency that substantially corresponds to the resonant frequency of the power transmitting or receiving element <NUM>, may be an output from the power transmitting or receiving element <NUM>. Although aspects disclosed herein may be generally directed to resonant wireless power transfer, persons of ordinary skill will appreciate that aspects disclosed herein may be used in non-resonant implementations for wireless power transfer.

Referring to <FIG>, the discussion will now turn to a description of wireless power reception in an electronic device in accordance with embodiments of the present disclosure. <FIG> shows an electronic device <NUM>, such as a smartphone for example. It will be understood, however, in other embodiments the electronic device <NUM> may be any portable electronic device such as a laptop, a computer tablet, and so on. The electronic device <NUM> may include means for enclosing the electronic components (not shown) that comprise the electronic device <NUM>; for example, enclosure <NUM>. In some embodiments, the enclosure <NUM> may include a casing <NUM>. The enclosure <NUM> may further include a transparent display cover <NUM>, for example, such as in a smartphone or other computing device having a display. The casing <NUM> may house the electronic components of the electronic device <NUM>.

<FIG> shows the casing <NUM> portion of the enclosure <NUM> with the display cover <NUM> removed and electronic components of the electronic device <NUM> taken out of the casing <NUM>. In some embodiments, the casing <NUM> may be entirely metal. In other embodiments, the casing <NUM> may comprise at least a metal back cover portion <NUM> (metal back cover) supported by a frame portion <NUM>. The frame portion <NUM> may comprise a non-metallic material, or a combination of metallic and non-metallic materials.

In some embodiments, the metal back cover <NUM> may have one or more openings <NUM> formed through the material that comprises the metal back cover <NUM>. The openings <NUM>, for example, may be to expose the lens and flash unit of a camera (not shown) of the electronic device <NUM>. The metal back cover <NUM> may otherwise be a continuous, uninterrupted, unbroken surface, as shown in <FIG> for example. In accordance with the present disclosure, the casing <NUM> may be configured to allow for wireless transfer of power to the electronic components (not shown) of the electronic device <NUM>. This aspect of the present disclosure is discussed below.

Referring to <FIG>, in some embodiments the electronic device <NUM> may not require openings on the back side of the device; for example, a computer tablet may have only a front-facing camera. Accordingly, in some embodiments the electronic device <NUM> may employ a metal back cover <NUM>' that has no openings formed through the material. The metal back cover <NUM>' may have a solid, unbroken, uninterrupted, continuous surface with no openings formed through it, such as shown in <FIG>.

<FIG> shows an embodiment of an electronic device <NUM>' in accordance with some embodiments of the present disclosure. The electronic device <NUM>' may include means for enclosing electronic components <NUM> that comprise the electronic device <NUM>'; for example, enclosure <NUM>'. In some embodiments, the enclosure <NUM>' may include a casing <NUM>' to house the electronic components <NUM>. In accordance with the present disclosure, the casing <NUM>' may include a non-conductive shell (support substrate) <NUM>' and a thin metal layer <NUM>. In some embodiments, the thin metal layer <NUM> formed on the support substrate <NUM>' may serve as the metal back cover <NUM> (<FIG>) which has openings for a camera lens and such. In other embodiments, the thin metal layer <NUM> may serve as the metal back cover <NUM>' (<FIG>) which has no openings.

As explained below, the thin metal layer <NUM> may have insufficient structural integrity due to its thin dimension. Accordingly, the support substrate <NUM>' may serve to provide mechanical stiffness and other structural support for the electronic device <NUM>'. The support substrate <NUM>' may comprise any electrically non-conductive material. In some embodiments, the support substrate <NUM>' may be non-ferromagnetic as well. Suitable materials may be lightweight, have strong mechanical properties, and have good heat dissipation performance to dissipate heat generated by the electronic components <NUM>. In some embodiments, for example, a carbon-fiber compound may be used. It will be appreciated, however, that in other embodiments other materials may be used such as carbon nanotube materials, ceramics based materials, fiberglass, and the like.

