Frequency Selective Surface and Electromagnetic Wave Absorber

Abstract

The FSS unit element (21) has: a plurality of conductors (31 to 34) extending from the central part of the element toward the outside; and circuit elements (41) connected to the plurality of conductors (31 to 34) at the central part of the element and arranged in a number smaller than the number of the plurality of conductors (31 to 34).

Description

Technical Field

[0001] The present application relates to a frequency selective surface and an electromagnetic wave absorber. Background Art

[0002] A frequency selective surface (hereinafter referred to as "FSS") selectively absorbs electromagnetic waves in a specific frequency band. The FSS is used, for example, for countermeasures against leakage of communication information or electromagnetic interference between systems.

[0003] The FSS has one or more FSS unit elements. The FSS unit element has one or more conductors. When electromagnetic waves are incident on the FSS, a current is induced in the conductor.

[0004] In the FSS unit element, in order to increase the amount of absorbed electromagnetic waves, circuit elements are sometimes assembled into the conductor. For example, in Patent Document 1, there is disclosed an FSS unit element in which circuit elements are assembled. In Patent Document 1, a resistor is disclosed as an example of the circuit element.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2009-38785 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] The FSS unit element disclosed in Patent Document 1 has a resistor for each conductor. Therefore, in the FSS unit element disclosed in Patent Document 1, the number of resistors corresponding to the number of conductors is required.

[0010] The present application has been completed to solve the above problems, and an object thereof is to provide a frequency selective surface capable of arranging circuit elements in a number smaller than the number of conductors.

[0011] Means for Solving the Problems

[0012] The frequency selective surface of the present application is formed by periodically arranging frequency selective surface unit elements. The frequency selective surface unit element has: a plurality of conductors that extend from the central part of the element in two mutually perpendicular directions towards the outside with the same length; and circuit elements that are connected to the plurality of conductors at the central part of the element and are arranged in a number less than the number of the plurality of conductors. The frequency selective surface has: a first arrangement that is formed by periodically arranging a plurality of frequency selective surface unit elements; a second arrangement that is formed by periodically arranging a plurality of frequency selective surface unit elements obtained by inverting the frequency selective surface unit elements in the first arrangement; a third arrangement that is formed by periodically arranging a plurality of frequency selective surface unit elements obtained by rotating the frequency selective surface unit elements in the first arrangement; and a fourth arrangement that is formed by periodically arranging a plurality of frequency selective surface unit elements obtained by rotating the frequency selective surface unit elements in the second arrangement.

[0013] Advantages of the Invention

[0014] According to the present application, circuit elements can be arranged in a number less than the number of conductors. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a front view showing the structure of a radio wave absorber having the FSS unit element of Embodiment 1.

[0016] Figure 2 is a front view showing the structure of an FSS having the FSS unit element of Embodiment 1.

[0017] Figure 3 is a front view showing the structure of the FSS unit element of Embodiment 1.

[0018] Figure 4 is a front view showing the structure of the FSS unit element of Embodiment 2.

[0019] Figure 5 is a front view showing another structure of the FSS unit element of Embodiment 2.

[0020] Figure 6 is a front view showing the structure of the FSS unit element of Embodiment 3.

[0021] Figure 7 is a front view showing another structure of the FSS unit element of Embodiment 3.

[0022] Figure 8 is a front view showing yet another structure of the FSS unit element of Embodiment 3.

[0023] Figure 9 ​​​​​​​​​is the front view showing the structure of the FSS of Embodiment 4.

[0024] Figure 10 is the front view showing another structure of the FSS of Embodiment 4.

[0025] Figure 11 is the front view showing the structure of the FSS of Embodiment 5.

[0026] Figure 12 Figure 12 A is the front view showing the structure of the FSS unit element of Embodiment 5. Figure 12 B is the front view showing the structure of the electromagnetic wave absorber of Embodiment 5.

[0027] Figure 13 Figure 13 A is the front view showing the structure of the existing FSS unit element. Figure 13 B is the front view showing the structure of the existing electromagnetic wave absorber.

