JP2021164010A - Electromagnetic wave absorption member and radar mechanism - Google Patents

Abstract

To provide an electromagnetic wave absorption member capable of absorbing unnecessary electromagnetic waves.SOLUTION: An electromagnetic wave absorption member provided around a radar device using a millimeter wave or a submillimeter wave, comprises: a first region; and a second region at a position different from the first region. Both of the first region and the second region contain a metal mesh pattern, a resin layer, and a metal layer in order from the inner face side to the outer face side, positioned on the radar device side. An occupancy of the metal mesh pattern of the first region is different from an occupancy of the metal mesh pattern of the second region.SELECTED DRAWING: Figure 1

Description

The present invention relates to an electromagnetic wave absorbing member provided around a radar device that uses millimeter waves or quasi-millimeter waves or around a communication unit of the radar device. The present invention also relates to a radar mechanism including a radar device and an electromagnetic wave absorbing member.

Radar devices are used to detect obstacles around the vehicle. The radar device transmits, for example, a quasi-millimeter wave having a frequency of 3 GHz to 30 GHz, and detects a reflected wave reflected by an obstacle and returned. For example, Patent Document 1 discloses a radar device provided between a rear bumper and a rear end panel of an automobile.

The transmitted wave from the radar device may be reflected by an object other than the assumed obstacle and returned to the radar device. In order to prevent such an unexpected reflected wave from being detected by the radar device, a cover member for regulating a part of the transmission range of the transmitted wave is provided around the radar device of Patent Document 1. .. As the cover member, a type that reflects electromagnetic waves and a type that absorbs electromagnetic waves have been proposed. As a type of cover member that reflects electromagnetic waves, one in which a metal tape is attached to the surface of a synthetic resin plate, one in which a metal layer is formed by vapor deposition or plating of metal on the surface of a synthetic resin, and the like have been proposed. As a type of cover member that absorbs electromagnetic waves, an electromagnetic wave absorbing member formed by mixing carbon into rubber has been proposed.

Japanese Patent No. 601346

In a member of the type that reflects electromagnetic waves, noise reflected by the member may be received by the radar device to cause erroneous detection. Considering this point, it is preferable to use an electromagnetic wave absorbing member that absorbs electromagnetic waves. On the other hand, there is a concern that the electromagnetic wave absorbing member using rubber, which is proposed in Patent Document 1, cannot efficiently absorb noise.

The present invention has been made in consideration of such a point, and an object of the present invention is to provide an electromagnetic wave absorbing member capable of suppressing erroneous detection of a radar device by absorbing unnecessary electromagnetic waves.

The present invention is an electromagnetic wave absorbing member provided around a radar device using millimeter waves or quasi-millimeter waves or around a communication unit of the radar device.
The first area and
A second region located at a position different from that of the first region is provided.
Both the first region and the second region include a metal mesh pattern, a resin layer, and a metal layer in this order from the inner surface side to the outer surface side.
The occupancy rate of the metal mesh pattern in the first region is different from the occupancy rate of the metal mesh pattern in the second region, and is an electromagnetic wave absorbing member.

In the electromagnetic wave absorbing member according to the present invention, the first region may be located on the side surface of the electromagnetic wave absorbing member, and the second region may be located on the back surface of the electromagnetic wave absorbing member.

In the electromagnetic wave absorbing member according to the present invention, the occupancy rate of the metal mesh pattern in the second region may be smaller than the occupancy rate of the metal mesh pattern in the first region.

In the electromagnetic wave absorbing member according to the present invention, the metal mesh pattern of the first region and the second region may include a plating layer.

In the electromagnetic wave absorbing member according to the present invention, the surface of the metal mesh pattern may include uneven portions.

In the electromagnetic wave absorbing member according to the present invention, the surface of the resin layer on the metal mesh pattern side may include a primer layer.

The present invention is a radar mechanism including a radar device using millimeter waves or quasi-millimeter waves, and the electromagnetic wave absorbing member described above located in the vicinity of the radar device or the communication unit of the radar device.

According to the electromagnetic wave absorbing member of the present invention, erroneous detection of the radar device can be suppressed by absorbing unnecessary electromagnetic waves.

