Patent Publication Number: US-2023161010-A1

Title: Near-infrared sensor cover

Description:
TECHNICAL FIELD 
     The present invention relates to a near-infrared ray sensor cover including a cover main body portion that is arranged in front in a transmission direction of a near-infrared ray transmitted from a near-infrared ray sensor, and has near-infrared ray transmission properties. 
     BACKGROUND ART 
     A near-infrared ray sensor may be mounted on a vehicle to detect surrounding conditions. The near-infrared ray sensor transmits near-infrared rays to the outside of the vehicle, and receives near-infrared rays reflected by hitting objects outside the vehicle, such as a preceding vehicle or a pedestrian. The transmitted and received near-infrared rays are used for detecting a position of the object, and are used for measuring a distance between the vehicle and the object, or a relative speed. When the near-infrared ray sensor is arranged in an exposed state, the near-infrared ray sensor will be seen from the outside of the vehicle and appearance will be impaired. Therefore, a near-infrared ray sensor cover that hides the near-infrared ray sensor and allows the near-infrared ray to pass therethrough is arranged in front of the near-infrared ray sensor in the transmission direction of the near-infrared ray. 
     The near-infrared ray sensor cover includes, for example, a base member and a decorative layer formed on a rear surface of the base member in the transmission direction of the near-infrared ray. The base member is formed of a transparent resin material having near-infrared ray transmission properties. The decorative layer is formed of a material that reflects visible light and has near-infrared ray transmission properties. 
     Therefore, the decorative layer can be seen from the front of the near-infrared ray sensor cover in the transmission direction through the transparent base member, and the near-infrared ray sensor cover is decorated with the decorative layer. In addition, a situation in which the near-infrared ray sensor can be seen is obstructed by the decorative layer. In this manner, appearance of the near-infrared ray sensor cover and a peripheral part thereof is improved. 
     In the near-infrared ray sensor cover, it is desired that the decorative layer be seen three-dimensionally in order to further improve the appearance. Therefore, for example, as illustrated in  FIG.  4   , the base member in a cover main body portion  62  includes a front base member  63  configuring a front portion of the base member in the transmission direction and a rear base member  65  configuring a rear portion. The decorative layer (not illustrated) is arranged between the front base member  63  and the rear base member  65  in a state of having irregularities in the transmission direction. 
     However, when a refractive index of the front base member  63  and a refractive index of the rear base member  65  are different, a near-infrared ray IR transmitted from a near-infrared ray sensor  60  is refracted when passing through a boundary surface between the rear base member  65  and the front base member  63 , and changes a traveling direction. As illustrated by a solid line in  FIG.  4   , an angle of the near-infrared ray IR transmitted from the near-infrared ray sensor  60  and an angle of the near-infrared ray IR refracted when passing through a front surface  64  of the front base member  63  are different. In other words, the angle of the near-infrared ray IR differs before and after passing through the cover main body portion  62 . 
     On the other hand, when a near-infrared ray sensor cover  61  is not arranged in front of the near-infrared ray sensor  60  in the transmission direction, the near-infrared ray IR transmitted from the near-infrared ray sensor  60  travels in the same direction as that when transmitted from the near-infrared ray sensor  60  without being refracted as indicated by a two-dot chain line in  FIG.  4   . 
     Then, as described above, a case where the near-infrared ray IR is emitted from the cover main body portion  62  (the front surface  64  of the front base member  63 ) at an angle different from that when transmitted from the near-infrared ray sensor  60 , makes it difficult for the near-infrared ray sensor  60  to correctly detect a position of an object OB outside the vehicle. The position of the detected object OB deviates from the position of the actual object OB. In  FIG.  4   , the object OB is actually positioned at a place indicated by the two-dot chain line, but it is erroneously detected that the object OB is positioned at a place indicated by the solid line in  FIG.  4   . As described above, the near-infrared ray IR transmitted from the near-infrared ray sensor  60  passes through the near-infrared ray sensor cover  61 , and accordingly, there is a concern that a performance of the near-infrared ray sensor  60  that detects the position of the object OB deteriorates. 
