Surface wave filter

Abstract

This surface wave filter includes: an external conductor having a shape surrounding a metal wire capable of propagating a surface wave; and a dielectric provided inside the external conductor and having a shape surrounding the metal wire. A first end of the external conductor is a short-circuit end, and a second end of the external conductor is an open end.

Description

Surface Acoustic Wave Filter

[0001] The present invention relates to wireless power transmission technology.

[0002] In recent years, various wireless power transmission technologies for wirelessly transmitting power have been proposed. As one of the wireless power transmission technologies, Non-Patent Document 1 discloses an antenna that transmits power wirelessly by propagating surface waves (Zenneck waves) of an electromagnetic field along a metal surface.

[0003] Experimental Realization of Zenneck Type Wave-based Non-Radiative, Non-Coupled Wireless Power Transmission (Scientific Reports 2020 Jan 22)

[0004] Surface waves in the electromagnetic field propagate confined near the surface of the metal and do not diffuse into space, resulting in higher transmission efficiency than wireless power transmission methods using radio waves, which propagate while spreading throughout space. However, surface waves propagate along the surface of the metal in all directions along the metal's surface. Transmission efficiency could be further improved if surface waves could be selectively propagated in specific directions. Furthermore, surface waves propagating in unintended directions may cause undesirable effects by interfering with nearby wireless systems, etc. Therefore, when transmitting power using surface waves, it is necessary to reduce the propagation of surface waves in unwanted directions.

[0005] The present invention has been made in view of the above points, and aims to provide a technique for reducing the propagation of surface waves in unnecessary directions in power transmission using surface waves.

[0006] According to the disclosed technology, there is provided a surface acoustic wave filter comprising: an outer conductor having a shape surrounding a metal wire capable of propagating a surface wave; and a dielectric provided inside the outer conductor and having a shape surrounding the metal wire, wherein a first end of the outer conductor is a short-circuited end and a second end of the outer conductor is an open end.

[0007] According to the disclosed technology, it is possible to reduce the propagation of surface waves in unnecessary directions in power transmission using surface waves.

[0008] FIG. 1 is a perspective view of a surface wave antenna. FIG. 2 is a cross-sectional view of a surface wave antenna. FIG. 3 is a diagram illustrating how a surface wave propagates along a metal wire. FIG. 4 is a diagram illustrating how a surface wave propagates in both directions A and B. FIG. 5 is a diagram for explaining a first embodiment. FIG. 6 is a diagram for explaining a second embodiment. FIG. 7 is a diagram for explaining a third embodiment. FIG. 8 is a diagram for explaining a fourth embodiment. FIG. 9 is a diagram for explaining a fifth embodiment.

[0009] Hereinafter, an embodiment of the present invention 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.

[0010] (Regarding the Surface Wave Antenna) In this embodiment, the configuration of the surface wave antenna that transmits and receives surface waves is not limited to a specific configuration, but here it is assumed that the surface wave antenna 100 shown in Figures 1 and 2 is used. The surface wave antenna 100 shown in Figures 1 and 2 is a directional surface wave antenna that transmits power only in the front direction of the antenna. Figure 1 is a perspective view of the surface wave antenna 100, and Figure 2 is a cross-sectional view of the surface wave antenna 100 as viewed from the side.

[0011] 1 and 2 , the surface wave antenna 100 includes a radiation electrode 50, a ground electrode 60, and a short stub 30, with a dielectric 20 provided on the short stub 30. A feed point 40 is provided to connect a pillar portion 70 extending from the radiation electrode 50 toward the short stub 30 to the ground electrode 60. The feed point 40 is connected in parallel with the short stub 30 to the radiation electrode 50 and the ground electrode 60. The feed point may also be referred to as a power feed section. The portion between the radiation electrode 50 and the ground electrode 60 constitutes a resonance section 10.

[0012] 1 and 2, the area of ​​the ground electrode 60 when viewed from the front is larger than the area of ​​the radiation electrode 50. However, this is not limitative.

[0013] In the surface wave antenna 100, the pillar 70 and the radiation electrode 50 are designed to have a size that allows them to resonate electrically at a quarter wavelength at the frequency of the high-frequency power that carries the power, and when high-frequency power of this frequency is input to the feed point 40, they resonate and generate a strong electric field in the surrounding area.

