Sub-surface wireless charging

In an embodiment, a sub-surface wireless charger includes a transmitter coil and a controller. The controller is configured to generate a protective pulse having a first energy, determine a characteristic of the transmitter coil based on the generated protective pulse, determine whether it is safe to begin wireless charging based on the determined characteristic, and when the controller determines that it is safe to begin wireless charging, generate an operating pulse having a second energy, where the second energy is higher than the first energy.

TECHNICAL FIELD

The present invention relates generally to an electronic system and method, and, in particular embodiments, to sub-surface wireless charging.

BACKGROUND

Wireless charging systems are becoming ubiquitous in today's society. For example, many smartphones and wearables implement wireless charging technology. Ease of use, greater reliability, spatial freedom, reduced connectors and openings, and the possibility of hermetically sealing are among the benefits offered by wireless charging. Wireless charging standards allow for interoperability between different devices and manufacturers. Some wireless charging standards, such as the Qi standard from the Wireless Power Consortium, are becoming widely adopted.

Wireless charging standards, such as the Qi standard, provide specifications that cover various aspects of the wireless charging process, including the frequency used to transmit wireless power from a wireless charger to a receiver, and communication protocols that allow a receiver to communicate with a wireless charger. The standards also provide specifications directed to safety of the wireless charger and the receiver.

SUMMARY

In accordance with an embodiment, a sub-surface wireless charger includes a transmitter coil and a controller. The controller is configured to generate a protective pulse having a first energy, determine a characteristic of the transmitter coil based on the generated protective pulse, determine whether it is safe to begin wireless charging based on the determined characteristic, and when the controller determines that it is safe to begin wireless charging, generate an operating pulse having a second energy, where the second energy is higher than the first energy.

In accordance with an embodiment, a sub-surface wireless charger includes a transmitter coil and a controller. The controller is configured to generate a first pulse having a first energy, receive a first response from a receiver via the transmitter coil during the first pulse, generate a second pulse having a second energy, the second energy being higher than the first energy, and prevent the sub-surface wireless charger from beginning wireless charging the receiver if a second response is not received from the receiver via the transmitter coil during the second pulse.

In accordance with an embodiment, a sub-surface wireless charger includes a transmitter coil and a controller. The controller is configured to generate a first pulse having a first energy, receive a first response from a receiver via the transmitter coil during the first pulse, cause the transmitter coil to be energized after the first pulse, while the transmitter coil is energized, determine whether the receiver is performing detuning, and stop energizing the transmitter coil or reduce an energy level flowing through the transmitter coil when the controller determines that the receiver is performing detuning.

In accordance with an embodiment, a wireless charger includes a sub-surface wireless charger having a first transmitter coil, and a repeater charger having a receiver coil and a second transmitter coil. The sub-surface wireless charger is configured to generate wireless power using the first transmitter coil at a first frequency. The repeater charger is configured to receive wireless power from the sub-surface wireless charger using the receiver coil, power a first circuit using the received wireless power, and generate wireless power using the second transmitter coil at a second frequency that is different from the first frequency.

In accordance with an embodiment, a device includes a plurality of sensing coils configured to receive wireless power from a sub-surface wireless charger; a measuring circuit coupled to the plurality of sensing coils and configured to sense a voltage across each of the plurality of sensing coils; a visual indicator; and a controller coupled to the measuring circuit. The controller is configured to determine a direction of a location of maximum coupling coefficient between the sub-surface wireless charger and the device based on an output of the measuring circuit, and indicate the direction of the location of maximum coupling coefficient via the visual indicator.

In accordance with an embodiment, a sub-surface wireless charger includes a non-volatile memory, a transmitter coil, and a controller. The controller is configured to, before calibration, transmit a first pulse having a first energy via the transmitter coil during a ping process, during calibration, transmit the first pulse having the first energy via the transmitter coil, receive a calibration code via the transmitter coil, store data corresponding to a second energy in the non-volatile memory based on the received calibration code, where the second energy is higher than the first energy, and after calibration, transmit a second pulse having the second energy via the transmitter coil, during the ping process.

In accordance with an embodiment, a wireless charger includes a sub-surface wireless charger including a transmitter coil and a first controller, and a foreign object detector. The foreign object detector includes a sensing coil, a second controller and a communication interface coupled to the sensing coil. The second controller is configured to determine a first average power at a location of the sensing coil based on a voltage across the sensing coil, and transmit data based on the first average power via the sensing coil using the communication interface. The first controller is configured to receive data from the transmitter coil, determine the first average power based on the received data, determine a second average power received by a receiver, and determine whether a foreign metallic object is present in a charging space of the sub-surface wireless charger by comparing the first average power with the second average power.

In accordance with an embodiment, a wireless charger includes a sub-surface wireless charger, and a ferrite sticker having a hollow shape and disposed in a charging space of the sub-surface wireless charger. The ferrite sticker is configured to be disposed between the sub-surface wireless charger and a receiver.

In accordance with an embodiment, a wireless charger includes a transmitter coil; and a metallic heatsink having a first surface attached to the transmitter coil. The transmitter coil is configured to produce a magnetic field when the transmitter coil is energized. The metallic heatsink has a second surface that has a shape that tracks magnetic lines of the magnetic field.

Corresponding numerals and symbols in different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the preferred embodiments and are not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The description below illustrates the various specific details to provide an in-depth understanding of several example embodiments according to the description. The embodiments may be obtained without one or more of the specific details, or with other methods, components, materials and the like. In other cases, known structures, materials or operations are not shown or described in detail so as not to obscure the different aspects of the embodiments. References to “an embodiment” in this description indicate that a particular configuration, structure or feature described in relation to the embodiment is included in at least one embodiment. Consequently, phrases such as “in one embodiment” that may appear at different points of the present description do not necessarily refer exactly to the same embodiment. Furthermore, specific formations, structures or features may be combined in any appropriate manner in one or more embodiments.

Embodiments of the present invention are described in a specific context, sub-surface wireless charging systems and methods. Embodiments of the present invention may be used in other systems, such as other wireless charging systems, for example.

It is understood that the term wireless charging is not limited to the charging of a battery, but includes wireless power transmission generally, unless stated otherwise.

In an embodiment of the present invention, an active alignment device is used for finding a location of maximum coupling coefficient between a sub-surface wireless charger and a receiver. The active alignment device uses a plurality of sensing coils to determine the direction of the location of maximum coupling coefficient and uses an indicator, such as a visual indicator, to indicate the direction of the location of maximum coupling coefficient. In some embodiments, the active alignment device is powered by the sub-surface wireless charger.

In an embodiment of the present invention, a testing device that includes a receiver coil is used to test whether a sub-surface wireless charger is capable of delivering a particular amount of wireless power once the sub-surface wireless charger is installed in a surface. The testing device includes a variable load that can be adjusted to mimic a particular power consumption, such as 10 W, for example. The testing device then measures the actual amount of wireless power received by the receiver coil, e.g., based on the voltage across the receiver coil and the current flowing through the receiver coil to determine whether the particular amount of wireless power was delivered. In some embodiments the testing device is implemented together with an active alignment device inside the same device.

In an embodiment of the present invention, a programmable sub-surface wireless charger is configured to generate an initial ping having an initial default ping power that is low enough to be safe, even in situations where a receiver and the sub-surface wireless charger are very close to each other (e.g., at 5 mm or less). A testing device equipped with a high inductance receiver coil receives the initial ping and transmits to the sub-surface wireless charger a programming command to reprogram the default ping power based on the voltage measured across the receiver coil of the testing device during a calibration procedure. The sub-surface wireless charger receives the reprogrammed command and changes the default ping power from the initial default ping power to an operating default ping power, where the operating default ping power is configured to generate a voltage across a receiver coil of a receiver within safe operating limits (e.g., between 3 V and 9 V). The new default setting is written in, e.g., non-volatile memory of the sub-surface wireless charger. In some embodiments, the sub-surface wireless charger is configured to not begin wirelessly charging until the testing device successfully reprograms the sub-surface wireless charger during the calibration procedure.

In an embodiment of the present invention, a protection circuit of a sub-surface wireless charger determines whether a receiver is unsafely close to the sub-surface wireless charger based on one or more changes in the characteristics of the transmitting coil of the sub-surface wireless charger. If it is determined that the receiver is unsafely close to the sub-surface wireless charger, the sub-surface wireless charger does not proceed with the ping process and subsequent wireless charging. The sub-surface wireless charger measures or determines the one or more characteristics of the transmitting coil by generating a protection pulse with low enough energy to be safe at very close distances, such as when the sub-surface wireless charger and the receiver are in contact with each other, and by measuring or detecting one or more properties of the oscillations that result from the protection pulse.

In some embodiments, the sub-surface wireless charger measures or determines the resonance frequency, the change in resonance frequency with respect to a predetermine resonance frequency value, the inductance of the transmitter coil, the change in inductance of the transmitter coil with respect to a predetermined inductance value, the damping factor, the change in damping factor with respect to a predetermined damping factor value, the quality factor, and/or the change in quality factor with respect to a predetermined quality factor value.

In an embodiment of the present invention, a multi-ping method is used to determine whether a receiver is too close to a sub-surface wireless charger. A first ping with a first energy is generated. A second ping with a second energy is generated after the first ping, where the second energy is higher than the first energy. If the sub-surface wireless charger receives data from the receiver during the first ping but not during the second ping, it is determined that the receiver is too close to the sub-surface wireless charger.

In some embodiments, a sub-surface wireless charger determines that a receiver is too close by detecting the detuning by the receiver. The sub-surface wireless charger determines whether the receiver is performing detuning by monitoring a voltage across a transmitter coil of the sub-surface wireless charger and determining whether a signal with a frequency lower than a first frequency (e.g., 1 kHz) has a first energy higher than an energy threshold.

In an embodiment of the present invention, a two-part wireless charger includes a sub-surface wireless charger disposed at a first surface of a surface, and a repeater charger disposed at a second surface of a surface. The sub-surface wireless charger transfers wireless power to the repeater charger and through the surface using resonance charging (e.g., at a frequency of 6.78 MHz). The repeater charger receives power from the sub-surface wireless charger and transmits wireless power to a receiver using inductive wireless charging (e.g., at a frequency between 80 kHz and 300 kHz). By using a repeater charger, the two-part wireless charger is advantageously capable to provide wireless power to a receiver when the surface is relatively thick (e.g., thicker than 20 mm, such as 25 mm, 30 mm, or thicker).

In some embodiments, the repeater charger that includes a controller that is used to demodulate data from a receiver and to control the power that is wirelessly transmitted to the receiver.

In some embodiments, the controller of the repeater charger performs foreign object detect (FOD) by determining the average power transmitted by a transmitter coil of the repeater charger and comparing the average power transmitted by a transmitter coil of the repeater charger with the average power received at a receiver coil of the receiver.

In some embodiments, the controller of the repeater charger transmits data to the sub-surface wireless charger (e.g., using load modulation) to cause the sub-surface wireless charger to adjust the level of wireless power transmitted to the repeater charger.

In some embodiments, a controller of the sub-surface wireless charger performs foreign object detect (FOD) by determining the average power transmitted by a transmitter coil of the repeater charger and comparing the average power transmitted by a transmitter coil of the repeater charger with the average power received at a receiver coil of the receiver. In some embodiments, the controller of the sub-surface wireless charger determines the average power transmitter by the transmitter coil of the repeater charger and the average power received by the receiver coil of the receiver based on data received from the transmitter coil of the sub-surface wireless charger.

In some embodiments, a repeater charger does not include a micro-controller. In such embodiments, the repeater charger causes any load modulation present in the transmitter coil of the repeater charger to propagate through the receiver coil of the repeater charger and to the transmitter coil of the sub-surface wireless charger. A controller of the sub-surface wireless charger is configured to demodulate data received from the transmitter coil of the sub-surface wireless charger and adjust the power delivered via the transmitter coil of the sub-surface wireless charger based on the received data. In some embodiments, the repeater charger includes an oscillator, where a driver of the repeater charger is configured to drive the transmitter coil of the repeater charger based on an output of the oscillator.

