Method and system for foreign object detection using gradient magnetic field implemented by magnetic induction waves

Abstract

This invention relates to the field of foreign object detection technology, specifically a method and system for foreign object detection using a gradient magnetic field generated by magnetically induced waves. The method includes the following steps: placing a detection antenna on the front side of the transmitter of a wireless charger; setting an excitation coil at the center of the front side of a printed circuit board; transmitting an excitation signal to the excitation coil using an excitation source to excite a magnetically induced wave mode; setting multiple detection coils on the back side of the printed circuit board; and real-time detecting the induced voltage formed at the detection coils. During wireless charging, if the real-time detected induced voltage changes, it is determined that a foreign object exists near the transmitter of the wireless charger. The magnetic field distribution of the magnetically induced wave mode of this invention has a significant gradient and is non-local. Therefore, regardless of the location of the foreign object on the detection antenna, the magnetic field will change drastically, enabling rapid and global foreign object detection.

Description

Technical Field

[0001] This invention relates to the field of foreign object detection technology, and specifically to a method and system for detecting foreign objects using a gradient magnetic field generated by magnetically induced waves. Background Technology

[0002] In recent years, the new energy vehicle market has expanded rapidly, leading to a surge in demand for electric vehicle charging. Wireless charging technology for electric vehicles has also matured significantly. Currently, the mainstream wireless charging principle is magnetic resonant coupling. During high-power charging, a high-intensity magnetic field is generated near the system, which can easily affect surrounding living and non-living objects. In particular, metallic foreign objects falling near the transmitter can generate eddy currents, affecting charging efficiency and posing significant safety hazards. Therefore, a foreign object detection (FOD) subsystem is a crucial component of wireless charging systems.

[0003] Currently, mainstream FOD (Focus on Discharge) implementation methods include: power loss-based detection methods, detection coil-based detection methods, ultrasonic / radar-based detection methods, and vision / temperature sensor-based detection methods. Each of these methods has inherent drawbacks in different aspects. For example, power loss-based detection methods have low accuracy and sensitivity and are unsuitable for high-power charging systems; detection coil-based methods require complex detection circuits, resulting in redundant size and space consumption; ultrasonic / radar-based methods require expensive equipment such as sonar, are susceptible to interference from external conditions such as obstruction and collisions, and have extremely high requirements for installation location; vision / temperature sensor-based methods require software algorithm support, have low stability and robustness, and are excessively affected by environmental factors. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method and system for foreign object detection using a gradient magnetic field realized by magnetically induced waves, thereby solving the aforementioned insurmountable shortcomings of existing FOD detection methods.

[0005] The technical solution to achieve the above objectives is: This invention provides a method for foreign object detection using a gradient magnetic field generated by magnetically induced waves, for use in wireless charging. The method includes the following steps: A detection antenna is provided, which includes a printed circuit board and a multi-turn metal coil arranged on the front and back of the printed circuit board. The multi-turn metal coils arranged on the front and back are arranged opposite to each other and connected through vias. A lumped capacitor is connected to each metal coil arranged on the front or back, thereby forming a metal coil resonant unit. A symmetry-breaking gradient is introduced into the array of the metal coil resonant units. The detection antenna is placed in front of the transmitter of the wireless charging device, and the detection antenna is positioned between the transmitter and receiver of the wireless charging device. An excitation coil is disposed at the center of the front side of the printed circuit board; An excitation source is provided and connected to the excitation coil. The excitation source is used to transmit an excitation signal to the excitation coil. The magnetic dipole formed by the ring current on the excitation coil excites a magnetically induced wave mode in the resonant unit of the array of metal coils. The magnetic field distribution of the excited magnetically induced wave mode has a gradient. Multiple detection coils are provided on the reverse side of the printed circuit board; The induced voltage generated at the detection coil is detected in real time. If the detected induced voltage changes during the wireless charging process, it is determined that there is a foreign object near the transmitter of the wireless charger.

[0006] A further improvement of the method for foreign object detection using a gradient magnetic field generated by magnetically induced waves in this invention lies in the step of introducing a symmetry-broken gradient into the array of the metal coil resonant units, which includes: Each metal coil resonant unit is set with a gradually varying linewidth, size, number of turns, thickness, or period length along one direction. The period length is the center distance between two adjacent metal open resonant rings, so that the phase coupling strength between adjacent metal coil resonant units is gradient-coupled. Alternatively, the inductance value of each metal coil resonant unit or the capacitance value of the lumped capacitor connected to each metal coil resonant unit can be set to change linearly and gradually, so that the phase coupling strength between adjacent metal coil resonant units is gradient-type coupling.

