Electromagnetic wave absorber evaluation apparatus and electromagnetic wave absorber evaluation method

Abstract

To provide an electromagnetic wave absorber evaluation device and an electromagnetic wave absorber evaluation method capable of precisely evaluating behavior of an electromagnetic wave absorber for millimeter wave band or submillimeter wave band electromagnetic waves.SOLUTION: In an electromagnetic wave absorber evaluation device 1, width (a), height (b), and length L of a casing 2 for housing a board 3 having microstrip lines 4, 5 for inputting and outputting signals, and an evaluation frequency ft obtained by the following formula (1) satisfies the following formula (2) in a frequency domain of 20GHz or higher, wherein α is expressed by the following formula (5).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electromagnetic wave absorber evaluation apparatus and an electromagnetic wave absorber evaluation method, and more particularly to an electromagnetic wave absorber evaluation apparatus and an electromagnetic wave absorber evaluation method for evaluating the characteristics of an electromagnetic wave absorber in the millimeter wave band or the sub-millimeter wave band. [Background technology]

[0002] In high-frequency communication devices equipped with processing circuits that process input signals and output them, a problem arises when coupling (electromagnetic field coupling) occurs between the input signal and the output signal via electromagnetic waves. In particular, when the processing circuit is housed in a metal enclosure, such coupling is exacerbated by the propagation and resonance of electromagnetic waves within the enclosure. As communication frequencies increase, the coupling problem becomes more pronounced. In recent years, many communication devices utilizing frequencies in the millimeter-wave range have been put on the market, but in these communication devices that communicate in high-frequency ranges such as the millimeter-wave and quasi-millimeter-wave ranges, the coupling problem within the enclosure becomes serious.

[0003] In high-frequency communication equipment, one method used to reduce coupling between signals in a circuit, such as between input and output signals, is to install an electromagnetic wave absorber in the part that covers the processing circuit, such as the inside of a metal casing. The electromagnetic wave absorber can be attached to the inner wall surface of the casing in the form of a sheet, or molded into a case and placed inside the casing. Typical materials for such electromagnetic wave absorbers include particles made of soft magnetic material dispersed in a matrix made of resin material or the like.

[0004] The electromagnetic wave absorption efficiency of an electromagnetic wave absorber depends heavily on the specific constituent materials, thickness, and the frequency of the electromagnetic waves to be absorbed. Therefore, when installing an electromagnetic wave absorber in a high-frequency communication device, it is important to confirm in advance whether the electromagnetic wave absorber to be used can sufficiently absorb the electromagnetic waves of the frequency to be absorbed and sufficiently suppress coupling within the enclosure, and to design the material composition and thickness of the electromagnetic wave absorber so that it can sufficiently absorb the electromagnetic waves of the frequency to be absorbed. To do this, it is necessary to actually place the electromagnetic wave absorber inside the enclosure and evaluate the electromagnetic wave absorption efficiency. As an example of such evaluation, Patent Document 1 describes an example in which an electromagnetic wave absorber made of a resin composite containing iron powder, ceramic powder, and synthetic resin is attached to the lid of a high-frequency circuit package, which has a package base and a lid attached to the package base, and the power transmission coefficient S of the high-frequency circuit package is evaluated. 21 This is being evaluated in the range of 0.1 GHz to 13.1 GHz. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2004-143347 [Overview of the project] [Problems that the invention aims to solve]

[0006] As described above, actually placing an electromagnetic wave absorber inside the enclosure and evaluating its electromagnetic wave absorption efficiency is important for verifying the performance of the electromagnetic wave absorber and for developing high-performance electromagnetic wave absorbers. In particular, in high-frequency regions such as the millimeter wave and sub-millimeter wave bands, the effects of coupling become serious, so there is a strong need to reduce coupling by using an electromagnetic wave absorber with sufficiently high electromagnetic wave absorption efficiency. However, due to the short wavelength of electromagnetic waves in the millimeter wave and sub-millimeter wave bands, they tend to exhibit complex behavior within the enclosure due to the occurrence of random resonances at many frequencies and the influence of structures inside the enclosure. If an actual device such as the high-frequency circuit package used in the embodiment of Patent Document 1 is used, the power transmission coefficient obtained is expected to show a complex frequency dependence. Furthermore, as will be explained below, as the inventor has clarified, even when using a test apparatus that is simpler than that of an actual device, the electromagnetic waves may exhibit complex behavior depending on the design of the test apparatus.

[0007] For example, as shown in Figure 1, a substrate 3 on which input and output microstrip lines 4 and 5 are formed is housed in a casing 2 which has a case-shaped electromagnetic wave absorber (not shown) inside. A millimeter-wave signal is input from the input microstrip line 4, and the electromagnetic wave transmittance S is measured through the output microstrip line 5. 21 The measurement results are shown in Figure 4(a). The dimensions of the housing are internal dimensions: width a = 22.6 mm, height b = 10.8 mm, and length L = 63.5 mm. As the electromagnetic wave absorber, a material in which soft magnetic powder (SUS 410L) is dispersed in resin (acrylic rubber) is used. The figure shows the measurement results when no electromagnetic wave absorber is installed in the housing, and when electromagnetic wave absorbers with soft magnetic powder content of 15 vol% and 40 vol% are installed, respectively. In Figure 4(a), the electromagnetic wave transmittance S 21The graph shows a complex shape with violent up-and-down fluctuations. Furthermore, it is difficult to clearly recognize differences in behavior that outweigh the violent up-and-down fluctuations among the three graphs, which differ in the presence or absence of electromagnetic wave absorbers and the content of soft magnetic powder, making it impossible to evaluate the effect of electromagnetic wave absorption by the electromagnetic wave absorbers. Moreover, Figure 4(b) shows the results of a simulation using electromagnetic field analysis by the finite element method, and violent up-and-down fluctuations are also observed in this graph. This suggests that the complex graph shape obtained from the measurements in Figure 4(a) is not due to accidental events such as experimental noise, but rather to essential causes such as the occurrence of electromagnetic wave resonance at multiple frequencies and the influence of structures within the enclosure.

[0008] Thus, in the millimeter-wave and sub-millimeter-wave regions, meaningful information may not be obtained even if one attempts to evaluate the performance of electromagnetic wave absorbers through actual measurements. For example, it may be difficult to obtain clear information on how much an electromagnetic wave absorber absorbs electromagnetic waves of a particular frequency. However, in high-frequency communication equipment, electromagnetic wave absorbers are required to sufficiently absorb electromagnetic waves of a predetermined frequency, and in order to select and design an appropriate electromagnetic wave absorber, it is necessary to clearly understand the behavior of the electromagnetic wave absorber with respect to electromagnetic waves of the target frequency.

[0009] The problem that this invention aims to solve is to provide an electromagnetic wave absorber evaluation device and an electromagnetic wave absorber evaluation method that can evaluate the behavior of an electromagnetic wave absorber with high accuracy to electromagnetic waves in the millimeter wave band or quasi-millimeter wave band. [Means for solving the problem]

[0010] To solve the above problems, the electromagnetic wave absorber evaluation apparatus and electromagnetic wave absorber evaluation method according to the present invention have the following configuration.

[0011] [1] The electromagnetic wave absorber evaluation device according to the present invention is a device for evaluating the characteristics of an electromagnetic wave absorber, having an inner dimension with a width a, a height b, and a length L, where b < a < L, and being made of a conductive material and capable of arranging the electromagnetic wave absorber inside, a substrate arranged inside the housing, an input microstrip line and an output microstrip line formed along the length direction of the housing on the substrate and spaced apart from each other in the length direction, a signal inspection unit capable of inputting an input signal having a frequency of 20 GHz or more from the input microstrip line and detecting an output signal output from the output microstrip line, and an evaluation frequency f obtained by the following formula (1) t satisfies the following formula (2) in the frequency range of 20 GHz or more. [Number] Here, m and p are each independently an integer of 1 or more. Also, n substances exist in the region surrounded by the housing, and the complex relative permeability of the i-th substance among the substances is μ ri , the complex relative permittivity is ε ri , the area occupied by the cross-section orthogonal to the length direction of the housing is S i , and α is expressed by formula (5) using μ r and ε r obtained from the following formulas (3) and (4). μ0 is the magnetic permeability of vacuum, and ε0 is the dielectric constant of vacuum. [Number]

[0012] [2] In the aspect of [1] above, it is preferable that termination resistors are respectively connected to the opposing ends in the input microstrip line and the output microstrip line.

