Electromagnetic wave reflector and electromagnetic wave absorbing sheet including the same

Abstract

To achieve an electromagnetic wave reflector which favorably reflects only electromagnetic waves of a desired frequency in a high frequency band above a millimeter wave band and can allow electromagnetic waves of other frequencies to pass therethrough.SOLUTION: There is provided an electromagnetic wave reflector 10 in which multiple conductor rings 2 are arranged and which selectively reflects electromagnetic waves of a predetermined frequency above a millimeter wave band. When X (mm) represents a radius of each conductor ring, Y (mm) represents a central distance between the conductor rings adjacent to each other, and Z (GHz) represents a frequency of an electromagnetic wave to be reflected, the relationship of Z=aXb+cYd+e (equation 1) is satisfied.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to an electromagnetic wave reflector having a plurality of conductor rings arranged at predetermined intervals, and an electromagnetic wave absorbing sheet having this electromagnetic wave reflector as a reflective layer. [Background technology]

[0002] An electromagnetic wave reflector (reflector) is known in which multiple ring-shaped members made of a conductor such as a metal material are arranged on the surface of a planar member made of a dielectric material such as resin, thereby selectively reflecting electromagnetic waves of a predetermined frequency while transmitting electromagnetic waves of other frequencies.

[0003] In such electromagnetic wave reflectors, also known as frequency selective plates, a technique is known in which the frequency band of the electromagnetic waves reflected by the electromagnetic wave reflector is broadened by alternately arranging multiple types of conductor rings with different radii (see Patent Document 1) and by making the conductor rings elliptical in shape with a major axis and a minor axis (see Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 01-149503 [Patent Document 2] Japanese Patent Application Publication No. 06-177639 Summary of the Invention [Problem to be solved by the invention]

[0005] The above-mentioned conventional electromagnetic wave reflector is made by changing the shape of the conductor rings that are aligned on the surface of a planar member made of a dielectric, thereby making it possible to broaden the frequency band of the electromagnetic waves reflected by the electromagnetic wave reflector and to suitably reflect electromagnetic waves in a practical range that is usually used in a specified bandwidth that is specified in communication technologies that utilize electromagnetic waves.

[0006] However, although it was known that the frequency of the electromagnetic waves reflected by an electromagnetic wave reflector varies depending on the circumferential length of the arranged conductor rings, the relationship between the frequency of the reflected electromagnetic waves and the spacing between the conductor rings was not fully understood, and in order to obtain an electromagnetic wave reflector capable of reflecting electromagnetic waves of a desired frequency, a method was adopted in which the circumferential length and spacing of the conductor rings were changed to check the reflection characteristics of the electromagnetic waves and realize an electromagnetic wave reflector with desirable reflection characteristics.

[0007] Furthermore, in recent years, with advances in technology for communicating large volumes of information, the frequency band of electromagnetic waves used has shifted from the so-called millimeter wave band (approximately 30 GHz to approximately 300 GHz) to higher frequency bands beyond this band; however, no electromagnetic wave reflector has been developed that can effectively reflect only electromagnetic waves in a specific frequency band among such high frequency band electromagnetic waves.

[0008] The present disclosure aims to solve the above-mentioned problems of the conventional technology and to provide an electromagnetic wave reflector that can effectively reflect only electromagnetic waves of a desired frequency in a high-frequency band equal to or higher than the millimeter wave band, while passing electromagnetic waves of other frequencies, and further to provide an electromagnetic wave absorbing sheet that can effectively absorb electromagnetic waves in a predetermined frequency band by using this electromagnetic wave reflector. [Means for solving the problem]

[0009] In order to solve the above problems, the present application discloses an electromagnetic wave reflector that has a plurality of conductor rings arranged therein and selectively reflects electromagnetic waves of a predetermined frequency equal to or higher than the millimeter wave band, where the radius of the conductor rings is X (mm), the center distance between adjacent conductor rings is Y (mm), and the frequency of the electromagnetic waves to be reflected is Z (GHz), Z=aX b +cY d +e (formula 1) The above relationship is satisfied.

[0010] In addition, the electromagnetic wave absorbing sheet disclosed in the present application is characterized in that it has the electromagnetic wave reflector disclosed in the present application as a reflective layer, and is formed by sequentially laminating a resistive film, a dielectric layer, and the electromagnetic wave reflector which is the reflective layer from the incident side of the electromagnetic waves. Effect of the Invention

[0011] The electromagnetic wave reflector disclosed in the present application has a relationship between the diameter X of the conductor ring, the center distance Y of the conductor ring, and the frequency Z of the electromagnetic wave to be selectively reflected, Z=aX b +cY d +e (Equation 1) holds true. For this reason, an electromagnetic wave reflector that reflects electromagnetic waves of a desired frequency can be realized by adjusting the shape of the conductor ring and the center distance thereof.

[0012] Furthermore, since the electromagnetic wave absorbing sheet disclosed in the present application has the electromagnetic wave reflector disclosed in the present application as a reflective layer, by setting the frequency reflected by the electromagnetic wave reflector to a desired value, it is possible to achieve frequency characteristics that effectively absorb electromagnetic waves of that frequency while transmitting electromagnetic waves of other frequencies. [Brief description of the drawings]

[0013] [Figure 1] 3 is an image diagram illustrating the shape of an electromagnetic wave reflector according to the present embodiment. FIG. [Diagram 2] 1 is a diagram showing the relationship between the radius X of the conductor rings, the center distance Y of the conductor rings, and the frequency Z of the reflected electromagnetic waves of an electromagnetic wave reflector that reflects electromagnetic waves with a frequency of 30 GHz±10 GHz. [Diagram 3] 1 is a diagram showing the relationship between the radius X of the conductor rings, the center distance Y of the conductor rings, and the frequency Z of the reflected electromagnetic waves of an electromagnetic wave reflector that reflects electromagnetic waves with a frequency of 150 GHz±30 GHz. [Figure 4] 1 is a diagram showing the relationship between the radius X of the conductor rings, the center distance Y of the conductor rings, and the frequency Z of the reflected electromagnetic waves of an electromagnetic wave reflector that reflects electromagnetic waves with a frequency of 300 GHz±30 GHz. [Diagram 5]4 is a diagram showing frequency characteristics of return loss of a first electromagnetic wave reflector described in the present embodiment. FIG. [Figure 6] 4 is a diagram showing frequency characteristics of transmission attenuation of a first electromagnetic wave reflector described in the present embodiment. FIG. [Figure 7] 6 is a diagram showing frequency characteristics of return loss of a second electromagnetic wave reflector described in the present embodiment. FIG. [Figure 8] 6 is a diagram showing frequency characteristics of transmission attenuation of a second electromagnetic wave reflector described in the present embodiment. FIG. [Figure 9] 11 is a diagram showing frequency characteristics of return loss of a third electromagnetic wave reflector described in the present embodiment. FIG. [Figure 10] 11 is a diagram showing frequency characteristics of transmission attenuation of a third electromagnetic wave reflector described in the present embodiment. FIG. [Figure 11] 1A and 1B are diagrams illustrating differences in electromagnetic wave reflection characteristics depending on the shape of a conductive loop. [Figure 12] 1 is a cross-sectional view for explaining a configuration of an electromagnetic wave absorbing sheet according to an embodiment of the present invention. [Figure 13] FIG. 4 is a diagram showing the frequency characteristics of the return loss of the electromagnetic wave absorbing sheet according to the present embodiment. [Figure 14] FIG. 4 is a diagram showing frequency characteristics of transmission attenuation of the electromagnetic wave absorbing sheet according to the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The electromagnetic wave reflector disclosed in the present application is an electromagnetic wave reflector in which a plurality of conductor rings are arranged and which selectively reflects electromagnetic waves of a predetermined frequency equal to or higher than the millimeter wave band, where the radius of the conductor rings is X (mm), the center distance between adjacent conductor rings is Y (mm), and the frequency of the electromagnetic waves to be reflected is Z (GHz), Z=aX b +cY d +e (formula 1) Satisfy the relationship.