In some embodiments, a sub-surface wireless charger that is implemented as an inductive charger performs FOD detection by using an FOD unit that is disposed between a receiver and the sub-surface wireless charger. The FOD unit comprises a sensing coil, a controller and a communication interface coupled to the sensing coil. The controller of the FOD unit determines a first average power at a location of the sensing coil of the FOD unit based on a voltage across the sensing coil of the FOD unit and transmits the data indicative of the first average power to the sub-surface wireless charger via the sensing coil using load modulation. A controller of the sub-surface wireless charger receives data associated with the first average power from the transmitter coil of the sub-surface wireless charger. The controller of the sub-surface wireless charger also receives data associated with a second average power received by a receiver via the transmitter coil of the sub-surface wireless charger. The controller of the sub-surface wireless charger then determines whether a metallic foreign object is present in the charging space of the sub-surface wireless charger based on comparing the first average power with the second average power.

In some embodiment, the FOD unit communicates with the sub-surface wireless charger by performing load modulation during an FOD data transmission time, where the FOD data transmission time is in between data transmission portions sent by the receiver to the sub-surface wireless charger. In some embodiments, the FOD unit determines whether the receiver is transmitting data by determining whether the voltage across the sensing coil includes a signal with a frequency between, e.g., 1 kHz and 2 kHz, that has an energy higher than a threshold.

In an embodiment of the present invention, a wireless charger includes a sub-surface wireless charger disposed below a surface and a top-side ferrite sticker disposed above the surface between a receiver and a top surface of the surface. In some embodiments, the ferrite sticker advantageously increases the coupling coefficient between sub-surface wireless charger and the receiver. In some embodiments, the top-side ferrite sticker includes a mark indicative of a location of maximum coupling coefficient between the sub-surface wireless charger and the receiver.

In an embodiment of the present invention, a sub-surface wireless charger includes a heatsink that has an outer surface that tracks the magnetic lines of the magnetic field generated by the transmitter coil of the sub-surface wireless charger. In some embodiments, such outer surface has a toroidal shape.

FIG. 1shows a schematic diagram of sub-surface wireless charging system100, according to an embodiment of the present invention. Sub-surface wireless charging system100includes sub-surface wireless charger102, surface104, and receiver106. Surface104includes top surface104a, and bottom surface104b. Sub-surface wireless charger102is attached to bottom surface104b(e.g., glued). Receiver106is disposed over top surface104a, e.g., when receiver106is to receive wireless power from sub-surface wireless charger102.

During normal operation, sub-surface wireless charger102receives power, e.g., from mains, and wirelessly transmits power through surface104using, e.g., a coil into charging space101. Receiver106wirelessly receives power from sub-surface wireless charger102and uses such received power to, e.g., operate receiver106, charge a battery (not shown) coupled to receiver106, and/or retransmit power (e.g., wirelessly), e.g., to another device (not shown).

The intensity of the power received by receiver106from sub-surface wireless charger102depends, in part, on the distance between receiver106and sub-surface wireless charger102. For example, generally, the closer receiver106is to sub-surface wireless charger102, the higher the intensity of wireless power received by receiver106from sub-surface wireless charger102.

Surface104may be, for example, a table, a wall, or another surface. Although surface104is illustrated as a planar horizontal surface, it is understood that surface104may be a vertical surface, such as a wall, or an inclined surface. In some embodiments, surface104may not be planar.

Receiver106may be, for example, a smartphone, a tablet, a laptop, a wearable, a power tool, or another battery operated portable device. Other devices are also possible. For example, in some embodiments, receiver106may not include a battery. In some embodiments, receiver106may be configured to operate only when wirelessly receiving power. In some embodiments, receiver106may not be a portable device. For example, receiver106may be attached to top surface104a. For example, receiver106may be a thermostat to control a heating, ventilation, and air conditioning (HVAC) of a house, and surface104is a vertical wall, where sub-surface wireless charger102is attached to the inside surface of the wall and the thermostat is attached to the outside surface of the wall.

Sub-surface wireless charger102may be capable of transferring 10 W of wireless power to receiver106. In some embodiments, sub-surface wireless charger102may be capable of transferring more than 10 W of wireless power to receiver106, such as 15W, 20 W, or more. In other embodiments, the maximum power that sub-surface wireless charger102is capable of transferring to receiver106may be lower than 10 W, such as 5 W or less.

In sub-surface wireless charging systems, such as sub-surface wireless charging system100, the coupling coefficient between the transmitter coil of the sub-surface wireless charger and the receiver coil of the receiver is generally low. For example,FIG. 2shows transmitter coil108of sub-surface wireless charger102and receiver coil110of receiver106having their respective coil centers aligned with centerline112, according to an embodiment of the present invention.

Transmitter coil108may be implemented, for example, using Litz wire. Other implementations are also possible.

Receiver coil106may be implemented, for example, using traces in a printed circuit board (PCB). Other implementations, such as using stamped metal, or Litz wires may also be used.

The coupling coefficient between transmitter coil108and receiver coil110when the centers of transmitter coil108and receiver coil110are aligned with centerline112and when thickness d1is 20 mm maybe, e.g., about 0.1. In some embodiments, centerline112is orthogonal to the winding loops of transmitter coil112.

The coupling coefficient is typically maximized when transmitter coil108and receiver coil110are aligned with centerline112. Less than perfect alignment (e.g., when the coil centers of transmitter coil108and receiver coil110are misaligned) causes the coupling coefficient to be lower, thereby reducing the efficiency of the wireless power transfer as well as the maximum amount of power that can be transferred by sub-surface wireless charger102into receiver106.

In some embodiments, sub-surface wireless charger102does not move with respect to surface104during normal operation. For example, in some embodiments, sub-surface wireless charger102is firmly attached (e.g., using glue) to bottom surface104bof surface104.

In some embodiments, surface104is transparent or semitransparent. In such embodiments, a user of receiver106(e.g., a human) may be able to find centerline112by looking through surface104and may be able to place receiver106such that the coil centers of transmitter coil108and receiver coil110are aligned. In other embodiments, surface104is not transparent. In such embodiments, a user of receiver106may rely on a marking (e.g., a label) in top surface104ato align receiver coil110with transmitter coil108. The user may use such marking as a reference for placing receiver106on top of surface104ato maximize the coupling coefficient between transmitter coil108and receiver coil110.

In an embodiment of the present invention, an active alignment device is used for finding a location of maximum coupling coefficient between a sub-surface wireless charger and a receiver. The active alignment device uses a plurality of sensing coils to determine the direction of the location of maximum coupling coefficient and uses an indicator, such as a visual indicator, to indicate the direction of the location of maximum coupling coefficient. In some embodiments, the active alignment device is powered by the sub-surface wireless charger.

FIG. 3shows a schematic diagram of active alignment device300, according to an embodiment of the present invention. The top portion ofFIG. 3shows a top view of a layout of active alignment device300. The bottom portion ofFIG. 3shows a cross-section view of active alignment device300.

Active alignment device300includes sensing coils3021,3022,3023, and3024, mark304, and enclosure306. In some embodiments, active alignment device300may include more than 4 sensing coils, such as 5, 10, 50, 64, or more. In some embodiments, active alignment device300may include less than four sensing coils, such as three, for example.

During normal operation, active alignment device300is disposed over top surface104aof surface104. As a user, such as a human, moves active alignment device300along top surface104a, each of the sensing coils302develops a voltage across the respective sensing coils302based on the intensity of the magnetic field received from sub-surface wireless charger102.

As active alignment device300moves closer to centerline112, voltages develop across sensing coils302. Sensing coils302that are closer than centerline112have larger voltages across them than sensing coils302that are farther from centerline112. Active alignment device300determines the direction of the location of centerline112with respect to mark304based on the differences between voltages across sensing coils302. When centerline112crosses mark304, active alignment device300is aligned with centerline112.

In some embodiments, mark304is symmetrically disposed with respect to the plurality of sensing coils302. For example, in some embodiments, the centers of each sensing coils302are symmetrically disposed with respect to mark304. For example, in some embodiments, distance d2and distance d3between centers of sensing coils are equal.

By symmetrically disposing mark304with respect to the plurality of sensing coils302, the location of mark304corresponds to a maximum coupling coefficient when each voltage across each sensing coil302is equal.

In other embodiments, mark304is not symmetrically disposed. In such embodiments, the none-symmetries are compensated, e.g., by mathematical computations such that the location of mark304corresponds to a maximum coupling coefficient when each of the compensated voltages across each sensing coil302is equal.

In some embodiments, the location in top surface104athat corresponds to a maximum coupling coefficient may not corresponds to centerline112(e.g., due to other materials being present or other particular geometries that may modify the shape of the magnetic field). In such embodiments, active alignment device300is advantageously capable of finding the location of maximum coupling coefficient, which may not correspond to centerline112. Using active alignment device300, thus, may advantageously maximize coupling coefficient between transmitter coil108and receiver coil110even in cases where surface104is transparent or semi-transparent.

FIG. 4shows a top view of active alignment device300showing enclosure306, according to an embodiment of the present invention. As shown inFIGS. 3 and 4, mark304is indicated by a hole in enclosure306. Having a hole in enclosure306to indicate mark304advantageously allows a user to use a marking device, such as a pencil or pen, to mark top surface104awhen active alignment device300identifies that the location of maximum coupling coefficient is at mark304.

In some embodiments, mark304may be indicated in other ways. For example, in some embodiments, a stamp mechanism at a bottom of active alignment device300may be disposed at the location of mark304. In such embodiments, when active alignment device300determines that the location of maximum coupling coefficient corresponds to mark304, the stamp mechanism is activated to mark top surface104a. In such embodiments, a hole in enclosure306to indicate mark304may be avoided. Other implementations are also possible.

As shown inFIG. 4, active alignment device300also includes light emitting diodes (LEDs)4021,4022,4023, and4024. LEDs402may be turned on and off to indicate the direction of the location of maximum coupling. For example, in some embodiments, if the voltage across sensing coils3021and3024is equal to voltage V1(e.g., 3 V), and the voltage across sensing coils3022and3023is equal to voltage V2lower than voltage V1(e.g., voltage V2equal to 2 V), LED4024turns on to indicate that the location of maximum coupling coefficient is to the left active alignment device300. When the voltages across all of sensing coils3021,3022,3023, and3024are the same, all LEDs4021,4022,4023, and4024turn on to indicate that the location of maximum coupling coefficient has been found, (e.g., which corresponds to mark304). It is understood that LEDs402may be turned on or off in different ways to indicate the direction of the location of maximum coupling coefficient.

In some embodiments, the number of LEDs402may be higher than 4, such as 5, 8, 10, 30, 50, 64, or more, or lower than 4, such as 3. In some embodiments, the number of LEDs402may be equal to the number of sensing coils302. In some embodiments, a display may be used instead of or in addition to LEDs402to indicate the direction of the location of maximum coupling coefficient. Other implementations are also possible. For example, in some embodiments, a speaker may be used, instead of, or in addition to visual indicators, to indicate the direction of the location of maximum coupling coefficient.

FIG. 5shows a schematic diagram of sensing circuit500for operating sensing coils302, according to an embodiment of the present invention. Sensing circuit500includes differential amplifier502, analog-to-digital converter (ADC)504, and controller506.

During normal operation, a voltage is generated across terminals of coil306based on the strength of the magnetic field flowing through the core area of sensing coil302. Such voltage is amplified by amplifier502and then converted into digital data by ADC504. Controller506receives the digital data from ADC504and controls, e.g., LEDs402based on the received digital data.