     In a radar device using an electromagnetic wave, as a method of suppressing refraction generated when the electromagnetic wave passes through a vehicle outer plate positioned in front of the radar device, Patent Literature 1 and Patent Literature 2 describe a technology for setting a thickness of the outer plate through which the electromagnetic wave passes to maximize a transmittance. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP-A-2009-156705 
     Patent Literature 2: JP-A-2017-211199 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, although the methods described in Patent Literature 1 and Patent Literature 2 can increase a transmittance of near-infrared rays, it is not possible to completely eliminate refraction. Therefore, it is required to further reduce a deviation of a detection position of an object OB by suppressing deterioration of a performance of a near-infrared ray sensor. 
     The present invention has been made in view of such circumstances, and an object thereof is to provide a near-infrared ray sensor cover capable of suppressing the deterioration of the performance of the near-infrared ray sensor that detects the position of the object. 
     Solution to Problem 
     In order to solve the above-mentioned problems, there is provided a near-infrared ray sensor cover including a cover main body portion that is arranged in front in a transmission direction of a near-infrared ray transmitted from a near-infrared ray sensor, and has near-infrared ray transmission properties, in which the cover main body portion has a first resin layer having a refractive index n 1  and a second resin layer formed on a front side of the first resin layer in the transmission direction and having a refractive index n 2  different from the refractive index n 1 , sets a rear surface of the first resin layer in the transmission direction as an incident surface of the near-infrared ray, and sets a front surface of the second resin layer as an emission surface of the near-infrared ray, and when an angle formed by the near-infrared ray refracted when passing through the emission surface and a normal line with respect to the emission surface is θ, an angle formed by the incident surface and the emission surface is x, an angle formed by a boundary surface between the first resin layer and the second resin layer and the emission surface is y, an angle formed by the near-infrared ray refracted when passing through the incident surface and a normal line with respect to the incident surface is α, an angle formed by the near-infrared ray incident on the boundary surface and a normal line with respect to the boundary surface is β, and an angle formed by the near-infrared ray refracted when passing through the boundary surface and the normal line with respect to the emission surface is δ, the incident surface is inclined with respect to the emission surface by the angle x defined based on the following (Equation 1) to (Equation 4) that establish relationships of the angles x, y, α, β, δ, and θ. 
       sin(θ+ x )= n 1 sin α  (Equation 1)
 
         n 1 sin β= n 2 sin(δ− y )   (Equation 2)
 
         n 2 sin δ=sin θ  (Equation 3)
 
         x+y−α−β= 0 or  x+y−α+β= 0   (Equation 4)
 
     According to the above configuration, when the near-infrared ray is transmitted from the near-infrared ray sensor, the near-infrared ray passes through the cover main body portion of the near-infrared ray sensor cover. The neat-infrared ray that passes through the cover main body portion is reflected by hitting the object in front in the transmission direction. The reflected near-infrared ray is received by the near-infrared ray sensor after passing through the cover main body portion. In the near-infrared ray sensor, a position of an object is detected by the transmitted and received near-infrared ray. 
     Here, the incident surface of the first resin layer is inclined with respect to the emission surface by the angle x defined based on (Equation 1) to (Equation 4). Therefore, when the near-infrared ray is transmitted from the near-infrared ray sensor such that an angle formed by the normal line with respect to the emission surface is θ, the near-infrared ray is incident on the incident surface at an angle (θ+x). The near-infrared ray is refracted at the angle α when passing through the incident surface, and then is incident on the boundary surface at the angle β. The near-infrared ray refracted at an angle (=δ−y) when passing through the boundary surface is incident on the emission surface at the angle δ, and is refracted at the angle θ when passing through the emission surface. In this manner, an angle of the near-infrared ray when transmitted from the near-infrared ray sensor and the angle θ refracted when passing through the emission surface are the same. As a result, the near-infrared ray sensor can detect the position of the object with the same accuracy as that when the near-infrared ray sensor cover is not provided. In other words, the near-infrared ray passes through the near-infrared ray sensor cover, and accordingly, a phenomenon in which a performance of the near-infrared ray sensor that detects the position of the object deteriorates is suppressed. 