[0015] With this configuration, the electromagnetic wave reflector disclosed in the present application can realize an electromagnetic wave reflector that selectively reflects electromagnetic waves of a predetermined frequency in a high frequency band equal to or higher than the millimeter wave band by adjusting the shape and arrangement spacing of the conductor rings that are formed.

[0016] In the electromagnetic wave reflector disclosed in the present application, when the frequency Z of the reflected electromagnetic wave is anywhere in the range of 30±10 (GHz), and when the conductor ring has X of 1.31 to 2.60 (mm) and Y of 3.27 to 6.50 (mm), a can be 2.3, b can be −6.9, c can be 126.6, d can be −0.9, and e can be −2.4.

[0017] Furthermore, in an electromagnetic wave reflector in which the frequency Z of the reflected electromagnetic wave is anywhere in the range of 150±30 (GHz), in the case of a conductor ring in which X is 0.31 to 0.45 (mm) and Y is 0.73 to 1.07 (mm), when a, b, c, d are 1.0, -3.7, c, d, -2.6, and further, when the line width W of the conductor ring is 0.02 to 0.035 (mm), the e can be set to satisfy e = -3800 x W2 + 553 x W + 95.16.

[0018] Furthermore, in an electromagnetic wave reflector in which the frequency Z of the reflected electromagnetic wave is anywhere in the range of 300±30 (GHz), in the case of a conductor ring in which X is 0.17 to 0.21 (mm) and Y is 0.40 to 0.47 (mm), the a is 1.0, the b is −2.9, the c is 1.0, the d is −2.6, and further, the line width W of the conductor ring is set to satisfy e=−57000×W2+4833×W+89.81 when W=0.02 to 0.035 (mm).

[0019] It is also preferable that the conductor rings all have the same radius (X) and line width (W), and are arranged in a lattice pattern with the same center distance (Y). In this way, it is possible to realize an electromagnetic wave reflector that satisfactorily reflects electromagnetic waves in a desired frequency band based on the radius X, width W, and center distance Y of the conductor rings.

[0020] It is also preferable that the maximum return loss at the frequency Z is −1 dB or less. Note that “return loss of −1 dB or less” means that the absolute value of the return loss is less than 1.

[0021] The electromagnetic wave absorbing sheet disclosed in the present application has the electromagnetic wave reflector disclosed in the present application as a reflective layer, and is laminated in this order from the electromagnetic wave incident side: a resistive film, a dielectric layer, and the electromagnetic wave reflector which is the reflective layer.

[0022] By adopting such a configuration, the electromagnetic wave absorbing sheet disclosed in the present application can be provided with electromagnetic wave absorbing properties that absorb electromagnetic waves of a desired frequency and transmit electromagnetic waves of other frequencies by adjusting the shape and center spacing of the conductor rings of the electromagnetic wave reflector used as the reflective layer.

[0023] Hereinafter, an electromagnetic wave reflector disclosed in the present application and an electromagnetic wave absorbing sheet using this electromagnetic wave reflector as a reflective layer will be described with reference to the drawings.

[0024] (Embodiment) [Electromagnetic wave reflector] FIG. 1 is a conceptual diagram illustrating the configuration of an electromagnetic wave reflector according to this embodiment.

[0025] As shown in FIG. 1, the electromagnetic wave reflector 10 is configured by arranging a plurality of conductor rings 2 in a lattice pattern (matrix pattern) at equal intervals in both the vertical and horizontal directions on a resin substrate 1 such as polyethylene terephthalate (PET).

[0026] In the electromagnetic wave reflector 10 according to this embodiment, as described below, the frequency of the electromagnetic wave reflected by the electromagnetic wave reflector 10 is determined by setting the radius (X) of the conductor ring 2 and the distance Y between the centers of adjacent conductor rings 2 to predetermined values. For this reason, it is preferable that the conductor rings 2 formed on the resin base material 1 have the same shape except for manufacturing errors. As an example, it is preferable that the error in the radius X of the conductor rings 2 is within ±5%, the error in the line width W of the conductor rings 2 is within ±3%, the difference between the major axis and minor axis of the circularity of the conductor rings 2 is within ±5%, and the error in the distance between the centers of the conductor rings 2 is within ±5%.

[0027] In this specification, the "radius X" of the conductor ring 2 refers to the distance from the center of the conductor ring 2 to the central part of the ring-shaped line with line width W, as shown in the enlarged view of Fig. 1. In other words, the radius of the outer periphery of the conductor ring 2 is (X+W / 2), and the radius of the inner periphery of the conductor ring 2 is (XW / 2).

[0028] Moreover, in both the vertical and horizontal directions, it is preferable that the error in the distance Y between the centers of adjacent conductor rings 2 is, for example, within ±5%.

[0029] The electromagnetic wave reflector 10 according to this embodiment can be produced by forming and arranging a ring-shaped conductor ring 2 using a conductive material on a base material 1 made of a resin such as polyethylene terephthalate (PET).

[0030] Examples of conductive materials that can be used to form the conductor ring 2 include inorganic conductive materials such as ITO (indium tin oxide), ATO (antimony doped tin oxide), and carbon black; organic conductive materials such as PEDOT-PSS, polyacetylene, and polythiophene; and metal plating films such as electroless plating films and electrolytic plating films. The conductivity of the formed conductor ring 2 is 1.0×10 7 It is preferable that the material has a resistance to deformation of 100% or more.

[0031] Methods for forming a plurality of conductor rings 2 on the substrate 1 include various printing methods such as an inkjet method and a screen printing method, a method in which a conductive material is applied to the entire surface of a substrate sheet, and then the area where the conductor ring 2 is to be formed is masked and the conductive material is removed from the area not covered by the mask using an acid or the like, and a method in which the conductive material is removed by irradiating laser light onto areas other than the conductor ring 2. In addition, a wide variety of conventional pattern formation methods suited to the characteristics of the conductive material to be used can be adopted, such as a photolithography method using a photocurable resin and a mask pattern, a method in which a deactivator that inhibits the function of an electroless plating catalyst is applied to the entire substrate, and then the deactivator is removed from the area where the conductor ring 2 is to be formed using light or heat, and then the electroless plating catalyst solution and the electroless plating solution are successively brought into contact with each other to form an electroless plating film on the conductor ring 2 area and an electrolytic plating film thereon.

[0032] As the base material 1 of the electromagnetic wave reflector 10, in addition to the above-mentioned PET, various resins, rubber materials, and further various dielectric materials (insulators) such as paper and wood can be used.

[0033] [Adjusting the reflected frequency] The relationship between the formation pattern of the conductor rings and the frequency reflected by the electromagnetic wave reflector in the electromagnetic wave reflector according to this embodiment will be described below.

[0034] The electromagnetic wave reflector according to this embodiment can selectively reflect electromagnetic waves of a predetermined frequency in a high frequency band equal to or higher than the millimeter wave band. As a result of the inventors' investigation, the relationship between the radius X (unit: mm) of the conductor ring 2, the center distance Y (unit: mm) between adjacent conductor rings, and the frequency Z (unit: GHz) of the electromagnetic wave reflected by the electromagnetic wave reflector 10 is as follows: Z=aX b +cY d +e (formula 1) It was also confirmed that, particularly for high-frequency electromagnetic waves, the value of "e," which corresponds to the intercept on the Z-axis of the above equation (1), changes depending on the width W of the conductor ring 2.

