Antenna and power transmission system

Abstract

The purpose of the present disclosure is to transmit a concentrated surface wave in a predetermined direction to a power receiving device, etc.　The present disclosure is an antenna consisting of: a resonance unit which is provided with a first electrode and a second electrode that face each other and a microstrip line that electrically connects the first electrode and the second electrode and in which the space between the first electrode and the second electrode has the electrical length of a half wavelength of a frequency related to power; and a ground plate that is electrically connected to the microstrip line at one point.

Description

Antennas, power transmission systems

[0001] The present disclosure relates to directional antennas.

[0002] Surface waves in the electromagnetic field propagate as if they are confined near the surface of the metal and do not diffuse into space, so transmission efficiency is higher than that of wireless power transmission methods that use radio waves, which propagate while spreading through space.

[0003] Wireless power transmission methods using electric field resonance antennas can achieve high transmission efficiency over short distances, but the generated electric field rapidly attenuates in the air, making it impossible to transmit power over long distances. However, when electromagnetic field waves propagate along a metal surface, the energy is confined near the metal surface rather than diffusing into the air, making it possible to transmit power over longer distances. These waves are called surface waves (Zennek waves). As prior art, Non-Patent Document 1 proposes an antenna that transmits power wirelessly by propagating surface waves along a metal surface.

[0004] Here, the conventional technology will be briefly described with reference to FIG. 7 . FIG. 7 is a perspective view of a conventional power transmitting antenna. As shown in FIG. 7 , a conventional power transmitting antenna 201 is mainly composed of an electrode 210, a primary coil 211, a secondary coil 212, a power feed point 216, and a ground (plate) 219. The primary coil 211 is electrically connected between the electrode 210 and the ground 219 and between the electrode 210 and the ground 219. The ground 219 is installed on the surface of the metal plate 100. The power feed point 216 is electrically connected to the secondary coil 212. The secondary coil 212 is magnetically coupled with the primary coil 211, thereby being able to input and output power to and from the electrode 210.

[0005] "Experimental Realization of Zenneck Type Wave-based Non-Radiative, Non-Coupled Wireless Power Transmission" (Scientific Reports 2020 Jan 22)

[0006] However, in conventional technology, the radiation directivity of the antenna is isotropic, transmitting surface waves in all directions (front, back, left, and right) along the metal surface, resulting in power being transmitted in directions other than the desired direction of the power receiving device, reducing transmission efficiency. Furthermore, surface waves radiated in unintended directions are reflected by the edges of the metal plate 100, interfering with the desired waves and creating null points on the metal with extremely low power receiving efficiency. As such, conventional antennas that generate surface waves lack directionality, resulting in the problem of propagating surface waves in all directions (front, back, left, and right) relative to the metal plate 100, as shown in Figure 7.

[0007] The present invention has been made to solve the above-mentioned problems, and has as its object to transmit surface waves intensively in a predetermined direction of a power receiving device or the like.

[0008] In order to solve the above problem, the invention of claim 1 is an antenna comprising: a first electrode and a second electrode facing each other; a microstrip line electrically connecting the first electrode and the second electrode; a resonator section having an electrical length of half the wavelength of a frequency related to power between the first electrode and the second electrode; and a ground plate electrically connected to the microstrip line at one point.

[0009] As described above, the present invention has the effect of enabling surface waves to be transmitted intensively in a predetermined direction.

[0010] Fig. 1 is a perspective view of a wireless power transmitting antenna according to an embodiment; Fig. 2 is a side view of a wireless power transmitting antenna according to an embodiment; Fig. 3 is a perspective view of the power transmitting antenna showing the operation of the wireless power transmitting antenna according to an embodiment; Fig. 4 is a side view of the power transmitting antenna showing the operation of the wireless power transmitting antenna according to an embodiment; Fig. 5 is a perspective view of the power transmitting antenna showing the operation of the wireless power transmitting antenna according to an embodiment; Fig. 6 is a diagram showing an application example of the present embodiment; Fig. 7 is a perspective view of a conventional wireless power transmitting antenna;

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0012] In this embodiment, a wireless power transmission antenna will be described, and in particular, a surface wave antenna with directivity that strengthens the power transmitted in the forward direction of the antenna and weakens the power transmitted in the lateral direction.

