Radio wave absorbing sheet set and radio wave absorbing sheet laminate

Abstract

The objective is to provide radio wave absorbing products that offer superior convenience. [Solution] A radio wave absorbing sheet set is provided, comprising a radio wave absorbing material, wherein the radio wave absorbing material has a plurality of radio wave absorbing sheets that are separated from each other, and the different radio wave absorbing sheets are configured to be stacked in close contact with each other, and each radio wave absorbing sheet has a dielectric layer and a resistive layer provided within the dielectric layer, and any pair of radio wave absorbing sheets included in the plurality of radio wave absorbing sheets have different radio wave absorbing characteristics from each other.

Description

Technical Field

[0001] The present invention relates to a radio wave absorbing sheet set and a radio wave absorbing sheet laminate.

Background Art

[0002] In Patent Document 1, a radio wave absorber that suppresses and absorbs reflection of unnecessary radio waves has been proposed. In the radio wave absorber of Patent Document 1, a resistance layer is provided on the surface of the dielectric layer on the radio wave incident side, and a reflection layer that reflects radio waves is provided on the opposite back surface. This radio wave absorber is a radio wave interference type radio wave absorber that absorbs radio waves by causing interference between the radio waves reflected by the resistance layer and the radio waves reflected by the reflection layer and canceling them out.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Conventional radio wave absorbers are provided for uses in specific frequency bands for each product. The use (corresponding frequency) is determined for each product, and there is a problem of low convenience for users.

[0005] An object of the present invention is to provide a radio wave absorber product with excellent convenience.

Means for Solving the Problems

[0006] According to the present invention, a radio wave absorbing sheet set is provided, comprising a radio wave absorbing material, wherein the radio wave absorbing material has a plurality of radio wave absorbing sheets that are separated from each other, the different radio wave absorbing sheets are configured to be stacked in close contact with each other, each radio wave absorbing sheet has a dielectric layer and a resistive layer provided within the dielectric layer, and any pair of radio wave absorbing sheets included in the plurality of radio wave absorbing sheets have different radio wave absorbing characteristics from each other.

[0007] According to the radio wave absorbing sheet set of the present invention, it is possible to select the applicable frequency band depending on how multiple radio wave absorbing materials (radio wave absorbing sheets) are combined, thereby improving user convenience. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1A is a schematic cross-sectional view showing each of the radio wave absorbing materials 10 and 20 (a plurality of radio wave absorbing sheets 10S and 20S that are separated from each other) of the radio wave absorbing sheet set 100 according to the embodiment. Figure 1B shows (a) an example of the planar structure of the resistive layer 1R, and (b) an example of the planar structure of the resistive layer 1R different from (a). Figure 1C shows an example of the layer configuration around the metal layer M and dielectric layer D. [Figure 2] Figure 2A shows the absorption characteristics (frequency characteristics (GHz) of the amount of reflection (dB), the same applies hereinafter) of the radio wave absorbing sheet 10S of the embodiment when radio waves are incident from the front side. Figure 2B shows the absorption characteristics of the radio wave absorbing sheet 10S of the embodiment when radio waves are incident from the back side. [Figure 3] Figure 3A shows the absorption characteristics of the radio wave absorbing sheet 20S of the embodiment when radio waves are incident from the front side. Figure 3B shows the absorption characteristics of the radio wave absorbing sheet 20S of the embodiment when radio waves are incident from the back side. [Figure 4] Figure 4A shows the radio wave absorbing sheet laminate 100A, Figure 4B shows the radio wave absorbing sheet laminate 100B, Figure 4C shows the radio wave absorbing sheet laminate 100C, and Figure 4D shows the radio wave absorbing sheet laminate 100D, each illustrated (in cross-sectional view). [Figure 5]Figure 5A shows the absorption characteristics of the radio wave absorbing sheet laminate 100A. Figure 5B shows the absorption characteristics of the radio wave absorbing sheet laminate 100B. [Figure 6] Figure 6A shows the absorption characteristics of the radio wave absorbing sheet laminate 100C. Figure 6B shows the absorption characteristics of the radio wave absorbing sheet laminate 100D. [Figure 7] Figure 7A shows the radio wave absorbing sheet laminate 100E, Figure 7B shows the radio wave absorbing sheet laminate 100F, Figure 7C shows the radio wave absorbing sheet laminate 100G, and Figure 7D shows the radio wave absorbing sheet laminate 100H, each in cross-sectional view. [Figure 8] Figure 8A shows the absorption characteristics of the radio wave absorbing sheet laminate 100E. Figure 8B shows the absorption characteristics of the radio wave absorbing sheet laminate 100F. [Figure 9] Figure 9A shows the absorption characteristics of the radio wave absorbing sheet laminate 100G. Figure 9B shows the absorption characteristics of the radio wave absorbing sheet laminate 100H. [Modes for carrying out the invention]

[0009] Embodiments of the present invention will be described below with reference to the drawings. The various features shown in the embodiments below can be combined with each other. Furthermore, each feature constitutes an independent invention. It should be noted that, for convenience, the terms "front face" and "rear face" may be used in the description of the embodiments to distinguish between them. However, this is merely a convenient distinction in the embodiments, and it simply means that if one side is the front face, the opposite side is the rear face. The designation of the front face and rear face in the embodiments is merely an example for explanation purposes and is not limiting; the designation of the front face and rear face is interchangeable. Also, the size of the components shown in the figures, especially the thickness of each layer, is not necessarily representative of reality, and the present invention is not limited by the dimensions of the illustrated configuration.

[0010] 1. Radio wave absorbing sheet set of the embodiment 1-1. Configuration of each component As shown in Figure 1A, the radio wave absorbing sheet set 100 comprises radio wave absorbing materials 10 and 20. The radio wave absorbing materials 10 and 20 have multiple radio wave absorbing sheets 10S and 20S that are separated from each other. Figure 1A shows a cross-sectional view of each radio wave absorbing sheet 10S and 20S. In reality, each radio wave absorbing sheet 10S and 20S can be provided in the form of a sheet of any size and can have a certain degree of spread in the direction of the sheet surface. Different radio wave absorbing sheets 10S and 20S are configured to be stacked in close contact with each other.

[0011] The radio wave absorbing sheet 10S of the embodiment has dielectric layers 1Df, 1Dr, a resistive layer 1R, and metal layers 1Mf, 1Mr. The resistive layer 1R is provided within the dielectric layers 1Df, 1Dr. The radio wave absorbing sheet 10S has a total thickness T10. The radio wave absorbing sheet 20S of the embodiment has dielectric layers 2Df, 2Dr, a resistive layer 2R, and metal layers 2Mf, 2Mr. The resistive layer 2R is provided within the dielectric layers 2Df, 2Dr. The radio wave absorbing sheet 20S has a total thickness T20.