[0013] [3] In the embodiment of [1] or [2] above, the substrate is arranged along the bottom surface of the housing, and the electromagnetic wave absorber can be arranged at least along the ceiling surface of the housing, opposite to the substrate, and the distance between the electromagnetic wave absorber arranged along the ceiling surface of the housing and the substrate is preferably 0.01 mm or more.

[0014] [4] In any one embodiment of [1] to [3] above, the input microstrip line and the output microstrip line each have a line width w, and the amount of displacement between them along the width direction of the housing is w / 2 or less.

[0015] [5] In any one embodiment of [1] to [4] above, the constituent material of the housing is preferably such that the electrical resistivity is 150 μΩ·cm or less, and the thickness of the portion covering at least the top and side surfaces of the substrate is 0.01 mm or more.

[0016] [6] In any one embodiment of [1] to [5] above, the input microstrip line and the output microstrip line are preferably located at a distance of b / 10 or more from the walls of the housing on both sides in the width direction of the housing.

[0017] [7] In any one embodiment of [1] to [6] above, the input microstrip line and the output microstrip line have their non-facing ends along the length direction of the housing, from the wall surface of the housing, to the evaluation frequency f t It is good if the wavelength is at least 1 / 6 of the corresponding wavelength.

[0018] [8] In the electromagnetic wave absorber evaluation method according to the present invention, an electromagnetic wave absorber evaluation apparatus according to any one of the above [1] to [7] is used, and the electromagnetic wave absorber to be evaluated is placed inside the housing, and the evaluation frequency f tThe characteristics of the electromagnetic wave absorber are evaluated by inputting an input signal in a frequency range including the specified frequency range through the input microstrip line and detecting the output signal output from the output microstrip line.

[0019] [9] In the embodiment described in [8] above, the characteristics of the electromagnetic wave absorber may be evaluated based on at least one of a comparison between the case in which the electromagnetic wave absorber is placed in the housing and the case in which it is not placed, and a comparison between the case in which different electromagnetic wave absorbers are placed.

[0020]

[10] In the embodiment of [8] or [9] above, the electromagnetic wave absorber is used in a high-frequency communication device having a communication frequency of 20 GHz or higher, and the communication frequency is the evaluation frequency f t In this case, it is advisable to design the dimensions of the housing so as to satisfy equations (1) and (2), and then evaluate the characteristics of the electromagnetic wave absorber in a frequency range that includes the communication frequency. [Effects of the Invention]

[0021] In the electromagnetic wave absorber evaluation apparatus according to the present invention having the configuration described in [1] above, when an input signal is input from the input microstrip line, if coupling occurs due to the propagation and resonance of electromagnetic waves within the housing, an output signal will be detected in the output microstrip line. If an electromagnetic wave absorber is installed inside the housing, the characteristics of the electromagnetic wave absorber, such as the electromagnetic wave absorption efficiency, can be evaluated based on the detected output signal. Here, the evaluation frequency f obtained by the above equation (1) is t However, by satisfying the above equation (2), the evaluation frequency f t The electromagnetic waves cause resonance within the enclosure. Therefore, the evaluation frequency f t If the characteristics of the electromagnetic wave absorber are evaluated, the output signal will be detected at high intensity due to resonance. This allows for evaluation of electromagnetic wave absorption, etc., at the evaluation frequency f tThe characteristics of electromagnetic wave absorbers in this region can be evaluated with high precision. Furthermore, since equation (2) is satisfied in the frequency range of 20 GHz and above, it becomes possible to perform high-precision evaluation of electromagnetic wave absorber characteristics using resonance in the millimeter-wave and quasi-millimeter-wave bands corresponding to the frequency range of 20 GHz and above.

[0022] In other words, even if the frequency used to evaluate the electromagnetic wave absorber is in the millimeter wave or quasi-millimeter wave region, the evaluation frequency f t By designing the dimensions of the enclosure appropriately according to equations (1) and (2) so that resonance occurs at the evaluation frequency f, the influence of internal structures and the effects of resonant occurrences at numerous frequencies can be avoided. t This allows for highly accurate characterization of electromagnetic wave absorbers. Furthermore, in equations (1) and (2) above, the contribution of materials present within the enclosure is expressed as the complex relative permeability μ of each material. ri and the complex relative permittivity ε ri , cross-sectional area S i Furthermore, it is taken in collectively by α, which is obtained from equations (3) to (5). Therefore, even if multiple materials are present inside the enclosure, the evaluation frequency f t And its evaluation frequency f t The relationship between the dimensions of the enclosure and the resonance that occurs can be defined simply and clearly.

[0023] In the embodiment described in [2] above, termination resistors are connected to the mutually opposing ends of the input microstrip line and the output microstrip line, so that the evaluation frequency f can be set without connecting the input microstrip line and the output microstrip line with any circuit or element. t When an input signal is applied, a high-intensity output signal is obtained due to the resonance of electromagnetic waves within the enclosure. Therefore, the evaluation of electromagnetic wave absorbers can be performed with high accuracy using a simple device configuration.

[0024] In the embodiment described in [3] above, the distance between the electromagnetic wave absorber, which is arranged along the ceiling surface of the enclosure, and the substrate is 0.01 mm or more. In the millimeter wave and sub-millimeter wave regions, the height b of the enclosure tends to decrease in accordance with the short wavelength of the electromagnetic waves. However, by ensuring a distance between the electromagnetic wave absorber and the microstrip lines formed on the substrate and preventing contact, it is possible to prevent an increase in the impedance of the microstrip lines due to contact with the electromagnetic wave absorber and the resulting reduction in the output signal.

[0025] In the embodiment described in [4] above, the input microstrip line and the output microstrip line are aligned in a straight line within a margin of w / 2, where w is the line width. As a result, the evaluation frequency f t When an input signal is applied, the output signal due to electromagnetic wave resonance within the enclosure becomes high-intensity, allowing for a clear evaluation of the electromagnetic wave absorption effect of the electromagnetic wave absorber. In actual high-frequency communication devices, microstrip lines are arranged in various configurations, and electromagnetic wave resonance can occur under complex conditions. However, in the evaluation device of the present invention, by simplifying the phenomenon, the characteristics of the electromagnetic wave absorber itself can be evaluated purely, excluding other factors.

[0026] In the embodiment described in [5] above, the electrical resistivity of the constituent material of the housing is 150 μΩ·cm or less, and the thickness of the plate covering at least the top and side surfaces of the substrate is 0.01 mm or more. In other words, the housing is made of a conductive material that has high conductivity and sufficient thickness. This allows the housing to adequately shield against external electromagnetic waves, and the characteristics of the electromagnetic wave absorber within the housing can be evaluated under conditions where the influence of external electromagnetic waves is reduced. Metal materials such as aluminum, copper, and brass have the above-mentioned electrical resistivity and can be suitably used to construct the housing.

[0027] In the embodiment described in [6] above, the input and output microstrip lines are located at a distance of b / 10 or more from the walls of the enclosure in the width direction of the enclosure. In the embodiment described in [7] above, the non-facing ends of the input microstrip line and the output microstrip line are, respectively, along the length of the housing, from the wall of the housing to the evaluation frequency f t It is more than 1 / 6 the wavelength of the corresponding wavelength. In these embodiments [6] and [7], the microstrip lines are sufficiently far from the walls of the enclosure, which makes it possible to highly suppress the situation in which the intensity of the output signal detected by the output microstrip line decreases when an input signal is input from the input microstrip line due to the influence of the walls of the enclosure.

