TRANSMISSION

FIELD OF THE INVENTION

The present invention relates to a system and method for monitoring efficiency and controlling power transfer across an inductive power coupling.

BACKGROUND

For safety, the power supplying side of a conductive couple is generally the female part, and does not have bare conductive elements protruding therefrom. A plug coupled to the device is the corresponding male part with bare pins. The size of the pins and holes are such that a child cannot insert his or her fingers thereinto. In high quality sockets, an earth connection is provided, and, only when a plug with a longer earth pin is inserted thereinto, is it possible to insert a pin (or anything else) into the holes connected to the current carrying live and neutral wires. Nevertheless, socket holes are dangerous and children do sometimes manage to insert pencils, pins and other objects into socket holes, sometimes with fatal results. Water can also cause shorting and may result in electrocution.

It can therefore be safer and more reliable to provide socket-less power outlets such as inductive couplers. Inductive power coupling allows energy to be transferred from a power supply to an electric load without connecting wires. A power supply is wired to a primary coil and an oscillating electric potential is applied across the primary coil which induces an oscillating magnetic field therearound. The oscillating magnetic field may induce an oscillating electrical current in a secondary coil, placed close to the primary coil. In this way, electrical energy may be transmitted from the primary coil to the secondary coil by electromagnetic induction without the two coils being conductively connected. When electrical energy is transferred inductively from a primary coil to a secondary coil, the pair are said to be inductively coupled. An electric load wired in series with such a secondary coil may draw energy from the power source when the secondary coil is inductively coupled to the primary coil.

Low power inductive electrical power transmission systems over extended surfaces are not new. One such example is described in United States Patent No. 7,164,255 to Hui. In Hui's system a planar inductive battery charging system is designed to enable electronic devices to be recharged. The system includes a planar charging module having a charging surface on which a device to be recharged is placed. Within the charging module, and parallel to the charging surface, at least one, and preferably an array of primary windings are provided. These couple energy inductively to a secondary winding formed in the device to be recharged. Such systems are adequate for charging batteries in that they typically provide a relatively low power inductive coupling. It will be appreciated however, that extended base units such as Hui's charging surface which transmit energy continually approximately uniformly over the whole area of the unit, are not suitable for use with high energy systems.

By not requiring holes for coupling pins, socket-less outlets may be disguised more effectively than conductive sockets, and are thus less obtrusive. A primary inductive coil, for example, may be concealed behind a surface. Generally, the fact that socket-less outlets are less obtrusive is advantageous. But being harder to spot than conventional power outlets has its disadvantages. The user must somehow locate the outlet before being able to use it by bringing a secondary coil into proximity therewith. The problem of locating such sockets is particularly acute where the power outlets are behind a concealing surface such as a desk top or wall, and the positions thereof are adjustable over a large area.

Locating mobile source 'hotspots' or sockets is particularly problematic in high power systems where no extended power transmission surface is provided. Moreover, a high power primary coil produces a large oscillating magnetic field. Where a secondary coil is inductively coupled to the primary coil, the resulting flux linkage causes power to be drawn into the secondary coil. Where there is no secondary coil to focus the power, the oscillating magnetic field causes high energy electromagnetic waves to be transmitted which may be harmful to bystanders. In contrast to low power systems, such as Hui's charging surface, where excess heat may be readily dissipated, uncoupled high power primary coils and their surroundings may become dangerously hot.

In order to provide power to electrical devices in an efficient manner it is important that certain parameters of the power are regulated. By feeding back such parameters as working voltage, current, temperature and the like, the power supply to an electric device may be optimized to minimize energy losses and to prevent excessive heating of the components. Consequently, it may be useful to provide a signal transfer channel for power regulation and the like. Thus a communication channel between source and load device is often provided alongside the power input channel in conventional conductive power supply systems. Methods for providing such a communication channel include wired connections to the device that are often packaged in the same cable as the power lines and conductively coupled to the load via conventional pin-and-socket type connectors.

Leak prevention systems which are able to detect power emanating from a primary coil of an inductive power source and to cut off power to the primary coil if no secondary coil is coupled thereto have been considered. However in order to prevent power leakage from a primary coil while a secondary coil is coupled thereto, a communication channel between the secondary and primary coil would be useful. Nevertheless due to the lack of connecting wires in inductive power couplings, conductive communication channels are not practical.

There is a need for a control system for inductive power outlets, which is capable of locating a concealed power outlet, preventing power leakage from the power outlet, locating secondary coils close to the power outlet and regulating power transfer from the power outlet to a secondary coil coupled thereto. The present invention addresses this need.

SUMMARY OF THE INVENTION

According to one aspect of the presently disclosed subject matter, there is provided an inductive power transmitter for inductive power transmission to an inductive power receiver, the inductive power transmitter comprising:

• a primary coil, capable of being inductively coupled to a secondary coil in the inductive power receiver;

• a power supply and an associate driver configured to provide a varying electrical potential from the power supply to the primary coil;

• a monitoring system configured to measure electrical flow parameters of the primary coil; and

• a controller configured to detect, based on the electrical flow parameters measured by the monitoring system, an error condition indicative of a foreign object introduced between the primary coil and the secondary coil, and to facilitate, when the error condition is detected, interrupting the electrical potential to the primary coil. It will be appreciated that herein the specification and claim, the term "foreign object" refers to an object, such as one made of a metal, which may interfere with the power transmission between the inductive power transmitter and the inductive power receiver, for example by draining power therefrom.

The monitoring system may comprise a voltage monitor configured to measure the voltage across the primary coil, and a current monitor configured to measure the current across the primary coil.

The inductive power transmitter may further comprise a circuit breaker configured interrupt the electrical potential to the primary coil, the controller being configured to direct operation of the circuit breaker, thereby facilitating the interruption.

The controller may comprise a microcontroller, i.e., the microcontroller may be a component of or constitute the controller.

The controller may be configured to detect an error condition by comparing the electrical flow parameters to one or more reference parameters. The controller may comprise a comparator configured to facilitate the comparing.

The controller may be further configured to calculate the reference parameters.

The controller may be configured to calculate the reference parameters based on the frequency of the varying electrical potential and at least one measured electrical flow parameters.

The inductive power transmitter may be configured to perform a startup foreign object test comprising:

• decreasing the frequency of the varying electrical potential through a plurality of frequencies from a first frequency to a second frequency;

• determining, by the controller, a threshold value for each of one or more of the electrical flow parameters for at least some of the plurality of frequencies, the threshold values corresponding to non-error conditions and constituting one of the reference parameters;

• monitoring, via the monitoring system, the electrical flow parameters; and

• detecting the error condition if one or more of the electrical flow parameters exceeds the threshold value.