[0013] [Configuration of the embodiment] Fig. 1 is a perspective view of a wireless power transmission antenna according to the embodiment, and Fig. 2 is a side view of the wireless power transmission antenna according to the embodiment.

[0014] 1 and 2 , a power transmitting antenna 1 according to the embodiment is installed on a metal plate 100. The power transmitting antenna 1 is mainly composed of a resonating unit 13 that resonates at a specific frequency, a feeding point 16 for inputting power to the resonating unit 13 or extracting power from the resonating resonating unit 13, a substrate 10, a via 15, and a ground (plate) 19.

[0015] The resonator 13 is mainly composed of an electrode 11, an electrode 12, and a microstrip line 14. The electrodes 11 and 12, the microstrip line 14, the via 15, and the ground 19 are made of conductors and can be made using a substrate with metal foil attached to a dielectric or a metal plate. The substrate 10 is made of an insulator.

[0016] The electrodes 11 and 12 are electrically connected to the substrate 10 in a state where they stand upright perpendicular to the substrate 10. The electrodes 11 and 12 are also provided so that their electrode surfaces face each other. The electrodes 11 and 12 may have any shape as long as they can store electric charge and generate an electric field around them.

[0017] The microstrip line 14 is provided on the substrate 10 and is electrically connected to the electrodes 11 and 12 between the electrodes 11 and 12 .

[0018] The via 15 penetrates the substrate 10 between the microstrip line 14 and the ground 19, electrically connecting the microstrip line 14 and the ground 19 at one point. The ground 19 is placed on the metal plate 100.

[0019] The feed point 16 is electrically connected to the microstrip line 14 and the ground 19. That is, the ground side of the feed point 16 is connected to the ground 19 to match the ground potential. Specifically, the via 15 electrically connects the center part of the microstrip line 14 between the electrode 11 and the electrode 12 to the ground 19 at one point. The feed point 16 is provided at an asymmetric position on the microstrip line 14 between the electrode 11 and the via 15, which matches the impedance of the power transmission circuit.

[0020] The metal plate 100 acts as a guide for the propagation of the surface wave. The surface wave radiated from the power transmitting antenna 1 propagates along the surface of this metal plate 100, thereby transmitting power efficiently. The ground 19 is capacitively coupled to the metal plate 100.

[0021] [Operation of the embodiment] Next, the operation of the power transmitting antenna 1 will be described with reference to Fig. 3 to Fig. 5. Fig. 3 and Fig. 5 are perspective views of the power transmitting antenna showing the operation of the wireless power transmitting antenna according to the embodiment. Fig. 4 is a side view of the power transmitting antenna showing the operation of the wireless power transmitting antenna according to the embodiment.

[0022] As shown in Fig. 3, the length from the electrode 11 to the electrode 12 of the power transmitting antenna 1 is λ / 2 (half wavelength). As such, the resonator 13 has an electrical length between the electrodes 11 and 12 that is half the wavelength of the frequency related to the power. Therefore, when high-frequency power is input to the resonator 13 and resonates, a standing wave with maximum voltage amplitude is generated at both ends (electrodes 11 and 12) of the resonator 13, as shown in Fig. 4, and the voltage amplitude becomes zero at the center of the resonator 13. The center of the resonator 13, where the voltage becomes zero, is connected to the ground 19 via the via 15. Furthermore, with reference to the current distribution, the current amplitude becomes zero at both ends of the resonator 13 and becomes maximum at the center of the resonator 13.