In some embodiments, an amplifier502and ADC504are used for each of the sensing coils302. In some embodiments, a single amplifier502and/or a single ADC504may be shared across two or more sensing coils302to determine the voltage across each of the sensing coils302and, e.g., control LEDs402based on the measured voltage. For example,FIG. 6shows a schematic diagram of sensing circuit600, according to an embodiment of the present invention.

Sensing circuit600operates in a similar manner as sensing circuit500. Sensing circuit600, however, includes analog multiplexers (AMUXs)602and604to share amplifier502and ADC504with n sensing coils302.

Measuring the voltage across each of the sensing coils302by ADC504when shared may be performed in any way known in the art. For example, in some embodiments, such measurements may be performed in a round-robin configuration. Such sampling of the voltage across sensing coils302may be performed in a few milliseconds or less (e.g., 10 ms or less).

Controller506may be implemented in any way known in the art. For example, some embodiments may implement controller506with a general purpose controller. Other embodiments may implement controller506using a digital signal processor (DSP) or a field programmable gate array (FPGA). Yet other embodiments may implement controller506using custom logic, such as an application-specific integrated circuit (ASIC). Other implementations are also possible.

In some embodiments, active alignment device300is powered by a battery (e.g., a Li-ion battery, AA batteries, or other types of rechargeable or non-rechargeable batteries). In some embodiments, active alignment device300is powered by mains (e.g., 120 VAC, 60 Hz power). In some embodiments, active alignment device300receives power to operate from sub-surface wireless charger102. For example,FIG. 7shows active alignment device700including receiver coil710, according to an embodiment of the present invention.

During normal operation, active alignment device700turns on when active alignment device700wirelessly receives power from sub-surface wireless charger102using receiver coil710. Active alignment device700, therefore, may operate in a similar manner as a receiver106having receiver coil110in the presence of wireless power emanating from sub-surface wireless charger102. Once powered, active alignment device700operates in a similar manner as active alignment device300.

FIG. 8shows a schematic diagram of wireless power receiver circuit800of active alignment device700, according to an embodiment of the present invention. As shown inFIG. 7, receiver coil710is configured to receive wireless power, e.g., from sub-surface wireless charger102. The voltage developed across receiver coil710is rectified using diode rectifier bridge804and provided to converter806. Converter806then generates DC voltage Vout, which is used to provide power to one or more circuits of active alignment device700. In some embodiments voltage Voutmay also be used for other purposes, such as to charge a rechargeable battery of active alignment device700.

Diode rectifier bridge804may be implemented in any way known in the art. Other rectification methods may also be used. For example, in some embodiments, a synchronous rectifier may be used.

Converter806may be implemented in any way known in the art. For example, in some embodiments, converter806may be implemented as a buck converter. Other implementations, such as boost, buck-boost, fly-back converters, and other switching converter topologies may also be used. In some embodiments, converter806may be implemented as a non-switching converter, such as an LDO.

Advantages of some embodiments include that during installation of a sub-surface wireless charger in a surface, a user may find the location that maximizes the coupling coefficient of the sub-surface wireless charging system without relying on visual observations of the location of the sub-surface wireless charger. Using an active alignment device advantageously allows a user to easily find the location of maximum coupling coefficient when the sub-surface wireless charger is installed in surfaces that are not transparent. A user may then mark the top surface of the surface at the identified location of maximum coupling coefficient to allow a user to quickly find the location of optimal wireless charging for receiver placement.

In an embodiment of the present invention, a testing device that includes a receiver coil is used to test whether a sub-surface wireless charger is capable of delivering a particular amount of wireless power once the sub-surface wireless charger is installed in a surface. The testing device includes a variable load that can be adjusted to mimic a particular power consumption, such as 10 W, for example. The testing device then measures the actual amount of wireless power received by the receiver coil, e.g., based on the voltage across the receiver coil and the current flowing through the receiver coil to determine whether the particular amount of wireless power was delivered. In some embodiments the testing device is implemented together with an active alignment device inside the same device.

A testing device, such as active alignment devices300and700may include functionality to perform a full power test. During a full power test, the testing device aims to check whether a sub-surface wireless charger can provide the rated maximum power to a receiver.FIG. 9shows a schematic diagram of testing device900, according to an embodiment of the present invention. In some embodiments, testing device900may be implemented as a dedicated device. In other embodiments, testing device900may also be implemented as part of another device. For example,FIG. 9shows testing device900being implemented as part of active alignment device700.

As shown inFIG. 9, converter806power variable load Rload. During normal operation, variable load Rloadis configured such that testing device900consumes the maximum rate power that sub-surface wireless charger102is capable to provide. For example, if sub-surface wireless charger102is rated to provide 10 W, variable load Rloadis configured such that testing device900consumes 10 W. It is understood that the rated power of sub-surface wireless charger102may be different, such as higher 12 W, 15 W, 20 W, or higher, or lower, such as 8 W, 5 W, or lower.

Once testing device900is consuming the maximum rate power, the voltage across receiver coil710is amplified by amplifier502and then converted into digital data by ADC504. Controller506receives the digital data from ADC504and determines if the testing device900is actually consuming the maximum rated power. If yes, sub-surface wireless charger102has passed the full power test. If not, sub-surface wireless charger102has failed the full power test.

Testing device900monitors whether full power is being received by monitoring the voltage across receiver coil710. Some embodiments may monitor whether full power is be received by monitoring other apartments. For example, some embodiments may monitor voltage Vout, or the voltage at the output of the rectifier circuit804. Other implementations are also possible. For example, some embodiments may monitor the voltage across one or more sensing coils302.

Since testing device900is only used with high loading during a small portion of time (e.g., a few tens of milliseconds), testing device900may be implemented with relaxed thermal dissipation considerations, which may advantageously result in lower costs of manufacturing testing device900.

Sub-surface wireless charger102is configured to provide power across surface104. A particular model of sub-surface wireless charger may be installed in different surfaces having different thicknesses, such as tables having thicknesses of 10 mm, 15 mm, 18 mm, 20 mm, 25 mm, or more. Since the coupling coefficient decreases as the distance between transmitter coil108and receiver coil110increases, the amount of power that receiver106receives when receiving power across a relatively short distance (e.g., 10 mm thick surface) may be substantially larger than the amount of power that receiver106receives when receiving power across a relatively large distance (e.g., 20 mm thick surface). If the wireless power received by receiver106is too low, receiver106may not operate properly. If the wireless power received by receiver106is too high, receiver106may not operate properly, get damage and/or produce a safety hazard.

Sub-surface wireless charger102may use a ping before beginning to wirelessly transmit power to receiver106. During the ping process, a pulse of energy is sent by sub-surface wireless charger102. Receiver106receives the pulse of energy and wirelessly transmits back to sub-surface wireless charger102information related to the amount of power received, such as, for example, information about the voltage across receiver coil110. Such communication from receiver106to sub-surface wireless charger102may be accomplished by using load modulation of a load coupled to receiver coil110.

The ping process may be used, for example, to determine whether sub-surface wireless charger102and receiver106are compatible to each other, to determine whether it is safe for sub-surface wireless charger102to begin wirelessly charging receiver106, and to determine the amount of power to be transmitted. For example, if during the ping process, sub-surface wireless charger102determines that the amount of power received by receiver106is too low, it may begin charging at a higher power. If during the ping process, sub-surface wireless charger102determines that the amount of power received by receiver106is too high, it may begin charging at a lower power or not begin charging.

It is possible, however, that the energy pulse sent during the ping process may be so high that risks causing damage to receiver106and/or produce a safety hazard. Therefore, it may be advantageous to keep the voltage produced across receiver coil110during an energy pulse during the ping process within an operating voltage range (e.g., between 3 V and 9 V).

FIG. 10shows waveforms1000of a voltage across receiver coil710during a ping process, according to an embodiment of the present invention. Curve1002shows the voltage across receiver coil710.

As shown inFIG. 10, ping energy pulse1004includes an overshoot portion and a steady state portion and lasts for time tping. During normal operation, voltage Vpingacross the receiver coil during the steady state portion of ping energy pulse1004is within an operating range. In some embodiments, the operating range is between 3V and 9 V. Other ranges are also possible.

During the steady state portion of ping energy pulse1004, data may be transferred from receiver coil710to sub-surface wireless charger102during data transmission portion1006, which lasts tdata. Data may be transmitted from receiver coil710to sub-surface wireless charger102, for example, by load modulation. Such data is received by sub-surface wireless charger102and detected, e.g., by monitoring the voltage across transmitter coil110. For example, load modulation may generate variations in the voltage across receiver coil110during the data transmission portion1006(e.g., at frequencies between 1 kHz and 2 kHz). Such voltage variations are inductively coupled to transmitter coil108, which exhibits corresponding variations in the voltage across transmitter coil108. Such variations in voltage across transmitter coil108may be detected by sub-surface wireless charger102.

In an embodiment of the present invention, a programmable sub-surface wireless charger is configured to generate an initial ping having an initial default ping power that is low enough to be safe, even in situations where a receiver and the sub-surface wireless charger are very close to each other (e.g., at 5 mm or less). A testing device equipped with a high inductance receiver coil receives the initial ping and transmits to the sub-surface wireless charger a programming command to reprogram the default ping power based on the voltage measured across the receiver coil of the testing device during a calibration procedure. The sub-surface wireless charger receives the reprogrammed command and changes the default ping power from the initial default ping power to an operating default ping power, where the operating default ping power is configured to generate a voltage across a receiver coil of a receiver within safe operating limits (e.g., between 3 V and 9 V). The new default setting is written in, e.g., non-volatile memory of the sub-surface wireless charger. In some embodiments, the sub-surface wireless charger is configured to not begin wirelessly charging until the testing device successfully reprograms the sub-surface wireless charger during the calibration procedure.

FIG. 11Ashows testing device1106and programmable sub-surface wireless charger1102, according to an embodiment of the present invention.FIG. 11Bshows a schematic diagram of programmable sub-surface wireless charger1102and testing device1106, according to an embodiment of the present invention. In some embodiments, testing device1100may be implemented as a dedicated device. In other embodiments, testing device1100may also be implemented as part of another device such as testing device900and/or active alignment device700.

During normal operation before calibration, programmable sub-surface wireless charger1102defaults to producing a safe energy pulse during the ping process. For example, controller1118causes driver1116drive transmitter coil1108to produce a safe energy pulse having a low energy during the ping process, where the amount of energy of the safe energy pulse is stored, e.g., in non-volatile memory1114. The safe energy pulse may have such a low energy that it is configured to produce a voltage across a receiver coil (e.g., receiver coil110) that is smaller than a lower limit of an operating voltage range (e.g., lower than 3 V) when the thickness of surface104is, e.g., 20 mm. By using a safe energy pulse, programmable sub-surface wireless charger1102advantageously prevents a user from damaging a receiver due to inadvertently placing the receiver at a very close distance from programmable sub-surface wireless charger1102(e.g., such as a distance of 5 mm or closer).

During installation, a user, such as a human, may use testing device1106to reprogram programmable sub-surface wireless charger1102such that the voltage Vpingacross a receiver coil (e.g., receiver coil110) is within the operating range (e.g., between 3 V and 9 V). To compensate for the low power of the default energy pulse, testing device1106includes high inductance receiver coil1110, which increases the coupling coefficient between transmitter coil1108and receiver coil1110and advantageously allows testing device1106to interact with sub-surface wireless charger1102during a calibration process. In some embodiments, testing device1106is powered by programmable sub-surface wireless charger1102during the calibration process.

During installation, testing device1106performs a calibration process. The calibration process begins by having testing device1106placed on top surface104a, e.g., at a location of maximum coupling coefficient. Testing device1106then receives the energy pulse from programmable sub-surface wireless charger1102via high inductance receiver coil1110. Controller1120determines the voltage across high inductance receiver coil1110, using, e.g., an ADC (not shown), and transmits data associated with the measured voltage to programmable sub-surface wireless charger1102, e.g., during data transmission portion1006, using, e.g., load modulation. In some embodiments, controller1120causes the load modulation to communicate with programmable sub-surface wireless charger1102using communication interface1122.