The electrical flow parameters may comprise the voltage and current across the primary coil. The inductive power transmitter may be configured to perform at least the decreasing, monitoring, and detecting of the startup foreign object test when charging is initiated.

The inductive power transmitter may be configured to perform a transmission foreign object check comprising:

• determining a relationship between two or more of the electrical flow parameters;

• determining a threshold value for the relationship, the threshold value corresponding to a non-error condition and constituting the reference parameters;

• monitoring, via the monitoring system, the electrical flow parameters, and calculating a measured relationship of the measured electrical flow parameters; and

• detecting the error condition if the measured relationship is beyond the threshold value.

The relationship may be based on at least the voltage and current across the primary coil. The relationship may be further based on the frequency of the varying electrical potential.

The inductive power transmitter may be configured to perform an idle foreign object check comprising:

• determining a reference signal decay time of a ping signal transmitted when an error condition does not exist;

• transmitting a test ping signal;

• measuring the signal decay time of the test ping signal and comparing it to the reference calibration decay time; and

• detecting the error condition if the signal decay time is below the reference decay time beyond a predetermined threshold.

The inductive power transmitter may be configured to perform the idle foreign object test when not transmitting power to an inductive power receiver.

The inductive power transmitter may further comprise a memory module, the reference parameters being stored in the memory module. The memory module may comprise non-volatile memory. The inductive power transmitter may further comprise a signal conditioner comprising a frequency changer configured to increase the frequency of an output signal of the monitoring system.

The signal conditioner may further comprise a filter configured to reduce noise of the output signal.

According to another aspect of the presently disclosed subject matter, there is provided a method for detecting a foreign object between an inductive power transmitter and an inductive power receiver, the method comprising:

• providing the inductive power transmitter, the being configured for inductive power transmission to an inductive power receiver and comprising a primary coil capable of being inductively coupled to a secondary coil in the inductive power receiver;

• measuring electrical flow parameters of the primary coil; and

• detecting, based on the measured electrical flow parameters, an error condition indicative of a foreign object introduced between the primary coil and the secondary coil.

The method may further comprise interrupting the electrical potential to the primary coil when the error condition is detected.

The inductive power receiver may further comprise a power supply and an associate driver configured to provide a varying electrical potential from the power supply to the primary coil, a monitoring system configured for the measuring, and a controller configured for the detecting, and for facilitating, when the error condition is detected, interrupting the electrical potential to the primary coil.

The monitoring system may comprise a voltage monitor configured to measure the voltage across the primary coil, and a current monitor configured to measure the current across the primary coil.

The inductive power transmitter may further comprise a circuit breaker configured interrupt the electrical potential to the primary coil, the controller being configured to direct operation of the circuit breaker, thereby facilitating the interruption.

The method the controller may comprise a microcontroller.

The detecting may comprise comparing the electrical flow parameters to one or more reference parameters. The inductive power transmitter may comprise a comparator configured to facilitate the comparing.

The inductive power transmitter may be further configured to calculate the reference parameters.

The method may further comprise calculating the reference parameters based on the frequency of the varying electrical potential and at least one measured electrical flow parameters.

The method may further comprise a submethod of performing a startup foreign object test, the submethod comprising:

• decreasing the frequency of the varying electrical potential through a plurality of frequencies from a first frequency to a second frequency;

• determining a threshold value for each of one or more of the electrical flow parameters for at least some of the plurality of frequencies, the threshold values corresponding to non-error conditions and constituting one of the reference parameters;

• monitoring the electrical flow parameters; and

• detecting the error condition if one or more of the electrical flow parameters exceeds the threshold value.

The electrical flow parameters may comprise the voltage and current across the primary coil.

The decreasing, monitoring, and detecting of the startup foreign object test may be performed when charging is initiated.

The may further comprise a submethod of performing a transmission foreign object test, the submethod comprising:

• determining a relationship between two or more of the electrical flow parameters;

• determining a threshold value for the relationship, the threshold value corresponding to a non-error condition and constituting the reference parameters;

• monitoring the electrical flow parameters;

• calculating a measured relationship of the measured electrical flow parameters; and • detecting the error condition if the measured relationship is beyond the threshold value.

The relationship may be based on at least the voltage and current across the primary coil. The relationship may be further based on the frequency of the varying electrical potential.

The method may further comprise a submethod of performing an idle foreign object test, the submethod comprising:

• determining a reference signal decay time of a ping signal transmitted when an error condition does not exist;

• transmitting a test ping signal;

• measuring the signal decay time of the test ping signal and comparing it to the reference calibration decay time; and

• detecting the error condition if the signal decay time is below the reference decay time beyond a predetermined threshold.

The idle foreign object test may be performed when the inductive power transmitter is not transmitting power to an inductive power receiver.

The method may further comprise increasing the frequency of an output signal of the monitoring system. It may still further comprise reducing noise of an output signal of the monitoring system.

The inductive power transmitter may further comprise a memory module, the reference parameters being stored in the memory module. The memory module may comprise non-volatile memory.

According to a further aspect of the presently disclosed subject matter, there is provided an inductive charging station comprising:

• an inductive power transmitter for inductive power transmission to an inductive power receiver, the inductive power transmitter comprising a primary coil, capable of being inductively coupled to a secondary coil in the inductive power receiver, and a power supply having an associate driver configured to provide a varying electrical potential from the power supply to the primary coil;

• a metal detecting array comprising a plurality of metal detectors having detector coils symmetrically arranged around the inductive power transmitter; and • a controller configured to detect a foreign object in the vicinity of the metal detecting array based on a change in a magnetic field of at least one of the detector coils.

The metal detecting array may comprise an even number of the detector coils. Each detector coils may be attached to an oscillator configured to produce an alternating current passing therethrough, thereby producing the magnetic field.

The controller may be configured to detect the foreign object based on a differential in the changes of different detector coils.

The inductive power transmitter may be as described above.

BRIEF DESCRIPTION OF THE FIGURES

For a better understanding of the invention and to show how it may be carried into effect, reference will now be made, purely by way of example, to the accompanying drawings.