[0028] Figure 14 is the graph showing the relationship between the frequency and the normalized reflection amount. Detailed Embodiments

[0029] Hereinafter, in order to explain the present application in more detail, the embodiments for implementing the present application will be described with reference to the drawings.

[0030] Embodiment 1

[0031] Use Figures 1 to 3 The FSS unit element 21 of Embodiment 1 will be described. Figure 1 is the front view showing the structure of the electromagnetic wave absorber 10 having the FSS unit element 21 of Embodiment 1. Figure 2 is the front view showing the structure of the FSS having the FSS unit element 21 of Embodiment 1. Figure 3 is the front view showing the structure of the FSS unit element 21 of Embodiment 1.

[0032] As Figure 1 shown, the electromagnetic wave absorber 10 is a so-called electromagnetic wave band filter that selectively absorbs electromagnetic waves in a specific frequency band. The electromagnetic wave absorber 10 has a substrate 11 and a conductor plate 12. The substrate 11 is, for example, a dielectric substrate. The front surface of the substrate 11 constitutes the FSS. The conductor plate 12 is provided on the back side of the substrate 11.

[0033] As Figure 2 shown, the FSS has a plurality of FSS unit elements 21. These FSS unit elements 21 are two-dimensionally and periodically arranged in the FSS.

[0034] As Figure 3 ​​​​​​​As shown, the FSS unit element 21 has, for example, a plurality of conductors 31 to 34 and one circuit element 41. That is, since the FSS unit element 21 has four conductors 31 to 34, it is a four-pole type FSS unit element.

[0035] The conductors 31 to 34 are conductors that induce current by the electric field 100 of the incident electromagnetic wave. The conductors 31 to 34 are formed in a linear shape and extend from the central portion of the FSS unit element 21 toward the outside. One end of the conductors 31 to 34 is disposed at the central portion of the FSS unit element 21, and the other end of the conductors 31 to 34 is disposed outside the central portion of the FSS unit element 21.

[0036] The circuit element 41 is disposed at the central portion of the FSS unit element 21 and is connected to one end of each of the conductors 31 to 34. One end of each of the conductors 31 to 34 is connected to four side surfaces of the circuit element 41, respectively. Therefore, the conductors 31 to 34 are integrally arranged in a cross shape, but are not limited to this arrangement. That is, the number of circuit elements 41 is less than the number of conductors 31 to 34. At this time, one ends of the conductors 31 to 34 may or may not be connected to each other.

[0037] In addition, in Figure 3 the arrow indicating the electric field 100 represents the polarization direction of the electric field 100.

[0038] The circuit element 41 responds to the current flowing in from the conductors 31 to 34. The circuit element 41 plays a specific role in a circuit such as a resistor or a circuit having a frequency characteristic, for example, through a circuit component such as a chip component or a conductor pattern.

[0039] Moreover, when an electromagnetic wave is incident on the radio wave absorber 10, a current is induced in the conductor among the conductors 31 to 34 that is closest to being parallel to the polarization direction of the electric field 100. When this current flows from the conductors 31 to 34 into the circuit element 41, the circuit element 41 makes a response corresponding to its type as described below.

[0040] When a resistance element is applied to the circuit element 41, the current flowing in the circuit element 41 incurs a loss due to the circuit element 41. Therefore, the energy of the incident electromagnetic wave is absorbed.

[0041] Therefore, the FSS unit element 21 can obtain the absorption characteristic of the incident electromagnetic wave by using only one resistance element. Therefore, compared with the existing unit element structure having a resistance element for each conductor, the number of resistance elements per unit element can be reduced. In addition, the resistance element is, for example, a resistor or a resistance film.

[0042] In the case where a capacitor element is applied to the circuit element 41, the current flowing through the circuit element 41 generates a capacitive effect in the circuit due to the circuit element 41. Therefore, by increasing the equivalent capacitance value of the FSS unit element 21, the frequency characteristics of the FSS unit element 21 shift to the low-frequency side. That is, the FSS can reduce its operating frequency while maintaining the size of the FSS unit element 21. Therefore, the FSS unit element 21 can be miniaturized.

