Electromagnetic wave scatterer

Abstract

This electromagnetic wave scatterer comprises a transmission-type scatterer and a reflection-type scatterer that face each other across a gap and have the same axis. The transmission-type scatterer transmits electromagnetic waves and changes the angle of the transmitted electromagnetic waves. The reflection-type scatterer reflects the electromagnetic waves and changes the angle of the reflected electromagnetic waves. The relative relationship between the transmission-type scatterer and the reflection-type scatterer can be changed.

Description

Electromagnetic wave scatterer

[0001] The present disclosure relates to an electromagnetic wave scatterer capable of controlling the scattering state of electromagnetic waves.

[0002] Wireless communication systems using high-frequency bands of millimeter waves and above have the advantage of being able to achieve high-speed and high-capacity communication compared to conventional systems. On the other hand, as the frequency increases, the propagation loss of free space per unit length increases, and the communicable distance decreases. In addition, as the frequency of electromagnetic waves increases, the directivity of electromagnetic waves increases, so the signal intensity in the blind area decreases significantly. That is, in a wireless communication system using a high-frequency band such as millimeter waves, the influence of obstacles such as buildings and walls is large.

[0003] The influence of obstacles can be mitigated by controlling the propagation direction of electromagnetic waves using an electromagnetic wave scatterer made of a dielectric or a conductor, for example, an artificial planar scatterer called a metasurface.

[0004] An electromagnetic wave scatterer that controls the direction in which electromagnetic waves scatter is designed based on the state of the incident wave and the desired scattering state, that is, the amplitude and angle (phase distribution) between the incident wave and the scattered wave. Therefore, it is necessary to change the characteristics of the electromagnetic wave scatterer according to the state of the incident wave and the desired scattered wave, the installation location, the surrounding environment, etc. In order to select a desired electromagnetic wave scatterer according to the state of electromagnetic waves on-site, it is necessary to prepare in advance a large number of electromagnetic wave scatterers with different designs. It is also necessary to consider manufacturing errors. Preparing electromagnetic wave scatterers with various designs in advance requires manufacturing the electromagnetic wave scatterers and managing them as inventory, which complicates and increases the cost of the design and manufacture of electromagnetic wave scatterers. When manufacturing an electromagnetic wave scatterer after the characteristics of the scatterer are determined, it is not necessary to prepare in advance a large number of electromagnetic wave scatterers with different designs, but it takes time until the electromagnetic wave scatterer is manufactured, so it is not possible to respond on-site.

[0005] One method for changing the characteristics of an electromagnetic wave scatterer without increasing the number of design elements is a method using a PIN diode, which is a switching element disclosed in Non-Patent Document 1. The electromagnetic wave scatterer in Non-Patent Document 1 has a metasurface and control circuit composed of a large number of unit elements, each having a PIN diode. In the metasurface of Non-Patent Document 1, the scattering state of the incoming electromagnetic wave is controlled by dynamically controlling the applied voltage to each PIN diode by the control circuit, thereby changing the reflection characteristics of each unit element.

[0006] GC Trichopoulos, et.al., “Design and evaluation of reconfigurable intelligent surfaces in real-world environment,” IEEE Open Journal of the Communication Society, vol. 3, pp. 462-474, 2022. K. Singh, et.al., “Designing efficient phase-gradient metasurfaces for near-field meta-steering systems,” IEEE Access, vol. 9, pp. 109080-109093 2021.

[0007] The electromagnetic wave scatterer described in Non-Patent Document 1 is expensive and complex because it requires numerous PIN diodes and control circuits. The same applies when other switching elements such as liquid crystals or varactor diodes are used as switching elements. In addition, since each switching element constituting the electromagnetic wave scatterer in Non-Patent Document 1 has only two states, quantization lobes are generated, causing a decrease in scattering intensity in the desired direction and scattering in unwanted directions.

[0008] Non-patent document 2 controls the beam direction of electromagnetic waves emitted from an antenna by rotating a scatterer, but it is a beam scanning antenna, not an electromagnetic wave scatterer.

[0009] Non-limiting embodiments of this disclosure provide electromagnetic wave scatterers capable of controlling the scattering state of electromagnetic waves without using switching elements. Even electromagnetic wave scatterers without switching elements contribute to providing electromagnetic wave scatterers that can control the scattering state according to the state of the incident electromagnetic waves, the desired scattering state, the installation environment, manufacturing tolerances, etc.

[0010] An electromagnetic wave scatterer according to one aspect of the present disclosure comprises a transmission scatterer and a reflection scatterer that are spaced apart from each other, facing each other and having the same axis, wherein the transmission scatterer transmits electromagnetic waves and changes the angle of the transmitted electromagnetic waves, and the reflection scatterer reflects electromagnetic waves and changes the angle of the reflected electromagnetic waves, and the relative relationship between the transmission scatterer and the reflection scatterer is changeable.

[0011] For both the transmission-type and reflection-type scatterers, those are used that achieve anomalous reflection, refraction, focusing, and diffusion of incident electromagnetic waves at the desired frequency. Since the scattering state of the electromagnetic wave scatterer is controlled by changing the relative relationship between the transmission-type and reflection-type scatterers, for example by mechanically rotating or moving them, a switching element is not required to control the scattering state.

[0012] These comprehensive or specific embodiments may be implemented as a system, apparatus, method, integrated circuit, computer program, or recording medium, or as any combination of a system, apparatus, method, integrated circuit, computer program, and recording medium.

