JP7058001B2 - Radio wave absorber and radio wave absorber supplies - Google Patents

Description

The present disclosure relates to a radio wave absorber and a radio wave absorber.

With the miniaturization and efficiency improvement of electronic devices, malfunctions due to radio waves emitted from electronic components have become a problem. As a countermeasure, a radio wave absorber is attached to an electronic device. The radio wave absorber is disclosed in Patent Document 1.

Japanese Patent Publication No. 2005-521782

The frequency of the radio wave that needs to be absorbed by the radio wave absorber differs depending on the application of the radio wave absorber. However, in the conventional radio wave absorber, the frequency band having a high effect of absorbing radio waves (hereinafter referred to as the radio wave absorption band) is a fixed frequency band. Therefore, in the past, it was necessary to prepare different radio wave absorbers for each application.

One aspect of the present disclosure is to provide a radio wave absorber and a radio wave absorbing product capable of changing the radio wave absorbing band.

One aspect of the present disclosure is a radio wave absorber containing a foam, wherein the foam comprises a base material containing an elastomer and nanocarbon dispersed in the foam, and the content of the nanocarbon is contained. Is a radio wave absorber which is 5 to 45 parts by mass with respect to 100 parts by mass of the base material.

The radio wave absorber, which is one aspect of the present disclosure, can change the radio wave absorption band by compressing the radio wave absorber. Further, when the radio wave absorber, which is one aspect of the present disclosure, is compressed, the radio wave absorption band changes to the high frequency side and the thickness decreases. Therefore, according to the radio wave absorber, which is one aspect of the present disclosure, it is possible to realize a radio wave absorber having a thin thickness and a radio wave absorption band on the high frequency side.

Another aspect of the present disclosure is a radio wave absorber comprising a radio wave absorber, which is one aspect of the present disclosure, and a compression unit that compresses at least a part of the radio wave absorber. The radio wave absorbing device, which is another aspect of the present disclosure, can compress at least a part of the radio wave absorber by the compression unit. Therefore, according to the radio wave absorbing product, which is another aspect of the present disclosure, the radio wave absorbing band of the radio wave absorber can be changed.

1A is a perspective view showing the configuration of the radio wave absorbing device 1, FIG. 1B is a side view showing the structure of the radio wave absorbing device 1 in a state where the radio wave absorber 3 is not compressed, and FIG. 1C is a side view showing the structure of the radio wave absorbing device 1. It is a side view which shows the structure of the radio wave absorption article 1 in the state which the absorber 3 is compressed. FIG. 2A is a perspective view showing the configuration of the radio wave absorbing product 101 excluding the radio wave absorber 3 and the metal plate 5, and FIG. 2B is a perspective view showing the configuration of the radio wave absorbing product 101. It is a graph which shows the measurement result of the reflection loss of Example A1. It is a graph which shows the measurement result of the reflection loss of Example A2. It is a graph which shows the measurement result of the reflection loss of Example A3. It is a graph which shows the measurement result of the reflection loss of Example A4. It is a graph which shows the measurement result of the reflection loss of the comparative example a1. It is a graph which shows the measurement result of the reflection loss of Example B1. It is a graph which shows the measurement result of the reflection loss of Example B1. It is a graph which shows the relationship between a compression rate and an absorption band. It is a graph which shows the relationship between a compression rate and an absorption band.

An embodiment of the present disclosure will be described.
1. 1. Radio wave absorber The radio wave absorber of the present disclosure includes a foam. The entire radio wave absorber may be a foam, or a part of the radio wave absorber may be a foam. The foam comprises a base material. The base material contains an elastomer. Examples of the elastomer include styrene-based elastomers, silicone-based elastomers, urethane-based elastomers, acrylic-based elastomers, polyester-based elastomers, synthetic rubbers, and the like. Examples of the styrene-based elastomer include styrene ethylene ethylene propylene styrene block copolymer (SEEPS), styrene isoprene styrene block copolymer (SIS), styrene butadiene styrene block copolymer (SBS), and styrene ethylene propylene block copolymer (Styrene propylene block copolymer). SEP), styrene ethylene butylene styrene block copolymer (SEBS), styrene ethylene propylene styrene block copolymer (SEPS), styrene rubber and the like.

