WO2021199917A1 - Method for manufacturing radio wave absorber, radio wave absorber, and radar mechanism - Google Patents

Method for manufacturing radio wave absorber, radio wave absorber, and radar mechanism Download PDF

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Publication number
WO2021199917A1
WO2021199917A1 PCT/JP2021/008774 JP2021008774W WO2021199917A1 WO 2021199917 A1 WO2021199917 A1 WO 2021199917A1 JP 2021008774 W JP2021008774 W JP 2021008774W WO 2021199917 A1 WO2021199917 A1 WO 2021199917A1
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Prior art keywords
radio wave
layer
wave absorber
conductive
absorption layer
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PCT/JP2021/008774
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French (fr)
Japanese (ja)
Inventor
誠 村中
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株式会社 ニフコ
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B15/00—Layered products comprising a layer of metal
    • B32B15/04—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material
    • B32B15/08—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B7/00—Layered products characterised by the relation between layers; Layered products characterised by the relative orientation of features between layers, or by the relative values of a measurable parameter between layers, i.e. products comprising layers having different physical, chemical or physicochemical properties; Layered products characterised by the interconnection of layers
    • B32B7/02—Physical, chemical or physicochemical properties
    • B32B7/025—Electric or magnetic properties
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P11/00—Apparatus or processes specially adapted for manufacturing waveguides or resonators, lines, or other devices of the waveguide type
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q17/00—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K9/00—Screening of apparatus or components against electric or magnetic fields

Definitions

  • the present invention includes a method for manufacturing a radio wave absorber, a radio wave absorber and a radar mechanism, more specifically, a method for manufacturing a radio wave absorber that absorbs millimeter waves or quasi-millimeter waves, the radio wave absorber, and the radio wave absorber. Regarding the radar mechanism.
  • a radar device is used to detect obstacles around the vehicle.
  • the radar device transmits, for example, millimeter waves (30 GHz to 300 GHz) or quasi-millimeter waves (3 GHz to 30 GHz), and detects reflected waves that are reflected by obstacles and returned.
  • Patent Document 1 describes a radar device provided between a rear bumper and a rear end panel of an automobile.
  • Radio waves transmitted from the radar device may be reflected by an object other than the assumed obstacle and return to 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 radio waves and a type that absorbs radio waves have been proposed.
  • cover member that reflects radio waves one in which a metal tape is attached to the surface of a synthetic resin plate, or one in which a metal layer is formed by vapor deposition or plating of metal on the surface of a synthetic resin has been proposed.
  • a radio wave absorber configured by mixing carbon into rubber has been proposed.
  • Patent Document 2 describes a millimeter-wave absorber in which a reflective layer made of a metal thin film or the like and an absorbing layer containing carbon black are laminated, and is a real number portion of the dielectric constant of the absorbing layer at a frequency of 50 GHz to 90 GHz. Is described as 3.0 or more.
  • Patent No. 601346 Japanese Unexamined Patent Publication No. 2004-296758
  • the position of the absorption peak of the radio wave absorber also varies, and the absorption peak may deviate from the desired frequency range. ..
  • the thickness (plate thickness) of the absorption layer varies
  • the position of the absorption peak of the radio wave absorber also varies. Variations in the thickness of the absorbent layer are particularly likely to occur when the absorbent layer is formed by injection molding.
  • the relative permittivity of the absorption layer varies, the position of the absorption peak of the radio wave absorber also varies. The relative permittivity of the absorbent layer is particularly likely to occur when the absorbent layer contains a conductive material.
  • FIG. 9 shows the experimental results of the absorption characteristics of the two-layer structure radio wave absorber when the thickness (t) of the absorption layer varies.
  • an object of the present invention is to provide a method for manufacturing a radio wave absorber having a conductive absorption layer formed by injection molding and having an absorption peak in a desired frequency band, a radio wave absorber, and a radar mechanism. And.
  • the method for manufacturing a radio wave absorber according to the present invention is as follows.
  • An absorbent layer containing a conductive material is formed by injection molding,
  • a reflective layer is formed on one of the main surfaces of the absorbent layer,
  • a conductive layer is formed on the other main surface of the absorption layer,
  • the conductive layer is processed into a plurality of conductive patches so that the area occupancy is based on the thickness of the absorbent layer.
  • the area occupancy rate is made smaller than the predetermined occupancy rate, and when the thickness of the absorption layer is thinner than the design value, the area occupancy rate is smaller than the occupancy rate. May also be increased.
  • the absorption layer is injection-molded using a material having a relative permittivity of 3.9 or more and 6.3 or less.
  • the conductive layer may be formed in at least a part of the other main surface of the absorption layer so that the area occupancy in the region is 90% or less.
  • the reflective layer may be formed of a metal that reflects millimeter or quasi-millimeter waves.
  • the reflective layer and the conductive layer may be formed at the same time by a double-sided plating method.
  • the radio wave absorber according to the present invention is A radio wave absorber that absorbs millimeter or quasi-millimeter waves
  • the absorption layer has a relative permittivity of 3.9 or more and 6.3 or less, and the area occupancy of the plurality of conductive patches in the region is 90% or less.
  • the reflective layer may be made of a metal that reflects millimeter waves or quasi-millimeter waves.
  • the metal may consist of plating.
  • the radar mechanism according to the present invention is Radar devices that use millimeter or quasi-millimeter waves, A cover member composed of the radio wave absorber and With The cover member is provided so that the other main surface of the absorption layer on which the plurality of conductive patches are formed faces the inner surface and / or the side surface of the radar device.
  • a radio wave absorber having a conductive absorption layer formed by injection molding and having an absorption peak in a desired frequency band.
  • FIG. 1 It is a flowchart for demonstrating an example of the manufacturing method of the radio wave absorber which concerns on embodiment. It is a figure which shows whether the radio wave absorber satisfies the absorption characteristic condition when the relative permittivity of an absorption layer is changed. This is an experimental result showing the frequency characteristics of the reflectance coefficient of the radio wave absorber when the relative permittivity of the absorption layer is changed. This is an experimental result showing the frequency characteristics of the reflectance coefficient of the radio wave absorber when the relative permittivity of the absorption layer is changed. This is an experimental result showing the frequency characteristics of the reflectance coefficient of the radio wave absorber when the area occupancy of the conductive patch is changed. It is a top view which shows a part of the radio wave absorber which concerns on embodiment. FIG.
  • FIG. 6 is a cross-sectional view taken along the line II of FIG. It is sectional drawing which shows an example of the radar mechanism which includes a radar device and a radio wave absorber. It is a figure which shows the absorption characteristic of the radio wave absorber of the two-layer structure when the thickness of the absorption layer changes.
  • an absorption layer containing a conductive material is formed by injection molding (step S1).
  • the absorbent layer is made of polypropylene (PP) and the conductive material is conductive carbon black.
  • the conductive material is not limited to carbon black, and may be carbon nanotubes or other materials such as fine particles of metal or metal oxide.
  • the relative permittivity of the absorption layer is determined so as to satisfy a predetermined absorption characteristic condition.
  • the absorption characteristic condition of the present embodiment is that there is a portion where the reflection coefficient of the radio wave absorber (three-layer type) is ⁇ 10 dB or more in the frequency band of 70 to 90 GHz.
  • FIG. 2 shows whether or not the radio wave absorber satisfies the absorption characteristic condition when the relative permittivity of the absorption layer is changed.
  • 3 (a), (b), (c), and (d) show the relative permittivity and thickness of the absorption layer of 3.4 and 2.5 mm, 3.9 and 3.4 mm, 4.5 and 2, respectively. It is a graph which shows the radio wave absorption characteristic of the radio wave absorber in the case of .3 mm, 4.8 and 1.2 mm.
  • the relative permittivity and thickness of the absorption layer are 5.5 and 1.2 mm, 6.3 and 1.1 mm, 7.1 and 2, respectively.
  • the conductive material contained in the absorption layer is not limited to polypropylene and conductive polypropylene containing carbon black.
  • the conductive material may be composed of other resins and conductive fillers.
  • the means for changing the relative permittivity of the absorbing layer is not limited to the means for changing the ratio of the conductive material in the absorbing layer.
  • the relative permittivity of the absorption layer may be changed by other means.
  • the thickness of the absorption layer in the examples shown in FIGS. 3 (d), 4 (a), and 4 (b) is 1.1 mm or 1.2 mm.
  • the thickness of the absorption layer in the examples shown in FIGS. 3 (a), 3 (c) and 4 (c) is 2.3 mm or 2.5 mm.
  • the thickness of the absorption layer is When they are substantially the same, the absorption peak of the radio wave absorber shifts as the relative permittivity of the absorption layer changes. More specifically, the higher the relative permittivity of the absorption layer, the lower the frequency of the absorption peak.
  • the absorption characteristic condition is satisfied when the relative permittivity of the absorption layer is 3.9 to 6.3.
  • the absorption layer is formed by injection molding using a material in which the ratio of the conductive material is adjusted so that the relative permittivity of the absorption layer is 3.9 or more and 6.3 or less. do.
  • a reflective layer is formed on one main surface (for example, the lower surface) of the absorption layer formed in step S1 (step S2).
  • the reflective layer is formed of a metal (nickel) that reflects millimeter or quasi-millimeter waves.
  • the reflective layer is formed by electroless plating.
  • the reflective layer may be formed by electrolytic plating.
  • a conductive layer is formed on the other main surface (for example, the upper surface) of the absorption layer formed in step S1 (step S3).
  • the conductive layer is formed by electroless plating.
  • the conductive layer may be formed by electrolytic plating.
  • the metal material of the reflective layer and the conductive layer may be an alloy containing nickel, aluminum, chromium, lead, gold, silver, copper, tin, zinc, iron or an alloy of these metals. good.
  • the degree of freedom regarding the shape of the absorbing layer can be increased.
  • the reflective layer 3 and the plurality of conductive patches 4 can be formed on the bowl-shaped absorbing layer, for example, as in the cover member 30 described later.
  • the conductive layer may be formed over the entire main surface of the absorption layer, or may be formed only in a part of the main surface (radio wave absorption region).
  • steps S2 and S3 may be performed in the reverse order. Further, a double-sided plating method may be used in which plating layers (reflection layer and conductive layer) are formed on both sides of the absorption layer at the same time.
  • a catalyst step of adhering a catalyst to the surface of the absorption layer may be carried out before the plating step.
  • the catalyst step may include, for example, a pickling step, a catalyst applying step, a water washing step, a catalyst activation step, a water washing step, and the like.