It is sectional drawing which shows an example of the radar mechanism which includes a radar apparatus and an electromagnetic wave absorption member. It is a top view which shows an example of the case where the 1st region of an electromagnetic wave absorption member is seen from the inner surface side. It is sectional drawing which shows the case which the 1st region of the electromagnetic wave absorption member was seen from the direction III-III of FIG. It is a top view which shows an example of the case where the 2nd region of an electromagnetic wave absorption member is seen from the inner surface side. It is sectional drawing which shows the case which the 2nd region of the electromagnetic wave absorption member was seen from the VV direction of FIG. It is a graph which shows an example of the shield characteristic of the 1st region and the 2nd region. It is a graph which shows other example of the shield property of the 1st region and the 2nd region. It is sectional drawing which shows an example of the manufacturing method of the electromagnetic wave absorption member. It is sectional drawing which shows an example of the manufacturing method of the electromagnetic wave absorption member. It is sectional drawing which shows an example of the manufacturing method of the electromagnetic wave absorption member. It is sectional drawing which shows one modification of the radar mechanism which includes a radar apparatus and an electromagnetic wave absorption member. It is sectional drawing which shows the radar mechanism which includes the radar apparatus which includes the frame which functions as an electromagnetic wave absorption member. It is sectional drawing which shows the radar apparatus 20 of FIG. 12 enlarged. It is a figure which shows the result of having evaluated the relationship between the occupancy rate of the inner metal layer, and the reflection coefficient in an Example.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings attached to the present specification, the scale, aspect ratio, etc. are appropriately changed from those of the actual product and exaggerated for the sake of ease of understanding.

FIG. 1 is a cross-sectional view showing an example of a radar mechanism 10 provided in an automobile. The radar mechanism 10 is provided, for example, on the inner surface 61 side of the rear bumper 60. In this case, the radar mechanism 10 can detect another vehicle approaching the own vehicle from behind as an obstacle.

The radar mechanism 10 includes a radar device 20 and a cover member 33 that surrounds the radar device 20. The radar device 20 may include a transmitter that transmits electromagnetic waves and a receiver that receives electromagnetic waves reflected by obstacles. Both the transmitter and the receiver may include an antenna. As the electromagnetic wave, millimeter wave or quasi-millimeter wave can be used. Millimeter waves have a wavelength of 1 mm or more and 10 mm or less (frequency of 30 GHz or more and 300 GHz or less). The quasi-millimeter wave has a wavelength of 10 mm or more and 100 mm or less (frequency of 3 GHz or more and 30 GHz or less).

The radar device 20 may include an inner surface 21, an outer surface 22, and a side surface 23. The outer surface 22 is a surface of the radar device 20 that faces the outside of the automobile, and faces, for example, the rear bumper 60. The inner surface 21 is located on the opposite side of the outer surface 22. The side surface 23 extends from the inner surface 21 to the outer surface 22.

In FIG. 1, reference numeral La is an electromagnetic wave that travels outward along the normal direction of the outer surface 22 of the radar device 20 and passes through the rear bumper 60, and is a so-called main beam. On the other hand, in the radar device 20, electromagnetic waves may be generated in addition to the main beam. For example, as indicated by reference numeral Lb, an electromagnetic wave traveling in a direction largely inclined with respect to the normal direction of the outer surface 22 can be generated. The electromagnetic wave Lb is also called a side lobe. Further, as indicated by the reference numeral Lc, an electromagnetic wave radiated from the inner surface 21 side of the radar device 20 may also be generated. The electromagnetic wave Lb and the electromagnetic wave Lc may have a frequency different from that of the electromagnetic wave La. For example, the electromagnetic wave Lb may have a first frequency F1 and the electromagnetic wave Lc may have a second frequency F2. The second frequency F2 of the electromagnetic wave Lc may be higher, lower, or the same as the first frequency F1 of the electromagnetic wave Lb.

When the electromagnetic wave Lb and the electromagnetic wave Lc are reflected by an object other than an obstacle targeted by the radar device 20 and returned to the radar device 20, erroneous detection may occur. In consideration of such a problem, in the present embodiment, it is proposed to configure the cover member 33 so that the electromagnetic wave Lb and the electromagnetic wave Lc can be absorbed. Hereinafter, the cover member 33 will be described.

The cover member 33 is a member provided around the radar device 20 in order to suppress the radar device 20 from detecting electromagnetic waves reflected by an object other than the target obstacle. The cover member 33 is configured to surround, for example, the side surface 23 of the radar device 20. As shown in FIG. 1, the portion of the cover member 33 located on the outer surface 22 side of the radar device 20 may be open. For example, the cover member 33 may include a side surface 31 that surrounds the side surface 23 of the radar device 20, and a back surface 32 that is located on the inner surface 21 side of the radar device 20.

The method of fixing the radar device 20 is arbitrary. For example, the radar device 20 may be located inside the cover member 33 in a state of being attached to a bracket (not shown) fixed to a part of the vehicle body of the automobile. In this case, a through hole for passing the bracket may be formed in, for example, the back surface 32 of the cover member 33.

As will be described in a modified example described later, a member for absorbing electromagnetic waves may be provided inside the radar device 20. The cover member 33 in the present embodiment and the member provided inside the radar device 20 in the modified example described later have a common structure except for the positional relationship with the radar device 20. In the following description, when the common structure is described, the cover member 33 is also referred to as an electromagnetic wave absorbing member 30.

