Antenna device and contactless power transmission system

Abstract

This antenna device is for use in a non-contact power transmission system and comprises a first resonant antenna having a first impedance and a second resonant antenna having a second impedance different from the first impedance.

Description

[Technical Field]

[0001] The present invention relates to a contactless power transfer system. [Background technology]

[0002] Resonant antennas that transmit wireless power using magnetic or electric field coupling can transmit power with higher transmission efficiency than antennas that transmit and receive radio waves, and are therefore used in battery-less contactless IC cards, wireless charging of smartphones, and power supply to electric vehicles.

[0003] However, it is known that with resonant antennas that use magnetic field coupling or electric field coupling, the impedance of the antenna changes and reflection increases when the distance between the antennas changes, so that transmission efficiency decreases depending on the distance between the antennas.

[0004] As a technique for solving this problem, for example, Patent Document 1 discloses a technique in which a means for detecting the power transmission / reception state determines whether or not the impedance matching condition is satisfied, and switches the impedance matching condition depending on the result. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-238372 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in order to actively detect the coupling state and perform switching control as in the prior art, power is required to carry out the process, making it impossible to transmit power efficiently.Furthermore, there are problems such as the circuit becoming more complex, the number of components increasing, and the board size increasing.

[0007] The present invention has been made in consideration of the above points, and aims to realize a contactless power transfer system that has little change in impedance even when the distance between antennas changes, and can transfer power with high transfer efficiency over a wide range. [Means for solving the problem]

[0008] According to the disclosed technology, there is provided an antenna device for use in a contactless power transmission system, comprising: a first resonant antenna having a first impedance; a second resonant antenna having a second impedance different from the first impedance; The antenna device is connected to a power transmitting and receiving circuit in the contactless power transfer system, and the first impedance is higher than the impedance of the power transmitting and receiving circuit, and the second impedance is lower than the impedance of the power transmitting and receiving circuit. An antenna arrangement is provided. [Effects of the Invention]

[0009] According to the disclosed technology, it is possible to realize a contactless power transfer system in which the change in impedance is small even when the distance between the antennas changes, and which can transfer power with high transfer efficiency over a wide range. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram illustrating an example of a basic configuration of a contactless power transmission system. [Figure 2] FIG. 10 is a diagram showing the reflection of a magnetic field antenna using an LC parallel resonant circuit. [Figure 3] FIG. 1 is a diagram showing the reflection of a magnetic field antenna using an LC series resonant circuit. [Figure 4] 1 is a diagram showing a power transmitting antenna 11 and a power receiving antenna 21 that use an LC parallel resonant circuit. [Figure 5] 1 is a diagram showing a power transmitting antenna 11 and a power receiving antenna 21 that use an LC series resonant circuit. [Figure 6]FIG. 10 is a diagram showing the relationship between the distance between antennas and impedance when a single high-impedance antenna is used. [Figure 7] FIG. 10 is a diagram showing the relationship between the distance between antennas and impedance when a single low-impedance antenna is used. [Figure 8] 1 is a diagram illustrating a configuration example of an antenna device according to an embodiment of the present invention. [Figure 9] 10 is a diagram showing the relationship between the distance between antennas and impedance when an antenna in which a high-impedance antenna and a low-impedance antenna are connected in parallel is used. FIG. [Figure 10] 1 is a diagram showing an example of the configuration of an antenna device including an LC series resonance magnetic field antenna and an electric field antenna that utilizes electric field coupling between electrodes. [Figure 11] 1 is a diagram illustrating a configuration example of an antenna device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention (the present embodiment) will be described with reference to the drawings. The embodiment described below is merely an example, and the embodiment to which the present invention is applied is not limited to the following embodiment.

[0012] (Example of a contactless power transmission system configuration and issues) An example of the basic configuration of a contactless power transfer system is shown in Fig. 1. As shown in Fig. 1, in the contactless power transfer system, the power transmitting side includes a power transmitting antenna 11, a matching circuit 12, an inverter 13, and a power supply 14. The power receiving side includes a power receiving antenna 21, a matching circuit 22, a rectifier circuit 23, and a load 24.

[0013] As shown in Fig. 1, the contactless power transfer system transfers power contactlessly between a power transmitting antenna 11 and a power receiving antenna 21 that face each other and form a coupling system. The power transmitting antenna 11 and the power receiving antenna 21 are magnetic field antennas made up of coils or electric field antennas made up of electrodes. Both the power transmitting antenna 11 and the power receiving antenna 21 are resonant antennas. A resonant antenna may also be called a "resonant antenna."

[0014] In contactless power transfer systems, unlike far-field antennas that continue to emit a constant amount of radio waves regardless of whether the other antenna is nearby or not, near-field magnetic field coupling antennas or electric field coupling antennas that utilize resonance between antennas do not emit power into the air when the other antenna is not nearby, and the power that has nowhere to go is reflected by the antenna and returned to the power transmission circuit.