[0028] In the electromagnetic wave absorber evaluation method according to the present invention having the configuration described in [8] above, the evaluation frequency f t Using the above electromagnetic wave absorber evaluation device equipped with a housing whose dimensions are designed so that resonance occurs at the evaluation frequency f t The system inputs an input signal in the frequency range including f to the input microstrip line and detects the output signal from the output microstrip line, thereby enabling evaluation of the frequency f t Even in the millimeter-wave or sub-millimeter-wave region, a high-intensity output signal can be obtained, and the characteristics of electromagnetic wave absorbers placed inside the enclosure can be evaluated with high accuracy while avoiding the influence of internal structures and the effects of resonances occurring randomly at numerous frequencies. Furthermore, by incorporating the contribution of materials present inside the enclosure collectively using α obtained from equations (3) to (5), the evaluation frequency f t The dimensions of the enclosure where resonance occurs can be easily and clearly defined.

[0029] In the embodiment described in [9] above, the characteristics of the electromagnetic wave absorber are evaluated based on at least one of a comparison between the case in which the electromagnetic wave absorber is placed in the housing and the case in which it is not placed, and a comparison between the case in which different electromagnetic wave absorbers are placed. For each of these situations, the behavior of the electromagnetic waves is compared based on the output signal, and the evaluation frequency f tThe characteristics of each electromagnetic wave absorber for electromagnetic waves in the millimeter wave and quasi-millimeter wave regions, including f, can be clearly evaluated. The dimensions of the enclosure are appropriately set, allowing for evaluation of the evaluation frequency f. t Because these electromagnetic waves resonate and produce a high-intensity output signal, differences in the behavior of electromagnetic waves due to the presence or absence and type of electromagnetic wave absorber are greatly reflected in changes to the output signal.

[0030] In the embodiment described in

[10] above, when evaluating an electromagnetic wave absorber used in a high-frequency communication device having a communication frequency of 20 GHz or higher, the communication frequency is evaluated as the evaluation frequency f t Assuming this is the case, the dimensions of the enclosure are designed to satisfy equations (1) and (2). Then, the characteristics of the electromagnetic wave absorber are evaluated in the frequency range that includes the communication frequency. Therefore, the characteristics of the electromagnetic wave absorber can be evaluated with high accuracy in the millimeter-wave and sub-millimeter-wave communication frequencies set for the high-frequency communication equipment to which the electromagnetic wave absorber is intended to be applied. In high-frequency communication equipment, it is necessary to effectively reduce coupling at the communication frequency, so by evaluating the electromagnetic wave absorber at that communication frequency, it is possible to select and design an electromagnetic wave absorber that exhibits high characteristics at that communication frequency, and a high effect can be obtained in improving the communication characteristics of the high-frequency communication equipment. [Brief explanation of the drawing]

[0031] [Figure 1] This is a perspective view showing an electromagnetic wave absorber evaluation device according to one embodiment of the present invention. [Figure 2] The above diagram shows the electromagnetic wave absorber evaluation apparatus, where (a) is a cross-sectional view taken perpendicular to the width direction at the center of the width direction, (b) is a cross-sectional view taken perpendicular to the length direction at the position of the microstrip line, and (c) is a plan view. [Figure 3] This figure compares the electromagnetic wave transmittance with and without an electromagnetic wave absorber when using an enclosure that satisfies equations (1) and (2) at 20 GHz or higher. (a) shows the measured results, and (b) shows the simulation results. [Figure 4]This is a diagram for comparing the electromagnetic wave transmittance depending on the presence or absence of an electromagnetic wave absorber and the difference in the content of soft magnetic powder when using a housing that does not satisfy equations (1) and (2) at frequencies above 20 GHz. (a) shows the measured results, and (b) shows the simulation results.

Mode for Carrying Out the Invention

[0032] Hereinafter, an electromagnetic wave absorber evaluation apparatus and an electromagnetic wave absorber evaluation method according to an embodiment of the present invention will be described with reference to the drawings. In this embodiment, the characteristics of an electromagnetic wave absorber with respect to electromagnetic waves in the millimeter wave region and the quasi-millimeter wave region are evaluated. In particular, the absorption efficiency of electromagnetic waves by the electromagnetic wave absorber is evaluated. Millimeter waves have frequencies of 30 to 300 GHz, but in the field of high-speed communication, generally, from the 28 GHz band to millimeter waves are included. Also, electromagnetic waves having frequencies of approximately 20 to 30 GHz are called quasi-millimeter waves. In this specification as well, generally, electromagnetic waves having frequencies of 20 GHz or higher are the objects of consideration.

[0033] [Schematic of Electromagnetic Wave Absorber Evaluation Apparatus] 1 and 2 show the schematic configuration of an electromagnetic wave absorber evaluation apparatus 1 according to an embodiment of the present invention. 1 shows a perspective view, 2(a) shows a cross-sectional view taken by cutting the central part in the width direction perpendicular to the width direction, (b) shows a cross-sectional view taken by cutting perpendicular to the length direction at the position of the microstrip line, and (c) shows a plan view. In 2(c), the ceiling surface of the housing is not shown.

[0034] The electromagnetic wave absorber evaluation apparatus (hereinafter, may be simply referred to as an evaluation apparatus) 1 according to this embodiment includes a housing 2 made of a conductive material, a substrate 3 provided with microstrip lines 4 and 5, and a signal inspection unit (not shown). The housing 2 is configured as a rectangular parallelepiped hollow case member having inner dimensions of width a, height b, and length L. Here, the relationship between the dimensions a, b, and L is b < a < L. The housing 2 can accommodate the substrate 3 and an electromagnetic wave absorber (not shown) inside.

[0035] In the illustrated configuration, the housing 2 is composed of a bottom plate 21 that forms the bottom surface of a rectangular parallelepiped and a top cover 22 that forms the five surfaces other than the bottom surface. By appropriately placing the circuit board 3 etc. on the bottom plate 21 and then covering it with the top cover 22, the housing 2 encloses the circuit board 3 in a rectangular parallelepiped shape. The bottom plate 21 is provided with a base portion 21a that protrudes upward from the position where the top cover 22 should be placed, and has a shape approximately the same as the inner dimensions of the bottom of the top cover 22. By placing the top cover 22 on top of this base portion 21a, the top cover 22 can be aligned with the bottom plate 21. The bottom plate 21 may be provided with ports, for example in the form of through holes, that allow connection of electrical signal input / output sections and elements such as termination resistors to microstrip lines 4, 5 provided on the circuit board 3.

[0036] The substrate 3 can be any substrate known for forming microstrip lines, and has a dielectric substrate 31 and a conductive layer 32 bonded to the back surface of the dielectric substrate 31. In the illustrated configuration, the surface of the substrate 3 has approximately the same dimensions as the upper surface of the base portion 21a of the housing 2 and the inner circumference of the bottom of the top cover 22. An input microstrip line 4 and an output microstrip line 5 are formed on the surface of the dielectric substrate 31. The input microstrip line 4 and the output microstrip line 5 are each formed as linear metal layers along the length direction of the housing 2. The input microstrip line 4 and the output microstrip line 5 are spaced apart from each other along the length direction of the housing 2, and no circuits or elements such as amplification circuits are placed between them.