[0043] Therefore, the FSS can adjust the frequency characteristics of the incident electromagnetic wave and miniaturize the FSS unit element 21 by using only one capacitor element. Therefore, compared with the existing unit element structure having a capacitor element for each conductor, the number of capacitor elements per unit element can be reduced. In addition, the capacitor element is a capacitor or a capacitive circuit formed by a gap between one ends of the conductors 31 to 34.

[0044] In the case where an inductor element is applied to the circuit element 41, the current flowing through the circuit element 41 generates an inductive effect in the circuit due to the circuit element 41. Therefore, by increasing the equivalent inductance value of the FSS unit element 21, the frequency characteristics of the FSS unit element 21 shift to the low-frequency side. That is, the FSS can reduce its operating frequency while maintaining the size of the FSS unit element 21. Therefore, the FSS unit element 21 can be miniaturized.

[0045] Therefore, the FSS can adjust the frequency characteristics of the incident electromagnetic wave and miniaturize the FSS unit element 21 by using only one inductor element. Therefore, compared with the existing unit element structure having an inductor element for each conductor, the number of inductor elements per unit element can be reduced. In addition, the inductor element is, for example, an inductor or an inductive circuit formed by meandering of a conductor.

[0046] In the case where an active element is applied to the circuit element 41, the conduction state with respect to the current flowing through the circuit element 41 can be changed, for example, by an external bias circuit. Therefore, the FSS can electrically change the characteristics of the FSS unit element 21.

[0047] Therefore, the FSS can obtain a dynamic control function for the incident electromagnetic wave by using only one active element. Therefore, compared with the existing unit element structure having an active element for each conductor, the number of active elements per unit element can be reduced. In addition, the active element is, for example, a diode or the like.

[0048] Here, in the case where passive components such as a resistance element, a capacitor element, and an inductor element are applied to the circuit element 41, the element value of the passive component becomes a value that is approximately equal to the value obtained by connecting two such passive components in series in the existing unit element structure having a passive component for each conductor.

[0049] As described above, the FSS unit element 21 of Embodiment 1 includes: a plurality of conductors 31 to 34 that extend outward from the element center; and a circuit element 41 that is connected to the plurality of conductors 31 to 34 at the element center and is arranged in a number smaller than the number of the plurality of conductors 31 to 34. Therefore, the FSS unit element 21 can arrange the circuit element 41 in a number smaller than the number of the conductors 31 to 34.

[0050] By setting the number of the circuit elements 41 to one, the FSS unit element 21 can reduce the manufacturing cost.

[0051] Embodiment 2

[0052] Use Figure 4 And Figure 5 The FSS unit element 23 of Embodiment 2 will be described. Figure 4 FIG. is a front view showing the structure of the FSS unit element 23 of Embodiment 2. Figure 5 FIG. is a front view showing another structure of the FSS unit element 23 of Embodiment 2.

[0053] As Figure 4 shown, the FSS unit element 23 includes, for example, a plurality of conductors 31 to 34 and a circuit element 51. Similar to the circuit element 41, the circuit element 51 applies any one of a resistance element, a capacitor element, an inductor element, and an active element.

[0054] In the FSS unit element 23, the conductors 31 to 34 are divided into a group of conductors 31 and 32 and a group of conductors 33 and 34. The conductors 31 and 32 connect a connection portion where one ends are connected to each other to the circuit element 51. The conductors 33 and 34 connect a connection portion where one ends are connected to each other to the circuit element 51.

[0055] The circuit element 51 has two terminals. Among them, one terminal of the circuit element 51 is connected to the connection portion of the conductors 31 and 32. In addition, the other terminal of the circuit element 51 is connected to the connection portion of the conductors 33 and 34.

[0056] As described above, in the FSS unit element 23, the respective connection portions of the two groups are connected to the circuit element 51, whereby the group of conductors 31 and 32 and the group of conductors 33 and 34 are arranged point-symmetrically with the circuit element 51 as the center.

[0057] In addition, in Figure 5In the FSS unit element 23 shown, the conductors 31 to 34 are divided into a group of conductors 31 and 32 and a group of conductors 33 and 34. However, each group does not have the above-mentioned connecting portion where one end of each group is connected to each other, but has an intersecting portion where they intersect each other.