[0015] Figure 2 shows the above phenomenon in a magnetic field antenna using an LC parallel resonant circuit. As shown in Figure 2, in a magnetic field antenna using an LC parallel resonant circuit, power is reflected without phase inversion, so the antenna can be regarded as a free end and has high impedance.

[0016] On the other hand, as shown in Figure 3, in a magnetic field antenna using an LC series resonant circuit, the phase is inverted and power is reflected, so the antenna can be considered as a fixed end and has low impedance.

[0017] If there is an opposing antenna near a resonant antenna, for example, the magnetic field created by the magnetically coupled power transmitting antenna 11 excites the resonance of the power receiving antenna 21, and the resonating power receiving antenna 21 creates a new magnetic field near the power transmitting antenna 11.

[0018] Therefore, as shown in Figure 4 (when an LC parallel resonant circuit is used) and Figure 5 (when an LC series resonant circuit is used), reflection from the power transmitting antenna 11 itself and reflection from the opposing antenna 21 are observed simultaneously. The reflection from the opposing antenna has an opposite sign to the reflection from the power transmitting antenna itself, and increases as the distance between the antennas becomes shorter.

[0019] As a result, the impedance of the antennas varies with the distance between the antennas, as shown in Figures 6 and 7. Figure 6 shows the case of a single high-impedance antenna, and Figure 7 shows the case of a single low-impedance antenna.

[0020] That is, in the case of a single high-impedance antenna as shown in Figure 6, the reflection from the opposing antenna increases as the distance between the antennas decreases, and at a certain distance the reflection from the opposing antenna cancels out and impedance matching is achieved, but as the distance between the antennas decreases further, the sign of the reflected wave reverses, the impedance further decreases, and reflection increases. Also, in the case of a single low-impedance antenna, the impedance increases as the distance between the antennas decreases, as shown in Figure 7.

[0021] In any case, efficient power transmission is possible only when the impedance of the antenna and the power transmission circuit match and reflection is suppressed, so the operable distance between antennas is limited to a narrow range, as shown in Figures 6 and 7.

[0022] (Configuration Example of Antenna Device and Contactless Power Transfer System According to the Present Embodiment) Fig. 8 is a diagram showing an example of the configuration of the antenna device 100 according to this embodiment. As shown in Fig. 8, the antenna device 100 has a configuration in which a high-impedance antenna 110 and a low-impedance antenna 120 are connected in parallel. In the example shown in Fig. 8, the high-impedance antenna 110 is an LC parallel resonance magnetic field antenna, and the low-impedance antenna 120 is an LC series resonance magnetic field antenna.

[0023] As shown in FIG. 6, the impedance of the high-impedance antenna 110 decreases as the distance between the antennas decreases, and conversely, as shown in FIG. 7, the impedance of the low-impedance antenna 120 increases as the distance between the antennas decreases.

[0024] 9 is a diagram showing the relationship between the impedance combined when antennas 110 and 120 are connected in parallel and the distance between the antennas. As shown by the dashed line in Fig. 9, the change in impedance relative to the distance between the antennas is small, making it possible to operate efficiently over a wide distance between the antennas.

[0025] Furthermore, as shown in Figure 8, by arranging the two resonant antennas 110, 120 so that their centers are at the same position, the distance between the two antennas 110, 120 and the opposing antennas becomes the same, which has the advantage of making design easier.

[0026] Note that "the same position" may mean that the centers of the two resonant antennas 110, 120 are at the same position when viewed from an antenna device on the opposite side of the antenna device consisting of the two resonant antennas 110, 120 in a contactless power transfer system. Also, "the same position" does not mean that the centers of the two antennas do not have to be exactly the same, and may be considered to be at the "same position" if the deviation is less than a certain threshold, for example.

[0027] As an antenna for the contactless power transmission system in this embodiment, in addition to a magnetic field antenna that uses magnetic field coupling between coils as shown in FIG. 8, an electric field antenna that uses electric field coupling between electrodes may also be used.

[0028] Alternatively, the configuration of the antenna device 200 shown in Fig. 10 may be used. The antenna device 200 shown in Fig. 10 includes an LC series resonance magnetic field antenna 220 as a low-impedance antenna, and an electric field antenna 210 that uses electric field coupling between electrodes as a high-impedance antenna.

[0029] 11 shows an example of the configuration of a contactless power transfer system according to this embodiment. This contactless power transfer system includes, on the power transmitting side, a high-impedance antenna 310, a low-impedance antenna 320, a matching circuit 330, an inverter 340, and a power supply 350, and, on the power receiving side, a high-impedance antenna 410, a low-impedance antenna 420, a matching circuit 430, a rectifier circuit 440, and a load 450. The high-impedance antenna 310 and the low-impedance antenna 320 are connected in parallel, and the high-impedance antenna 410 and the low-impedance antenna 420 are also connected in parallel.