[0013] According to this disclosure, the upper and lower scatterers constituting the electromagnetic wave scatterer are manufactured without using switching elements and using a single predetermined design. The relative relationship between the upper and lower scatterers can be changed, for example, by rotation or movement, to suit the state of the incident electromagnetic wave, the desired scattering state, the installation environment, and manufacturing tolerances. By changing the relative relationship between the upper and lower scatterers, for example by angle or distance, the scattering state of the reflected electromagnetic wave, for example by direction or degree of diffusion, can be controlled.

[0014] Further advantages and effects of one embodiment of this disclosure will be made apparent from the specification and drawings. Such advantages and / or effects are provided by several embodiments and features described in the specification and drawings, but not all of them are necessarily provided in order to obtain one or more identical features.

[0015] Structure of the electromagnetic wave scatterer Perspective view of the upper unit element Top view of the upper unit element Bottom view of the upper unit element Perspective view of the lower unit element Top view of the lower unit element Bottom view of the lower unit element Diagram showing the transmission amplitude |S21| at 28 GHz when the shape of the upper unit element is changed Diagram showing the transmission phase ∠S21 at 28 GHz when the shape of the upper unit element is changed Diagram showing the reflection amplitude |S11| at 28 GHz when the shape of the lower unit element is changed Diagram showing the reflection phase ∠S11 at 28 GHz when the shape of the lower unit element is changed Top view of the upper scatterer Figure 1: Electric field distribution in the xz plane when a plane wave polarized in the x direction is incident on the upper scatterer from the +z direction. Top view of the lower scatterer. Electric field distribution in the xz plane when a plane wave polarized from the +z direction to the x direction is incident on the lower scatterer. Perspective view of the electromagnetic wave scatterer composed of the upper and lower scatterers. Reflection direction when the rotation angle φt of the upper scatterer is fixed at 0 degrees and the rotation angle φr of the lower scatterer is changed. Analysis results of the radar cross-section (RCS) of an in-plane bistatic radar when a plane wave polarized from the +z direction to the x direction is incident on the electromagnetic wave scatterer. Analysis results of the RCS of an in-plane bistatic radar when the elevation angle is 2π / 3 (rad) Analysis results of the RCS of an in-plane bistatic radar when the elevation angle is 2π / 3 (rad) Top view of the upper scatterer Figure showing the electric field distribution in the xz plane when a plane wave polarized in the x direction is incident on the upper scatterer from the +z direction Top view of the lower scatterer Figure showing the electric field distribution in the xz plane when a plane wave polarized in the x direction is incident on the lower scatterer from the +z direction Perspective view of an electromagnetic wave scatterer constructed by arranging the upper and lower scatterers with space in the z-axis direction Value of the focal length F when the distance d is changed with ft = 30 mm, fr = 5 mm Value of the focal length F when ft = 40 mm, fr = -5 mm A unit element constructed using only dielectrics or conductors and not having a planar structure A unit element composed of a mesh-like conductor and an optically colorless and transparent dielectric A unit element composed of multiple dielectric layers and conductor layers Example of using an electromagnetic wave scatterer

[0016] The embodiments of this disclosure will be described in detail below, with reference to the drawings as appropriate. However, some unnecessarily detailed explanations may be omitted. For example, detailed explanations of already well-known matters and redundant explanations of substantially identical configurations may be omitted. This is to avoid the following explanation becoming unnecessarily verbose and to facilitate understanding for those skilled in the art.

[0017] The drawings and the following description are provided for the benefit of those skilled in the art to fully understand this disclosure and are not intended to limit the subject matter described in the claims.

[0018] <First Embodiment> In the first embodiment, the relative relationship is changed by rotating at least one of the upper and lower scattering bodies with respect to the axis of rotation.

[0019] Figure 1 shows the configuration of an electromagnetic wave scatterer. The electromagnetic wave scatterer has an upper scatterer 10 and a lower scatterer 20. The upper scatterer 10 is a transmission type scatterer that transmits electromagnetic waves of a desired frequency and changes the angle of the transmitted electromagnetic waves, while the lower scatterer 20 is a reflection type scatterer that reflects electromagnetic waves of a desired frequency and changes the angle of the reflected electromagnetic waves (reflecting them at an angle other than specular reflection). The upper scatterer 10 is the scatterer to which the electromagnetic waves are first incident, and the lower scatterer 20 is the scatterer to which the electromagnetic waves that have passed through the upper scatterer 10 are incident. In other words, the incident electromagnetic waves pass through the upper scatterer 10, are reflected by the lower scatterer 20, and then pass through the upper scatterer 10 again.

[0020] The upper scatterer 10 and the lower scatterer 20 are each composed of metasurfaces. The upper scatterer 10 and the lower scatterer 20 are each produced using circular substrates made of dielectric material of the same size and have the same axis of rotation 30, but they do not have to be circular substrates. The upper scatterer 10 and the lower scatterer 20 can be rotated relative to each other with respect to the center of the circular substrate as the axis of rotation 30, and can also be rotated as a single unit. The upper scatterer 10 and the lower scatterer 20 may be rotated by the user, or they may be rotated by a motor operated by a control signal from a control circuit (not shown).

[0021] (Configuration of Unit Elements) Figure 2 is a perspective view of the unit elements (hereinafter referred to as "upper unit elements") that constitute the upper scattering body 10. The x-axis, y-axis, and z-axis shown in Figure 2 are set for the upper unit elements.

[0022] The upper unit element is square when viewed from the z-axis direction and has five layers of dielectric material, consisting of a first dielectric 11, second dielectric 12 arranged on both sides of the first dielectric 11, and a third dielectric 13 arranged on the side of the second dielectric 12 opposite to the first dielectric 11. A first conductor 14 is formed on the side (top surface) of the third dielectric 13 opposite to the second dielectric 12 (upper surface), and a second conductor 15 is formed on the side (bottom surface) of the third dielectric 13 opposite to the second dielectric 12 (lower surface). The dielectric material may also be referred to as a dielectric layer or a substrate. The thickness of the upper unit element is smaller than the wavelength of the electromagnetic wave.