The data transmitted from testing device1106to programmable sub-surface wireless charger1102during the data transmission portion1006may include, for example, the voltage measured, an identification code identifying testing device1106as a testing device, and a command code. In some embodiments, the command code may be used, for example, to cause programmable sub-surface wireless charger1102to reprogram the default amount of energy producing during the ping process such that the ping voltage Vpingto be produced across receiver coil106is within a safe operating range, e.g., based on the measured voltage across receiver coil1106. The new default energy value of the energy pulse may be stored, e.g., in non-volatile memory1114.

Once programmable sub-surface wireless charger1102is reprogrammed to a new default value, a new energy pulse may be sent with the new default value. Once, e.g., testing device1106determines that the new default value produces a voltage across a receiver coil (e.g., such as receiver coil110) that is within the operating range, testing device1106sends a command, e.g., during the data transmission portion1006, to cause programmable sub-surface wireless charger1102to write into non-volatile memory1114the new default value.

After the calibration process, programmable sub-surface wireless charger1102uses the new default energy value as the energy of the pulse during a ping process during normal operation, and may operate in a similar manner as sub-surface wireless charger102.

In some embodiments, programmable sub-surface wireless charger1102is configured to not begin wireless charging, even in the presence of receiver106, until programmable sub-surface wireless charger1102is reprogrammed by testing device1106during the calibration process.

In some embodiments, programmable sub-surface wireless charger1102includes a DIB switch, potentiometer, or other means for a user to manually program the default value of the voltage Vping. In such embodiments, testing device1106may provide an indicator, such as a visual indicator, to indicate to a user whether the voltage Vpingis too high, too low, or acceptable.

It is understood that the high inductance value of high inductance receiver coil1106causes the voltage produced across high inductance receiver coil1106to be higher than the voltage that would have been produced across a conventional receiver coil, such as receiver coil110. Testing device1106may compensate for such a difference by taking into account the difference in inductance between the high inductance receiver coil1106and receiver coil110. For example, in an embodiment, the inductance value of high inductance receiver coil1106may be 24 μH while the inductance value of receiver coil110may be 8 μH. In such embodiment, the voltage measured across high inductance receiver coil1106may be compensated by a factor of 4 when adjusting the new default value of programmable sub-surface wireless charger1102such that the voltage across receiver coil110falls within the operating range. Other inductance values are also possible. For example, in some embodiments, receiver coil1106may be implemented without a high inductance coil, such as receiver coil110.

By using a testing device and a programmable sub-surface wireless charger, some embodiments advantageously allow for producing an energy pulse during a ping process that produces a voltage across a receiver coil that is within an operating range (e.g., 3 V to 9 V). Advantageously, the same model of programmable sub-surface wireless charger may be used in surfaces of various thicknesses (e.g., from 10 mm to 25 mm) while achieving a voltage across the receiver coil that is within an operating range. Using a testing device and a programmable sub-surface wireless charger, thus, advantageously allows for causing a sub-surface wireless charger to comply with standards related to ping voltages, such as the Qi standard.

FIG. 12shows a flowchart of embodiment method1200of calibrating a programmable sub-surface wireless charger, according to an embodiment of the present invention. Method1200may be implemented, for example, by sub-surface wireless charger1102and testing device1106. Other wireless chargers and receivers may implement method1200.

During step1202, a programmable sub-surface wireless charger detects the proximity of a receiver. Proximity of a receiver may be detected, for example, by detecting a change in inductance of the transmitter coil of the programmable sub-surface wireless charger. Some embodiments may detect proximity of a receiver in other ways, such as by monitoring other characteristics of the transmitter coil of the programmable sub-surface wireless charger, such as the series resistance of the transmitter coil of the programmable sub-surface wireless charger, using a sensing coil, an external sensor, or in any other way.

Once a receiver has been detected, the programmable sub-surface wireless charger generates a safe pulse having a safe energy, where the safe energy may have such a low energy that it is configured to produce a voltage across a receiver coil that is smaller than a lower limit of an operating voltage range (e.g., lower than 3 V) when the distance between the programmable sub-surface wireless charger and the receiver is higher than a minimum operating distance (e.g., higher than 15 mm).

During step1206, the programmable sub-surface wireless charger determines whether the receiver is a calibration device or not. In some embodiments, programmable sub-surface wireless charger determines whether the receiver is a calibration device based on whether the receiver responds to the safe pulse and/or whether the receiver transmits an identification code to the programmable sub-surface wireless charger (e.g., using load modulation).

If the receiver is not a calibration device, the programmable sub-surface wireless device returns to step1202, repeating the sequence. If the receiver is a calibration device, calibration process1214takes place.

During step1208, the calibration device measures the voltage across a receiver coil of the calibration device and reports date based on such voltage measurement to the programmable sub-surface wireless charger (e.g., using load modulation). During step1210, the programmable sub-surface wireless charger adjusts the energy value of the energy pulse based on the data received from the calibration device. In some embodiments, the programmable sub-surface wireless charger generates during step1210a new energy pulse with the adjusted energy value and the calibration device measures the voltages across the receiver coil of the calibration device and transmit associated data back to the programmable sub-surface wireless charger to verify that the adjusted energy value of the energy pulse causes the voltage across a receiver coil to be within operating parameters, where the adjusted energy value is higher than the energy value of the safe pulse.

Once the adjusted energy value of the energy pulse is determined, the adjusted energy value is stored in non-volatile memory during step1212to be used for operating pulses during the ping process of wireless charging.

After calibration process1214concludes, the programmable sub-surface wireless charger operates in a similar manner as sub-surface wireless charger102, the sub-surface wireless charger detects the proximity of a receiver during step1216, begins a ping process using an operating pulse having the adjusted energy value during step1218, and begins wireless charging based on the ping process during step1220.

Sub-surface wireless charger102is typically configured to transmit power to receiver106that is located at an operating distance, e.g., between 15 mm and 25 mm, such as 20 mm. During normal operation, therefore, the coupling coefficient between sub-surface wireless charger102and receiver106is typically low, such as 0.1 or 0.2. It is possible, however, that a user may bring receiver106into close proximity to the sub-surface wireless charger102, such as in contact or at a distance of 1 mm or 2 mm, for example. For example, a user may detach sub-surface wireless charger102from surface104and bring receiver106and sub-surface wireless charger102into contact.

If receiver106and sub-surface wireless charger102come into very close proximity (e.g., less than 5 mm), the coupling coefficient between sub-surface wireless charger102and receiver106may increase to, e.g., 0.5, 0.8, 0.9 or higher. The voltage across receiver coil110caused by sub-surface wireless charger102when the coupling coefficient is 0.9 may be 9 times higher than the voltage across receiver coil110caused by sub-surface wireless charger102when the coupling coefficient is 0.1. Therefore, receiver106in such a scenario may get damage and/or create a safety hazard. Such damage may be caused by sub-surface wireless charger102actively transferring power to receiver106, as well as by sub-surface wireless charger102generating an energy pulse during the ping process, for example.

The inductance of transmitter coil108may be modified when a receiver coil is in close proximity to transmitter coil108. For example, a receiver coil that includes a ferrite material may cause the inductance of the transmitter coil to increase.

In an embodiment of the present invention, a protection circuit of a sub-surface wireless charger determines whether a receiver is unsafely close to the sub-surface wireless charger based on one or more changes in the characteristics of the transmitting coil of the sub-surface wireless charger. If it is determined that the receiver is unsafely close to the sub-surface wireless charger, the sub-surface wireless charger does not proceed with the ping process and subsequent wireless charging. The sub-surface wireless charger measures or determines the one or more characteristics of the transmitting coil by generating a protection pulse with low enough energy to be safe at very close distances, such as when the sub-surface wireless charger and the receiver are in contact with each other, and by measuring or detecting one or more properties of the oscillations that result from the protection pulse.

In some embodiments, the sub-surface wireless charger measures or determines the resonance frequency, the change in resonance frequency with respect to a predetermine resonance frequency value, the inductance of the transmitter coil, the change in inductance of the transmitter coil with respect to a predetermined inductance value, the damping factor, the change in damping factor with respect to a predetermined damping factor value, the quality factor, and/or the change in quality factor with respect to a predetermined quality factor value.

FIG. 13shows a schematic diagram of protection circuit1300of sub-surface wireless charger102, according to an embodiment of the present invention. Protection circuit1300may also be implemented in other sub-surface wireless chargers, such as programmable sub-surface wireless charger1102, as well as other types of wireless chargers. Protection circuit1300includes capacitor1302, driver1304, amplifier1306, ADC1308, controller1310, and non-volatile memory1314. Capacitor1302may be used as the resonant capacitor for power transfer.

During normal operation, before beginning to transmit wireless power and before sending the energy pulse during the ping process, protection circuit1300determines one or more characteristics of transmitter coil108and then determines whether it is safe to proceed with the ping process and subsequent wireless charging. For example, in some embodiments, before beginning to transmit wireless power and before sending the energy pulse during the ping process, controller1310causes driver1304to charge capacitor1302(e.g., to 3 V) while switch1312is open. Once capacitor1302is charged (e.g., once capacitor1302reaches a predetermined voltage), controller1310closes switch1312, which causes transmitter coil108to generate a wireless power pulse of low intensity (e.g., a protection pulse). The resonant tank that includes transmitter col108and capacitor1302then oscillates according to its resonance frequency.

Since the resonance frequency is based on the inductance of transmitter coil108, some embodiments determine the inductance of transmitter coil108by measuring the resonance frequency of the oscillations caused by the protection pulse. Such inductance is then compared with a predetermined inductance stored in memory1314to determine whether receiver106is too close. If controller1310determines that receiver106is too close, it takes action, such as preventing wireless charging and the ping process to start.

Switch1312is configured to connect/disconnect nodes N1and N2to/from each other, as shown inFIG. 13. Switch1312may be implemented with a transistor, solid state relay, or in any other way known in the art. In some embodiments, a first switch coupled between node N1and ground, and a second switch coupled between N2and ground are used instead of switch1312.

FIG. 14Ashows curve1402that illustrates the change in inductance ΔL of transmitter coil108versus distance between sub-surface wireless charger102and receiver106, according to an embodiment of the present invention. The change in inductance ΔL may correspond to the difference between the measured inductance of transmitter coil108when receiver106is at a particular distance and a predetermined inductance Lo. In some embodiments, the predetermined inductance Lois determined during manufacturing or testing of sub-surface wireless charger102, for example.

As shown by curve1402, when receiver106is very far from sub-surface wireless charger102, the inductance of transmitter coil108is equal to the predetermined inductance Lo. As receiver106gets closer to sub-surface wireless charger102, the inductance of transmitter coil108increases. When inductance change ΔL is greater than threshold ΔL1, controller1310determines that receiver106is too close and, e.g., prevents the ping process and subsequent charging to occur.

In some embodiments, the predetermined inductance Lois determined and stored in memory1314during testing or manufacturing of sub-surface wireless charger102. It is understood that the value of Loand/or ΔL may not indicate an exact inductance value. For example, in some embodiments, another value based on the inductance, such as a resonance frequency fothat corresponds to Lomay be stored in memory1314. Other implementations are also possible.

Driver1304is configured to produce a voltage across capacitor1302and may be implemented in any way known in the art. For example, in some embodiments, an LDO or other converter or circuit may be used to charge capacitor1302.

Controller1310is configured to determine whether it is safe to begin the ping process and subsequent wireless charging. In some embodiments, controller1310may be implemented together with a central controller of sub-surface wireless charger102. Controller1310may be implemented in any way known in the art. For example, some embodiments may implement controller1310with a general purpose controller. Other embodiments may implement controller1310using a digital signal processor (DSP) or a field programmable gate array (FPGA). Yet other embodiments may implement controller506using custom logic, such as an application-specific integrated circuit (ASIC). Other implementations are also possible.