[0037] The input microstrip line 4 has an input terminal 41 at one end and a termination terminal 42 at the other end. The output microstrip line 5 has an output terminal 52 at one end and a termination terminal 51 at the other end. The termination terminal 42 of the input microstrip line 4 and the termination terminal 51 of the output microstrip line 5 face each other on the substrate 3. From the viewpoint of improving the evaluation accuracy in the evaluation device 1, it is preferable that termination resistors (not shown) are connected to each of the two termination terminals 42 and 51. An input signal can be input to the input terminal 41 of the input microstrip line 4 from the signal inspection unit. The output signal output from the output terminal 52 of the output microstrip line 5 can be detected by the signal inspection unit.

[0038] The signal inspection unit is a device that receives an electrical signal with a frequency of 20 GHz or higher as an input signal into the input microstrip line 4, and can detect the output signal output from the output microstrip line 5. A known network analyzer can be suitably used as the signal inspection unit.

[0039] As described above, an electromagnetic wave absorber can be placed inside the housing 2 on which the substrate 3 equipped with microstrip lines 4 and 5 is located. The electromagnetic wave absorber is composed of a material in which powder of a soft magnetic material (soft magnetic powder) is dispersed in a matrix made of an organic polymer, and can absorb and attenuate electromagnetic waves. In this embodiment, the shape of the electromagnetic wave absorber and its arrangement inside the housing 2 are not specifically limited, but for example, a sheet-shaped electromagnetic wave absorber can be attached to the inside of the ceiling surface (top surface) of the housing 2 so that the top of the substrate 3 is covered with the electromagnetic wave absorber. Similarly, sheet-shaped electromagnetic wave absorbers may also be attached to the inside of the walls on both sides in the width direction and both sides in the length direction of the housing. Alternatively, the electromagnetic wave absorber may be molded into a case shape that is slightly smaller than the top lid 22 of the housing 2, and placed over the substrate 3 so as to surround it in a total of five directions (top and sides), and the housing 2 may be placed over the outside of the case-shaped electromagnetic wave absorber.

[0040] [Dimensions of the enclosure] In the evaluation apparatus 1 according to the present embodiment, the dimensions of the housing 2, that is, the width a, the height b, and the length L (where b < a < L), are defined in relation to the evaluation frequency f. t are defined.

[0041] Specifically, the evaluation frequency f obtained by the following formula (1) satisfies the following formula (2) at a frequency of 20 GHz or higher. In other words, the solution where the evaluation frequency f and the dimensions a, b, L of the housing 2 satisfy the relationships of the following formulas (1) and (2) exists in the region where f t is 20 GHz or higher. t ≧ 20 GHz. t

Equation

Equation

[0042] If the evaluation frequency f that satisfies the above formulas (1) and (2) t is used to evaluate the characteristics of the electromagnetic wave absorber by the evaluation apparatus 1, resonance of the electromagnetic wave having the evaluation frequency f occurs inside the housing 2, and coupling occurs between the input signal of the input microstrip line 4 and the output signal of the output microstrip line 5 via the electromagnetic wave. Therefore, a higher-intensity output signal can be obtained compared to the case where resonance does not occur. Further, the evaluation frequency f t t ​Because these resonances exist in the region above 20 GHz, it is possible to perform characterization of electromagnetic wave absorbers utilizing such resonances in the millimeter-wave and sub-millimeter-wave bands.

[0043] The derivation of equations (1) and (2) based on the conditions under which resonance occurs will be explained below. If the inside of housing 2 has relative permeability μ r0 , relative permittivity ε r0 Assuming the enclosure is filled with a uniform medium, the frequency f0 at which TE wave resonance can occur within the enclosure 2 is given by equation (6) below.

number

[0044] However, in reality, the interior of the enclosure 2 is not filled with a uniform medium, but rather contains multiple materials with different permeability and / or dielectric constants, such as the substrate 3 and the electromagnetic wave absorber to be evaluated. Therefore, we introduce a method to treat the contributions of these materials in an integrated manner. To do this, we consider a cross-section perpendicular to the length of the enclosure 2, as shown in Figure 2(b).

[0045] Here, n materials exist in the region enclosed by the enclosure 2, and the complex relative permeability of the i-th material among these n materials is μ. ri , complex relative permittivity is ε ri Let S be the area occupied by the i-th material in a cross-section perpendicular to the length direction of the housing 2. i Let's assume that the representative complex relative permeability μ is obtained from equations (3) and (4) shown below using these parameters. r and representative complex relative permittivity ε rThe following is calculated. Note that the term ab in the denominator of equations (3) and (4) represents the cross-sectional area of ​​the housing 2 perpendicular to the length direction.

number

[0046] In the case of the cross-section shown in Figure 2(b), we can consider air as the substance i=1 and the dielectric substrate 31 constituting the substrate 3 as the substance i=2. That is, in equations (3) and (4), μ r1 and ε r1 Substitute the complex relative permeability and complex relative permittivity of air, and for S1, substitute the area of ​​the region occupied by air in the cross-section of Figure 2(b). Also, μ r2 and ε r2 As shown, the complex relative permeability and complex relative permittivity of the dielectric substrate 31 can be substituted, and as S2, the area of ​​the region occupied by the dielectric substrate 31 in the same cross-section can be substituted. Furthermore, if an electromagnetic wave absorber is provided inside the housing 2, the contribution of the electromagnetic wave absorber can be similarly added to equations (3) and (4) as a material i=3. The walls of the housing 2 and the conductive layer 32 of the substrate 3 do not need to be considered as they are made of non-magnetic conductive material (metal).

[0047] In the illustrated configuration, the state of the cross-section perpendicular to the length is uniform throughout the entire length, except for some regions near both ends in the length direction. Therefore, as shown in Figure 2(b), the representative complex relative permeability μ is obtained by considering only one cross-section. r and representative complex relative permittivity ε r It is sufficient to calculate μ. From the viewpoint of simplicity of the configuration of the evaluation device 1, it is preferable to have a configuration in which the material is uniformly arranged along the length direction of the housing 2, but the arrangement of material inside the housing 2 does not necessarily have to be uniform along the length direction. In such cases, cross-sections are cut out along the length direction of the housing 2 at each location where the arrangement of material is different, and for each cross-section, μ is calculated using equations (3) and (4). r and ε r You just need to calculate the μ.r and ε r The values ​​are summed up across the entire cross-section and the average is taken to obtain the final representative complex relative permeability μ r and representative complex relative permittivity ε r That's all you need to do.

[0048] Regarding the contribution of multiple materials present within the housing 2 to the propagation and resonance phenomena of electromagnetic waves, a uniform medium exists within the housing 2, and this material is represented by the complex relative permeability and complex relative permittivity, as shown by the representative complex relative permeability μ obtained based on equations (3) and (4). r and representative complex relative permittivity ε r An approximation can be applied that treats it as having μ. The validity of this approximation is confirmed experimentally, as shown in later examples. When this approximation is applied, the frequency f at which TE wave resonance can occur in the housing 2 is given by μ in equation (6) above. r0 μ r , ε r0 to ε r This is expressed by equation (7) below, with the substitution.

number

number

[0049] Equation (7) is obtained by setting n=0, and further setting m≠0 and p≠0, resulting in equation (1), which is shown below.

number

[0050] Furthermore, in this embodiment, the evaluation frequency f obtained by equation (1) is t However, as shown in equation (8) below, the lowest frequency f min and the highest frequency f max Make sure it fits within that space.

number

number

[0051] f in equation (9a) min This is obtained by setting m=1 and n=p=0 in the general formula for the resonant frequency in equation (7). In other words, TE 100 It corresponds to the mode. Also, f in equation (9b) max This is obtained by setting n=1 and m=p=0 in the general formula for the resonant frequency in equation (7). In other words, TE 010 Supports the mode. These are the lowest frequencies f min and the highest frequency f max The two modes corresponding to this are the lowest-order modes of the TE wave resonance and have high Poynting energy. As shown in equation (8), the evaluation frequency f t those lowest frequencies f min and the highest frequency f max By keeping it between these intervals, the evaluation frequency f t In this resonance mode, it becomes easier to obtain a high Poynting energy.