[0012] Resistive layers 1R and 2R have functions related to the reflection and transmission of radio waves. Resistive layers 1R and 2R can reflect a portion of the incident radio waves and allow the remaining radio waves to pass through.

[0013] The resistive layer 1R can be equipped with a function related to the selection of the frequency of radio waves that pass through it. In one embodiment, for example, the resistive layer 1R has a so-called frequency-selective surface formed thereon, and the frequency of the radio waves that pass through it is a predetermined frequency. Further details will be described later in "3. Specific Configuration of Each Layer (Material, Characteristics, Thickness, etc.)" under "3-2-1. Configuration of Resistive Layer 1R".

[0014] The dielectric layers 1Df and 1Dr of the radio wave absorbing sheet 10S of the embodiment have a first dielectric layer 1Df (hereinafter also simply referred to as dielectric layer 1Df) and a second dielectric layer 1Dr (hereinafter also simply referred to as dielectric layer 1Dr). The resistive layer 1R is disposed between dielectric layer 1Df and dielectric layer 1Dr. The dielectric layers 2Df and 2Dr of each radio wave absorbing sheet 20S of the embodiment have a first dielectric layer 2Df (hereinafter also simply referred to as dielectric layer 2Df) and a second dielectric layer 2Dr (hereinafter also simply referred to as dielectric layer 2Dr). The resistive layer 2R is disposed between dielectric layer 2Df and dielectric layer 2Dr. The dielectric constant of the first dielectric layer (dielectric layers 1Df and 2Df) and the dielectric constant of the second dielectric layer (dielectric layers 1Dr and 2Dr) may be the same. The thicknesses T1f and T2f of the first dielectric layer (dielectric layers 1Df and 2Df) and the thicknesses T1r and T2r of the second dielectric layer (dielectric layers 1Dr and 2Dr) may be different.

[0015] In one embodiment, the radio wave absorbing sheet 10S further comprises a pair of metal layers 1Mf and 1Mr. One of the pair of metal layers 1Mf and 1Mr (metal layer 1Mf) is placed in the dielectric layer 1Df on the front side of the radio wave absorbing sheet 10S. The other of the pair of metal layers 1Mf and 1Mr (metal layer 1Mr) is placed in the dielectric layer 1Dr on the back side of the radio wave absorbing sheet 10S. In another embodiment, the radio wave absorbing sheet 20S further comprises a pair of metal layers 2Mf and 2Mr. One of the pair of metal layers 2Mf and 2Mr (metal layer 2Mf) is placed in the dielectric layer 2Df on the front side of the radio wave absorbing sheet 20S. The other of the pair of metal layers 2Mf and 2Mr (metal layer 2Mr) is placed in the dielectric layer 2Dr on the back side of the radio wave absorbing sheet 20S. Each metal layer 1Mf, 1Mr, 2Mf, and 2Mr is configured to be peelable from each dielectric layer 1Df, 1Dr, 2Df, and 2Dr.

[0016] The metal layers 1Mf, 1Mr, 2Mf, and 2Mr are configured to be able to reflect radio waves that have passed through the resistance layers (resistance layers 1R and 2R). That is, the metal layers 1Mf, 1Mr, 2Mf, and 2Mr are "reflective layers" that reflect radio waves that have passed through all of the dielectric layer and the resistance layers. Since the metal layers 1Mf, 1Mr, 2Mf, and 2Mr do not need to allow radio waves to pass through, unlike the resistance layers 1R and 2R, they may have as low a resistance value as possible.

[0017] Each of the radio wave absorption sheets 10S and 20S of the embodiment may further include adhesive layers ad1 and ad2 (see FIG. 1C) and a film spf (see FIG. 1C). In FIG. 1C, the metal layer M is a generalized name for the metal layers 1Mf, 1Mr, 2Mf, and 2Mr, and the dielectric layer D is a generalized name for 1Df, 1Dr, 2Df, and 2Dr. That is, in FIG. 1C, when the metal layer M corresponds to the metal layer 1Mf, the dielectric layer D corresponds to the dielectric layer 1Df. The film spf can be formed of, for example, a separator film. The separator film is mainly a film for the purpose of separating layers. The adhesive layers ad1 and ad2 in the radio wave absorption sheet 10S are disposed between the metal layer 1Mf and the dielectric layer 1Df, and between the metal layer 1Mr and the dielectric layer 1Dr, respectively. The pair of adhesive layers ad1 and ad2 in the radio wave absorption sheet 20S are disposed between the metal layer 2Mf and the dielectric layer 2Df, and between the metal layer 2Mr and the dielectric layer 2Dr, respectively. Since this adhesive layer adhesively attaches each layer in a peelable manner, the metal layers 1Mf, 1Mr, 2Mf, and 2Mr can be peeled off from the dielectric layers 1Df, 1Dr, 2Df, and 2Dr, respectively.

[0018] Each of the radio wave absorption sheets 10S and 20S in the embodiment may further have a pair of protective layers pt (see FIG. 1C). One of the pair of protective layers pt may be arranged to cover the metal layer M (metal layers 1Mf and 2Mf) on one side (front side) of each of the radio wave absorption sheets 10S and 20S. The other of the pair of protective layers pt (not shown) may be arranged to cover the metal layer M (metal layers 1Mr and 2Mr) on the other side (back side) of each of the radio wave absorption sheets 10S and 20S. Each protective layer pt can be formed by, for example, coating on each metal layer M (metal layers 1Mf, 1Mr, 2Mf, and 2Mr).

[0019] 1-2. Characteristics of Each Radio Wave Absorption Sheet Hereinafter, the characteristics of each of the radio wave absorption sheets 10S and 20S will be described. Each of the radio wave absorption sheets 10S and 20S is, as an example, a sheet-like member and is configured to absorb radio waves. Each of the radio wave absorption sheets 10S and 20S may be formed in a sheet-like shape having flexibility as a whole. Each of the radio wave absorption sheets 10S and 20S may further have another layer member (for example, a reinforcing member, etc.), and the reinforcing member may be arbitrarily peelable. Alternatively, a reinforcing member may be additionally provided as a set part, and the reinforcing member may be arbitrarily attached for reinforcement.

[0020] In the embodiment, the radio wave absorption characteristics of the radio wave absorption sheet 10S (see FIGS. 2A and 2B) and the radio wave absorption characteristics of the radio wave absorption sheet 20S (see FIGS. 3A and 3B) are different from each other. Also, in the embodiment, as an example, each of the radio wave absorption sheets 10S and 20S is a reversible absorber. Each of the radio wave absorption sheets 10S and 20S in the embodiment is configured such that, as an example, the radio wave absorption characteristics when radio waves are incident from the front side (for example, see FIGS. 2A and 3A) and the radio wave absorption characteristics when radio waves are incident from the back side (for example, see FIGS. 2B and 3B) are different.