[0035] For this reason, in the electromagnetic wave reflector 10 disclosed in the present application, the shape of the conductor rings 2 formed, i.e., the radius of each ring, or the radius, line width, and center distance, should be adjusted according to the frequency Z to be reflected; in other words, the shape (radius, line width) of the conductor rings 2 and the center distance Y can be set to predetermined values ​​to make the reflected frequency a desired one. In the present application, being reflected by the electromagnetic wave reflector 10 means that the power of the electromagnetic wave reflected by the electromagnetic wave reflector is 90% or more relative to the electromagnetic wave power incident on the electromagnetic wave reflector 10, that is, the electromagnetic wave power attenuated is 10% or less. When the return loss of the electromagnetic wave at the electromagnetic wave reflector 10 is expressed in dB, it can be expressed that the maximum return loss of the reflected wave relative to the incident wave is -1 dB or less (the absolute value of the numerical value is smaller than 1), and it is more preferable that the return loss is -0.5 dB or less.

[0036] It has been found that the coefficients a, b, and c in (Equation 1) have different values ​​depending on the frequency of the reflected electromagnetic wave. Therefore, in the following explanation, the center frequencies of the reflected electromagnetic waves are divided into three bands, 30 GHz, 150 GHz, and 300 GHz.

[0037] (30GHz±10GHz) FIG. 2 shows the relationship between frequency Z (GHz), radius X (mm) and center distance Y (mm) of the conductor ring when the frequency of the electromagnetic wave reflected by the electromagnetic wave absorber is 30 GHz±10 GHz, that is, 20 to 40 GHz.

[0038] 2 plots values ​​of center distance Y (mm) of conductor ring 2 for which the frequency of electromagnetic waves reflected by electromagnetic wave reflector 10 is 30 GHz±10 GHz, which is the set condition, when radius X is set to 1.31 to 2.60 mm and line width W is set to 0.020 to 0.035 mm, taking into consideration the numerical range in which conductor ring 2 can be accurately formed. Also, reference numeral 21 denotes a line connecting each plot.

[0039] The determination of the conditions for the relationship between Z and the change in center distance Y was performed by a simulation using full-wave three-dimensional electromagnetic field software "Ansys HFSS (product name: manufactured by ANSYS, Inc.)" that uses the finite element method.

[0040] Then, using the coordinates shown in Figure 2, the method of least squares was used to determine the conditions under which the range satisfying the above conditions can be expressed in the form of Equation 1. As a result, the coefficients in Equation 1 were obtained as a = 2.3, b = -6.9, c = 126.6, d = -0.9, and e = -2.4.

[0041] In addition, when the frequency of the reflected electromagnetic wave is 30 GHz ± 10 GHz, if the line width W of the conductor ring 2 is in the range of 0.02 to 0.035 mm set above, the value of the constant e in (Equation 1) can be understood as a constant value. -69 +126.6Y -0.9 The coefficient of determination between -2.4 and each point plotted in Figure 2 was 1.00, indicating that the formula and the simulation results matched extremely well.

[0042] (150GHz±30GHz) FIG. 3 shows the relationship between frequency Z (GHz), radius X (mm) and center distance Y (mm) of the conductor ring when the frequency of the electromagnetic wave reflected by the electromagnetic wave absorber is 150 GHz±30 GHz, that is, 120 to 180 GHz.

[0043] It was found that the higher the frequency of the electromagnetic wave reflected by the electromagnetic wave reflector 10, the smaller the radius of the conductor ring 2 that should be formed in the electromagnetic wave reflector 10. For this reason, the radius X was calculated to be 0.31 to 0.45 mm as the size of the conductor ring 2 for reflecting electromagnetic waves of 150 GHz±30 GHz. The line width W was set to 0.020 to 0.035 mm, the same as in the case of 30 GHz±10 GHz above.

[0044] Figure 3 plots the center distance Y (mm) of the conductor rings 2 when the frequency of the electromagnetic wave reflected by the electromagnetic wave reflector 10 is the set condition of 150 GHz ± 30 GHz under these conditions. It was found that when the center wavelength of the reflected frequency is 150 GHz, the positions of the plot points obtained from the simulation results differ depending on the line width W of the conductor ring 2, and the lines connecting them also appear different. Of the results shown in Figure 3, the thick solid line 31 indicates the case where W = 0.020 mm, the thin solid line 32 indicates the case where W = 0.025 mm, the dashed line 33 indicates the case where W = 0.030 mm, and the dashed line 34 indicates the case where W = 0.035 mm.

[0045] Then, using the method of least squares, the conditions for expressing the range that satisfies the above conditions in the form of Equation 1 were found from the coordinates shown in Figure 3. As a result, the coefficients in Equation 1 were obtained as a = 1.0, b = -3.7, c = 1.0, and d = -2.6.

[0046] In addition, the constant e corresponding to the line width mentioned above is related to W as e=-3800W 2 This could be expressed as +553W+95.16.

[0047] When the coefficient of determination between the above formula and each plot point, which is the simulation result, was calculated, the coefficient of determination was 0.97 to 0.99 under all conditions, indicating that the obtained formula and the simulation results were in extremely good agreement.

[0048] (300GHz±30GHz) FIG. 4 shows the relationship between frequency Z (GHz), radius X (mm) and center distance Y (mm) of the conductor ring when the frequency of the electromagnetic wave reflected by the electromagnetic wave absorber is 300 GHz±30 GHz, that is, 270 to 330 GHz.

[0049] The radius of the conductor ring 2 for reflecting electromagnetic waves of 300 GHz±30 GHz is further reduced, and the calculation is performed with the radius X set to 0.17 to 0.21 mm. The line width W is set to 0.020 to 0.035 mm, as in the above examples.

[0050] Figure 4 plots the center distance Y (mm) of the conductor rings 2 when the frequency of the electromagnetic wave reflected by the electromagnetic wave reflector 10 is the set condition of 300 GHz ± 30 GHz under these conditions. When the center wavelength of the reflected frequency is 300 GHz, as in the case of 150 GHz, the positions of the plot points obtained from the simulation results differ depending on the line width W of the conductor ring 2, and the lines connecting them also appear different. Among the results shown in Figure 4, the thick solid line 41 indicates the case where W = 0.020 mm, the thin solid line 42 indicates the case where W = 0.025 mm, the dashed line 43 indicates the case where W = 0.030 mm, and the dashed line 44 indicates the case where W = 0.035 mm.

[0051] Then, using the method of least squares, the conditions for expressing the range that satisfies the above conditions in the form of Equation 1 were found from the coordinates shown in Figure 4. As a result, the coefficients in Equation 1 were obtained as a = 1.0, b = -2.9, c = 1.0, and d = -2.6.

[0052] In addition, the constant e corresponding to the line width mentioned above is related to W as e=-57000W 2 It could be expressed as +4833W+89.81.

[0053] When the coefficient of determination between the above formula and each plot point, which is the simulation result, was calculated, the coefficient of determination was 0.98 to 0.99 under all conditions, indicating that the obtained formula and the simulation results were in extremely good agreement.

[0054] Next, the results of evaluation of the frequency characteristics of electromagnetic waves incident on the electromagnetic wave reflector designed using the above-mentioned (Equation 1) will be shown.

