TECHNICAL FIELD

The invention relates to multi-antenna transmitters, more particularly, the invention relates to a method of a wireless power transfer, a wireless power transmitter, and a wireless power receiver.

BACKGROUND

Multi-antenna transmitters are widely used for efficient far-field wireless power transfer (WPT). These transmitters rely on focusing their high gain beams towards the receiver(s) location(s) to overcome losses during propagation. The location of the power receiver is typically unknown to the transmitter and may dynamically change over time. For this reason, in conventional WPT systems, the receiver node sends a beacon signal to the transmitter (at the same frequency used for power transmission) for localization and beamforming. In an existing approach, beacon signal generation is done either by using a dedicated communication circuitry or by backscattering an incident interrogating signal. The limitation of using a dedicated communication circuitry is that it usually requires the use of a dedicated battery.

Existing battery-less methods of wireless power transfer rely on transmitting an interrogating signal from the transmitter to the receiver at the same frequency of wireless power transmission. The receiving node then backscatters (reflects) this signal to the transmitting node at the same frequency band. Then, the backscattered signal is used for channel estimation and localization of the receiving node. Such method might create a high interference level at the transmitting node since it needs to simultaneously receive a weak signal and typically transmit a strong interrogating signal at the same frequency. Accordingly, a need for an improved method exists.

SUMMARY

In view of the above, it is an objective underlying the present application to provide a method of a wireless power transfer, a wireless power transmitter, and a wireless power receiver for minimizing self-interference at the wireless power transmitter and eliminating battery dependence at the receiver node. This is achieved by the features of the independent claims. Further implementations are apparent from the dependent claims, the description, and the figures.

A method of a wireless power transfer, a wireless power transmitter and a wireless power receiver is provided.

According to a first aspect, there is provided a method of a wireless power transfer. The method includes broadcasting a first signal from a wireless power transmitter at a first frequency. The method includes receiving the first signal by a wireless power receiver. The method includes generating an n-th harmonic from the first signal in the wireless power receiver. The method includes transmitting the n-th harmonic from the wireless power receiver as a beacon signal at the second frequency being n times higher than the first frequency. The method includes receiving the beacon signal by the wireless power transmitter. The method includes tuning the wireless power transmitter for transmitting a wireless power transfer (WPT) signal in a direction towards the wireless power receiver using the beacon signal. The method includes transmitting the WPT signal at the second frequency from the wireless power transmitter in the direction towards the wireless power receiver.

The method for wireless power transfer provides efficient wireless power transfer as the beacon signal is generated from the receiver node at the required frequency for WPT without the need for a battery.

The method enables accurate passive detection of wireless power receivers. Further, the method eliminates interference and cross-talk between the transmitter antenna elements that are caused due to simultaneous transmission and reception of signals between the wireless power transmitter and the wireless power receiver. The method further eliminates a need for a dedicated battery or an on-chip communication system at the wireless power receiver. The wireless power receiver is capable of generating the required beacon signal for efficient WPT without relying on opportunistic ambient energy harvesting that is uncontrollable. Further, the method limits a need for decoupling structures (e.g., electromagnetic bandgap structures or complex feeding networks) at the wireless power transmitter to detect the beacon signal at the frequency needed for the WPT. According to an implementation, the broadcasting of the first signal includes increasing a power of the broadcasting gradually by the wireless power transmitter until the receiving of the beacon signal.

According to an implementation, the receiving of the first signal in the wireless power receiver includes receiving the first signal by means of one or more first receiver antennas configured for operating at the first frequency, and the generating of the n-th harmonic from the first signal includes using one or more rectifier circuits connected to the one or more first receiver antennas to rectify the first signal with generating the n-th harmonic of the first signal and filtering the n-th harmonic out using a bandpass filter.

According to an implementation, the transmitting of the n-th harmonic from the wireless power receiver includes transmitting the n-th harmonic by means of the one or more first receiver antennas being further configured for operating at the second frequency or one or more other receiver antennas configured for operating at the second frequency.