The electromagnetic wave absorbing member 30 includes a first region 30A capable of absorbing the electromagnetic wave Lb of the first frequency F1 and a second region 30B capable of absorbing the electromagnetic wave Lc of the second frequency F2. The second region 30B is at a different position from the first region 30A. In the example shown in FIG. 1, the first region 30A is located on the side surface 31 of the electromagnetic wave absorbing member 30, and the second region 30B is located on the back surface 32 of the electromagnetic wave absorbing member 30. The first region 30A can absorb the electromagnetic wave Lb that has reached the side surface 31 of the electromagnetic wave absorbing member 30. The second region 30B can absorb the electromagnetic wave Lc that has reached the back surface 32 of the electromagnetic wave absorbing member 30. In this way, by setting the absorption characteristics of the electromagnetic wave absorbing member 30 according to the traveling direction and frequency of the unnecessary electromagnetic waves radiated from the radar device 20, the unnecessary electromagnetic waves can be efficiently removed.

Hereinafter, the first region 30A and the second region 30B will be described in detail. First, the first region 30A will be described. FIG. 2 is a plan view showing an example of the case where the first region 30A is viewed from the inner surface side of the electromagnetic wave absorbing member 30. FIG. 3 is a cross-sectional view showing a case where the first region 30A is viewed from the direction III-III of FIG. The inner surface of the electromagnetic wave absorbing member 30 is a surface of the electromagnetic wave absorbing member 30 located on the radar device 20 side. The outer surface of the electromagnetic wave absorbing member 30 is a surface of the electromagnetic wave absorbing member 30 located on the opposite side of the inner surface.

As shown in FIGS. 2 and 3, the first region 30A includes the metal mesh pattern 40, the resin layer 35, and the metal layer 46 in this order from the inner surface side to the outer surface side located on the radar device 20 side.

The resin layer 35 is a layer containing a resin material having an insulating property, and is, for example, a resin substrate. The resin layer 35 includes an inner surface 36 located on the radar device 20 side and an outer surface 37 located on the opposite side of the inner surface 36. Resin materials include low-density polyethylene, high-density polyethylene, i-polypropylene, petroleum resin, polystyrene, s-polystyrene, chroman-inden resin, terpene resin, styrene-divinylbenzene copolymer, ABS resin, methyl polyacrylate, and the like. Ethyl polyacrylate, polyacrylic nitrile, methyl methacrylate, ethyl methacrylate, polycyanoacrylate, polyvinyl acetate, polyvinyl alcohol, polyvinyl formal, polyvinyl acetal, polyvinyl chloride, vinyl chloride / vinyl acetate copolymer, vinyl chloride / Ethylene copolymer, polyvinylidene fluoride, vinylidene fluoride / ethylene copolymer, vinylidene fluoride / propylene copolymer, 1,4-transpolybutadiene, polyoxymethylene, polyethylene glycol, polypropylene glycol, phenol / formarin resin, cresol -Formalin resin, resorcin resin, melamine resin, xylene resin, toluene resin, griptal resin, modified griptal resin, polyethylene terephthalate, polybutylene terephthalate (PBT), unsaturated polyester resin, allyl ester resin, polycarbonate, 6-nylon, 6 , 6-Nylon or 6,10-Nylon and other polyamides, polybenzimidazole, polyamideimide, silicon resin, silicon rubber, silicone resin, furan resin, polyurethane resin, epoxy resin, polyphenylene oxide, polydimethylphenylene oxide, polyphenylene oxide or Polydimethylphenylene oxide and triallyl isocyanul blend, (polyphenylene oxide or polydimethylphenylene oxide, triallyl isocyanul, peroxide) blend, polyxylene, polyphenylensulfide (PPS), polysulfone (PSF), polyether sulfone (PES) ), Polyether ether ketone (PEEK), polyimide (PPI, Capton), liquid crystal resin, a blend of these plurality of materials, and the like can be used. The thickness T1 of the resin layer 35 is, for example, 1 mm or more and 3 mm or less.

As shown in FIGS. 2 and 3, the metal mesh pattern 40 of the first region 30A includes a plurality of inner metal layers 41 arranged on the inner surface 36 of the resin layer 35 in the first cycle P1 with a gap 42. For example, as shown in FIG. 2, the metal mesh pattern 40 has a quadrangle in a plan view and includes a plurality of inner metal layers 41 arranged in two orthogonal directions. The first period P1 is equal to the sum of the width W1 of the inner metal layer 41 and the width S1 of the gap 42 constituting the first region 30A.