[0055] Fig. 5 shows a simulation result of the frequency characteristic of the return loss in the first electromagnetic wave reflector designed for a reflected electromagnetic wave frequency of 30 GHz, and Fig. 6 shows a simulation result of the frequency characteristic of the transmission loss in the first electromagnetic wave reflector designed for a reflected electromagnetic wave frequency of 30 GHz.

[0056] The first electromagnetic wave reflector, whose frequency characteristics are shown in Figures 5 and 6, was designed based on the results of the above-mentioned study with the frequency of the reflected electromagnetic waves set to 30 GHz, and the conductor rings were arranged vertically and horizontally in a grid pattern with the inner diameter of the conductor ring (distance from the center of the conductor ring to the inside of the ring) = 1.73 mm, the center distance between adjacent conductor rings = 4.33 mm, and the line width of the conductor ring = 0.025 mm.

[0057] 5, it was confirmed that the return loss, which is the amount of attenuation of the power of the electromagnetic wave reflected by the electromagnetic wave reflector relative to the power of the electromagnetic wave incident on the first electromagnetic wave reflector, was approximately 0 dB at the set frequency of 30 GHz, that is, the power of the electromagnetic wave incident on the first electromagnetic wave reflector was reflected at almost 100%. On the other hand, it can be seen that when the frequency of the incident electromagnetic wave shifts from 30 GHz by 5 GHz, the return loss at the first electromagnetic wave reflector decreases by approximately 2 dB, that is, the power of the reflected electromagnetic wave becomes 0.6 times.

[0058] 6, the transmission attenuation, which is the power of the electromagnetic wave that transmits through the first electromagnetic wave reflector relative to the electromagnetic wave power incident on the first electromagnetic wave reflector, is -45 dB at the set 30 GHz, and the transmitted power is 0.003%. On the other hand, for electromagnetic waves with frequencies of 25 GHz or less, which are shifted by ±5 GHz, or with frequencies of 35 GHz or more, the transmission attenuation is -4 to -5 dB or less, and it is understood that 30% or more of the electromagnetic wave is transmitted through the first electromagnetic wave reflector.

[0059] From the above, it is understood that the first electromagnetic wave reflector does not absorb electromagnetic waves around 30 GHz, but almost entirely reflects them.

[0060] Fig. 7 shows the simulation results of the frequency characteristics of the return loss in the second electromagnetic wave reflector designed for a reflected electromagnetic wave frequency of 150 GHz, while Fig. 8 shows the simulation results of the frequency characteristics of the transmission loss in the second electromagnetic wave reflector designed for a reflected electromagnetic wave frequency of 30 GHz.

[0061] The second electromagnetic wave reflector, whose frequency characteristics are shown in Figures 7 and 8, was designed based on the results of the above-mentioned study with the frequency of the reflected electromagnetic waves set to 150 GHz, and the conductor rings were arranged vertically and horizontally in a grid pattern with an inner diameter of 0.36 mm, a center distance between adjacent conductor rings of 0.89 mm, and a line width W of 0.025 mm.

[0062] 7, it was confirmed that the return loss, which is the attenuation of the power of the electromagnetic wave reflected by the electromagnetic wave reflector relative to the power of the electromagnetic wave incident on the second electromagnetic wave reflector, was approximately 0 dB at the set frequency of 150 GHz, that is, the power of the electromagnetic wave incident on the second electromagnetic wave reflector was reflected at almost 100%. On the other hand, it is understood that when the frequency of the incident electromagnetic wave deviates from 150 GHz by ±25 GHz, the return loss at the second electromagnetic wave reflector decreases by approximately 2 dB, that is, the power of the reflected electromagnetic wave becomes 0.6 times.

[0063] From the above, it is seen that the second electromagnetic wave reflector does not absorb electromagnetic waves around 150 GHz, but almost entirely reflects them.

[0064] 8, the transmission attenuation, which is the power of the electromagnetic wave that passes through the second electromagnetic wave reflector relative to the electromagnetic wave power incident on the second electromagnetic wave reflector, is -52 dB at the set 150 GHz, and the transmitted power is reduced to 0.0006%. On the other hand, for electromagnetic waves with frequencies of 125 GHz or less, which are shifted by ±25 GHz, or with frequencies of 175 GHz or more, the transmission attenuation is -4 to -6 dB or less, and it is understood that 25% or more of the electromagnetic wave passes through the second electromagnetic wave reflector.

[0065] Fig. 9 shows a simulation result of the frequency characteristic of the return loss in the third electromagnetic wave reflector designed for a reflected electromagnetic wave frequency of 300 GHz, and Fig. 10 shows a simulation result of the frequency characteristic of the transmission loss in the third electromagnetic wave reflector designed for a reflected electromagnetic wave frequency of 300 GHz.

[0066] The third electromagnetic wave reflector, whose frequency characteristics are shown in Figures 9 and 10, was designed based on the results of the above-mentioned study with the frequency of the reflected electromagnetic waves set to 300 GHz, and the conductor rings were arranged vertically and horizontally in a grid pattern with an inner diameter of 0.19 mm, a center distance between adjacent conductor rings of 0.43 mm, and a line width of conductor rings of 0.025 mm.

[0067] 9, it was confirmed that the return loss, which is the attenuation of the power of the electromagnetic wave reflected by the electromagnetic wave reflector relative to the power of the electromagnetic wave incident on the third electromagnetic wave reflector, was approximately 0 dB at the set frequency of 300 GHz, that is, the power of the electromagnetic wave incident on the third electromagnetic wave reflector was reflected at almost 100%. On the other hand, it is found that when the frequency of the incident electromagnetic wave deviates from 300 GHz by ±50 GHz, the return loss at the second electromagnetic wave reflector decreases by approximately 2 dB, that is, the power of the reflected electromagnetic wave becomes 0.6 times.

[0068] As shown by reference numeral 101 in FIG. 10, the transmission attenuation, which is the power of the electromagnetic wave transmitted through the third electromagnetic wave reflector relative to the electromagnetic wave power incident on the third electromagnetic wave reflector, is −60.5 dB at the set 300 GHz, and the transmitted power is 9.0E. -05 On the other hand, for electromagnetic waves with frequencies of 250 GHz or less, which are shifted by ±50 GHz, or electromagnetic waves with frequencies of 350 GHz or more, the transmission attenuation is −6 to −7.5 dB or less, and it is found that 25% or more of the electromagnetic waves are transmitted through the third electromagnetic wave reflector.

[0069] From the above, it is found that the third electromagnetic wave reflector does not absorb electromagnetic waves around 300 GHz, but almost entirely reflects them.

[0070] As described above, it has been confirmed that the electromagnetic wave reflector according to this embodiment can reflect electromagnetic waves of a desired frequency above the millimeter wave band with high reflection characteristics, such as a return loss of almost 0 dB, i.e., a reflectance of almost 100%, by adjusting the shape (radius X and line width W) of the conductor rings formed and the center distance Y between the conductor rings. Therefore, it can be used well as an electromagnetic wave reflector that can selectively reflect only desired electromagnetic waves. Furthermore, the electromagnetic wave reflector according to this embodiment can transmit electromagnetic waves of frequencies other than the predetermined frequency set for the reflector. Therefore, it can be used well as a frequency filter that selectively transmits electromagnetic waves other than the predetermined frequency.

[0071] In addition to electromagnetic wave reflectors using circular conductor rings as disclosed in the present application, an electromagnetic wave reflector capable of selecting the frequency of the electromagnetic waves to be reflected can be formed by arranging multiple conductors of other closed shapes, such as rectangular shapes (hereinafter referred to as "conductive loops") on a dielectric substrate.