With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention; the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice. In the accompanying drawings:

Fig. 1 is a block diagram showing the main elements of an inductive power coupling incorporating a signal transfer system according to a first embodiment of the invention;

Fig. 2a-d show another embodiment of the signal transfer system in which a control signal is transmitted through an inductive energy coupling;

Fig. 3 is a schematic diagram showing a signal transfer system integrated into a contactless inductive power coupling system for powering a computer;

Fig. 4 is a flowchart showing a method for transferring a transmission signal through an inductive energy coupling in accordance with the invention. Fig. 5 is a block diagram representing another embodiment of the signal transfer system incorporated into an efficiency monitor for monitoring the efficiency of power transmission by an inductive power outlet;

Fig. 6a is a schematic diagram of an inductive power outlet with an electrical load inductively coupled thereto, monitored by an efficiency monitor;

Fig. 6b is a schematic diagram of the inductive power outlet of Fig. 6a wherein a power drain has been introduced between the primary and secondary coils;

Fig. 7 is a flow diagram of a method for using the signal transfer system to monitor the efficiency of power transmission by an inductive power outlet;

Fig. 8 is a block diagram showing the main elements of an inductive power transmitter and an associated inductive power receiver;

Figs. 9 through 11 are flow diagram illustrating different foreign object tests performed by the inductive power transmitter illustrated in Fig. 8; and

Fig. 12 is a schematic illustration of a inductive charging station according to the presently disclosed subject matter.

DETAILED DESCRIPTION

Reference is now made to Fig. 1 showing a block diagram of the main elements of an inductive power coupling 200 incorporating a signal transfer system 100 according to a first embodiment of the invention;

The inductive power coupling 200 consists of a primary inductive coil 220 and a secondary inductive coil 260. The primary coil 220 is wired to a power supply 240 typically via a driver 230 which provides the electronics necessary to drive the primary coil 220. Driving electronics may include a switching unit providing a high frequency oscillating voltage supply, for example. The secondary coil 260 is wired to an electric load 280.

When the secondary coil 260 is brought into proximity with the primary coil 220, the pair of coils forms an inductive couple and power is transferred from the primary coil 220 to the secondary coil 260. In this way a power outlet 210 may provide power to an electric device 290.

The signal transfer system 100 comprises: a signal generator 120, for generating a control signal Sc; a transmitter 140 for transmitting said control signal Sc; and a receiver 160 for receiving said control signal Sc- Although in the signal transfer system 100 described herein, the transmitter 140 is incorporated into the power outlet 210 and the receiver 160 is incorporated into the electrical device 290, it will be appreciated that a transmitter 140 may alternatively or additionally be incorporated into the electrical device 290 and a receiver 160 may alternatively or additionally be incorporated into the power outlet 210.

The control signal Sc communicates encoded data pertaining to the power transmission. This data may be pertinent to regulating efficient power transmission. Examples of such data includes parameters such as: required operating voltage, current, temperature or power for the electric load 280, the measured voltage, current, temperature or power supplied to the electric load 280 during operation, the measured voltage, current, temperature or power received by the electric load 280 during operation and the like.

In other embodiments, the control signal Sc may communicate data relating to the coordinates of the primary inductive coil 220 for the purposes of indicating the location of the power outlet 210. Alternatively, the control signal Sc may communicate data relating to the identity or presence of the electric load 280 such as the location of the secondary coil 260, or an identification code or the electric device 290 or its user.

Various transmitters 140 and receivers 160 may be used with the signal transfer system. Where the primary and secondary coils 220, 260 are galvanically isolated for example, optocouplers may have a light emitting diode serving as a transmitter 140 which sends encoded optical signals over short distances to a photo- transistor which serves as a receiver 160. Optocouplers typically need to be aligned such that there is a line-of- sight between transmitter and receiver. In systems where alignment between the transmitter 140 and receiver 160 may be problematic, optocoupling may be inappropriate and alternative systems may be preferred such as ultrasonic signals transmitted by piezoelectric elements or radio signals such as Bluetooth, WiFi and the like. Alternatively the primary and secondary coils 220, 260 may themselves serve as the transmitter 140 and receiver 160.

Coil-to-coil Signal Transfer

One aspect of the present embodiments relate to a signal transfer system for transferring a transmission signal regarding an electric load connectable via an inductive energy coupling to a power source. The inductive energy coupling comprises a primary coil connectable to the power source in inductive alignment with a secondary coil connectable to the electric load, the system comprises at least one ancillary load; at least one switching unit comprising a modulator for modulating a bit-rate signal with an input signal to create a modulated signal and a switch for intermittently connecting the ancillary load to the secondary coil according to the modulated signal; at least one current monitor for monitoring primary current drawn by the primary coil and producing a primary current signal, and at least one correlator for cross-correlating the primary current signal with the bit-rate signal for producing an output signal.

The switching unit preferably also comprises a controller configured to encode data into the input signal. Typically, the switching unit further comprises a frequency divider and the inductive energy coupling transfers energy with a driving frequency and the bit rate frequency is an integer fraction of the driving frequency.

The inductive energy coupling is typically a device wherein the primary coil is galvanically isolated from said secondary coil. The device may include a transformer, a DC-to-DC converter, an AC-to-DC converter, an AC-to-AC converter, a flyback transformer, a flyback converter, a full-bridge converter, a half-bridge converter, a buck converter, a boost converter, a buck-boost converter, a SEPIC converter or a zeta converter, for example.

Optionally, the input signal carries encoded data pertaining to, for example, the presence of the electric load, required operating voltage for the electric load, required operating current for the electric load, required operating temperature for the electric load, measured operating voltage for the electric load, measured operating current for the electric load, measured operating temperature for the electric load, and / or a user identification code.

In one embodiment, a contactless inductive coupling is provided, comprising the signal transfer system wherein the primary coil is embedded in a power jack and the secondary coil is embedded in a power plug galvanically isolated from the power jack.

An aspect of the technology described herein, teaches a method for transferring a signal through an inductive energy coupling, wherein the inductive energy coupling comprises a primary coil connected to a power source and a secondary coil connected to an electric load, the method comprising the following steps: providing an input signal, providing a bit-rate signal, modulating the bit-rate signal with the input signal to create a modulated signal, connecting an ancillary load to the secondary coil intermittently according to the modulated signal, monitoring a primary current drawn by the primary coil and producing a primary current signal; and cross-correlating the primary current signal with the bit-rate signal to generate an output signal.