[0052] Using the above formulas (8) and (9b), (9b), formula (2) reproduced below is obtained.

Number

[0053] As described above, by satisfying formula (1), resonance occurs at the desired evaluation frequency f t for evaluating the characteristics of the electromagnetic wave absorber, and further, by satisfying formula (2), resonance occurs strongly at that evaluation frequency f t That is, in the relationship with the evaluation frequency f t if the housing 2 of the evaluation apparatus 1 is designed such that the width a, height b, and length L satisfy formulas (1) and (2), when an input signal of the evaluation frequency f t is input to the input microstrip line 4, a high-intensity output signal can be obtained from the output microstrip line 5. Then, phenomena such as the influence of structures (excluding the dielectric substrate 31 and the electromagnetic wave absorber) existing in the housing 2, high-order resonances occurring randomly at short frequency intervals, and the influence of external noise are suppressed, and the characteristics of the electromagnetic wave absorber at the evaluation frequency f t can be evaluated with high precision. Since millimeter waves and quasi-millimeter waves have short wavelengths, if the dimensions of the housing 2 do not satisfy formulas (1) and (2), the influence of those phenomena becomes large, and it may not be possible to evaluate the characteristics of the electromagnetic wave absorber at the desired evaluation frequency f t with sufficient accuracy.

[0054] Also, in this embodiment, the evaluation frequency f t satisfying formulas (1) and (2) exists in the frequency range of 20 GHz or higher, so that the evaluation frequency f tThe dimensions a, b, and L of the housing 2 are then set. This allows the evaluation of the characteristics of the electromagnetic wave absorber for electromagnetic waves in the millimeter wave and quasi-millimeter wave regions with frequencies of 20 GHz or higher to be performed with high precision in the evaluation device 1 by utilizing the resonance of electromagnetic waves. The evaluation frequency f that satisfies equations (1) and (2) is t However, if one or more exist in the region of 20 GHz or higher, such evaluation frequency f t The specific size and number of are not particularly limited. However, from the viewpoint of performing high-precision evaluation of electromagnetic wave absorbers in the millimeter wave region and the relatively high-frequency region within the quasi-millimeter wave region, it is preferable to have an evaluation frequency f that satisfies equations (1) and (2). t However, it is preferable that one or more exist in the region of 23 GHz or higher, and even 26 GHz or higher. Furthermore, from the viewpoint of enabling high-precision evaluation of electromagnetic wave absorbers at frequencies near 28 GHz, which are currently mainly used for communication in the millimeter wave band, the evaluation frequency f that satisfies equations (1) and (2) is preferable. t However, it is preferable that at least one exists in the range of 26 GHz or higher and 30 GHz or lower. Furthermore, considering the possibility of further increasing the communication frequency, evaluation frequencies f that satisfy equations (1) and (2) are also found in the range of over 30 GHz, and even over 50 GHz and over 80 GHz. t It is preferable that a solution exists. Furthermore, from the viewpoint of enabling the use of resonance in evaluation tests over a wide range of frequencies, the evaluation frequency f that satisfies equations (1) and (2) is desirable. t However, it is preferable to have two or more, even five or more, or even ten or more. However, if many resonances occur at close frequencies, the analysis in evaluating the electromagnetic wave absorber becomes complicated, so the evaluation frequency f per 10 GHz in the frequency range is preferred. t The number of these should be 5 or less.

[0055] Furthermore, although multiple materials are present within the housing 2 of the evaluation device 1, equations (1) and (2) use a single α defined by equations (3) to (5) as a representative value to incorporate the contributions of the permeability and dielectric constant of these multiple materials. In this way, by formulating equations (1) and (2) in a simple form using the approximately obtained representative value α, the dimensions of the housing 2 can be expressed as an evaluation frequency f t In relation to that, it can be set simply and clearly.

[0056] [Various parameters in the configuration of an electromagnetic wave absorber evaluation device] As described above, in the evaluation device 1 according to the embodiment of the present invention, the width a, height b, and length L of the housing 2 are set to the evaluation frequency f t In relation to the above, the detailed dimensions and shape are not particularly limited as long as they are determined to satisfy equations (1) and (2) above at 20 GHz or higher. However, having the following parameters is preferable from the viewpoint of reducing unwanted influences from structures inside the housing 2 and the influence of external noise, and improving the accuracy of the evaluation of the electromagnetic wave absorber.

[0057] First, the width a, height b, and length L of the enclosure 2 are determined by an evaluation frequency f, which is arbitrarily set in the millimeter-wave or sub-millimeter-wave region. t Depending on the circumstances, the above equations (1) and (2) are not particularly limited as long as they are satisfied in the range of 20 GHz or higher, but the evaluation frequency f is often used in the 28 GHz band which is frequently used in millimeter-wave communication. t Assuming the settings are configured as described above, a, b, and L can be suitably set within the following ranges. In particular, the following ranges can be suitably applied when the minimum measurement frequency is 26 GHz or higher and the maximum measurement frequency is 30 GHz or lower. • 5mm ≤ a ≤ 13mm • 4mm ≤ b ≤ 30mm 40mm ≤ L ≤ 56mm Here, the above ranges are preferred for b and L from the viewpoint of ease of preparation and measurement of the evaluation device 1. For a, the above range is set so that when b and L are within those ranges, the above equations (1) and (2) are easily satisfied in the frequency range of 20 GHz or higher. Furthermore, L can be suitably set to a value between 3 and 11 times a.

[0058] When an electromagnetic wave absorber is placed inside the housing 2, at least along the ceiling surface of the housing 2, it is preferable that a distance is maintained between the electromagnetic wave absorber placed along the ceiling surface and the substrate 3 placed along the bottom surface (bottom plate 21) of the housing 2, so that they do not come into contact. Furthermore, it is preferable that this distance be 0.01 mm or more. In the millimeter wave and sub-millimeter wave regions, the height b of the housing 2 tends to decrease in accordance with the short wavelength of electromagnetic waves. However, by ensuring a distance between the electromagnetic wave absorber and the substrate 3, and preventing the electromagnetic wave absorber from coming into contact with the micro-microstrip lines 4 and 5, it is possible to prevent an increase in the impedance of the micro-strip lines 4 and 5 due to contact with the electromagnetic wave absorber and the resulting reduction in the output signal, thereby enabling accurate characterization of the electromagnetic wave absorber using the coupling between the two micro-strip lines 4 and 5.

[0059] Furthermore, it is preferable that the input microstrip line 4 and the output microstrip line 5 are aligned in a straight line along the length of the housing 2 with as little error as possible. For example, if the line width (width of macro microstrip lines 4 and 5) is w, it is preferable that the input microstrip line 4 and the output microstrip line 5 are aligned in a straight line within a margin of w / 2 in the width direction of the housing 2. If the input microstrip line 4 and the output microstrip line 5 are aligned in a straight line, the evaluation frequency f t The resonance at this point becomes stronger, making it easier to obtain a high-intensity output signal. Also, as the internal structure of the enclosure 2 approaches the ideal model used in the derivation of equations (1) and (2), the conditions under which resonance occurs approach the theoretical values ​​expressed by equations (1) and (2). Therefore, the evaluation frequency f tThis makes it easier to evaluate the characteristics of the electromagnetic wave absorber itself, eliminating the influence of other factors. In actual high-frequency communication devices, microstrip lines can be arranged in various ways, and electromagnetic wave resonance can occur under complex conditions. However, in this evaluation device 1, knowledge about the characteristics of the electromagnetic wave absorber itself can be obtained under simplified conditions. Based on this knowledge, the electromagnetic wave absorber can be applied to various high-frequency communication devices. The line width w should be determined such that the characteristic impedance Z0 calculated by the following equation (10) is equal to the characteristic impedance of the input / output section of the signal inspection unit (typically 50Ω).