[0058] Specifically, one end of the conductor 31 is connected to a middle portion other than one end and the other end of the conductor 32. At this time, one end of the conductor 32 is connected to one terminal of the circuit element 51. In addition, one end of the conductor 33 is connected to a middle portion other than one end and the other end of the conductor 34. At this time, one end of the conductor 34 is connected to the other terminal of the circuit element 51.

[0059] As described above, in another FSS unit element 23, one end of each group is connected to the circuit element 51. As a result, the group of conductors 31 and 32 and the group of conductors 33 and 34 are arranged point-symmetrically with the circuit element 51 as the center.

[0060] In the above, the FSS unit element 23 of Embodiment 2 is provided with groups composed of the conductors 31, 32 and the conductors 33, 34 having connecting portions where one end of each group is connected to each other, and the connecting portions of each group are connected to the circuit element 51. In addition, the FSS unit element 23 of Embodiment 2 is provided with groups composed of the conductors 31, 32 and the conductors 33, 34 that intersect each other, and one end of the conductors 32, 34 of each group is connected to the circuit element 51. Therefore, the FSS unit element 23 can reduce the connection positions in the circuit element 51 that are connected to the conductors 31 to 34.

[0061] Embodiment 3

[0062] Use Figures 6 to 8 The FSS unit element 24 of Embodiment 3 will be described. Figure 6 It is a front view showing the structure of the FSS unit element 24 of Embodiment 3. Figure 7 It is a front view showing another structure of the FSS unit element 24 of Embodiment 3. Figure 8 It is a front view showing yet another structure of the FSS unit element 24 of Embodiment 3.

[0063] The FSS unit element 24 of Embodiment 3 has a structure obtained by adding the circuit element 52 to the FSS unit element 23 of Embodiment 2. This circuit element 52, like the circuit elements 41 and 51, applies any one of a resistance element, a capacitor element, an inductor element, and an active element. In addition, the circuit element 52 has two terminals.

[0064] For example, Figure 6 The FSS unit element 24 shown is obtained by adding the circuit element 52 to Figure 4The structure obtained from the FSS unit element 23 shown. The circuit elements 51 and 52 are connected in series between the group of conductors 31 and 32 and the group of conductors 33 and 34.

[0065] One terminal of the circuit element 51 is connected to the connection part of the conductors 31 and 32, and the other terminal of the circuit element 51 is connected to one terminal of the circuit element 52. In addition, the other terminal of the circuit element 52 is connected to the connection part of the conductors 33 and 34. Therefore, in Figure 6 the FSS unit element 24 shown, the group of conductors 31 and 32 and the group of conductors 33 and 34 are arranged point-symmetrically with the circuit elements 51 and 52 as the center.

[0066] In addition, in Figure 6 the FSS unit element 24 shown, the circuit elements 51 and 52 can also be connected in parallel between the connection part of the conductors 31 and 32 and the connection part of the conductors 33 and 34.

[0067] Figure 7 The FSS unit element 24 shown is the structure obtained by adding the circuit element 52 to Figure 5 the FSS unit element 23 shown. The circuit elements 51 and 52 are connected in series between the group of conductors 31 and 32 and the group of conductors 33 and 34.

[0068] One terminal of the circuit element 51 is connected to one end of the conductor 32, and the other terminal of the circuit element 51 is connected to one terminal of the circuit element 52. In addition, the other terminal of the circuit element 52 is connected to one end of the conductor 34. Therefore, in Figure 6 the FSS unit element 24 shown, the group of conductors 31 and 32 and the group of conductors 33 and 34 are arranged point-symmetrically with the circuit elements 51 and 52 as the center.

[0069] Figure 8 The FSS unit element 24 shown is the structure obtained by adding the circuit element 52 to Figure 5 the FSS unit element 23 shown. The circuit elements 51 and 52 are connected in parallel between the group of conductors 31 and 32 and the group of conductors 33 and 34.