  • the conductive layer is processed into a plurality of conductive patches so that the area occupancy is based on the thickness of the absorption layer (step S4).
  • the processing of the conductive layer is performed, for example, by irradiating the conductive layer with laser light to partially remove the conductive layer.
  • the conductive layer may be processed by using a blade or by etching.
  • the plurality of conductive patches formed in step S4 have a quadrangular shape, but the specific shape is not particularly limited as long as they are not connected to each other.
  • the "area occupancy” is the conductivity of the sum of the areas of the plurality of conductive patches in the region (conductive patch forming region) in which the plurality of conductive patches are provided on the main surface of the absorption layer. It is the ratio to the area of the patch forming area. For example, when the conductive patch is formed over the entire surface of the main surface of the absorbing layer, the area occupancy is a value obtained by dividing the total area of each conductive patch by the area of the main surface of the absorbing layer.
  • step S4 the area occupancy of the plurality of conductive patches is determined based on the thickness of the absorbing layer.
  • the thickness measured for the absorption layer formed in step S1 is used as the thickness of the absorption layer.
  • the area occupancy rate is made smaller than the predetermined occupancy rate (predetermined occupancy rate), and conversely, when it is thinner than the design value, the area occupancy rate is set to the predetermined occupancy rate. Make it larger than. Thereby, even when the thickness of the absorption layer formed by injection molding deviates from the design value, the absorption peak can be adjusted to a desired frequency range. This will be described in detail below.
  • the absorption peak of the radio wave absorber shifts when the thickness of the absorption layer changes. More specifically, when the thickness of the absorption layer is thicker than the design value, the frequency of the absorption peak decreases, and conversely, when the thickness of the absorption layer is thinner than the design value, the frequency of the absorption peak increases. Further, as described with reference to FIGS. 3 and 4, the higher the relative permittivity of the absorption layer, the lower the frequency of the absorption peak.
  • FIG. 5 shows the measurement of the absorption peak when the area occupancy of the conductive patch is changed when the thickness and the relative permittivity of the absorbent layer are fixed (thickness: 2.30 mm, relative permittivity: 4.5). The result is shown. It can be seen that as the area occupancy decreases to 94%, 90%, 85%, and 72%, the absorption peak becomes deeper and shifts to the higher frequency side.
  • the area occupancy of the conductive patch is set to the predetermined occupancy. By making it smaller than, the absorption peak of the radio wave absorber is shifted to the high frequency side.
  • the thickness of the absorption layer formed by injection molding is thinner than the design value (that is, when the absorption peak of the radio wave absorber shifts to the high frequency side), the area occupancy of the conductive patch is occupied as a predetermined value. By making it larger than the rate, the absorption peak of the radio wave absorber is shifted to the low frequency side.
  • the area occupancy of the conductive patch is made smaller than the predetermined occupancy. This shifts the absorption peak of the radio wave absorber to the high frequency side.
  • the relative permittivity of the absorption layer is lower than the design value (that is, when the absorption peak of the radio wave absorber shifts to the high frequency side)
  • the area occupancy of the conductive patch is larger than the predetermined occupancy.
  • the absorption peak of the radio wave absorber can be made to fall within a desired frequency range. Therefore, even when the absorption layer is formed by using a method such as injection molding in which the thickness is likely to vary, a desired absorption peak can be realized. Therefore, injection molding can be adopted for cost reduction. Further, even when the relative permittivity of the absorption layer varies, a desired absorption peak can be realized.
  • the relative permittivity of the absorbent layer is particularly likely to occur when the absorbent layer contains a conductive material.
  • the absorbent layer is injection-molded using a material adjusted to have a relative permittivity of 3.9 or more and 6.3 or less
  • the conductive layer is the other main surface of the absorbent layer ( It is formed in at least a part of the region (upper surface) (conductive patch forming region) so that the area occupancy in the region is 90% or less.
  • a radio wave absorber having a conductive absorption layer formed by injection molding and having an absorption peak in a desired frequency band can be obtained. Can be manufactured.
  • FIG. 6 is a plan view showing a part of the radio wave absorber 1 according to the present embodiment
  • FIG. 7 is a cross-sectional view taken along the line II of FIG.
  • the radio wave absorber 1 is a radio wave absorber that absorbs millimeter waves or quasi-millimeter waves, and as shown in FIGS. 6 and 7, the conductive absorption layer 2 and the absorption layer 2 It includes a reflective layer 3 formed on one main surface and a plurality of conductive patches 4 formed on at least a part of the other main surface of the absorbing layer 2 (conductive patch forming region).
  • the reflective layer 3 and the plurality of conductive patches 4 are made of metal plating.
  • the absorption layer 2 is a layer containing a conductive material such as carbon black and formed by injection molding.
  • the thickness T of the absorption layer 2 is, for example, 0.5 mm or more and 4 mm or less.
  • the absorption layer 2 is made of polypropylene in which conductive carbon black is dispersed.
  • the reflective layer 3 arrives at the radio wave absorber 1 from the conductive patch 4 side and reflects the radio waves transmitted through the absorbing layer 2. Further, the reflective layer 3 reflects radio waves arriving at the radio wave absorber 1 from the reflective layer 3 side.
  • the reflective layer 3 is made of a metal (nickel) that reflects millimeter waves or quasi-millimeter waves.
  • the thickness of the reflective layer 3 is, for example, 0.2 ⁇ m or more, may be 0.3 ⁇ m or more, or may be 0.5 ⁇ m or more. By making the thickness of the reflective layer 3 0.2 ⁇ m or more, the surface resistance of the reflective layer 3 can be reduced, and the radio waves arriving at the radio wave absorber 1 can be reflected by the reflective layer 3.
  • the thickness of the reflective layer 3 may be 1.0 ⁇ m or less, 0.8 ⁇ m or less, 0.7 ⁇ m or less, or 0.6 ⁇ m or less. By reducing the thickness of the reflective layer 3 to 1.0 ⁇ m or less, the cost of the reflective layer 3 can be reduced.
  • the plurality of conductive patches 4 are configured to be isolated from each other by processing the conductive layers formed on the main surface of the absorption layer 2 with a laser or the like. As shown in FIG. 6, the conductive patches 4 are provided apart from each other by a plurality of grid-like grooves 5. The absorption layer 2 is exposed in the groove 5.
  • the thickness of the conductive patch 4 is preferably 0.1 ⁇ m or more, more preferably 0.2 ⁇ m or more.
  • the thickness of the inner metal layer 41 is preferably 2 ⁇ m or less, more preferably 1 ⁇ m or less.
  • the conductive patches 4 are formed in a square shape (square), but the shape of the conductive patches 4 is not limited to this unless they are connected to each other.
  • the shape of the conductive patch 4 may be triangular or hexagonal, or may be circular or elliptical.
  • the dielectric constant of the conductive mesh pattern including the conductive patch 4 and the groove 5 is higher than the dielectric constant of the absorption layer 2.
  • the conductive mesh pattern acts on radio waves as a layer having a high dielectric constant. A part of the radio wave incident on the conductive mesh pattern is reflected by the conductive mesh pattern, and the other part of the radio wave passes through the conductive mesh pattern and is incident on the absorption layer 2. The characteristics of the conductive mesh pattern with respect to the reflection and transmission of radio waves are determined based on the dielectric constant of the conductive mesh pattern.
  • the dielectric constant of the conductive mesh pattern depends on the area occupancy of the conductive patch 4 and the like.
  • the absorption layer 2 has a relative permittivity of 3.9 or more and 6.3 or less, and the area occupancy of the plurality of conductive patches 4 in the conductive patch forming region is large. It is 90% or less.
  • the absorption characteristic condition can be satisfied. Specifically, even when the thickness T of the absorption layer 2 varies to some extent (for example, ⁇ 0.05 mm), it satisfies the absorption characteristic that there is a portion having a reflectance coefficient of -10 dB in the frequency band of 70 to 90 GHz. be able to.
  • the ratio of the conductive PP is 50% or more and 95% or less, so that the relative permittivity of the absorption layer 2 is 3.9 or more and 6.3 or less.
  • the area occupancy of the conductive patch 4 is 90% or less by reducing the area (patch size) of the conductive patch 4 under the condition that the width of the groove 5 is constant. For example, in FIG. 6, if the width S of the groove 5 is 0.1 mm and the length W of one side of the square conductive patch 4 is 0.9 mm, the area occupancy is about 90%.
  • the insulating material constituting the absorption layer 2 is not limited to polypropylene.
  • 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, polyacrylic Ethyl acid acid, 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 Polymer, polyvinylidene fluoride, vinylidene fluoride / ethylene copolymer, vinylidene fluoride / propylene copolymer, 1,4-trans
  • the metal material constituting the reflective layer 3 and the conductive patch 4 is not limited to nickel.
  • the metal material an alloy containing nickel, aluminum, chromium, lead, gold, silver, copper, tin, zinc, iron, or an alloy of these metals may be used.
  • the metal materials of the reflective layer 3 and the conductive patch 4 may be different metals from each other.
  • FIG. 8 is a cross-sectional view showing a radar mechanism 10 provided in an automobile.
  • the radar mechanism 10 is provided so as to face the inner surface 61 of the rear bumper 60 so that another vehicle approaching the own vehicle from behind can be detected as an obstacle. It is configured.
  • the radar mechanism 10 includes a radar device 20 that transmits and receives millimeter waves or quasi-millimeter waves, and a cover member 30 composed of a radio wave absorber 1.
  • the radar device 20 includes 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 and faces the bottom surface of the cover member 30.
  • the side surface 23 is a surface that connects the inner surface 21 and the outer surface 22, and faces the side surface (wall surface) of the cover member 30.
  • the method of fixing the radar device 20 is arbitrary.
  • the radar device 20 may be located inside the cover member 30 in a state of being attached to a bracket (not shown) fixed to a part of the vehicle body of the automobile.
  • a through hole for passing the bracket is formed on the bottom surface of the cover member 30.
  • the symbol La is a radio 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 indicates a so-called main beam.
  • radio waves may be generated in addition to the main beam.
  • Lb a radio wave traveling in a direction significantly inclined with respect to the normal direction of the outer surface 22 may be generated.
  • This radio wave Lb is also called a side lobe.
  • Lc radio waves radiated from the inner surface 21 side of the radar device 20 may also be generated.
  • the radio wave Lb and the radio wave Lc may have a frequency different from that of the radio wave La.