According to an implementation, the tuning of the wireless power transmitter for transmitting the WPT signal in a direction towards the wireless power receiver includes determining a direction or/and a location of the wireless power receiver by a digital signal processing unit of the wireless power transmitter using an angle of arrival estimation method or a localization method based on the beacon signal.

According to an implementation, the tuning of the wireless power transmitter for transmitting the WPT signal in a direction towards the wireless power receiver includes: receiving the beacon signal by a phase conjugation circuity through one or more of antenna elements of an antenna array of the wireless power transmitter, and computing a complex conjugate of the beacon signal, and the transmitting of the WPT signal at the second frequency from the wireless power transmitter in the direction towards the wireless power receiver includes amplifying the complex conjugate of the beacon signal and re-transmitting the amplified complex conjugate of the beacon signal as the WPT signal by means of the antenna array.

According to an implementation, receiving the WPT signal by the wireless power receiver, and acknowledging WPT reception from the wireless power receiver to the wireless power transmitter using a feedback protocol. According to an implementation, the receiving of the WPT signal by the wireless power receiver includes receiving the WPT signal by means of one or more second receiver antennas configured for operating at the second frequency.

According to a second aspect, there is provided a wireless power transmitter. The wireless power transmitter includes a first transmitter module, a second transmitter module, and a tuning module. The first transmitter module configured for broadcasting a first signal at a first frequency. The second transmitter module configured for receiving a beacon signal at a second frequency being n times higher than the first frequency from a wireless power receiver and transmitting a wireless power transfer (WPT) signal at the second frequency. The tuning module configured for tuning the second transmitter module for transmitting the WPT signal in a direction towards the wireless power receiver using the beacon signal. The second transmitter module is configured for transmitting the WPT signal at the second frequency in the direction towards the wireless power receiver in response to the tuning.

The wireless power transmitter for wireless power transfer provides efficient wireless power transfer as the beacon signal is generated from the receiver node at the required frequency for WPT without the need for a battery. Further, by using the wireless power transmitter, selfinterference at the wireless power transmitter is minimized and battery dependence at the receiver node is eliminated.

The wireless power transmitter enables accurate passive detection of wireless power receivers. Further, the wireless power transmitter eliminates interference and cross-talk between the transmitter antenna elements of that are caused due to simultaneous transmission and reception of signals between the wireless power transmitter and the wireless power receiver. The wireless power transmitter allows implementing the method of wireless power transfer described above that in turn eliminates a need of a dedicated battery or an on-chip communication system at the wireless power receiver. The wireless power receiver is capable of generating the required beacon signal for efficient WPT without relying on opportunistic ambient energy harvesting that is uncontrollable. Further, the wireless power transmitter limits a need for decoupling structures (e.g., electromagnetic bandgap structures or complex feeding networks) at the wireless power transmitter to detect the beacon signal at the frequency needed for the WPT. According to an implementation, the first transmitter module includes a single first antenna configured for broadcasting the first signal at the first frequency on a wide beam.

According to an implementation, the first transmitter module includes one or more of first antennas configured for broadcasting the first signal at the first frequency on different directions of its total field over time.

According to an implementation, the first transmitter module is configured for increasing a power of the broadcasting of the first signal gradually until the receiving of the beacon signal by the second transmitter module.

According to an implementation, the tuning module includes a digital signal processing unit configured for determining a direction and/or a location of the wireless power receiver using an angle of arrival estimation method or a localization method based on the beacon signal.

According to an implementation, the second transmitter module includes a second antenna array consisting of one or more of second antennas configured for receiving the beacon signal and transmitting the WPT signal at the second frequency, the tuning module includes a phase conjugation circuit configured for receiving the beacon signal from the one or more of second antennas and computing a complex conjugate of the beacon signal, and wherein the second transmitter module is configured for amplifying the complex conjugate of the beacon signal and re-transmitting the amplified complex conjugate of the beacon signal as the WPT signal by means of the second antenna array.