Examples of the silicone-based elastomer include silicone rubber and the like. As the elastomer, one of the above examples may be used alone, or two or more of them may be mixed and used.

The base metal further contains, for example, a softener. When the base material contains a styrene-based elastomer, it is preferable to further contain a softening agent. Examples of the softener include hydrocarbon-based process oils such as paraffin-based process oils and naphthen-based process oils. As the hydrocarbon-based process oil, paraffin-based process oil or naphthenic process oil may be used alone, or they may be mixed and used. The base material may further contain additives other than the softening agent (however, excluding the foaming agent and nanocarbon).

As the foam, a foam having closed cells is preferable. In the case of a foam having closed cells, the hygroscopicity is lowered, and the change in characteristics due to the hygroscopicity can be suppressed. Examples of the method for forming the foam include a method in which a base material and a foaming agent are mixed and foamed. The blending amount of the foaming agent can be, for example, 1 to 20 parts by mass with respect to 100 parts by mass of the base material. When the blending amount of the foaming agent is 1 part by mass or more, the base material forms a foamed structure. When the blending amount of the foaming agent is 20 parts by mass or less, the foam has a stable shape and the radio wave absorption band can be changed.

When the base material contains a styrene-based elastomer as a main component, the blending amount of the foaming agent is preferably 1 to 10 parts by mass with respect to 100 parts by mass of the base material. The foaming ratio in foaming the foam is, for example, 1.45 to 3.6 times.

The radio wave absorber of the present disclosure comprises nanocarbon. Nanocarbon is dispersed in the foam. The content of nanocarbon is 5 to 45 parts by mass with respect to 100 parts by mass of the base material. Since the content of nanocarbon is 5 parts by mass or more with respect to 100 parts by mass of the base material, the resistance value of the base material of the insulator can be adjusted in the range from the semiconductor to the conductor, so that the radio wave absorption band can be designed. It becomes possible to absorb radio waves.

When the content of nanocarbon is 45 parts by mass or less with respect to 100 parts by mass of the base material, the raw material containing the base material and nanocarbon can be kneaded. When the base material contains a silicone-based elastomer as a main component, the content of nanocarbon is preferably 5 to 25 parts by mass with respect to 100 parts by mass of the base material.

Nanocarbon is not particularly limited and can be appropriately selected and used. As the nanocarbon, vapor phase grown carbon fiber is preferable. When the nanocarbon is a gas phase growth carbon fiber, the amount of change in the radio wave absorption band when the radio wave absorber is compressed becomes larger.

The diameter of the vapor-grown carbon fiber is preferably 0.01 μm to 0.2 μm. The fiber length of the vapor-grown carbon fiber is preferably 1 μm to 500 μm. The aspect ratio of the vapor-grown carbon fiber is preferably 10 to 500. When the diameter, fiber length, and aspect ratio of the vapor-grown carbon fiber are within the above ranges, the amount of change in the radio wave absorption band when the radio wave absorber is compressed becomes larger.

The form of the radio wave absorber is not particularly limited, and examples thereof include a plate shape, a columnar shape, a prismatic shape, a spherical shape, and an irregular shape.
2. 2. Radio wave absorbing product The radio wave absorbing product includes the radio wave absorber of the present disclosure and a compression unit that compresses at least a part of the radio wave absorber. The compression unit is preferably configured so that the degree of compression of the radio wave absorber can be changed.

1A to 1C show a radio wave absorbing product 1 which is one form of the present disclosure. The radio wave absorber 1 includes a plate-shaped radio wave absorber 3, a metal plate 5, a pair of pressing plates 7 and 9, a screw 11, and a nut 13.

The radio wave absorber 3 and the metal plate 5 are overlapped with each other. The pair of pressing plates 7 and 9 sandwich the radio wave absorber 3 and the metal plate 5 from both sides. A plurality of through holes 15 are formed on the outer peripheral sides of the pressing plates 7 and 9, respectively. The screw 11 is inserted from the pressing plate 7 into the through hole 15 of the pressing plates 7 and 9. The nut 13 is attached to a screw 11 protruding from the through hole 15 of the pressing plate 9. The pressing plate 9 can also be used as a metal reflector. When the pressing plate 9 is a metallic reflector, the pressing plate 7 is on the incident side and is made of an insulating resin or glass that transmits radio waves.