     In the near-infrared ray sensor cover, the second resin layer is made of a front base member formed of a transparent resin material and composed of an uneven surface having irregularities in a transmission direction as a rear surface in the transmission direction, the first resin layer is made of a rear base member formed of a resin material, arranged on a rear side of the front base member in the transmission direction, and composed of an uneven surface having irregularities so as to he engaged with the uneven surface of the front base member as a front surface in the transmission direction, and a decorative layer made of a material that reflects visible light and has near-infrared ray transmission properties is formed between the front base member and the rear base member. 
     According to the above configuration, when visible light is incident on the cover main body portion from the front of the near-infrared ray sensor cover in the transmission direction, the visible light passes through the front base member and is reflected by the decorative layer. When the near-infrared ray sensor cover is seen from the front in the transmission direction, the decorative layer appears to be positioned on the rear side (back side) of the front base member through the front base member. In this manner, the near-infrared ray sensor cover is decorated with the decorative layer, and the appearance of the near-infrared ray sensor cover and the peripheral part thereof is improved. 
     In particular, the rear surface of the front base member in the transmission direction is composed of the uneven surface. The decorative layer is formed on the uneven surface and has irregularities in the transmission direction. Therefore, when the near-infrared ray sensor cover is seen from the front in the transmission direction, the decorative layer appears three-dimensionally, that is, in a three-dimensional shape in the transmission direction. Therefore, the appearance of the near-infrared ray sensor cover and the peripheral part thereof is further improved. 
     Furthermore, the decorative layer is positioned in front of the near-infrared ray sensor in the transmission direction. The reflection of visible light on the decorative layer is performed in front of the near-infrared ray sensor in the transmission direction. The decorative layer has a function of hiding the near-infrared ray sensor. Therefore, the near-infrared ray sensor is unlikely to he seen from the front of the near-infrared ray sensor cover in the transmission direction. Therefore, the appearance of the near-infrared ray sensor cover and the peripheral part thereof is improved compared with a case where the near-infrared ray sensor is incorporated in an exposed state or the near-infrared ray sensor can be seen through the near-infrared ray sensor cover. 
     Incidentally, when the near-infrared ray is transmitted from the near-infrared ray sensor, the near-infrared ray passes through the rear base member, the decorative layer, and the front base member in the cover main body portion in order. The near-infrared ray reflected by hitting the object in front of the near-infrared ray sensor cover in the transmission direction, passes through the front base member, the decorative layer, and the rear base member in the cover main body portion in order, and then is received by the near-infrared ray sensor. In the near-infrared ray sensor, the position of the object is detected by the transmitted and received near-infrared ray. 
     In this case, as described above, the angle of the near-infrared ray when transmitted from the near-infrared ray sensor and the angle θ refracted when passing through the emission surface are the same. The near-infrared ray sensor can detect the position of the object with the same accuracy as that when the near-infrared ray sensor cover is not provided, and the phenomenon in which the performance of the near-infrared ray sensor that detects the position of the object deteriorates is suppressed. 
     Advantageous Effects of Invention 
     According to the near-infrared ray sensor cover, it is possible to suppress deterioration of a performance of the near-infrared ray sensor that detects a position of an object. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a view illustrating an embodiment of a near-infrared ray sensor cover, and is a schematic diagram for describing a relationship between rear and front base members and a path through which a near-infrared ray passes. 
         FIG.  2    is a side sectional view illustrating the near-infrared ray sensor cover according to the embodiment together with a near-infrared ray sensor. 