[0014] The short stub 30 is a quarter-wavelength transmission line with a shorted tip, and can be made from, for example, a coaxial line. Because it has an open end at the feed point 40, it serves to prevent current from flowing to the back of the antenna. Charges of the same magnitude but opposite signs alternately accumulate in the radiation electrode 50 and ground electrode 60, generating electric field waves in the surrounding area.

[0015] An example of the generated electric field is shown by the electric field lines in Figure 2. At this time, longitudinal waves of the electric field oscillating parallel to the direction of propagation are generated in the forward direction of the radiation electrode 50, and transverse waves of the electric field oscillating perpendicular to the direction of propagation are generated in the lateral direction of the columnar portion 70.

[0016] 3 and 4 show how the surface wave transmitted from the surface wave antenna 100 propagates along the metal wire 80. Figures 3 and 4 show cross-sectional views including the central axis of the antenna.

[0017] The surface wave transmitted from the surface wave antenna 100 propagates along the surface of the metal wire 80. When the metal wire branches into two directions, A and B, as shown in Figure 4, the surface wave also branches and propagates in both directions A and B. In this case, if a power receiver is located in direction A, not only will power leak into direction B where there is no power receiver, reducing the power transmitted in direction A, but the surface wave propagating in direction B may also cause problems such as radio interference.

[0018] Configurations for solving the above problems will be described below using first to fifth embodiments. The first embodiment is the most basic configuration.

[0019] (First Example) In the first example, a surface acoustic wave filter 95 as shown in Fig. 5 is provided to block surface waves propagating in unwanted directions and deliver more power in a required direction. Here, a situation similar to that described with reference to Fig. 4 is assumed, in which the power receiver is located in direction A and the surface acoustic wave filter 95 blocks surface waves propagating in direction B. The surface acoustic wave filter 95 in Fig. 5 is shown in a cross section including the central axis so that its structure can be clearly seen.

[0020] The surface acoustic wave filter 95 is a quarter-wave coaxial cable, and the metal wire 82 serves as the central conductor of the cable. Note that the surface acoustic wave filter 95 does not include the metal wire 82, and when the surface acoustic wave filter 95 is in use, the metal wire 82 serves as the central conductor of the surface acoustic wave filter 95.

[0021] 5, one end of the coaxial cable is an open end and the other end is a short-circuited end, and the outer conductor 90 and the metal wire 82 are electrically connected to form a short stub. A dielectric is present inside the outer conductor 90 (between the external moving body and the metal wire 82). A perspective view of the surface acoustic wave filter 95 is shown in FIG.

[0022] That is, the surface acoustic wave filter 95 includes an external conductor 90 having a shape surrounding a metal wire 82 capable of propagating a surface wave, and a dielectric provided inside the external conductor 90 and having a shape surrounding the metal wire 82, with a first end of the external conductor 90 being a short-circuited end and a second end of the external conductor being an open end. The distance (length) between the first end (short-circuited end) and the second end (open end) is a quarter wavelength at the frequency of the surface wave.

[0023] The structure of the surface acoustic wave filter 95, like the short stub 30 installed behind the surface acoustic wave antenna 100, functions to prevent a standing wave from occurring in the stub and flowing through the metal wire 82. Therefore, the surface acoustic wave does not propagate in the direction B in FIG.

[0024] Hereinafter, second to fifth embodiments of the surface acoustic wave filter 95 will be described as variations thereof.

[0025] Second Embodiment A surface acoustic wave filter 95 according to a second embodiment is shown in Figures 7 and 8. Figure 7 is a cross-sectional view including the central axis of the surface acoustic wave filter 95, and Figure 8 is a cross-sectional view taken along a plane perpendicular to the central axis as viewed from the short-circuited end.

[0026] 7 and 8, a surface acoustic wave filter 95 according to the second embodiment includes a coupling electrode 93 that is shaped to surround a metal wire 82 inside an external conductor 90, and the short-circuited end is coupled to the metal wire 82 in a non-contact manner via the coupling electrode 93. In addition, a coil 92 is connected between the coupling electrode 93 and the external conductor 90. The reason for connecting the coil 92 is as follows.