[0021] To enable reversible use, each of the metal layers 1Mf, 1Mr, 2Mf, and 2Mr in each of the radio wave absorbing sheets 10S and 20S according to the embodiment is configured to be peelable. This allows for the use of either "peeling off the metal layers 1Mf and 2Mf on the front side" or "peeling off the metal layers 1Mr and 2Mr on the back side" depending on the situation, when different absorption characteristics are achieved on both sides by devising the layer configuration of the dielectric layer and resistive layer. This offers superior convenience.

[0022] Each of the radio wave absorbing sheets 10S and 20S can be provided, for example, as a radio wave interference type (also called λ / 4 type or reflective type) radio wave absorbing sheet. A radio wave interference type absorbing sheet can be constructed, for example, based on the principle of radio wave absorption, such that d = λ / 4 = πc / (2ω√ε) is satisfied, based on the thickness d of a dielectric layer with dielectric constant ε and the wavelength λ (=1 / frequency) of the radio waves to be absorbed when they propagate within the dielectric.

[0023] The radio wave absorbing sheet 10S in Figures 2A and 2B is, for example, a reversible absorber capable of covering the 28GHz, 84GHz, and 140GHz bands. The composition of each layer in Figures 2A and 2B is as follows: the resistive layer 1R has a resistance of 187Ω / sq ​​(for example). The dielectric layers 1Df and 1Dr are made of acrylic OCA (for example). The thickness T1f of the dielectric layer 1Df (see Figure 1A) is 550μm (for example). The thickness T1r of the dielectric layer 1Dr (see Figure 1A) is 1100μm (for example). In other words, the thickness T1r is twice the thickness T1f (for example).

[0024] In Figure 2A, the metal layer 1Mf on the front side of the radio wave absorbing sheet 10S has been peeled off, leaving the metal layer 1Mr on the back side. The metal layer 1Mr on the back side functions as a reflective layer. A characteristic graph is shown when an incident wave is incident from the front side.

[0025] In Figure 2B, the metal layer 1Mf on the front side of the radio wave absorbing sheet 10S is left intact, while the metal layer 1Mr on the back side has been removed. The metal layer 1Mf on the front side functions as a reflective layer. A characteristic graph is shown for when an incident wave is incident from the back side.

[0026] The radio wave absorbing sheet 20S in Figures 3A and 3B is a reversible absorber. The composition of each layer in Figures 3A and 3B is as follows: the resistive layer 2R has a resistance of 187 Ω / sq (for example). The dielectric layers 2Df and 2Dr are made of acrylic OCA (for example). The thickness T2f of the dielectric layer 2Df (see Figure 1A) is 300 μm (for example). The thickness T2r of the dielectric layer 2Dr (see Figure 1A) is 600 μm (for example). In other words, the thickness T2r is twice the thickness T2f (for example).

[0027] In Figure 3A, the metal layer 2Mf on the front side of the radio wave absorbing sheet 20S has been peeled off, leaving the metal layer 2Mr on the back side. The metal layer 2Mr on the back side functions as a reflective layer. A characteristic graph is shown when an incident wave is incident from the front side.

[0028] In Figure 3B, the metal layer 2Mf on the front side of the radio wave absorbing sheet 20S is left intact, while the metal layer 2Mr on the back side has been removed. The metal layer 2Mf on the front side functions as a reflective layer. A characteristic graph is shown for when an incident wave is incident from the back side.

[0029] 2. Usage of the embodiment (Radio wave absorbing sheet laminate) 2-1. Overview Referring to Figures 4A to 4D and 7A to 7D, the configurations of the radio wave absorbing sheet laminates 100A to 100H according to the embodiment will be described. Each radio wave absorbing sheet laminate 100A to 100H is formed by closely laminating multiple radio wave absorbing sheets 10S and 20S of the radio wave absorbing sheet set 100. Note that the figures are provided to facilitate understanding of the configurations of each radio wave absorbing sheet laminate 100A to 100H, and the sizes of the components shown in the figures, especially the thickness of each layer, are not necessarily accurate to reality. The present invention is not limited by the dimensions of the illustrated configurations.

[0030] Each of the radio wave absorbing sheet laminates 100A to 100H is, for example, a sheet-like member and is configured to absorb radio waves. Each of the radio wave absorbing sheet laminates 100A to 100H may be formed as a flexible sheet. Each of the radio wave absorbing sheet laminates 100A to 100H may further have another layer member (for example, a reinforcing member to reinforce each of the radio wave absorbing sheet laminates 100A to 100H).

[0031] Each of the radio wave absorbing sheet laminates 100A to 100H has two resistive layers, 1R and 2R. This makes the interference of radio waves more complex and combined, enabling the absorption of radio waves across a wide frequency band. Resistive layer 1R is also referred to as the "first resistive layer 1R," and resistive layer 2R is also referred to as the "second resistive layer 2R."

[0032] Each of the radio wave absorbing sheet laminates 100A to 100H can be provided, for example, as a radio wave interference type (also called λ / 4 type or reflective type) radio wave absorbing sheet. A radio wave interference type absorbing sheet can be constructed, for example, based on the principle of radio wave absorption, with a dielectric constant ε and a thickness d of a dielectric layer, where d = λ / 4 = πc / (2ω√ε) depending on the wavelength λ (= 1 / frequency) of the radio wave to be absorbed during propagation within the dielectric.

[0033] 2-2. Combination Patterns In the radio wave absorbing sheet set 100 of this embodiment, the applicable frequency band can be adjusted by combining multiple double-sided absorbers (radio wave absorbing materials 10, 20). The following describes the configurations (8 patterns) when they are used in combination. Note that each can also be used individually, in which case both sides can be used, resulting in 4 patterns, for a total of 12 patterns (12 ways) of use, offering a wide variety of options.

[0034] 2-2-1. Pattern 1 (Radio wave absorbing sheet laminate 100A) The characteristics obtained from the radio wave absorbing sheet laminate 100A shown in Figure 4A are illustrated in Figure 5A. The radio wave absorbing sheet laminate 100A is made by leaving the metal layer 2Mr intact, peeling off the other metal layers 1Mf, 1Mr, and 2Mf, and then bonding the back and front surfaces (see Figure 1A) of the radio wave absorbing sheets 10S and 20S together.

[0035] 2-2-2. Second pattern (Radio wave absorbing sheet laminate 100B) The properties obtained from the radio wave absorbing sheet laminate 100B shown in Figure 4B are illustrated in Figure 5B. The radio wave absorbing sheet laminate 100B is made by leaving the metal layer 1Mf and peeling off the other metal layers 1Mr, 2Mf, and 2Mr, then bonding the back and front surfaces (see Figure 1A) of the radio wave absorbing sheets 10S and 20S together.