In accordance with the present disclosure, the casing <NUM>' may be configured for wireless transfer of power to the electronic components <NUM> of the electronic device <NUM>'. The thin metal layer <NUM> may be made from any suitable electrically conductive material, such as for example, aluminum, magnesium, carbon steel, stainless steel, other metallic alloys, and the like. In some embodiments, the thin metal layer <NUM> may have a thickness less than <NUM> in order to facilitate wireless power transfer. In a particular embodiment, for example, the thickness of thin metal layer <NUM> may be <NUM> mils (approximately <NUM>) or less. In some embodiments, the thin metal layer <NUM> may be formed as part separate from the support substrate <NUM>' and then attached to the support substrate <NUM>'. In other embodiments, the thin metal layer <NUM>' may be deposited onto the support substrate <NUM>', for example, using a suitable deposition method.

In accordance with the present disclosure, the thin metal layer <NUM> may serve a dual purpose. The use of a metallic material for the back cover of the electronic device <NUM>' allows for the incorporation of an aesthetic design element to the electronic device <NUM>'. At the same time, the task of housing the electronic components <NUM> and providing structural support for the electronic device <NUM>' is provided by the support substrate <NUM>' rather than the thin metal layer <NUM>. This allows the thin metal layer <NUM> to be configured for the wireless transfer of power to the electronic device <NUM>'. This aspect of the present disclosure is discussed in more detail below.

As noted above, with respect to <FIG>, the casing <NUM> may be configured to allow for wireless transfer of power to the electronic components (not shown) of the electronic device <NUM>. Referring to <FIG>, for example, in some embodiments the casing <NUM> may include an electrically conductive power receiving element <NUM> disposed on the interior surface of the metal back cover <NUM> of the casing <NUM>. More particularly, the power receiving element <NUM> may be disposed in a given area <NUM> of the metal back cover <NUM> that is defined by a solid, unbroken, uninterrupted, continuous surface portion of the material used for the metal back cover <NUM>.

In some embodiments, the power receiving element <NUM> may comprise a conductive trace formed on a flexible printed circuit board (PCB), for example, by printing, etching, photolithography, etc. The power receiving element <NUM> may be formed in the shape of a coil having any number of turns. <FIG>, for example, shows that power receiving element <NUM> comprises three turns. In some embodiments, the power receiving element <NUM> may have additional turns. The power receiving element <NUM> may be affixed directly to the interior surface of metal back cover <NUM>, for example, using an adhesive, epoxy material, or other suitable affixing means.

The power receiving element <NUM> may include or otherwise be connected to terminals <NUM> to provide power to electronic components (not shown) of the electronic device <NUM>. In some embodiments, for example, the terminals <NUM> may be connected to a rectifier circuit (not shown) to produce a DC voltage that can be provided to the electronic components; for example, a rechargeable battery, a power management circuit, and so on.

Referring to <FIG> and <FIG>, the casing <NUM>' shown in <FIG> may likewise include an electrically conductive power receiving element <NUM>. In some embodiments, the power receiving element <NUM> may be disposed on the support substrate <NUM>' <FIG>, for example, shows an exploded view of electronic device <NUM>', illustrating some additional details in accordance with the present disclosure. In some embodiments, a recessed portion <NUM> may be formed in the outwardly facing surface of the support substrate <NUM>' to hold the power receiving element <NUM>. The recessed portion <NUM> may be provided so that the thin metal layer <NUM> can be formed (e.g., as an inlay) atop the power receiving element <NUM> without any bumps on the surface of thin metal layer <NUM>. In other embodiments, the power receiving element <NUM> may be formed directly atop the surface of the support substrate <NUM>' without a recessed portion; for example, so that an outline of some or all of power receiving element <NUM> in the design can be incorporated in the design of the backside of the casing <NUM>'.

The power receiving element <NUM> may include terminals <NUM> for connection to a rectifier circuit <NUM> in the electronic components <NUM> of the electronic device <NUM>'. <FIG> illustrates an example of an embodiment in which the power receiving element <NUM> may be arranged on the inwardly facing surface of the support substrate <NUM>'. The figure shows the power receiving element <NUM> disposed on the inwardly facing surface of support substrate <NUM>', but in other embodiments the power receiving element <NUM> may be arranged in a recess similar to the arrangement shown in <FIG>.