number

[0060] Furthermore, it is preferable that the input microstrip line 4 and the output microstrip line 5 are located at a distance of b / 10 or more from the walls on both sides in the width direction of the housing 2 (d1 ≥ b / 10). Moreover, it is preferable that these microstrip lines 4 and 5 are positioned at the central position (position b / 2) along the width direction of the housing 2, for example, the error from the central position in the width direction should be within the range of ±b / 10. With respect to the length direction of the housing 2, the input end 41 of the input microstrip line 4 and the output end 52 of the output microstrip line 5 should be located at a distance of at least b / 10 from the walls in the length direction of the housing 2 from the evaluation frequency f t The corresponding wavelength λ (the wavelength in the space inside the enclosure 2, i.e., 1 / (f t It is preferable that the distance is 1 / 6 or more of α)) (d2≧λ / 6). In these cases, the microstrip lines 4 and 5 are positioned sufficiently far from the walls on both sides in the width direction and the length direction, and the electromagnetic waves contributing to the coupling between the microstrip lines 4 and 5 are less affected by the walls of the housing 2. As a result, changes in the output signal due to the influence of the walls are less likely to occur, and the accuracy of the evaluation of the electromagnetic wave absorber itself can be improved.

[0061] The constituent material of the housing 2 is not particularly limited as long as it is a conductive material, especially a non-magnetic metal. However, it is preferable that the electrical resistivity of the constituent material of the housing 2 is 150 μΩ·cm or less, and more preferably 100 μΩ·cm or less. Furthermore, it is preferable that the plate thickness of the portion covering at least the top and side surfaces of the substrate 3, that is, the plate thickness t of at least each surface of the top cover 22, is 0.01 mm or more. More preferably, the plate thickness of the base portion 21a of the bottom plate 21 is also 0.01 mm or more. In this way, if the housing 2 is made of a conductive material that has high conductivity and sufficient thickness, external electromagnetic waves can be sufficiently shielded by the housing 2. Then, the characteristics of the electromagnetic wave absorber inside the housing 22 can be evaluated under conditions in which the influence of external electromagnetic waves is sufficiently reduced. Metal materials such as aluminum, copper, and brass (gold foil) have electrical resistivity within the above range. These materials may be plated with other metals as appropriate.

[0062] [Method for evaluating electromagnetic wave absorbers] Next, a method for evaluating an electromagnetic wave absorber according to one embodiment of the present invention will be described. In the evaluation method according to this embodiment, the characteristics of the electromagnetic wave absorber are evaluated using the electromagnetic wave absorber evaluation apparatus 1 according to the embodiment of the present invention described above.

[0063] During the evaluation, the electromagnetic wave absorber to be tested is appropriately placed inside the housing 2 of the evaluation device 1, and the evaluation frequency f t An electrical signal within the frequency range including is input to the input terminal 41 of the input microstrip line 4. Then, the output signal output from the output terminal 52 of the output microstrip line 5 is detected. Based on the behavior of this output signal, the characteristics of the electromagnetic wave absorber can be evaluated. For example, for a specific frequency, the electromagnetic wave transmittance S 21 By evaluating this, the electromagnetic wave absorption efficiency of the electromagnetic wave absorber at that frequency can be evaluated. Electromagnetic wave transmittance S 21 The lower the value, the higher the electromagnetic wave absorption efficiency and the higher the decoupling efficiency. Here, the electromagnetic wave transmittance S 21 Let V1 be the voltage of the input signal and V2 be the voltage of the output signal, S 21[dB] is calculated as [dB] = 20log(V2 / V1). In this evaluation device 1, the dimensions of the housing 2 are determined based on the above equations (1) and (2) for an evaluation frequency f of 20 GHz or higher. t Since it is set up so that electromagnetic wave resonance occurs, a high-intensity output signal is obtained through coupling between the input signal and the output signal, and the evaluation frequency f t This allows for highly accurate evaluation of electromagnetic wave absorbers in this context.

[0064] When evaluating an electromagnetic wave absorber, it is preferable to perform the above evaluation both with and without an electromagnetic wave absorber placed inside the housing 2, and / or with multiple electromagnetic wave absorbers of different compositions and thicknesses, in order to clarify the differences in behavior with respect to electromagnetic waves depending on the presence or absence of the electromagnetic wave absorber, its composition, thickness, etc., and to compare the results obtained in each of these cases. In this way, the predetermined evaluation frequency f t This allows for the selection of electromagnetic wave absorbers with desired characteristics, such as high electromagnetic wave absorption efficiency. Furthermore, the evaluation results become more readily available as basic information for designing and developing such suitable electromagnetic wave absorbers.

[0065] When the presence or type of electromagnetic wave absorber is changed in this way, the representative complex relative permeability μ can be obtained using equations (3) and (4). r and representative complex relative permittivity ε r As the value of changes, the resonant frequency, represented by equation (7), which corresponds to the dimensions a, b, and L of the designed enclosure 2, may change. In such cases, the frequency used for evaluation is the evaluation frequency f used to determine the dimensions of enclosure 2, so that the characteristics of the electromagnetic wave absorber can be evaluated under the conditions in which resonance occurs. t It is best to set it to a range that includes and has a width. As for how to determine the specific dimensions of housing 2, for example, for the case where no electromagnetic wave absorber is placed inside housing 2, μ is given by equations (3) and (4). r and ε r Calculate the desired evaluation frequency f set to 20 GHz or higher, and use these values ​​to determine the desired evaluation frequency f tThe dimensions a, b, and L of the housing 2 should be determined such that equations (1) and (2) are satisfied between the two. Alternatively, as shown in later embodiments, if the dimensions of the housing 2 are predetermined based on manufacturing convenience or constraints on the materials used, the evaluation frequency f can be calculated by substituting these predetermined dimensions a, b, and L into equations (1) and (2). t However, if the frequency is 20 GHz or higher and within the acceptable frequency range for evaluation, it is sufficient to determine that the enclosure 2 can be used for evaluation. In either case, the evaluation frequency f that satisfies equations (1) and (2) is... t Within a measurement frequency range set to be sufficiently wide, including the above, evaluation can be performed by detecting the input and output signals while changing the presence and / or type of electromagnetic wave absorber. Preferably, for each electromagnetic wave absorber to be evaluated, it is good to confirm that the resonant frequency for which equations (1) and (2) hold is included within the measurement frequency range. Note that the minimum frequency f set in equations (9a) and (9b) min and the highest frequency f max This merely represents the frequencies of the two lowest-order resonant modes in the enclosure 2, and the lower and upper limits of the actual measurement frequency range are f min and f max It does not have to match. However, the upper limit of the measurement frequency range is f max It is preferable to set it to the above level.

[0066] When considering applying an electromagnetic wave absorber, whose characteristics are evaluated by the evaluation method according to this embodiment, or whose composition and thickness are designed based on the evaluation results, to an actual high-frequency communication device, in order for the electromagnetic wave absorber to sufficiently reduce coupling within the device housing of the high-frequency communication device, it is necessary for the electromagnetic wave absorber to efficiently absorb electromagnetic waves having a communication frequency specifically set for the high-frequency communication device. In this case, when performing the evaluation method according to this embodiment, the communication frequency of the high-frequency communication device, which is set to 20 GHz or higher, is set to the evaluation frequency f tAssuming this is the case, the dimensions a, b, and L of the housing 2 should be set to satisfy equations (1) and (2) above. Then, the electromagnetic wave absorber using the housing 2 should be evaluated in the frequency range that includes the communication frequency. This will allow the characteristics of the electromagnetic wave absorber to be evaluated under conditions where resonance occurs at the actual communication frequency, and the characteristics of the electromagnetic wave absorber at that communication frequency can be evaluated with high accuracy. By using the obtained evaluation results, it becomes possible to select and design an electromagnetic wave absorber that exhibits excellent characteristics in actual high-frequency communication equipment.