In some embodiments, the presence of metal, e.g., from the case of a receiver, may cause the inductance of transmitter coil108to decrease. For example,FIG. 14Bshows curve1403that illustrates the change in inductance ΔL of transmitter coil108versus distance between sub-surface wireless charger102and metal, according to an embodiment of the present invention. Therefore, some embodiments may prevent the ping process and subsequent charging to start when the change in inductance ΔL of transmitter coil108is below a second threshold ΔL2.

Some embodiments only allow the ping process to start when the change in inductance ΔL of transmitter coil108is below threshold ΔL1and above the second threshold ΔL2.

Materials like aluminum typically cause a change in the inductance of transmitter coil108when in close proximity to transmitter coil108. Some materials, such as iron, may not cause a big change in the inductance of transmitter coil108when in close proximity to transmitter coil108. However, materials such as iron may cause the series resistance Rsof transmitter coil108to increase, thus affecting the damping factor of the oscillations caused by the protection pulse.

In some embodiments, controller1310may prevent the ping process and subsequent wireless charging to start when the series resistance of transmitter coil108is above a predetermined threshold RT. Controller1310may determine the series resistance Rs (or a change of series resistance ΔR) of transmitter coil108by determining the damping factor ζ (or a change in damping factor Δζ) of the oscillations generated by the protection pulse and/or by determining the quality factor Q (or a change in quality factor ΔQ) of the resonant tank that includes transmitter coil108and capacitor1302. It is understood that predetermined values that correspond to series resistance, damping factor, quality factor, and/or resonance frequency to aid in determining the change of the corresponding series resistance, damping factor, quality factor, and/or resonance frequency may be stored in memory1314.

In some embodiments, controller1310may combine information from the damping factor, quality factor, resonance frequency and/or inductance of transmitter coil108to determine whether or not to allow the ping process to start.

In some embodiments, controller1310causes a plurality of protection determinations before allowing the ping process to start. For example, in some embodiments, controller1310may determine at two, three, or more different times the change in inductance ΔL before determining that it is safe to start the ping process. For example, in some embodiments, controller1310may only allow the ping process to start when the change in inductance ΔL is between thresholds ΔL1and ΔL2for three consecutive protection determinations.

Although the protection determinations in this example only refers to a change in inductance, it is understood that changes in series resistance, quality factor, and/or resonance frequency may also be used.

In some embodiments, each protection determination is made every, e.g., 400 ms. Other times, such as smaller than 400 ms, higher than 400 ms are possible. In some embodiments, the time between each protection determination varies.

Advantages of some embodiments include the capability of the sub-surface wireless charger of detecting whether a receiver is unsafely close, and protecting such receiver from damage that may have been caused by beginning the ping process or wireless charging the receiver when the receiver is unsafely close. The sub-surface wireless charger is capable of detecting whether the receiver is unsafely close based on various characteristics that advantageously allow for the detection of different receivers that includes different materials, such as iron or aluminum.

FIG. 15shows a flowchart of embodiment method1500of protecting a receiver, according to an embodiment of the present invention. Method1500may be implemented, for example, by sub-surface wireless charger102or1102. Other wireless chargers may implement method1500.

During step1502, a sub-surface wireless charger, such as wireless charger102, detects the proximity of receiver1502. Proximity may be detected, for example, by detecting a change in inductance of transmitter coil108. Some embodiments may detect proximity of a receiver in other ways, such as by monitoring other characteristics of transmitter coil108, such as the series resistance, using a sensing coil, an external sensor, or in any other way.

During step1504, the sub-surface wireless charger generates a protective pulse, such as described with respect to protection circuit1200.

During step1506, the sub-surface wireless charger determines one or more changes in characteristics of the transmitter coil of the sub-surface wireless charger, such as transmitter coil108. The characteristics that may be determined include a change in inductance, resonance frequency, damping factor, and/or quality factor.

In some embodiments, step1506may be repeated. For example, in some embodiments, step1506is repeated until the value of the determination does not vary (e.g., until the determination of the change in inductance ΔL is the same three consecutive times). In other embodiments, step1506is repeated a fixed number of times (e.g., three times). Other implementations are also possible.

The change in the one or more characteristics of the transmitter coil is compared with safe limits during step1508. For example, in some embodiments, three consecutive determinations of the change in inductance ΔL are compared with thresholds ΔL1and ΔL2.

If the one or more characteristics of the transmitter coil are outside the safe limits, the sub-surface wireless charger may wait during step1510, and retest the system by generating a protective pulse during step1504. In some embodiments, the sub-surface wireless charger may stop retesting the system after a finite number of tries, such as three, for example.

If the one or more characteristics of the transmitter coil are inside the safe limits, the sub-surface wireless charger starts the ping process, e.g., in compliance with a standard, such as the Qi standard, by generating a ping1512. The wireless charger then adjusts the power based on the ping process during step1514and then begins the wireless charging during step1516.

A receiver, such as receiver106, may include a protection circuit to protect receiver against damage. For example,FIG. 16shows receiver106operating during the ping process at different voltages across coil110, according to an embodiment of the present invention. When the voltage is too low (below voltage V1) or to high (above voltage V2), receiver106may not transmit any data during the data transmission portion1006of the ping energy pulse1004. Between voltages V1and V2, receiver106transmits data during the data transmission portion1006, e.g., in accordance with a particular standard, such as the Qi standard. For voltages above voltage V3, receiver106may self-protect, e.g., by connecting and disconnecting detuning capacitors to/from receiver coil110to try to limit the voltage across receiver coil110. Above voltage V4, damage may occur.

The self-protection mechanism of connecting/disconnecting detuning capacitors to/from receiver coil110may also occur, e.g., during wireless charging when the voltage across receiver coil110is higher than voltage V3.

In some embodiments, voltage V1may be 3 V, voltage V2may be 15 V, voltage V3may be 16 V, and voltage V4may be 20 V. Other voltages may also be used.

In an embodiment of the present invention, a multi-ping method is used to determine whether a receiver is too close to a sub-surface wireless charger. A first ping with a first energy is generated. A second ping with a second energy is generated after the first ping, where the second energy is higher than the first energy. If the sub-surface wireless charger receives data from the receiver during the first ping but not during the second ping, it is determined that the receiver is too close to the sub-surface wireless charger.

FIG. 17shows a flowchart of embodiment method1700of protecting a receiver, according to an embodiment of the present invention. Method1700may be implemented, for example, by sub-surface wireless charger102or1102. Other wireless chargers may implement method1700.

During step1702, a sub-surface wireless charger generates a first ping having a first energy. The initial first energy may correspond to a default ping energy, e.g., determined during calibration with testing device1106. If the sub-surface wireless charger does not receive a response from the receiver during step1704, the sub-surface wireless charger increases the first energy during step170-6and sends a new first ping during step1702with the increased first energy. Steps1706and1702are repeated until the receiver responds, until a maximum number of repetitions (e.g., 5) or until a maximum first energy is used). In some embodiments, the sub-surface wireless charger determines whether the receiver has responded based on whether data has been received during the data transmission portion1006of the ping.

If the sub-surface wireless charger receives a response from the receiver during step1704, the sub-surface wireless charger generates a second ping having a second energy, where the second energy is higher than the first energy. During step1710, the sub-surface wireless charger checks whether a response from the receiver has been received. If not, it is determined during step1714that the receiver is too close. If yes, the sub-surface wireless charger proceeds to begin wireless charging during step1712.

Although method1700has been illustrated with two pings (the first ping and the second ping), more pings may be used in some embodiments.

In some embodiments, a sub-surface wireless charger determines that a receiver is too close by detecting the detuning by the receiver. The sub-surface wireless charger determines whether the receiver is performing detuning by monitoring a voltage across a transmitter coil of the sub-surface wireless charger and determining whether a signal with a frequency lower than a first frequency (e.g., 1 kHz) has a first energy higher than an energy threshold. For example, in some embodiments, an amplitude modulation of 2 Vppat 100 Hz across the transmitter coil is indicative of receiver detuning.

Detuning is the process by which a receiver reduces the voltage across the receiver coil by connecting and disconnecting capacitors to the receiver coil. The connecting and disconnecting the capacitors to the receiver coil modulates the voltage across the receiver coil, which in turn may be inductively coupled to the transmitter coil of the sub-surface wireless charger and may be detected by the sub-surface wireless charger. For example,FIG. 18shows curves1002and1806illustrating the voltage across receiver coil110during a ping process, with and without detuning, respectively, according to an embodiment of the present invention.

As shown by curve1002and1802, the frequency content during the data transmission portion1006during a ping process without detuning is higher than the frequency content during the data transmission portion1806during a ping process with detuning. For example, without detuning, the data may be modulated at frequencies between 1 kHz and 2 kHz, as shown by curve1002. Detuning exhibits voltage variations at frequencies below 1 kHz during the data transmission portion1806, such as frequencies between 15 Hz and 1 kHz, as shown by curve1802.

In some embodiments, sub-surface wireless charger102may detected the detuning by monitoring the frequency content of the voltage across transmitter coil108during the time in which the data transmission portion1006of the ping is expected. The frequency may be determined by sampling the voltage with an ADC and performing digital computations, by performing an FFT, by measuring the time between peaks of the voltage across transmitter coil108, by detecting zero crossings of the voltage across transmitter coil108and measuring the time between zero crossings, or any other way known the art. In some embodiments, sub-surface wireless charger102may detected the detuning by monitoring the frequency content of the voltage across transmitter coil108during the time in which the data transmission portion1006is not expected.

FIG. 19shows a flowchart of embodiment method1900of protecting a receiver, according to an embodiment of the present invention. Method1900may be implemented, for example, by sub-surface wireless charger102or1102. Other wireless chargers may implement method1900.

During step1902, a sub-surface wireless charger generates a first ping having a first energy. The initial first energy may correspond to a default ping energy, e.g., determined during calibration with testing device1106. If the sub-surface wireless charger detects detuning (e.g., by identifying the presence of a signal with a frequency between 15 Hz and 1 kHz) during step1904, the sub-surface wireless charger determines that the receiver is too close during step1906.

If the sub-surface wireless charger does not detect detuning during step1904, the sub-surface wireless charger generates a second ping having a second energy, where the second energy is higher than the first energy. During step1910, the sub-surface wireless charger checks whether detuning is detected. If yes, it is determined during step1906that the receiver is too close. If no, the sub-surface wireless charger proceeds to begin wireless charging during step1912.

In some embodiments steps1908and1910may be omitted. In other embodiments, more than two pings may be used to before step1912.

In some embodiments, sub-surface wireless charger102may detect whether the receiver is too close during wireless charging by detecting detuning by receiver106. For example,FIG. 20shows curves2002and2006illustrating the voltage across receiver coil110during wireless charging, with and without detuning, respectively, according to an embodiment of the present invention. As shown by curve2002, after the ping energy pulse1004, sub-surface wireless charger102begins the wireless charging2004. During wireless charging2004, receiver106sends data to sub-surface wireless charger102during data transmission portion1006. Such data may be used by sub-surface wireless charger102for various purposes, such as to adjust the power transfer level.

In some embodiments, if receiver106abruptly moves closer to sub-surface wireless charger102at time tm, the voltage across receiver coil110increases and receiver106may self-protect by detuning, such as shown by portion2010of curve2006. Sub-surface wireless charger102may detect such detuning and stop wireless charging.

FIG. 21shows a flowchart of embodiment method2100of protecting a receiver, according to an embodiment of the present invention. Method2100may be implemented, for example, by sub-surface wireless charger102or1102. Other wireless chargers may implement method2100.