By tightening the nut 13, the distance D between the pressing plate 7 and the pressing plate 9 can be reduced. When the nut 13 is loosened, the interval D increases.
The state shown in FIG. 1C is a state in which the interval D is smaller than the state shown in FIG. 1B. As shown in FIG. 1C, the radio wave absorber 3 is compressed by reducing the interval D. The smaller the interval D, the more remarkable the degree of compression of the radio wave absorber 3. The radio wave absorber 1 can change the degree of compression of the radio wave absorber 3 by changing the tightening amount of the nut 13.

When the radio wave absorber 3 is compressed, the radio wave absorption band of the radio wave absorber 3 changes. The greater the degree of compression of the radio wave absorber 3, the larger the amount of change in the radio wave absorption band. After the radio wave absorber 3 is once compressed, the nut 13 is loosened and the interval D is widened, so that the radio wave absorber 3 returns to its original form.

2A and 2B show a radio wave absorbing device 101, which is another embodiment of the present disclosure. The radio wave absorbing device 101 includes a pair of pressing plates 7 and 9, and an interval adjusting jig 17. One through hole 15 is formed in the vicinity of one end of the pressing plates 7 and 9, respectively. The interval adjusting jig 17 includes a rod-shaped main body portion 19 and a lever 21 provided at one end of the main body portion 19. The main body 19 is inserted from the pressing plate 7 into the through holes 15 of the pressing plates 7 and 9. The interval adjusting jig 17 has a function of reducing the interval D between the pressing plate 7 and the pressing plate 9 when the lever 21 is rotated in one direction, and widening the interval D when the lever 21 is rotated in the opposite direction.

The pair of pressing plates 7 and 9 sandwich the radio wave absorber 3 and the metal plate 5 from both sides. The radio wave absorber 3 is compressed by rotating the lever 21 to one side and reducing the interval D. The smaller the interval D, the more remarkable the degree of compression of the radio wave absorber 3. The radio wave absorber 101 can change the degree of compression of the radio wave absorber 3 by changing the amount of rotation of the lever 21.

When the radio wave absorber 3 is compressed, the radio wave absorption band of the radio wave absorber 3 changes. The greater the degree of compression of the radio wave absorber 3, the larger the amount of change in the radio wave absorption band. After the radio wave absorber 3 is once compressed, the lever 21 is rotated in the opposite direction to widen the interval D, and the radio wave absorber 3 returns to its original form.

The radio wave absorbers 1 and 101 can be attached to, for example, a wall surface of a building, a pier of a bridge, or the like. The radio wave absorbers 1 and 101 can change the radio wave absorption band of the radio wave absorber 3 by changing the interval D even after they are attached. Various known techniques can be used for the mechanism for adjusting the interval D. Further, either the pressing plate 7 or 9 can be shared with a metal reflector without using the metal plate 5. In that case, the other side is the incident side, and it is composed of an insulating resin or glass that transmits radio waves.

3. 3. Example (3-1) Production of Radio Absorbents of Examples A1 to A4 and Comparative Example a1 The radio wave absorbers of Examples A1 to A4 and Comparative Example a1 were manufactured as follows. Silicone rubber, nanocarbon, and a foaming agent constituting the base material were blended in the blending ratio as shown in Table 1 below.

上記表１中のナノカーボンは気相成長炭素繊維である。上記表１中のナノカーボンは、昭和電工株式会社製の市販品（品名：VGCF（登録商標）-H、平均繊維径150 nm、繊維長10μm）である。実施例Ａ１～Ａ３における発泡剤は、大日精化工業株式会社製の市販品（品名：ダイフォームH850D）である。実施例Ａ４における発泡剤は、大日精化工業株式会社製の市販品（品名：ダイフォームH750D）である。

The nanocarbons in Table 1 above are vapor-grown carbon fibers. The nanocarbons in Table 1 above are commercially available products manufactured by Showa Denko KK (product name: VGCF (registered trademark) -H, average fiber diameter 150 nm, fiber length 10 μm). The foaming agents in Examples A1 to A3 are commercial products (product name: Dieform H850D) manufactured by Dainichiseika Kogyo Co., Ltd. The foaming agent in Example A4 is a commercially available product (product name: Dieform H750D) manufactured by Dainichiseika Kogyo Co., Ltd.