Referring to <FIG>, wireless power transfer may include placing the electronic device <NUM>, <NUM>' in proximity to a charging surface (charging pad, etc.) <NUM> of a wireless power transmitting device <NUM>. The charging surface <NUM> may include a transmit coil <NUM>. During a wireless power transfer operation, the transmit coil <NUM> may be energized, for example, by providing an AC excitation current to the transmit coil <NUM>. In response, the transmit coil <NUM> may generate a magnetic field <NUM>. When the electronic device <NUM>, <NUM>' is placed in proximity to the charging surface <NUM>, the externally generated magnetic field <NUM> may couple to the power receiving element (<NUM>, <FIG>) in the electronic device <NUM>, <NUM>'. This aspect of the present disclosure will be explained in more detail in connection with <FIG>. The AC excitation current may operate any suitable frequency. In some embodiments, for example, the AC excitation current may operate at frequencies according to any of the various standards for wireless power transfer. For example, the AirFuel/A4WP (Alliance for Wireless Power) wireless power transfer standard specifies an operating frequency of <NUM> and the WPC wireless power standard, developed by the Wireless Power Consortium (WPC), specifies frequencies in the range of <NUM> - <NUM>.

<FIG> shows additional detail in the area <NUM> of the metal back cover <NUM> of the casing (<NUM>, <FIG>). The casing <NUM> may include means for inducing eddy currents. For example, the externally generated magnetic field <NUM> may induce eddy currents in the metal back cover <NUM>. The eddy currents may circulate in planes perpendicular to the magnetic flux of the externally generated magnetic field <NUM>. In order to avoid cluttering the figure, <FIG> shows eddy currents <NUM>, <NUM> only in the area <NUM> of the metal back cover <NUM>. It will be understood by persons of ordinary skill, however, that eddy currents are not necessarily restricted to the area <NUM>.

Eddy currents generally concentrate near the exterior surface of the metal back cover <NUM> surface adjacent to the transmit coil <NUM>, due to the skin effect. The density of the eddy currents decreases (decays) with distance from the exterior surface of the metal back cover <NUM> toward the interior surface of the metal back cover <NUM>. Accordingly, the density of eddy currents <NUM> at the exterior surface of the metal back cover <NUM> is greater than the density of eddy currents <NUM> at the interior surface of the metal back cover <NUM>. <FIG> illustrates this graphically using a plot of current density the eddy currents at different depths (t) in the metal back cover <NUM>, where the exterior surface defines a depth of t = <NUM>.

The depth of penetration ("skin depth") of the eddy currents into the metal back cover <NUM> varies with the frequency of the power used (e.g., AC excitation current) to excite the transmit coil <NUM> and the material that comprises the metal back cover <NUM>. The skin depth may be expressed by the following: <MAT>.

In some embodiments, the excitation frequency of the power used to excite the transmit coil <NUM> may be in the <NUM>'s of KHz to <NUM>'s of KHz; for example, the WPC standard specifies frequencies in the range <NUM> - <NUM>. In some embodiments, the transmit coil <NUM> may be connected to a tuning circuit <NUM> to define a resonant circuit <NUM>. The excitation frequency may be substantially equal to a resonant frequency of the resonant circuit <NUM>. The tuning circuit <NUM> may be any suitable combination of reactive elements (e.g., a capacitor network). In some embodiments, the power receiving element <NUM> may be connected to a tuning circuit <NUM> to define a resonant circuit <NUM> that has a resonant frequency substantially equal to the excitation frequency of the power used to excite the transmit coil <NUM>. The tuning circuit <NUM>, likewise, may be any suitable combination of reactive elements, such as a capacitor network for example. As an example, the tuning circuits <NUM>, <NUM> may use the circuit design of tuning circuit <NUM> shown in <FIG>. It will be understood that in various embodiments, the tuning circuits <NUM>, <NUM> may employ any suitable circuit design.

In response to the eddy currents <NUM>, <NUM>, a magnetic field <NUM> can be generated in the metal back cover <NUM> that emanates from the metal back cover <NUM>. In accordance with the present disclosure, means may be provided to couple to the magnetic field <NUM> generated by the eddy currents <NUM>, <NUM>. For example, portions of the magnetic field <NUM> that emanate from interior surface of area <NUM> in the metal back cover <NUM> may couple to the power receiving element <NUM> of the electronic device <NUM> (<FIG>). This can induce a flow of current in the power receiving element <NUM>, which can be rectified and provided to electronic components (not shown) of the electronic device <NUM>.