[0070] One terminal of the circuit element 51 and one terminal of the circuit element 52 are connected to one end of the conductor 32. In addition, the other terminal of the circuit element 51 and the other terminal of the circuit element 52 are connected to one end of the conductor 34. Therefore, in Figure 8 the FSS unit element 24 shown, the group of conductors 31 and 32 and the group of conductors 33 and 34 are arranged point-symmetrically with the circuit elements 51 and 52 as the center.

[0071] As described above, the FSS unit element 24 of Embodiment 3 is provided with a group composed of conductors 31, 32 and conductors 33, 34 having connection portions connected to each other at one end, and the connection portions of each group are connected to circuit elements 51, 52. In addition, the FSS unit element 24 of Embodiment 3 is provided with a group composed of conductors 31, 32 and conductors 33, 34 that cross each other, and one ends of the conductors 32, 34 of each group are connected to circuit elements 51, 52. Therefore, the FSS unit element 23 can arrange the circuit elements 51, 52 in a number smaller than the number of the plurality of conductors 31 to 34.

[0072] Embodiment 4

[0073] Use Figure 9 And Figure 10 The FSS of Embodiment 4 will be described. Figure 9 It is a front view showing the structure of the FSS of Embodiment 4. Figure 10 It is a front view showing another structure of the FSS of Embodiment 4.

[0074] Here, in the FSS formed by periodically arranging the FSS unit elements 23, 24 of the above-described Embodiments 2 and 3, the orientations of the FSS unit elements 23, 24 are the same. In the case of adopting such a structure, in the FSS, when a polarized wave is incident, a cross-polarized wave is generated in a direction substantially perpendicular to the incident direction of the polarized wave, and the reflection and transmission of the cross-polarized wave become problems.

[0075] Therefore, the FSS of Embodiment 4 aims to solve the above problems and adopts a structure in which the orientations of the FSS unit elements 23, 24 are partially changed to suppress the generation of cross-polarized waves. In addition, in the FSS of Embodiment 4, the case of applying the FSS unit element 23 shown in Figure 5 the FSS unit element 23 shown in the above-described Embodiments 2 and 3 will be described.

[0076] Figure 9 The FSS shown in the above has arrangements 61, 62 formed by periodically arranging the FSS unit elements 23. The orientations of the FSS unit elements 23 in arrangement 61 and the orientations of the FSS unit elements 23 in arrangement 62 are different from each other.

[0077] For example, arrangement 61 is Figure 5It is formed by periodically arranging a plurality of FSS unit elements 23 shown. The arrangement 62 is formed by periodically arranging the arrangement obtained by reversing each FSS unit element 23 of the arrangement 61 by 180 degrees with the center line in the vertical direction of the FSS as the center. In addition, the arrangement 62 can also be formed by periodically arranging the arrangement obtained by reversing each FSS unit element 23 of the arrangement 61 by 180 degrees with the center line in the horizontal direction of the FSS as the center. The arrangement 61 constitutes the first arrangement, and the arrangement 62 constitutes the second arrangement.

[0078] Therefore, when electromagnetic waves are incident on the FSS of the radio wave absorber 10, currents flow on each FSS unit element 23 of the arrangement 61 and each FSS unit element 23 of the arrangement 62. Along with this, cross-polarized waves are reflected and transmitted, generating reflected waves and transmitted waves.

[0079] At this time, the electric fields of the reflected wave and the transmitted wave can be decomposed into two orthogonal components, namely the main polarization component and the cross-polarization component. The main polarization component is the component in the direction where the orientation of the electric field is the same as the incident direction of the polarized wave, and the cross-polarization component is the component in the direction where the orientation of the electric field is orthogonal to the incident direction of the polarized wave.

[0080] As described above, the orientation of the FSS unit element 23 in the arrangement 61 is reversed with respect to the orientation of the FSS unit element 23 in the arrangement 62. Therefore, the main polarization components of the reflected wave and the transmitted wave generated in the arrangement 61 and the main polarization components of the reflected wave and the transmitted wave generated in the arrangement 62 have the same phase and the same amplitude. In addition, the cross-polarization components of the reflected wave and the transmitted wave generated in the arrangement 61 and the cross-polarization components of the reflected wave and the transmitted wave generated in the arrangement 62 have opposite phases and the same amplitude.