[0067] As described above, the desired evaluation frequency f t The method of designing the dimensions of the evaluation device's housing 2 based on the conditions under which resonance occurs, and then evaluating the characteristics of the electromagnetic wave absorber, can be applied not only to actual measurements but also to simulations. For example, the housing 2 designed according to equations (1) and (2) can be incorporated into a model, and a simulation using electromagnetic field analysis by the finite element method can be performed. By using both actual measurements and simulations to examine the configuration of the electromagnetic wave absorber, it may be possible to deepen our understanding of the characteristics of the electromagnetic wave absorber, such as by systematically designing and developing the electromagnetic wave absorber compared to using only actual measurements. [Examples]

[0068] The present invention will be described more specifically below using examples. However, the present invention is not limited to the following examples.

[0069] [1] First, we verified the validity of the relationship between the dimensions of the enclosure and the resonant frequency given by equations (1) to (5) above.

[0070] [Evaluation Method] <Preparation of evaluation equipment> An evaluation device with the structure shown in Figures 1 and 2 was fabricated. The parameters related to the structure of the evaluation device were as follows. • Cabinet Width a: 11mm Height b: 4.5 mm Length L: 55mm Top lid material: 3mm thick gold-plated brass plate • Microstrip tracks Track width w:0.76mm Length: 17mm each for input and output. Distance between input and output tracks: 13mm Width direction position: For both the input and output sides, the error range should be within ±0.05 mm relative to the center of the chassis in the width direction. Distance (d2) from the wall surfaces on both sides in the longitudinal direction: 4 mm

[0071] <Measurement of electromagnetic wave transmittance> Using the above evaluation device, the electromagnetic wave transmittance S 21 Measurements were performed. The measurements were carried out using a network analyzer, by inputting an electrical signal in the range of 26 to 40 GHz into the input microstrip line and detecting the output from the output microstrip line. Measurements were performed in two cases: one in which no electromagnetic wave absorber was installed inside the enclosure, and another in which a case-shaped electromagnetic wave absorber was placed inside the enclosure. The electromagnetic wave absorber was constructed by dispersing soft magnetic powder made of SUS 410L in an amount of 40 volume% in acrylic rubber as the matrix resin, and molding it to a thickness of 0.8 mm.

[0072] <Conducting the simulation> The same evaluation test that was measured as described above was reproduced by simulation, and the electromagnetic wave transmittance S 21 The following estimations were made. Here, simulations were performed for the case where no electromagnetic wave absorber is installed inside the enclosure, the case where a case-shaped electromagnetic wave absorber, the same as in the above-mentioned measurement test, is installed inside the enclosure, and the case where a case-shaped resin molded body of the same shape as the electromagnetic wave absorber is formed only from matrix resin without mixing in soft magnetic powder and placed inside the enclosure. The simulations were performed using electromagnetic field analysis by the finite element method. The frequency range used here was 26 to 30 GHz.

[0073] <Calculation of Resonant Frequency> The value of α was estimated for the above evaluation device by calculations using equations (3) to (5). In this process, the following materials were considered as components within the enclosure. • Air (i=1) μ r1 =1 ε r1 =1 S1 = 37.906 mm 2 • Dielectric substrate (i=2) μ r2 =1 ε r2 =2.2 S2 = 2.794 mm 2 • Electromagnetic wave absorber (i=3) μ r3 =18.7-0.6j ε r3 =0.5-0.4j (j is the imaginary unit) S3 = 8,800 mm 2 Furthermore, the following values ​​were used as physical constants. The permeability of vacuum μ0 = 4π / 10 7 [N·A -2 ] The permittivity of vacuum is ε0 = 10 7 / (4πc 2 )[F·m -1 ] Speed ​​of light c=299792458[m / s] The value of α obtained using the above parameters is 3.34 × 10⁻⁶. -9 It was [s / m].

[0074] Using the α obtained above, the lowest frequency f can be obtained from equations (9a) and (9b). min and the highest frequency f max When we calculated these f, we got the following results. min and f max The range defined by this overlaps in part with the 26-40 GHz range applied to the above-mentioned measurements. ·f min = 13.63GHz ·f max =33.31GHz

[0075] Next, substitute the values ​​of a, b, L, and α above into equation (1) and evaluate the frequency f t The value of was calculated. In this process, a number of evaluation frequencies f were evaluated by combining m and p. t These can be obtained, but of them, the lowest frequency f mentioned above min and the highest frequency f max We recorded what was present in the frequency range between [the specified values].

[0076] [Evaluation Results] Figure 3(a) shows the measurement results of electromagnetic wave transmittance obtained through actual measurements. When examining the spectrum without an electromagnetic wave absorber, four sharp peak structures can be seen in the range of approximately 27 GHz to 36 GHz. These peaks are thought to be due to electromagnetic wave resonance.

[0077] Table 1 below shows the peak frequencies of each of the peaks obtained by measurement. In addition, the resonant frequency (evaluation frequency f) calculated by substituting a, b, L, and α into equation (1) is also shown. t Of the calculated values, the main ones in the 20GHz and above range are classified as mode type (T m0p ) is shown together. In the table, those with similar frequencies based on actual measurements and calculations are displayed in the same row.

[0078] [Table 1]

[0079] According to Table 1, for each of the peaks #1 to #4 observed in the measurements, the calculated resonant frequencies appear at adjacent frequencies. For peaks #1 and #2, it is thought that the resonant peaks of multiple modes obtained in the calculations overlap and appear as a single resonant peak in the measurements. The results in Table 1 show that the measured resonant frequencies are in good agreement with the calculations. In other words, in the calculation of the resonant frequency, an approximate treatment is introduced in which a representative value α is used, which combines the contributions of multiple materials into one using equations (3) to (5), but since it is in good agreement with the measured resonant frequencies, this treatment is confirmed to be appropriate. Furthermore, using equations (1) to (5), the evaluation frequency f is set so that resonance occurs in the desired frequency range. t The method for defining the relationship between the dimensions a, b, and L of the enclosure can be said to be effective in light of the actual measurement results.

[0080] Furthermore, in the spectrum shown in Figure 1(a) when no electromagnetic wave absorber is placed, as described above, four clear peaks that can be interpreted as originating from electromagnetic wave resonance are observed in the frequency range below approximately 36 GHz, whereas at higher frequencies, the electromagnetic wave transmittance values ​​fluctuate wildly, making it difficult to confirm a clear peak structure. In this high-frequency range, f max This corresponds to frequencies above (33.31 GHz). TE 010 f corresponding to the mode max In the above frequency range, it is interpreted that the value of electromagnetic wave transmittance f f is observed because higher-order resonances occur randomly at low intensity and small frequency intervals. Therefore, as shown in equation (2), the evaluation frequency f t The upper limit of f max The appropriateness of setting it to less than is supported.

[0081] Next, looking at the measurement results in Figure 3(a) when an electromagnetic wave absorber is placed inside the enclosure, the electromagnetic wave transmittance is lower than when no electromagnetic wave absorber is placed in the entire frequency range below 36 GHz, and all the sharp peaks caused by resonance that appeared when no electromagnetic wave absorber was placed have disappeared. This is interpreted as the electromagnetic waves propagating inside the enclosure being absorbed and attenuated by the electromagnetic wave absorber, and the coupling between the input signal of the input macromicrostrip line and the output signal of the output microstrip line being reduced. In this way, by measuring and comparing the electromagnetic wave transmittance with and without an electromagnetic wave absorber inside the enclosure in a range that includes frequencies in which electromagnetic wave resonance occurs inside the enclosure and gives high electromagnetic wave transmittance, the effect of electromagnetic wave absorption by placing the electromagnetic wave absorber can be clearly confirmed.