According to a third aspect, there is provided a wireless power receiver. The wireless power receiver includes a first receiver module and a second receiver module. The first receiver module configured for receiving a first signal at a first frequency from a wireless power transmitter. The first receiver module configured for generating an n-th harmonic from the first signal. The first receiver module configured for transmitting the n-th harmonic as a beacon signal at a second frequency being n times higher than the first frequency. The second receiver module configured for receiving a wireless power transfer, WPT, signal from the wireless power transmitter at the second frequency. The wireless power receiver for wireless power transfer provides efficient wireless power transfer as the beacon signal is generated from the receiver node at the required frequency for WPT without the need for a battery. Further, self-interference is minimized at the wireless power transmitter and eliminates battery dependence at the receiver node.

Further, the wireless power receiver allows implementing the method of wireless power transfer described above that in turn eliminates interference and cross-talk between the transmitter antenna elements of that are caused due to simultaneous transmission and reception of signals between the wireless power transmitter and the wireless power receiver. The use of the wireless power receiver according to the method further eliminates a need of a dedicated battery or an on-chip communication system at the wireless power receiver. The wireless power receiver is capable of generating the required beacon signal for efficient WPT without relying on opportunistic ambient energy harvesting that is uncontrollable. Further, the wireless power receiver limits a need for decoupling structures (e.g., electromagnetic bandgap structures or complex feeding networks) at the wireless power transmitter to detect the beacon signal at the frequency needed for the WPT.

According to an implementation, the first receiver module includes: one or more first receiver antennas configured for operating at the first frequency to receive the first signal, and one or more rectifier circuits configured for rectifying the first signal with generating the n-th harmonic of the first signal and filtering the n-th harmonic out using a bandpass filter.

According to an implementation, each of the one or more rectifier circuits includes a singlediode rectifier in a series or shunt configuration.

According to an implementation, each of the one or more rectifier circuits includes one or more of diodes.

Harmonics generated from the one or more diodes in the one or more rectifier circuits are recycled and re-transmitted when excited by the first signal at the first frequency composed by its fundamental component only. According to an implementation, the first receiver module is configured for transmitting the n- th harmonic as the beacon signal by means of the one or more first receiver antennas being further configured for operating at the second frequency or one or more other receiver antennas configured for operating at the second frequency.

According to an implementation, the second receiver module includes one or more second receiver antennas configured for operating at the second frequency to receive the WPT signal.

According to an implementation, the one or more other receiver antennas are a part of the one or more second receiver antennas.

Therefore, in contradistinction to the prior art, the disclosed method minimizes self-interference at the wireless power transmitter and eliminates battery dependence at the receiver node.

Details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description, drawings, and claims.

BRIEF DESCRIPTION OF DRAWINGS

In the following embodiments of the invention are described in more detail with reference to the attached figures and drawings, in which:

FIG. 1 illustrates a block diagram of a wireless power transmitter and a wireless power receiver in accordance with an implementation of the invention; and

FIGS. 2A-2B are flow diagrams that illustrate a method of wireless power transfer in accordance with an implementation of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Implementations of the invention provide a method of a wireless power transfer, a wireless power transmitter, and a wireless power receiver for minimizing self-interference at the wireless power transmitter and eliminating battery dependence at the receiver node.

In the following description, reference is made to the accompanying figures, which form part of the disclosure, and which show, by way of illustration, specific aspects of embodiments of the invention or specific aspects in which embodiments of the present invention may be used. It is understood that embodiments of the invention may be used in other aspects and comprise structural or logical changes not depicted in the figures. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.

For instance, it is understood that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if one or a plurality of specific method steps are described, a corresponding device may include one or a plurality of units, e.g. functional units, to perform the described one or plurality of method steps (e.g. one unit performing the one or plurality of steps, or a plurality of units each performing one or more of the plurality of steps), even if such one or more units are not explicitly described or illustrated in the figures. On the other hand, for example, if a specific apparatus is described based on one or a plurality of units, e.g. functional units, a corresponding method may include one step to perform the functionality of the one or plurality of units (e.g. one step performing the functionality of the one or plurality of units, or a plurality of steps each performing the functionality of one or more of the plurality of units), even if such one or plurality of steps are not explicitly described or illustrated in the figures. Further, it is understood that the features of the various exemplary embodiments and/or aspects described herein may be combined with each other, unless specifically noted otherwise.

