JP2023138311A - Electromagnetic wave absorber/reflector, planar antenna, and manufacturing method of electromagnetic wave absorber/reflector - Google Patents

Abstract

To provide a thin electromagnetic wave absorber/reflector that can support frequencies of several GHz or less without increasing the size of a conductor pattern formed on the surface of a base material.SOLUTION: An electromagnetic wave absorber/reflector includes a base material and a unit pattern of a conductor provided periodically on the surface of the base material, and a part of the unit pattern overlaps a part of an adjacent unit pattern in the stacking direction of the base materials with a dielectric layer interposed therebetween.SELECTED DRAWING: Figure 3

Description

The present invention relates to an electromagnetic wave absorber/reflector, a planar antenna, and a method for manufacturing an electromagnetic wave absorber/reflector.

Metamaterials are artificial structures that manipulate the electromagnetic or thermal properties and mechanical vibrations of materials. Metasurfaces and frequency selection plates are a type of two-dimensional metamaterial, and have artificial surfaces that manipulate the properties of materials against electromagnetic waves. For example, as shown in FIG. 1, a metasurface is formed by a periodic two-dimensional array of conductive patterns P. By appropriately designing the size, pitch (distance between centers) of the pattern P, dielectric constant of the base material supporting the conductive pattern P, etc., characteristics such as absorption, reflection, and oscillation of electromagnetic waves of a specific frequency can be controlled. Ru. The specific frequency, that is, the resonant frequency f, is calculated using the inductance L _eff and capacitance C _eff of the equivalent LC circuit of pattern P: f=1/2π(L _eff・C _eff )^1/2
It is estimated that

The size of the pattern P having a periodic structure is set to 1/2 or less of the wavelength λ of the electromagnetic wave of the target, and is generally set to about 1/10 to 1/4 of the wavelength. Currently, in the 28 GHz band or higher used in the 5G mobile communication standard, electromagnetic wave absorbers are required to prevent electromagnetic wave self-poisoning inside communication devices. The size of a metamaterial or metasurface that absorbs the 28 GHz band is approximately several mm, which is too large to be installed inside small communication devices, making it difficult to install. Furthermore, when dealing with low-frequency electromagnetic waves of several GHz or less, the size and pitch of the conductive patterns are several centimeters or more. With such a configuration in which large-sized patterns are repeatedly arranged, it is difficult to introduce the electromagnetic wave absorber into a narrow space. For oscillation applications, the size of antennas for low frequencies increases.

A soft magnetic noise suppression sheet that utilizes magnetic loss is used as a low frequency absorber of 1 GHz or less. The amount of electromagnetic wave absorption of a soft magnetic noise suppression sheet depends on its thickness, which increases the thickness and weight of the sheet. Furthermore, at frequencies exceeding 1 GHz, the amount of absorption of electromagnetic waves decreases. A configuration has been proposed in which a capacitor is soldered between conductor patches that constitute a unit pattern of a metamaterial to realize absorption of low-frequency electromagnetic waves (see, for example, Patent Document 1 and Non-Patent Document 1).

A configuration in which a capacitor element is soldered between conductive patches is expensive and unsuitable for mass production. When using soldered capacitor elements, the thickness of the capacitor element occurs in addition to the thickness of the metamaterial layer. For electromagnetic waves of 1 GHz, the thickness of the metamaterial layer alone is sub-millimeter, but if the capacitor element is included, the thickness is from 1 millimeter to several millimeters.

In one aspect, the present invention provides a thin electromagnetic wave absorbing or reflecting body that can accommodate a desired frequency without increasing the size of a conductive pattern formed on the surface of a base material. In the following, "electromagnetic wave absorbing or reflecting body" will be referred to as "electromagnetic wave absorbing/reflecting body".

In one embodiment, the electromagnetic wave absorber/reflector is
base material and
a unit pattern of conductors provided periodically on the surface of the base material;
A portion of the unit pattern overlaps a portion of the adjacent unit pattern in the stacking direction of the base material with a dielectric layer interposed therebetween.

In another embodiment, the electromagnetic wave absorber/reflector is
base material and
a first group of unit patterns formed of a first conductor on the surface of the base material;
a dielectric layer covering at least a portion of the first group of unit patterns;
a second group of unit patterns provided on the dielectric layer and formed of a second conductor so as not to overlap with the first group of unit patterns in the stacking direction with the dielectric layer in between; ,
has.

A thin electromagnetic wave absorbing/reflecting body and a method for manufacturing the same can be realized without increasing the size of a conductor pattern formed on the surface of a base material.