[0023] The impedance is small at the center of the resonator 13 because the voltage is small and the current is large. As you move from the center of the resonator 13 to the edge, the voltage increases and the current decreases, so the impedance increases. Although not shown in Figure 4, if the feed point 16 is located at a position where the voltage-to-current ratio is exactly 50 Ω, as shown in Figure 2, impedance matching can be achieved between the transmitting antenna 1 and the transmitting circuit when a transmitting circuit with an impedance of 50 Ω is connected to the feed point 16. The same applies to the receiving antenna, and impedance matching can be achieved between the receiving antenna and the receiving circuit.

[0024] Next, the reason why the power transmitting antenna 1 has directivity will be described with reference to FIG.

[0025] When high-frequency power is input to the resonator 13 and resonates, a voltage is generated between the electrodes 11 and 12, creating a potential difference between them and the metal plate 100, generating surface waves of an electric field between the electrodes 11 and 12 and the metal plate 100. The generated surface waves propagate along the surface of the metal plate 100. The charges accumulated on the electrodes 11 and 12 are the same in magnitude but opposite in sign (i.e., the voltages on the electrodes 11 and 12 are in opposite phase). At this time, the surface waves generated from the electrodes 11 and 12 have opposite phases in the (right) direction of Figure 5 and therefore cancel each other out. They also cancel out in the (left) direction.

[0026] The surface wave traveling in the (forward) direction from electrode 12 inverts in phase as it travels the half-wavelength distance from electrode 12 to electrode 11, so it becomes in phase with the surface wave generated from electrode 11 and constructively interacts with it. Surface waves traveling in the (backward) direction also constructively interact with each other in a similar manner. Ultimately, no surface waves are generated in the left-right direction, and strong surface waves are generated only in the front-to-back direction. This makes it possible to realize a directional antenna that transmits power using surface waves on metal plate 100.

[0027] 1 to 5, the metal plate 100 is described, but it does not necessarily have to be in a plate shape. Therefore, the surface of the metal plate 100 is an example of a metal surface.

[0028] Furthermore, an antenna having the exact same structure as the power transmitting antenna can also be used as the power receiving antenna.

[0029] [Application Example of the Embodiment] Next, an application example of the power transmitting antenna 1 and the power receiving antennas of this embodiment will be described with reference to Fig. 6. Fig. 6 is a diagram showing an application example of this embodiment. In Fig. 6, the power transmitting device 101 is configured with the power transmitting antenna 1, and the power receiving devices 101a and 101b are configured with power receiving antennas. Furthermore, the power transmitting antenna 1 and the power receiving antennas form a power transmission system capable of transmitting power between the power transmitting antenna 1 and the power receiving antennas.

[0030] 6 , by placing a power transmitting device 101 having a power transmitting circuit 116 connected to a power feeding point 16, a power receiving device 101a having a power receiving circuit 116a connected to a power feeding point 16, and a power receiving device 101b having a power receiving circuit 116b connected to a power feeding point 16 on the same metal plate 100 and facing each other, it is possible to transmit power by surface waves on the metal plate 100. Note that electrode 111 corresponds to the electrode 11 described above, and electrode 112 corresponds to the electrode 12 described above.

[0031] The power transmission circuit 116 is composed of a power supply device that supplies power, an inverter that converts the power into high-frequency power, and an impedance matching circuit. The power receiving circuits 116a and 116b are composed of an impedance matching circuit, a converter that converts high-frequency power into direct current, and a load that uses or stores the received power.

[0032] As seen from the power transmitting device 101 in Fig. 6, a strong surface wave is sent to the power receiving device 101a, which is in the forward direction (see Fig. 5), and therefore a large amount of power can be transmitted. On the other hand, no surface wave is generated to the power receiving device 101b, which is in the right direction (see Fig. 5) as seen from the power transmitting device 101, and therefore power cannot be transmitted. By utilizing such antenna directivity and pointing the antenna 1 in the direction of the target to which power is to be transmitted, power can be transmitted efficiently and intensively.