[0007] A further improvement of the method for detecting foreign objects using a gradient magnetic field realized by magnetically induced waves in this invention is that it further includes: using a phase-gradient injection method to inject the excitation signal generated by the excitation source, so that the spatial superposition of the magnetic flux response produces directional intensity attenuation.

[0008] A further improvement of the method for detecting foreign objects using a gradient magnetic field achieved by magnetically induced waves is that, when setting the excitation coil, the excitation coil is arranged around the outside of a metal coil located at the center.

[0009] A further improvement of the method for detecting foreign objects using a gradient magnetic field realized by magnetically induced waves is that, when setting the detection coil, the detection coil is arranged around the outside of a metal coil located at the center. The detection coil is arranged around the outside of a metal coil located at the corner of the printed circuit board; The detection coil is arranged around the outside of a metal coil located in the middle of the side of the printed circuit board.

[0010] This invention also provides a system for foreign object detection using a gradient magnetic field generated by magnetically induced waves, used for foreign object detection during wireless charging. The foreign object detection system includes: The detection antenna includes a printed circuit board and multiple turns of metal coils arranged on the front and back sides of the printed circuit board. The multiple turns of metal coils arranged on the front and back sides are arranged opposite each other and connected through vias. A lumped capacitor is connected to each metal coil arranged on the front or back side, thereby forming a metal coil resonant unit. A symmetry-breaking gradient is introduced into the array of the metal coil resonant units. The detection antenna is located in front of the transmitter of the wireless charging device and is located between the transmitter and receiver of the wireless charging device. The excitation coil is located at the center of the front side of the printed circuit board; An excitation source is connected to the excitation coil. The excitation source is used to transmit an excitation signal to the excitation coil. The magnetic dipole formed by the ring current on the excitation coil excites a magnetically induced wave mode in the resonant unit of the array of metal coils. The magnetic field distribution of the excited magnetically induced wave mode has a gradient. Multiple detection coils are located on the reverse side of the printed circuit board; A detection circuit is connected to the detection coil. The detection circuit is used to detect the induced voltage formed at the detection coil in real time during the wireless charging process, and to determine whether the induced voltage changes. When the induced voltage changes, it is determined that there is a foreign object near the transmitter of the wireless charging device.

[0011] A further improvement of the system for detecting foreign objects using a gradient magnetic field generated by magnetically induced waves is that each metal coil resonant unit is set with a gradually varying linewidth, size, number of turns, thickness, or period length along one direction. The period length is the center distance between two adjacent open metal resonant rings, so that the phase coupling strength between adjacent metal coil resonant units is gradient-coupled. Alternatively, the inductance value of each metal coil resonant unit or the capacitance value of the lumped capacitor connected to each metal coil resonant unit can be set to change linearly and gradually, so that the phase coupling strength between adjacent metal coil resonant units is gradient-type coupling.

[0012] A further improvement of the system for detecting foreign objects using a gradient magnetic field generated by magnetically induced waves is that the excitation signal generated by the excitation source adopts a phase-gradient injection method, so that the spatial superposition of the magnetic flux response produces directional intensity attenuation.

[0013] A further improvement of the system for detecting foreign objects using a gradient magnetic field generated by magnetically induced waves is that the excitation coil is arranged around the outside of a metal coil located at the center.

[0014] A further improvement of the system for detecting foreign objects using a gradient magnetic field generated by magnetically induced waves is that the detection coil is arranged around the outside of a metal coil located at the center, around the outside of a metal coil located at a corner of the printed circuit board, and around the outside of a metal coil located at the center of the side of the printed circuit board.

[0015] The beneficial effects of the method and system for foreign object detection using gradient magnetic fields induced by magnetically induced waves, as described in this invention, are as follows: The foreign object detection method and system of the present invention proposes a detection antenna in which, at a specific frequency, the magnetic dipole formed by the current in the excitation coil will excite a magnetically induced wave mode in the resonant unit of the metal coil. The magnetic field distribution in this mode has obvious gradient characteristics. Unlike the local detection in the traditional method, the magnetic field in the magnetically induced wave mode has the characteristic of non-locality. Therefore, no matter where the foreign object appears in the detection antenna, the magnetic field will change drastically, enabling rapid and global foreign object detection.

[0016] The foreign object detection method and system of the present invention have a detection area coverage of over 90%, exceeding most current mainstream methods; the main components of the detection antenna are PCB board and copper foil, which are extremely low in cost, simple in structure, easy to install, and occupy a small volume; the topology of the detection circuit and the complexity of the required microcontroller program are lower than those of mainstream methods, and the overall cost is reduced by at least 50%. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the reverse side of the printed circuit board of the detection antenna in the method and system for detecting foreign objects using a gradient magnetic field realized by magnetically induced waves, as described in this invention.