First, the above raw materials were stirred and mixed at room temperature for 10 minutes using a defoaming mixer. Next, the raw material after stirring and mixing was poured into a mold having a desired height, and the mold was heated together with the mold in a constant temperature bath at 110 ° C. for 5 minutes. At this time, the curing of the silicone rubber was promoted, and a cured product cured like a rubber was obtained. Next, the cured product was taken out of the mold, transferred to a constant temperature bath at 170 ° C., and heated for 10 minutes. By this heating, foaming of the foaming agent was started, and a foamed structure was formed.

Through the above steps, the radio wave absorbers of Examples A1 to A4 and Comparative Example a1 were obtained. The radio wave absorbers of Examples A1 to A4 include foam. The foam includes a base material containing silicone rubber and nanocarbon dispersed in the foam. The foaming ratios and densities of the radio wave absorbers of Examples A1 to A4 and Comparative Example a1 are as shown in Table 1 above.

(3-2) Manufacture of the radio wave absorber of Example B1 The radio wave absorber of Example B1 was manufactured as follows. The styrene-based elastomer and the softening agent constituting the base material, the nanocarbon, and the foaming agent were blended in the blending ratio as shown in Table 2 below.

上記表２中のナノカーボンは気相成長炭素繊維である。上記表２中のナノカーボンは、昭和電工株式会社製の市販品（品名：VGCF（登録商標）-H、平均繊維径150 nm、繊維長10μm）である。発泡剤は、大日精化工業株式会社製の市販品（品名：ダイフォームH850D）である。

The nanocarbons in Table 2 above are vapor-grown carbon fibers. The nanocarbons in Table 2 above are commercially available products manufactured by Showa Denko KK (product name: VGCF (registered trademark) -H, average fiber diameter 150 nm, fiber length 10 μm). The foaming agent is a commercial product (product name: Dieform H850D) manufactured by Dainichiseika Kogyo Co., Ltd.

The above raw materials were put into a twin-screw extruder, kneaded and extruded to obtain a sheet-shaped electromagnetic wave absorber. The radio wave absorber is a foam. The twin-screw extruder includes a T-die (sheet die). The T-die dimensions are 160 mm in width and 2 mm in thickness. The T-die temperature is 140 ° C.

By the above steps, the radio wave absorber of Example B1 was obtained. The radio wave absorber of Example B1 contains a foam. The foam comprises a base material and nanocarbon. The base material contains a styrene-based elastomer and a softening agent. Nanocarbon is dispersed in the foam. The foaming magnification and density in the radio wave absorber of Example B1 are as shown in Table 2 above.

(3-3) Measurement of radio wave absorption characteristics (reflection loss) The measurement system for radio wave absorption characteristics is a free space microwave measurement system (HVS Free Space Measurement System) manufactured by HVS Technologies, Inc. Was used.

The method for measuring the reflection loss is the free space method, which is a measurement method based on JIS R 1679 (vertical incident). The frequency range is 5.6 GHz to 75 GHz.
The measurement procedure is as follows.

(i) In order to measure the blank value, only the metal plate made of aluminum is placed in the measurement sample holder of the free space microwave measurement system, and S11 is measured.
(ii) The metal plate used in (i) above and the sample are placed on top of each other in the sample holder.

(iii) Adjust the compressibility R of the sample to a predetermined value. The compression rate R is a value represented by the following equation (1). The compression ratio R represents the degree to which the sample is compressed.

式（１）においてｄ_０は、圧縮されていないときのサンプルの厚さである。ｄは測定の時点におけるサンプルの厚さである。ｄ_０及びｄは、金属板の厚さを含まない値である。
圧縮率Ｒの単位は％である。

In equation (1), d ₀ is the thickness of the sample when it is not compressed. d is the thickness of the sample at the time of measurement. d ₀ and d are values that do not include the thickness of the metal plate.
The unit of the compression ratio R is%.

(iv) Measure S11.
(v) The reflection loss is calculated by subtracting S11 measured in (iv) above from S11 measured in (i) above.