[0023] The upper unit element is a structure that enables the refraction of incident electromagnetic waves, that is, a structure that transmits incident electromagnetic waves and changes their phase, and may be a structure other than that shown in Figure 2. For example, it may be a structure in which multiple dielectrics and conductors are stacked or arranged with spaces between them, and each dielectric or conductor may have air gaps or holes. The dielectric does not have to be five layers, the dielectrics in each layer may all be different, or there may be an even number of layers. The upper unit element is sufficient if a conductor is formed on the surface of the dielectric.

[0024] Figure 3 shows a top view of the upper unit element. In Figure 3, the same components as in Figure 2 are denoted by the same reference numerals.

[0025] The first conductor 14 has an annular structure with four gaps of width g. In other words, the first conductor 14 is divided into four parts by four gaps. The first conductor 14 has a square annular shape with gaps at the midpoints of each side. The first conductor 14 has a four-fold symmetric structure (also called a four-fold rotational symmetric structure or four-fold symmetric structure) with respect to the axis of rotation 16 (central axis) of the first conductor 14, which is an axis perpendicular to the upper surface of the third dielectric 13. That is, the first conductor 14 has a structure that becomes the same when rotated 90 degrees around the axis of rotation 16. The first conductor 14 may have a structure other than that shown in Figure 3.

[0026] Figure 4 is a bottom view of the upper unit element. In Figure 4, the same components as in Figure 2 are denoted by the same reference numerals.

[0027] The second conductor 15 has an annular structure with gaps at each corner. In other words, the annular second conductor 15 is divided into sides. In the example in Figure 4, the second conductor 15 has a square annular shape with gaps at the corners of each side. The second conductor 15 has a four-fold symmetric structure with respect to the axis of rotation 16 of the second conductor 15. The second conductor 15 has a conductor length Lt.

[0028] The first conductor 14 is formed so as to overlap the second conductor 15 when viewed from the top surface (+Z direction), with the first dielectric 11, the second dielectric 12, and the third dielectric 13 in between. The gaps in the first conductor 14 and the gaps in the second conductor 15 do not overlap when viewed from the top surface (+ z direction (hereinafter referred to as the "+z direction")) or the bottom surface (- z direction (hereinafter referred to as the "-z direction")).

[0029] Figure 5 is a perspective view of the unit element (hereinafter referred to as "lower unit element") that constitutes the lower scatterer 20. The x, y, and z axes shown in Figure 5 are set for the lower unit element.

[0030] The lower unit element is a square with sides shorter than the wavelength of the electromagnetic wave when viewed from the z-axis direction, and comprises a first dielectric 11, a second dielectric 12 arranged on both sides of the first dielectric 11, and a third dielectric 13 arranged on the side of the second dielectric 12 opposite to the first dielectric 11. A third conductor 24 is formed on the side (upper surface) of the third dielectric 13 opposite to the second dielectric 12, and a fourth conductor 25 is formed on the side (lower surface) of the third dielectric 13 opposite to the second dielectric 12. The dielectric may also be called a dielectric layer or a substrate. The first to third dielectrics of the lower scatterer 20 may be the same as or different from the first to third dielectrics of the upper scatterer 10. The dielectric does not have to be five layers, the dielectrics of each layer may all be different, or there may be an even number of layers. The lower unit element only needs to have conductors formed on the surface of the dielectric. The thickness of the lower unit element is smaller than the wavelength of the electromagnetic wave.

[0031] The lower unit element may be any structure that reflects incident electromagnetic waves, that is, any structure that reflects incident electromagnetic waves and changes their phase, and may be a structure other than that shown in Figure 5. For example, it may be a structure in which multiple dielectrics and conductors are stacked or arranged with spaces between them, and each dielectric or conductor may have a gap or hole. The third conductor 24 may be a structure other than that shown in Figure 5.

[0032] Figure 6 is a top view of the lower unit element. In Figure 6, the same components as in Figure 5 are denoted by the same reference numerals.

[0033] The third conductor 24 has a deformed cross structure. The third conductor 24 has a cross structure and conductors perpendicular to the cross from each endpoint of the cross structure. The distance from each endpoint of the cross structure to each endpoint of the perpendicular conductor is equal. The length of the conductor from one endpoint of the perpendicular conductor to the endpoint of the perpendicular conductor connected to the other endpoint of the cross structure is Lr. The third conductor 24 has a four-fold symmetric structure with respect to its axis of rotation 16. In other words, the third conductor 24 has a structure that becomes the same when rotated 90 degrees around the axis of rotation 16. If Lr is short, only the cross structure is used, and the conductors perpendicular to the cross may be omitted.

[0034] Figure 7 is a bottom view of the lower unit element. In Figure 7, the same components as in Figure 5 are denoted by the same reference numerals.

[0035] The lower unit element has a fourth conductor 25. The fourth conductor 25 is formed on the surface (bottom surface) of the other third dielectric 13 opposite to the second dielectric 12, and is formed to cover the entire surface of the third dielectric 13.

[0036] (Characteristics of the Unit Element) First, the characteristics of the upper unit element will be described. A three-dimensional electromagnetic field analysis was performed on the upper unit element using the finite element method. In performing the three-dimensional electromagnetic field analysis on the upper unit element, port 1 was set as a port that performs input and output from the +z direction, and port 2 was set as a port that performs input and output from the -z direction, and periodic boundary conditions were applied to the ± directions of the x axis (hereinafter referred to as "±x direction") and the ± directions of the y axis (hereinafter referred to as "±y direction").