[0072] Therefore, as a comparative example, an electromagnetic wave reflector in which conductive loops each having a square shape with the same length and width were arranged in a grid pattern in the vertical and horizontal directions was assumed, and the characteristics were compared with an electromagnetic wave reflector in which conductor rings, which are circular conductive loops described in the present embodiment, were arranged in a grid pattern.

[0073] FIG. 11 is a diagram showing the configuration of an electromagnetic wave reflector for which characteristics were compared depending on the shape of the conductor.

[0074] Fig. 11(a) is a diagram for explaining the configuration of an electromagnetic wave reflector in which circular conductor rings according to this embodiment are arranged, and Fig. 11(b) is a diagram for explaining the configuration of an electromagnetic wave reflector in which square conductive loops with equal length and width are arranged, assumed as a comparative example. Note that both diagrams show the shape of one unit of repeated conductive elements, including the peripheral area of ​​the conductive loop.

[0075] The conditions were determined by setting the reflected frequency to 150 GHz for a reflector in which multiple conductive loops of two shapes, circular and square, were arranged in a matrix in the vertical and horizontal directions. In order to make each conductive loop the same size, the distance between the opposing sides of the square conductive loop (the distance between the center lines of the sides) was set to be approximately the same as the diameter of the circular conductor ring.

[0076] As a result, it was found that in the case of the circular conductive loop shown in Figure 11(a), a reflection characteristic with a reflectance of 99.99% or more can be obtained by setting the diameter 2X = 0.58 mm, the line width W = 0.02 mm, and the length of one side of the area occupied by one element Y = 0.730 mm.

[0077] On the other hand, when the square-shaped conductive loops shown in Figure 11(b) are arranged, the distance between the center lines of the opposing sides of the loops is a = 0.16 mm, the line width W = 0.04 mm, and the length of one side of the area occupied by one element P = 0.42 mm, and it was confirmed that reflection characteristics with a reflectivity of 99.99% or more can be obtained, as in the case of a conductor ring.

[0078] In this way, even if the conductive loop is not shaped like a circular conductor ring, it is possible to obtain an electromagnetic wave reflector that is comparable in terms of the reflection characteristics for electromagnetic waves with a desired frequency of 150 GHz. However, as can be seen by comparing Figures 11(a) and 11(b), in the electromagnetic wave reflector made of a circular conductive loop as shown in Figure 11(a), the line width W of the conductor forming the loop is small, and therefore less conductive material is required when actually producing the electromagnetic wave reflector. Specifically, in the case of the circular conductive loop shown in Figure 11(a), the line width W of the conductor forming the loop is small, and therefore less conductive material is required when actually producing the electromagnetic wave reflector. 2 The area occupied by the circular conductive loop element is 0.0691 mm 2 (about 7%). In contrast, in the case of the square conductive loop shown in FIG. 11(b), the 2 The area occupied by the square conductive loop element is 0.145 mm 2(About 15%). As a result, when a square conductive loop is used, the area occupied by the element is about twice as large as when a circular conductive loop is used.

[0079] For this reason, the difference in the conductive materials required to manufacture an electromagnetic wave reflector in which a large number of conductive loops are arranged becomes large, and the manufacturing cost of an electromagnetic wave reflector using a conductor ring, which is a circular conductive loop as shown in this embodiment, can be reduced. In addition, since the circular conductive loop has small anisotropy in shape, it is preferable to use a square conductive loop in that it is thought that there is little difference in reflection performance due to polarization or incident angle.

[0080] As described above, in the electromagnetic wave reflector of this embodiment, by adjusting the radius X and width W of the circular conductor rings arranged on the substrate and the arrangement interval Y of the arranged conductor rings, it is possible to reflect electromagnetic waves of a desired frequency Z in a high frequency band equal to or higher than the millimeter wave band.

[0081] Electromagnetic waves, which have been increasingly used in recent years and are expected to be used at even higher frequencies in the future, tend to travel in a straighter line, making it difficult for the electromagnetic waves to deviate from one another, and if there is an obstacle between the electromagnetic wave source and the receiving device, the electromagnetic waves cannot reach their destination. In such cases, a reflecting member that reflects the electromagnetic waves may be used, but if the reflecting member also reflects electromagnetic waves of unnecessary frequencies, the electromagnetic waves become noise and the S / N ratio decreases. In such cases, the electromagnetic wave reflector according to the present embodiment, which can effectively reflect only electromagnetic waves of the desired frequency, is extremely useful.

[0082] In the above embodiment, only three cases of 30 GHz±10 GHz, 150 GHz±30 GHz, and 300 GHz±30 GHz are exemplified as the frequencies of the electromagnetic waves reflected by the electromagnetic wave reflector. However, the electromagnetic wave reflector disclosed in the present application can be applied to electromagnetic wave reflectors that reflect not only the millimeter wave band of about 30 GHz to about 300 GHz but also high frequency electromagnetic waves of about 1 THz, as expressed by (Equation 1) "Z=aX b +cY dBy using the condition "+e", it is possible to obtain an electromagnetic wave reflector that reflects electromagnetic waves of a desired frequency.

[0083] [Electromagnetic wave absorbing sheet using electromagnetic wave reflector as a reflective layer] As described above, the electromagnetic wave reflector disclosed in the present application has a reflection characteristic that selectively reflects electromagnetic waves of a predetermined frequency equal to or higher than the millimeter wave band by adjusting the shape and arrangement interval of the formed conductor rings. By utilizing this, it is possible to realize an electromagnetic wave absorbing sheet that effectively absorbs the electromagnetic waves of the predetermined frequency reflected by the electromagnetic wave reflector and transmits electromagnetic waves of frequencies other than the predetermined frequency by using the electromagnetic wave reflector as a reflection layer of an electromagnetic interference type electromagnetic wave absorbing sheet.

[0084] In the following, the electromagnetic wave absorbing sheet will be described by taking as an example a case where an electromagnetic wave reflector that reflects electromagnetic waves of 30 GHz is used as the reflective layer.

[0085] FIG. 12 is a cross-sectional view showing the structure of an electromagnetic wave absorbing sheet explained as this embodiment.

[0086] Note that FIG. 12 is a diagram provided to facilitate understanding of the configuration of the electromagnetic wave absorbing sheet according to this embodiment, and the sizes and thicknesses of the components shown in the diagram are not depicted based on reality.

[0087] The electromagnetic wave absorbing sheet 200 exemplified in this embodiment is formed by laminating a resistive film 201, a dielectric layer 202, and an electromagnetic wave reflector 10 which is a reflective layer. Although omitted in Fig. 12, an adhesive layer can be laminated on the back side of the electromagnetic wave reflector 10, i.e., the surface of the electromagnetic wave reflecting layer 10 opposite to the side on which the dielectric layer 202 is disposed. In addition, a protective layer can be laminated on the front side of the resistive film 201, i.e., the surface of the resistive film 201 opposite to the side on which the dielectric layer 202 is disposed.

[0088] In the electromagnetic wave absorbing sheet 200 according to this embodiment, an electromagnetic wave 211 having a frequency of 30 GHz incident on the dielectric layer 202 is reflected at the interface between the dielectric layer 202 and the electromagnetic wave reflector 10 arranged on the back side of the dielectric layer 202, and is again emitted to the outside as a reflected wave 212. At this time, the thickness d of the dielectric layer 202 is set to a wavelength λ of the incident electromagnetic wave, which is ¼ of the effective wavelength (d=λ / 4=πC / 2ω√ε r , ω: angular frequency, ε r : dielectric constant of the dielectric layer), the phase 211a of the incident wave 211 (more precisely, the phase of the surface reflected wave reflected on the surface of the electromagnetic wave absorbing sheet 200) and the phase 212a of the reflected wave 212 (the phase of the reflected wave reflected on the surface of the electromagnetic wave reflector 10) cancel each other out, so that the reflected wave 212 from the electromagnetic wave absorbing sheet 200 is essentially absorbed.