FIG. 2 is a diagram showing a typical conductive pattern used in a metasurface. FIG. 1 is a basic configuration diagram of an electromagnetic wave absorber/reflector according to an embodiment. FIG. 2 is a schematic plan view of an electromagnetic wave absorber/reflector according to the first embodiment. FIG. 4 is a diagram showing a configuration example of the AA cross section of the electromagnetic wave absorbing/reflecting body in FIG. 3; 4 is another configuration example of the AA cross section of the electromagnetic wave absorber/reflector in FIG. 3. 4 is yet another configuration example of the AA cross section of the electromagnetic wave absorber/reflector in FIG. 3. 5 is a manufacturing process diagram of the electromagnetic wave absorber/reflector of FIG. 4. FIG. 5 is a manufacturing process diagram of the electromagnetic wave absorber/reflector of FIG. 4. FIG. 5 is a manufacturing process diagram of the electromagnetic wave absorber/reflector of FIG. 4. FIG. 6 is a manufacturing process diagram of the electromagnetic wave absorber/reflector of FIG. 5. FIG. 6 is a manufacturing process diagram of the electromagnetic wave absorber/reflector of FIG. 5. FIG. 6 is a manufacturing process diagram of the electromagnetic wave absorber/reflector of FIG. 5. FIG. FIG. 5 is a schematic cross-sectional view showing a configuration example of capacity enhancement of the electromagnetic wave absorber/reflector shown in FIG. 4; FIG. 6 is a schematic cross-sectional view showing a configuration example of capacity enhancement of the electromagnetic wave absorbing/reflecting body of FIG. 5; FIG. 7 is a diagram showing an example of capacitor adjustment of the electromagnetic wave absorber/reflector according to the second embodiment. FIG. 7 is a diagram showing another example of capacitor adjustment of the electromagnetic wave absorber/reflector. It is a figure showing the example of composition of the electromagnetic wave absorber/reflector of a 3rd embodiment. It is a figure showing another example of composition of an electromagnetic wave absorber/reflector of a 3rd embodiment. This is an example of a configuration of capacitive coupling using a gap. FIG. 2 is a configuration diagram of a characteristic evaluation model. FIG. 7 is a diagram showing changes in absorption frequency characteristics when the amount of overlap in the in-plane direction of the unit patterns of the upper layer and the lower layer is changed. FIG. 6 is a diagram showing changes in absorption frequency characteristics when the interval in the stacking direction between unit patterns in the upper layer and the lower layer is changed.

In one embodiment, a structure is provided in which a part of a unit pattern of a conductor that is repeatedly arranged overlaps a part of an adjacent unit pattern with a dielectric layer in between in the stacking direction, so that a capacitance is created between the upper and lower patterns. combine. The magnitude of capacitive coupling (ie, capacitance) can be set to a desired value by designing the area of overlap, the thickness of the dielectric layer, and the dielectric constant. In another embodiment, when viewed from a direction perpendicular to the substrate, the unit patterns of the upper layer and the lower layer do not overlap in the in-plane direction, but form capacitive coupling in the direction horizontal to the substrate. By creating a desired amount of capacitive coupling between patterns using part of the unit pattern, properties such as absorption, reflection, and oscillation for lower frequency electromagnetic waves can be achieved while keeping the size of the unit pattern small. be able to.

The capacitive coupling provided between adjacent unit patterns can be formed by a printing method such as inkjet, screen printing, or spraying. A thin electromagnetic wave absorbing/reflecting body is manufactured by forming the capacitive coupling portion with a thin coated film. The characteristics against electromagnetic waves can be easily controlled by simply changing the overlapping area of the capacitive coupling portion, the thickness of the dielectric layer, and the material. Furthermore, by forming multiple types of capacitive coupling, it is possible to have multiple absorption or reflection spectra, or to make them broad.

The specific configuration of the electromagnetic wave absorber/reflector of the embodiment will be shown below. In the embodiments, the same components may be denoted by the same reference numerals and redundant descriptions may be omitted.

FIG. 2 is a basic configuration diagram of the electromagnetic wave absorber/reflector 10 of the embodiment. The electromagnetic wave absorber/reflector 10 has unit patterns 15 of conductors provided periodically on the surface of the base material 11. For convenience of illustration, only a portion of the repeating pattern of the electromagnetic absorber/reflector 10 is shown. A capacitive coupling portion 12 is provided between adjacent unit patterns 15 . The capacitive coupling portion 12 is formed by overlapping adjacent unit patterns 15. A portion of a certain unit pattern 15 and a portion of an adjacent unit pattern 15 overlap in a direction perpendicular to the base material 11 (layering direction) with a dielectric material in between.

Unlike the configuration in which a capacitor element is soldered between conductor patches, the capacitive coupling portion 12 is formed using the same coating film as the unit pattern 15. By selecting the overlapping area of the unit patterns 15, the thickness of the dielectric layer inserted therebetween, and the dielectric constant, a desired amount of capacitive coupling can be obtained. The base material 11 on which the unit patterns 15 are formed may be a dielectric base material or a base material in which a dielectric film is formed on a metal foil. The base material 11 may be an inorganic dielectric material such as a thin glass plate, or may be an insulating resin film. Alternatively, a resin film formed by a printing method such as inkjet, screen printing, or spraying may be used. When a resin material is used as the base material 11, a flexible electromagnetic wave absorber/reflector 10 is obtained, and the electromagnetic wave absorber/reflector 10 can be applied to curved surfaces, curved surfaces, etc.

The vertical and horizontal sizes and center-to-center distance of the unit pattern 15 are generally determined according to the wavelength of the target frequency. In contrast, in the embodiment, the capacitive coupling portion 12 is formed using a thin coated film, and the magnitude of the capacitive coupling can be set to a desired value. Therefore, by shifting the resonance frequency of the electromagnetic wave absorber/reflector 10 to the lower frequency side while maintaining the pattern size for higher frequencies, a thinner and smaller electromagnetic wave absorber/reflector 10 is realized.