[0037] As shown in Figure 3, the gap width in the first conductor 14 is g. Also, as shown in Figure 4, the conductor length of the second conductor 15 is Lt. The first dielectric 11 has a thickness of 1.3 mm and a relative permittivity of 3.78, the second dielectric 12 has a thickness of 0.025 mm and a relative permittivity of 2.72, and the third dielectric 13 has a thickness of 0.05 mm and a relative permittivity of 3.31. The upper unit element has a side length smaller than the wavelength of the incident electromagnetic wave. The side lengths of each dielectric in the x and y directions are 5.0 mm. The width of the first conductor 14 and the second conductor 15 is 0.3 mm. The distance between the ends of the first conductor 14 and the second conductor 15 and the third dielectric 13 is 0.1 mm.

[0038] Figures 8 and 9 show the transmission amplitude |S21| and transmission phase ∠S21 at 28 GHz when the shape of the upper unit element is changed, respectively. Figures 8 and 9 show the transmission amplitude |S21| and transmission phase ∠S21 at 28 GHz when the conductor length Lt of the second conductor 15 is changed while maintaining the Lt + g = 4.3 mm of the first conductor 14. Figures 8 and 9 show the analysis results when a plane wave (TEM wave) having a wave vector and Poynting vector from the +z direction to the -z direction and polarization in the x-axis direction is incident on the upper unit element.

[0039] As shown in Figure 8, a transmission amplitude of -1.8 dB or higher is obtained for any conductor length Lt in the range of 0.5 mm < Lt < 4.0 mm.

[0040] Furthermore, as shown in Figure 9, by changing the conductor length Lt in the range of 0.5 mm < Lt < 4.0 mm, it is possible to change the transmission phase by approximately 315 degrees.

[0041] That is, the upper unit element can change the phase of the transmitted electromagnetic wave over a range of approximately 315 degrees while generally transmitting the incident electromagnetic wave. In other words, the upper unit element can control the transmission phase while maintaining a high transmittance by changing the conductor length of the second conductor 15. This is presumably because the currents having a phase difference flowing on the first conductor 14 and the second conductor 15 generate a virtual magnetic current, which serves as a secondary wave source for generating the electromagnetic field after transmission. In other words, it is presumably due to the fact that the upper unit element is operating as a Huygens surface.

[0042] Since the upper unit element has a four-fold symmetry structure with respect to the rotation axis 16 (z-axis), even when an electromagnetic wave having a polarization in the y direction is incident, it has the same characteristics as when an electromagnetic wave having a polarization in the x direction is incident. That is, the upper unit element has both polarization characteristics.

[0043] Next, the characteristics of the lower unit element will be described. Three-dimensional electromagnetic field analysis using the finite element method was performed on the lower unit element. In performing three-dimensional electromagnetic field analysis using the finite element method on the lower unit element, Port 1 was set as a port for input / output from the +z direction, and periodic boundary conditions were applied in the ±x and ±y directions.

[0044] As shown in FIG. 6, the conductor length of the third conductor 24 is Lr. The first dielectric 11 has a thickness of 1.0 mm and a relative permittivity of 3.78, the second dielectric 12 has a thickness of 0.025 mm and a relative permittivity of 2.72, and the third dielectric 13 has a thickness of 0.05 mm and a relative permittivity of 3.3. The lower unit element has a side length smaller than the wavelength of the incident electromagnetic wave. The side lengths of each dielectric in the x and y directions are 3.5 mm. The widths of the third conductor 24 and the fourth conductor 25 are 0.3 mm. The distance between the third conductor 24 and the fourth conductor 25 and the end of the third dielectric 13 is 0.2 mm.

[0045] FIGS. 10 and 11 are diagrams showing the reflection amplitude |S11| and reflection phase ∠S11 at 28 GHz when the shape of the lower unit element is changed. FIGS. 10 and 11 show the reflection characteristics while changing Lr. FIGS. 10 and 11 have a wave number vector and a pointing vector from the +z direction to the -z direction, and show the analysis results when a plane wave (TEM wave) having a polarization in the + direction of the x-axis (hereinafter referred to as the “+x direction”) is incident on the lower unit element.

[0046] As shown in FIG. 10, a reflection amplitude of -0.5 dB or more is obtained in the range of 0.5 mm < Lr < 5.1 mm.

[0047] As shown in FIG. 11, by changing Lr in the range of 0.5 mm < Lr < 5.1 mm, it is possible to change the reflection phase by 360 degrees or more.

[0048] That is, the lower unit element can change the phase of the electromagnetic wave reflected over 360 degrees while generally reflecting the incident electromagnetic wave. In other words, the lower unit element can arbitrarily control the reflection phase while maintaining a high reflectivity by changing the conductor length. This is because most of the electromagnetic wave incident by the fourth conductor 25 is reflected, while the distribution of the current flowing on the third conductor 24 and the fourth conductor 25 changes due to the change in the conductor length of the third conductor 24.

[0049] Since the lower unit element has a four-fold symmetry structure with respect to the rotation axis 16 (z-axis), the same characteristics as when an electromagnetic wave having a polarization in the x direction is incident are realized even when an electromagnetic wave having a polarization in the y direction is incident. That is, the lower unit element has both polarization characteristics.