The inner metal layer 41 includes, for example, a plating layer formed by a plating treatment. As the metal material constituting the inner metal layer, nickel, aluminum, chromium, lead, gold, silver, copper, tin, zinc, iron, alloys of these metals and the like can be used. The thickness T2 of the inner metal layer 41 is preferably 0.1 μm or more, and more preferably 0.2 μm or more. The thickness T2 of the inner metal layer 41 is preferably 2 μm or less, more preferably 1 μm or less.

The first period P1 of the metal mesh pattern 40 of the first region 30A is smaller than the wavelength of the electromagnetic wave to be absorbed by the electromagnetic wave absorbing member 30. In this case, the region where the metal mesh pattern 40 spreads can affect the electromagnetic waves as one continuous layer. In the following description, when the action of the region where the metal mesh pattern 40 spreads on the electromagnetic wave is described, the "space where the metal mesh pattern 40 spreads" is also simply referred to as "metal mesh pattern 40". The first period P1 is, for example, 3 mm or less, may be 2 mm or less, or may be 1 mm or less. The width W1 of the inner metal layer 41 of the metal mesh pattern 40 of the first region 30A is, for example, 2 mm or less, may be 1 mm or less, or may be 0.5 mm or less. The width S1 of the gap 42 of the metal mesh pattern 40 of the first region 30A is, for example, 1 mm or less, 0.5 mm or less, or 0.2 mm or less.

Since the inner metal layer 41 has conductivity, the dielectric constant of the metal mesh pattern 40 is higher than the dielectric constant of the resin layer 35. The metal mesh pattern 40 can act on electromagnetic waves as a layer having a high dielectric constant. A part of the electromagnetic wave incident on the metal mesh pattern 40 is reflected by the metal mesh pattern 40, and the other part of the electromagnetic wave passes through the metal mesh pattern 40 and is incident on the resin layer 35. The characteristics of the metal mesh pattern 40 with respect to the reflection and transmission of electromagnetic waves are determined based on the dielectric constant of the metal mesh pattern 40.

The dielectric constant of the metal mesh pattern 40 depends on the material of the inner metal layer 41, the occupancy of the inner metal layer 41, and the like. The occupancy rate is the ratio of the total area of the plurality of inner metal layers 41 to the area of the area where the metal mesh pattern 40 spreads. The occupancy rate is calculated in a region where a plurality of inner metal layers 41 are regularly arranged. The occupancy rate E1 of the inner metal layer 41 in the metal mesh pattern 40 of the first region 30A is, for example, 95% or less, 90% or less, 80% or less, 70% or less. You may.

The outer metal layer 46 is a metal layer located on the outer surface 37 side of the resin layer 35. As indicated by reference numerals Lb2 and Lb3 in FIG. 3, the outer metal layer 46 can reflect electromagnetic waves that have passed through the metal mesh pattern 40, entered the resin layer 35, and reached the outer surface 37.

The outer metal layer 46 may include a plating layer formed by the plating treatment, similarly to the inner metal layer 41. Alternatively, the outer metal layer 46 may be a layer formed on the outer surface 37 of the resin layer 35 by a method different from that of the inner metal layer 41. As the metal material constituting the outer metal layer 46, the same material as the inner metal layer 41 can be used. The thickness of the outer metal layer 46 may be the same as the thickness of the inner metal layer 41.

The function of the first region 30A will be described with reference to FIG. As shown by reference numeral Lb1 in FIG. 3, a part of the electromagnetic wave Lb incident on the first region 30A at the incident angle θ1 is reflected by the inner metal layer 41 of the metal mesh pattern 40. Further, as indicated by reference numeral Lb2, the other part of the electromagnetic wave Lb incident on the first region 30A at the incident angle θ1 passes through the metal mesh pattern 40, enters the resin layer 35, and is reflected by the outer metal layer 46. After that, the metal mesh pattern 40 is transmitted again. When the following relational expression (1) is established between the difference Δ1 between the path of the electromagnetic wave Lb1 and the path of the electromagnetic wave Lb2 and the first wavelength λ1 of the electromagnetic wave Lb, the electromagnetic wave Lb1 and the electromagnetic wave Lb2 weaken each other.
Δ1 = (1/4 + m) × λ1 (m is an integer) ... (1)

The difference Δ1 between the path of the electromagnetic wave Lb1 and the path of the electromagnetic wave Lb2 is the incident angle θ1, the occupancy rate E1 of the inner metal layer 41 in the metal mesh pattern 40 of the first region 30A, the thickness of the resin layer 35, the dielectric constant of the resin layer 35, and the like. Determined based on. By appropriately setting the occupancy rate E1, the electromagnetic wave Lb1 and the electromagnetic wave Lb2 can be weakened against each other in the first region 30A. In other words, the first region 30A can absorb the electromagnetic wave Lb having the first wavelength λ1 (first frequency F1). As a result, it is possible to suppress the occurrence of erroneous detection of the radar device 20 due to the electromagnetic wave Lb having the first wavelength λ1 (first frequency F1).