[0018] Figure 2 This is a schematic diagram of a metal coil resonant unit and a detection coil located at the corner of the printed circuit board of the detection antenna in the method and system for detecting foreign objects using a gradient magnetic field realized by magnetic induced waves, as described in this invention.

[0019] Figure 3 This invention relates to a method and system for detecting foreign objects using a gradient magnetic field generated by magnetically induced waves, and the gradient magnetic field distribution diagram in the magnetically induced wave mode.

[0020] Figure 4 This is a schematic diagram of the framework structure of the system for detecting foreign objects using a gradient magnetic field generated by magnetically induced waves, as described in this invention.

[0021] Figure 5 This is an example diagram of a car wireless charging system used in the method and system for foreign object detection based on a gradient magnetic field generated by magnetically induced waves, as described in this invention. Detailed Implementation

[0022] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0023] See Figure 1 This invention provides a method and system for foreign object detection using a gradient magnetic field generated by magnetically induced waves, for use in wireless charging of electric vehicles. The method and system include a detection antenna and a circuit. Utilizing a gradient magnetic field generated by a magnetically induced wave mode in the system, foreign object detection is non-local; regardless of the location of the foreign object on the detection antenna, the magnetic field changes drastically, enabling rapid and global foreign object detection. The method and system for foreign object detection using a gradient magnetic field generated by magnetically induced waves are described below with reference to the accompanying drawings.

[0024] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0025] See Figure 1 This diagram illustrates the reverse side of the printed circuit board of the detection antenna in the method for foreign object detection using a gradient magnetic field generated by magnetically induced waves, as described in this invention. (See also...) Figure 2 This diagram illustrates the method for foreign object detection using a gradient magnetic field generated by magnetically induced waves, and the structural schematic of a metal coil resonant unit located at the corner of the printed circuit board of the detection antenna in the system, along with the detection coil. The following is a related illustration... Figure 1 and Figure 2 The present invention describes a system for detecting foreign objects using a gradient magnetic field generated by magnetically induced waves.

[0026] like Figure 1 and Figure 2As shown, the foreign object detection system of the present invention, which utilizes a gradient magnetic field realized by magnetically induced waves for foreign object detection during wireless charging, includes a detection antenna, an excitation coil, an excitation source, a detection coil 24, and a detection circuit. The detection antenna includes a printed circuit board 21 and multi-turn metal coils 22 arranged on the front and back sides of the printed circuit board 21. The multi-turn metal coils 22 arranged on the front and back sides are arranged opposite each other and connected through vias 211. Each metal coil 22 arranged on the front or back side is connected to a lumped capacitor 23, thus forming a metal coil resonant unit. A symmetry-broken gradient is introduced into the array of metal coil resonant units 22. The detection antenna is located on the front side of the wireless charging transmitter. The line is located between the transmitter and receiver of the wireless charging device; the excitation coil is located at the center of the front side of the printed circuit board 21; the excitation source is connected to the excitation coil, and the excitation source is used to transmit the excitation signal to the excitation coil. The magnetic dipole formed by the ring current on the excitation coil excites the magnetic induced wave mode in the resonant unit of the array of metal coils. The magnetic field distribution of the excited magnetic induced wave mode has a gradient; there are multiple detection coils, and multiple detection coils 24 are located on the back side of the printed circuit board 21; the detection circuit is connected to the detection coil 24. The detection circuit is used to detect the induced voltage formed at the detection coil 24 in real time during the wireless charging process, and to determine whether the induced voltage changes. When the induced voltage changes, it is determined that there is a foreign object near the transmitter of the wireless charging device.

[0027] When the wireless charging transmitter is located on the ground, the detection antenna of the present invention is located above the wireless charging transmitter, and the front side of the printed circuit board 21 (the side where the excitation coil is located) is close to the wireless charging transmitter, and the back side of the printed circuit board 21 (the side where the detection coil is located) is close to the wireless charging receiver. The detection coil is located close to the ground, which can better detect foreign objects on the ground.

[0028] Preferably, the multi-turn metal coils 22 on the front and back of the printed circuit board 21 are positioned correspondingly, that is, they are arranged back-to-back and aligned. The metal coils 22 are made of copper wire. Figure 2 In the example shown, the copper wire is wound four times, which can be referred to as a four-turn metal coil, and the wound metal coil is circular. Vias are provided on the printed circuit board 21, connecting the front and back sides of the printed circuit board 21. The connection (electrical connection) between the front and back metal coils 22 is achieved by placing wires or plating copper in the vias. The via 211 can be located at the end inside the metal coil 22 or at the end outside the metal coil 22.