When the electromagnetic wave absorber/reflector 10 is used as an electromagnetic wave absorber sheet, the entire structure including the capacitive coupling part 12 is Impedance is adjusted. When the reflection coefficient Γ approaches zero, the characteristic impedance of the electromagnetic wave absorber/reflector 10 apparently matches the impedance of air, which is the electromagnetic wave propagation medium. In this case, the incident electromagnetic waves are hardly reflected and are absorbed inside the electromagnetic wave absorber/reflector 10.

When the electromagnetic wave absorber/reflector 10 is used as a reflector, the impedance of the capacitive coupling portion 12 is adjusted so that the reflection coefficient Γ is maximized, that is, the impedance of the electromagnetic wave absorber/reflector 10 is apparently infinite. It's okay. Alternatively, the phase difference may be controlled so that the electromagnetic waves reflected by adjacent unit patterns 15 go in a desired direction. When the electromagnetic wave absorber/reflector 10 is used as a planar array antenna, the magnitude of capacitive coupling is determined so that radio waves are radiated and received with maximum power at the target frequency.

If there is no capacitive coupling portion 12, frequency selectivity is determined by the size and pitch of the unit pattern 15, and the unit pattern 15 must be made large for low frequencies of several GHz or less. In the embodiment, by forming the capacitive coupling part 12 with a part of the unit pattern 15 and realizing a desired size of capacitive coupling, the unit pattern 15 can be kept small in size and correspond to a lower frequency band. be able to.

In the example of FIG. 2, a square conductor pattern is used as the unit pattern 15, but the shape of the unit pattern 15 is not limited to a square. Triangular or hexagonal conductor patterns are arranged in a repeating periodic arrangement, and capacitive coupling portions 12 are provided between adjacent unit patterns in which parts of each unit pattern overlap in a direction perpendicular to the base material 11. It's okay. Alternatively, the capacitive coupling portions 12 may be provided between adjacent unit patterns 15 by arranging unit patterns of circles, ellipses, and polygons in a lattice arrangement or alternately.

The capacitive coupling portion 12 does not need to be provided between all adjacent unit patterns 15, but may be provided between at least two adjacent unit patterns 15. The magnitudes of the capacitive couplings provided in the electromagnetic wave absorber/reflector 10 do not need to be the same, and multiple types of capacitive couplings may be provided. These specific configurations will be explained in the following embodiments.

<First embodiment>
FIG. 3 is a schematic plan view of the electromagnetic wave absorber/reflector 10 of the first embodiment. The electromagnetic wave absorber/reflector 10 employs the basic configuration shown in FIG. On the surface of the base material 11, unit patterns 15 of conductors having substantially the same size and shape are periodically formed. "Substantially the same" means that the size and shape are set to be the same in terms of design, and may include manufacturing errors within an allowable range.

At least some of the plurality of unit patterns 15 have arms 151 extending toward adjacent unit patterns 15. An arm 151 of a certain unit pattern 15 and an arm 151 of an adjacent unit pattern 15 overlap in the stacking direction with the dielectric layer 13 interposed therebetween. The capacitive coupling portion 12 is formed by the upper and lower arms 151 that overlap in the stacking direction and the dielectric layer 13 sandwiched between them.

The entire unit pattern 15 including the arm 151 may be formed by a printing method such as inkjet or screen printing. Alternatively, the main body portion of the unit pattern 15 excluding the arms 151 may be formed by room temperature sputtering or the like, and the capacitive coupling portion 12 may be formed by a printing method. Among the printing methods, the inkjet method is advantageous because it can discharge a conductive material and an insulating material to a precise position on the base material 11 at a desired timing. Even when using a flexible polymeric material for the base material 11, a printing method that can easily form a pattern at room temperature is advantageous.

FIG. 4 shows a configuration example of the electromagnetic wave absorber/reflector 10 in FIG. 3 taken along the line AA. In the electromagnetic wave absorber/reflector 10A of FIG. 4, the dielectric layer 13 is provided only in the region where the unit patterns 15 overlap. The unit pattern 15 provided on the base material 11 has an arm 151 at the end, and the arm 151 overlaps the arm 151 of an adjacent unit pattern. A dielectric layer 13 is inserted between the lower arm 151 and the upper arm 151 to form a capacitive coupling portion 12 and to electrically isolate adjacent unit patterns 15 .

FIG. 5 shows another configuration example of the electromagnetic wave absorber/reflector 10 taken along the line AA in FIG. 3. In the electromagnetic wave absorber/reflector 10B of FIG. 5, the dielectric layer 13 is formed on the entire surface of the base material 11. A unit pattern 15-1 provided below the dielectric layer 13 and a unit pattern 15-2 provided above the dielectric layer 13 overlap each other at the arm 151 with the dielectric layer 13 sandwiched therebetween. Capacitive coupling portion 12 is formed between lower arm 151 and upper arm 151 sandwiching dielectric layer 13, and adjacent unit patterns 15 are electrically isolated.

FIG. 6 shows still another configuration example of the AA cross section of the electromagnetic wave absorber/reflector 10 of FIG. The electromagnetic wave absorber/reflector 10C shown in FIG. 6 has a ground layer 16 on the back surface of the base material 11 in addition to the structure shown in FIG. Capacitance is formed between each unit pattern 15 and the ground layer 16, and the magnitude of phase delay can be controlled for each unit pattern 15. In FIG. 6, the ground layer 16 is provided in the structure of FIG. 4, but it goes without saying that the ground layer 16 may be applied to the structure of FIG.