The first region 30A can realize a function related to the shield characteristic other than weakening the electromagnetic wave Lb1 and the electromagnetic wave Lb2. For example, as shown by reference numeral Lb3 in FIG. 3, an electromagnetic wave transmitted through the metal mesh pattern 40 and incident on the resin layer 35 may be repeatedly reflected between the inner metal layer 41 and the outer metal layer 46. In this case, the electromagnetic wave Lb3 is attenuated while passing through the resin layer 35. In this way, the resin layer 35 can also contribute to the absorption characteristics of electromagnetic waves in the first region 30A.

Next, the second region 30B will be described. FIG. 4 is a plan view showing an example of the case where the second region 30B is viewed from the inner surface side of the electromagnetic wave absorbing member 30. FIG. 5 is a cross-sectional view showing a case where the second region 30B is viewed from the VV direction of FIG. Regarding the portion of the second region 30B that can be configured in the same manner as the first region 30A, the same reference numerals as those used in the first region 30A are used, and duplicate description will be omitted.

Similar to the first region 30A, the second region 30B also includes the metal mesh pattern 40, the resin layer 35, and the outer metal layer 46 in this order from the inner surface side to the outer surface side located on the radar device 20 side.

As shown in FIGS. 4 and 5, the metal mesh pattern 40 of the second region 30B includes a plurality of inner metal layers 41 arranged on the inner surface 36 of the resin layer 35 in the second cycle P2 with a gap 42. The second period P2 is equal to the sum of the width W2 of the inner metal layer 41 and the width S2 of the gap 42 constituting the second region 30B.

The function of the second region 30B will be described with reference to FIG. As shown by reference numeral Lc1 in FIG. 5, a part of the electromagnetic wave Lc incident on the second region 30B at the incident angle θ2 is reflected by the inner metal layer 41 of the metal mesh pattern 40. Further, as indicated by the reference numeral Lc2, the other part of the electromagnetic wave Lc incident on the second region 30B at the incident angle θ2 passes through the metal mesh pattern 40, enters the resin layer 35, and is reflected by the outer metal layer 46. After that, the metal mesh pattern 40 is transmitted again. When the following relational expression (2) is established between the difference Δ2 between the path of the electromagnetic wave Lc1 and the path of the electromagnetic wave Lc2 and the second wavelength λ2 of the electromagnetic wave Lc, the electromagnetic wave Lc1 and the electromagnetic wave Lc2 weaken each other.
Δ2 = (1/4 + n) × λ2 (n is an integer) ... (2)

Similar to the difference Δ1, the difference Δ2 between the path of the electromagnetic wave Lc1 and the path of the electromagnetic wave Lc2 is the incident angle θ2, the occupancy rate E2 of the inner metal layer 41 in the metal mesh pattern 40 of the second region 30B, the thickness of the resin layer 35, and the resin. It is determined based on the dielectric constant of the layer 35 and the like. By appropriately setting the occupancy rate E2, the electromagnetic wave Lc1 and the electromagnetic wave Lc2 can be weakened against each other in the second region 30B. That is, similarly to the first region 30A, the second region 30B can absorb the electromagnetic wave Lc having the second wavelength λ2 (second frequency F2). As a result, it is possible to suppress the occurrence of erroneous detection of the radar device 20 due to the electromagnetic wave Lc having the second wavelength λ2 (second frequency F2).

The second period P2 of the metal mesh pattern 40 of the second region 30B may be smaller than the first period P1 of the metal mesh pattern 40 of the first region 30A. The second period P2 of the metal mesh pattern 40 of the second region 30B is, for example, 3 mm or less, may be 2 mm or less, or may be 1 mm or less. The width W2 of the inner metal layer 41 of the metal mesh pattern 40 of the second region 30B may be smaller than the width W1 of the inner metal layer 41 of the metal mesh pattern 40 of the first region 30A. The width W2 of the inner metal layer 41 of the metal mesh pattern 40 of the second region 30B is, for example, 2 mm or less, may be 1 mm or less, or may be 0.5 mm or less. The width S2 of the gap 42 of the metal mesh pattern 40 in the second region 30B is, for example, 1 mm or less, 0.5 mm or less, or 0.2 mm or less.

The occupancy rate E2 of the inner metal layer 41 in the metal mesh pattern 40 of the second region 30B may be smaller than the occupancy rate E1 of the inner metal layer 41 in the metal mesh pattern 40 of the first region 30A. The occupancy rate E2 of the inner metal layer 41 in the metal mesh pattern 40 of the second region 30B is, for example, 95% or less, 90% or less, 80% or less, 70% or less. You may. The difference between the occupancy rate E1 and the occupancy rate E2 may be 3% or more, 5% or more, or 10% or more.