In some embodiments, the material for metal back cover <NUM> may include metals such as copper, aluminum, magnesium, carbon steel, titanium, stainless steel, and the like. In other embodiments, the metal back cover <NUM> may comprise a combination (e.g., a composite of metals, an alloy of metals, etc.) of two or more of copper, aluminum, magnesium, carbon steel, titanium, stainless steel. In other embodiments, other suitable metals may be used, individually or in combination. The use of these materials allow for the metal back cover <NUM> to be sufficiently thin to allow for a skin depth that allows sufficient eddy currents to form at the interior surface of the metal back cover <NUM> to generate a magnetic field for wireless power transfer. In some embodiments, <FIG> for example, the thickness t<NUM> of the material may be less the <NUM>. In other embodiments, the thickness t<NUM> may be <NUM> to <NUM>. These thickness values are merely illustrative, and the thickness t<NUM> can be other values in other embodiments.

At certain excitation frequencies (e.g., >> <NUM>'s kHz), the eddy currents can remain concentrated substantially to the exterior surface of the metal back cover <NUM> due to the skin effect, while eddy currents at the interior surface of the metal back cover <NUM> can be attenuated as illustrated by the graph in <FIG>. Accordingly, the magnetic field induced by the eddy currents at the interior surface of the metal back cover <NUM> may not couple sufficient power to the power receiving element <NUM>. By comparison, at lower excitation frequencies (e.g., <NUM>), eddy currents are less attenuated across the entire metal back cover <NUM> as illustrated by the graph in <FIG>. The eddy currents on the interior surface of the metal back cover <NUM> are therefore higher at a lower excitation frequency than at a higher excitation frequency, and thus can induce a stronger magnetic field from the interior surface to provide sufficiently strong coupling to the power receiving element <NUM>.

<FIG> illustrates operation when the metal back cover (e.g., <NUM>, <FIG>, <NUM>', <FIG>) comprises a thin metal layer <NUM> (<FIG>). As described above, the thin metal layer <NUM> may have a thickness of about <NUM> or less, and in some embodiments may be suitable for wireless power transfer at low excitation frequencies; e.g., <NUM> or less. In some embodiments, the externally generated magnetic field <NUM> may penetrate the thin metal layer <NUM>, as depicted in <FIG> for example, and couple to the power receiving element <NUM>. It is noted that the wireless standards and excitation frequencies disclosed herein are merely examples to illustrate this aspect of the present disclosure in the context of known wireless charging systems. It will be appreciated that the support substrate <NUM>' can allow for the thickness of thin metal layer <NUM> to be adapted for a variety of different implementations to work with a variety of different frequency ranges, and is not necessarily limited to any particular frequency range.

Referring to <FIG>, in some embodiments, a layer of ferrite material <NUM> may be positioned between the power receiving element <NUM> and the metal back cover <NUM>. The ferrite material <NUM> may serve to improve the mutual coupling of the generated magnetic field (<NUM>, <FIG>) and the power receiving element <NUM>. For example, the ferrite material <NUM> may enhance penetration of the externally generated magnetic field (<NUM>, <FIG>) through the metal back cover <NUM>, thus enhancing the induction of eddy currents in the metal back cover <NUM>.

Referring to <FIG>, in some embodiments, a layer of ferrite material <NUM> maybe provided on top of the power receiving element <NUM> so that the power receiving element <NUM> is positioned between the ferrite material <NUM> and the metal back cover <NUM>. The ferrite material <NUM> may serve to enhance the coupling of the magnetic field <NUM> generated in the metal back cover <NUM> to the power receiving element <NUM> as explained above. In addition, the ferrite material <NUM> may also serve to shield electronic components (not shown) comprising the electronic device <NUM> from the magnetic field <NUM>. In still other embodiments, though not shown, the power receiving element <NUM> may be sandwiched between a first layer and a second layer of ferrite material. The ferrite material <NUM> may serve to channel the magnetic field <NUM> generated by the eddy currents such that flux is concentrated near the power receiving element <NUM>.

Referring to <FIG>, in some embodiments, the power receiving element <NUM> may be disposed on the outwardly facing surface of the support structure <NUM>', and a layer of ferrite material 912a may be provided between the power receiving element <NUM> and the thin metal layer <NUM> to enhance penetration of the externally generated magnetic field <NUM> through the thin metal layer <NUM> and improve mutual coupling between the externally generated magnetic field (<NUM>, <FIG>) and the power receiving element <NUM>. In some embodiments, a layer of ferrite material 912b may be provided instead of or in addition to ferrite material 912a. The ferrite material 912b may be placed on the inside surface of the support structure <NUM>'.