[0050] (Structure and Characteristics of Upper and Lower Scatterers) First, refraction using the upper scatterer 10 will be described. Figure 12 is a top view of the upper scatterer 10. The upper scatterer 10 is formed by arranging a number of upper unit elements with different gap widths g on a circular substrate in the xy plane. The upper scatterer 10 and the lower scatterer 20 only need to be designed to transmit or reflect electromagnetic waves at a desired frequency. For example, at least one of the upper scatterer 10 and the lower scatterer 20 may be a frequency-selective plate made of a rectangular annular conductor or a circular annular conductor. The upper scatterer 10 may also be called an upper metasurface. In Figure 12, the same components as in Figure 2 are denoted by the same reference numerals. Note that the shape of the dielectric substrate on which the unit elements are arranged does not necessarily have to be circular; it may be a polygon such as a square, and the unit elements do not have to be planar. Also, the dielectric substrate only needs to be large enough to accommodate multiple unit elements, and is not limited to the number of elements shown in Figure 12.

[0051] The structural parameters of the upper unit elements constituting the upper scatterer 10 may be determined, for example, based on the phase distribution of the incident wave and the transmission phase characteristics shown in Figure 8, so as to obtain a desired transmission phase distribution. This makes it possible to converge, diffuse, and bend the electromagnetic field incident on the upper scatterer 10 at a desired position and direction. Figure 12 shows that each upper unit element has a gap width g corresponding to the x-axis, specifically, the gap width g becomes narrower the more it is formed in the +x direction, and the gap width g becomes wider the more it is formed in the - direction of the x-axis (hereinafter referred to as the "-x direction"), and upper unit elements formed in multiple locations in the y-axis direction have the same gap width g.

[0052] Figure 13 shows the electric field distribution in the xz plane at 28 GHz when a plane wave polarized in the x direction is incident on the upper scatterer 10 shown in Figure 12 from the +z direction. Figure 13 shows the electric field distribution when each upper unit element constituting the upper scatterer 10 is designed so that the incident plane wave is refracted in the xz plane at approximately 13 degrees. From Figure 13, it can be seen that the incident plane wave is refracted in the 13-degree +x direction as designed. Here, since the distribution of the transmission phase of the upper scatterer 10 can be arbitrarily controlled, the control of the transmitted wave is not limited to refraction in the 13-degree direction. The incident electromagnetic wave is not limited to a plane wave propagating from the +z direction to the -z direction, but may also be a plane wave or spherical wave incident at an oblique direction with respect to the z axis of the upper scatterer 10. Since the upper unit elements constituting the upper scatterer 10 have bipolarization characteristics, the upper scatterer 10, which is composed of an array of upper unit elements, also has bipolarization characteristics.

[0053] Next, reflection by the lower scatterer 20 will be described. Figure 14 is a top view of the lower scatterer 20. The lower scatterer 20 is formed by arranging a number of lower unit elements with different conductor lengths Lr on a circular substrate in the xy plane. The lower scatterer 20 may also be called a lower metasurface. In Figure 14, the same components as in Figure 5 are denoted by the same reference numerals.

[0054] The lower unit elements constituting the lower scatterer 20 may be determined, for example, based on the phase distribution of the incident electromagnetic wave and the reflection phase characteristics shown in Figure 10, so as to obtain a desired reflection phase distribution. This allows the lower scatterer 20 to focus, diffuse, and reflect the incident electromagnetic field. In Figure 14, each lower unit element has a conductor length Lr corresponding to the x-axis, and multiple lower unit elements formed in the y-axis direction have the same conductor length Lr.

[0055] Figure 15 shows the electric field distribution in the xz plane at 28 GHz when a plane wave polarized in the x direction is incident on the lower scatterer 20 shown in Figure 14 from the +z direction. Figure 15 shows the electric field distribution when each lower unit element constituting the lower scatterer 20 is designed to reflect a perpendicularly incident plane wave in a direction of approximately 26 degrees. According to Figure 15, it can be seen that the incident plane wave is reflected in the 26-degree direction as designed. Here, since the lower scatterer 20 can arbitrarily control the reflected phase distribution, the control of the reflected wave is not limited to reflection in the 26-degree direction. The incident electromagnetic wave is not limited to a plane wave propagating from the +z direction to the -z direction, but may also be a plane wave or spherical wave incident obliquely with respect to the z-axis of the lower scatterer 20, for example. Since the lower unit elements constituting the lower scatterer 20 have bipolarization characteristics, the lower scatterer 20, which is composed of an array of lower unit elements, also has bipolarization characteristics.

[0056] The upper scatterer 10 and the lower scatterer 20 have different patterns for the first conductor 14 and the second conductor 15 arranged on the circular substrate, and different patterns for the third conductor 24 and the fourth conductor 25. The dielectric components of the upper scatterer 10 and the lower scatterer 20 may be the same or different. The dielectric substrates of the upper scatterer 10 and the lower scatterer 20 may have different thicknesses.

[0057] (Control of reflection direction using upper scatterer 10 and lower scatterer 20) As an example of controlling the scattering state of electromagnetic waves, the reflection angle θref (angle with respect to the z axis) is controlled using an upper scatterer 10 and a lower scatterer 20. Figure 16 shows a perspective view of an electromagnetic wave scatterer composed of an upper scatterer 10 and a lower scatterer 20. In Figure 16, the upper scatterer 10 and the lower scatterer 20 are arranged with space between them in the z-axis direction. For example, the upper scatterer 10 is composed of a number of upper unit elements designed so that plane waves arriving and incident from the +z direction are refracted by 13 degrees and transmitted, and the lower scatterer 20 is composed of a number of lower unit elements designed so that plane waves arriving and incident from the +z direction are reflected at a tilt of 26 degrees. The refraction angle or reflection angle of the upper scatterer 10 and the lower scatterer 20 is selected based on the control range of the reflection angle within the elevation plane of the electromagnetic wave scatterer. The refraction angle and reflection angle are not limited to 13 degrees and 26 degrees. In Figure 16, the upper scatterer 10 and lower scatterer 20, which constitute the electromagnetic wave scatterer that controls the reflection angle θref, are rotated by φt and φr from the x-axis, respectively.