  • the radio wave Lb has a first frequency F1 and the radio wave Lc has a second frequency F2.
  • the second frequency F2 of the radio wave Lc may be higher, lower, or the same as the first frequency F1 of the radio wave Lb.
  • the code Lx indicates a reflected wave in which the radio wave La is reflected by an obstacle targeted by the radar device 20 and returned.
  • radio waves other than the reflected wave Lx may return to the radar mechanism 10.
  • the reflected wave Ly for example, a main beam that is reflected by the inner surface 61 of the rear bumper 60 and then reflected by an object other than an obstacle targeted by the radar device 20 can be considered.
  • radio waves other than the main beam generated in the radar device 20 return to the radar device 20 as reflected waves Ly.
  • a radio wave other than the reflected wave Lx such as the reflected wave Ly, reaches the radar device 20, erroneous detection may occur.
  • the cover member 30 is a member provided around the radar device 20 in order to suppress the detection of radio waves other than the reflected wave Lx by the radar device 20.
  • the cover member 30 is formed in a bowl shape using the radio wave absorber 1 described above. That is, in the cover member 30, a plurality of conductive patches 4 are provided on the inner surface of the absorption layer 2 formed in a bowl shape, and the reflection layer 3 is provided on the outer surface of the absorption layer 2.
  • the cover member 30 is provided so that the main surface of the absorption layer 2 on which the plurality of conductive patches 4 are formed faces both the inner surface 21 and the side surface 23 of the radar device 20.
  • the cover member 30 may be provided so that the main surface of the absorption layer 2 on which the plurality of conductive patches 4 are formed faces only one of the inner surface 21 and the side surface 23 of the radar device 20.
  • the radio wave Lb and the radio wave Lc radiated from the radar device 20 are sufficiently absorbed, and the reflected wave Ly reflected by an object other than an obstacle is reflected by the reflection layer 3. .. As a result, it is possible to prevent or suppress the radar device 20 from erroneously detecting radio waves reflected by an object other than an obstacle.
  • a cover member 30 as a radio wave absorber is provided around the radar device 20, but a radio wave absorber may be provided inside the radar device 20.
  • the cover member 30 is arranged inside the case of the radar device 20 and covers a portion other than the radio wave transmitting / receiving surface of the communication unit.
  • Radio wave absorber 2 Absorbent layer 3 Reflective layer 4 Conductive patch 5 Groove 10 Radar mechanism 20 Radar device 21 Inner surface 22 Outer surface 23 Side 30 Cover member 31 Side 32 Back 60 Rear bumper 61 Inner surface La, Lb, Lc, Lx, Ly radio waves

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  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Manufacturing & Machinery (AREA)
  • Shielding Devices Or Components To Electric Or Magnetic Fields (AREA)
  • Radar Systems Or Details Thereof (AREA)
  • Laminated Bodies (AREA)
  • Aerials With Secondary Devices (AREA)

Abstract

[Problem] To provide a radio wave absorber having a conductive absorption layer formed through injection molding and having an absorption peak in a desired frequency band. [Solution] A method for manufacturing a radio wave absorber 1 which absorbs a millimeter wave or a sub-millimeter wave involves: forming an absorption layer 2 including a conductive material through injection molding; forming a reflection layer 3 on one main surface of the absorption layer 2; forming a conductive layer on the other main surface of the absorption layer 2; and machining the conductive layer to be a plurality of conductive patches 4 so as to achieve an area occupancy ratio based on the thickness of the absorption layer 2.

Description

電波吸収体の製造方法、電波吸収体およびレーダ機構Manufacturing method of radio wave absorber, radio wave absorber and radar mechanism
　本発明は、電波吸収体の製造方法、電波吸収体およびレーダ機構、より詳しくは、ミリ波または準ミリ波を吸収する電波吸収体の製造方法、当該電波吸収体、および当該電波吸収体を備えるレーダ機構に関する。 The present invention includes a method for manufacturing a radio wave absorber, a radio wave absorber and a radar mechanism, more specifically, a method for manufacturing a radio wave absorber that absorbs millimeter waves or quasi-millimeter waves, the radio wave absorber, and the radio wave absorber. Regarding the radar mechanism.
　車両の周囲の障害物を検出するためにレーダ装置が用いられている。レーダ装置は、例えばミリ波（３０ＧＨｚ～３００ＧＨｚ）または準ミリ波（３ＧＨｚ～３０ＧＨｚ）を送信し、障害物によって反射されて戻ってくる反射波を検出する。例えば特許文献１には、自動車のリヤバンパとリヤエンドパネルとの間に設けられたレーダ装置が記載されている。 A radar device is used to detect obstacles around the vehicle. The radar device transmits, for example, millimeter waves (30 GHz to 300 GHz) or quasi-millimeter waves (3 GHz to 30 GHz), and detects reflected waves that are reflected by obstacles and returned. For example, Patent Document 1 describes a radar device provided between a rear bumper and a rear end panel of an automobile.
　レーダ装置から送信される電波は、想定している障害物以外の物体によって反射されてレーダ装置に戻ってくることがある。このような想定外の反射波がレーダ装置によって検出されることを抑制するため、特許文献１のレーダ装置の周囲には、送信波の一部の送信範囲を規制するカバー部材が設けられている。カバー部材としては、電波を反射するタイプのもの、および電波を吸収するタイプのものが提案されている。 Radio waves transmitted from the radar device may be reflected by an object other than the assumed obstacle and return 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 radio waves and a type that absorbs radio waves have been proposed.
　電波を反射するタイプのカバー部材としては、合成樹脂板の表面に金属テープを貼着したものや、合成樹脂の表面に金属の蒸着またはめっきにより金属層を形成したものなどが提案されている。電波を吸収するタイプのカバー部材としては、ゴム中にカーボンを混入することにより構成された電波吸収体が提案されている。 As a type of cover member that reflects radio waves, one in which a metal tape is attached to the surface of a synthetic resin plate, or one in which a metal layer is formed by vapor deposition or plating of metal on the surface of a synthetic resin has been proposed. As a type of cover member that absorbs radio waves, a radio wave absorber configured by mixing carbon into rubber has been proposed.
　電波を反射するタイプの部材においては、部材によって反射されたノイズがレーダ装置によって受信されて誤検出が生じる可能性がある。この点を考慮すると、電波を吸収する電波吸収体が用いられることが好ましい。例えば、特許文献２には、金属薄膜等からなる反射層と、カーボンブラックを含有する吸収層とが積層されたミリ波吸収体であって、周波数５０ＧＨｚ～９０ＧＨｚにおける吸収層の誘電率の実数部を３．０以上としたものが記載されている。 In a member that reflects radio waves, noise reflected by the member may be received by the radar device, causing erroneous detection. Considering this point, it is preferable to use a radio wave absorber that absorbs radio waves. For example, Patent Document 2 describes a millimeter-wave absorber in which a reflective layer made of a metal thin film or the like and an absorbing layer containing carbon black are laminated, and is a real number portion of the dielectric constant of the absorbing layer at a frequency of 50 GHz to 90 GHz. Is described as 3.0 or more.
特許第６０１１３４６号Patent No. 601346 特開２００４－２９６７５８号公報Japanese Unexamined Patent Publication No. 2004-296758
　ところで、電波を吸収するタイプの電波吸収体においては、吸収層のパラメータがばらつくと、電波吸収体の吸収ピークの位置にもばらつきが生じ、吸収ピークが所望の周波数範囲から外れてしまうことがある。例えば、吸収層の厚み（板厚）がばらつくと、電波吸収体の吸収ピークの位置にもばらつきが生じる。吸収層の厚みのばらつきは、吸収層を射出成形により形成する場合に特に生じやすい。また、吸収層の比誘電率がばらつくと、電波吸収体の吸収ピークの位置にもばらつきが生じる。吸収層の比誘電率は、吸収層が導電性材料を含有する場合に特に生じやすい。 By the way, in a radio wave absorber of the type that absorbs radio waves, if the parameters of the absorption layer vary, the position of the absorption peak of the radio wave absorber also varies, and the absorption peak may deviate from the desired frequency range. .. For example, if the thickness (plate thickness) of the absorption layer varies, the position of the absorption peak of the radio wave absorber also varies. Variations in the thickness of the absorbent layer are particularly likely to occur when the absorbent layer is formed by injection molding. Further, if the relative permittivity of the absorption layer varies, the position of the absorption peak of the radio wave absorber also varies. The relative permittivity of the absorbent layer is particularly likely to occur when the absorbent layer contains a conductive material.
　図９は、吸収層の厚み（ｔ）がばらついたときの、２層構造の電波吸収体の吸収特性の実験結果を示している。このように吸収層の厚みがわずかにばらつくことで、吸収ピークが大きく変化する。 FIG. 9 shows the experimental results of the absorption characteristics of the two-layer structure radio wave absorber when the thickness (t) of the absorption layer varies. By slightly varying the thickness of the absorption layer in this way, the absorption peak changes significantly.
　そこで、本発明は、射出成形により形成された導電性の吸収層を有し、かつ所望の周波数帯に吸収ピークを有する電波吸収体の製造方法、電波吸収体およびレーダ機構を提供することを目的とする。 Therefore, an object of the present invention is to provide a method for manufacturing a radio wave absorber having a conductive absorption layer formed by injection molding and having an absorption peak in a desired frequency band, a radio wave absorber, and a radar mechanism. And.
　本発明に係る電波吸収体の製造方法は、
　ミリ波または準ミリ波を吸収する電波吸収体の製造方法であって、
　導電性材料を含有する吸収層を射出成形により形成し、
　前記吸収層の一方の主面に反射層を形成し、
　前記吸収層の他方の主面に導電層を形成し、
　前記吸収層の厚みに基づく面積占有率となるように、前記導電層を複数の導電性パッチに加工する。 The method for manufacturing a radio wave absorber according to the present invention is as follows.
A method for manufacturing a radio wave absorber that absorbs millimeter waves or quasi-millimeter waves.
An absorbent layer containing a conductive material is formed by injection molding,
A reflective layer is formed on one of the main surfaces of the absorbent layer,
A conductive layer is formed on the other main surface of the absorption layer,
The conductive layer is processed into a plurality of conductive patches so that the area occupancy is based on the thickness of the absorbent layer.