[0027] In a power transmission system using surface waves, an existing communication line or the like can be used as the metal wire that mediates the propagation of the surface waves. In many cases, the surface of the communication line is coated and insulated, making it difficult to electrically connect the communication line to the outer conductor 90 of the surface acoustic wave filter 95. However, because surface waves are carried at high frequencies, by employing the configuration of the second embodiment, the coupling electrode 93 and the metal wire 82 are capacitively coupled, and the coupling electrode 93 and the metal wire 82 can be electrically connected without contact.

[0028] In this case, by connecting a coil 92 in series with an inductance L that satisfies 2πf = 1 / √(LC) so as to cancel out the capacitance C between the coupling electrode 93 and the metal wire 82, it is possible to achieve the same state as when the outer conductor 90 is electrically connected directly to the metal wire 82, where f is the frequency of the surface wave.

[0029] The surface acoustic wave filter 95 may have a slit 96 as shown in FIG. 8 so that it can be attached to an already laid cable later.

[0030] 9 and 10 show a surface acoustic wave filter 95 according to a third embodiment. Fig. 9 is a cross-sectional view including the central axis of the surface acoustic wave filter 95, and Fig. 10 is a cross-sectional view taken along a plane perpendicular to the central axis as viewed from the short-circuited end. Here, differences from the second embodiment will be described.

[0031] As shown in FIGS. 9 and 10, in the third embodiment, a switch 97 is provided between an outer conductor 90 and a coupling electrode 93 of a surface acoustic wave filter 95 in place of the coil 92 .

[0032] When the switch 97 between the external conductor 90 and the coupling electrode 93 is opened, the surface acoustic wave filter 95 no longer functions to block the current flowing through the metal wire 82, and the surface acoustic wave passes through the surface acoustic wave filter 95. In other words, whether or not the surface acoustic wave is allowed to pass can be controlled by opening or closing the switch 97 between the external conductor 90 and the coupling electrode 93.

[0033] 11 and 12 show a surface acoustic wave filter 95 according to a fourth embodiment. Fig. 11 is a cross-sectional view including the central axis of the surface acoustic wave filter 95, and Fig. 12 is a cross-sectional view taken along a plane perpendicular to the central axis as viewed from the short-circuited end. Here, differences from the second and third embodiments will be described.

[0034] As shown in FIGS. 11 and 12, a surface acoustic wave filter 95 according to the fourth embodiment includes both a coil 92 for canceling the capacitance between a coupling electrode 93 and a metal wire 82 and a switch 97 for controlling whether or not a surface acoustic wave is passed through the coil 92.

[0035] 11 and 12 , one end of the coil 92 is connected to the coupling electrode 93, the other end of the coil 92 is connected to one end of the switch 97, and the other end of the switch 97 is connected to the external conductor 90. However, this is just an example. One end of the switch 97 may be connected to the coupling electrode 93, the other end of the switch 97 may be connected to one end of the coil 92, and the other end of the coil 92 may be connected to the external conductor 90.

[0036] The surface acoustic wave filter 95 in the fourth embodiment has the effect of realizing the same state as when the outer conductor 90 is electrically connected directly to the metal wire 82, as described in the second embodiment, and also has the effect of being able to control whether or not to pass surface waves by opening and closing the switch 97.

[0037] 13 is a configuration diagram of a fifth embodiment. As shown in FIG. 13, in the fifth embodiment, two surface acoustic wave filters 150 and 160 are attached to metal wires 81 and 82 branching off from a metal wire 80 extending from a surface acoustic wave antenna 100. The surface acoustic wave filters 150 and 160 are the surface acoustic wave filters described in the third embodiment, but the surface acoustic wave filters described in the fourth embodiment may also be used.

[0038] The propagation of surface waves in direction A can be turned on / off by opening and closing the switch 151 of the surface wave filter 150, and the propagation of surface waves in direction B can be turned on / off by opening and closing the switch 161 of the surface wave filter 160.

[0039] In the example shown in Figure 13, the switch 151 of the surface acoustic wave filter 150 attached in the direction A is open, and the switch 161 of the surface acoustic wave filter 160 attached in the direction B is closed, so propagation in the direction B is suppressed and surface waves propagate only in the direction A.

[0040] Similarly, even when there are three or more branched metal wires, by attaching a surface wave filter with a switch to each metal wire, the propagation of the surface wave in each metal wire can be freely controlled.