Referring to <FIG>, in some embodiments, the power receiving element <NUM> may be disposed on the inwardly facing surface of the support structure <NUM>'. The layer of ferrite material 912b and support structure <NUM>' may sandwich the power receiving element <NUM> to enhance penetration of the externally generated magnetic field <NUM> through the thin metal layer <NUM> and improve mutual coupling between the externally generated magnetic field (<NUM>, <FIG>) and the power receiving element <NUM>. In some embodiments, the layer of ferrite material 912a may be provided instead of or in addition to ferrite material 912b.

The description will now turn to a discussion of some results from a High Frequency Structure Simulator (HFSS™) analysis of magnetic fields generated in a metal plate as a function of frequency of the external excitation magnetic field. In particular, a comparison of the generated magnetic flux for very low frequency external magnetic fields (e.g., about <NUM>), low frequency external magnetic fields (e.g., about <NUM>), and relatively high frequency external magnetic fields (e.g., about <NUM>) will be discussed.

<FIG> illustrates a setup for the simulation. For the purposes of the simulation, the receive and transmit coils are identical. The receive coil (e.g., power receiving element <NUM>) is shown to be above the metal plate, and the transmit coil is shown to be below the metal plate. For the purposes of the simulation, the metal plate is characterized as having a thickness of <NUM> and a conductivity of <NUM> siemens/m.

<FIG> illustrate a frequency sweep result for an electromagnetic simulation for the setup shown in <FIG>. The simulation frequencies vary from about <NUM> to <NUM>. <FIG> shows the sweep result from <NUM> to <NUM>. The plot shows mutual inductance M on the vertical scale and frequency in kHz on the horizontal scale. <FIG> shows the sweep result from about <NUM> to <NUM>. The plot shows mutual inductance M on the vertical scale and frequency in MHz on the horizontal scale. Three regions (<NUM>,<NUM>, <NUM>) are defined based on frequency ranges. The map simulation of <FIG> shows that current in the transmit coil flows in the opposite direction as current in the receive coil and eddy currents in the metal plate. The strength of the surrounding magnetic field is shown in gray scale.

Referring to <FIG>, <FIG>, for a given thickness of a metal plate (e.g. <NUM>), we see that at a very low frequency (<NUM>), M is positive because eddy currents on the metal plate are substantially uniformly strong and magnetic flux direction in the transmit coil is that same as the magnetic flux direction in the receive coil. The <FIG> shows the magnetic flux lines for very low frequency excitations. At low frequencies, the magnetic flux is additive. <FIG> shows a simulated heat map illustrating the field strength at different areas of the metal plate. The field strength is generally high on the side of the transmit coil and on the side of the receive coil, with an area of low field strength. The area of low field strength is due to the symmetry of the eddy current in that area of the metal plate.

Referring to <FIG>, <FIG>, at a low frequency (<NUM>), mutual inductance M is negative because the eddy current is not uniform across the metal plate. This causes the induced magnetic flux to be directed in the opposite direction of the magnetic flux from the transmit coil. <FIG> shows the magnetic flux lines and <FIG> shows the corresponding magnitude of magnetic field strength. A weak area of magnetic field is observed around the center of the receive coil due to symmetry of the eddy current, similar to <FIG>.

Referring to <FIG>, <FIG>, at a relatively high frequency (<NUM>), the eddy current on the metal plate is very small throughout the metal plate (<FIG>) and M is accordingly almost zero. <FIG> shows the field strength to be low for much of area on the side of the receive coil.

Claim 1:
An apparatus for wireless power reception in a portable electronic device comprising:
a casing (<NUM>) configured to house electronic components of the portable electronic device, the casing comprising a non-conductive support substrate (<NUM>) to house the electronic components and a metal layer (<NUM>) disposed on the support substrate; and
a power receiving element (<NUM>) disposed in a given area (<NUM>) of the metal layer (<NUM>) that is defined by a solid, unbroken, uninterrupted, continuous surface portion of the metal layer, with a layer of ferrite material (<NUM>) disposed between the power receiving element (<NUM>) and the metal layer;
the power receiving element configured to magnetically couple to an externally generated magnetic field and,
wherein the metal layer is configured such that the externally generated magnetic field penetrates the metal layer to generate eddy currents in the metal layer, the eddy currents generating an induced magnetic field, the metal layer further configured to magnetically couple the induced magnetic field to the power receiving element to produce an induced voltage in the power receiving element;
a rectifier for rectifying the induced voltage to produce a DC voltage for powering one or more of the electronic components of the electronic device.