Terms such as "a first", "a second", "a third", and "a fourth" (if any) in the summary, claims, and foregoing accompanying drawings of the invention are used to distinguish between similar objects and are not necessarily used to describe a specific sequence or order. It should be understood that the terms so used are interchangeable under appropriate circumstances, so that the implementations of the invention described herein are, for example, capable of being implemented in sequences other than the sequences illustrated or described herein. Furthermore, the terms "include" and "have" and any variations thereof, are intended to cover a non-exclusive inclusion. For example, a process, a method, a system, a product, or a device that includes a series of steps or units, is not necessarily limited to expressly listed steps or units but may include other steps or units that are not expressly listed or that are inherent to such process, method, product, or device.

FIG. 1 illustrates a block diagram 100 of a wireless power transmitter 102 and a wireless power receiver 110 in accordance with an implementation of the invention. The block diagram 100 includes the wireless power transmitter 102, a first transmitter module 104, a second transmitter module 106, a tuning module 108, the wireless power receiver 110, a first receiver module 112 that includes a radio frequency (RF)-to-RF and direct current (DC), RF-to-RF and DC, conversion module 116A, and a second receiver module 114 that includes an RF-to-DC conversion module 116B. The RF-to-DC conversion module 116A and the RF-to-RF and DC conversion module 116B are a part or one or more rectifier circuits of the first receiver module 112 and the second receiver module 116, correspondingly, that are configured for rectifying the first signal with generating the n-th harmonic of the first signal. The RF-to-RF and DC conversion module 116B is also configured for generating a DC to produce an optional DC output that can be used for other purposes. In an implementation, each or any of the conversion modules 116A and 116B comprises a single-diode rectifier in a series or shunt configuration. In another implementation, each or any of the conversion modules 116A and 116B comprises a plurality of diodes. In further implementations, the conversion modules 116A and 116B comprise one or more of a transistor, a bridge, and a voltage doubler.

The first transmitter module 104 is configured for broadcasting a first signal at a first frequency. The second transmitter module 106 configured for receiving a beacon signal at a second frequency being n times higher than the first frequency from the wireless power receiver 110 and transmitting a wireless power transfer (WPT) signal at the second frequency. The tuning module 108 is configured for tuning the second transmitter module 106 for transmitting the WPT signal in a direction towards the wireless power receiver 110 using the beacon signal. The second transmitter module 106 is configured for transmitting the WPT signal at the second frequency in the direction towards the wireless power receiver 110 in response to the tuning.

The wireless power transmitter 102 and the wireless power receiver 110 provide efficient wireless power transfer as the beacon signal is generated from the receiver node at the required frequency for WPT without the need for a battery. Further, by using the wireless power transmitter 102 and the wireless power receiver 110, self-interference at the wireless power transmitter 102 is minimized and battery dependence at the receiver node is eliminated.

The wireless power transmitter 102 and the wireless power receiver 110 minimize selfinterference at the wireless power transmitter 102 and eliminate battery dependence at the receiver node by initially sending a relatively low-power signal at a first frequency from the wireless power transmitter 102 that is up-converted at the wireless power receiver 110 node to a second frequency which is then used by the wireless power transmitter 102 for estimating the wireless power transfer channel and/or localizing the wireless power receiver 110.