[0058] The reflection direction of an electromagnetic wave scatterer can be determined by the following equations (1) and (2).

[0059] Here, kx and ky are given by equations (3) and (4) below, respectively. Here, k is the wavenumber of the reflected wave, kx is the x component of k, ky is the y component of k, αt is the average phase change per unit length of the upper scatterer 10 (average phase gradient), αr is the average phase change per unit length of the lower scatterer 20 (average phase gradient), φt is the rotation angle of the upper scatterer 10 from the x axis, and φr is the rotation angle of the lower scatterer 20 from the x axis.

[0060] Since k, αt, and αr are constants, the reflection direction (θref, φref) of the electromagnetic wave scatterer can be controlled by the rotation angles φr and φr. Because the electromagnetic wave passes through the upper scatterer 10 twice and is reflected once by the lower scatterer 20, from the viewpoint of reducing the blind spot of the electromagnetic wave, if αr is twice αt, it is possible to make θref = 0 degrees, i.e., reflection toward the zenith. It is desirable that αr is 1.5 to 2.5 times αt.

[0061] For the desired reflection direction, the minimum reflection angle θmin and the maximum reflection angle θmax can be determined by the following equations (5) and (6). Note that as θmax increases, the effective area decreases and the amount of electromagnetic waves transmitted from the edge of the substrate without passing through the scatterer increases, thus decreasing the amount of reflection in the desired direction. Therefore, the maximum reflection angle θmax is designed taking these factors into consideration.

[0062] Here, δt is the bending angle of the upper scatterer 10, and δr is the reflection angle of the lower scatterer 20, and the following (7) and (8) hold true.

[0063] Figure 17 shows the reflection direction when the rotation angle φt of the upper scatterer 10 is fixed at 0 degrees and the rotation angle φr of the lower scatterer 20 is changed. Figure 17 shows the case where αt = 0.130 (rad / mm) and αr = 0.254 (rad / mm), but other phase change amounts may also be used. According to Figure 17, the reflection angle θref can be dynamically controlled by controlling the rotation angle φr of the lower scatterer 20. Furthermore, according to equations (2) to (4) and Figure 17, the reflected azimuth angle φref (angle on the xy plane) also changes simultaneously with the change in the rotation angle φr of the lower scatterer 20.

[0064] After rotating the lower scatterer 20 to achieve a desired reflection angle θref, the azimuth angle φref of the reflected wave can be adjusted to a desired direction by rotating the upper and lower scatterers by the same angle while maintaining the relative rotation angles of the upper and lower scatterers 10 and 20. In other words, by mechanically rotating the upper scatterer 10 and lower scatterer 20 shown in Figure 16, the two dimensions of the direction of the reflected wave, namely the reflection angle θref and the azimuth angle φref, can be controlled.

[0065] As can be seen from Figure 17 and equations (1) to (4), an electromagnetic wave scatterer generally achieves its smallest reflection angle θref when the refraction and reflection directions of the upper scatterer 10 and the lower scatterer 20 are opposite. That is, when |φt - φr| = π (rad) holds for rotation angles φt and φr, the electromagnetic wave scatterer achieves its smallest reflection angle θref.

[0066] Figure 18A shows the analysis results of the radar cross-section (RCS) of a bistatic radar in the elevation plane at 28 GHz when a plane wave polarized from the +z direction to the x direction is incident on an electromagnetic wave scatterer. Since the plane wave is incident from the +z direction, the depression angle θ is the angle with respect to the +z direction, i.e., the reflection angle θref. Figure 18A shows that one example satisfying |φt - φr| = π (rad) is when φt = 0 and φr = π. Here, the distance between the upper scatterer 10 and the lower scatterer 20 is 7.5 mm. According to Figure 18A, the reflection angle θref is 0 degrees, i.e., reflection in the +z direction is obtained.

[0067] As another example of reflection angle control, Figures 18B and 18C show the analysis results of the RCS of a bistatic radar in the elevation plane at 28 GHz when φr = 2π / 3 (rad) and π / 3 (rad), respectively. According to Figures 18B and 18C, the reflection angle θref (Depression angle θ) changes with the rotation of the upper scatterer 10. The deviation from the reflection angle θref and reflection in unwanted directions shown in Figures 18A to C are presumed to be due to analysis errors, the fact that the metasurface is composed of a finite number of unit elements, the transmission phase control range of the upper scatterer 10 being 360 degrees or less, and the characteristic changes of the unit elements due to the electromagnetic waves being incident at an oblique angle to the z-axis. By changing the shape of the unit elements and increasing the number of upper and lower unit elements constituting the upper scatterer 10 and lower scatterer 20, the deviation from the reflection angle θref and reflection in unwanted directions can be reduced.

[0068] As described above, an electromagnetic wave scatterer constructed by arranging an upper scatterer 10 and a lower scatterer 20 with a gap between them allows for two-dimensional control of the direction in which incident electromagnetic waves are reflected by rotating the upper scatterer 10 and the lower scatterer 20 around the center of a circular substrate. In other words, the scattering direction can be continuously controlled while suppressing quantization lobes without using a large number of switching elements.

[0069] The upper scatterer 10 and the lower scatterer 20 are designed according to the range over which the angle of reflection can be controlled by rotation.

[0070] <Second Embodiment> In the second embodiment, the relative relationship is changed by moving at least one of the upper and lower scattering bodies along the axis of rotation. In the second embodiment, rotation is not required, but for the sake of explanation, it is referred to as the axis of rotation.