[0029] Furthermore, each metal coil resonant unit 22 is configured with a gradually varying linewidth, size, number of turns, thickness, or period length along one direction, with the period length being the center distance between two adjacent metal open resonant rings, so that the phase coupling strength between adjacent metal coil resonant units is gradient-coupled; or, the inductance value of each metal coil resonant unit 22 or the capacitance value of the lumped capacitor 23 connected to each metal coil resonant unit 22 is configured with a linearly gradually varying value, so that the phase coupling strength between adjacent metal coil resonant units is gradient-coupled.

[0030] The gradual change in linewidth, size, number of turns, thickness, or period length, or the linear gradual change in inductance or capacitance of each metal coil resonant unit 22, occurs from the center to both sides or from one side to the other. For example, the metal resonant units 22 can be arranged in a gradually changing one-dimensional direction along the surface of the printed circuit board 21, which can be horizontal, vertical, or diagonal (i.e., from one side to the other), or from the inside to the outside or from the outside to the inside (i.e., from the center to both sides or from both sides to the center). Figure 1 As shown, changing the size of the metal coil resonant unit 22, making the size decrease linearly from the middle to both sides, leads to changes in the mutual inductance and coupling between different metal coil resonant units 22, thereby achieving the effect of constructing a gradient field.

[0031] The method for introducing symmetry breaking in this invention includes, but is not limited to: changing the geometric parameters of the resonant unit (metal open-circuit resonant ring), such as its size, linewidth, number of turns, and thickness, or the parameters of lumped elements such as capacitors and inductors. Changing just one parameter can introduce symmetry breaking. In principle, changing these parameters changes the coupling strength between the resonant units, causing the magnetic field excited by the excitation source to change from isotropic uniform propagation / coupling to anisotropic non-uniform / gradient coupling.

[0032] Furthermore, a lumped capacitor is connected to the end of each metal coil 22 disposed on the reverse side of the printed circuit board 21. The capacitance values ​​of each lumped capacitor can be equal or can be set to vary linearly as needed.

[0033] Furthermore, the metal coils 22 are arranged at intervals along the horizontal and vertical directions on both the front and back sides of the printed circuit board 21, forming an array of multiple metal coils 22. The size and spacing of the metal coils 22 can be determined according to the size of the printed circuit board 21. The size, line width, and cycle length of the metal coils 22 can be designed according to the actual detection requirements. The selection of their size can be determined based on the size of the foreign object to be detected. For example, in Figure 1In the example shown, the period length of the metal coil 22 is 33 mm (i.e., the center-to-center distance between two adjacent metal coils 22), and each metal coil 22 is wound with copper wire with a line width of 0.5 mm. The inner diameter of the metal coil 22 ring is 12 mm, and the outer diameter is 16 mm. In another preferred embodiment, each metal coil 22 can be obtained by etching copper foil with a thickness of 1 oz, and the copper foil is disposed on both sides of the printed circuit board 21.

[0034] Furthermore, such as Figure 2 As shown, the detection coil 24 surrounds the outside of the metal coil 22 located at the corresponding position. Figure 2 In the example shown, the dimensions of the detection coil 24 can be set according to actual detection needs. Specifically, it can be set according to the size of the foreign object to be detected. For example, the outer diameter of the detection coil 24 can be set to 16.5mm, and the line width of the detection coil 24 is smaller than the line width of the metal coil 22. The detection coil 24 has a lead-out terminal on one side, which is used to connect to the detection circuit. The detection coil 24 is made of copper. The detection coil 24 has one turn, i.e., one loop, and is circular. Of course, the structure of the detection coil 24 is not limited to one turn; it can also have multiple turns.

[0035] Combination Figure 1 As shown, there are multiple detection coils 24. Figure 1 In the example shown, there are 9 detection coils 24, located at... Figure 1The metal coils identified by numbers 1 to 9 have the following configurations: one detection coil 24 surrounds the outer edge of the central metal coil 22; four detection coils 24 surround the outer edge of the metal coil 22 located at the corners of the printed circuit board 21; and four more detection coils 24 surround the outer edge of the metal coil 22 located at the center of the side of the printed circuit board 21. This arrangement of the detection coils 24 allows for the determination of the location of foreign objects based on changes in the induced voltage of the corresponding detection coils 24. Furthermore, the size of the foreign object can be predicted based on the number of changes in the induced voltage of the detection coils 24. For example, if the induced voltage of the detection coils 24 located around the metal coils 22 identified by numbers 1 and 3 changes, it can be determined that the foreign object is located in the area corresponding to these two detection coils. If it is necessary to alert the user to the location of the foreign object, a contour area corresponding to the outer contour of the printed circuit board 21 can be displayed on the user's mobile terminal. Then, the positions of numbers 1 and 3 can be displayed within this contour area, and the foreign object location area can be displayed, circling the positions of numbers 1 and 3. For example, when a foreign object is located directly above the printed circuit board 21, and the induced voltage of the four detection coils 24 corresponding to numbers 1, 3, 4, and 6 changes, it indicates that the foreign object is located within the area specified by numbers 1, 3, 4, and 6. The outline of the foreign object can then be drawn based on the intensity of the changes in the induced voltage of the four detection coils, thus determining the predicted size of the foreign object. When drawing the outline of the foreign object, if the intensity of the change in the induced voltage of the detection coil is large, a point closer to that detection coil can be selected for drawing; if the intensity of the change in the induced voltage of the detection coil is small, a point farther away from that detection coil can be selected for drawing.