Additionally, the wireless power transmitter 102 and the wireless power receiver 110 enable accurate passive detection of wireless power receivers. Further, the wireless power transmitter 102 and the wireless power receiver 110 eliminate interference and cross-talk between the transmitter antenna elements that are caused due to simultaneous transmission and reception of signals between the wireless power transmitter 102 and the wireless power receiver 110. The wireless power transmitter 102 and the wireless power receiver 110 further eliminate a need of a dedicated battery or an on-chip communication system at the wireless power receiver 110. The wireless power receiver 110 is capable of generating the required beacon signal for efficient WPT without relying on opportunistic ambient energy harvesting that is uncontrollable. Further, the wireless power transmitter 102 and the wireless power receiver 110 limit a need for decoupling structures (e.g., electromagnetic bandgap structures or complex feeding networks) at the wireless power transmitter 102 to detect the beacon signal at the frequency needed for the WPT. Optionally, the second transmitter module 106 includes a complete RF front-end including oscillators, filters, mixers, couplers, amplifiers, circulators and all the necessary circuitry to transmit and receive signals at the second frequency nf. Optionally, the second transmitter module 106 is connected to a digital signal processing unit which performs angle of arrival estimation and/or localization methods on the received beacon signals to determine the direction and/or location of the wireless power receiver 110.

Optionally, the second transmitter module 106 is connected to a phase conjugation (time reversal) circuitry which may be analog or hybrid analog-digital circuit. The phase conjugation circuit receives the beacon signal at each antenna element of the antenna array, computes the complex conjugate of the received signal, amplify it and re-transmit it as WPT signal using the antenna array. In this way, the WPT signal is directed towards the receiver(s) which generated the beacon(s) in a retro-directive scheme.

Optionally, the type of antenna elements in the first transmitter module 104 and the second transmitter module 106 are identical. Optionally, different antenna types are used within each module including, but not limited to, dipoles, monopoles, patches, horns, etc. Optionally, the first transmitter module 104 includes a single first antenna configured for broadcasting the first signal at the first frequency on a wide beam, covering its total field of view.

Optionally, the first transmitter module 104 includes one or more of first antennas configured for broadcasting the first signal at the first frequency on different directions of its total field of view over time.

Optionally, the first transmitter module 104 is configured for increasing a power of the broadcasting of the first signal gradually until the receiving of the beacon signal by the second transmitter module 106.

Optionally, the tuning module 108 includes a digital signal processing unit configured for determining a direction and/or a location of the wireless power receiver 110 using an angle of arrival estimation method or a localization method based on the beacon signal.

Optionally, the second transmitter module 106 includes a second antenna array consisting of one or more of second antennas configured for receiving the beacon signal and transmitting the WPT signal at the second frequency, the tuning module 108 includes a phase conjugation circuit configured for receiving the beacon signal from the one or more of second antennas and computing a complex conjugate of the beacon signal, and wherein the second transmitter module 106 is configured for amplifying the complex conjugate of the beacon signal and retransmitting the amplified complex conjugate of the beacon signal as the WPT signal by means of the second antenna array.

The first receiver module 112 is configured for receiving the first signal at the first frequency from the wireless power transmitter 102, generating the n-th harmonic from the first signal, and transmitting the n-th harmonic as the beacon signal at the second frequency being n times higher than the first frequency. The second receiver module 114 is configured for receiving the WPT signal from the wireless power transmitter 102 at the second frequency.

Optionally, the first receiver module 112 includes one or more first receiver antennas configured for operating at the first frequency to receive the first signal, and one or more rectifier circuits configured for rectifying the first signal with generating the n-th harmonic of the first signal and filtering the n-th harmonic out using a bandpass filter.

Optionally, each of the one or more rectifier circuits includes a single-diode rectifier in a series or shunt configuration.

Optionally, each of the one or more rectifier circuits includes one or more of diodes. As it was mentioned earlier, the RF-to-RF and DC conversion module 116A can be a part of the one or more rectifier circuits including the single-diode rectifier or one or more diodes.

Harmonics generated from the one or more diodes in the one or more rectifier circuits are recycled and re-transmitted when excited by a signal consisting of its fundamental frequency (at a different frequency from that used for the WPT).

Optionally, the first receiver module 112 is configured for transmitting the n-th harmonic as the beacon signal by means of the one or more first receiver antennas being further configured for operating at the second frequency or one or more other receiver antennas configured for operating at the second frequency.

Optionally, the second receiver module 114 includes one or more second receiver antennas configured for operating at the second frequency to receive the WPT signal.

Optionally, the one or more other receiver antennas are a part of the one or more second receiver antennas.