7A to 7C show the manufacturing process of the electromagnetic wave absorber/reflector 10A of FIG. 4 in a top view and a cross-sectional view. In FIG. 7A, a first group of unit patterns 15-1 is formed on the base material 11. When the final unit patterns 15 are arranged in a grid as shown in FIG. 3, the first group of unit patterns 15-1 are formed in an alternate arrangement.

In FIG. 7B, the dielectric layer 13 is partially provided to cover the arms 151 of the unit patterns 15-1 of the first group. Dielectric layer 13 may be formed on arm 151 by inkjet. The dielectric layer 13 does not need to be provided on all arms 151 and may be formed only on selected arms 151.

In FIG. 7C, a second group of unit patterns 15-2 is formed, and an electromagnetic wave absorber/reflector 10A is obtained. The arm 151 of the unit pattern 15-2 of the second group is formed on the dielectric layer 13, and the arm 151 of the unit pattern 15-1 of the first group formed under the dielectric layer 13 in the stacking direction. overlap. The entire unit pattern 15-2 of the second group may be formed by inkjet, or the area of unit pattern 15-2 except the arm 151 may be formed by screen printing, and the arm 151 may be formed by inkjet.

By adjusting the width of the arms 151 or their overlapping lengths, the area of the capacitive coupling portion 12 can be adjusted. The thickness of the dielectric layer 13 can be controlled by controlling the film formation process. Therefore, capacitive coupling of a desired magnitude can be formed between two adjacent unit patterns 15. A ground layer 16 (see FIG. 6) may be formed on the back surface of the base material 11 before the step in FIG. 7A or after the step in FIG. 7C.

8A to 8C show the manufacturing process of the electromagnetic wave absorber/reflector 10B of FIG. 5 in a top view and a cross-sectional view. In FIG. 8A, a first group of unit patterns 15-1 is formed on the base material 11. When the final unit patterns 15 are arranged in a grid as shown in FIG. 3, the first group of unit patterns 15-1 are formed in an alternate arrangement. The unit pattern 15-1 is formed by an appropriate method such as a printing method or room temperature sputtering.

In FIG. 8B, a dielectric layer 13 is formed to cover the entire surface of the base material 11 on which the unit patterns 15-1 are formed. The dielectric layer 13 may be formed as a coating film by a printing method, or may be formed by a method other than the printing method. In FIG. 8C, a second group of unit patterns 15-2 is formed on the dielectric layer 13 to obtain an electromagnetic wave absorber/reflector 10B. The arm 151 of the unit pattern 15-2 of the second group overlaps the arm 151 of the lower unit pattern 15-1 in the stacking direction with the dielectric layer 13 in between.

The entire second group of unit patterns 15-2 may be formed by a printing method. The area other than the arm 151 of the unit pattern 15-2 may be formed by screen printing, and the arm 151 may be formed by an inkjet method or a spray method. A desired amount of capacitive coupling can be achieved by adjusting at least one of the width of the arm 151 and the length of the overlap to adjust the area of the capacitive coupling portion 12, or by controlling the thickness of the dielectric layer 13. can be formed. A ground layer 16 (see FIG. 6) may be formed on the back surface of the base material 11 before the step in FIG. 8A or after the step in FIG. 8C.

9A is a schematic cross-sectional view showing an example of a configuration for increasing the capacity of the electromagnetic wave absorber/reflector in FIG. 4, and FIG. 9B is a schematic cross-sectional view showing an example of the configuration for increasing the capacity of the electromagnetic wave absorber/reflector in FIG. By further overlapping the dielectric layer 13D (or 13E) and the conductive layer 15-3 on the capacitive coupling portion 12, the capacitance can be increased. In this case, similar to a multilayer capacitor, the capacitance C is
C=ε(S/d)N[F]
It is expressed as Here, S is the area where the conductive layers overlap in the stacking direction, d is the interval between the conductive layers in the stacking direction, ε is the dielectric constant, and N is the number of stacked layers. By increasing the number of laminated layers, capacitance can be increased.

In the first embodiment, the area of the capacitive coupling portion 12 can be increased by adjusting at least one of the width of the arm 151 of the unit pattern 15 and the overlapping length. Further, the dielectric layer 13 can be formed thinly within a range where electrical insulation between adjacent unit patterns 15 is ensured. By increasing the overlapping area of the arms 151 or decreasing the thickness of the dielectric layer 13, capacitive coupling can be increased and the resonance frequency can be shifted to the lower frequency side. The capacitive coupling portion 12 is formed during the formation process of the unit pattern 15. The height of the capacitive coupling portion 12 formed in the thin film process from the surface of the base material 11 is from several μm to several tens of μm or less. Compared to a configuration in which capacitor elements are soldered together, a thin capacitive coupling is formed through a simple process. The electromagnetic wave absorber/reflector 10 (or 10A to 10E) can be adjusted to a desired frequency while keeping the size of the unit pattern 15 small.

<Second embodiment>
FIG. 10 shows an example of capacitor adjustment of the electromagnetic wave absorber/reflector 20 of the second embodiment. In the first embodiment, the area of the capacitive coupling portion 12 is controlled by adjusting at least one of the width of the arms 151 of adjacent unit patterns 15 and the length of their overlap. In FIG. 10, the magnitude of capacitive coupling is adjusted by partially changing the shape of the arm.