[0036] Furthermore, the excitation coil is arranged around the outside of the metal coil located at the center. This excitation coil is located on the front side of the printed circuit board 21. Its structure is similar to that of the detection coil 24, except that its line width is thicker than that of the detection coil 24, while the line width of the excitation coil is smaller than that of the metal coil 22. The outer diameter of the excitation coil is also 16.5 mm. A lead-out terminal is formed on one side of the excitation coil, which is connected to an excitation source to provide an excitation signal to the excitation coil. This excitation coil has one turn, i.e., one complete loop, and is circular. Of course, the structure of the excitation coil is not limited to one turn; it can also have multiple turns.

[0037] In one specific embodiment of the present invention, there are multiple detection antennas, and the array of multiple detection antennas is arranged to cover the area where the wireless charging transmitter is located.

[0038] Accordingly, the number of excitation circuits and detection circuits corresponding to the detection antennas is consistent with the number of detection antennas. Each excitation circuit can be connected to an excitation source, or each excitation circuit can be connected to an excitation source. The excitation circuit outputs an excitation signal of a specific frequency to the excitation coil.

[0039] Specifically, in use, the foreign object detection system of the present invention can be placed above or in front of the transmitter of the wireless charging device, with the detection coil of the foreign object detection system facing the receiver of the wireless charging device. Figure 5 As shown, the wireless charging transmitter (transmitting coil) is located on the ground. The foreign object detection system of this invention is also located on the ground and above the transmitter. Alternatively, the foreign object detection system and the wireless charging transmitter can be integrated and encapsulated in a housing. This housing is then placed on the ground or embedded in a groove in the ground surface, with the upper surface of the housing flush with the ground. The foreign object detection system inside the housing is located on top, while the wireless charging transmitter is located below. A wireless charging receiver is installed on the chassis of the car. During wireless charging, the car drives over the wireless charging transmitter to begin wireless charging. When a metallic foreign object appears within the working range of the wireless charging system, the gradient magnetic field distribution of the foreign object detection system is disrupted, causing a change in the induced voltage on the detection coil. The digital value calculated from the induced voltage (the calculation and judgment functions can be implemented by a microcontroller) differs from the value in the absence of a foreign object, indicating the presence of a foreign object.

[0040] In a preferred embodiment, the phase shift caused by the foreign object can significantly change the gradient magnetic field, establishing a mapping relationship between phase shift, gradient response, and voltage output, thereby enabling accurate identification of the foreign object. Specifically, the phase shift caused by the foreign object affects the magnetic field distribution, thus affecting the gradient slope and causing a change in the induced voltage at the detection coil, thereby confirming the presence of the foreign object.

[0041] In the foreign object detection system of this invention, during operation, the excitation source transmits an excitation signal of a specific frequency to the excitation coil through the excitation circuit. The magnetic dipole formed by the ring current in this excitation coil excites a magnetically induced wave mode in the metal coil resonant unit array. The magnetic field distribution under this mode exhibits a significant gradient, such as... Figure 3 As shown, the detection coil located on the printed circuit board generates an induced power supply under the action of a magnetic field, and transmits the analog voltage value back to the detection circuit. The microcontroller in the detection circuit converts the analog voltage value into a digital value and records it as the standard value for the system when it is in a foreign object-free state. When a foreign object appears in the system, the gradient magnetic field distribution is disrupted, and the induced voltage on the detection coil changes. The microcontroller detects that the digital value is different from that in the foreign object-free state and determines that a foreign object is present.

[0042] like Figure 4 As shown, the working process of the circuit part of the present invention is as follows: the excitation circuit of the present invention outputs an excitation signal of a specific frequency to the excitation coil. The magnetic dipole formed by the ring current excites a magnetic induced wave mode in the metal coil resonant unit array. At this time, the high impedance detection port (i.e. the detection coil) located on the reverse side of the printed circuit board (PCB) forms an induced voltage under the action of the magnetic field and transmits the analog voltage value back to the detection circuit part.