[0030] Of the high-impedance antenna 310 and the low-impedance antenna 320, the high-impedance antenna 310 has an impedance higher than the impedance of the power transmission / reception circuit (e.g., matching circuit 330) to which it is connected, and the low-impedance antenna 320 has an impedance lower than the impedance of the power transmission / reception circuit.

[0031] Furthermore, of the high-impedance antenna 410 and the low-impedance antenna 420, the high-impedance antenna 410 has an impedance higher than the impedance of the power transmission / reception circuit (e.g., matching circuit 430) to which it is connected, and the low-impedance antenna 420 has an impedance lower than the impedance of the power transmission / reception circuit.

[0032] As shown in the configuration example of Figure 11, by connecting two resonant antennas with different impedances in parallel on each of the transmitting and receiving sides, it is possible to cancel out the change in impedance of each antenna in response to a change in the distance between the antennas, thereby reducing the change in impedance in response to a change in the distance between the antennas.

[0033] The type, shape, arrangement, etc. of the antenna are not limited to those given as examples above. Furthermore, the technology according to the present invention can be applied not only to contactless power transfer systems whose sole purpose is power transfer, but also to contactless IC card systems that simultaneously transfer power and perform communication. A contactless IC card system that simultaneously transfers power and performs communication is an example of a "contactless power transfer system."

[0034] (Effects of the embodiment) The technology according to the present embodiment described above makes it possible to reduce the degree of change in antenna impedance with respect to the distance between opposing antennas in a contactless power transfer system, maintain an impedance matching state even when the distance between the antennas changes, suppress reflections, and efficiently transmit power over a wide distance range.

[0035] Furthermore, since there is no need to actively detect or control the coupling state, power consumption can be reduced, the number of circuit components can be reduced, and the board can be made smaller.

[0036] (Addendum) This specification discloses at least the antenna device and contactless power transmission system described in the following items. (Section 1) An antenna device used in a contactless power transmission system, a first resonant antenna having a first impedance; a second resonant antenna having a second impedance different from the first impedance; An antenna device comprising: (Section 2) The first resonant antenna and the second resonant antenna are connected in parallel. 2. The antenna device according to claim 1. (Section 3) The first resonant antenna and the second resonant antenna are arranged so that the center of the first resonant antenna and the center of the second resonant antenna are at the same position. 3. The antenna device according to claim 1 or 2. (Section 4) The antenna device is connected to a power transmitting and receiving circuit in the contactless power transfer system, and the first impedance is higher than the impedance of the power transmitting and receiving circuit, and the second impedance is lower than the impedance of the power transmitting and receiving circuit. 1. The antenna device according to claim 1, wherein the antenna device is a semiconductor integrated circuit. (Section 5) A contactless power transmission system in which a first antenna device which is an antenna device described in any one of paragraphs 1 to 4 and a second antenna device which is an antenna device described in any one of paragraphs 1 to 4 are arranged opposite each other.

[0037] Although the present embodiment has been described above, the present invention is not limited to such a specific embodiment, and various modifications and changes are possible within the scope of the gist of the present invention described in the claims. [Explanation of symbols]

[0038] 11 Power transmission antenna 12 Matching circuit 13 Inverter 14 Power supply 21 Receiving antenna 22 Matching circuit 23 Rectifier circuit 24 Load 100 Antenna device 110 High Impedance Antenna 120 Low Impedance Antenna 200 Antenna device 220 Magnetic Field Antenna 210 Electric Field Antenna 310 High Impedance Antenna 320 Low Impedance Antenna 330 matching circuit 340 inverter 350 power supply 410 High Impedance Antenna 420 Low Impedance Antenna 430 matching circuit 440 rectifier circuit 450 load

Claims

1. An antenna device used in a contactless power transmission system, a first resonant antenna having a first impedance; a second resonant antenna having a second impedance different from the first impedance; The antenna device is connected to a power transmitting and receiving circuit in the contactless power transfer system, and the first impedance is higher than the impedance of the power transmitting and receiving circuit, and the second impedance is lower than the impedance of the power transmitting and receiving circuit. Antenna device.

2. The first resonant antenna and the second resonant antenna are connected in parallel. The antenna device according to claim 1 .

3. The first resonant antenna and the second resonant antenna are arranged so that the center of the first resonant antenna and the center of the second resonant antenna are at the same position.

3. The antenna device according to claim 1 or 2.

4. A contactless power transmission system in which a first antenna device which is an antenna device described in any one of claims 1 to 3 and a second antenna device which is an antenna device described in any one of claims 1 to 3 are arranged opposite each other.

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