According to another aspect, a method for regulating power transfer across a contactless inductive coupling is taught wherein the output signal provides details of power requirements of the load. Typically the input signal is provided by encoding data regarding at least one power requirement of the electric load into the input signal. Optionally and typically, the power requirement depends on parameters such as operating voltage, operating current and / or operating temperature. Alternatively the input signal is provided by monitoring at least one operating parameter of the electric load and encoding monitored parameter data into the input signal. Optionally the parameter is selected from the group comprising operating voltage, operating current and operating temperature. Typically the method for transferring a signal through an inductive energy coupling includes a preliminary step of detecting the presence of an electric load.

Reference is now made to Figs 2a-d wherein a signal transfer system 2100 according to a second general embodiment of the invention is shown. With particular reference to Fig. 2a, the signal transfer system 2100 is configured to transmit a transmission signal through an inductive energy coupling 2200. The inductive energy coupling 2200 consists of a primary coil Lj which may be connected to a power source 2240 and a secondary coil L2 _, galvanically isolated therefrom, across which an electric load 2280 may be connected either directly or via an AC-DC converter 2270.

A transmission circuit 2140 may be connected in parallel with the electric load 2280. The transmission circuit 2140 comprises an ancillary load 2142 connected to the secondary coil L2 via a switching unit 2144. Typically the ancillary load 2142 is much smaller than the electric load 2280.

A corresponding reception circuit 2160 is connected to the primary coil Lj of the inductive energy coupling 2200 and comprises a current monitor 2162, such as an ammeter in series with the primary coil Li, and a correlator 2164.

The switching unit 2144 is configured to receive an input signal S; _n and a bit- rate signal F . A modulator (not shown) modulates the bit-rate signal F _b with the input signal S; _N to produce a modulated signal SM- The ancillary load 2142 is intermittently connected to the secondary coil L ₂ at a rate determined by the modulated signal S _M -

The power source 2240, such as an alternating-current voltage source, intermittent direct current voltage source or the like, is configured and operable to produce a primary voltage Vj which oscillates at a driving frequency F _d - The oscillating primary voltage Vj in coil Lj induces a secondary voltage V ₂ (t) in the secondary coil L ₂ . The secondary voltage V ₂ (t) is optionally passed through an AC- DC converter 22 producing a direct-current voltage V ₂₂ (t).

The electric load 2280 which is coupled to the secondary coil L ₂ - either directly or via the AC-DC converter 2270 - draws a load current I ₂₂ . The power P ₂₂ provided to the load 2280 is given by the scalar product of the voltage V ₂₂ and the load current I ₂₂ . When the ancillary load 2144 is connected, an additional ancillary current ¾4 is also drawn. Thus, with the ancillary load 2144 connected, the total power P ₂ drawn by the secondary coil L ₂ is given by:

i ^> ₂ ( = v ₂₂ ( ^{« [} ₂₂ + ½ ₄ ( ^]

where the ancillary current signal i24(t) varies with the modulated signal SM- The input power Pj(t) provided to the primary coil Lj is given by:

1( = ν ₁ ( · ₁₀ (

where the primary voltage Vj(t) oscillates at the driving frequency F _d which is determined by the power supply 2240.

Input power Pj(t) provided by the primary coil Lj is generally proportional to the total power P ₂₂ (t) drawn by the secondary coil L ₂ , and the primary voltage Vi(t) is determined by the power supply. Perturbations in the primary current o(t) supplied to the primary coil Lj are thus in proportion with i24(t).

The current monitor 2162 monitors the primary current Iio(t) over time, producing a primary current signal S _P which typically has similar characteristics to the modulated signal SM- The correlator 2164 is configured to cross-correlate the primary current signal S _P with the bit rate F _b . The output signal S _out of the correlator 2164 therefore has the same characteristics as the input signal S _m .

In this manner, information carried by the input signal S; _N is transmitted from the transmission circuit 2140 and is retrievable by the receiver circuit 2160 from the output signal S _ou t- It is noted that the signal transfer system 2100 described herein, transmits a transmission signal across the same inductive power coupling 2200 as used for power transmission. This is in contradistinction to prior art transmission systems, which use additional elements to provide signal transmission channels separate from the power transmission channels. In consequence of this innovative approach, additional transmission elements such as optocouplers, piezoelectric elements, supplementary coil pairs and the like are not generally required.

With reference now to Fig. 2b, an exemplary transmission circuit 2140 of the signal transfer system 2100 of Fig. 2a is shown. An AC-to-DC converter 2270 comprising a diode 2272 and a capacitor 2274, which is connected in parallel to the secondary coil L2, converts an AC secondary voltage V2 from the secondary coil L2 into a DC load voltage V22 which is connected across an electric load 2280.

The connection between the ancillary load 2142 and the load voltage V2 is controlled by a switching unit 2144 which includes a frequency divider 2145, microcontroller 2146 and a switch 2147. The frequency divider 2145 provides the bit- rate signal F which is passed to the microcontroller 2146. The microcontroller 2146 is configured to modulate the bit-rate signal F _b according to input signals including control signals Sc from the electric load 2280 and external signals SE- as described hereinbelow.

Control signals Sc may be used to regulate the power supply. Control signals Sc typically provide data relating to load parameters. Typically these include the required operating voltage, current and temperature and the actual measured operating voltage, current and temperature as monitored during operation of the load.

External Signals SE may be used to provide the transmission circuit 2140 with external data to be digitally encoded into the input signal S; _n by the microcontroller 2146 and transmitted to the receiver circuit 2160. External information, may, for example, provide useful supplementary data such as a user identification code, a pass key, battery level of the load device and the like.

It will be appreciated that the ability to transmit supplementary information such as external signals SE through the inductive energy coupling 2200 presents a further advantage over prior art systems which are only suitable for transmitting control signals.

Fig. 2c shows a schematic representation of an exemplary receiver circuit 2160 in accordance with the signal transfer system of Fig. 2a, consisting of a current monitor 2162, a frequency divider 2166, a correlator 2164 and a microcontroller 2168. The frequency divider 2166 provides the bit-rate signal F _b which is typically an integer fraction of the driving frequency F _d . The current monitor 2162 provides a primary current signal S _P which is passed to the correlator 2164 for cross-correlatation with the bit-rate signal Fb. The resulting output signal S _ou t is passed to a microcontroller 2168 which may use the output signal S _out to pass a control signal Sc to control the power source 2240 so as to regulate the power provided to the electric load 2280. The microcontroller 2168 may also be used to extract external signals SE from the output signal.