　また、前記電波吸収体の製造方法において、
　前記吸収層の厚みが設計値よりも厚い場合、前記面積占有率を所定の占有率よりも小さくし、前記吸収層の厚みが前記設計値よりも薄い場合、前記面積占有率を前記占有率よりも大きくするようにしてもよい。 Further, in the method for manufacturing the radio wave absorber,
When the thickness of the absorption layer is thicker than the design value, the area occupancy rate is made smaller than the predetermined occupancy rate, and when the thickness of the absorption layer is thinner than the design value, the area occupancy rate is smaller than the occupancy rate. May also be increased.
　また、前記電波吸収体の製造方法において、
　前記吸収層は、比誘電率が３．９以上６．３以下の比誘電率を有する材料を用いて射出成形され、
　前記導電層は、前記吸収層の前記他方の主面の少なくとも一部の領域に、前記領域における面積占有率が９０％以下になるように形成されてもよい。 Further, in the method for manufacturing the radio wave absorber,
The absorption layer is injection-molded using a material having a relative permittivity of 3.9 or more and 6.3 or less.
The conductive layer may be formed in at least a part of the other main surface of the absorption layer so that the area occupancy in the region is 90% or less.
　また、前記電波吸収体の製造方法において、
　前記反射層は、ミリ波または準ミリ波を反射する金属により形成されてもよい。 Further, in the method for manufacturing the radio wave absorber,
The reflective layer may be formed of a metal that reflects millimeter or quasi-millimeter waves.
　また、前記電波吸収体の製造方法において、
　前記反射層および前記導電層は、両面めっき法により同時に形成されてもよい。 Further, in the method for manufacturing the radio wave absorber,
The reflective layer and the conductive layer may be formed at the same time by a double-sided plating method.
　本発明に係る電波吸収体は、
　ミリ波または準ミリ波を吸収する電波吸収体であって、
　導電性材料を含有し、射出成形で形成された吸収層と、
　前記吸収層の一方の主面に形成された反射層と、
　前記吸収層の他方の主面の少なくとも一部の領域に形成された複数の導電性パッチと、を備え、
　前記吸収層は、３．９以上６．３以下の比誘電率を有し、かつ前記領域における前記複数の導電性パッチの面積占有率が９０％以下である。 The radio wave absorber according to the present invention is
A radio wave absorber that absorbs millimeter or quasi-millimeter waves
An absorbent layer containing a conductive material and formed by injection molding,
A reflective layer formed on one of the main surfaces of the absorbing layer and
It comprises a plurality of conductive patches formed in at least a part of the other main surface of the absorption layer.
The absorption layer has a relative permittivity of 3.9 or more and 6.3 or less, and the area occupancy of the plurality of conductive patches in the region is 90% or less.
　また、前記電波吸収体において、
　前記反射層は、ミリ波または準ミリ波を反射する金属により構成されていてもよい。 In addition, in the radio wave absorber,
The reflective layer may be made of a metal that reflects millimeter waves or quasi-millimeter waves.
　また、前記電波吸収体において、
　前記金属はめっきからなるようにしてもよい。 In addition, in the radio wave absorber,
The metal may consist of plating.
　本発明に係るレーダ機構は、
　ミリ波または準ミリ波を用いるレーダ装置と、
　前記電波吸収体で構成されたカバー部材と、
　を備え、
　前記カバー部材は、前記複数の導電性パッチが形成された前記吸収層の前記他方の主面が前記レーダ装置の内面および／または側面に対向するように設けられている。 The radar mechanism according to the present invention is
Radar devices that use millimeter or quasi-millimeter waves,
A cover member composed of the radio wave absorber and
With
The cover member is provided so that the other main surface of the absorption layer on which the plurality of conductive patches are formed faces the inner surface and / or the side surface of the radar device.
　本発明によれば、射出成形により形成された導電性の吸収層を有し、かつ所望の周波数帯に吸収ピークを有する電波吸収体を提供できる。 According to the present invention, it is possible to provide a radio wave absorber having a conductive absorption layer formed by injection molding and having an absorption peak in a desired frequency band.
実施形態に係る電波吸収体の製造方法の一例を説明するためのフローチャートである。It is a flowchart for demonstrating an example of the manufacturing method of the radio wave absorber which concerns on embodiment. 吸収層の比誘電率を変えたときに、電波吸収体が吸収特性条件を満たすかどうかを示す図である。It is a figure which shows whether the radio wave absorber satisfies the absorption characteristic condition when the relative permittivity of an absorption layer is changed. 吸収層の比誘電率を変えたときの、電波吸収体の反射係数の周波数特性を示す実験結果である。This is an experimental result showing the frequency characteristics of the reflectance coefficient of the radio wave absorber when the relative permittivity of the absorption layer is changed. 吸収層の比誘電率を変えたときの、電波吸収体の反射係数の周波数特性を示す実験結果である。This is an experimental result showing the frequency characteristics of the reflectance coefficient of the radio wave absorber when the relative permittivity of the absorption layer is changed. 導電性パッチの面積占有率を変えたときの、電波吸収体の反射係数の周波数特性を示す実験結果である。This is an experimental result showing the frequency characteristics of the reflectance coefficient of the radio wave absorber when the area occupancy of the conductive patch is changed. 実施形態に係る電波吸収体の一部を示す平面図である。It is a top view which shows a part of the radio wave absorber which concerns on embodiment. 図６のＩ－Ｉ線に沿う断面図である。FIG. 6 is a cross-sectional view taken along the line II of FIG. レーダ装置および電波吸収体を備えるレーダ機構の一例を示す断面図である。It is sectional drawing which shows an example of the radar mechanism which includes a radar device and a radio wave absorber. 吸収層の厚さが変化したときの、２層構造の電波吸収体の吸収特性を示す図である。It is a figure which shows the absorption characteristic of the radio wave absorber of the two-layer structure when the thickness of the absorption layer changes.
　以下、本発明に係る実施形態について図面を参照しながら説明する。なお、本件明細書に添付する図面においては、理解のしやすさの便宜上、適宜縮尺および縦横の寸法比等を、実物のそれらから変更し誇張してある。 Hereinafter, embodiments according to 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.
＜電波吸収体の製造方法＞
　図１のフローチャートを参照しつつ、実施形態に係る電波吸収体の製造方法について説明する。 <Manufacturing method of radio wave absorber>
The manufacturing method of the radio wave absorber according to the embodiment will be described with reference to the flowchart of FIG.
　まず、導電性材料（導電性フィラー）を含有する吸収層を射出成形により形成する（ステップＳ１）。例えば、吸収層はポリプロピレン（ＰＰ）からなり、導電性材料は導電性のカーボンブラックである。なお、導電性材料はカーボンブラックに限られず、カーボンナノチューブ、または、金属もしくは金属酸化物の微粒子等の他の材料でもよい。 First, an absorption layer containing a conductive material (conductive filler) is formed by injection molding (step S1). For example, the absorbent layer is made of polypropylene (PP) and the conductive material is conductive carbon black. The conductive material is not limited to carbon black, and may be carbon nanotubes or other materials such as fine particles of metal or metal oxide.
　吸収層は所定の吸収特性条件を満たすようにその比誘電率が定められている。本実施形態の吸収特性条件は、７０～９０ＧＨｚの周波数帯で電波吸収体（３層型）の反射係数が－１０ｄＢとなる部分が１ＧＨｚ以上存在するという条件である。 The relative permittivity of the absorption layer is determined so as to satisfy a predetermined absorption characteristic condition. The absorption characteristic condition of the present embodiment is that there is a portion where the reflection coefficient of the radio wave absorber (three-layer type) is −10 dB or more in the frequency band of 70 to 90 GHz.
　図２は、吸収層の比誘電率を変更した場合に、電波吸収体が吸収特性条件を満たすかどうかを示している。図３（ａ）、（ｂ）、（ｃ）、（ｄ）はそれぞれ、吸収層の比誘電率及び厚みが３．４及び２．５ｍｍ、３．９及び３．４ｍｍ、４．５及び２．３ｍｍ、４．８及び１．２ｍｍの場合における電波吸収体の電波吸収特性を示すグラフである。同様に、図４（ａ）、（ｂ）、（ｃ）はそれぞれ、吸収層の比誘電率及び厚みが５．５及び１．２ｍｍ、６．３及び１．１ｍｍ、７．１及び２．５ｍｍの場合における電波吸収体の電波吸収特性を示すグラフである。吸収層の比誘電率を変更するため、ここでは、吸収層（ポリプロピレン）に含まれる導電性ポリプロピレン（導電ＰＰ）の割合を変更している。 FIG. 2 shows whether or not the radio wave absorber satisfies the absorption characteristic condition when the relative permittivity of the absorption layer is changed. 3 (a), (b), (c), and (d) show the relative permittivity and thickness of the absorption layer of 3.4 and 2.5 mm, 3.9 and 3.4 mm, 4.5 and 2, respectively. It is a graph which shows the radio wave absorption characteristic of the radio wave absorber in the case of .3 mm, 4.8 and 1.2 mm. Similarly, in FIGS. 4A, 4B, and 4C, the relative permittivity and thickness of the absorption layer are 5.5 and 1.2 mm, 6.3 and 1.1 mm, 7.1 and 2, respectively. It is a graph which shows the radio wave absorption characteristic of the radio wave absorber in the case of 5 mm. In order to change the relative permittivity of the absorption layer, the ratio of the conductive polypropylene (conductive PP) contained in the absorption layer (polypropylene) is changed here.
　なお、吸収層に含まれる導電性材料が、ポリプロピレン及びカーボンブラックを含む導電性ポリプロピレンに限られることはない。導電性材料は、その他の樹脂及び導電性フィラーによって構成されていてもよい。また、吸収層の比誘電率を変更する手段が、吸収層における導電性材料の割合を変更するという手段に限られることはない。その他の手段を用いて吸収層の比誘電率を変更してもよい。 The conductive material contained in the absorption layer is not limited to polypropylene and conductive polypropylene containing carbon black. The conductive material may be composed of other resins and conductive fillers. Further, the means for changing the relative permittivity of the absorbing layer is not limited to the means for changing the ratio of the conductive material in the absorbing layer. The relative permittivity of the absorption layer may be changed by other means.