[0081] As a result, the cross-polarization components cancel each other out at a distance, and this cross-polarization component becomes "0". That is, the generation of cross-polarized waves is suppressed.

[0082] In addition, the arrangements 61 and 62 can also be structures in which the orientations of the FSS unit elements 23 are reversed with the center line in the horizontal direction as the center. In addition, the arrangements 61 and 62 are rectangular, but they can also be semi-circular. Moreover, it can be that the arrangement 61 is circular and the arrangement 62 is annular, and this annular is located concentrically on the outer periphery of the circular arrangement 61.

[0083] As another example, in Figure 10 the shown FSS, a plurality of arrangements 61 and 62 are respectively provided. In Figure 10 the example, the case where two sets of the above-mentioned arrangements 61 and 62 in an inverted relationship are shown is illustrated. In Figure 10 the example, two sets of the arrangements 61 and 62 are provided, but it can also be three or more sets.

[0084] As described above, the FSS of Embodiment 4 has an arrangement 61 in which a plurality of FSS unit elements 23 are periodically arranged, and an arrangement 62 in which a plurality of FSS unit elements 23 are periodically arranged with an orientation different from the orientation of the FSS unit elements 23 in the arrangement 61. Therefore, the FSS can suppress the generation of cross-polarized waves.

[0085] Embodiment 5

[0086] Use Figures 11 to 14 Embodiment 5 will be described. Figure 11 It is a front view showing the structure of the FSS of Embodiment 5.

[0087] The FSS of Embodiment 5 can obtain the same effect as the suppression of cross-polarized waves obtained by the FSS of Embodiment 4 without depending on the incident polarization wave.

[0088] Figure 11 The FSS shown has arrangements 61 to 64 in which the orientations of the FSS unit elements 23 are the same as each other. In the arrangements 61 to 64, the orientations of the arranged FSS unit elements 23 are different from each other.

[0089] For example, the arrangement 61 is formed by periodically arranging Figure 5 the plurality of FSS unit elements 23 shown. The arrangement 62 is formed by periodically arranging the arrangement obtained by rotating each FSS unit element 23 in the arrangement 61 90 degrees to the left or right. The arrangement 63 is formed by periodically arranging the arrangement obtained by inverting each FSS unit element 23 in the arrangement 61 180 degrees about the center line in the vertical direction of the FSS. The arrangement 64 is formed by periodically arranging the arrangement obtained by inverting each FSS unit element 23 in the arrangement 63 90 degrees to the left or right. The arrangement 61 constitutes the first arrangement, and the arrangements 62 to 63 constitute the second arrangement.

[0090] Therefore, by having the arrangements 61 to 64 in which the orientations of the FSS unit elements 23 are different from each other, the FSS can suppress the generation of cross-polarized waves regardless of the incident direction of the polarization wave, and can make the reflection characteristic or the transmission characteristic a characteristic independent of the incident direction of the polarization wave.

[0091] Next, use Figures 12 to 14 to describe the radio wave absorber 10 having the FSS of Embodiment 5 and the radio wave absorber 90 having the existing FSS.

[0092] Figure 12 A is a front view showing the structure of the FSS unit element 23 of Embodiment 5. Figure 12 B is a front view showing the structure of the radio wave absorber 10 of Embodiment 5. Figure 13A is a front view showing the structure of an existing FSS unit element 91. Figure 13 B is a front view showing the structure of an existing electromagnetic wave absorber 90.

[0093] Figure 12 The FSS unit element 23 shown in A has the same structure as Figure 4 the structure of the FSS unit element 23 shown. That is, in this FSS unit element 23, the group of conductors 31, 32 and the group of conductors 33, 34 are arranged point-symmetrically with a circuit element 51 as the center. This circuit element 51 is an application of a resistance element.

[0094] As Figure 12 shown in B, the arrangements 61 - 64 forming the FSS are formed by periodically arranging a plurality of FSS unit elements 23. This periodic arrangement is the same as Figure 11 the periodic arrangement shown, so its description is omitted. Additionally, Figure 12 the electromagnetic wave absorber 10 shown in B has a substrate 11 on which the above FSS is formed on the front surface, and a conductor plate 12 disposed on the opposite side of the front surface of the substrate 11.