FIG. 6 is a graph showing an example of the shield characteristics of the first region and 30A and the second region 30B. In FIG. 6, the horizontal axis represents the frequency of the electromagnetic wave incident on the first region 30A or the second region 30B, and the vertical axis represents the reflection coefficient of the electromagnetic wave reflected by the first region 30A or the second region 30B.

As shown in FIG. 6, the first region and 30A show a negative peak at a predetermined frequency determined based on the above relational expression (1). The second region 30B shows a negative peak at a predetermined frequency determined based on the above relational expression (2). By appropriately setting the occupancy of the metal mesh pattern 40 in each of the first region 30A and the second region 30B, the negative peak of the first region 30A is positioned at the first frequency F1, and the negative peak of the second region 30B is negative. The peak can be positioned at the second frequency F2. As a result, the first region 30A and the second region 30B can efficiently absorb the electromagnetic wave Lb and the electromagnetic wave Lc, respectively, so that it is possible to suppress the occurrence of erroneous detection of the radar device 20.

FIG. 7 is a graph showing other examples of the shield characteristics of the first region and 30A and the second region 30B. As shown in FIG. 7, even if the first frequency F1 in which the negative peak of the first region 30A is located and the second frequency F2 in which the negative peak of the second region 30B is located are coincident or substantially coincident with each other. good.

As shown in FIGS. 3 and 5, the incident angle θ1 of the electromagnetic wave Lb incident on the first region 30A is different from the incident angle θ2 of the electromagnetic wave Lc incident on the second region 30B. Therefore, if the occupancy rate E1 of the metal mesh pattern 40 in the first region 30A and the occupancy rate E2 of the metal mesh pattern 40 in the second region 30B are the same, the position of the negative peak in the first region 30A is , Different from the position of the negative peak in the second region 30B. According to the present embodiment, by appropriately setting the difference between the occupancy rate E1 and the occupancy rate E2, as shown in FIG. 7, the position of the negative peak in the first region 30A and the negative peak position in the second region 30B are negative. The position of the peak can be matched or almost matched.

Next, an example of the method for manufacturing the electromagnetic wave absorbing member 30 described above will be described.

First, as shown in FIG. 8, the resin layer 35 is prepared. For example, a resin substrate constituting the resin layer 35 is prepared.

As shown in FIG. 8, the inner surface 36 of the resin layer 35 may include the uneven portion 38. The uneven portion 38 can be formed on the inner surface 36 of the resin layer 35, for example, by molding a resin material using a mold containing the corresponding uneven portion.

Subsequently, as shown in FIG. 9, the inner surface 36 of the resin layer 35 may be subjected to a primer treatment to form the primer layer 39 on the inner surface 36. As shown in FIG. 9, the primer layer 39 may also be formed on the outer surface 37 of the resin layer 35. The primer treatment may include a molecular bonding treatment.

The molecular bonding treatment includes a supply step of supplying the molecular bonding agent to the inner surface 36 of the resin layer 35 and a drying step of drying the molecular bonding agent on the inner surface 36. In the supply step, the molecular bonding agent can be supplied to the inner surface 36 by coating, dipping, spraying or the like. In the drying step, the molecular bonding agent can be dried, for example, by heating the resin layer 35.

Subsequently, as shown in FIG. 10, an inner metal layer 41 is formed on the inner surface 36 side of the resin layer 35. For example, the inner metal layer 41 may be formed by plating. The outer metal layer 46 may be formed on the outer surface 37 side of the resin layer 35 at the same time as the inner metal layer 41.

As shown in FIG. 10, the uneven portion 43 corresponding to the uneven portion 38 of the inner surface 36 may appear on the inner metal layer 41. Such a concavo-convex portion 43 can be formed by reducing the thickness of the primer layer 39 and the thickness of the inner metal layer 41 to such an extent that it can follow the concavo-convex portion 38.

Since the inner metal layer 41 includes the uneven portion 43, the surface area of the inner metal layer 41 can be increased as compared with the case where the inner metal layer 41 is flat. As a result, the shielding characteristics of the inner metal layer 41 can be improved as compared with the case where the inner metal layer 41 is flat.

The characteristics of the uneven portion 43 of the inner metal layer 41 can be represented by the arithmetic mean roughness Ra and the maximum height Rz defined in JIS B 0601: 2001.
The arithmetic mean roughness Ra of the inner metal layer 41 is preferably 0.5 μm or more, and more preferably 1 μm or more. The arithmetic average roughness Ra of the inner metal layer 41 is preferably 10 μm or less, and more preferably 7 μm or less.
The maximum height Rz of the inner metal layer 41 is preferably 10 μm or more, and more preferably 15 μm or more. The maximum height Rz of the inner surface 36 of the inner metal layer 41 is preferably 100 μm or less, more preferably 70 μm or less.
As a measuring instrument for measuring the arithmetic mean roughness Ra and the maximum height Rz, a KEYENCE laser microscope VKX100 / 110 can be used.