         FIG.  3    is a partial side sectional view illustrating a part of a cover main body portion in  FIG.  2    in an enlarged manner. 
         FIG.  4    is a view illustrating a near-infrared ray sensor cover in the related art, and is a schematic view for describing a relationship between rear and front base members and a path through which a near-infrared ray passes. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an embodiment in which a near-infrared ray sensor cover is embodied will be described with reference to  FIGS.  1  to  3   . 
     In the following description, a forward direction of a vehicle will be referred to as a front and a rearward direction will be referred to as a rear. Further, it is assumed that a left-right direction is a vehicle width direction and coincides with a left-right direction when the vehicle moves forward. Further, in each of  FIGS.  1  to  3   , in order to set a size of each part of the near-infrared ray sensor cover to be recognizable, a scale is appropriately changed to show each part. The same applies to  FIG.  4   , which describes the related art. 
     As illustrated in  FIGS.  1  and  2   , a near-infrared ray sensor  11  is installed at a front end portion of a vehicle  10 . The near-infrared ray sensor  11  transmits a near-infrared ray IR having a wavelength of approximately 900 nm toward the front of the vehicle  10 , and receives the near-infrared ray IR reflected by hitting an object OB outside the vehicle, such as a preceding vehicle or a pedestrian. 
     As described above, since the near-infrared ray sensor  11  transmits the near-infrared ray IR toward the front of the vehicle  10 , a transmission direction of the near-infrared ray IR by the near-infrared ray sensor  11  is a direction from the rear to the front of the vehicle  10 . A front of the near-infrared ray IR in the transmission direction substantially coincides with the front of the vehicle  10 , and a rear in the same transmission direction substantially coincides with the rear of the vehicle  10 . Therefore, in the following description, the front of the near-infrared ray IR in the transmission direction is simply referred to as “front part”, “front” or the like, and the rear in the same transmission direction is simply referred to as “rear part”, “rear” or the like. 
     The latter half of the outer shell part of the near-infrared ray sensor  11  is composed of a case  12 , and the first half part of the outer shell part is composed of a cover  15 . The case  12  is formed of a resin material such as polybutylene terephthalate resin (PBT) in a shape of a bottomed cylinder with an open front surface. In the case  12 , a transmitting unit  13  for transmitting the near-infrared ray IR and a receiving unit  14  for receiving the near-infrared ray IR are arranged. 
     The cover  15  is arranged on a front side of the case  12  and directly covers the transmitting unit  13  and the receiving unit  14 . The cover  15  is formed of a resin material containing a visible light cutting pigment, for example, polycarbonate resin (PC), polymethylmethacrylate resin (PMMA), cycloolefin polymer (COP), resin glass, or the like. 
     As illustrated in  FIG.  2   , the near-infrared ray sensor cover  20  includes a plate-shaped cover main body portion  21  and an attaching unit  49  that protrudes rearward from a rear surface of the cover main body portion  21 . The cover main body portion  21  is positioned in front of the cover  15 . The near-infrared ray sensor cover  20  is attached to a front end portion of a vehicle body in the attaching unit  49 . The near-infrared ray sensor cover  20  has a function of covering the near-infrared ray sensor  11  from the front and also has a function as a garnish for decorating the front portion of the vehicle  10 . 
     As illustrated in  FIGS.  1  and  3   , a frame part of the cover main body portion  21  is composed of a base member. The base member is made of a front base member  22  that configures a front portion which is a part outside the vehicle and a rear base member  26  that configures a rear portion which is a part inside the vehicle. The rear base member  26  corresponds to a first resin layer, and the front base member  22  corresponds to a second resin layer. 