[0041] (Summary of the embodiment) As described above, the surface acoustic wave filter in this embodiment is a stub-type filter in the form of a coaxial cable, which is provided on a metal surface (e.g., the surface of a metal wire) through which surface waves can propagate, and has a length of one-quarter wavelength at the frequency of the surface waves, one end being an open end, and the other end being a short-circuited end.

[0042] In the surface acoustic wave filter, a coupling electrode may be connected to the short-circuited end, and the metal wire and the coupling electrode may be capacitively coupled. Also, a switch may be provided between the short-circuited end of the outer conductor of the surface acoustic wave filter and the coupling electrode.

[0043] (Effects of the technology relating to the embodiment) By providing a surface wave filter according to the present embodiment on a metal wire that propagates the surface waves output from the surface wave antenna, the surface waves that propagate along the metal surface of the metal wire can be blocked from traveling further along the metal wire than the point where the surface wave filter is provided.

[0044] Furthermore, by using a surface acoustic wave filter with a switch, it is possible to control whether the surface acoustic wave is propagated or reflected by opening or closing the switch.

[0045] This allows the surface waves propagating along the surface of the metal wire to be concentrated in only the desired direction, resulting in an efficient power transmission system with minimal loss. Furthermore, by eliminating propagation in unnecessary directions, interference with surrounding wireless systems can be suppressed, ensuring safety for the human body.

[0046] When using communication lines that were not originally laid for power transmission, wires supporting railway bridges, or reinforcing bars inside buildings as transmission media for surface waves, these metal wires do not extend only in the desired direction to deliver power, so surface wave filters that can control the propagation direction of surface waves are particularly effective.

[0047] By providing a coupling electrode and a coil that are capacitively coupled to the metal wire, the surface acoustic wave filter can be easily attached by simply covering the metal wire with the surface acoustic wave filter.

[0048] The following additional notes are provided regarding the above-described embodiments.

[0049] <Additional Notes> (Additional Item 1) A surface acoustic wave filter comprising: an external conductor having a shape surrounding a metal wire capable of propagating a surface wave; and a dielectric provided inside the external conductor and having a shape surrounding the metal wire, wherein a first end of the external conductor is a short-circuited end and a second end of the external conductor is an open end. (Additional Item 2) A surface acoustic wave filter according to Additional Item 1, wherein the length of the surface acoustic wave filter is a quarter wavelength at the frequency of the surface wave. (Additional Item 3) A surface acoustic wave filter according to Additional Item 1 or 2, wherein a coupling electrode having a shape surrounding the metal wire is provided inside the external conductor. (Additional Item 4) The surface acoustic wave filter according to Additional Item 3, wherein a coil is provided between the coupling electrode and the external conductor at the first end. (Additional Item 5) A surface acoustic wave filter according to Additional Item 3, wherein a switch is provided between the coupling electrode and the external conductor at the first end. (Supplementary Item 6) The surface acoustic wave filter according to Supplementary Item 3, further comprising a switch and a coil at the first end portion between the coupling electrode and the outer conductor.

[0050] 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.

[0051] REFERENCE SIGNS LIST 10 Resonator 20 Dielectric 30 Short stub 40 Feeding point 50 Radiation electrode 60 Ground electrode 80, 81, 82 Metal wire 90 Outer conductor 91 Dielectric 92 Coil 93 Coupling electrode 96 Notch 97, 151, 161 Switch 95, 150, 160 Surface acoustic wave filter 100 Surface acoustic wave antenna

Claims

1. A surface acoustic wave filter comprising: an outer conductor having a shape surrounding a metal wire capable of propagating surface waves; and a dielectric provided inside the outer conductor and having a shape surrounding the metal wire, wherein a first end of the outer conductor is a short-circuited end and a second end of the outer conductor is an open end.

2. The surface acoustic wave filter according to claim 1, wherein the length of the surface acoustic wave filter is a quarter wavelength at the frequency of the surface acoustic wave.

3. The surface acoustic wave filter according to claim 1, further comprising a coupling electrode formed inside the outer conductor and having a shape that surrounds the metal wire.

4. The surface acoustic wave filter according to claim 3, further comprising a coil at the first end between the coupling electrode and the external conductor.

5. The surface acoustic wave filter according to claim 3, further comprising a switch at the first end between the coupling electrode and the external conductor.

6. The surface acoustic wave filter according to claim 3, further comprising a switch and a coil at the first end between the coupling electrode and the external conductor.

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