Subsequently, a processing step of partially processing the inner metal layer 41 is carried out. As a result, the above-mentioned gap 42 can be formed in the inner metal layer 41. The processing step includes, for example, a step of irradiating the inner metal layer 41 with a laser beam to partially remove the inner metal layer 41.

In the region corresponding to the first region 30A, for example, on the side surface 31 of the electromagnetic wave absorbing member 30, the inner metal layer 41 is processed so that the width of the inner metal layer 41 is W1. In the region corresponding to the second region 30B, for example, on the back surface 32 of the electromagnetic wave absorbing member 30, the inner metal layer 41 is processed so that the width of the inner metal layer 41 is W2. In this way, the electromagnetic wave absorbing member 30 including the first region 30A and the second region 30B can be obtained.

According to the present embodiment, the unnecessary electromagnetic waves are made efficient by providing the first region 30A and the second region 30B in the electromagnetic wave absorbing member 30 according to the traveling direction and frequency of the unnecessary electromagnetic waves emitted from the radar device 20. Can be removed as a target. As a result, it is possible to suppress the occurrence of erroneous detection in the radar device 20.

Further, according to the present embodiment, by forming the metal mesh pattern 40 by the plating treatment, the degree of freedom in the shape of the inner surface of the electromagnetic wave absorbing member 30 on which the metal mesh pattern 40 is formed can be increased. Therefore, for example, a molded product of a resin material can be used as the resin layer 35 of the electromagnetic wave absorbing member 30.

Further, according to the present embodiment, the inner metal layer 41 constituting the metal mesh pattern 40 is formed by applying a primer treatment to the inner surface 36 of the resin layer 35 and providing the uneven portion 38 on the inner surface 36 of the resin layer 35. The thickness of the metal can be reduced. Thereby, the cost of the electromagnetic wave absorbing member 30 can be reduced. Further, since the uneven portion 43 can be provided on the inner metal layer 41 of the metal mesh pattern 40, the shielding characteristics of the metal mesh pattern 40 can be improved.

It is possible to make various changes to the above-described embodiment. Hereinafter, a modified example will be described with reference to the drawings as necessary. In the following description and the drawings used in the following description, the same codes as those used for the corresponding parts in the above-described embodiment will be used for the parts that can be configured in the same manner as in the above-described embodiment. Duplicate explanations will be omitted. Further, when it is clear that the action and effect obtained in the above-described embodiment can be obtained in the modified example, the description thereof may be omitted.

(First modification)
In the above-described embodiment, the first region 30A having the metal mesh pattern 40 having the occupancy rate E1 is located on the side surface 31, and the second region 30B having the metal mesh pattern 40 having the occupancy rate E2 different from the occupancy rate E1 is located. An example located on the back surface 32 is shown. However, the arrangement of the first region 30A and the second region 30B is arbitrary and can be appropriately determined according to the traveling direction and frequency of the unnecessary electromagnetic wave emitted from the radar device 20. For example, as shown in FIG. 11, the second region 30B may be located at a position different from that of the first region 30A on the side surface 31 of the electromagnetic wave absorbing member 30.

(Second modification)
In the above-described embodiment, an example is shown in which the cover member 33 provided around the radar device 20 functions as the electromagnetic wave absorbing member 30. In this modification, an example in which the frame 28 provided around the communication unit 24 of the radar device 20 functions as the electromagnetic wave absorbing member 30 will be described.

FIG. 12 is a cross-sectional view showing an example of the radar mechanism 10. The radar device 20 includes a communication unit 24 and a frame 28 provided around the communication unit 24. The communication unit 24 includes at least one of a transmitter and a receiver. The frame 28 may hold the communication unit 24. The radar device 20 may include a case 29 that covers the communication unit 24 and the frame 28.

FIG. 13 is an enlarged cross-sectional view showing the radar device 20 of FIG. The frame 28 may include a side surface 26 that surrounds the side surface of the communication unit 24, and a back surface 27 that is located on the inner surface 21 side of the radar device 20.

As shown in FIG. 13, the frame 28 includes a first region 30A and a second region 30B. The first region 30A is configured to be able to absorb the electromagnetic wave Lb of the first frequency F1 as in the case of the above-described embodiment. The second region 30B is configured to be able to absorb the electromagnetic wave Lc of the second frequency F2, as in the case of the above-described embodiment. That is, the frame 28 can function as the electromagnetic wave absorbing member 30 in the same manner as the cover member 33 of the above-described embodiment. As shown in FIG. 13, the first region 30A may be located on the side surface 26 and the second region 30B may be located on the back surface 27.