The electromagnetic wave absorber/reflector 20 has a plurality of unit patterns 25 arranged periodically on the surface of the base material 21 . At least some of the plurality of unit patterns 25 have arms 251 extending toward adjacent unit patterns 25. The arms 251 of two adjacent unit patterns 25 overlap in the stacking direction (direction perpendicular to the base material 11) with the dielectric layer 13 in between, and a capacitive coupling portion 22 is formed.

The arm 251 includes a base 252 connected to the outer periphery of the unit pattern 15 and a wide portion 253 at the tip of the base 252. The wide portion 253 overlaps the wide portion 253 of the arm 251 of the adjacent unit pattern 25 in the stacking direction to form the capacitive coupling portion 22 . By increasing the area of the wide portion 253, capacitive coupling can be increased. Alternatively, the capacitive coupling may be increased by reducing the thickness of the dielectric layer 13.

Similar to the first embodiment, the unit patterns 25 and the dielectric layer 13 are formed easily and with high alignment accuracy by a printing method such as an inkjet method.

FIG. 11 shows an example of capacitor adjustment of the electromagnetic wave absorber/reflector 30. In the first embodiment, the overlap between two adjacent unit patterns 15 is adjusted by the length of the overlap in the direction in which the arm 151 extends. In FIG. 11, the magnitude of capacitive coupling is adjusted by adjusting the overlap of the arms 351 in the width (w) direction.

The electromagnetic wave absorber/reflector 30 has a plurality of unit patterns 35 arranged periodically on the surface of the base material 31 . At least some of the plurality of unit patterns 35 have arms 351 extending toward adjacent unit patterns 35. A portion of the arm 351 overlaps a portion of the arm 351 of an adjacent unit pattern 35 in the stacking direction with the dielectric layer 13 in between, and a capacitive coupling portion 32 is formed.

By changing the overlapping amount of the arms 351 in the width (w) direction, the area of the capacitive coupling portion 32 changes, but the length L (size) of the unit pattern 35 in the vertical and horizontal directions does not change. A change in the length L of the unit pattern 35 affects the characteristic frequency. The magnitude of capacitive coupling can be changed by keeping the length L of the unit pattern 35 constant in the vertical and horizontal directions. This suppresses the influence on the characteristic frequency due to size variation of the unit pattern 35, and facilitates control of the resonance frequency by the capacitive coupling section 32.

Similar to the first embodiment, the unit patterns 25 and the dielectric layer 13 can be easily formed with high alignment accuracy using a printing method such as an inkjet method. The amount of overlap in the width direction between the lower arm 351-1 and the upper arm 351-2 can be controlled with the alignment accuracy of the inkjet. The amount of overlap in the width direction between adjacent arms does not necessarily have to be constant, and only some arms may be overlapped in the width direction with the dielectric layer 13 interposed therebetween. As a result, a thin electromagnetic wave absorbing/reflecting body 30 capable of supporting a low frequency band of several GHz or less can be realized while suppressing an increase in the unit pattern 35.

<Third embodiment>
FIG. 12 shows a configuration example of the electromagnetic wave absorber/reflector 40 of the third embodiment. In the third embodiment, capacitive couplings of different sizes are provided. By providing the electromagnetic wave absorber/reflector 40 with multiple types of capacitive coupling, the bandwidth of the electromagnetic waves to be absorbed or reflected can be widened.

The electromagnetic wave absorber/reflector 40 has a plurality of unit patterns 45 arranged periodically on the surface of the base material 41 . Some or all of the plurality of unit patterns 45 have at least one of arms 451 and 452 extending toward the adjacent unit pattern 45. The width w of arms 451 and 452 may be different. By changing the width w of the arms 451 and 452 or the overlapping length in the direction orthogonal to the arm width w, the area of the capacitive coupling portion can be changed.

For example, capacitive coupling parts 42a, 42b, and 42c having different capacitances may be provided in order from the one with the smallest overlapping area. The number of types of capacitive coupling parts is not limited to three types, and may be two types or four or more types. By gradually changing the magnitude of capacitive coupling, it is possible to widen the target frequency band.

The configuration of FIG. 12 can also accommodate a frequency band of several GHz or less by shifting the resonance frequency to the lower frequency side while keeping the size of the unit pattern 45 small.

FIG. 13 shows an example of the configuration of the electromagnetic wave absorber/reflector 50. In FIG. 13, horizontal capacitive coupling across an air layer with respect to the unit pattern plane is used as part of the plurality of types of capacitive coupling. Unit patterns that form capacitive coupling in the horizontal direction do not need to overlap in the stacking direction. The electromagnetic wave absorber/reflector 50 has a plurality of unit patterns 55 arranged periodically on the surface of the base material 51 . Some or all of the plurality of unit patterns 55 have arms 551 extending toward the adjacent unit patterns 55. A first capacitive coupling portion 52a is formed at a location where the arms 551 of two adjacent unit patterns 55 overlap in the stacking direction with the dielectric layer 13 in between. A second capacitive coupling portion 52b is formed by a pair of arms 551 sandwiching a gap 552 at a location where the arms 551 of two adjacent unit patterns do not overlap in the stacking direction, that is, at a location where they are separated in the in-plane direction. By changing the width of the gap 552, the types of capacitive coupling may be further increased.