[0089] The electromagnetic wave reflector 10 formed by lamination on the back surface side of the dielectric layer 202 functions as a reflective layer that reflects electromagnetic waves incident on the surface on the dielectric layer 202 side, which is the boundary surface with the dielectric layer 202.

[0090] In the electromagnetic wave absorbing sheet of this embodiment, the electromagnetic wave reflector 10 is used as a reflective layer, so that the electromagnetic wave of a predetermined frequency (30 GHz as an example) reflected by the electromagnetic wave reflector 10 becomes a reflected wave 212, and the electromagnetic waves of other frequencies that are not reflected by the electromagnetic wave reflector 10 pass through the electromagnetic wave absorbing sheet 200 as a transmitted wave 213.

[0091] The resistive film 201 is formed on the front side of the dielectric layer 202, i.e., on the electromagnetic wave incident side opposite the side of the dielectric layer 202 on which the electromagnetic wave reflector 10 is laminated, and performs impedance matching between the electromagnetic wave absorbing sheet 200 and the air.

[0092] When electromagnetic waves propagating through the air are incident on the electromagnetic wave absorbing sheet 200, it is important to make the input impedance value of the electromagnetic wave absorbing sheet 200 close to 377Ω, which is the impedance value in air (actually the impedance value of a vacuum), in order to prevent the electromagnetic waves from being reflected or scattered and degraded in their electromagnetic wave absorbing characteristics when they are incident on the electromagnetic wave absorbing sheet 200. The resistive film 201 can be formed as a film of a conductive organic polymer. In this case, since the resistive film 201 has flexibility, when both the dielectric layer 202 and the electromagnetic wave reflector 10 have flexibility, it is possible to configure the electromagnetic wave absorbing sheet 200 that has flexibility as a whole.

[0093] Next, each member constituting the electromagnetic wave absorbing sheet according to this embodiment will be described in detail.

[0094] <Resistance film> The resistive film 201 of the electromagnetic wave absorbing sheet 200 according to this embodiment can be made as a thin film of an electrically conductive inorganic material.

[0095] Specifically, a resistive film can be produced by coating a metal oxide such as indium tin oxide (ITO), indium oxide, tin oxide, or zinc oxide, a metal nitride, or a mixture of these, onto a resin substrate such as polyethylene terephthalate (PET) using a thin film formation method such as ion plating, vapor deposition, sputtering, or various coating methods.

[0096] Moreover, the resistive film 201 of the electromagnetic wave absorbing sheet 200 according to this embodiment can also be fabricated as a thin film of a conductive polymer. When the resistive film 201 is formed of a polymer film, a conjugated conductive organic polymer can be used as the conductive organic polymer, and it is preferable to use polythiophene or a derivative thereof, or polypyrrole or a derivative thereof.

[0097] In addition, organic polymers whose main chains are composed of a π-conjugated system can be used as the resistive film, and examples of the organic polymers that can be used include polyacetylene-based conductive polymers, polyphenylene-based conductive polymers, polyphenylenevinylene-based conductive polymers, polyaniline-based conductive polymers, polyacene-based conductive polymers, polythiophenevinylene-based conductive polymers, and copolymers of these.

[0098] In addition, a polyanion can be used as a counter anion for the conductive organic polymer used in the resistive film 201. The polyanion is not particularly limited, but it is preferable that the conjugated conductive organic polymer used in the resistive film 1 described above contains an anion group that can cause chemical oxidation doping. Examples of such an anion group include groups represented by the general formulas -O-SO3X, -O-PO(OX)2, -COOX, and -SO3X (wherein X represents a hydrogen atom or an alkali metal atom). Among them, the groups represented by -SO3X and -O-SO3X are particularly preferable because they have an excellent doping effect on the conjugated conductive organic polymer.

[0099] The conductive organic polymers may be used alone or in combination of two or more. Among the materials exemplified above, a polymer consisting of one or two selected from polypyrrole, poly(3-methoxythiophene), poly(3,4-ethylenedioxythiophene), poly(2-anilinesulfonic acid), and poly(3-anilinesulfonic acid) is preferred because it has higher transparency and conductivity.

[0100] 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).

[0101] In addition, in the resistive film 201 of the electromagnetic wave absorbing sheet 200 according to this embodiment, a dopant can be used in combination to control the electrical conductivity of the conductive organic polymer and match the input impedance of the electromagnetic wave absorbing sheet 200 with the impedance value in air. As the dopant, 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. The surface resistance value of the resistive film can be adjusted by the blending ratio of the conductive organic polymer and the dopant. As an example, a preferred blending ratio of the conductive organic polymer and the dopant can be conductive polymer:dopant=1:2 to 1:4 in mass ratio.

[0102] Furthermore, it is preferable that the material forming the resistive film 201 further contains polyvinylidene fluoride and water-soluble polyester. By containing these, the weather resistance of the resistive film 201 is improved, so that the change over time in the surface resistance value of the resistive film 201 can be suppressed, and the design tolerance of the material and thickness of the protective layer that protects the resistive film 201 can be expanded.

[0103] The content of the conductive organic polymer in the resistive film 201 is preferably 10% by mass or more and 35% by mass or less with respect to the total mass of the solid content contained in the resistive film composition. If the content is less than 10% by mass, the conductivity of the resistive film 201 tends to decrease. For this reason, as a result of setting the surface electrical resistance value of the resistive film 201 within a predetermined range in order to achieve impedance matching, the film thickness of the resistive film increases, and the electromagnetic wave absorbing sheet 200 as a whole tends to become thicker and the optical characteristics tend to deteriorate. On the other hand, if the content exceeds 35% by mass, the structure of the conductive organic polymer reduces the application suitability when coating the resistive film, making it difficult to form a good resistive film, and the haze of the resistive film 201 increases, which also tends to deteriorate the optical characteristics.

[0104] The resistive film 201 may also be configured to include a carbon material such as a carbon microcoil, a carbon nanotube, or graphene.

[0105] Carbon microcoils are a type of vapor-grown carbon fiber obtained mainly by catalytically activated pyrolysis of acetylene, and are materials that have a 3D-helical / spiral structure with a coil diameter on the order of microns. The coil diameter is preferably 1 to 10 μm, the carbon fiber forming the coil has a diameter of 0.1 to 1 μm, and the coil length is preferably 1 to 10 mm.

[0106] Specifically, the carbon nanotubes can be obtained by a vapor phase growth method such as an arc discharge method, a laser evaporation method, a pyrolysis method, etc. The carbon nanotubes used as the resistive film of the electromagnetic wave absorbing sheet according to this embodiment may be either single-walled or multi-walled.

[0107] Graphene can be obtained by, for example, a peeling and transfer method, a SiC pyrolysis method, a chemical vapor deposition method, a method of cutting carbon nanotubes, etc. As the graphene used as the resistive film 201 of the electromagnetic wave absorbing sheet 200 according to this embodiment, it is preferable to use flake-shaped powdered graphene, from the viewpoint of easily obtaining a desired aspect ratio and of the orientation in the electromagnetic wave absorbing sheet 200.