[0033] [Examples of Use of the Present Embodiment] The following are examples of specific applications in which the power transmitting antenna 1 of the present embodiment is used to transmit power using surface waves that propagate on a metal surface.

[0034] (1) Electric Vehicles, Automated Guided Vehicles The power transmission device 101 transmits power wirelessly to vehicles traveling on roads or in factories. In this case, by installing a metal plate under the road or on the floor of a factory and transmitting power as a surface wave in the direction of the vehicle's movement, power can be continuously transmitted even while the vehicle is moving. In other words, when transmitting power, the power receiving antenna itself can move on the metal surface.

[0035] (2) Parked drones and mobile devices The power transmission device 101 wirelessly transmits power to drones that have landed on a charging station or to mobile devices that have been casually placed. Compared to conventional point-to-point power supply using a pair of opposing coils, the power supply area can be expanded laterally along the metal plate, which reduces the positioning precision required for charging and improves usability.

[0036] (3) IoT Sensor Network The power transmission device 101 transmits power wirelessly to battery-less sensors attached to the surface of metal devices or buildings. Since the surface waves carrying power can bend along the metal surface, power can be supplied by going around the metal surface even if the sensor is not directly visible as long as it is attached to the metal.

[0037] As described above, the power transmitting antenna 1 of this embodiment can transmit power along a metal surface using surface waves of an electromagnetic field, concentrating the power only in the front-rear direction, without transmitting the power in the left-right direction, thereby enabling highly efficient power transmission to a power receiving device.

[0038] Furthermore, the power transmitting antenna 1 does not transmit power in unnecessary directions (left and right directions), and the power receiving antenna does not receive power coming from unintended directions (left and right directions), so there is no interference between surface waves coming from both the front and back and the left and right, resulting in an extreme drop in received power.

[0039] Furthermore, by suppressing unnecessary radiation of electromagnetic waves, the risk of causing electromagnetic interference to surrounding electronic devices can be reduced.

[0040] With normal wireless power transmission, power cannot be transmitted unless the power transmitting device is within sight of the power receiving device. However, by using surface waves, power can be transmitted by going around the metal surface even if the other device (power receiving device) is not within sight.

[0041] When transmitting power using surface waves, the power itself does not move inside the metal but propagates through the space near the metal, so even if the conductivity of the metal that guides the surface waves is low, power transmission with little loss (high efficiency) is possible.

[0042] [Supplementary Note] The power transmitting antenna 1 of this embodiment is an example of an antenna, which includes not only antennas for wireless power transmission but also antennas for communication.

[0043] REFERENCE SIGNS LIST 1 power transmission antenna (example of antenna) 10 substrate 11 electrode (example of first electrode) 12 electrode (example of second electrode) 13 resonance portion 14 microstrip line 15 via 16 power feeding point 19 ground (ground plate) 100 metal plate

Claims

1. An antenna comprising: a resonator section having opposing first and second electrodes and a microstrip line electrically connecting the first and second electrodes, the resonator section having an electrical length of half the wavelength of the frequency related to the power between the first and second electrodes; and a ground plate electrically connected to the microstrip line at one point.

2. The antenna described in claim 1, comprising: a via that electrically connects a central portion of the microstrip line between the first electrode and the second electrode and the ground plate at one point; and a feed point provided at an asymmetric position between the via that matches the impedance of a power transmission circuit on the microstrip line and the first electrode.

3. An antenna as described in claim 1 or 2, wherein the surface waves of the electromagnetic field radiated from the antenna propagate along the metal surface on which the antenna is installed, and the antenna itself is capable of moving along the metal surface.

4. A power transmission system comprising a power transmitting antenna and a power receiving antenna configured with the antenna according to claim 1 or 2, capable of transmitting power between the power transmitting antenna and the power receiving antenna.

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