The configuration of FIG. 13 can also accommodate a frequency band of several GHz or less by shifting the resonance frequency to the lower frequency side while keeping the size of the unit pattern 55 small. Note that, as shown in FIG. 14, an insulating layer 131 may be applied to the gap 552 to suppress dielectric breakdown while forming the second capacitive coupling portion 52b. With this configuration, electrical insulation between adjacent arms 551 can be ensured, and capacitive coupling portions can be realized at intervals narrower than the accuracy limit of the selected construction method. This makes it possible to increase the selectivity of wavelengths that can be designed.

<Evaluation of absorption characteristics (calculated values)>
FIG. 15 shows an evaluation model using a cross pattern. The size of the cross is L, the line width of the cross is w, the overlapping length of the lower layer unit pattern 15-1 and the upper layer unit pattern 15-2 is G, the thickness of the base material 11 is t_film, and the conductivity forming the unit pattern is The thickness of the layer is t_metal, the thickness of the dielectric layer 13 between the base material 11 and the lower unit pattern 15-1 is d1, and the dielectric layer is between the lower unit pattern 15-1 and the upper unit pattern 15-2. Let the thickness of layer 13 be d2. When the unit pattern 15-1 in the lower layer and the unit pattern 15-2 in the upper layer overlap when viewed in the direction perpendicular to the plane, the overlap length G, that is, the amount of overlap in the in-plane direction between the unit patterns in the upper layer and the lower layer is correct. Take it so that If there is a gap in the in-plane direction as shown in FIG. 14, the overlap length G will be a negative value.

Regarding the above structure, the dielectric constant ε of the base material 11 is 3.4, the dielectric loss tangent tan δ is 0.004, the dielectric constant ε of the dielectric layer 13 is 3.02, the dielectric loss tangent tan δ is 0.028, and the dielectric constant of the conductive layer 13 is The calculation results are shown in FIGS. 16 and 17, assuming that the conductivity is 2×10^7 [Siemens/m]. The calculation is based on the amount of absorption determined from the intensity of reflection of electromagnetic waves incident on the pattern surface.

In FIG. 16, L=1.0 [mm], w=0.3 [mm], t_metal=0.2 [μm], t_film=100 [μm], d=1.6 [μm], d2=10 It is a graph showing the relationship between frequency and absorption amount when the overlap length G is changed from 0 [mm] to 0.30 [mm] when [μm]. The larger the overlapping length G between the lower layer unit pattern 15-1 and the upper layer unit pattern 15-2, the lower the absorption frequency. Therefore, by adjusting the overlapping length G according to the design, an absorber with a desired absorption frequency can be obtained. can be obtained.

If the vertical direction of the metal pattern is not considered, the unit cell size of the repeating pattern in the horizontal direction is LG = 0.7 mm or more and 1.0 mm or less, which is at least 1/20 of the absorption peak wavelength. It is. Further, the thickness is approximately 112 μm, which is at least 1/120 of the wavelength of the frequency peak, making it possible to achieve a thinner structure.

In FIG. 17, L=1.0 [mm], w=0.7 [mm], t_metal=0.2 [μm], t_film=100 [μm], d=1.6 [μm], G=0 .1 [mm] is a graph showing the relationship between frequency and absorption amount when d2 is changed from 5 [μm] to 20 [μm]. The absorption frequency decreases as the thickness d2 of the dielectric layer 13 between the lower layer unit pattern 15-1 and the upper layer unit pattern 15-2 decreases, so by adjusting d2 according to the design, a desired absorption frequency can be obtained. An absorber can be obtained. Furthermore, by varying the thickness d2 of the dielectric layer 13 that separates the upper and lower unit patterns, the absorption peak of the absorber can be made broad. The "variations" here include manufacturing variations, process variations, and variations given by design. For example, variations in landing position and film thickness during film formation by inkjet printing can be utilized for broad absorption characteristics. The variation provided in the design includes control of the amount of variation in the manufacturing process. For example, by performing a design in which d2 is varied in the range of 10 [μm] to 15 [μm], an absorber having absorption at approximately 24 to 32 [GHz] can be obtained. In addition to the thickness d2 of the dielectric layer 13 between the upper and lower unit patterns, by providing variations in the size of the unit patterns, the area of the capacitive coupling part, the thickness of the base material 11, and the thickness of the conductive layer, broad can be absorbed.

If the vertical direction of the metal pattern is not considered, the unit cell size of the repeating pattern in the horizontal direction is LG=0.9 mm, which is at least 1/19 of the absorption peak wavelength. Further, the thickness is approximately 112 μm, which is at least 1/150 of the wavelength of the frequency peak, making it possible to achieve a thinner structure.

Although the electromagnetic wave absorber/reflector of the embodiment has been described above based on a specific configuration example, the configuration of the electromagnetic wave absorber/reflector is not limited to the above-mentioned example. The features of each configuration example may be combined with each other as long as there is no contradiction. For example, the calculation results shown in FIGS. 16 and 17 using the evaluation model shown in FIG. 15 apply to any of the configurations of the first to third embodiments. Broad absorption characteristics can be achieved by providing designed variations in at least one of the thickness of the dielectric layer 13, the size of the unit pattern 15, the area of the capacitive coupling portion, and the thickness of the base material 11.