[0108] As the resin in which the carbon material is dispersed, a water-soluble polyester resin can be used.

[0109] Moreover, the resistive film 201 using a conductive organic polymer can be formed by applying a coating composition as a paint for forming the resistive film 201 onto a substrate and drying it.

[0110] The method of applying the resistive coating paint on the substrate may be, for example, a bar coating method, a reverse coating method, a gravure coating method, a microgravure coating method, a die coating method, a dipping method, a spin coating method, a slit coating method, a spray coating method, or the like. Drying after application may be performed under conditions that allow the solvent component of the resistive coating paint to evaporate, and is preferably performed at 100 to 150°C for 5 to 60 minutes. If the solvent remains in the resistive coating, the strength tends to be inferior. Drying methods include, for example, hot air drying, heat drying, vacuum drying, and natural drying. If necessary, the resistive coating may be formed by irradiating the coating with UV light (ultraviolet rays) or EB (electron beam) to harden the coating.

[0111] The base material used to form the resistive film 201 is not particularly limited, and various materials such as resin, rubber, glass, and ceramics can be used.

[0112] <Dielectric layer> The dielectric layer 202 of the electromagnetic wave absorbing sheet 200 according to this embodiment can be formed of a dielectric material such as titanium oxide, polyvinylidene fluoride, polyester resin, glass, silicone rubber, etc. The dielectric layer can be formed as a single layer of one type of material, or can be formed as a laminate of two or more layers of the same or different types of materials. The dielectric layer 202 can be formed by a coating method, a press molding method, an extrusion molding method, etc.

[0113] As described above, the electromagnetic wave absorbing sheet 200 according to this embodiment absorbs electromagnetic waves by canceling out the surface reflected wave reflected on the surface of the electromagnetic wave absorbing sheet 200 due to interference between the surface reflected wave and the reflected wave reflected on the surface of the electromagnetic wave reflector 10 with a phase shift of 1 / 2 wavelength. Note that, in the electromagnetic wave absorbing sheet 200 according to this embodiment, the electromagnetic wave reflector 10 that reflects electromagnetic waves of a predetermined frequency (30 GHz as an example) is used as the reflective layer, and therefore the thickness (d in FIG. 12) of the dielectric layer 202 is determined corresponding to the wavelength, which is the reciprocal of the frequency of the electromagnetic wave reflected by the electromagnetic wave reflector 10.

[0114] In addition, the value of d is d=λ / 4 when there is a space between the resistive film 201 and the electromagnetic wave reflector 10, that is, when the dielectric layer 202 is made of air with a dielectric constant of 1. However, when the dielectric constant of the dielectric layer 202 is ε r If , then d=1 / (4√ε r ) and the thickness d of the dielectric layer 102 is expressed as 1 / (4√ε r ) By forming the dielectric layer 202 to be thin, the entire electromagnetic wave absorbing sheet 200 can be made thin, which contributes to realizing a lightweight electromagnetic wave absorbing sheet 100 and an electromagnetic wave absorbing sheet 200 with excellent flexibility.

[0115] <Reflection layer (electromagnetic wave reflector)> In the electromagnetic wave absorbing sheet 200 according to this embodiment, the above-mentioned electromagnetic wave reflector 10 is used as the reflective layer. The electromagnetic wave reflector 10 according to this embodiment can reflect electromagnetic waves of a predetermined frequency by adjusting the shape and arrangement interval of the conductor rings 2 (see FIG. 1) formed therein, and can effectively absorb electromagnetic waves of a predetermined frequency by matching the thickness d of the dielectric layer 202 to the frequency of the electromagnetic waves reflected by this electromagnetic wave reflector 10 as described above.

[0116] <Adhesive layer> Although not shown in Fig. 12, in the electromagnetic wave absorbing sheet 200 according to this embodiment, an adhesive layer can be appropriately provided on the back side of the electromagnetic wave reflector 10, which is the reflective layer. By providing the adhesive layer, the electromagnetic wave absorbing sheet 200 can be easily attached to a predetermined location. The adhesive layer can be easily formed by applying a sticky resin paste.

[0117] It should be noted that the adhesive layer is not an essential component of the electromagnetic wave absorbing sheet 200 according to this embodiment, and when placing the electromagnetic wave absorbing sheet 200 at a predetermined location, an adhesive component may be placed on the side of the component to which the electromagnetic wave absorbing sheet 200 is attached. Also, when placing the electromagnetic wave absorbing sheet 200 at a predetermined location, an adhesive method such as supplying an adhesive between the electromagnetic wave absorbing sheet 200 and the placement location or using double-sided tape can be adopted.

[0118] <Protective layer> 12, a protective layer can be formed on the surface of the resistive film 201, that is, on the outermost surface of the electromagnetic wave absorbing sheet 200 on the side where the electromagnetic waves are incident. As described above, if the resistance value of the resistive film 201 does not match the impedance in air, the electromagnetic wave absorbing characteristics of the electromagnetic wave absorbing sheet 200 will be reduced. The protective layer is a film that protects the resistive film 201 from being damaged by external forces and from changes in its surface resistance value due to the effects of ultraviolet rays and moisture, and is particularly useful in protecting a conductive organic polymer film when the resistive film 201 is a conductive organic polymer film.

[0119] The protective layer is not an essential component of the electromagnetic wave absorbing sheet 200 according to this embodiment, and when there is little concern about changes in the surface resistance value due to adhesion of moisture to the surface or damage to the surface of the resistive film 201 due to the conductive organic polymer material, it is possible to select a configuration of the electromagnetic wave absorbing sheet 200 without a protective layer.

[0120] The protective layer may be made of a resin material such as polyethylene terephthalate. Although the resin material used as the protective layer has a certain resistance value, by setting the thickness of the protective layer thin, the influence of the presence or absence of the protective layer on the surface resistance value of the electromagnetic wave absorbing sheet 200 can be kept at a practically negligible level.

[0121] <Electromagnetic wave absorption characteristics, electromagnetic wave transmission characteristics> FIG. 13 shows the change in return loss, which is the amount of attenuation when an electromagnetic wave incident on an electromagnetic wave absorbing sheet is reflected, depending on the frequency, in decibels (dB) in the electromagnetic wave absorbing sheet according to this embodiment.

[0122] In determining the return loss indicated by reference numeral 131 in FIG. 13, the following electromagnetic wave absorbing sheet was assumed.

[0123] The resistor film was assumed to be formed using a resistor film solution made by adding and mixing the following components: (1) 36.7 parts of conductive polymer dispersion (PEDOT-PSS) (PH-1000 (product name: manufactured by Heraeus Corporation)) Solid content concentration 1.2% by mass (2) 5.6 parts of PVDF dispersion LATEX32 (product name: manufactured by Arkema Co., Ltd.), Solid concentration: 20% by weight, Solvent: Water (3) 0.6 parts of water-soluble polyester solution Pluscoat Z561 (Product name: Made by Kawaoka Kogyo Co., Ltd.) Solid content concentration 25% by mass (4) Organic solvent (dimethyl sulfoxide) 9.9 parts (5) Water-soluble solvent (ethanol) 30.0 parts (6) Water 17.2 parts.

[0124] The resistive film solution prepared with the above composition was applied to a polyethylene terephthalate sheet (50 μm thick) as a substrate by bar coating in an amount that would result in a thickness of approximately 120 nm after drying, and then heated at 150°C for 5 minutes to form a film. The surface resistance of the resistive film in this case was 377 Ω / sq.

[0125] The dielectric layer was assumed to be made of urethane OCA (dielectric constant = 2.3) with a thickness of 1.41 mm.