　図３（ｄ）、図４（ａ）、図４（ｂ）に示す例における吸収層の厚みは１．１ｍｍ又は１．２ｍｍである。図３（ａ）、図３（ｃ）、図４（ｃ）に示す例における吸収層の厚みは２．３ｍｍ又は２．５ｍｍである。図３（ｄ）、図４（ａ）、図４（ｂ）の比較、及び図３（ａ）、図３（ｃ）、図４（ｃ）の比較から分かるように、吸収層の厚みが略同一である場合、吸収層の比誘電率が変化すると電波吸収体の吸収ピークはシフトする。より具体的には、吸収層の比誘電率が高いほど吸収ピークの周波数は下がる。 The thickness of the absorption layer in the examples shown in FIGS. 3 (d), 4 (a), and 4 (b) is 1.1 mm or 1.2 mm. The thickness of the absorption layer in the examples shown in FIGS. 3 (a), 3 (c) and 4 (c) is 2.3 mm or 2.5 mm. As can be seen from the comparison of FIGS. 3 (d), 4 (a) and 4 (b), and the comparison of FIGS. 3 (a), 3 (c) and 4 (c), the thickness of the absorption layer is When they are substantially the same, the absorption peak of the radio wave absorber shifts as the relative permittivity of the absorption layer changes. More specifically, the higher the relative permittivity of the absorption layer, the lower the frequency of the absorption peak.
　図３および図４から分かるように、吸収層の比誘電率が３．９～６．３の場合において吸収特性条件が満たされる。この結果に基づいて、本実施形態では、吸収層の比誘電率が３．９以上６．３以下になるように導電性材料の割合が調整された材料を用いて吸収層を射出成形で形成する。 As can be seen from FIGS. 3 and 4, the absorption characteristic condition is satisfied when the relative permittivity of the absorption layer is 3.9 to 6.3. Based on this result, in the present embodiment, the absorption layer is formed by injection molding using a material in which the ratio of the conductive material is adjusted so that the relative permittivity of the absorption layer is 3.9 or more and 6.3 or less. do.
　次に、ステップＳ１で形成された吸収層の一方の主面（例えば下面）に反射層を形成する（ステップＳ２）。反射層は、ミリ波または準ミリ波を反射する金属（ニッケル）により形成される。例えば、反射層は、無電解めっきにより形成される。なお、電解めっきにより反射層を形成してもよい。 Next, a reflective layer is formed on one main surface (for example, the lower surface) of the absorption layer formed in step S1 (step S2). The reflective layer is formed of a metal (nickel) that reflects millimeter or quasi-millimeter waves. For example, the reflective layer is formed by electroless plating. The reflective layer may be formed by electrolytic plating.
　次に、ステップＳ１で形成された吸収層の他方の主面（例えば上面）に導電層を形成する（ステップＳ３）。例えば、導電層は、無電解めっきにより形成される。なお、電解めっきにより導電層を形成してもよい。 Next, a conductive layer is formed on the other main surface (for example, the upper surface) of the absorption layer formed in step S1 (step S3). For example, the conductive layer is formed by electroless plating. The conductive layer may be formed by electrolytic plating.
　反射層および導電層の金属材料は、ニッケルのほかに、ニッケルを含む合金、または、アルミ、クロム、鉛、金、銀、銅、スズ、亜鉛、鉄もしくはこれらの金属の合金などであってもよい。 In addition to nickel, the metal material of the reflective layer and the conductive layer may be an alloy containing nickel, aluminum, chromium, lead, gold, silver, copper, tin, zinc, iron or an alloy of these metals. good.
　めっき処理によって導電層や反射層を形成することにより、吸収層の形状に対する自由度を高めることができる。これにより、例えば後述のカバー部材３０のように、椀状の吸収層に反射層３および複数の導電性パッチ４を形成することができる。 By forming a conductive layer or a reflective layer by plating, the degree of freedom regarding the shape of the absorbing layer can be increased. As a result, the reflective layer 3 and the plurality of conductive patches 4 can be formed on the bowl-shaped absorbing layer, for example, as in the cover member 30 described later.
　ステップＳ３において導電層は、吸収層の主面の全面にわたって形成されてもよいし、あるいは、主面の一部の領域（電波吸収領域）にのみ形成されてもよい。 In step S3, the conductive layer may be formed over the entire main surface of the absorption layer, or may be formed only in a part of the main surface (radio wave absorption region).
　なお、ステップＳ２とステップＳ３は逆順に行ってもよい。また、吸収層の両面に同時にめっき層（反射層および導電層）を形成する両面めっき法を用いてもよい。 Note that steps S2 and S3 may be performed in the reverse order. Further, a double-sided plating method may be used in which plating layers (reflection layer and conductive layer) are formed on both sides of the absorption layer at the same time.
　また、めっき工程の前に、吸収層の表面に触媒を付着させる触媒工程を実施してもよい。触媒工程は、例えば、酸洗工程、触媒付与工程、水洗工程、触媒活性化工程、水洗工程などを含んでいてもよい。 Further, a catalyst step of adhering a catalyst to the surface of the absorption layer may be carried out before the plating step. The catalyst step may include, for example, a pickling step, a catalyst applying step, a water washing step, a catalyst activation step, a water washing step, and the like.
　次に、吸収層の厚みに基づく面積占有率となるように、導電層を複数の導電性パッチに加工する（ステップＳ４）。導電層の加工は、例えばレーザ光を導電層に照射して導電層を部分的に除去することで行う。導電層の加工は、刃（ブレード）を用いて行ってもよいし、あるいはエッチングにより行ってもよい。ステップＳ４で形成される複数の導電性パッチは四角形状であるが、互いに接続していなければ、具体的な形状は特に限定されない。 Next, the conductive layer is processed into a plurality of conductive patches so that the area occupancy is based on the thickness of the absorption layer (step S4). The processing of the conductive layer is performed, for example, by irradiating the conductive layer with laser light to partially remove the conductive layer. The conductive layer may be processed by using a blade or by etching. The plurality of conductive patches formed in step S4 have a quadrangular shape, but the specific shape is not particularly limited as long as they are not connected to each other.
　ここで、「面積占有率」とは、吸収層の主面のうち複数の導電性パッチが設けられた領域（導電性パッチ形成領域）における、複数の導電性パッチの面積の総和の、導電性パッチ形成領域の面積に対する比率のことである。例えば、導電性パッチが吸収層の主面の全面にわたって形成される場合、面積占有率は、各導電性パッチの面積の総和を吸収層の主面の面積で割った値となる。 Here, the "area occupancy" is the conductivity of the sum of the areas of the plurality of conductive patches in the region (conductive patch forming region) in which the plurality of conductive patches are provided on the main surface of the absorption layer. It is the ratio to the area of the patch forming area. For example, when the conductive patch is formed over the entire surface of the main surface of the absorbing layer, the area occupancy is a value obtained by dividing the total area of each conductive patch by the area of the main surface of the absorbing layer.
　ステップＳ４において、複数の導電性パッチの面積占有率は吸収層の厚みに基づいて決定される。吸収層の厚みとしては、ステップＳ１で形成された吸収層に対して測定された厚みを用いる。吸収層の厚みが設計値よりも厚い場合、面積占有率を事前に定めた占有率（所定の占有率）よりも小さくし、反対に設計値よりも薄い場合は面積占有率を所定の占有率よりも大きくする。これにより、射出成形により形成された吸収層の厚みが設計値からずれた場合であっても、吸収ピークを所望の周波数範囲に調整することができる。このことについて以下に詳細に説明する。 In step S4, the area occupancy of the plurality of conductive patches is determined based on the thickness of the absorbing layer. As the thickness of the absorption layer, the thickness measured for the absorption layer formed in step S1 is used. When the thickness of the absorption layer is thicker than the design value, the area occupancy rate is made smaller than the predetermined occupancy rate (predetermined occupancy rate), and conversely, when it is thinner than the design value, the area occupancy rate is set to the predetermined occupancy rate. Make it larger than. Thereby, even when the thickness of the absorption layer formed by injection molding deviates from the design value, the absorption peak can be adjusted to a desired frequency range. This will be described in detail below.
　図９で説明したように、吸収層の厚みが変化すると電波吸収体の吸収ピークはシフトする。より具体的には、吸収層の厚みが設計値よりも厚いと吸収ピークの周波数は下がり、反対に吸収層の厚みが設計値よりも薄いと吸収ピークの周波数は上げる。また、図３及び図４で説明したように、吸収層の比誘電率が高いほど吸収ピークの周波数は下がる。 As explained in FIG. 9, the absorption peak of the radio wave absorber shifts when the thickness of the absorption layer changes. More specifically, when the thickness of the absorption layer is thicker than the design value, the frequency of the absorption peak decreases, and conversely, when the thickness of the absorption layer is thinner than the design value, the frequency of the absorption peak increases. Further, as described with reference to FIGS. 3 and 4, the higher the relative permittivity of the absorption layer, the lower the frequency of the absorption peak.
　一方、図５に示すように、導電性パッチの面積占有率が小さくなるにつれて電波吸収体（３層型）の吸収ピークは高周波数側にシフトする。図５は吸収層の厚さおよび比誘電率を固定した場合において（厚さ：２．３０ｍｍ、比誘電率：４．５）、導電性パッチの面積占有率を変えたときの吸収ピークの測定結果を示している。面積占有率が９４％、９０％、８５％、７２％と小さくなるにつれて、吸収ピークは深くなるとともに高周波数側にシフトすることが分かる。 On the other hand, as shown in FIG. 5, the absorption peak of the radio wave absorber (three-layer type) shifts to the high frequency side as the area occupancy of the conductive patch decreases. FIG. 5 shows the measurement of the absorption peak when the area occupancy of the conductive patch is changed when the thickness and the relative permittivity of the absorbent layer are fixed (thickness: 2.30 mm, relative permittivity: 4.5). The result is shown. It can be seen that as the area occupancy decreases to 94%, 90%, 85%, and 72%, the absorption peak becomes deeper and shifts to the higher frequency side.
　したがって、射出成形により形成された吸収層の厚みが設計値よりも厚い場合（すなわち、電波吸収体の吸収ピークが低周波数側にシフトする場合）、導電性パッチの面積占有率を所定の占有率よりも小さくすることで、電波吸収体の吸収ピークを高周波数側にシフトさせる。 Therefore, when the thickness of the absorption layer formed by injection molding is thicker than the design value (that is, when the absorption peak of the radio wave absorber shifts to the low frequency side), the area occupancy of the conductive patch is set to the predetermined occupancy. By making it smaller than, the absorption peak of the radio wave absorber is shifted to the high frequency side.