The horizontal capacitive coupling portion 52b using the gap 552 in FIG. 13 may be combined with the electromagnetic wave absorbing/reflecting body 20, 30, or 40. In that case, in order to prevent the gap 552 from becoming electrically conductive depending on printing accuracy, an insulating layer 131 may be provided in the gap 552 as shown in FIG. 14. The cross-sectional shape of the capacitive coupling part in the stacking direction of the electromagnetic wave absorbers/reflectors 20, 30, 40, and 50 may adopt either FIG. 4 or FIG. A layer 16 may also be provided. The shapes of the unit patterns 25, 35, 45, 55 of the electromagnetic wave absorbers/reflectors 20, 30, 40, 50 are not limited to rectangles, and may be circular (including perfect circles and ellipses), polygons other than rectangles (for example, triangles, (hexagonal, cross-shaped, etc.). When the unit patterns 25, 35, 45, and 55 have a hexagonal shape, a plurality of unit patterns can be arranged in a honeycomb shape as a periodic arrangement.

When applying the electromagnetic wave absorber/reflector of the embodiment to a planar or curved array antenna, a feeding point is provided in each unit pattern. The feeding point is provided at a position that matches the impedance of the corresponding unit pattern. Generally, the oscillation frequency (resonance frequency) of a two-dimensional array antenna is determined by the size (length of one side) of the conductor pattern and the spacing between the patterns, and at low frequencies of several GHz or less, the conductor pattern becomes larger. . On the other hand, by using the capacitive coupling structure of the embodiment, it is possible to support the emission and reception of radio waves of several GHz or less without increasing the size of the conductive pattern.

In the manufacturing process of the electromagnetic wave absorber/reflector, at least a portion of the unit pattern of the conductor is formed by a printing method. The arm constituting the capacitive coupling portion may be formed by an inkjet method using conductive ink as the conductive material. Furthermore, at least a portion of the dielectric layer 13 is formed by a printing method. The portion of the dielectric layer 13 that constitutes the capacitive coupling portion may be formed by an inkjet method using insulating ink such as polyimide-based ink.

In either case, by controlling the degree of overlap between adjacent unit patterns (including the non-overlapping gap 552) or the thickness of the dielectric layer, the desired capacitance of the thin film structure can be achieved between the unit patterns. A bond can be formed. As a result, it is possible to shift the target frequency to the lower frequency side and realize a thin electromagnetic wave absorbing/reflecting body in which the unit pattern is suppressed from increasing in size.

The electromagnetic wave absorbing/reflecting body can be applied to the housing of a smartphone, for example, as an electromagnetic wave absorbing sheet. An adhesive layer may be provided on the back surface (ground layer side) of the base material and the adhesive layer may be attached to the inside of the casing. Since the size of the unit pattern is suppressed, it is easy to introduce it into electronic devices such as small smartphones and mobile phones.

The above disclosure may take the following aspects.
(Section 1)
base material and
a unit pattern of conductors provided periodically on the surface of the base material;
a part of the unit pattern overlaps a part of the adjacent unit pattern in the lamination direction of the base material with a dielectric layer interposed therebetween;
Electromagnetic wave absorber/reflector.
(Section 2)
The unit pattern has an arm extending toward the adjacent unit pattern, and the arm overlaps the arm of the adjacent unit pattern in the stacking direction with the dielectric layer interposed therebetween to form a capacitive coupling portion. There is,
Item 1. Electromagnetic wave absorber/reflector according to item 1.
(Section 3)
The capacitive coupling portion includes a first capacitive coupling portion that overlaps in the stacking direction with a first area, and a second capacitive coupling portion that overlaps in the stacking direction and has a second area different from the first area. ,
Item 2. Electromagnetic wave absorber/reflector according to item 2.
(Section 4)
The capacitive coupling portion includes a first capacitive coupling portion that overlaps in the stacking direction, and a second capacitive coupling portion that is formed in a gap separating two adjacent unit patterns in an in-plane direction.
Item 2. Electromagnetic wave absorber/reflector according to item 2.
(Section 5)
the second capacitive coupling section includes an insulating layer in the gap;
Item 4. Electromagnetic wave absorber/reflector according to item 4.
(Section 6)
the arm overlaps the arm of the adjacent unit pattern in the length direction;
Item 2. Electromagnetic wave absorber/reflector according to item 2.
(Section 7)
the arm overlaps the arm of the adjacent unit pattern in the width direction;
Item 2. Electromagnetic wave absorber/reflector according to item 2.
(Section 8)
The arm has a wide part where the width of the arm is increased, and the arm overlaps the arm of the adjacent unit pattern at the wide part.
Item 2. Electromagnetic wave absorber/reflector according to item 2.
(Section 9)
the capacitive coupling portion is formed of conductive ink;
9. The electromagnetic wave absorber/reflector according to any one of items 2 to 8.
(Section 10)
having a designed variation in at least one of the thickness of the dielectric layer, the size of the unit pattern, the area of the capacitive coupling part, and the thickness of the base material;
10. The electromagnetic wave absorber/reflector according to any one of items 2 to 9.
(Section 11)
base material and
a first group of unit patterns formed of a first conductor on the surface of the base material;
a dielectric layer covering at least a portion of the first group of unit patterns;
a second group of unit patterns provided on the dielectric layer and formed of a second conductor so as not to overlap with the first group of unit patterns in the stacking direction with the dielectric layer in between; ,
An electromagnetic wave absorber/reflector with
(Section 12)
The electromagnetic wave absorber/reflector according to any one of Items 1 to 11,
a power feeding point provided in the unit pattern;
antenna with.
(Section 13)
Forming a first group of unit patterns with a conductor on the surface of the base material,
forming a dielectric layer covering at least a portion of the first group of unit patterns;
forming a second group of unit patterns of a conductor on the dielectric layer, with the dielectric layer sandwiched therebetween, so as to overlap the part of the unit patterns of the first group in the stacking direction;
Method of manufacturing electromagnetic wave absorber/reflector.
(Section 14)
Variations in at least one of the thickness of the dielectric layer, the size of the unit patterns of the first group, the size of the unit patterns of the second group, the area of the regions overlapping in the lamination direction, and the thickness of the base material are controlled. have it,
14. A method for producing an electromagnetic wave absorber/reflector according to item 13.
(Section 15)
Forming a first group of unit patterns with a conductor on the surface of the base material,
forming a dielectric layer covering at least a portion of the first group of unit patterns;
forming a second group of unit patterns of a conductor on the dielectric layer, with the dielectric layer in between, so as not to overlap the part of the unit patterns of the first group in the stacking direction; ,
Method of manufacturing electromagnetic wave absorber/reflector.