[0043] The working principle of this invention is as follows: The detection antenna proposed in this invention consists of a metal coil resonant unit array on a PCB (printed circuit board), one excitation coil, and nine receiving coils (the number of receiving coils is not limited to nine; it can be more or less, but there must be at least one receiving coil). At a specific frequency, the magnetic dipole formed by the current in the excitation coil will excite a magnetically induced wave mode in the resonant unit array. The magnetic field distribution in this mode has a significant gradient; this means that the magnetic field strength varies greatly at different locations on the detection antenna board, and the digital quantity (the value converted from the induced voltage) corresponding to different detection ports (i.e., detection coils) is also different. Therefore, this... The magnetically induced wave (MOV) mode is more sensitive to foreign objects of different locations and sizes, resulting in higher detection accuracy. The propagation of MOV in the resonant coil array exhibits strong directionality and is related to the impedance of the excitation and detection coils. Therefore, adjusting the impedance of the excitation and detection coils can control the propagation path and intensity of the MOV. At specific frequencies, different input and output impedances correspond to different MOV modes. Thus, in the initial design phase, the MOV mode implemented by the system can be adjusted by modifying the impedance of the excitation and detection coils. Adjusting the coil impedance can be achieved by adjusting the coil dimensions, including coil size, linewidth, and number of turns. Unlike localized detection in traditional methods, the magnetic field in the MOV mode is non-local. Therefore, regardless of the location of the foreign object on the detection antenna, the magnetic field will change drastically, enabling rapid and global foreign object detection.

[0044] For a single resonant coil (i.e., a metal coil resonant unit), each resonant coil can be considered as an RLC circuit (i.e., a series resistor, capacitor, and inductor) system, where the capacitance, inductance, and corresponding resonant frequency are all adjustable parameters. If we consider a one-dimensional case, i.e., using N resonant coils with identical electromagnetic parameters to form a one-dimensional array system, then after exciting the first resonant coil, the electromagnetic wave will propagate sequentially to the second, third, and so on up to the Nth coil, forming a traveling wave mode with a definite phase delay. Since the energy in these resonant coils all comes from the magnetic induction voltage generated by coupling, the electromagnetic wave in this propagation mode is called a "magnetically induced wave" or "magnetically induced wave." Similarly, the above one-dimensional case can be extended to a two-dimensional array, forming a two-dimensional magnetically induced wave propagation system; in this case, electromagnetic energy couples and diffuses in two directions, and its phase evolution is determined by the mutual inductance matrix between each unit and the self-resonance characteristics. The essence of this mode is a collective excited state driven by discretized magnetic coupling.

[0045] Magnetic induced waves have the following two characteristics: ① Because the coupling between resonant units has different paths and directions, a single excitation coil can correspond to multiple receiving coils; ② Its phase evolution is highly sensitive to changes in the local electromagnetic environment. Based on these characteristics, the principle of magnetic induced waves can be used to detect the location and size of foreign objects. Specifically, multiple detection ports can be set up within the detection area, and the detection results of all ports can be summarized and encoded; the location of the foreign object can be determined according to the different positions of the ports, and the size of the foreign object can be determined according to the different numbers of ports.

[0046] The conditions for realizing a gradient magnetic field under the principle of magnetically induced waves are as follows: ① A controllable symmetry breaking must be introduced based on the realization of a uniform magnetic field—for example, systematically adjusting the capacitance or geometric dimensions of adjacent coils along a certain direction to form a linearly changing resonant frequency gradient; ② The excitation signal adopts a phase-gradient injection method (such as a linear phase ramp) so that the spatial superposition of the magnetic flux response produces directional intensity attenuation. Based on the above constraints, magnetically induced waves can generate a stable gradient magnetic field with a definite spatial derivative in a two-dimensional plane.

[0047] The following experiment was conducted on the foreign object detection system of the present invention: A detection antenna was constructed by etching resonant units of specific size and period constant onto an FR4 board (50cm x 60cm). An excitation coil was placed on the front side of the central region, and multiple detection coils were evenly arranged on the back side. The excitation signal was then transmitted to the excitation coil, and the induced voltage of the receiving coil was detected by a detection circuit. A foreign object was placed on top of the FR4 board. During the experiment, a plastic shell was placed on top of the FR4 board for isolation, and the foreign object was placed on the plastic shell. The experiment revealed that the induced voltage of the detection coil at the corresponding position of the foreign object changed, and the closer the foreign object was to the detection coil, the greater the change in induced voltage. The experiment showed that the present invention can achieve foreign object detection, positioning, and size recognition within a 50cm x 60cm area.