[0036] 2-2-3. Third pattern (Radio wave absorbing sheet laminate 100C) The properties obtained from the radio wave absorbing sheet laminate 100C shown in Figure 4C are illustrated in Figure 6A. The radio wave absorbing sheet laminate 100C is made by leaving the metal layer 2Mr intact, peeling off the other metal layers 1Mf, 1Mr, and 2Mf, and bonding the front surfaces of the radio wave absorbing sheets 10S and 20S together (see Figure 1A).

[0037] 2-2-4. Fourth pattern (Radio wave absorbing sheet laminate 100D) The properties obtained from the radio wave absorbing sheet laminate 100D shown in Figure 4D are illustrated in Figure 6B. The radio wave absorbing sheet laminate 100D is made by leaving the metal layer 1Mr intact, peeling off the other metal layers 1Mf, 2Mf, and 2Mr, and bonding the front surfaces of the radio wave absorbing sheets 10S and 20S together (see Figure 1A).

[0038] 2-2-5. Pattern 5 (Radio wave absorbing sheet laminate 100E) The characteristics obtained from the radio wave absorbing sheet laminate 100E shown in Figure 7A are illustrated in Figure 8A. The radio wave absorbing sheet laminate 100E is made by leaving the metal layer 2Mf and peeling off the other metal layers 1Mf, 1Mr, and 2Mr, and then bonding the front and back surfaces (see Figure 1A) of the radio wave absorbing sheets 10S and 20S.

[0039] 2-2-6. Pattern 6 (Radio wave absorbing sheet laminate 100F) The characteristics obtained from the radio wave absorbing sheet laminate 100F shown in Figure 7B are illustrated in Figure 8B. The radio wave absorbing sheet laminate 100F is made by leaving the metal layer 1Mr intact, peeling off the other metal layers 1Mf, 2Mf, and 2Mr, and then bonding the front and back surfaces (see Figure 1A) of the radio wave absorbing sheets 10S and 20S together.

[0040] 2-2-7. Pattern 7 (Radio wave absorbing sheet laminate 100G) The properties obtained from the radio wave absorbing sheet laminate 100G shown in Figure 7C are illustrated in Figure 9A. The radio wave absorbing sheet laminate 100G is made by leaving the metal layer 2Mf and peeling off the other metal layers 1Mf, 1Mr, and 2Mr, and then bonding the back surfaces of the radio wave absorbing sheets 10S and 20S together (see Figure 1A).

[0041] 2-2-8. Pattern 8 (Radio wave absorbing sheet laminate 100H) The properties obtained from the radio wave absorbing sheet laminate 100H shown in Figure 7D are illustrated in Figure 9B. The radio wave absorbing sheet laminate 100H is made by leaving the metal layer 1Mf and peeling off the other metal layers 1Mr, 2Mf, and 2Mr, then bonding the back surfaces of the radio wave absorbing sheets 10S and 20S together (see Figure 1A).

[0042] 2-3. Absorption characteristics In this embodiment, the "radio wave absorption rate" corresponds to the ratio of the amount of radio waves absorbed to the amount of radio waves incident on each radio wave absorbing sheet laminate 100A to 100H. The amount of radio waves can be expressed, for example, by converting radio waves into electrical power. For example, a radio wave absorption rate of 80% is approximately 7 dB when converted to decibels (dB), and a radio wave absorption rate of 90% is 10 dB.

[0043] Each of the radio wave absorbing sheet laminates 100A to 100H may have an absorption peak of -10 dB or more in the frequency band of 18 GHz or higher. Each of the radio wave absorbing sheet laminates 100A to 100H can be provided as a multiband absorber, exhibiting absorption characteristics in various ranges from approximately 18 GHz to several hundred GHz.

[0044] The "first characteristic" and "second characteristic" described below represent the absorption characteristics that can be achieved by each of the radio wave absorbing sheet laminates 100A to 100H. The first and second characteristics represent the relationship between the frequency of the radio wave and the absorption rate of the radio wave (reflection attenuation of the radio wave).

[0045] 2-3-1. First example of radio wave absorption characteristics (first characteristic) Several configurations (electromagnetic wave absorbing sheet laminates 100A, 100C, 100E, 100G: see Figures 4A, 4C, 7A, and 7C) can exhibit the "first characteristic". In these configurations, of the electromagnetic waves incident on the surface dielectric layer (dielectric layer 1Df or 1Dr), those with predetermined frequencies pass through the resistive layer 1R, while the rest are reflected by the resistive layer 1R. The electromagnetic waves reflected by the resistive layer 1R are referred to as the "first electromagnetic waves". A portion of the electromagnetic waves that pass through the resistive layer 1R are reflected by the resistive layer 2R. The electromagnetic waves reflected by the resistive layer 2R are referred to as the "second electromagnetic waves". The electromagnetic waves that pass through the resistive layer 1R pass through the resistive layer 2R and are reflected by the metal layer 2Mf or 2Mr, which acts as a reflective layer. The electromagnetic waves reflected by each metal layer 2Mf and 2Mr are referred to as the "third electromagnetic waves".

[0046] The incident radio waves interfere with the first, second, and third radio waves mentioned above, causing the radio waves to be absorbed by each of the radio wave absorbing sheet laminates 100A, 100C, 100E, and 100G. In other words, because the phases of the radio waves are different, the radio waves are attenuated, and thus appear to be absorbed.

[0047] The first characteristic may be a characteristic in which the frequency range in which the radio wave absorption rate is 80% or higher accounts for 60% or more of the frequency range of 18 GHz to 500 GHz. Preferably, the first characteristic may be a characteristic in which the range in which the radio wave absorption rate is 80% or higher accounts for 65% or more, 70% or higher, 75% or higher, 80% or higher, 85% or higher, 90% or higher, 95% or higher, or 100% of the frequency range of 18 GHz to 500 GHz. Preferably, the first characteristic may be a characteristic in which the range in which the radio wave absorption rate is 90% or higher accounts for 65% or more, 70% or higher, 75% or higher, 80% or higher, 85% or higher, 90% or higher, 95% or higher, or 100% of the frequency range of 18 GHz to 500 GHz.

[0048] Furthermore, the first characteristic is that the radio wave absorption rate has an absorption peak in the frequency range of 18 GHz to 500 GHz. Specifically, the number of absorption peaks may be, for example, 1, 2, 3, 4, or 5, and may be within the range of any two of the values ​​exemplified here. In addition, it is preferable that this absorption peak is a peak where the radio wave absorption rate is 90% or higher.