　反対に、射出成形により形成された吸収層の厚みが設計値よりも薄い場合（すなわち、電波吸収体の吸収ピークが高周波数側にシフトする場合）、導電性パッチの面積占有率を所定の占有率よりも大きくすることで、電波吸収体の吸収ピークを低周波数側にシフトさせる。 On the contrary, when the thickness of the absorption layer formed by injection molding is thinner than the design value (that is, when the absorption peak of the radio wave absorber shifts to the high frequency side), the area occupancy of the conductive patch is occupied as a predetermined value. By making it larger than the rate, the absorption peak of the radio wave absorber is shifted to the low frequency side.
　また、吸収層の比誘電率が設計値よりも高い場合（すなわち、電波吸収体の吸収ピークが低周波数側にシフトする場合）、導電性パッチの面積占有率を所定の占有率よりも小さくすることで、電波吸収体の吸収ピークを高周波数側にシフトさせる。 Further, when the relative permittivity of the absorption layer is higher than the design value (that is, when the absorption peak of the radio wave absorber shifts to the low frequency side), the area occupancy of the conductive patch is made smaller than the predetermined occupancy. This shifts the absorption peak of the radio wave absorber to the high frequency side.
　反対に、吸収層の比誘電率が設計値よりも低い場合（すなわち、電波吸収体の吸収ピークが高周波数側にシフトする場合）、導電性パッチの面積占有率を所定の占有率よりも大きくすることで、電波吸収体の吸収ピークを低周波数側にシフトさせる。 On the contrary, when the relative permittivity of the absorption layer is lower than the design value (that is, when the absorption peak of the radio wave absorber shifts to the high frequency side), the area occupancy of the conductive patch is larger than the predetermined occupancy. By doing so, the absorption peak of the radio wave absorber is shifted to the low frequency side.
　このように面積占有率を吸収層の厚み、比誘電率などのパラメータに応じて調整することにより、電波吸収体の吸収ピークが所望の周波数範囲に入るようにすることができる。このため、射出成形のような、厚みのばらつきが生じやすい方法を用いて吸収層を形成する場合であっても、所望の吸収ピークを実現することができる。したがって、低コスト化のために射出成形を採用することができる。また、吸収層の比誘電率がばらつく場合であっても、所望の吸収ピークを実現することができる。吸収層の比誘電率は、吸収層が導電性材料を含有する場合に特に生じやすい。 By adjusting the area occupancy rate according to parameters such as the thickness of the absorption layer and the relative permittivity in this way, the absorption peak of the radio wave absorber can be made to fall within a desired frequency range. Therefore, even when the absorption layer is formed by using a method such as injection molding in which the thickness is likely to vary, a desired absorption peak can be realized. Therefore, injection molding can be adopted for cost reduction. Further, even when the relative permittivity of the absorption layer varies, a desired absorption peak can be realized. The relative permittivity of the absorbent layer is particularly likely to occur when the absorbent layer contains a conductive material.
　本実施形態では、吸収層は、３．９以上６．３以下の比誘電率を有するように調整された材料を用いて射出成形され、かつ、導電層は、吸収層の他方の主面（上面）の少なくとも一部の領域（導電性パッチ形成領域）に、当該領域における面積占有率が９０％以下になるように形成される。 In the present embodiment, the absorbent layer is injection-molded using a material adjusted to have a relative permittivity of 3.9 or more and 6.3 or less, and the conductive layer is the other main surface of the absorbent layer ( It is formed in at least a part of the region (upper surface) (conductive patch forming region) so that the area occupancy in the region is 90% or less.
　以上説明したように、本実施形態に係る電波吸収体の製造方法によれば、射出成形により形成された導電性の吸収層を有し、かつ所望の周波数帯に吸収ピークを有する電波吸収体を製造することができる。 As described above, according to the method for manufacturing a radio wave absorber according to the present embodiment, a radio wave absorber having a conductive absorption layer formed by injection molding and having an absorption peak in a desired frequency band can be obtained. Can be manufactured.
＜電波吸収体＞
　図６および図７を参照して、実施形態に係る電波吸収体について詳しく説明する。図６は本実施形態に係る電波吸収体１の一部を示す平面図であり、図７は図６のＩ－Ｉ線に沿う断面図である。 <Radio wave absorber>
The radio wave absorber according to the embodiment will be described in detail with reference to FIGS. 6 and 7. FIG. 6 is a plan view showing a part of the radio wave absorber 1 according to the present embodiment, and FIG. 7 is a cross-sectional view taken along the line II of FIG.
　本実施形態に係る電波吸収体１は、ミリ波または準ミリ波を吸収する電波吸収体であって、図６および図７に示すように、導電性の吸収層２と、この吸収層２の一方の主面に形成された反射層３と、吸収層２の他方の主面の少なくとも一部の領域（導電性パッチ形成領域）に形成された複数の導電性パッチ４とを備えている。本実施形態では、反射層３と複数の導電性パッチ４は、金属めっきから構成される。 The radio wave absorber 1 according to the present embodiment is a radio wave absorber that absorbs millimeter waves or quasi-millimeter waves, and as shown in FIGS. 6 and 7, the conductive absorption layer 2 and the absorption layer 2 It includes a reflective layer 3 formed on one main surface and a plurality of conductive patches 4 formed on at least a part of the other main surface of the absorbing layer 2 (conductive patch forming region). In this embodiment, the reflective layer 3 and the plurality of conductive patches 4 are made of metal plating.
　吸収層２は、カーボンブラック等の導電性材料を含有し、射出成形で形成された層である。吸収層２の厚みＴは、例えば０．５ｍｍ以上４ｍｍ以下である。本実施形態では、吸収層２は導電性のカーボンブラックが分散されたポリプロピレンからなる。 The absorption layer 2 is a layer containing a conductive material such as carbon black and formed by injection molding. The thickness T of the absorption layer 2 is, for example, 0.5 mm or more and 4 mm or less. In the present embodiment, the absorption layer 2 is made of polypropylene in which conductive carbon black is dispersed.
　反射層３は、導電性パッチ４側から電波吸収体１に到来し、吸収層２を透過した電波を反射する。また、反射層３は、反射層３側から電波吸収体１に到来する電波を反射する。反射層３は、ミリ波または準ミリ波を反射する金属（ニッケル）により構成されている。 The reflective layer 3 arrives at the radio wave absorber 1 from the conductive patch 4 side and reflects the radio waves transmitted through the absorbing layer 2. Further, the reflective layer 3 reflects radio waves arriving at the radio wave absorber 1 from the reflective layer 3 side. The reflective layer 3 is made of a metal (nickel) that reflects millimeter waves or quasi-millimeter waves.
　反射層３の厚みは、例えば０．２μｍ以上であり、０．３μｍ以上であってもよく、０．５μｍ以上であってもよい。反射層３の厚みを０．２μｍ以上にすることにより、反射層３の表面抵抗を小さくし、電波吸収体１に到来する電波を反射層３によって反射することができる。また、反射層３の厚みは、１．０μｍ以下であり、０．８μｍ以下であってもよく、０．７μｍ以下であってもよく、０．６μｍ以下であってもよい。反射層３の厚みを１．０μｍ以下にすることにより、反射層３のコストを低減することができる。 The thickness of the reflective layer 3 is, for example, 0.2 μm or more, may be 0.3 μm or more, or may be 0.5 μm or more. By making the thickness of the reflective layer 3 0.2 μm or more, the surface resistance of the reflective layer 3 can be reduced, and the radio waves arriving at the radio wave absorber 1 can be reflected by the reflective layer 3. The thickness of the reflective layer 3 may be 1.0 μm or less, 0.8 μm or less, 0.7 μm or less, or 0.6 μm or less. By reducing the thickness of the reflective layer 3 to 1.0 μm or less, the cost of the reflective layer 3 can be reduced.
　複数の導電性パッチ４は、吸収層２の主面に形成された導電層をレーザ等を用いて加工することにより互いに孤立したものとして構成されている。図６に示すように、格子状の複数本の溝５により各導電性パッチ４は離間して設けられている。溝５には吸収層２が露出している。 The plurality of conductive patches 4 are configured to be isolated from each other by processing the conductive layers formed on the main surface of the absorption layer 2 with a laser or the like. As shown in FIG. 6, the conductive patches 4 are provided apart from each other by a plurality of grid-like grooves 5. The absorption layer 2 is exposed in the groove 5.
　導電性パッチ４の厚みは、好ましくは０．１μｍ以上であり、より好ましくは０．２μｍ以上である。また、内側金属層４１の厚みは、好ましくは２μｍ以下であり、より好ましくは１μｍ以下である。 The thickness of the conductive patch 4 is preferably 0.1 μm or more, more preferably 0.2 μm or more. The thickness of the inner metal layer 41 is preferably 2 μm or less, more preferably 1 μm or less.
　なお、図６では、導電性パッチ４は四角形状（正方形）に形成されているが、互いに接続していなければ、導電性パッチ４の形状はこれに限定されない。例えば、導電性パッチ４の形状は、三角形もしくは六角形であってもよいし、あるいは円形もしくは楕円形等であってもよい。 Note that, in FIG. 6, the conductive patches 4 are formed in a square shape (square), but the shape of the conductive patches 4 is not limited to this unless they are connected to each other. For example, the shape of the conductive patch 4 may be triangular or hexagonal, or may be circular or elliptical.
　導電性パッチ４が導電性を有しているので、導電性パッチ４と溝５からなる導電メッシュパターンの誘電率は、吸収層２の誘電率に比べて高い。導電メッシュパターンは、高い誘電率を有する層として電波に作用する。導電メッシュパターンに入射した電波の一部は、導電メッシュパターンによって反射され、電波のその他の一部は、導電メッシュパターンを透過して吸収層２に入射する。電波の反射および透過に関する導電メッシュパターンの特性は、導電メッシュパターンの誘電率に基づいて決まる。導電メッシュパターンの誘電率は、導電性パッチ４の面積占有率などに依存する。 Since the conductive patch 4 has conductivity, the dielectric constant of the conductive mesh pattern including the conductive patch 4 and the groove 5 is higher than the dielectric constant of the absorption layer 2. The conductive mesh pattern acts on radio waves as a layer having a high dielectric constant. A part of the radio wave incident on the conductive mesh pattern is reflected by the conductive mesh pattern, and the other part of the radio wave passes through the conductive mesh pattern and is incident on the absorption layer 2. The characteristics of the conductive mesh pattern with respect to the reflection and transmission of radio waves are determined based on the dielectric constant of the conductive mesh pattern. The dielectric constant of the conductive mesh pattern depends on the area occupancy of the conductive patch 4 and the like.