The wireless power transmitter 102 and the wireless power receiver 110 may be implemented as a system for wirelessly charging mobile phones. A mobile phone case with the described wireless power receiver 110 could be used to charge a phone having depleted battery when placed in the vicinity of the wireless power transmitter 102.

Further, the wireless power transmitter 102 and the wireless power receiver 110 may be implemented as intemet-of-things (loT) sensors having fixed locations (e.g., industrial loT or industry 4.0) or dynamic locations (e.g., wearables or implanted sensors). The wireless power transmitter 102 and the wireless power receiver 110 may be used for efficient detection and WPT for such sensors. Further, the wireless power transmitter 102 and the wireless power receiver 110 may be implemented as sensors implanted in a human body where hazardous batteries cannot be used.

Optionally the first transmitter module 104 is a dual-polarized single antenna transmitter working at a frequency f broadcasting a signal omnidirectional within its field-of-view. The first transmitter module 104 monotonically increases the transmitted power until a signal at 2f is received at the second transmitter module 106. At the wireless power receiver 110, the first receiver module 112 is also a dual-polarized single antenna receiver. The first receiver module 112 receives signals omni-directionally at frequency f and is connected to a non-linear diode rectifier circuit. The first receiver module 112 is optimized to efficiently generate the second- order harmonic from the signal received at frequency f and filter out the other frequency components. The generated second-order harmonic signal is transmitted through a single omnidirectional dual-polarized antenna working at frequency 2f. This second-harmonic signal serves as a beacon signal to localize the wireless power receiver 110 and initiates an efficient WPT beam. The beacon signal at 2f is received by the second receiver module 114 which consists of a planar array of antenna elements designed at 2f. Each antenna element is connected to a retro-directive circuit in which the received component of the beacon signal is amplified while applying phase conjugation to re-direct a WPT beam towards the wireless power receiver 110. The WPT beam at 2f is received by the second receiver module 114 which includes an array of dual-polarized antenna elements working at frequency 2f. Each polarization of each antenna element is connected to a separate rectifier circuit optimized to maximize the RF-to- DC conversion efficiency. The rectifier circuit might be a single-diode topology to minimize the conversion losses and maximize the efficiency. The DC output of all the rectifiers of the same polarization is combined together and connected to a boost converter. Two boost converters are present (one for each polarization). The boost converters are used to convert the DC output voltage from each polarization to the same level and then combined using a third boost converter that adjusts the output DC voltage to match the requirements of a DC load.

The above-described configuration of the receiver module 114 guarantees maximum DC power delivery to the load from the incident RF signals regardless of their polarization. After generating enough DC power, the wireless power receiver 110 might turn on a microcontroller circuit to send feedback to the wireless power transmitter 102 about the received power level and the status of battery charging if present. The feedback signal may be transmitted using separate on-chip modules such as Bluetooth low-energy, as an example.

Since the location of the wireless power receiver 110 is initially not known to the wireless power transmitter 102 an Omni-directional antenna is used to broadcast the signal at frequency f towards as many directions as possible in order to reach the wireless power receiver 110. Similarly, the wireless power receiver 110 uses an Omni-directional antenna at frequency f to receive from as many directions as possible. The above-described configuration of the receiver module 114 relies on generating the second-harmonic at 2f from the signal f. An advantage of the above-described configuration of the receiver module 114 is that better conversion efficiency is obtained from the rectifier when the second-harmonic is generated, as compared to other higher-order harmonics. Further, as the frequency increases, the path loss increases, and consequently the lower will be the power level of the received beacon signal at the wireless power transmitter 102. Usage of the second-harmonic provides a good compromise between the harmonic conversion efficiency as well as an acceptable path loss.

In the above-described configuration of the receiver module 114, the interference at the wireless power transmitter 102 is eliminated because initially a signal is transmitted at a different frequency from the one used for receiving the beacon signal. The wireless power transmitter 102 and the wireless power receiver 110 within the wireless power transmitter 102 operate at different frequencies in a half-duplex setup, and thus, eliminate interference.