During step2102, a sub-surface wireless charger monitors the voltage across the transmitter coil. In some embodiments, the voltage across the transmitter coil is periodically monitored. In other embodiments, the voltage across the transmitter coil is continuously monitored. If detuning is detected during step2104, it is determined during step2106that the receiver is too close, and action may be taken, such as stop wireless charging. If no detuning is detected during step2104, the voltage across the transmitter coil is monitored, repeating the sequence.

It is understood that methods1700,1900, and2100may be combined in various ways. For example,FIG. 22shows a flowchart of embodiment method2200of protecting a receiver, according to an embodiment of the present invention. Method2200may be implemented, for example, by sub-surface wireless charger102or1102. Other wireless chargers may implement method2200. Other implementations are also possible.

In some embodiments, sub-surface wireless charger102may be implemented as an inductive wireless charger that transmits wireless power at, e.g., frequencies between 80 kHz and 300 kHz, such as a frequency between 110 kHz and 205 kHz, for example. In other embodiments, sub-surface wireless charger102may be implement as a resonant wireless charger that transmits wireless power at higher frequencies, such as frequencies higher than 1 MHz, such as 6.78 MHz or higher, for example.

In an embodiment of the present invention, a two-part wireless charger includes a sub-surface wireless charger disposed at a first surface of a surface, and a repeater charger disposed at a second surface of a surface. The sub-surface wireless charger transfers wireless power to the repeater charger and through the surface using resonance charging (e.g., at a frequency of 6.78 MHz). The repeater charger receives power from the sub-surface wireless charger and transmits wireless power to a receiver using inductive wireless charging (e.g., at a frequency between 80 kHz and 300 kHz). By using a repeater charger, the two-part wireless charger is advantageously capable to provide wireless power to a receiver when the surface is relatively thick (e.g., thicker than 20 mm, such as 25 mm, 30 mm, or thicker). The repeater charger also allows for limiting the exposure of the receiver to magnetic field to just a limited area, thus, advantageously preventing heating of the metal enclosure or other metallic elements in the vicinity of the receiver coil.

FIG. 23shows a schematic diagram of sub-surface wireless charging system2300that includes two-part wireless charger2302, according to an embodiment of the present invention. Two part wireless charger2302includes sub-surface wireless charger2304and repeater charger2306.

During normal operation sub-surface wireless charger2304transmits wireless power to repeater charger2306. Repeater charger2306receives the wireless power from sub-surface wireless charger2304and transmits wireless power to receiver106. Receiver106receives wireless power, e.g., in a similar manner as described with respect toFIG. 1.

By using repeater charger2306, two-part wireless charger2302is advantageously capable to transmit wireless power at distances of, e.g., 30 mm, or higher. For example, in some embodiments, two part wireless charger2302is capable of efficiently wirelessly transfer power across surface104when thickness d1is 30 mm or higher. For example, in some embodiments, two part wireless charger2302transfer power across surface104when thickness d1is 30 mm at an efficiency higher than 50%.

In some embodiments, sub-surface wireless charger2304operates as a resonant wireless charger at a first frequency and repeater charger2306receives the wireless power from sub-surface wireless charger2304at the first frequency and generates wireless power at a second frequency lower than the first frequency while operating as an inductive wireless charger. In such embodiments, receiver106receives wireless power from repeater charger2306at the second frequency. In some embodiments, the first frequency is 6.78 MHz and the second frequency is between 80 kHz and 300 kHz. Other frequencies may also be used.

FIGS. 24 and 25show transmitter coil2402of sub-surface wireless charger2304and repeater coils2502and2504of repeater charger2306, respectively, according to an embodiment of the present invention. Specific winding details are omitted for clarity purposes

Transmitter coil2402may implemented as planar coil, such as a PCB antenna. Other implementations, such as using stamped metal, or Litz wires may also be used.

In some embodiments, ferrite layer2404may be disposed below at least portions of transmitter coil2402or all of transmitter coil2402. In some embodiments, ferrite layer2404is used to increase the coupling coefficient between transmitter coil2402and repeater coil2502, which may aid in efficient wireless transfer of energy. In some embodiments, ferrite layer2404may be much thinner than 1 mm, such as 0.1 mm or lower. Using a very thin ferrite layer2404in combination with a thin planar transmitter coil2404(such as implemented as traces in a PCB) advantageously allows for a low profile implementation (e.g., profile P1being less than 2 mm thick, such as 1 mm thick, or lower) of transmitter coil2402and ferrite layer2404.

As shown byFIG. 24, transmitter coil2402may have a square shape when viewed from the top. Other shapes, such as rectangular, circular, octagonal, or others, such as hollow shapes, including circular or oval ring shapes, hollow square shapes, hollow rectangular shapes, and others, may also be used.

As shown inFIG. 25, repeater charger2306includes repeater coils2502and2504. Repeater coil2502is configured to receive power from transmitter coil2402. The power received by repeater coil2502is used to power the transmission of wireless power by repeater coil2504.

In some embodiments, ferrite layer2508may be disposed on top of at least portions of repeater coil2502or all of repeater coil2502. In some embodiments, ferrite layer2508is used to increase the coupling coefficient between transmitter coil2402and repeater coil2502, which may aid in efficient wireless transfer of energy.

Repeater coil2502may have a hollow square shape when viewed from the top. Other hollow shapes, such as circular or oval ring shapes, hollow rectangular shapes, may also be used.

In some embodiments, the outer perimeter of repeater coil2502(e.g., the outer perimeter of the square ring shape of repeater coil2502) may be equal to the outer perimeter of transmitter coil2402(e.g., the perimeter of the square shape of transmitter coil2402). In other embodiments, the outer perimeter of repeater coil2502may be different (e.g., longer or shorter) than the outer perimeter transmitter coil2402.

Repeater coil2504may have a circular shape when viewed from the top. Other shapes, such as oval, square, rectangular, octagonal, or others, as well as hollow shaped, such as circular ring shapes, oval ring shapes, or hollow square, rectangular or octagonal shapes may also be used.

In some embodiments, ferrite layer2506may be disposed below at least portions of repeater coil2504or all of repeater coil2504. In some embodiments, ferrite layer2506is used to increase the coupling coefficient between repeater coil2504and receiver coil110, which may aid in efficient wireless transfer of energy.

FIG. 26shows a schematic diagram of sub-surface wireless charging system2600, according to an embodiment of the present invention. Sub-surface wireless charging system2300may be implemented as sub-surface wireless charging system2600.

During normal operation, transmitter coil2402transmits power to repeater coil2502using resonant wireless charging at a frequency of, e.g., 6.78 MHz. Repeater charger2406receives power from transmitter coil2402using repeater coil2502and rectifies it using diode bridge rectifier2602. Driver2604receives power from diode bridge rectifier2602and drives repeater coil2504. Repeater coil2504transmits power to receiver coil110using inductive wireless charging at a frequency, e.g., between 80 kHz and 300 kHz. Receiver106receives power from repeater coil2504using receiver coil110.

Diode rectifier bridge2602may be implemented in any way known in the art. Other rectification methods may also be used. For example, in some embodiments, a synchronous rectifier may be used.

Driver2604may be implemented in any way known in the art. For example, in some embodiments, driver2604may be implemented with a half bridge. In other embodiments, a full bridge may be used. In some embodiments, driver2604may operate as a class-E amplifier. Other implementations are also possible.

In some embodiments, repeater charger2306includes a controller that is used to demodulate data from receiver106and to control the power that is wirelessly transmitted to receiver106. For example,FIG. 27shows a schematic diagram of sub-surface wireless charging system2700, according to an embodiment of the present invention. Sub-surface wireless charging system2300may be implemented as sub-surface wireless charging system2700. Sub-surface wireless charging system2700may operate in a similar manner as sub-surface wireless charging system2600.

As shown inFIG. 27, repeater charger2706includes controller2702. During normal operation, controller2702demodulates data from receiver106, e.g., such as data received during data transmission portion1006. Controller2702then uses such data to adjust the amount of power transmitted by repeater coil2504. For example, if receiver106sends to repeater charger2706indicating that the voltage across receiver coil110is too high, controller2702then causes driver2604to reduce the amount of power transmitted by repeater coil2504.

In some embodiments, controller2702, in response to a request by receiver106to increase/decrease power, e.g., received during data transmission portions1006, adjusts the frequency at which power is transmitted by repeater coil2504. In some embodiments, controller2702instead of, or in addition to adjusting the frequency at which power is transmitted by repeater coil2504, causes driver2604to adjust the voltage at which it drives transmitter coil2504.

In some embodiments, controller2702implements foreign object detection (FOD). For example, in some embodiments, controller2702determines the average power transmitted by repeater coil2504and compares it with the average power received by receiver coil110. If the power difference between the transmitter power and the received power is higher than a threshold, controller2702determines that a foreign object (e.g., a metallic foreign object) is present and takes action, such as reducing the power transmitted by repeater coil2504or stopping wireless charging.

In some embodiments, a repeater charger includes a controller that requests sub-surface wireless charger2304to adjust the power transmitted by transmitter coil2402based on data that receiver106sends via receiver coil110. For example,FIG. 28shows a schematic diagram of sub-surface wireless charging system2800, according to an embodiment of the present invention. Sub-surface wireless charging system2300may be implemented as sub-surface wireless charging system2800. Sub-surface wireless charging system2800may operate in a similar manner as sub-surface wireless charging system2700.

As shown inFIG. 28, repeater charger2806includes controller2802and communication interface2804. During normal operation, controller2802demodulates data from receiver106, e.g., such as data received during data transmission portion1006. Controller2802then communicates some or all of the data received from receiver106to sub-surface wireless charger2304to cause sub-surface wireless charger2404to adjust the amount of power transmitted from transmitter coil2402to repeater coil2502based on data sent by receiver106via transmitter coil110. In such embodiments, controller2812of sub-surface wireless charger2304demodulates data received by transmitter coil2402from repeater coil2502and causes driver2812of sub-surface wireless charger2304to adjust the power transmitted by transmitter coil2402based on such data.

In some embodiments, controller2802may also use data received from receiver106to adjust the amount of power transmitted by repeater coil2504in a similar manner as controller1702.

In some embodiments, controller2802may implement FOD detection in a similar manner as controller2702. In some embodiments, when controller2802determines that a foreign object is present, controller2802transmits data indicative of the presence of a foreign object to sub-surface wireless charger2304via communication interface2804, e.g., to cause sub-surface wireless charger2304to reduce the amount of power transmitted by transmitter coil2402or to stop wireless charging (e.g., using controller2812and driver2810).

Communication interface2804is configured to transmit data to transmitter coil2402via repeater coil2502using, e.g., data modulation.

In some embodiments, a repeater charger does not include a micro-controller. For example,FIG. 29shows a schematic diagram of sub-surface wireless charging system2900, according to an embodiment of the present invention. Sub-surface wireless charging system2300may be implemented as sub-surface wireless charging system2900. Sub-surface wireless charging system2900may operate in a similar manner as sub-surface wireless charging system2600.

As shown inFIG. 29, repeater charger2906includes oscillator2902. During normal operation, repeater charger transmits wireless power using repeater coil2504without actively controlling the amount of power transmitted by repeater coil2504. For example, driver2604may drive repeater coil2504at a switching frequency based on oscillator2902and at a voltage that is based on the voltage received from diode bridge2602.

When receiver110transmits data via receiver coil110during data transmission portion1006, e.g., using load modulation, such data is propagated through repeater coil2504, driver2604, and diode bridge rectifier2602, causing a signal modulation in repeater coil2502, which in turn causes a signal modulation in transmitter coil2402. Such signal modulation in transmitter coil2402is received by a controller of sub-surface wireless charger2304(not shown), which demodulates data received by transmitter coil2402from repeater coil2502and causes a driver of transmitter coil2402(not shown) to adjust the power transmitted by transmitter coil2402based on such data.