[0048] This invention also provides a method for detecting foreign objects using a gradient magnetic field generated by magnetically induced waves, which is used for detecting foreign objects during wireless charging. The method is described below.

[0049] The foreign object detection method of the present invention includes the following steps: A detection antenna is provided, which includes a printed circuit board and a multi-turn metal coil arranged on the front and back sides of the printed circuit board. The multi-turn metal coils arranged on the front and back sides are arranged opposite to each other and connected through vias. A lumped capacitor is connected to each metal coil arranged on the front or back side, thereby forming a metal coil resonant unit. A symmetry-breaking gradient is introduced into the array of the metal coil resonant units. Place the detection antenna in front of the wireless charging transmitter, positioning it between the wireless charging transmitter and receiver. An excitation coil is placed at the center of the front side of the printed circuit board; An excitation source is provided and connected to an excitation coil. The excitation source transmits the excitation signal to the excitation coil. The magnetic dipole formed by the ring current on the excitation coil excites a magnetically induced wave mode in the resonant unit of the array of metal coils. The magnetic field distribution of the excited magnetically induced wave mode has a gradient. Multiple detection coils are set on the reverse side of the printed circuit board; The induced voltage generated at the detection coil is detected in real time. If the detected induced voltage changes during the wireless charging process, it is determined that there is a foreign object near the transmitter of the wireless charger.

[0050] Furthermore, the step of introducing a symmetry-breaking gradient into the array of metal coil resonant units includes: Each metal coil resonant unit is set with a gradually varying linewidth, size, number of turns, thickness, or period length along one direction. The period length is the center distance between two adjacent metal open resonant rings, so that the phase coupling strength between adjacent metal coil resonant units is gradient-type coupling. Alternatively, the inductance value of each metal coil resonant unit or the capacitance value of the lumped capacitor connected to each metal coil resonant unit can be set to change linearly and gradually, so that the phase coupling strength between adjacent metal coil resonant units is gradient-type coupling.

[0051] Furthermore, it also includes: using a phase-gradient injection method to inject the excitation signal generated by the excitation source, so that the spatial superposition of the magnetic flux response produces directional intensity attenuation.

[0052] Furthermore, when setting up the excitation coil, the excitation coil is wrapped around the outside of the metal coil located at the center.

[0053] Furthermore, when setting up the detection coil, the detection coil is wrapped around the outside of the metal coil located at the center; The detection coil is wrapped around the outside of a metal coil located at the corner of the printed circuit board; The detection coil is wrapped around the outside of a metal coil located in the middle of the side of the printed circuit board.

[0054] In one specific embodiment of the present invention, the method further includes: The location of the foreign object can be determined by the position of the detection coil that detects changes in the induced voltage.

[0055] In one specific embodiment of the present invention, multiple detection antennas are provided, and multiple detection antenna arrays are arranged to cover the area where the wireless charging transmitter is located.

[0056] The foreign object detection system and method of the present invention have a detection area coverage of over 90%, exceeding most current mainstream methods; the main components of the detection antenna are PCB board and copper foil, which are extremely low in cost, simple in structure, easy to install, and occupy a small volume; the topology of the detection circuit and the complexity of the required microcontroller program are lower than those of mainstream methods, and the overall cost is reduced by at least 50%.

[0057] The present invention has been described in detail above with reference to the accompanying drawings and embodiments. Those skilled in the art can make various modifications to the present invention based on the above description. Therefore, certain details in the embodiments should not be construed as limiting the present invention, and the scope of protection of the present invention shall be defined by the appended claims.

Claims

1. A method for foreign object detection using a gradient magnetic field generated by magnetically induced waves, used for foreign object detection during wireless charging, characterized in that, The foreign object detection method includes the following steps: A detection antenna is provided, which includes a printed circuit board and a multi-turn metal coil arranged on the front and back of the printed circuit board. The multi-turn metal coils arranged on the front and back are arranged opposite to each other and connected through vias. A lumped capacitor is connected to each metal coil arranged on the front or back, thereby forming a metal coil resonant unit. A symmetry-breaking gradient is introduced into the array of the metal coil resonant units. The detection antenna is placed in front of the transmitter of the wireless charging device, and the detection antenna is positioned between the transmitter and receiver of the wireless charging device. An excitation coil is disposed at the center of the front side of the printed circuit board; An excitation source is provided and connected to the excitation coil. The excitation source is used to transmit an excitation signal to the excitation coil. The magnetic dipole formed by the ring current on the excitation coil excites a magnetically induced wave mode in the resonant unit of the array of metal coils. The magnetic field distribution of the excited magnetically induced wave mode has a gradient. Multiple detection coils are provided on the reverse side of the printed circuit board; The induced voltage generated at the detection coil is detected in real time. If the detected induced voltage changes during the wireless charging process, it is determined that there is a foreign object near the transmitter of the wireless charger.