[0049] 2-3-2. A second example of radio wave absorption characteristics (second characteristic) Several configurations (electromagnetic wave absorbing sheet laminates 100B, 100D, 100F, 100H: see Figures 4B, 4D, 7B, 7D) can exhibit a "second characteristic". In these configurations, some of the electromagnetic waves incident on the surface dielectric layer (dielectric layer 2Dr or 2Df) are reflected by the resistive layer 2R. The electromagnetic waves reflected by the resistive layer 2R are called "fourth electromagnetic waves". Of the electromagnetic waves that pass through the resistive layer 2R, those with predetermined frequencies pass through the resistive layer 1R, and the rest are reflected by the resistive layer 1R. The electromagnetic waves reflected by the resistive layer 1R are called "fifth electromagnetic waves". The electromagnetic waves that pass through the resistive layer 1R are reflected by the metal layer 1Mf or 1Mr, which acts as a reflective layer. The radio waves reflected by each metal layer with a 1Mf and 1Mr rating are referred to as "sixth radio waves."

[0050] The incident radio waves interfere with the fourth, fifth, and sixth radio waves mentioned above, causing the radio waves to be absorbed by the radio wave absorbing sheet laminates 100B, 100D, 100F, and 100H. In other words, because the phases of the radio waves are different, the radio waves are attenuated, and thus appear to be absorbed.

[0051] The second characteristic may be a characteristic in which the frequency range in which the radio wave absorption rate is 80% or higher accounts for 50% or more of the frequency range from 18 GHz to 500 GHz. Preferably, the second characteristic may be a characteristic in which the range in which the radio wave absorption rate is 80% or higher accounts for 55% or higher, 60% or higher, or 65% or higher in the frequency range from 18 GHz to 500 GHz. Preferably, the second characteristic may be a characteristic in which the range in which the radio wave absorption rate is 90% or higher accounts for 55% or higher, 60% or higher, or 65% or higher in the frequency range from 18 GHz to 500 GHz.

[0052] Furthermore, the second characteristic is that the radio wave absorption rate has an absorption peak in the frequency range of 18 GHz to 500 GHz. Specifically, the number of absorption peaks may be, for example, 1, 2, 3, 4, or 5, and may be within the range of any two of the values ​​exemplified here. In addition, it is preferable that this absorption peak is a peak where the radio wave absorption rate is 90% or higher.

[0053] It is preferable that the frequency of the absorption peak of the first characteristic described above and the frequency of the absorption peak of this second characteristic are different from each other.

[0054] 3. Specific composition of each layer (materials, properties, thickness, etc.) 3-1. Dielectric layer Various dielectric materials can be used for the dielectric layers 1Df, 1Dr, 2Df, and 2Dr. The dielectric layers 1Df, 1Dr, 2Df, and 2Dr can be configured to include a polymer material. This polymer material may be, for example, synthetic resins (including thermoplastic elastomers) such as polyvinyl chloride, polyvinylidene fluoride, acrylic resin, ethylene vinyl acetate copolymer, polyurethane, acrylic urethane resin, ionomer, polyolefin, polypropylene, polyethylene, silicone resin, polyester, polystyrene, polyimide, polyamide, polysulfone, polyethersulfone, and epoxy resin, or synthetic rubbers such as polyisoprene rubber, polystyrene-butadiene rubber, polybutadiene rubber, chloroprene rubber, acrylonitrile butadiene rubber, butyl rubber, acrylic rubber, ethylene propylene rubber, and silicone rubber. These may be used individually or in combination of two or more to constitute the polymer material.

[0055] Furthermore, each dielectric layer 1Df, 1Dr, 2Df, and 2Dr may be composed of materials such as glass, titanium oxide, alumina, and barium titanate.

[0056] Each dielectric layer 1Df, 1Dr, 2Df, and 2Dr may be composed of the same dielectric material or of different dielectric materials. Furthermore, each dielectric layer 1Df, 1Dr, 2Df, and 2Dr may be composed of multiple dielectric layers stacked on top of each other. Also, the thicknesses of each dielectric layer 1Df, 1Dr, 2Df, and 2Dr may be the same or different. In addition, each dielectric layer 1Df, 1Dr, 2Df, and 2Dr may have an adhesive layer formed on its surface facing the radio wave incident surface. In other words, each dielectric layer 1Df, 1Dr, 2Df, and 2Dr may include an adhesive layer, and the dielectric layers and adhesive layers do not necessarily have to be considered as separate components.

[0057] The relative permittivity of each dielectric layer 1Df, 1Dr, 2Df, and 2Dr can be set as appropriate. Specifically, for example, these could be 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, and 10, and may also be within the range of any two of the values ​​exemplified here. The relative permittivity of each dielectric layer 1Df, 1Dr, 2Df, and 2Dr may be the same or different.

[0058] 3-2.Resistance layer 3-2-1. Configuration of the resistive layer 1R As shown in Figure 1B, the resistive layer 1R can, for example, employ a periodic structure 1RS. This periodic structure 1RS is formed to have periodicity within the plane of the resistive layer 1R so as to pass through a predetermined range of frequencies. In other words, the resistive layer 1R can, for example, employ a structure with a frequency-selective surface (patch-type resonator structure).

[0059] Here, the predetermined frequency range through which the resistive layer 1R passes specifically includes, for example, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 400, and 500, and may also include the range between any two of the values ​​exemplified here. Note that the predetermined frequency range through which the resistive layer 1R passes may be divided into multiple frequency ranges. For example, if defined using the values ​​listed above, it could be a frequency range of 10 GHz or more and 40 GHz or less, and a frequency range of 80 GHz or more and 120 GHz or less.

[0060] The shape of the periodic structure 1RS is not particularly limited. For example, as shown in Figure 1B(a), the periodic structure 1RS can be composed of a plurality of resistive element portions 1Ra arranged to have periodicity in the plane of the resistive layer 1R. In the example shown in Figure 1B(a), the resistive element portion 1Ra is shown as a circular ring shape, but it is not limited to this, and may be other shapes such as rectangular.

[0061] Furthermore, as shown in Figure 1B(b), the periodic structure 1RS can extend across the entire area of ​​the resistive layer 1R and be composed of a periodic mesh structure. Thus, the shape of the periodic structure 1RS is not particularly limited.

[0062] Furthermore, the periodicity of the periodic structure 1RS may exist in one direction (for example, the vertical or horizontal direction in the figure) or in two directions (for example, the vertical and horizontal directions in the figure) within the plane of the resistive layer 1R.

[0063] The resistance value (Ω / sq) of the resistive layer 1R is, specifically, for example, 20, 30, 40, 50, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, and 200, and may also be within the range of any two of the values ​​exemplified here. For example, the resistance value (Ω / sq) of the resistive layer 1R is, for example, 20 or more and 200 or less.

[0064] Furthermore, the thickness (μm) of the resistive layer 1R is specifically, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, and may also be within the range of any two of the values ​​exemplified here.

[0065] 3-2-2. Configuration of the resistive layer 2R The resistive layer 2R has the function of reflecting some of the radio waves that have passed through the resistive layer 1R and allowing the rest to pass through. The resistive layer 2R does not necessarily have a function of selecting the frequency of the radio waves that are allowed to pass through, and in the embodiment, the resistive layer 2R may be a so-called solid layer. The resistive layer 2R may be composed of a sheet-like structure in which the entire region inside the outer edge of the resistive layer 2R is filled with the constituent material of the resistive layer 2R.