It may be advantageous to implement FOD in a sub-surface wireless charger, e.g., for safety reasons. In a sub-surface wireless charger, such as sub-surface wireless charger102, FOD may be implemented for example, by determining the average power transmitted by transmitter coil108, determining the amount of power received by receiver coil110, and if the difference between the transmitted power and the receiver power is greater than a threshold, a foreign object is detected.

When sub-surface wireless charger102is implemented as an inductive charger (e.g., generating power at frequencies between 80 kHz and 300 kHz), sub-surface wireless charger102may determine the average power transmitted by transmitter coil108by measuring or determining the voltage across transmitter coil108and the current flowing through transmitter coil108. Since coupling coefficient of sub-surface wireless charger102may be small (e.g., lower than 0.2), and because the voltage across transmitter coil108and the current flowing through transmitter coil108may be out of phase, the magnitude of the voltage across transmitter coil108and the current flowing through transmitter coil108are generally big. For example, when sub-surface wireless charge102is transmitting 15 W to receiver106, the peak voltage across transmitter coil106may be 600 Vppand the peak current flowing through transmitter coil106may be 40 App.

In an embodiment of the present invention, a sub-surface wireless charger is disposed below a bottom surface of a surface. An FOD unit disposed at a top surface of a surface and having a sensing coil determines an average power at the top surface of the surface and transmits such information to the sub-surface wireless charger. The sub-surface wireless charger then determines whether a foreign object is present in the charging space when a difference between the average power determined by the FOD unit and the average power received by receiver106is greater than a threshold. Since the voltage/current induced across the sensing coil of the FOD unit is smaller than the voltage/current at the transmitter coil of the sub-surface wireless charger, the FOD advantageously determines the average power without measuring high voltages or currents. Avoiding measuring high voltage or currents to determine the average power may advantageously increase the accuracy of the measurement of the average power.

FIG. 30shows a schematic diagram of sub-surface wireless charging system3000, according to an embodiment of the present invention. Sub-surface wireless charging system3000includes sub-surface wireless charger3002and FOD unit3004. Sub-surface wireless charger3002may operate in a similar manner as sub-surface wireless charger102or1102.

During normal operation, FOD unit3004measures or determines the average power at top surface104a, e.g., by measuring the voltage across a sensing coil of FOD unit3004(not shown) and the current flowing through the sensing coil. FOD unit3004then transmits information indicative of the average power available at top surface104ato sub-surface wireless charger3002using, e.g., load modulation.

Since surface104generally does not include metallic objects, in some embodiments, determining whether a foreign (metallic) object is within the charging space includes only determining whether a foreign object is between FOD unit3004and receiver106. Such determination may be performed by determining the average power available at FOD unit3004, and comparing it with the average power received by receiver coil110. If the power difference between the power available at FOD unit3004and the power received by receiver coil110is higher than a threshold, it is determined that a foreign object is within the charging space of sub-surface wireless charging3002.

In some embodiments, FOD3004includes a mark to aid in finding the location of a maximum coupling coefficient between transmitter coil3006and receiver coil110.

FIG. 31shows sensing coil3102and circuit3104of FOD unit3004, according to an embodiment of the present invention. Specific winding details are omitted for clarity purposes.

As shown inFIG. 31, the sensing coil may have a hollow square shape when viewed from the top. Other hollow shapes, including circular or oval ring shapes, hollow rectangular shapes, and others, may also be used.

Circuit3104is configured to measure the available average power at FOD unit3004based on voltage across sensing coil3102and current flowing through sensing coil3102and transmits such information back to sub-surface wireless charger3002using, e.g., load modulation. Circuit3104may be implemented with a PCB, flex PCB, for example. AlthoughFIG. 31shows circuit3104implemented in a square area, other implementations, are also possible.

FIG. 32shows a schematic diagram of sub-surface wireless charging system3000, according to an embodiment of the present invention. As shown inFIG. 32, transmitter coil3006of sub-surface wireless charger3002transmits power. The power transmitted by transmitter coil3006is received by receiver coil110(not shown). Receiver106communicates with sub-surface wireless charger3002by, e.g., using load modulation. Sub-surface wireless charger3002receives information, such as power received by receiver106, and controls wireless charging based on such information, e.g., in a similar manner as sub-surface wireless charger102or1102, for example.

The power transmitted by transmitter coil3006is also received by sensing coil3102. Such power is used to power controller3206and communication interface3204via, e.g., diode bridge3202, and possibly a converter (not shown), such as an LDO, for example.

During normal operation, controller3206determines the average power available at the location of sensing coil3102by measuring the voltage across sensing coil3102and the current flowing through sensing coil3102using, e.g., an amplifier (not shown), and an ADC (not shown), for example. Controller3206then communicates with sub-surface wireless charger3002by modulating the load in accordance with the information to be transmitted (e.g., containing the measured average power).

Such load modulation creates variations in the voltage/current flowing through sensing coil3102which are coupled to transmitter coil3006and are demodulated by controller3212of sub-surface wireless charger3002. Since sub-surface wireless charger3002is also received information from receiver106about power being received by receiver106, e.g., by load modulation, sub-surface wireless charger3002is advantageously capable of detecting foreign objects between top surface104aand receiver106without monitoring voltages and current at transmitter coil3006.

FIG. 33shows curve3302illustrating communication between FOD unit3004and receiver106, and sub-surface wireless charger3002, according to an embodiment of the present invention.

As shown by curve3302, communication between receiver106and sub-surface wireless charger3002during wireless charging occurs during the data transmission portion1006(e.g., at frequencies between 1 kHz and 2 kHz). The time t1006of each data transmission portion1006may be, for example, between 1 ms and 25 ms. Longer times or shorter times are also possible.

The time T1006between each data transmission portion1006may be, for example, between 7 ms and 250 ms. Longer times or shorter times are also possible.

In an embodiment of the present invention, FOD unit3004performs load modulation to communicate with sub-surface wireless charger3002during FOD data transmission time3306in between data transmission portions1006. For example, in some embodiments, FOD unit3004monitors the time between data transmission portions1006by monitoring the voltage across sensing coil3102. For example, when the voltage across sensing coil3102varies at frequencies, e.g., between 1 kHz and 2 kHz, receiver106is communicating with sub-surface wireless charger3002during a data transmission portion1006. When the voltage across sensing coil3102does not vary at frequencies, e.g., between 1 kHz and 2 kHz, receiver106is not communicating with sub-surface wireless charger3002. FOD unit3004, then, performs load modulation to communicate with sub-surface wireless charger3002during FOD data transmission time3306in between data transmission portions1006.

FIG. 34shows a flowchart of embodiment method3400of communicating with a sub-surface wireless charger when the sub-surface wireless charger is communicating with a receiver, according to an embodiment of the present invention. Method3400may be implemented, for example, by FOD unit3004. Other devices may also implement method3400.

During step3402, a first device having a sensing coil, such as FOD unit3004, located in the charging space of a sub-surface wireless charger, monitors the sensing coil to detect data transmissions between a receiver and the sub-surface wireless charger. In some embodiments, the first device measures the voltage across the sensing coil and performs FFT to determine whether data transmission is occurring based on the frequencies present in the voltage across the sensing coil. For example, in some embodiments, data transmission causes the voltage across the sensing coil to vary at frequencies between 1 kHz and 2 kHz. In such embodiments, the first device determines that data transmission is occurring when frequencies between 1 kHz and 2 kHz are present in the voltage across the sensing coil.

During step3404, the first device identifies times of non-transmission. For example, in some embodiments, the first device determines the time between data transmissions by starting a timer when a data transmission ends and stops the timer when a new data transmission begins. The resulting time being the time of non-transmission. In other embodiments, the first device uses a time stamp and compares the time stamp with an RTC clock, for example. Other implementations are also possible.

During step3406, the first device communicates with the sub-surface wireless charger by performing load modulation using the sensing coil during the identified non-transmission times. For example, in some embodiments, the first device performs load modulation for a fixed amount of time, beginning a second time after the data transmission between the receiver and the sub-surface wireless charger ends. Other implementations are also possible.

A sub-surface wireless charger, such as sub-surface wireless charger102is configured to operate at low coupling coefficients between, such as 0.1, e.g., given the distance between sub-surface wireless charger and receiver102, e.g., based on the thickness of surface104. Increasing the coupling coefficient may be desirable, which may advantageously increase the amount of power that can be wirelessly transfer from sub-surface wireless charger102to receiver106.

In an embodiment of the present invention, a top-side ferrite sticker disposed between receiver106and top surface104aadvantageously increases the coupling coefficient between sub-surface wireless charger102and receiver106. For example,FIG. 35shows a schematic diagram of sub-surface wireless charging system3500including top-side ferrite sticker3502, according to an embodiment of the present invention.

As shown inFIG. 35, top-side ferrite sticker3502is disposed between top surface104aand receiver106. During normal operation, the ferrite material in top-side ferrite sticker3502increases the coupling coefficient between sub-surface wireless charger102and receiver106. In some embodiments, top-side ferrite sticker3502may double the coupling coefficient (e.g., from 0.1 to 0.2) between sub-surface wireless charger102and receiver106. In some embodiments, top-side ferrite sticker3502may include a mark or may otherwise be indicative of a location of maximum coupling coefficient between sub-surface wireless charger102and receiver106.

FIGS. 36 to 38show schematic diagrams of possible implementations of top-side ferrite sticker3502, according to embodiments of the present invention. Other shapes may also be used.

In some embodiments, distance d3502_2is between 80 mm and 100 mm, distance d33502_1is between 40 mm and 50 mm, and distance d3502_3is between 0.1 mm and 0.2 mm. Other dimensions are also possible.

Advantages of embodiments such as shown inFIG. 38includes that less material may be used while still substantially increasing the coupling coefficient between sub-surface wireless charger102and receiver106. For example,FIG. 39shows a way of cutting a strip of ferrite sticker3902to implement the top-side ferrite sticker ofFIG. 38with minimum waste, according to an embodiment of the present invention.

In some embodiments, wireless power transmission efficiency is increased by substantially reducing or eliminating the generation of Eddie currents in the enclosure of a sub-surface-wireless charger. In some embodiments, a metallic enclosure of a sub-surface wireless charger has an outer surface that is parallel to (i.e., tracks) the magnetic lines of the magnetic field generated by the transmitter coil during wireless charging. In some embodiments, at least a portion of an outer surface of the enclosure of the sub-surface wireless charger has a toroidal shape.

FIG. 40shows graph4000illustrating the magnetic field lines of sub-surface wireless charger102during wireless charging, according to an embodiment of the present invention. As shown by curves4002and4004, for example, the magnetic field lines of sub-surface wireless charger102during wireless charging has a toroidal shape at location4006.

Since sub-surface wireless charger102is configured to operate at a distance from receiver106that is relatively long (e.g., greater than 10 mm, such as 20 mm), the presence of receiver102does not substantially perturb the shape of the magnetic field lines of sub-surface wireless charger102during wireless charging. For example,FIG. 41shows graph4100illustrating the magnetic field lines of sub-surface wireless charger102during wireless charging in the presence of receiver106, according to an embodiment of the present invention. As shown by curves4102and4104, for example, the magnetic field lines of sub-surface wireless charger102during wireless charging has a toroidal shape at location4006and are substantially similar to curves4002and4004at location4006.

FIG. 42shows a perspective view of sub-surface wireless charger102, according to an embodiment of the present invention. As shown inFIG. 42, sub-surface wireless charger102includes metallic heatsink4202. Transmitter coil108(not shown inFIG. 42) is disposed on top of portion4204of metallic heatsink4202.

As shown inFIG. 42, outer portion4206of metallic heatsink4202has a toroidal shape that is substantially similar to the shape of the magnetic field lines generated by sub-surface wireless charger102during wireless charging (illustrated, for example, inFIGS. 40 and 41). The toroidal shape of metallic heatsink4202advantageously substantially reduces or eliminates Eddie currents generated in the metallic heatsink.