　本実施形態に係る電波吸収体１においては、吸収層２が３．９以上６．３以下の比誘電率を有し、かつ導電性パッチ形成領域における複数の導電性パッチ４の面積占有率が９０％以下である。かかる電波吸収体１によれば、吸収層２が射出成形により形成されたものであっても吸収特性条件を満たすことができる。詳しくは、吸収層２の厚みＴがある程度（例えば±０．０５ｍｍ）ばらつく場合であっても、７０～９０ＧＨｚの周波数帯で反射係数が－１０ｄＢとなる部分が１ＧＨｚ以上存在するという吸収特性を満たすことができる。 In the radio wave absorber 1 according to the present embodiment, the absorption layer 2 has a relative permittivity of 3.9 or more and 6.3 or less, and the area occupancy of the plurality of conductive patches 4 in the conductive patch forming region is large. It is 90% or less. According to the radio wave absorber 1, even if the absorption layer 2 is formed by injection molding, the absorption characteristic condition can be satisfied. Specifically, even when the thickness T of the absorption layer 2 varies to some extent (for example, ± 0.05 mm), it satisfies the absorption characteristic that there is a portion having a reflectance coefficient of -10 dB in the frequency band of 70 to 90 GHz. be able to.
　本実施形態では、導電ＰＰの割合を５０％以上９５％以下とすることで、吸収層２の比誘電率を３．９以上６．３以下としている。また、導電性パッチ４の面積占有率は、溝５の幅が一定の条件下、導電性パッチ４の面積（パッチサイズ）を小さくすることで９０％以下としている。例えば、図６において、溝５の幅Ｓを０．１ｍｍ、正方形状の導電性パッチ４の一辺の長さＷを０．９ｍｍとすると、面積占有率は約９０％となる。 In the present embodiment, the ratio of the conductive PP is 50% or more and 95% or less, so that the relative permittivity of the absorption layer 2 is 3.9 or more and 6.3 or less. The area occupancy of the conductive patch 4 is 90% or less by reducing the area (patch size) of the conductive patch 4 under the condition that the width of the groove 5 is constant. For example, in FIG. 6, if the width S of the groove 5 is 0.1 mm and the length W of one side of the square conductive patch 4 is 0.9 mm, the area occupancy is about 90%.
　なお、吸収層２を構成する絶縁材料はポリプロピレンに限られない。材料として、低密度ポリエチレン、高密度ポリエチレン、ｉ－ポリプロピレン、石油樹脂、ポリスチレン、ｓ－ポリスチレン、クロマン・インデン樹脂、テルペン樹脂、スチレン・ジビニルベンゼン共重合体、ＡＢＳ樹脂、ポリアクリル酸メチル、ポリアクリル酸エチル、ポリアクリルニトリル、メタクリル酸メチル、メタクリル酸エチル、ポリシアノアクリレート、ポリ酢酸ビニル、ポリビニルアルコール、ポリビニルホルマール、ポリビニルアセタール、ポリ塩化ビニル、塩化ビニル・酢酸ビニル共重合体、塩化ビニル・エチレン共重合体、ポリフッ化ビニリデン、フッ化ビニリデン・エチレン共重合体、フッ化ビニリデン・プロピレン共重合体、１，４－トランスポリブタジエン、ポリオキシメチレン、ポリエチレングリコール、ポリプロピレングリコール、フェノール・ホルマリン樹脂、クレゾール・フォルマリン樹脂、レゾルシン樹脂、メラミン樹脂、キシレン樹脂、トルエン樹脂、グリプタル樹脂、変性グリプタル樹脂、ポリエチレンテレフタレート、ポリブチレンテレフタレート（ＰＢＴ）、不飽和ポリエステル樹脂、アリルエステル樹脂、ポリカーボネート、６－ナイロン、６，６－ナイロン又は６，１０－ナイロンなどのポリアミド、ポリベンズイミダゾール、ポリアミドイミド、ケイ素樹脂、シリコンゴム、シリコーン樹脂、フラン樹脂、ポリウレタン樹脂、エポキシ樹脂、ポリフェニレンオキサイド、ポリジメチルフェニレンオキサイド、ポリフェニレンオキサイドまたはポリジメチルフェニレンオキサイドとトリアリルイソシアヌルブレンド物、（ポリフェニレンオキサイドまたはポリジメチルフェニレンオキサイド、トリアリルイソシアヌル、パーオキサイド）ブレンド物、ポリキシレン、ポリフェニレンスルファイド（ＰＰＳ）、ポリスルホン（ＰＳＦ）、ポリエーテルスルホン（ＰＥＳ）、ポリエーテルエーテルケトン（ＰＥＥＫ）、ポリイミド（ＰＰＩ、カプトン）、液晶樹脂、これら複数材料のブレンド物などを用いてもよい。 The insulating material constituting the absorption layer 2 is not limited to polypropylene. 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, polyacrylic Ethyl acid acid, 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 Polymer, polyvinylidene fluoride, vinylidene fluoride / ethylene copolymer, vinylidene fluoride / propylene copolymer, 1,4-transpolybutadiene, polyoxymethylene, polyethylene glycol, polypropylene glycol, phenol / formalin resin, cresol formal Marine resin, resorcin resin, melamine resin, xylene resin, toluene resin, glyptal resin, modified glyptal resin, polyethylene terephthalate, polybutylene terephthalate (PBT), unsaturated polyester resin, allyl ester resin, polycarbonate, 6-nylon, 6,6 -Polymer such as nylon or 6,10-nylon, polybenzimidazole, polyamideimide, silicon resin, silicon rubber, silicone resin, furan resin, polyurethane resin, epoxy resin, polyphenylene oxide, polydimethylphenylene oxide, polyphenylene oxide or polydimethyl Phenylene 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 may be used.
　また、反射層３および導電性パッチ４を構成する金属材料はニッケルに限られない。金属材料として、ニッケルを含む合金、または、アルミ、クロム、鉛、金、銀、銅、スズ、亜鉛、鉄もしくはこれらの金属の合金などを用いてもよい。 Further, the metal material constituting the reflective layer 3 and the conductive patch 4 is not limited to nickel. As the metal material, an alloy containing nickel, aluminum, chromium, lead, gold, silver, copper, tin, zinc, iron, or an alloy of these metals may be used.
　また、反射層３および導電性パッチ４の金属材料は、互いに異なる金属であってもよい。 Further, the metal materials of the reflective layer 3 and the conductive patch 4 may be different metals from each other.
＜レーダ機構＞
　次に、図８を参照して、電波吸収体１の応用例のレーダ機構１０について説明する。図８は、自動車に設けられているレーダ機構１０を示す断面図である。 <Radar mechanism>
Next, the radar mechanism 10 of the application example of the radio wave absorber 1 will be described with reference to FIG. FIG. 8 is a cross-sectional view showing a radar mechanism 10 provided in an automobile.
　図８に示すように、レーダ機構１０は、リヤバンパ６０の内面６１に対向するように設けられており、後方から自車両に接近してくる他車両などを障害物として検出することができるように構成されている。 As shown in FIG. 8, the radar mechanism 10 is provided so as to face the inner surface 61 of the rear bumper 60 so that another vehicle approaching the own vehicle from behind can be detected as an obstacle. It is configured.
　レーダ機構１０は、ミリ波または準ミリ波を送受信するレーダ装置２０と、電波吸収体１で構成されたカバー部材３０と、を備えている。 The radar mechanism 10 includes a radar device 20 that transmits and receives millimeter waves or quasi-millimeter waves, and a cover member 30 composed of a radio wave absorber 1.
　レーダ装置２０は、図８に示すように、内面２１、外面２２および側面２３を含む。外面２２は、レーダ装置２０の面のうち自動車の外側を向いている面であり、例えばリヤバンパ６０と対向している。内面２１は、外面２２の反対側に位置しており、カバー部材３０の底面に対向している。側面２３は、内面２１と外面２２を接続する面であり、カバー部材３０の側面（壁面）に対向している。 As shown in FIG. 8, the radar device 20 includes 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 and faces the bottom surface of the cover member 30. The side surface 23 is a surface that connects the inner surface 21 and the outer surface 22, and faces the side surface (wall surface) of the cover member 30.
　なお、レーダ装置２０の固定方法は任意である。例えば、レーダ装置２０は、自動車の車体の一部に固定されているブラケット（図示せず）に取り付けられた状態で、カバー部材３０の内部に位置するようにしてもよい。この場合、例えば、カバー部材３０の底面にはブラケットを通すための貫通孔が形成される。 The method of fixing the radar device 20 is arbitrary. For example, the radar device 20 may be located inside the cover member 30 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, for example, a through hole for passing the bracket is formed on the bottom surface of the cover member 30.
　図８において、符号Ｌａは、レーダ装置２０の外面２２の法線方向に沿って外側に進みリヤバンパ６０を透過する電波であり、いわゆる主ビームを示す。一方、レーダ装置２０においては、主ビーム以外にも電波が発生し得る。例えば符号Ｌｂで示すように、外面２２の法線方向に対して大きく傾斜した方向に進む電波が発生し得る。この電波Ｌｂは、サイドローブとも称される。また、符号Ｌｃで示すように、レーダ装置２０の内面２１側から放射される電波も発生し得る。電波Ｌｂ及び電波Ｌｃは、電波Ｌａとは異なる周波数を有することもある。例えば、電波Ｌｂが第１周波数Ｆ１を有し、電波Ｌｃが第２周波数Ｆ２を有する。電波Ｌｃの第２周波数Ｆ２は、電波Ｌｂの第１周波数Ｆ１よりも高くてもよく、低くてもよく、同一であってもよい。 In FIG. 8, the symbol La is a radio 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 indicates a so-called main beam. On the other hand, in the radar device 20, radio waves may be generated in addition to the main beam. For example, as indicated by reference numeral Lb, a radio wave traveling in a direction significantly inclined with respect to the normal direction of the outer surface 22 may be generated. This radio wave Lb is also called a side lobe. Further, as indicated by the reference numeral Lc, radio waves radiated from the inner surface 21 side of the radar device 20 may also be generated. The radio wave Lb and the radio wave Lc may have a frequency different from that of the radio wave La. For example, the radio wave Lb has a first frequency F1 and the radio wave Lc has a second frequency F2. The second frequency F2 of the radio wave Lc may be higher, lower, or the same as the first frequency F1 of the radio wave Lb.