FIGS. 2A-2B are flow diagrams that illustrate a method of wireless power transfer in accordance with an implementation of the invention. At step 202, a first signal from a wireless power transmitter is broadcasted at a first frequency. At step 204, the first signal is received by a wireless power receiver. At step 206, an n-th harmonic is generated from the first signal in the wireless power receiver. At step 208, the n-th harmonic is transmitted from the wireless power receiver as a beacon signal at the second frequency being n times higher than the first frequency. At step 210, the beacon signal is received by the wireless power transmitter. At step 212, the wireless power transmitter is tuned for transmitting a wireless power transfer (WPT) signal in a direction towards the wireless power receiver using the beacon signal. At step 214, the WPT signal is transmitted at the second frequency from the wireless power transmitter in the direction towards the wireless power receiver. The method for wireless power transfer provides efficient wireless power transfer as the beacon signal is generated from the receiver node at the required frequency for WPT without the need for a battery.

Additionally, the method enables accurate passive detection of wireless power receivers. Further, the method eliminates interference and cross-talk between the transmitter antenna elements that are caused due to simultaneous transmission and reception of signals between the wireless power transmitter and the wireless power receiver. The method further eliminates a need of a dedicated battery or an on-chip communication system at the wireless power receiver. The wireless power receiver is capable of generating the required beacon signal for efficient WPT without relying on opportunistic ambient energy harvesting that is uncontrollable. Further, the method limits a need for decoupling structures (e.g., electromagnetic bandgap structures or complex feeding networks) at the wireless power transmitter to detect the beacon signal at the frequency needed for the WPT.

Optionally, the broadcasting of the first signal includes increasing a power of the broadcasting gradually by the wireless power transmitter until the receiving of the beacon signal.

Optionally, the receiving of the first signal in the wireless power receiver includes receiving the first signal by means of one or more first receiver antennas configured for operating at the first frequency, and the generating of the n-th harmonic from the first signal includes using one or more rectifier circuits connected to the one or more first receiver antennas to rectify the first signal with generating the n-th harmonic of the first signal and filtering the n-th harmonic out using a bandpass filter.

Optionally, the transmitting of the n-th harmonic from the wireless power receiver includes transmitting the n-th harmonic by means of the one or more first receiver antennas being further configured for operating at the second frequency or one or more other receiver antennas configured for operating at the second frequency.

Optionally, the tuning of the wireless power transmitter for transmitting the WPT signal in a direction towards the wireless power receiver includes determining a direction or/and a location of the wireless power receiver by a digital signal processing unit of the wireless power transmitter using an angle of arrival estimation method or a localization method based on the beacon signal.

Optionally, the tuning of the wireless power transmitter for transmitting the WPT signal in a direction towards the wireless power receiver includes receiving the beacon signal by a phase conjugation circuity through one or more of antenna elements of an antenna array of the wireless power transmitter, and computing a complex conjugate of the beacon signal, and the transmitting of the WPT signal at the second frequency from the wireless power transmitter in the direction towards the wireless power receiver includes amplifying the complex conjugate of the beacon signal and re-transmitting the amplified complex conjugate of the beacon signal as the WPT signal by means of the antenna array.

Optionally, the WPT signal is received by the wireless power receiver, and the WPT reception is acknowledged from the wireless power receiver to the wireless power transmitter using a feedback protocol.

Optionally, the receiving of the WPT signal by the wireless power receiver includes receiving the WPT signal by means of one or more second receiver antennas configured for operating at the second frequency.

It should be understood that the arrangement of components illustrated in the figures described are exemplary and that other arrangement may be possible. It should also be understood that the various system components (and means) defined by the claims, described below, and illustrated in the various block diagrams represent components in some systems configured according to the subject matter disclosed herein. For example, one or more of these system components (and means) may be realized, in whole or in part, by at least some of the components illustrated in the arrangements illustrated in the described figures.

In addition, while at least one of these components are implemented at least partially as an electronic hardware component, and therefore constitutes a machine, the other components may be implemented in software that when included in an execution environment constitutes a machine, hardware, or a combination of software and hardware.