Metallic heatsink4202may be implemented using metals such as Nickle or Zinc. Other metals may also be used.

FIG. 43shows a bottom view of sub-surface wireless charger102, according to an embodiment of the present invention. As shown inFIG. 43, metallic heatsink4202includes a plurality of fins4302that advantageously aid in dissipating heat, e.g., generated during wireless charging.

FIG. 44shows a perspective view of sub-surface wireless charger102, according to an embodiment of the present invention. As shown inFIG. 44, transmitter coil108is disposed on top of heatsink4202and has a ring shape. PCB4402is also disposed on top of heatsink4202and includes sub-surface wireless charger102circuitry.

A device including: a plurality of sensing coils configured to receive wireless power from a sub-surface wireless charger; a measuring circuit coupled to the plurality of sensing coils and configured to sense a voltage across each of the plurality of sensing coils; a visual indicator; and a controller coupled to the measuring circuit and configured to: determine a direction of a location of maximum coupling coefficient between the sub-surface wireless charger and the device based on an output of the measuring circuit, and indicate the direction of the location of maximum coupling coefficient via the visual indicator.

The device of example 1, where the visual indicator includes a plurality of light emitting diodes (LEDs).

The device of one of examples 1 or 2, where the controller turns on all of the plurality of LEDs when the device is located at the location of maximum coupling coefficient between the sub-surface wireless charger and the device.

The device of one of examples 1 to 3, where the plurality of LEDs include N LEDs and the plurality of sensing coils include N sensing coils, where N is an integer number greater than 3.

The device of one of examples 1 to 4, where the measuring circuit includes an amplifier coupled to a sensing coil of the plurality of sensing coils, and an analog-to-digital converter (ADC) coupled to an output of the amplifier.

The device of one of examples 1 to 5, further including a mark that is symmetrically disposed with respect to the plurality of sensing coils.

The device of one of examples 1 to 6, further including a receiver coil, where the device is configured to be powered by the sub-surface wireless charger via the receiver coil.

The device of one of examples 1 to 7, further including a variable load, where the controller is further configured to: adjust the variable load to consume a predetermined amount of power; determine an amount of power received based on a voltage across the receiver coil and a current flowing through the receiver coil; and determine whether an actual amount of power received is at least equal to the predetermined amount of power.

The device of one of examples 1 to 8, where the receiver coil is a high inductance receiver coil, and where the controller is further configured to: receive a first pulse having a first energy from the sub-surface wireless charger; measure a voltage across the high inductance receiver coil; determine a calibration code based on the measured voltage; and transmit the calibration code to the sub-surface wireless charger via the high inductance receiver coil by load modulation.

A sub-surface wireless charger including: a non-volatile memory; a transmitter coil; and a controller configured to: before calibration, transmit a first pulse having a first energy via the transmitter coil during a ping process, during calibration, transmit the first pulse having the first energy via the transmitter coil, receive a calibration code via the transmitter coil, store data corresponding to a second energy in the non-volatile memory based on the received calibration code, where the second energy is higher than the first energy, and after calibration, transmit a second pulse having the second energy via the transmitter coil, during the ping process.

The sub-surface wireless charger of example 10, where the controller is configured to not begin wireless charging before calibration.

The sub-surface wireless charger of one of examples 10 or 11, where the controller is configured to transmit the first pulse after detecting a receiver is proximate the sub-surface wireless charger based on a characteristic of the transmitter coil.

A sub-surface wireless charger includes: a transmitter coil; and a controller configured to: generate a protective pulse having a first energy, determine a characteristic of the transmitter coil based on the generated protective pulse, determine whether it is safe to begin wireless charging based on the determined characteristic, when the controller determines that it is safe to begin wireless charging, generate an operating pulse having a second energy, where the second energy is higher than the first energy.

The sub-surface wireless charger of example 13, where the protective pulse is configured to avoid causing a receiver to transmit data to the sub-surface wireless charger via the transmitter coil.

The sub-surface wireless charger of one of examples 13 or 14, further including: a capacitor coupled to the transmitter coil; and a switch coupled to the transmitter coil, where the controller is configured to generate the protective pulse by: opening the switch, causing the capacitor to charge to a first voltage, and closing the switch to cause the capacitor and the transmitter coil to operate as a resonant tank.

The sub-surface wireless charger of one of examples 13 to 15, where the characteristic of the transmitter coil includes an inductance of the transmitter coil, a series resistance of the transmitter coil, or a damping factor of a resonant tank that includes the transmitter coil.

The sub-surface wireless charger of one of examples 13 to 16, further including: an amplifier coupled to the transmitter coil; and an analog-to-digital converter (ADC) coupled to an output of the amplifier, where the controller is configured to determine the characteristic of the transmitter coil based on an output of the ADC.

The sub-surface wireless charger of one of examples 13 to 17, where the controller is configured to determine that it is not safe to begin wireless charging when an inductance of the transmitter coil is higher than a first threshold or lower than a second threshold, and where the first threshold is higher than the second threshold.

A sub-surface wireless charger includes: a transmitter coil; and a controller configured to: generate a first pulse having a first energy, receive a first response from a receiver via the transmitter coil during the first pulse, generate a second pulse having a second energy, the second energy being higher than the first energy, and prevent the sub-surface wireless charger from beginning wireless charging the receiver if a second response is not received from the receiver via the transmitter coil during the second pulse.

A sub-surface wireless charger includes: a transmitter coil; and a controller configured to: generate a first pulse having a first energy, receive a first response from a receiver via the transmitter coil during the first pulse, cause the transmitter coil to be energized after the first pulse, while the transmitter coil is energized, determine whether the receiver is performing detuning, and stop energizing the transmitter coil or reduce an energy level flowing through the transmitter coil when the controller determines that the receiver is performing detuning.

The sub-surface wireless charger of example 20, where the controller determines whether the receiver is performing detuning by: monitoring a voltage across the transmitter coil; and determining whether a signal with a frequency lower than 1 kHz has a second energy higher than a threshold.

The sub-surface wireless charger of one of examples 20 or 21, where the controller is configured to cause the transmitter coil to be energized during a second pulse.

The sub-surface wireless charger of one of examples 20 to 22, where the controller is configured to cause the transmitter coil to be energized during wireless charging of the receiver.

A wireless charger including: a sub-surface wireless charger having a first transmitter coil; and a repeater charger having a receiver coil and a second transmitter coil, where the sub-surface wireless charger is configured to generate wireless power using the first transmitter coil at a first frequency, and where the repeater charger is configured to: receive wireless power from the sub-surface wireless charger using the receiver coil, power a first circuit using the received wireless power, and generate wireless power using the second transmitter coil at a second frequency that is different from the first frequency.

The wireless charger of example24, where the first frequency is higher than the second frequency.

The wireless charger of one of examples 24 or 25, where the first frequency is 6.78 MHz and the second frequency is between 80 kHz and 300 kHz.

The wireless charger of one of examples 24 to 26, where the second transmitter coil surrounds the receiver coil.

The wireless charger of one of examples 24 to 27, where the repeater charger includes a first ferrite layer disposed above the second transmitter coil and a second ferrite layer disposed below the receiver coil.

The wireless charger of one of examples 24 to 28, where the first circuit includes a rectifier coupled to the receiver coil, and a driver coupled between the rectifier and the second transmitter coil.

The wireless charger of one of examples 24 to 29, where the sub-surface wireless charger includes a ferrite layer disposed below the first transmitter coil, the ferrite layer having a thickness of about 0.1 mm or less.

The wireless charger of one of examples 24 to 30, where the first transmitter coil is formed as traces in a printed circuit board (PCB).

The wireless charger of one of examples 24 to 31, where an outer perimeter of the first transmitter coil is substantially equal to an outer perimeter of the receiver coil.

The wireless charger of one of examples 24 to 32, where the repeater charger further includes a driver configured to drive the second transmitter coil, and a controller configured to: receive data from the second transmitter coil; demodulate the data received from the second transmitter coil; and control the driver based on the demodulated data.

The wireless charger of one of examples 24 to 33, where the repeater charger further includes a controller configured to: receive data from the second transmitter coil, the received data including an indication of a first average power received by a receiver; determine a second average power transmitted by the second transmitter coil; and determine whether a foreign metallic object is present in a charging space of the repeater charger by comparing the first average power with the second average power.

The wireless charger of one of examples 24 to 34, where the repeater charger further includes a communication interface coupled to the receiver coil, and a controller configured to: receive data from the second transmitter coil; and cause the communication interface to transmit, via the receiver coil, data based on the received data from the second transmitter coil via load modulation.

The wireless charger of one of examples 24 to 35, where the sub-surface wireless charger further includes a driver coupled to the first transmitter coil and a second controller configured to: receive data from the repeater charger via the first transmitter coil; demodulate the received data; and control the driver based on the demodulated data.

The wireless charger of one of examples 24 to 36, where the second controller is configured to: determine a first average power received by a receiver based on the received data from the repeater charger; determine a second average power transmitted by the second transmitter coil; and determine whether a foreign metallic object is present in a charging space of the repeater charger by comparing the first average power with the second average power.

The wireless charger of one of examples 24 to 37, where the second controller is configured to determine the second average power transmitted by the second transmitter coil based on the received data from the repeater charger.

The wireless charger of one of examples 24 to 38, where the sub-surface wireless charger further includes a driver coupled to the first transmitter coil and a second controller, where the repeater charger is configured to cause voltage variations across the second transmitter coil that are between a third frequency and a fourth frequency to propagate to the receiver coil, and where the second controller is configured to: receive data from the repeater charger via the first transmitter coil, where the received data is based on the voltage variations across the second transmitter coil between the third frequency and the fourth frequency;

demodulate the received data; and control the driver based on the demodulated data.

The wireless charger of one of examples 24 to 39, where the repeater charger further includes a second driver coupled to the second transmitter coil and an oscillator circuit coupled to the second driver, the second driver configured to drive the second transmitter coil based on an output of the oscillator circuit.

The wireless charger of one of examples 24 to 40, where the third frequency is 1 kHz and the fourth frequency is 2 kHz.

A wireless charger including: a sub-surface wireless charger including a transmitter coil and a first controller; and a foreign object detector including a sensing coil, a second controller and a communication interface coupled to the sensing coil, where the second controller is configured to: determine a first average power at a location of the sensing coil based on a voltage across the sensing coil, and transmit data based on the first average power via the sensing coil using the communication interface, and where the first controller is configured to: receive data from the transmitter coil, determine the first average power based on the received data, determine a second average power received by a receiver, and determine whether a foreign metallic object is present in a charging space of the sub-surface wireless charger by comparing the first average power with the second average power.

The wireless charger of example 42, where the sensing coil has a hollow shape and surrounds the second controller.

The wireless charger of one of examples 42 or 43, where the second controller is configured to: determine whether the receiver is sending data via the transmitter coil based on a voltage across the sensing coil; and transmit data to the sub-surface wireless charger when the receiver is not sending data via the transmitter coil.

The wireless charger of one of examples42 to 44, where the second controller is configured to determine whether the receiver is sending data via the transmitter coil by determining whether the voltage across the sensing coil includes a signal with a frequency between 1 kHz and 2 kHz and that has an energy higher than a threshold.

A wireless charger including: a sub-surface wireless charger; and a ferrite sticker having a hollow shape and disposed in a charging space of the sub-surface wireless charger and configured to be disposed between the sub-surface wireless charger and a receiver.

A wireless charger including: a transmitter coil; and a metallic heatsink having a first surface attached to the transmitter coil, where the transmitter coil is configured to produce a magnetic field when the transmitter coil is energized, and where the metallic heatsink has a second surface that has a shape that tracks magnetic lines of the magnetic field.

The wireless charger of example 47, where the second surface has a toroidal shape.