　また、図８において、符号Ｌｘは、レーダ装置２０が対象とする障害物によって電波Ｌａが反射されて戻ってきた反射波を示している。一方、符号Ｌｙで示すように、反射波Ｌｘ以外の電波がレーダ機構１０に戻ってくることがある。反射波Ｌｙの例としては、例えば、リヤバンパ６０の内面６１によって反射された後、レーダ装置２０が対象とする障害物以外の物体によって反射された主ビームが考えられる。その他にも、レーダ装置２０において発生する主ビーム以外の電波が反射波Ｌｙとしてレーダ装置２０に戻ってくることが考えられる。反射波Ｌｙのような、反射波Ｌｘ以外の電波がレーダ装置２０に到達すると、誤検出が生じるおそれがある。 Further, in FIG. 8, the code Lx indicates a reflected wave in which the radio wave La is reflected by an obstacle targeted by the radar device 20 and returned. On the other hand, as indicated by the reference numeral Ly, radio waves other than the reflected wave Lx may return to the radar mechanism 10. As an example of the reflected wave Ly, for example, a main beam that is reflected by the inner surface 61 of the rear bumper 60 and then reflected by an object other than an obstacle targeted by the radar device 20 can be considered. In addition, it is conceivable that radio waves other than the main beam generated in the radar device 20 return to the radar device 20 as reflected waves Ly. When a radio wave other than the reflected wave Lx, such as the reflected wave Ly, reaches the radar device 20, erroneous detection may occur.
　カバー部材３０は、反射波Ｌｘ以外の電波がレーダ装置２０によって検出されることを抑制するためにレーダ装置２０の周囲に設けられている部材である。このカバー部材３０は、前述した電波吸収体１を用いて椀状に構成されている。すなわち、カバー部材３０では、椀状に形成された吸収層２の内面に複数の導電性パッチ４が設けられ、吸収層２の外面に反射層３が設けられている。 The cover member 30 is a member provided around the radar device 20 in order to suppress the detection of radio waves other than the reflected wave Lx by the radar device 20. The cover member 30 is formed in a bowl shape using the radio wave absorber 1 described above. That is, in the cover member 30, a plurality of conductive patches 4 are provided on the inner surface of the absorption layer 2 formed in a bowl shape, and the reflection layer 3 is provided on the outer surface of the absorption layer 2.
　本実施形態では、カバー部材３０は、複数の導電性パッチ４が形成された吸収層２の主面がレーダ装置２０の内面２１および側面２３の両方に対向するように設けられている。なお、複数の導電性パッチ４が形成された吸収層２の主面がレーダ装置２０の内面２１および側面２３のいずれか一方にのみ対向するようにカバー部材３０が設けられてもよい。 In the present embodiment, the cover member 30 is provided so that the main surface of the absorption layer 2 on which the plurality of conductive patches 4 are formed faces both the inner surface 21 and the side surface 23 of the radar device 20. The cover member 30 may be provided so that the main surface of the absorption layer 2 on which the plurality of conductive patches 4 are formed faces only one of the inner surface 21 and the side surface 23 of the radar device 20.
　本実施形態に係るレーダ機構１０によれば、レーダ装置２０から放射された電波Ｌｂや電波Ｌｃを十分に吸収するとともに、障害物以外の物体によって反射された反射波Ｌｙを反射層３で反射させる。その結果、レーダ装置２０が障害物以外の物体によって反射された電波を誤って検出することを防止ないし抑制できる。 According to the radar mechanism 10 according to the present embodiment, the radio wave Lb and the radio wave Lc radiated from the radar device 20 are sufficiently absorbed, and the reflected wave Ly reflected by an object other than an obstacle is reflected by the reflection layer 3. .. As a result, it is possible to prevent or suppress the radar device 20 from erroneously detecting radio waves reflected by an object other than an obstacle.
　なお、上記のレーダ機構１０ではレーダ装置２０の周りに電波吸収体としてのカバー部材３０が設けられたが、レーダ装置２０の内部に電波吸収体が設けられてもよい。この場合、カバー部材３０は、レーダ装置２０のケース内部に配置され、通信部の電波送受信面以外の部分を覆う。 In the above radar mechanism 10, a cover member 30 as a radio wave absorber is provided around the radar device 20, but a radio wave absorber may be provided inside the radar device 20. In this case, the cover member 30 is arranged inside the case of the radar device 20 and covers a portion other than the radio wave transmitting / receiving surface of the communication unit.
　上記の記載に基づいて、当業者であれば、本発明の追加の効果や種々の変形を想到できるかもしれないが、本発明の態様は、上述した実施形態に限定されるものではない。特許請求の範囲に規定された内容およびその均等物から導き出される本発明の概念的な思想と趣旨を逸脱しない範囲で種々の追加、変更および部分的削除が可能である。 Based on the above description, those skilled in the art may be able to conceive of additional effects and various modifications of the present invention, but the embodiments of the present invention are not limited to the above-described embodiments. Various additions, changes and partial deletions are possible without departing from the conceptual idea and purpose of the present invention derived from the contents defined in the claims and their equivalents.
１　電波吸収体
２　吸収層
３　反射層
４　導電性パッチ
５　溝
１０　レーダ機構
２０　レーダ装置
２１　内面
２２　外面
２３　側面
３０　カバー部材
３１　側面
３２　背面
６０　リヤバンパ
６１　内面
Ｌａ，Ｌｂ，Ｌｃ，Ｌｘ，Ｌｙ　電波 1 Radio wave absorber 2 Absorbent layer 3 Reflective layer 4 Conductive patch 5 Groove 10 Radar mechanism 20 Radar device 21 Inner surface 22 Outer surface 23 Side 30 Cover member 31 Side 32 Back 60 Rear bumper 61 Inner surface La, Lb, Lc, Lx, Ly radio waves

Claims (9)

  1. 　ミリ波または準ミリ波を吸収する電波吸収体の製造方法であって、
    　導電性材料を含有する吸収層を射出成形により形成し、
    　前記吸収層の一方の主面に反射層を形成し、
    　前記吸収層の他方の主面に導電層を形成し、
    　前記吸収層の厚みに基づく面積占有率となるように、前記導電層を複数の導電性パッチに加工する、
    　電波吸収体の製造方法。     A method for manufacturing a radio wave absorber that absorbs millimeter waves or quasi-millimeter waves.
    An absorbent layer containing a conductive material is formed by injection molding,
    A reflective layer is formed on one of the main surfaces of the absorbent layer,
    A conductive layer is formed on the other main surface of the absorption layer,
    The conductive layer is processed into a plurality of conductive patches so that the area occupancy is based on the thickness of the absorbent layer.
    Manufacturing method of radio wave absorber.
  2. 　前記吸収層の厚みが設計値よりも厚い場合、前記面積占有率を所定の占有率よりも小さくし、
    　前記吸収層の厚みが前記設計値よりも薄い場合、前記面積占有率を前記占有率よりも大きくする、請求項１に記載の電波吸収体の製造方法。     When the thickness of the absorption layer is thicker than the design value, the area occupancy is made smaller than the predetermined occupancy.
    The method for manufacturing a radio wave absorber according to claim 1, wherein when the thickness of the absorption layer is thinner than the design value, the area occupancy is made larger than the occupancy.
  3. 　前記吸収層は、３．９以上６．３以下の比誘電率を有する材料を用いて射出成形され、
    　前記導電層は、前記吸収層の前記他方の主面の少なくとも一部の領域に、前記領域における面積占有率が９０％以下になるように形成される、請求項１または２に記載の電波吸収体の製造方法。     The absorption layer is injection-molded using a material having a relative permittivity of 3.9 or more and 6.3 or less.
    The radio wave absorption according to claim 1 or 2, wherein the conductive layer is formed in at least a part of the other main surface of the absorption layer so that the area occupancy in the region is 90% or less. How to make a body.
  4. 　前記反射層は、ミリ波または準ミリ波を反射する金属により形成される、請求項１～３のいずれかに記載の電波吸収体の製造方法。 The method for manufacturing a radio wave absorber according to any one of claims 1 to 3, wherein the reflective layer is formed of a metal that reflects millimeter waves or quasi-millimeter waves.
  5. 　前記反射層および前記導電層は、両面めっき法により同時に形成される、請求項１～４のいずれかに記載の電波吸収体の製造方法。 The method for manufacturing a radio wave absorber according to any one of claims 1 to 4, wherein the reflective layer and the conductive layer are simultaneously formed by a double-sided plating method.
  6. 　ミリ波または準ミリ波を吸収する電波吸収体であって、
    　導電性材料を含有し、射出成形で形成された吸収層と、
    　前記吸収層の一方の主面に形成された反射層と、
    　前記吸収層の他方の主面の少なくとも一部の領域に形成された複数の導電性パッチと、を備え、
    　前記吸収層は、３．９以上６．３以下の比誘電率を有し、かつ前記領域における前記複数の導電性パッチの面積占有率が９０％以下である、電波吸収体。     A radio wave absorber that absorbs millimeter or quasi-millimeter waves
    An absorbent layer containing a conductive material and formed by injection molding,
    A reflective layer formed on one of the main surfaces of the absorbing layer and
    A plurality of conductive patches formed in at least a part of the other main surface of the absorption layer.
    The absorption layer is a radio wave absorber having a relative permittivity of 3.9 or more and 6.3 or less, and an area occupancy of 90% or less of the plurality of conductive patches in the region.
  7. 　前記反射層は、ミリ波または準ミリ波を反射する金属により構成されている、請求項６に記載の電波吸収体。 The radio wave absorber according to claim 6, wherein the reflective layer is made of a metal that reflects millimeter waves or quasi-millimeter waves.
  8. 　前記金属はめっきからなる、請求項７に記載の電波吸収体。 The radio wave absorber according to claim 7, wherein the metal is plated.
  9. 　ミリ波または準ミリ波を用いるレーダ装置と、
    　請求項６～８のいずれかに記載の電波吸収体で構成されたカバー部材と、
    　を備え、
    　前記カバー部材は、前記複数の導電性パッチが形成された前記吸収層の前記他方の主面が前記レーダ装置の内面および／または側面に対向するように設けられている、レーダ機構。     Radar devices that use millimeter or quasi-millimeter waves,
    A cover member composed of the radio wave absorber according to any one of claims 6 to 8.
    With
    The cover member is a radar mechanism provided so that the other main surface of the absorption layer on which the plurality of conductive patches are formed faces the inner surface and / or the side surface of the radar device.
PCT/JP2021/008774 2020-03-30 2021-03-05 Method for manufacturing radio wave absorber, radio wave absorber, and radar mechanism WO2021199917A1 (en)

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