An exemplary use of the receiver circuit 2160 of Fig. 2c is highlighted in Fig. 2d which shows the receiver circuit 2160 configured to control a flyback power source 2240F. In a flyback converter, a direct current voltage source 2242 is intermittently connected to a primary coil Lj by a switch 2244. This produces a varying voltage signal Vj(t) in the primary coil Lj which induces a secondary voltage V ₂ in a secondary coil L ₂ (Fig. 2a). The secondary coil L ₂ is generally connected to a smoothing circuit such the AC-DC converter 2270 shown in Fig. 2b to produce a DC output.

The switch 2244 is controlled by a driver 2248 which receives a pulsing signal F _d from a clock 2246. The pulsing signal F _d determines the frequency with which the direct current voltage source 2242 is connected to the primary coil Lj. The power delivered to the primary coil Lj may be regulated by varying the duty cycle of the switch 2244. The duty cycle is the proportion of the time between pulses during which the switch 2244 is closed.

Fig. 2d shows the innovative use of the signal transfer system 2100 which receives a feedback signal transferred between the primary and secondary power transmission coils and received by the receiver circuit 2160. This is an improvement on prior art flyback converters, wherein additional elements such as optocouplers or the like have been used to transmit feedback signals.

The microcontroller 2168 generates a control signal Sc which is relayed to the driver 2248. The control signal Sc determines the duty cycle of the switch 2248 and so may be used to regulate power transmission.

Although only a flyback converter is represented in Fig. 2d it is noted that a control signal Sc thus transmitted may be used to regulate power transfer in a variety of transmission assemblies such as a transformer, a DC-to-DC converter, an AC-to- DC converter, an AC-to-AC converter, a flyback transformer, a full-bridge converter, a half-bridge converter or a forward converter for example. As an example of the signal transfer system 100 (Fig. 1), with reference to Fig. 3, according to a third embodiment of the invention, a signal transfer system 3100 may be integrated into a contactless inductive power coupling system 3200 where power is inductively transmitted from a jack unit 3212 to a plug unit 3292 galvanically isolated therefrom. A transmission circuit 3140 embedded in the plug unit 3292 may be used to transmit control signals Sc to a receiver circuit 3160 in the jack 3212. Thus once the primary Lj and secondary L ₂ coils are aligned, control signals may be passed between the plug 3292 and jack 3212 units with no need to align additional components such as optocouplers, and the like.

Where a contactless plug 3292 is used, for example to power a portable computer 3290 having on-board power cells 3280, the signal transfer system 3100 may be used to detect the presence of the load 3290 producing a detection signal SDL and then to provide the jack 3212 with signals relating to the identity of the user SID and the serial number SS _N or other identifier of the laptop computer 3290. Signals regarding the operating voltage and current required by the PC may be provided as a regulatory signal S _Q which may also provide supplementary information such as information related to the power level of the cells 3280, for example. Using this signal S _Q , the signal transfer system 3100 may be used to select between powering the computer 3290 directly, recharging the power cells 3280 thereof, or both powering and recharging, depending on defaults and predetermined criteria. It is further noted that when used for recharging cells 3280, the ability to monitor the temperature of the cells 3280 during recharging may be used to prevent overheating.

Referring to Fig. 4, a flowchart showing a method for transferring a transmission signal through an inductive energy coupling in accordance with another embodiment of the invention is presented. With further reference to Fig. 2a, an Input Signal S; _n - Step (a) and a Bit-rate Signal F - Step (b) are provided to the transmission circuit 2140. The Bit-rate Signal F _b is then modulated by the Input Signal S; _n , producing a Modulated Signal SM - Step (c). An ancillary load 2142 is then connected to the second coil L ₂ intermittently according to the Modulated Signal SM - Step (e). The receiver circuit 2160 monitors the primary current drawn by the primary coil Li to produce a Primary Current Signal Sp - Step (e). This Primary Current Signal Sp is then cross-correlated with the Bit-rate Signal F _b to generate an Output Signal S _out - Step (f). The basic signal transfer system and method described hereinabove are capable of variation. For example, it will be appreciated that through the use of such a system, information regarding a load 2280 may be transmitted to the power outlet 2210 across the inductor coils Lj and L ₂ of the inductive coupling 2200, as a signal superimposed on the power transmitted, without requiring additional data transmitting components.

Power Coupling Efficiency

Embodiments of the invention are directed to providing methods for monitoring the efficiency of power transmission by an inductive power outlet comprising at least one primary coil wired to a power supply, for inductively coupling with a secondary coil wired to an electric device. The method comprises the steps of: measuring the input power delivered to the primary coil, measuring the output power received by the electric device, communicating the input power to a processor, communicating the output power to the processor and the processor determining an index of power-loss.

In one specific application, the index of power-loss is an efficiency quotient Q, being the ratio of the output power to the input power, and the method comprises the further step of: disconnecting the primary coil from the power supply if the efficiency quotient Q is below a threshold value. Typically the threshold efficiency quotient is in the range of from 75% to 95%.

In another application, the index of power-loss is an efficiency differential Δ, being the difference between the output power to the input power, and the method comprises the further step of: disconnecting the primary coil from the power supply if the efficiency differential Δ is above a threshold value.

A further aspect of the technology described herein relates to an efficiency monitor for monitoring the efficiency of power transmission by an inductive power outlet of the type including at least one primary coil wired to a power supply, for inductively coupling with a secondary coil wired to an electric device. The efficiency monitor includes: at least one input power monitor for measuring the input power delivered to the primary coil; at least one output power monitor for measuring the output power received by the secondary coil; at least one processor for determining an index of power-loss; and at least one communication channel for communicating the input power and the output power to the processor. Typically the efficiency monitor also includes at least one circuit-breaker for disconnecting the primary coil from the power supply. Preferably the input power monitor is incorporated within the power outlet and the output power monitor is incorporated within the electric device.

Optionally, the electric device comprises at least one transmitter for transmitting the output power to a receiver incorporated in the power outlet. The transmitter may include one or more light emitting diodes, radio transmitters, optocouplers, or ancillary load transmitter circuits, for example.

According to preferred embodiments, the efficiency monitor includes one or more hazard detectors in communication with the processor. Such hazard detectors may include magnetic sensors, heat sensors, electromagnetic radiation sensors and Hall probes, for example.

Reference is now made to Fig. 5 showing a block diagram of a signal transfer system 4100. The signal transfer system 4100 is incorporated into an efficiency monitor 4300 for monitoring the efficiency of power transmission by an inductive power outlet 4210.