[0095] In Figure 12 A and Figure 12 B's example, the FSS unit element 23 is arranged within a square with a side length of 15 mm in the FSS. This square forms one cell. The widths of conductors 31 - 34 are 0.5 mm. The length of the circuit element 51 is 0.28 mm. The element value of the circuit element 51 is 320 Ω. The length including the circuit element 51 between the group of conductors 31, 32 and the group of conductors 33, 34, that is, the length between the other ends of conductors 31, 33 and the length between the other ends of conductors 32, 34, is 12 mm. In addition, conductor pieces perpendicular to the length direction of the conductors 31 - 34 are respectively formed at the other ends of the conductors 31 - 34, and the length of this conductor piece is 4 mm.

[0096] The FSS of the electromagnetic wave absorber 10 is a square with a side length of 300 mm. That is, one side of this FSS is composed of 20 cells. The thickness of the substrate 11 is 1.6 mm. The relative dielectric constant of the substrate 11 is 4.4. The conductor plate 12 is disposed 6 mm away from the back surface of the substrate 11. Additionally, the up-down direction of the electromagnetic wave absorber 10 is the x-axis direction, with the downward direction being the positive direction. The left-right direction of the electromagnetic wave absorber 10 is the y-axis direction, with the rightward direction being the positive direction. The front-back direction of the electromagnetic wave absorber 10 is the z-axis direction, with the forward direction being the positive direction.

[0097] In Figure 13In the existing FSS unit element 91 shown in A, one ends of conductors 31 to 34 are directly connected to each other. Four circuit elements 51 as resistance elements are respectively provided in the middle parts of conductors 31 to 34, in other words, respectively provided in parts other than one ends and the other ends of conductors 31 to 34. In Figure 13 In the existing electromagnetic wave absorber 90 shown in B, a plurality of FSS unit elements 91 are periodically arranged in the FSS. That is, the existing FFS does not have arrangements 61 to 64.

[0098] In addition, regarding Figure 13 A and Figure 13 the dimensions, coordinate systems, etc. of each part in the examples of B, they are the same as those of each part in the examples of Figure 12 A and Figure 12 B, so the description is omitted. However, the element value of the circuit element 51 applied to the existing FSS unit element 91 is 100 Ω.

[0099] Figure 14 is a graph showing the relationship between frequency (GHz) and normalized reflection amount (dB). Specifically, Figure 14 is a graph showing the normalized reflection amount in the +z-axis direction when an x-axis direction polarized wave is incident on the electromagnetic wave absorber 10 of Embodiment 5 and the existing electromagnetic wave absorber 90 from the +z-axis direction. Among them, the normalized reflection amount is defined by the reflection power of the main polarization component (i.e., the x-axis direction polarization component of the reflected wave) of the reflected wave based on the conductor plate 12 having the same area as the area of the FSS and the reflection power of the main polarization component (i.e., the x-axis direction polarization component of the reflected wave) and the cross polarization component (i.e., the y-axis direction polarization component of the reflected wave) of the reflected wave based on the electromagnetic wave absorbers 10 and 90. In addition, Figure 14 The four line types shown represent the x-axis direction polarization component and the y-axis direction polarization component of the reflected wave based on the existing electromagnetic wave absorber 90, and the x-axis direction polarization component and the y-axis direction polarization component of the reflected wave based on the electromagnetic wave absorber 10 of Embodiment 5.

[0100] As Figure 14As shown, compared with the existing electromagnetic wave absorber 90, the electromagnetic wave absorber 10 of Embodiment 5 reduces the number of circuit elements 51 to one-fourth while achieving electromagnetic wave absorption performance equivalent to that of the existing electromagnetic wave absorber 90 for the X-axis polarization component of the reflected wave (about 10 dB). In addition, in the electromagnetic wave absorber 10 of Embodiment 5, the value of the Y-axis polarization component of the reflected wave is a very small value compared with the value of the X-axis polarization component of the reflected wave. Therefore, it can be confirmed that the electromagnetic wave absorber 10 is effective in reducing the Y-axis polarization component of the reflected wave. In addition, it can be seen that the electromagnetic wave absorber 10 has a point-symmetric structure in which the groups of conductors 31 and 32 and the groups of conductors 33 and 34 have the same shape even when rotated 90 degrees to the left or right around the circuit element 51. Therefore, there is no dependence on the incident polarized wave.