[0071] (Structure and characteristics of the upper scatterer 40 and lower scatterer 50) In c, the electromagnetic wave scatterer has an upper scatterer 40 and a lower scatterer 50, and is capable of changing the diffusion state of electromagnetic waves. The second embodiment is the same as the first embodiment except that the upper unit elements and lower unit elements arranged in the upper scatterer 40 and lower scatterer 50 are different from the upper unit elements and lower unit elements arranged in the upper scatterer 10 and lower scatterer 20 of the first embodiment. In other words, the phase of the electromagnetic waves that pass through and the phase of the electromagnetic waves that are reflected are different in the first embodiment and the second embodiment. The upper scatterer 40 and lower scatterer 50 only need to be designed to transmit or reflect electromagnetic waves at a desired frequency, and may be frequency selectors made of, for example, a rectangular annular conductor or a circular annular conductor. For the sake of simplicity, the configuration of each upper unit element and each lower unit element used in the second embodiment is described as being the same as the configuration of each upper unit element and each lower unit element used in the first embodiment, but they may have different configurations.

[0072] The scattering of electromagnetic waves by the upper scatterer 40 will now be explained. Figure 19 shows an example of a top view of the upper scatterer 40. The upper scatterer 40 is constructed by arranging a large number of different lower unit elements on a circular substrate in the xy plane. The upper scatterer 40 is composed of upper unit elements having a gap width g corresponding to the distance from the center (rotation axis 30) of the circular substrate. The structure of the upper unit elements constituting the upper scatterer 40 shown in Figure 19 is not limited as long as they are designed to transmit most of the incident electromagnetic waves and change their phase.

[0073] Figure 20 shows the electric field distribution in the xz plane at 28 GHz when a plane wave polarized in the x direction is incident on the upper scatterer 40 shown in Figure 19 from the +z direction. The upper scatterer 40 shows the electric field distribution when each upper unit element is arranged so that the focal length of the transmitted wave is 40 mm. That is, the upper scatterer 40 has a phase distribution that transmits as a convex lens. According to Figure 20, the electromagnetic wave of the incident plane wave is focused.

[0074] Next, the lower scatterer 50 will be described. Figure 21 shows an example of a top view of the lower scatterer 50. The lower scatterer 50 is formed by arranging a number of different lower unit elements on a circular substrate in the xy plane. Figure 21 shows an arrangement of lower unit elements having a conductor length Lr corresponding to the distance from the center (rotation axis 30) of the circular substrate.

[0075] Figure 22 shows the electric field distribution in the xz plane at 28 GHz when a plane wave polarized in the x direction is incident on the lower scatterer 50 shown in Figure 21 from the +z direction. The lower scatterer 50 is arranged such that each lower unit element reflects a plane wave incident perpendicularly, with a focal length of -5 mm. That is, the lower scatterer 50 has a phase distribution that reflects like a concave mirror. According to Figure 22, the electromagnetic wave of the incident plane wave is reflected while converging.

[0076] (Control of Diffusion State Using Upper Scatterer 40 and Lower Scatterer 50) The scattering state of the electromagnetic wave scatterer is controlled by controlling the distance d between the upper scatterer 40 and the lower scatterer 50. Figure 23 shows a perspective view of an electromagnetic wave scatterer constructed by arranging the upper scatterer 40 and the lower scatterer 50 with space between them in the z-axis direction. Figure 23 shows an example in which the upper scatterer 40 is composed of a large number of upper unit elements designed to have a focal length of 40 mm, and the lower scatterer 50 is composed of a large number of lower unit elements designed to have a focal length of -5 mm. Here, the focal lengths of the upper scatterer 40 and the lower scatterer 50 are selected based on the desired focal length range for the electromagnetic wave scatterer, and other focal lengths may be used.

[0077] The focal length F of an electromagnetic wave scatterer can be expressed by the following equation (9). Here, ft is the focal length of the upper scatterer 40, fr is the focal length of the lower scatterer 50, and d is the distance between the upper scatterer 40 and the lower scatterer 50.

[0078] Figure 24A shows the values ​​of the focal length F when the distance d is varied, with ft = 30 mm and fr = 5 mm. Figure 24B shows the values ​​of the focal length F when the distance d is varied, with ft = 40 mm and fr = -5 mm. In Figures 24A and 24B, the focal length F is derived using equation (9). According to Figures 24A and 24B, the focal length F changes with the change in distance d. In other words, the focal length F is controlled by changing the distance d.

[0079] Figure 24B shows that when the focal length F is negative, the reflected electromagnetic waves converge. Since electromagnetic waves that converge at focal length F begin to diffuse again beyond focal length F, it can be said that the degree of diffusion of reflected electromagnetic waves is controlled by changing the distance d, regardless of whether the focal length F is positive or negative.

[0080] The electromagnetic wave scatterer can control the focal length of reflected electromagnetic waves by moving the upper scatterer 40 or the lower scatterer 50 along the rotation axis 30, thereby changing the distance d between the upper scatterer 40 and the lower scatterer 50. In other words, the focal length of the scatterer can be controlled continuously and dynamically without using a large number of switching elements. The distance d may be changed by the user using spacers or the like, or it may be changed by a motor that operates based on a control signal from a control device (not shown).

[0081] The upper scatterer 40 and the lower scatterer 50 should be designed according to the range over which the focal length can be controlled by the distance d.

[0082] As described above, an electromagnetic wave scatterer constructed by arranging an upper scatterer 10 and a lower scatterer 20 with a gap between them allows control of the focal length of the scatterer, i.e., the degree of electromagnetic wave diffusion, by moving the upper scatterer 10 and the lower scatterer 20 along the rotation axis 30 of the circular substrate.