[0082] Furthermore, the simulation results in Figure 3(b) show that when no electromagnetic wave absorber is provided, peaks appear around 27.5 GHz and 29.8 GHz. These frequencies correspond well to peaks #1 and #2 in Table 1. In other words, it is confirmed that there is a high degree of consistency among the three results regarding the resonant frequency: the measured values, the simulation, and the calculation based on equation (1). When an electromagnetic wave absorber is provided, the electromagnetic wave absorption rate decreases significantly, and the two peaks disappear. This result also matches the measured values. On the other hand, when a case made only of resin is provided, as indicated by the arrows, only the position of the resonant peak shifts, and no resonance attenuation occurs.

[0083] The above tests confirmed the validity of using α, obtained by equations (3) to (5), as a parameter representing the contribution of the material inside the enclosure to the electromagnetic wave resonance phenomenon within the enclosure. Furthermore, equations (1) and (2) incorporating α were used at the evaluation frequency f t By applying a housing with dimensions that satisfy the relationship, it was demonstrated that high-intensity output signals can be obtained by utilizing resonance in both actual measurements and simulations, thereby enabling highly accurate evaluation of the characteristics of the electromagnetic wave absorber.

[0084] [2] The dimensions of the enclosure are such that the evaluation frequency f t In relation to the given conditions, even when equations (1) and (2) were not satisfied, the electromagnetic wave transmittance was evaluated by actual measurements and simulations.

[0085] [Evaluation Method] The same tests as described in [1] above were performed. However, the dimensions of the enclosure were changed as follows. Width a:22.6mm Height b: 10.8 mm Length L: 63.5mm The measurements and simulations were performed under three conditions: without an electromagnetic wave absorber inside the enclosure; with an electromagnetic wave absorber containing 40 volume% of soft magnetic powder, similar to the test [1] above; and with an electromagnetic wave absorber containing only 15 volume% of soft magnetic powder.

[0086] [Evaluation Results] Figures 4(a) and 4(b) show the results of the measurements and simulations, respectively. In both cases, complex spectral behavior was obtained, with electromagnetic wave transmittance fluctuating slightly up and down. Since the simulations also show spectral shapes that are as complex as or even more complex than those in the experiments, it can be said that these complex spectral shapes are due to essential phenomena occurring within the enclosure, rather than to non-essential phenomena during the measurements, such as accidental noise or fluctuations in measurement conditions.

[0087] Furthermore, both actual measurements and simulations show that even when the presence or absence of an electromagnetic wave absorber, or the content of soft magnetic powder within the electromagnetic wave absorber, changes do not reveal any clear changes in behavior in the spectrum that exceed the level of the aforementioned minute vertical fluctuations. In other words, it is difficult to perform a meaningful characterization of the electromagnetic wave absorber.

[0088] When the dimensions a, b, and L of the enclosure used here are substituted into equations (1) and (2), the resonant frequency (evaluation frequency f) that satisfies equations (1) and (2) is obtained. t) exists only in the low-frequency region below 13.5 GHz and not in the region above 20 GHz. In other words, in the frequency range in which measurements and simulations were performed, there were no conditions that gave a clear resonance peak as in the case of test [1], and this is thought to be the reason why the measurements and simulations yielded a complex spectral shape as shown in Figure 4. These complex spectral shapes are thought to be due to high-order resonances occurring randomly at low intensity and small frequency intervals, similar to the region above 36 GHz in Figure 3(a).

[0089] Although embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments and examples, and various modifications are possible without departing from the spirit of the invention. [Explanation of symbols]

[0090] 1. (Electromagnetic wave absorber) evaluation device 2 cabinets 21 Bottom plate 22 Top lid 3 circuit boards 31 Dielectric substrate 32 Conductive layer 4. Microstrip lines for input 41 Input terminal 42 Termination section 5. Output microstrip lines 51 Termination section 52 Output terminal a. Width of the enclosure b. Height of the enclosure L Length of the enclosure t Thickness of the enclosure w track width

Claims

1. A device for evaluating the characteristics of an electromagnetic wave absorber, A housing made of a conductive material having internal dimensions of width a, height b, and length L, where b < a < L, and capable of arranging the electromagnetic wave absorber inside, A circuit board arranged inside the aforementioned housing, On the substrate, an input microstrip line and an output microstrip line are formed along the longitudinal direction of the housing, respectively, and spaced apart from each other in the longitudinal direction. It includes a signal inspection unit that can receive an input signal having a frequency of 20 GHz or higher from the input microstrip line and detect an output signal output from the output microstrip line, The evaluation frequency f is obtained by the following formula (1). ｔ However, an electromagnetic wave absorber evaluation device that satisfies the following equation (2) in the frequency range of 20 GHz or higher. [Math 1] Here, m and p are independent integers greater than or equal to 1. Also, there are n materials in the region enclosed by the enclosure, and the complex relative permeability of the i-th material is μ ｒｉ , complex relative permittivity is ε ｒｉ The area occupied by the cross-section of the housing perpendicular to the longitudinal direction is S ｉ As such, α is μ obtained from equations (3) and (4) below. ｒ and ε ｒ Using this, it is expressed by equation (5). μ ０ ε is the permeability of vacuum. ０ is the permittivity of vacuum. [Math 2]

2. The electromagnetic wave absorber evaluation apparatus according to claim 1, wherein termination resistors are connected to the mutually opposing ends of the input microstrip line and the output microstrip line, respectively.

3. The substrate is arranged along the bottom surface of the housing, The electromagnetic wave absorber can be positioned at least along the ceiling surface of the housing, facing the substrate. The electromagnetic wave absorber evaluation apparatus according to claim 1, wherein the distance between the electromagnetic wave absorber arranged along the ceiling surface of the housing and the substrate is 0.01 mm or more.

4. The electromagnetic wave absorber evaluation apparatus according to claim 1, wherein the input microstrip line and the output microstrip line each have a line width w, and the amount of displacement between them along the width direction of the housing is w / 2 or less.

5. The electromagnetic wave absorber evaluation apparatus according to claim 1, wherein the constituent material of the housing has an electrical resistivity of 150 μΩ·cm or less, and the thickness of the portion covering at least the top and side surfaces of the substrate is 0.01 mm or more.

6. The electromagnetic wave absorber evaluation apparatus according to claim 1, wherein the input microstrip line and the output microstrip line are located at a distance of b / 10 or more from the walls of the housing on both sides in the width direction of the housing.

7. The end portions of the input microstrip line and the output microstrip line that do not face each other are respectively separated from the wall surface of the housing along the length direction of the housing by at least 1 / 6 of the wavelength corresponding to the evaluation frequency f ｔ The electromagnetic wave absorber evaluation device according to claim 1, wherein the separation is more than 1 / 6 of the wavelength corresponding to the evaluation frequency f

8. Using the electromagnetic wave absorber evaluation apparatus described in any one of claims 1 to 7, The electromagnetic wave absorber to be evaluated is placed inside the aforementioned enclosure, The aforementioned evaluation frequency f ｔ An electromagnetic wave absorber evaluation method, comprising inputting an input signal containing a frequency range through the input microstrip line and detecting an output signal output from the output microstrip line to evaluate the characteristics of the electromagnetic wave absorber.

9. A comparison of the case in which the electromagnetic wave absorber is placed in the housing and the case in which it is not placed, and The electromagnetic wave absorber evaluation method according to claim 8, comprising evaluating the characteristics of the electromagnetic wave absorber based on at least one of comparisons of cases in which different electromagnetic wave absorbers are arranged.

10. The electromagnetic wave absorber is used in high-frequency communication equipment having a communication frequency of 20 GHz or higher. The communication frequency is the evaluation frequency f ｔ Assuming this is the case, the dimensions of the housing are designed to satisfy equations (1) and (2), The electromagnetic wave absorber evaluation method according to claim 8, comprising evaluating the characteristics of the electromagnetic wave absorber in a frequency range including the aforementioned communication frequency.

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