The above steps (i) to (v) were repeated while changing the compressibility R of the sample. The measurement result for Example A1 is shown in FIG. The measurement results for Example A2 are shown in FIG. The measurement results for Example A3 are shown in FIG. The measurement result for Example A4 is shown in FIG. The measurement results for Comparative Example a1 are shown in FIG. The measurement results for Example B1 are shown in FIGS. 8 and 9.

Each measurement result shows the reflection loss when the radio wave absorber is not compressed and when it is compressed at a predetermined compression rate R. In FIG. 9, "double thickness" indicates a reflection loss when the thickness is doubled without compressing the radio wave absorber.

As shown in FIGS. 3 to 6 and 8, it can be seen that when the radio wave absorber of this embodiment is compressed, the absorption band shifts to the high frequency side. From FIGS. 3 and 7, it can be seen that the width of the absorbed absorption band to be transferred is increased by adding the foaming agent. From FIGS. 3 and 4, it can be seen that the larger the foaming agent, the higher the absorption peak frequency and the larger the amount of reflection loss. From FIGS. 3 and 5, it can be seen that as the amount of nanocarbon increases, the absorption peak frequency is on the low frequency side and the amount of reflection loss increases. From FIGS. 3 and 6, it can be seen that when the foaming magnification is increased, the absorption peak frequency is on the high frequency side and the amount of reflection loss increases.

上記の試験結果から、電波吸収体を圧縮させると、吸収帯域が高周波側に移行することが分かった。
４．他の実施形態
以上、本開示の実施形態について説明したが、本開示は上述の実施形態に限定されることなく、種々変形して実施することができる。 8 and 9 show the return loss measured according to JIS R 1679 (vertical incident). From FIG. 8, it can be seen that the radio wave absorption band changes to the high frequency side when compressed. From FIG. 9, it can be seen that the radio wave absorption band changes to the low frequency side when the thickness is doubled without compression.
For Examples A1, A2, A3, A4 and Comparative Example a1, the absorption band was measured by changing the compression rate. The results are shown in Table 3 and FIG. Further, for Example B1, the absorption band was measured by changing the compression rate. The results are shown in Table 4 and FIG.

From the above test results, it was found that when the radio wave absorber is compressed, the absorption band shifts to the high frequency side.
4. Other Embodiments Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and can be variously modified and implemented.

(1) The function of one component in each of the above embodiments may be shared by a plurality of components, or the function of the plurality of components may be exerted by one component. Further, a part of the configuration of each of the above embodiments may be omitted. Further, at least a part of the configuration of each of the above embodiments may be added or substituted with respect to the configuration of the other embodiments. It should be noted that all aspects included in the technical idea specified from the wording described in the claims are embodiments of the present disclosure.

(2) In addition to the above-mentioned radio wave absorber and radio wave absorber, the present disclosure may be realized in various forms such as an electronic device having the radio wave absorber as a component, a radio wave absorption method, and a method for manufacturing a radio wave absorber. can.

1, 101 ... Radio wave absorber, 3 ... Radio wave absorber, 5 ... Metal plate, 7, 9 ... Press plate, 11 ... Screw, 13 ... Nut, 15 ... Through hole, 17 ... Spacing adjustment jig, 19 ... Main body , 21 ... Lever

Claims (4)

A radio wave absorber containing foam
The foam is
Base material containing elastomer and
The nanocarbon dispersed in the foam and
Equipped with
The content of the nanocarbon is 5 to 45 parts by mass with respect to 100 parts by mass of the base material.
The elastomer is silicone rubber.
The nanocarbon is a vapor deposition carbon fiber having a fiber length of 1 μm to 500 μm.
The absorption peak frequency of the radio wave absorber when the compression rate is 20% shifts to a higher frequency side of 0.5 GHz or more and 3.7 GHz or less than the absorption peak frequency when the compression rate is 0%. Radio absorber. The radio wave absorber according to claim 1.
The vapor phase grown carbon fiber is a radio wave absorber having a diameter of 0.01 μm to 0.2 μm and an aspect ratio of 10 to 500. The radio wave absorber according to claim 1 or 2 ,
A compression unit that compresses at least a part of the radio wave absorber, and
A radio wave absorber equipped with. The radio wave absorbing product according to claim 3 ,
The compression unit is a radio wave absorbing product configured so that the degree of compression of the radio wave absorber can be changed.

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