The inductive power outlet 4210 consists of a primary coil 4220 wired to a power supply 4240 via a driver 4230 which provides the electronics necessary to drive the primary coil 4220. Driving electronics may include a switching unit providing a high frequency oscillating voltage supply, for example.

If a secondary coil 4260 is brought into proximity with the primary coil 4220, the pair of coils forms an inductive couple, and power is transferred from the primary coil 4220 to the secondary coil 4260. In this way the power outlet 4210 may provide power to an electric device 4262 comprising an electric load 4280 wired in series with the secondary coil 4260.

The efficiency monitor 4300 consists of an input power monitor 4122 incorporated within the power outlet 4210 and an output power monitor 4124 incorporated within the electric device 4290, both in communication with a processor 4162.

The input power monitor 4122 is configured to measure the input power P; _n provided by the primary coil 4220 and communicates this value to the processor 4162. The output power monitor 4124 is configured to measure the output power P _out received by the secondary coil 4260 and communicates this value to the processor 4162. The processor 4162 is configured to receive the values of the input power P; _n and the output power P _out and to calculate an index of power-loss. The index of power loss indicates how much power is leaking from the inductive couple. The index of power-loss may be the efficiency quotient Q which is the ratio between them, P _out /P _m , which is an indication of the efficiency of the inductive coupling. Alternatively the index of power loss may be the efficiency differential Δ which is the difference between P _out and P; _n .

The processor 4162 may additionally or alternatively be configured to trigger a circuit-breaker 4280 thereby cutting off the primary coil 4220 from the power supply 4240 when the efficiency quotient Q falls below a predetermined threshold or the efficiency differential Δ rises above a predetermined threshold. Typically, this predetermined threshold for the efficiency quotient Q is in the range of from about 75% to 95%, and more preferably about 85%.

With reference to Fig. 6a, an efficiency monitor 5300 for an inductive power outlet 5210 is shown. Inductive power outlet 5210 consists of a primary coil 5220 wired to a power source 5240 via an efficiency monitor 5300 all concealed behind a facing layer 5642 of a horizontal platform 5640 such as a desk-top, a kitchen worktop, a conference table or a work bench. The facing layer may be a sheet of self- adhesive plastic film, plastic, vinyl, Formica or wood veneer, for example.

In other embodiments a primary coil 5220 may be concealed beneath or within flooring such as rugs, fitted carpet, parquet, linoleum, floor tiles, tiling, paving and the like. Alternatively the primary coil 5220 may be concealed behind or within a vertical surface such as a wall of a building or a cabinet, for example behind wallpaper or stretched canvas or the like.

The primary coil 5220 may be used to power an electrical device 5290 such as a computer wired to a secondary coil 5260. The electrical device 5290 is placed upon the surface 5642 of a platform 5640 such that the secondary coil 5260 is aligned with the primary coil 5220 therebeneath.

The efficiency of the power outlet 5210 is monitored by an efficiency monitor 5300. An input power monitor 5122 is incorporated within the power outlet 5210 behind the platform 5640 and is in direct conductive communication with a processor 5162. An output power monitor 5124 is incorporated within the electrical device 5290 and is not physically connected to the power outlet 5210. The output power monitor 5124 communicates with the processor 5162 via a signal transfer system 5100 comprising a transmitter 5140 incorporated within the electrical device 5290 which is configured to transmit a signal to a receiver 5160 incorporated within the power outlet 5210.

The transmitter 5140 may be a standard transmitter such as those widely used in computing and telecommunications, such as an Infra-red, Wi-fi or Bluetooth transmitter or the like. Indeed, any light emitting diodes, radio transmitters, optocouplers or other such transmitters of radiation for which the platform 5640 is translucent may be used. Alternatively a fiber optic pathway may be provided through the platform.

In certain embodiments, an optical transmitter, such as a light emitting diode (LED) for example, is incorporated within the power outlet 5210 and is configured and operable to transmit electromagnetic radiation of a type and intensity capable of penetrating the casing of the electrical device 5290, and the surface layer 5642. An optical receiver, such as a photodiode, a phototransistor, a light dependent resistors of the like, is incorporated within the primary unit for receiving the electromagnetic radiation transmitted through the surface layer 5642.

It is noted that many materials are partially translucent to infra-red light. It has been found that relatively low intensity infra red signals from LEDs and the like, penetrate several hundred microns of common materials such as plastic, cardboard, Formica or paper sheet, to a sufficient degree that an optical receiver, such as a photodiode, a phototransistor, a light dependent resistors or the like, behind a sheet of from 0.1 mm to 2 mm of such materials, can receive and process the signal. For example a signal from an Avago HSDL-4420 LED transmitting at 850nm over 24 degrees, may be detected by an Everlight PD15-22C-TR8 NPN photodiode, from behind a 0.8 mm Formica sheet. For signalling purposes, a high degree of attenuation may be tolerated, and penetration of only a small fraction, say 0.1 % of the transmitted signal intensity may be sufficient. Thus an infra-red signal may be used to provide a communication channel between primary and secondary units galvanically isolated from each other by a few hundred microns of wood, plastic, Formica, wood veneer, glass or the like.

The transmitter 5140 and receiver 5160 may be laterally displaced from the primary coil 5220 and secondary coil 5260. In preferred embodiments, however, the transmitter 5140 is located at the center of the secondary coil 5260 and the receiver 5160 is located at the center of the primary coil 5220. This permits alignment to be maintained through 360 degree rotation of the secondary coil 5260 relative to the primary coil 5220.

The processor 5162 is configured to receive the values of the input power P; _n , directly from the input power monitor 5122, and the output power P _out , via the receiver 5160. The processor 5162 then calculates the efficiency quotient Q. In normal usage as represented in Fig. 6a, the processor records an efficiency quotient Q higher than a predetermined threshold so power transmission continues uninterrupted. When the efficiency quotient Q falls below a predetermined threshold, this indicates that power is being drawn from the primary coil 5220 by some power drain other than the secondary coil 5260.

Fig. 6b is a schematic diagram of the inductive power outlet 5210 of Fig. 6a wherein a power drain such as a conductive sheet of metallic foil 5800 is introduced between the primary coil 5220 and the secondary coil 5260. The oscillating magnetic field produced by the primary coil 5220 when connected to a high frequency oscillating voltage from a driver 5230, produces eddy currents in the conductive sheet 5800 thereby heating the conductive sheet and draining power from the primary coil 5220. Such a power drain may be wasteful and/or dangerous. It will be appreciated that leak prevention systems which cut off power to the primary coil 5220 if no secondary coil 5260 is coupled thereto, would fail to detect this hazard.