[0066] The resistance value (Ω / sq) of the resistive layer 2R is, specifically, for example, 20, 30, 40, 50, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, and 200, and may also be within the range of any two of the values ​​exemplified here. For example, the resistance value (Ω / sq) of the resistive layer 2R is, for example, 20 or more and 200 or less.

[0067] Furthermore, the thickness (μm) of the resistive layer 2R is specifically, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, and may also be within the range of any two of the values ​​exemplified here.

[0068] The resistive layers 1R and 2R do not necessarily have to extend across the entire surface area. For example, one of the resistive layers 1R and 2R may have a smaller area than the other. For example, when viewing each radio wave absorbing sheet laminate 100A to 100H from a direction parallel to the thickness direction, the entire formation area of ​​resistive layer 1R may be inside the outer edge of resistive layer 2R. In other words, when viewing each radio wave absorbing sheet laminate 100A to 100H from a direction parallel to the thickness direction, the entire resistive layer 1R may overlap with a part of resistive layer 2R.

[0069] 3-2-3. Constituent materials of each resistive layer The constituent materials for resistive layers 1R and 2R can be, for example, conductive organic polymer films, sputtered films, vapor-deposited films, etc. Furthermore, since the resistance value of the above-mentioned conductive organic polymer films, sputtered films, and vapor-deposited films can be controlled by the film thickness and formation density, resistive layers with a desired resistance value can be easily formed. The constituent materials for resistive layers 1R and 2R may be the same or different.

[0070] As the conductive organic polymers used as the resistive layers 1R and 2R, conjugated conductive organic polymers are used, and it is preferable to use polythiophene or its derivatives, or polypyrrole or its derivatives.

[0071] Furthermore, for the resistive layers 1R and 2R, organic polymers whose main chains are composed of π-conjugated systems can be used, and polyacetylene-based conductive polymers, polyphenylene-based conductive polymers, polyphenylene-vinylene-based conductive polymers, polyaniline-based conductive polymers, polyacene-based conductive polymers, polythiophene-vinylene-based conductive polymers, and copolymers thereof can be used.

[0072] Polyanions can be used as counteranions for the conductive organic polymers used in the resistive layers 1R and 2R. While the polyanions are not particularly limited, those containing anionic groups that can induce chemical oxidation doping in the conjugated conductive organic polymer can be employed. Examples of such anionic groups include those represented by the general formulas -O-SO3X, -O-PO(OX)2, -COOX, and -SO3X (where X is a hydrogen atom or alkali metal atom). Among these, groups represented by -SO3X and -O-SO3X can be employed due to their excellent doping effect on the conjugated conductive organic polymer.

[0073] The above conductive organic polymers may be used individually or in combination of two or more. Among the materials exemplified above, polymers consisting of one or two selected from polypyrrole, poly(3-methoxythiophene), poly(3,4-ethylenedioxythiophene), poly(2-aniline sulfonic acid), and poly(3-aniline sulfonic acid) are preferred because they offer higher transparency and conductivity.

[0074] In particular, as a combination of a conjugated conductive organic polymer and a polyanion, it is preferable to use poly(3,4-ethylenedioxythiophene: PEDOT) and polystyrene sulfonic acid (PSS).

[0075] Furthermore, in the resistive layers 1R and 2R according to this embodiment, dopants can be used in combination to control the electrical conductivity of the conductive organic polymer and obtain a predetermined resistance value. As dopants, halogens such as iodine and chlorine, Lewis acids such as BF3 and PF5, protonic acids such as nitric acid and sulfuric acid, transition metals, alkali metals, amino acids, nucleic acids, surfactants, dyes, chloranil, tetracyanoethylene, TCNQ, etc. can be used.

[0076] The content of conductive organic polymer in resistive layers 1R and 2R is preferably 10% by mass or more and 35% by mass or less, relative to the total mass of solids contained in the resistive layer composition. If the content is less than 10% by mass, the conductivity of the resistive layer tends to decrease. As a result, when the surface electrical resistance of the resistive layer is set within a predetermined range to achieve impedance matching, the film thickness of the resistive layer increases, which tends to make the overall thickness of each radio wave absorbing sheet 10S, 20S and each radio wave absorbing sheet laminate 100A to 100H increase, and if light transmission is present, the optical properties tend to decrease. On the other hand, if the content exceeds 35% by mass, the coating suitability when coating the resistive layer decreases due to the structure of the conductive organic polymer, making it difficult to form a good resistive layer, and if light transmission is present, the haze of the resistive layer increases, which also tends to decrease the optical properties.

[0077] Furthermore, the resistive layers 1R and 2R may be configured to include carbon materials such as carbon microcoils, carbon nanotubes, and graphene.

[0078] Carbon microcoils are a type of vapor-grown carbon fiber primarily obtained by catalytically activated pyrolysis of acetylene, and are materials with a 3D-helical / spiral structure on the order of microns in coil diameter. Preferably, the coil diameter is 1 μm to 10 μm, the carbon fiber diameter forming the coil is 0.1 μm to 1 μm, and the coil length is 1 mm to 10 mm.

[0079] Carbon nanotubes can be obtained by various methods, such as vapor phase growth methods including arc discharge, laser evaporation, and thermal decomposition. The carbon nanotubes used as resistive layers 1R and 2R may be single-layer or multi-layer.

[0080] Graphene can be obtained by methods such as peel transfer, SiC pyrolysis, chemical vapor deposition, and carbon nanotube cutting. For the graphene used as the resistive layers 1R and 2R, flaky powdered graphene can be used, as it allows for easy acquisition of the desired aspect ratio and provides orientation in the radio wave absorbing sheet laminates 100A to 100H. A water-soluble polyester resin can be used as the resin for dispersing the carbon material.

[0081] The resistive layers 1R and 2R can be formed by applying a coating composition, which is a resistive layer-forming paint, onto a resin substrate and drying it. Methods for applying the resistive layer-forming paint to the substrate include, for example, bar coating, reverse coating, gravure coating, microgravure coating, die coating, dipping, spin coating, slit coating, and spray coating. Drying after application should be carried out under conditions that allow the solvent components of the resistive layer-forming paint to evaporate, preferably at 100-150°C for 5-60 minutes. Alternatively, the resistive layers 1R and 2R may be formed by curing the coating film by irradiating it with UV light (ultraviolet light) or EB (electron beam) as needed. The substrate used to form the resistive layers 1R and 2R is not particularly limited, but a transparent substrate is preferred. Various materials such as PET resin, rubber, glass, and ceramics can be used for such a transparent substrate.