[0083] <Third Embodiment> The electromagnetic wave scatterer used in this disclosure only needs to have the property of changing electromagnetic waves to a desired state, and the shape of the conductor or dielectric of the upper unit element and the lower unit element may be configured other than those shown in Figures 2 to 7. The third embodiment is the same as the first and second embodiments except that the configuration of the upper unit element and the lower unit element is different from that of the first and second embodiments.

[0084] Figure 25A shows a unit element composed solely of dielectric or conductor materials and lacking a planar structure. The left side shows a top view, and the right side shows a perspective view.

[0085] Furthermore, Figure 25B shows the unit element of Figure 5, which is composed of a mesh-like conductor and an optically colorless and transparent dielectric. The left side shows a top view, and the right side shows a perspective view. Figure 25B may be difficult to see.

[0086] Furthermore, Figure 25C shows a unit element formed by stacking three layers of dielectric material with a square annular conductor and a circular conductor formed on its surface. The left side shows a top view, and the right side shows a perspective view. According to Figure 25C, the transmitted amplitude characteristics can be improved by stacking multiple unit elements.

[0087] As described above, even when a scattering body is constructed using various unit elements, the state of electromagnetic waves scattered at a desired frequency can be controlled by designing the upper and lower scattering bodies based on the range over which the desired scattering state can be controlled, and by mechanically moving or rotating the upper and lower scattering bodies.

[0088] <Example of Use> Figure 26 shows an example of using the electromagnetic wave scatterer of this disclosure. It shows an example in which communication becomes possible by using the electromagnetic wave scatterer 2640 when the electric field strength of the electromagnetic waves from the base station 2610 is reduced by an obstacle 2630, and the base station 2610 and terminal 2620 cannot communicate. By scattering the electromagnetic waves incident from the base station 2610 to the electromagnetic wave scatterer 2640 in a desired direction, terminal 2620 can receive the electromagnetic waves transmitted by the base station 2610. In other words, even in an environment with poor communication conditions, it is possible to achieve good communication conditions by installing the electromagnetic wave scatterer 2640.

[0089] <Modification> In the second embodiment, the arrangement of each unit element does not have to be rotationally symmetric with respect to the rotation axis 30. Unit elements having a conductor length Lr corresponding to the distance and direction from the rotation axis 30 may be arranged. For example, the gap width g between unit elements having a distance D in the +x axis direction may be the same gap width g as that between unit elements having a distance 2D in the -x axis direction.

[0090] The number of upper scatterers constituting an electromagnetic wave scatterer may be two or more, not just one. When an electromagnetic wave scatterer is constructed using multiple upper scatterers, the lower scatterer (the scatterer that reflects electromagnetic waves) is placed at the bottom, and multiple upper scatterers (scatterers that transmit electromagnetic waves) are placed above it.

[0091] The upper and lower scatterers should be designed according to the range over which the angle of reflection can be controlled by rotation. By combining the upper and lower scatterers on-site, an electromagnetic wave scatterer with a wide control range can be constructed. Therefore, by preparing multiple upper and lower scatterers with different designs, it becomes possible to respond to a wider variety of radio wave conditions on-site.

[0092] All disclosures in the specification, drawings, and abstract contained in the Japanese application No. 2024-217637, filed on December 12, 2024, are incorporated herein by reference.

[0093] One embodiment of the present disclosure is suitable for an electromagnetic wave scatterer capable of controlling the scattering state of electromagnetic waves.

[0094] 10, 40 Upper scatterer 20, 50 Lower scatterer 11, 12, 13 Dielectric 14, 15, 24, 25 Conductor 16, 30 Rotation axis

Claims

1. An electromagnetic wave scatterer comprising a transmission scatterer and a reflection scatterer that are spaced apart from each other, facing each other and having the same axis, wherein the transmission scatterer transmits electromagnetic waves and changes the angle of the transmitted electromagnetic waves, the reflection scatterer reflects electromagnetic waves and changes the angle of the reflected electromagnetic waves, and the relative relationship between the transmission scatterer and the reflection scatterer can be changed.

2. The electromagnetic wave scatterer according to claim 1, wherein at least one of the reflective scatterer and the transmissive scatterer is composed of a metasurface.

3. The electromagnetic wave scatterer according to claim 2, wherein the metasurface is composed of an array of a plurality of unit elements, each of which has a side length smaller than the wavelength of the incident electromagnetic wave at a desired frequency and is made of a dielectric and a conductor.

4. The electromagnetic wave scatterer according to claim 3, wherein the unit element has a four-fold rotationally symmetric structure.

5. The electromagnetic wave scatterer according to claim 1, wherein the change in the relative relationship is a rotation of at least one of the transmission scatterer and the reflection scatterer with respect to the axis.

6. The electromagnetic wave scatterer according to claim 1, wherein the change in the relative relationship is the movement of at least one of the transmission scatterer and the reflection scatterer along the axis.

7. The electromagnetic wave scatterer according to claim 1, further comprising a control circuit for rotating or moving at least one of the transmission scatterer and the reflection scatterer.

8. The electromagnetic wave scatter according to claim 7, wherein the control circuit mechanically rotates or moves at least one of the transmission type scatterer and the reflection type scatterer according to the amplitude or phase distribution of the incident electromagnetic wave and the amplitude or phase distribution of the desired scattered wave.

9. The electromagnetic wave scatterer according to claim 2, wherein the reflective scatterer has one entire surface that is a conductor.

10. The electromagnetic wave scatterer according to claim 2, wherein at least one of the transmission-type scatterer and the reflection-type scatterer is a frequency-selective plate.

11. The electromagnetic wave scatterer according to claim 2, wherein the average phase change per unit length of the reflective scatterer is between 1.5 and 2.5 times the average phase change per unit length of the transmissive scatterer.

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