In contradistinction to previous systems known to the inventors, embodiments of the present invention measure the efficiency quotient Q. Consequently, when a power drain is introduced, such as that shown in Fig. 6b, for example, the output power P _o u _t received by the secondary coil 5260 is lower than normal and the efficiency quotient Q may therefore drop below the predetermined threshold. The efficiency monitor 5300 is thus able to detect the hazard.

According to certain embodiments, additional detectors (not shown) may be incorporated within the power outlet 5210, the platform 5640 or the electrical device 5290 for monitoring other scientific effects which may be indications of possible hazards such as the magnetic field generated by the primary coil 5220, or the temperature of the platform 5640 for example. Such detectors may function in accordance with one or more of a variety of principles, including, inter alia, magnetic sensing means, Hall probes, heat sensors or electromagnetic sensors.

The processor 5162 may assess the level of the hazard detected by processing the various signals received according to a predetermined logical sequence. If necessary, the processor 5162 may trigger a circuit-breaker 5280 thereby cutting off the primary coil 5220 from the power supply 5240. Depending on the nature of the hazard, the processor 5162 may additionally or alternatively alert a user to the hazard. The alert may be a visual or audio alarm for example, such as a buzzer or light incorporated in the power transmission surface, or a signal sent to the computer 5290 which displays a warning 5294 on its visual display 5296 or emits a warning sound.

In preferred embodiments the output power P _out may be monitored and encoded into the input signal S _m . The coil-to-coil signal generator shown in Fig. 2a may be used to transmit the input signal S; _n from a transmission circuit 2140 (Fig. 2a) incorporated within an electrical device 290 (Fig. 1) and is retrievable by the receiver circuit 2160 (Fig. 2a) incorporated within the power outlet 210 (Fig. 1) from the output signal S _out - The retrieved signal may then be communicated to a processor which uses it to calculate the efficiency quotient Q.

Reference is now made to Fig. 7 showing a flow diagram of a method for monitoring the efficiency of power transmission by an inductive power outlet according to a further embodiment of the present invention. The method includes the following steps:

a) measuring the input power delivered to a primary coil;

b) measuring the output power received by an electric device; c) communicating the input power P; _n to a processor;

d) communicating the output power P _out to the processor;

e) determining an index of power-loss, such as an efficiency quotient Q or efficiency differential Δ;

f) optionally, disconnecting the primary coil from the power supply, for example if the efficiency quotient Q is below a threshold value (fl) or the efficiency differential Δ is above a threshold value (f2), thereby preventing power leakage.

As illustrated in Fig. 8, an inductive power transmitter, which is generally indicated at 7000, is provided. The inductive power transmitter 7000 is configured to transmit power (e.g., electrical power) inductively to an inductive power receiver 7002, which comprises a secondary coil 7004 connected to a load 7006.

The inductive power transmitter 7000 comprises a primary coil 7008, a power supply 7010 and an associated driver 7012, a monitoring system 7014, a controller 7016, and one or more memory modules 7018, which may comprise at least one of volatile and non-volatile memory.

The primary coil 7008 is configured to be inductively coupled to the secondary coil 7004 for transmitting power thereto, according to any suitable method, many which are well-known in the art.

The driver 7012 is configured to provide a varying electric potential from the power supply 7010 to the primary coil 7008.

The monitoring system 7014 is configured to measure (directly or indirectly) electrical flow parameters of the primary coil 7008. The electrical flow parameters may include the voltage and/or current across the primary coil 7008. As such, the monitoring system 7014 may comprise a voltage monitor 7020 configured to measure the voltage across the primary coil 7008, and a current monitor 7022 configured to measure the current across the primary coil. It will be noted that while the voltage and current monitors 7020, 7022 are illustrated schematically as being distinct element, a single element may be provided which performs the functions of both without departing from the scope of the present disclosure, mutatis mutandis.

The controller 7016, which may comprise or be constituted by a microcontroller, is configured to detect, based on the electrical flow parameters measured by the monitoring system 7014, an error condition. The error condition may be indicative of a foreign object introduced between the primary coil and the secondary coil, which affects the relationship among at least some of the electrical flow parameters. The controller 7016 is configured to facilitate interrupting the electrical potential to the primary coil, for example when the error condition is detected.

It will be appreciated that while Fig. 8 illustrates control relationships (in broken lines) between the controller 7016 and other elements of the inductive power transmitter 7000, these are by way of illustration only and are non-limiting. One skilled in the art will recognize that other control relationships may exist, and those shown may not exist in practice, mutatis mutandis.

The electrical potential may be interrupted in any convenient fashion. According to some examples, the controller 7016 may direct the power supply 7010 and/or driver 7012 to stop the supply of power. According to other examples, the inductive power transmitter 7000 may comprise a circuit breaker 7024, which is configured to selectively connect/disconnect the power supply 7010 to/from the primary coil 7008. This may be useful, for example, when a single power supply 7010 is used to simultaneously provide power to multiple primary coils 7008, thereby allowing the electrical potential to each primary coil to be interrupted with affecting the supply to the other ones.

In addition, a signal conditioner 7026 may be provided, downstream of the monitoring system 7014, configured to produce a signal from which an error condition may be more easily detected. For example, it may comprise a frequency changer 7028 configured to increase the frequency of an output signal of the monitoring system. Furthermore, it may comprise a filter 7030, such as a Butterworth filter, configured to reduce noise of the output signal.

The controller 7016 may be configured to carry out one of one or more methods to detect an error condition. In order to accomplish this, e.g., reference parameters, indicative of either an error condition or of a non-error condition, are compared to values measured by the monitoring system 7014. In order to facilitate this, the controller 7016 may comprise a comparator 7032.

According to some examples, the controller 7016 is configured to calculate reference parameters of one or more of the electrical flow parameters. The frequency of the input signal, i.e., of the electric potential provided by the driver 7012, may also be taken into account when calculating the reference parameters. According to other examples, reference parameters used by the controller 7016 are provided in advance, e.g., stored in the volatile or non-volatile memory of the memory module 7018.

The inductive power transmitter 7000 may be configured to perform one or more type of foreign object tests to detect an error condition. As illustrated in Fig. 9, a startup foreign object test, generally indicated at 7100, may be performed as follows (it will be appreciated that while elements of the inductive power transmitter which perform some of the steps are listed, it is by way of example only, and some of the steps may be performed by elements other than those listed without departing from the scope of the presently disclosed subject matter, mutatis mutandis):

• In step 7102, the frequency of the varying electrical potential through a plurality of frequencies from a first frequency to a second frequency is decreased.