[0082] 3-3. Metal layer (reflection layer) As the metal layers 1Mf, 1Mr, 2Mf, and 2Mr that can be used as reflective layers, metal foils or metal plates can be employed. In order to give flexibility to the radio wave absorbing sheet laminates 100A to 100H, metal foil is more preferable as the constituent material of the metal layers 1Mf, 1Mr, 2Mf, and 2Mr, and various metal foils such as silver foil, copper foil, aluminum foil, and gold foil can be used. When considering cost and the effects of oxidation in air, aluminum foil can be used as the reflective layer (metal layers 1Mf, 1Mr, 2Mf, and 2Mr). Metal foils such as aluminum foil that form the reflective layer (metal layers 1Mf, 1Mr, 2Mf, and 2Mr) can be easily produced by rolling metal materials. Furthermore, when forming a reflective layer (metal layer 1Mf, 1Mr, 2Mf, 2Mr) with a vapor-deposited metal film on the surface of a non-metallic material, it is preferable to appropriately select a vapor deposition method, which has been conventionally used for forming various vapor-deposited films, taking into consideration the heat resistance temperature of the metal material to be deposited and the non-metallic material such as the resin that serves as the substrate.

[0083] The thickness (μm) of each metal layer, 1Mf, 1Mr, 2Mf, and 2Mr, can be, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, and 500 (μm), and may be within the range of any two of the values ​​exemplified here. The thicknesses of each metal layer, 1Mf, 1Mr, 2Mf, and 2Mr, may be different from each other.

[0084] 3-4.Adhesive layer Examples of adhesive layers ad1 and ad2 (see Figure 1C) that can be used in the embodiment include, for example, known materials used as adhesive layers in adhesive tapes, acrylic adhesives, rubber adhesives, silicone adhesives, etc. Tackifiers and crosslinking agents can be used to adjust the adhesive strength and reduce adhesive residue. The adhesive strength can be, for example, 5N / 10mm to 12N / 10mm. The thickness (μm) of each adhesive layer ad1 and ad2 can be, specifically, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 110, 120, 130, 140, 150, 160, 170 The ranges are 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, and 450, and the range may be between any two of the numbers exemplified here.

[0085] In this embodiment, when the dielectric constant of each adhesive layer ad1 and ad2 is a1, and the dielectric constant of each dielectric layer 1Df, 1Dr, 2Df, and 2Dr bonded to each adhesive layer ad1 and ad2 is a2, the following equation may be satisfied: 0.9 × a2 ≤ a1 ≤ 1.1 × a2. Here, when k1 and k2 are coefficients, the following equation may be satisfied: k1 × a2 ≤ a1 ≤ k2 × a2. k1 may be, for example, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, or 0.99, and may be within the range between any two of the values ​​exemplified here. k2 may be, for example, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, or 1.1, and may be within the range between any two of the values ​​exemplified here.

[0086] 3-5. Film The film SPF shown in Figure 1C can be made of, for example, a separator film. Adhesive layer ad1 is placed on one side of the film SPF, and adhesive layer ad2 is placed on the other side of the film SPF. A separator film is a film primarily intended for separating layers. Specifically, the surface of the film SPF is easily peelable even if adhesives or resins adhere to it. The film SPF is configured to be peelable from adhesive layer ad2. In other words, the film SPF is connected to adhesive layer ad1 on the side with adhesive layer ad1 (metal layer M side) so that it does not peel off, but the side with adhesive layer ad2 (dielectric layer D side) is configured to peel off from adhesive layer ad2. Peelability can be ensured by surface treatment of the film (for example, coating or fine texture processing). In other words, the film SPF has the surface treatment applied to the side with adhesive layer ad2. The film SPF can be made of materials such as polyester (PET), polypropylene (PP), and polyethylene (PE). For example, when peeling a metal layer 1Mf from a dielectric layer 1Df, as shown in Figure 1C, the protective layer pt, metal layer M (metal layer 1Mf), adhesive layer ad1, and film spf will be separated from the adhesive layer sd2 and dielectric layer D (dielectric layer 1Df).

[0087] 3-6.Protective layer There are no limitations on the material of the protective layer pt. For each metal layer of 1Mf, 1Mr, 2Mf, and 2Mr, any material can be used for the protective layer pt from the viewpoint of suitable protection and suitable peelability.

[0088] In the radio wave absorbing sheet set 100 of the embodiment described above, the applicable frequency band can be adjusted by combining multiple double-sided absorbers (radio wave absorbing materials 10, 20). By combining double-sided radio wave absorbers with different frequency absorption characteristics, there is an advantage in being able to support various multibands. In this embodiment, as an example, two types of radio wave absorbing materials 10, 20 (radio wave absorbing sheets 10S, 20S) are used, but even with just these two types, it is possible to achieve more than 12 different multiband configurations. "12 configurations" refers to the sum of four characteristics when using radio wave absorbing sheets 10S, 20S individually (see Figures 2A, 2B, 3A, 3B), and eight characteristics when these are combined (see Figures 5A, 5B, 6A, 6B, 8A, 8B, 9A, and 9B).

[0089] The number of radio wave absorbers may be three or more, which enables a large number of multiband applications. While currently each product exists for specific frequency band applications, this offers the advantage of allowing users to arbitrarily combine and select the necessary frequency bands. Specifically, in one embodiment, the radio wave absorbing sheet set 100 has two radio wave absorbing materials 10 and 20 (two radio wave absorbing sheets 10S and 20S that are separated from each other). However, it is not limited to this, and the radio wave absorbing sheet set 100 may include three or more radio wave absorbing materials (three or more radio wave absorbing sheets that are separated from each other). In this case, any pair of radio wave absorbing sheets included in these three or more radio wave absorbing sheets will have different radio wave absorption characteristics.

[0090] The radio wave absorbing sheets 10S, 20S and radio wave absorbing sheet laminates 100A to 100H of the embodiment can be used, for example, in the GHz frequency band. However, it is not limited to this, and by appropriately adjusting the material and / or thickness of each layer of the embodiment, it may also be applied to the absorption of radio waves in the MHz band or lower.

[0091] Furthermore, each of the radio wave absorbing sheets 10S, 20S, or each of the radio wave absorbing sheet laminates 100A to 100H according to the embodiment can also be used by peeling off the metal layers on both sides. For example, the destination to which each of the radio wave absorbing sheets 10S, 20S, or each of the radio wave absorbing sheet laminates 100A to 100H is attached may be a metal layer that functions as a reflective layer. In this case, the reflective layers on both sides may be peeled off to expose the adhesive layers on both sides, and one of the adhesive layers may be attached to the metal layer to which it is attached.

[0092] Various embodiments are illustrated below. The embodiments shown below can be combined with each other. [Note 1] It is a set of radio wave absorbing sheets, Equipped with radio wave absorbing material, The aforementioned radio wave absorbing material has a plurality of radio wave absorbing sheets that are separated from each other. The different radio wave absorbing sheets are configured to be stacked in close contact with each other. Each of the aforementioned radio wave absorbing sheets has a dielectric layer and a resistive layer provided within the dielectric layer. A set of radio wave absorbing sheets in which any pair of radio wave absorbing sheets included in the plurality of radio wave absorbing sheets has different radio wave absorbing characteristics from each other.