[0126] The electromagnetic wave shielding layer used was an electromagnetic wave reflector that reflects 30 GHz electromagnetic waves and whose electromagnetic wave reflection characteristics are shown in Figure 5. That is, the conductor rings formed on the electromagnetic wave shielding layer had a radius X of 1.73 mm, a center distance Y between adjacent conductor rings of 4.33 mm, and a line width W of 0.025 mm, and were arranged vertically and horizontally in a lattice pattern.

[0127] As shown by reference numeral 131 in Fig. 13, the return loss of this electromagnetic wave absorbing sheet is about -18 dB at a peak frequency of 30 GHz, and it was confirmed that the electromagnetic wave absorbing sheet satisfactorily absorbs the electromagnetic wave at a frequency of 30 GHz, at which the electromagnetic wave reflection characteristics of the electromagnetic wave reflector used as the electromagnetic wave shielding layer reach a peak. Note that the electromagnetic wave absorbing sheet shown in this embodiment uses an electromagnetic wave reflector that selectively reflects electromagnetic waves of a predetermined frequency as a reflective layer that reflects electromagnetic waves, and due to the interference effect caused by determining the thickness of the dielectric layer based on the frequency of the electromagnetic wave to be absorbed, it is possible to increase the return loss for absorbing a desired frequency compared to the case where a conductor such as a metal is used as the reflective layer.

[0128] FIG. 14 shows frequency characteristics of the transmission attenuation in the electromagnetic wave absorbing sheet described in this embodiment.

[0129] 14, in the electromagnetic wave absorbing sheet according to this embodiment, the transmission attenuation of the electromagnetic wave passing through the electromagnetic wave absorbing sheet at about 27.5 GHz is large, at about -21 dB. Also, the transmission attenuation of the electromagnetic waves in the frequency bands of 22 GHz or less and 36 GHz or more is smaller than -6 dB, and it is found that the electromagnetic waves outside the frequency band near 30 GHz, which is the predetermined frequency, are hardly attenuated or reflected by the electromagnetic wave absorbing sheet and pass through the electromagnetic wave absorbing sheet.

[0130] In this way, it has been confirmed that by using the electromagnetic wave reflector disclosed in the present application as a reflective layer, it is possible to realize an electromagnetic wave absorbing sheet that does not reflect or transmit electromagnetic waves of a frequency band different from the electromagnetic waves of the frequency reflected by the electromagnetic wave reflector.

[0131] As described above, in the electromagnetic wave absorbing sheet shown in this embodiment, by using an electromagnetic wave reflector that can reflect only electromagnetic waves of a desired frequency as a reflective layer, it is possible to realize an electromagnetic wave absorbing sheet with unique electromagnetic wave absorption characteristics that can reduce both reflected waves and transmitted waves of electromagnetic waves having a specific frequency.

[0132] For this reason, the electromagnetic wave absorbing sheet can be suitably used in cases where it is necessary for electromagnetic waves to pass through it, such as when absorbing unwanted electromagnetic waves inside an antenna transmitter that transmits electromagnetic waves in the air, but where it is desired to obtain a reflection attenuation effect for electromagnetic waves of a certain frequency.

[0133] As described above, the electromagnetic wave reflector, which is the reflective layer, is configured with conductor rings arranged at a predetermined interval, so that the electromagnetic wave reflector, which is the reflective layer, has a certain aperture ratio by using a light-transmitting material as the base material of the electromagnetic wave reflector. In this case, by adopting light-transmitting materials for all of the constituent members such as the resistive film, the dielectric layer, and further the optional protective layer and adhesive layer, the electromagnetic wave absorbing sheet as a whole can have a certain level of light-transmittance or more.

[0134] In this way, it is possible to realize an electromagnetic wave absorbing sheet that can absorb undesired electromagnetic waves while allowing the interior or exterior to be visually confirmed, such as, for example, a curtain in a room placed in an electromagnetic wave shielding state. Also, in the case of disposing a screen-like electromagnetic wave absorber to absorb undesired electromagnetic waves when measuring electromagnetic wave characteristics, by attaching the electromagnetic wave absorbing sheet and allowing light to pass through the sheet together with a support member used as a screen, it becomes possible to easily observe the state of the measuring equipment or the equipment to be measured on the other side of the electromagnetic wave absorber. [Industrial Applicability]

[0135] The electromagnetic wave reflector disclosed in the present application can be configured to selectively reflect electromagnetic waves of a desired frequency above the millimeter wave band by adjusting the shape and arrangement interval of the conductor rings arranged on the substrate. In addition, the electromagnetic wave absorbing sheet disclosed in the present application can have frequency characteristics of absorbing electromagnetic waves of a predetermined frequency and transmitting electromagnetic waves of other frequencies by using the electromagnetic wave reflector as a reflective layer. Therefore, it is useful as a member that selectively reflects or absorbs electromagnetic waves of high frequencies above the millimeter wave band. [Explanation of symbols]

[0136] 1 Base material 2 Conductor Ring 10 Electromagnetic wave reflector

Claims

1. An electromagnetic wave reflector having a plurality of conductor rings arranged therein, which selectively reflects electromagnetic waves having a predetermined frequency equal to or higher than the millimeter wave band, Let X (mm) be the radius of the conductor ring, Y (mm) be the center distance between adjacent conductor rings, and Z (GHz) be the frequency of the reflected electromagnetic wave. Z = aX b + cY d + e (Equation 1) An electromagnetic wave reflector characterized in that the above relationship is satisfied.

2. In the electromagnetic wave reflector, the frequency Z of the reflected electromagnetic wave is in the range of 30±10 (GHz), In the case of a conductor ring in which X is 1.31 to 2.60 (mm) and Y is 3.27 to 6.50 (mm), 2. The electromagnetic wave reflector according to claim 1, wherein a is 2.3, b is −6.9, c is 126.6, d is −0.9, and e is −2.

4.

3. In the electromagnetic wave reflector, the frequency Z of the reflected electromagnetic wave is in the range of 150±30 (GHz), In the case of a conductor ring in which X is 0.31 to 0.45 (mm) and Y is 0.73 to 1.07 (mm), The a is 1.0, the b is −3.7, the c is 1.0, and the d is −2.6, moreover, When the line width W of the conductor ring is 0.02 to 0.035 (mm), The e is e = -3800 x W 2 2. The electromagnetic wave reflector according to claim 1, which satisfies +553×W+95.

16.

4. In the electromagnetic wave reflector, the frequency Z of the reflected electromagnetic wave is in the range of 300±30 (GHz), In the case of a conductor ring in which X is 0.17 to 0.21 (mm) and Y is 0.40 to 0.47 (mm), The a is 1.0, the b is −2.9, the c is 1.0, and the d is −2.6, moreover, When the line width W of the conductor ring is 0.02 to 0.035 (mm), The above e is e = -57000 x W 2 The electromagnetic wave reflector according to claim 1 , which satisfies +4833×W+89.

81.

5. 2. The electromagnetic wave reflector according to claim 1, wherein the conductor rings all have the same radius (X) and line width (W), and are arranged in a lattice pattern with the same center distance (Y) between each conductor ring.

6. 2. The electromagnetic wave reflector according to claim 1, wherein the maximum return loss at said frequency Z is −1 dB or less.

7. 7. An electromagnetic wave absorbing sheet comprising the electromagnetic wave reflector according to claim 1 as a reflective layer, and a resistive film, a dielectric layer, and the electromagnetic wave reflector as the reflective layer laminated in this order from the electromagnetic wave incident side.

Images