2. The method for detecting foreign objects using a gradient magnetic field generated by magnetically induced waves as described in claim 1, characterized in that, The step of introducing a symmetry-breaking gradient into the array of metal coil resonant units includes: Each metal coil resonant unit is set with a gradually varying linewidth, size, number of turns, thickness, or period length along one direction. The period length is the center distance between two adjacent metal open resonant rings, so that the phase coupling strength between adjacent metal coil resonant units is gradient-coupled. Alternatively, the inductance value of each metal coil resonant unit or the capacitance value of the lumped capacitor connected to each metal coil resonant unit can be set to change linearly and gradually, so that the phase coupling strength between adjacent metal coil resonant units is gradient-type coupling.

3. The method for detecting foreign objects using a gradient magnetic field achieved by magnetically induced waves as described in claim 1, characterized in that, Also includes: The excitation signal generated by the excitation source is injected using a phase gradient method so that the spatial superposition of the magnetic flux response produces directional intensity attenuation.

4. The method for detecting foreign objects using a gradient magnetic field achieved by magnetically induced waves as described in claim 1, characterized in that, When setting up the excitation coil, the excitation coil is wrapped around the outside of the metal coil located at the center.

5. The method for detecting foreign objects using a gradient magnetic field achieved by magnetically induced waves as described in claim 1, characterized in that, When setting up the detection coil, the detection coil is wrapped around the outside of the metal coil located at the center; The detection coil is arranged around the outside of a metal coil located at the corner of the printed circuit board; The detection coil is arranged around the outside of a metal coil located in the middle of the side of the printed circuit board.

6. A system for foreign object detection using a gradient magnetic field generated by magnetically induced waves, used for foreign object detection during wireless charging, characterized in that, The foreign object detection system includes: The detection antenna includes a printed circuit board and multiple turns of metal coils arranged on the front and back sides of the printed circuit board. The multiple turns of metal coils arranged on the front and back sides are arranged opposite each other and connected through vias. A lumped capacitor is connected to each metal coil arranged on the front or back side, thereby forming a metal coil resonant unit. A symmetry-breaking gradient is introduced into the array of the metal coil resonant units. The detection antenna is located in front of the transmitter of the wireless charging device and is located between the transmitter and receiver of the wireless charging device. The excitation coil is located at the center of the front side of the printed circuit board; An excitation source is connected to the excitation coil. The excitation source is used to transmit an excitation signal to the excitation coil. The magnetic dipole formed by the ring current on the excitation coil excites a magnetically induced wave mode in the resonant unit of the array of metal coils. The magnetic field distribution of the excited magnetically induced wave mode has a gradient. Multiple detection coils are located on the reverse side of the printed circuit board; A detection circuit is connected to the detection coil. The detection circuit is used to detect the induced voltage formed at the detection coil in real time during the wireless charging process, and to determine whether the induced voltage changes. When the induced voltage changes, it is determined that there is a foreign object near the transmitter of the wireless charging device.

7. The system for detecting foreign objects using a gradient magnetic field generated by magnetically induced waves as described in claim 6, characterized in that, Each metal coil resonant unit is set with gradually varying linewidth, size, number of turns, thickness, or period length along one direction. The period length is the center distance between two adjacent metal open resonant rings, so that the phase coupling strength between adjacent metal coil resonant units is gradient-coupled. Alternatively, the inductance value of each metal coil resonant unit or the capacitance value of the lumped capacitor connected to each metal coil resonant unit can be set to change linearly and gradually, so that the phase coupling strength between adjacent metal coil resonant units is gradient-type coupling.

8. The system for detecting foreign objects using a gradient magnetic field achieved by magnetically induced waves as described in claim 6, characterized in that, The excitation signal generated by the excitation source adopts a phase gradient injection method so that the spatial superposition of the magnetic flux response produces directional intensity attenuation.

9. The system for detecting foreign objects using a gradient magnetic field induced by magnetically induced waves as described in claim 6, characterized in that, The excitation coil surrounds the outside of the metal coil located at the center.

10. The system for detecting foreign objects using a gradient magnetic field realized by magnetically induced waves as described in claim 6, characterized in that, The detection coil is arranged around the outside of the metal coil located at the center, around the outside of the metal coil located at the corner of the printed circuit board, and around the outside of the metal coil located at the middle of the side of the printed circuit board.

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