[0093] [Note 2] The radio wave absorbing sheet set described in Appendix 1, Each of the radio wave absorbing sheets further comprises a pair of metal layers, One of the pair of metal layers is placed on the dielectric layer on the front side of each of the radio wave absorbing sheets. The other of the pair of metal layers is arranged on the dielectric layer on the back side of each of the radio wave absorbing sheets. A set of radio wave absorbing sheets, wherein each of the metal layers is configured to be peelable from each of the dielectric layers.

[0094] [Note 3] The radio wave absorbing sheet set described in Appendix 2, Each of the radio wave absorbing sheets further comprises a pair of adhesive layers, Each of the aforementioned adhesive layers is disposed between each of the aforementioned metal layers and each of the aforementioned dielectric layers in a set of radio wave absorbing sheets.

[0095] [Note 4] The radio wave absorbing sheet set described in Appendix 3, A set of radio wave absorbing sheets that satisfies 0.9 × a2 ≤ a1 ≤ 1.1 × a2, where a1 is the dielectric constant of each adhesive layer and a2 is the dielectric constant of each dielectric layer bonded to each adhesive layer.

[0096] [Note 5] A radio wave absorbing sheet set as described in Appendix 3 or Appendix 4, Each of the radio wave absorbing sheets further comprises a pair of films, A set of radio wave absorbing sheets, each of which is configured to be peelable from the adhesive layer.

[0097] [Note 6] A radio wave absorbing sheet set described in any one of the appendices 2 to 5, Each of the radio wave absorbing sheets further comprises a pair of protective layers. One of the pair of protective layers is arranged to cover the one metal layer, A set of radio wave absorbing sheets, wherein the other of the pair of protective layers is arranged to cover the metal layer of the other layer.

[0098] [Note 7] A radio wave absorbing sheet set described in any one of the appendices 1 to 6, A set of radio wave absorbing sheets, each of which is configured such that its radio wave absorption characteristics differ when radio waves are incident from the front side and when radio waves are incident from the back side.

[0099] [Note 8] A radio wave absorbing sheet set described in any one of the appendices 1 to 7, Each of the aforementioned radio wave absorbing sheets has a dielectric layer comprising a first dielectric layer and a second dielectric layer. The resistive layer is disposed between the first dielectric layer and the second dielectric layer. The dielectric constant of the first dielectric layer and the dielectric constant of the second dielectric layer are the same. A set of radio wave absorbing sheets in which the thickness of the first dielectric layer and the thickness of the second dielectric layer are different.

[0100] [Note 9] A radio wave absorbing sheet laminate in which the plurality of radio wave absorbing sheets of the radio wave absorbing sheet set described in any one of Appendix 1 to Appendix 8 are tightly bonded and laminated together.

[0101] While embodiments have been described above, these are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications are permitted. The embodiments and their variations are included within the scope and essence of the invention, as well as within the scope of the invention and its equivalents as described in the claims. [Explanation of Symbols]

[0102] 100: Radio wave absorbing sheet set 100A~100H: Radio wave absorbing sheet laminate 10, 20: Radio wave absorbing material 10S, 20S: Radio wave absorbing sheet 1Df: Dielectric layer (first dielectric layer) 1Dr: Dielectric layer (second dielectric layer) 1R: Resistance layer (1st resistance layer) 1Mf, 1Mr: Metal layer 1RS: Periodic structure 1Ra: Resistive element section 2Df: Dielectric layer (first dielectric layer) 2Dr: Dielectric layer (second dielectric layer) 2R: Resistance layer (second resistance layer) 2Mf, 2Mr: Metal layer

Claims

1. It is a set of radio wave absorbing sheets, Equipped with radio wave absorbing material, The aforementioned radio wave absorbing material has a plurality of radio wave absorbing sheets that are separated from each other. The different radio wave absorbing sheets are configured to be stacked in close contact with each other. Each of the aforementioned radio wave absorbing sheets has a dielectric layer and a resistive layer provided within the dielectric layer. A set of radio wave absorbing sheets in which any pair of radio wave absorbing sheets included in the plurality of radio wave absorbing sheets has different radio wave absorbing characteristics from each other.

2. A radio wave absorbing sheet set according to claim 1, Each of the radio wave absorbing sheets further comprises a pair of metal layers, One of the pair of metal layers is placed on the dielectric layer on the front side of each of the radio wave absorbing sheets. The other of the pair of metal layers is arranged on the dielectric layer on the back side of each of the radio wave absorbing sheets. A set of radio wave absorbing sheets, wherein each of the metal layers is configured to be peelable from each of the dielectric layers.

3. A radio wave absorbing sheet set according to claim 2, Each of the radio wave absorbing sheets further comprises a pair of adhesive layers, Each of the aforementioned adhesive layers is disposed between each of the aforementioned metal layers and each of the aforementioned dielectric layers in a set of radio wave absorbing sheets.

4. A radio wave absorbing sheet set according to claim 3, A set of radio wave absorbing sheets that satisfies 0.9 × a2 ≤ a1 ≤ 1.1 × a2, where a1 is the dielectric constant of each adhesive layer and a2 is the dielectric constant of each dielectric layer bonded to each adhesive layer.

5. A radio wave absorbing sheet set according to claim 3, Each of the radio wave absorbing sheets further comprises a pair of films, A set of radio wave absorbing sheets, each of which is configured to be peelable from the adhesive layer.

6. A radio wave absorbing sheet set according to claim 2, Each of the radio wave absorbing sheets further comprises a pair of protective layers. One of the pair of protective layers is arranged to cover the one metal layer, A set of radio wave absorbing sheets, wherein the other of the pair of protective layers is arranged to cover the metal layer of the other layer.

7. A radio wave absorbing sheet set according to any one of claims 1 to 6, A set of radio wave absorbing sheets, each of which is configured such that its radio wave absorption characteristics differ when radio waves are incident from the front side and when radio waves are incident from the back side.

8. A radio wave absorbing sheet set according to claim 7, Each of the aforementioned radio wave absorbing sheets has a dielectric layer comprising a first dielectric layer and a second dielectric layer. The resistive layer is disposed between the first dielectric layer and the second dielectric layer. The dielectric constant of the first dielectric layer and the dielectric constant of the second dielectric layer are the same. A set of radio wave absorbing sheets in which the thickness of the first dielectric layer and the thickness of the second dielectric layer are different.

9. A radio wave absorbing sheet laminate in which the plurality of radio wave absorbing sheets of the radio wave absorbing sheet set described in any one of claims 1 to 6 are closely attached and laminated.

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