• In step 7104, the controller 7016 determines a threshold value for each of one or more of the electrical flow parameters (for example the voltage and current across the primary coil 7008) for at least some of the plurality of frequencies, the threshold values corresponding to non-error conditions and constituting one of the reference parameters.

• In step 7106, the monitoring system 7014 monitors the electrical flow parameters.

• In step 7108, the error condition is detected by the controller 7016 if one or more of the electrical flow parameters exceeds the threshold value.

Startup foreign object test 7100 may be particularly useful, for example, when charging is initiated, i.e., during a so-called "soft start".

As illustrated in Fig. 10, a transmission foreign object test, generally indicated at 7120, may be performed as follows (it will be appreciated that while elements of the inductive power transmitter which perform some of the steps are listed, it is by way of example only, and some of the steps may be performed by elements other than those listed without departing from the scope of the presently disclosed subject matter, mutatis mutandis):

• In step 7122, a relationship between two or more of the electrical flow parameters is determined. The relationship may be based on at least the voltage and current across the primary coil. The relationship may be further based on the frequency of the varying electrical potential.

• In step 7124, a threshold value for the relationship, corresponding to a non-error condition and constituting the reference parameters, is determined.

• In step 7126, the monitoring system monitors the electrical flow parameters.

• In step 7128, a measured relationship of the measured electrical flow parameters is calculated.

• In step 7130, the error condition is detected if the measured relationship is beyond the threshold value.

The detection in step 7130 is based on the finding that the ratio between peak DC voltage and the current is always above a certain threshold value in the case of an error condition (i.e., if there is a foreign object between the inductive power transmitter and the inductive power receiver), and below it when an error condition does not exist. This relationship may take the driving frequency of the varying electric potential into account.

As illustrated in Fig. 11, an idle foreign object test, generally indicated at 7140, may be performed as follows (it will be appreciated that while elements of the inductive power transmitter which perform some of the steps are listed, it is by way of example only, and some of the steps may be performed by elements other than those listed without departing from the scope of the presently disclosed subject matter, mutatis mutandis):

• In step 7142, a calibration ping signal is transmitted at a time when it is known that the error condition does not exist. This may be done, for example, during manufacture.

• In step 7144, the signal decay time of the calibration ping signal is measured and recorded, for example in non-volatile memory of the memory module 7018.

• In step 7146, a test ping signal is transmitted, and the signal decay time thereof is recorded.

• In step 7148, an error condition is detected if the signal decay time of the test ping signal is below the signal decay time of the calibration ping signal, beyond a predetermined threshold.

It will be appreciated that the signal decay time may be obtained in any suitable fashion without departing from the scope of the presently disclosed subject matter, mutatis mutandis. For example, it may be transmitted thereto from an external source, for example taking into account environment conditions (parameters of a charging surface, etc.)

The foreign object test 7140 may be modified by recording the peak voltage and/or current during a ping, mutatis mutandis. In this respect, it will be appreciated that a small electric potential may be provided to the primary coil 7008 for the purpose of the foreign object test 7140 is necessary.

It is further noted that perturbations in the self-resonance of the system may indicate the presence of a foreign body. Accordingly, self-resonance of the system may be determined at intervals such that any perturbations may be detected indicating the possible presence of such foreign objects. The idle foreign object test 7140 may be particularly useful, for example, when the inductive power transmitter is in an idle state, i.e., while it is not engaged in power transfer.

As illustrated in Fig. 12, an inductive charging station, which is generally indicated at 8000, may be provided, to assist in detection of foreign objects. The inductive charging station 8000 may, e.g., integrated into a charging surface. The inductive charging station comprises an inductive power transmitter 8002, a metal detecting array 8004, and a controller 8006.

The inductive power transmitter 8002 may be provided according to any suitable design, many of which are known in the art. For example, it may comprise a primary coil 8008, which is capable of being inductively coupled to a secondary coil, and a power supply having an associate driver (both not shown in Fig. 12) configured to provide a varying electrical potential from the power supply to the primary coil. According to some examples, the inductive power transmitter 8002 is provided in accordance with that described above with reference to Figs. 8 through 11. The controller 8006 may be configured to work with, or may constitute a part of, the controller 7016 described above with reference to Figs. 8 through 11.

The metal detecting array 8004 comprises a plurality of metal detectors 8010, each of which may be provided according to any suitable design, many of which are known in the art. For example, each of the metal detectors may comprise a metal detector coil 8012. The metal detectors 8010 are arranged symmetrically around the inductive power transmitter 8002. It will be noted in this regard that the inductive power transmitter 8002 does not need to be arranged symmetrically with the metal detectors 8010, e.g., it may be eccentrically positioned therebetween. According to some examples, the metal detecting array 8004 comprises an even number (i.e., 2, 4, 6, etc.) of metal detectors 8010.

The metal detecting array 8004 may comprise an oscillator 8014, configured to produce an alternating current passing through each of the detector coils 8012, thereby producing the magnetic field. It will be appreciated that while the oscillator 8014 is connected to each of the detector coils 8012, it is only illustrated as being connected to one of them. It addition, it will be appreciated that a single oscillator 8014 may be provided for the entire metal detecting array 8004, or more than one, with each oscillator being connected to one or more of the metal detecting coils. The controller 8006 is configured to detect a foreign object in the vicinity of the metal detecting array 8004, based on a change in a magnetic field of at least one of the detector coils 8012, which is indicative of the presence of a metal object in the vicinity. According to some examples, the controller 8006 is configured to detect the foreign object by the comparing the changes in the magnetic fields of the coils. The detecting may thus be based on a differential in the changes of different detector coils. This allows the metal detecting array 8004 to be used to detect small metal objects. It may additionally be configured to interrupt the supply of power via the primary coil 8008, for example by interrupting power supply thereto.

Thus a number of related technologies are presented that use signal transfer systems across an inductive power coupling to regulate the power and to detect and align the two coils.

The scope of the present invention is defined by the appended claims and includes both combinations and sub combinations of the various features described hereinabove as well as variations and modifications thereof, which would occur to persons skilled in the art upon reading the foregoing description.

In the claims, the word "comprise", and variations thereof such as "comprises", "comprising" and the like indicate that the components listed are included, but not generally to the exclusion of other components.