According to this modification, by providing the electromagnetic wave absorbing member 30 inside the radar device 20, unnecessary electromagnetic waves can be efficiently removed inside the radar device 20. Further, by appropriately setting the occupancy rate E1 of the metal mesh pattern 40 of the first region 30A and the occupancy rate E2 of the metal mesh pattern 40 of the second region 30B, the electromagnetic waves absorbed by the first region 30A and the second region 30B are absorbed. Frequency and angle of incidence can be adjusted.

Next, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the description of the following Examples as long as the gist of the present invention is not exceeded.

(Example 1)
The electromagnetic wave absorbing member 30 is configured so that the occupancy rate E1 of the inner metal layer 41 in the metal mesh pattern 40 of the first region 30A is 72%. The width W1 of the inner metal layer 41 was 0.2 mm, and the width S1 of the gap 42 was 0.07 mm. The thickness of the resin layer 35 was 2.3 mm. Subsequently, the reflectance coefficient of the first region 30A was measured. The results are shown in FIG. The negative peak was located at about 104 GHz.

(Example 2)
The electromagnetic wave absorbing member 30 is configured so that the occupancy rate E1 of the inner metal layer 41 in the metal mesh pattern 40 of the first region 30A is 85%. The width W1 of the inner metal layer 41 was 0.4 mm, and the width S1 of the gap 42 was 0.07 mm. The thickness of the resin layer 35 was 2.3 mm. Subsequently, the reflectance coefficient of the first region 30A was measured. The results are shown in FIG. The negative peak was located at about 99 GHz.

(Example 3)
The electromagnetic wave absorbing member 30 is configured so that the occupancy rate E1 of the inner metal layer 41 in the metal mesh pattern 40 of the first region 30A is 89%. The width W1 of the inner metal layer 41 was 0.6 mm, and the width S1 of the gap 42 was 0.07 mm. The thickness of the resin layer 35 was 2.3 mm. Subsequently, the reflectance coefficient of the first region 30A was measured. The results are shown in FIG. The negative peak was located at about 96 GHz.

(Example 4)
The electromagnetic wave absorbing member 30 is configured so that the occupancy rate E1 of the inner metal layer 41 in the metal mesh pattern 40 of the first region 30A is 94%. The width W1 of the inner metal layer 41 was 1.2 mm, and the width S1 of the gap 42 was 0.07 mm. The thickness of the resin layer 35 was 2.3 mm. Subsequently, the reflectance coefficient of the first region 30A was measured. The results are shown in FIG. No clear negative peak could be observed.

As shown in FIG. 14, the position and height of the negative peak can be adjusted by changing the occupancy of the inner metal layer 41 in the metal mesh pattern 40.

10 Radar mechanism 20 Radar device 21 Inner surface 22 Outer surface 23 Side surface 24 Communication unit 26 Side surface 27 Back surface 28 Frame 29 Case 30 Electromagnetic wave absorbing member 30A First area 30B Second area 31 Side surface 32 Back surface 33 Cover member 35 Resin layer 36 Inner surface 37 Outer surface 40 Metal mesh pattern 41 Inner metal layer 42 Gap 46 Outer metal layer 60 Rear bumper 61 Inner surface La 1st electromagnetic wave Lb 2nd electromagnetic wave Lc 3rd electromagnetic wave

Claims (7)

An electromagnetic wave absorbing member provided around a radar device that uses millimeter waves or quasi-millimeter waves or around a communication unit of the radar device.
The first area and
A second region located at a position different from that of the first region is provided.
Both the first region and the second region include a metal mesh pattern, a resin layer, and a metal layer in this order from the inner surface side to the outer surface side.
An electromagnetic wave absorbing member in which the occupancy rate of the metal mesh pattern in the first region is different from the occupancy rate of the metal mesh pattern. The first region is located on the side surface of the electromagnetic wave absorbing member.
The electromagnetic wave absorbing member according to claim 1, wherein the second region is located on the back surface of the electromagnetic wave absorbing member. The electromagnetic wave absorbing member according to claim 2, wherein the occupancy rate of the metal mesh pattern in the second region is smaller than the occupancy rate of the metal mesh pattern in the first region. The electromagnetic wave absorbing member according to any one of claims 1 to 3, wherein the metal mesh pattern of the first region and the second region includes a plating layer. The electromagnetic wave absorbing member according to claim 4, wherein the surface of the metal mesh pattern includes an uneven portion. The electromagnetic wave absorbing member according to claim 4 or 5, wherein the surface of the resin layer on the metal mesh pattern side includes a primer layer. Radar devices that use millimeter or quasi-millimeter waves,
A radar mechanism comprising the electromagnetic wave absorbing member according to any one of claims 1 to 6 surrounding the radar device.

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