[0101] As described above, the FSS of Embodiment 5 has an arrangement 61 in which a plurality of FSS unit elements 23 are periodically arranged, and arrangements 62 to 64 in which a plurality of FSS unit elements 23 are periodically arranged with an orientation different from that of the FSS unit elements 23 in the arrangement 61. Therefore, the FSS can suppress the generation of cross-polarized waves.

[0102] In addition, the electromagnetic wave absorber 10 of Embodiment 5 has the FSS of Embodiments 4 and 5, a substrate 11 on which the FSS is formed, and a conductor plate 12 disposed on the side opposite to the surface of the substrate 11 on which the FSS is formed. Therefore, the electromagnetic wave absorber 10 can suppress the generation of cross-polarized waves.

[0103] In addition, the present application can, within the scope of its disclosure, achieve free combination of each embodiment, or deformation of any structural element in each embodiment, or omission of any structural element in each embodiment.

[0104] Industrial Applicability

[0105] The frequency selective surface of the present invention can arrange circuit elements in a smaller number than the number of conductors by having circuit elements arranged in a smaller number at the central part of the element. Therefore, it is suitable for frequency selective surfaces and the like.

[0106] Reference Numeral Explanation

[0107] 10, 90: electromagnetic wave absorber; 11: substrate; 12: conductor plate; 21, 23, 24, 91: FSS unit element; 31 to 34: conductor; 41, 51, 52: circuit element; 61 to 64: arrangement; 100: electric field.

Claims

1. A frequency selective surface which is formed by periodically arranging unit elements of the frequency selective surface. The unit element of the frequency selective surface has: A plurality of conductors extending in two mutually perpendicular directions from the central portion of the element toward the outside with the same length; and a circuit element which is connected to the plurality of conductors at the central portion of the element and is arranged in a number less than the number of the plurality of conductors. It is characterized in that the frequency selective surface has: a first arrangement which is formed by periodically arranging a plurality of unit elements of the frequency selective surface; a second arrangement which is formed by periodically arranging a plurality of unit elements of the frequency selective surface after inverting the unit elements of the frequency selective surface in the first arrangement by 180 degrees; a third arrangement which is formed by periodically arranging a plurality of unit elements of the frequency selective surface after rotating the unit elements of the frequency selective surface in the first arrangement by 90 degrees; and a fourth arrangement which is formed by periodically arranging a plurality of unit elements of the frequency selective surface after rotating the unit elements of the frequency selective surface in the second arrangement by 90 degrees.

2. The frequency selective surface according to claim 1, characterized in that a plurality of groups are provided, and each group is composed of a plurality of conductors having connecting portions connected to each other at one end, and the connecting portions of each group are connected to the circuit element.

3. The frequency selective surface according to claim 1, characterized in that a plurality of groups are provided, and each group is composed of a plurality of intersecting conductors, and one end of any one of the plurality of conductors in each group is connected to the circuit element.

4. The frequency selective surface according to claim 1, characterized in that the circuit element is a resistive element.

5. The frequency selective surface according to claim 1, characterized in that the circuit element is a capacitive element.

6. The frequency selective surface according to claim 1, characterized in that the circuit element is an inductive element.

7. The frequency selective surface according to claim 1, characterized in that the circuit element is an active element.

8. The frequency selective surface according to claim 1, characterized in that the circuit element is a passive element.

9. An electromagnetic wave absorber, characterized in that, The electromagnetic wave absorber has: the frequency selective surface according to any one of claims 1 to 8; a substrate on which the frequency selective surface is formed; and a conductor plate which is arranged on the opposite side of the surface of the substrate on which the frequency selective surface is formed.

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