10, 10A to 10E, 20, 30, 40, 50 Electromagnetic wave absorber/reflector 11, 21, 31, 41, 51 Base material 12, 22, 32, 42a to 42c, 52a, 52b Capacitive coupling part 13 Dielectric layer 131 Insulating layer 15, 15-1, 15-2, 25, 35, 45, 55 Unit pattern 151, 251, 351, 451, 452, 551 Arm 552 Gap

Patent No. 4926099

Bui Xuan Khuyen, et al., "Ultra-subwavelength thickness for dual/triple-band methamaterial absorber at very low frequency", Sci Rep. (2018) 8(1):11632

Claims (15)

base material and
a unit pattern of conductors provided periodically on the surface of the base material;
a part of the unit pattern overlaps a part of the adjacent unit pattern in the lamination direction of the base material with a dielectric layer interposed therebetween;
Electromagnetic wave absorber/reflector. The unit pattern has an arm extending toward the adjacent unit pattern, and the arm overlaps the arm of the adjacent unit pattern in the stacking direction with the dielectric layer interposed therebetween to form a capacitive coupling portion. There is,
The electromagnetic wave absorber/reflector according to claim 1. The capacitive coupling portion includes a first capacitive coupling portion that overlaps in the stacking direction with a first area, and a second capacitive coupling portion that overlaps in the stacking direction and has a second area different from the first area. ,
The electromagnetic wave absorber/reflector according to claim 2. The capacitive coupling portion includes a first capacitive coupling portion that overlaps in the stacking direction, and a second capacitive coupling portion that is formed in a gap separating two adjacent unit patterns in an in-plane direction.
The electromagnetic wave absorber/reflector according to claim 2. the second capacitive coupling section includes an insulating layer in the gap;
The electromagnetic wave absorber/reflector according to claim 4. the arm overlaps the arm of the adjacent unit pattern in the length direction;
The electromagnetic wave absorber/reflector according to claim 2. the arm overlaps the arm of the adjacent unit pattern in the width direction;
The electromagnetic wave absorber/reflector according to claim 2. The arm has a wide part where the width of the arm is increased, and the arm overlaps the arm of the adjacent unit pattern at the wide part.
The electromagnetic wave absorber/reflector according to claim 2. the capacitive coupling portion is formed of conductive ink;
The electromagnetic wave absorber/reflector according to claim 2. There is variation in at least one of the thickness of the dielectric layer, the size of the unit pattern, the area of the capacitive coupling part, and the thickness of the base material,
The electromagnetic wave absorber/reflector according to any one of claims 2 to 9. base material and
a first group of unit patterns formed of a first conductor on the surface of the base material;
a dielectric layer covering at least a portion of the first group of unit patterns;
a second group of unit patterns provided on the dielectric layer and formed of a second conductor so as not to overlap with the first group of unit patterns in the stacking direction with the dielectric layer in between; ,
An electromagnetic wave absorber/reflector with The electromagnetic wave absorber/reflector according to claim 1 or 11;
a power feeding point provided in the unit pattern;
antenna with. Forming a first group of unit patterns with a conductor on the surface of the base material,
forming a dielectric layer covering at least a portion of the first group of unit patterns;
forming a second group of unit patterns of a conductor on the dielectric layer so as to overlap the part of the first group of unit patterns in the stacking direction with the dielectric layer in between;
Method of manufacturing electromagnetic wave absorber/reflector. Variation in at least one of the following: the thickness of the dielectric layer, the size of the unit patterns of the first group, the size of the unit patterns of the second group, the area of the regions overlapping in the lamination direction, and the thickness of the base material. have it,
A method for manufacturing an electromagnetic wave absorber/reflector according to claim 13. Forming a first group of unit patterns with a conductor on the surface of the base material,
forming a dielectric layer covering at least a portion of the first group of unit patterns;
A second group of unit patterns is formed of a conductor on the dielectric layer, with the dielectric layer in between, so as not to overlap the part of the first group of unit patterns in the stacking direction. ,
Method of manufacturing electromagnetic wave absorber/reflector.

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