     The front base member  22  is formed of a transparent resin material having near-infrared ray IR transmission properties, and has a refractive index n 2 . The transparency here includes not only colorless transparency but also colored transparency (colored transparency). As a corresponding resin material, the above-mentioned PC and PMMA are representative, but transparent acrylonitrile-butadiene-styrene copolymer resin (ABS) and the like can also be mentioned. A refractive index of PC is 1.59, a refractive index of PMMA is 1.49, and a refractive index of transparent ABS is 1.57. In the present embodiment, the front base member  22  is formed of PC. 
     A refractive index is a physical quantity that is a basis for propagation of light (here, near-infrared rays) in a substance, and is expressed by “propagation speed of light in air or propagation speed of light in a substance”. Since the propagation speed of light differs depending on the substance, the refractive index also differs depending on the substance. 
     A front surface  23  of the front base member  22  is composed of a single fiat surface that is substantially orthogonal to a front-rear direction. The flat surface here refers to a surface having no irregularities, and is not limited to a flat surface, but also includes a surface that is gently curved as a whole. On the other hand, a rear surface of the front base member  22  is composed of an uneven surface  24  having irregularities in the front-rear direction. 
     The rear base member  26  is formed of a resin material having a refractive index n 1  different from a refractive index n 2  of the front base member  22 , and has near-infrared ray IR transmission properties. The rear base member  26  may be formed of, for example, a resin material (PMMA, ABS, and the like) that is transparent and different from the resin material (PC) that forms the front base member  22 . Further, the rear base member  26  may be formed of another transparent resin material. Examples thereof include methyl methacrylate-styrene copolymer resin (MBS), polyamide resin (PA), polystyrene resin (PS) and the like. A refractive index of MBS is 1.50, a refractive index of PA is 1.51, and a refractive index of PS is 1.60. Further, the rear base member  26  may be formed of an opaque resin material. In the present embodiment, the rear base member  26  is formed of PMMA. 
     A front surface of the rear base member  26  is composed of an uneven surface  27  having irregularities so as to be engaged with the uneven surface  24  of the front base member  22 . The uneven surface  24  and the uneven surface  27  correspond to a boundary surface between the front base member  22  and the rear base member  26 . 
     The front base member  22  and the rear base member  26  are connected to each other by a connecting unit (not illustrated) provided therearound. As illustrated in  FIG.  3   , a hard coat layer  31  having near-infrared ray IR transmission properties and a hardness higher than that of the front base member  22  is laminated on the front surface  23  of the front base member  22 . The hard coat layer  31  is formed, for example, by applying a known surface treatment agent to the front surface  23 . Examples of the surface treatment agent include organic hard coat agents such as acrylate-based, oxetane-based, and silicone-based agents, inorganic hard coat agents, and organic-inorganic hybrid hard coat agents. Further, as the hard coat agent, a type that is cured by irradiation with ultraviolet rays (UV) may be used, or a type that is cured by applying heat may be used. 
     The hard coat layer  31  may be composed of a hard coat film having the hardness higher than that of the front base member  22 . As the hard coat film, a film formed by applying the surface treatment agent on a film base member made of a transparent resin material such as PC or PMMA can be used. 
     A water-repellent layer  32  is laminated on a front surface of the hard coat layer  31 . The water-repellent layer  32  is composed of, for example, an organic coating film, a silicone film, or the like. A decorative layer  35  and a black presser layer  36  are provided between the front base member  22  and the rear base member  26 . The decorative layer  35  is formed of a material having a high transmittance for near-infrared ray IR and a low transmittance for visible light, and is in close contact with the uneven surface  24 . The decorative layer  35  may be composed of only a colored decorative layer such as black or blue, may be composed only of a bright decorative layer having a metallic luster, or may be composed of a combination of the colored decorative layer and the bright decorative layer. In the present embodiment, the decorative layer  35  is composed of a combination of the colored decorative layer and the bright decorative layer. 
     As the decorative layer  35 , a decorative film on which the colored decorative layer or the bright decorative layer described above is formed may be used. The black presser layer  36  is a layer for allowing the near-infrared ray IR to pass therethrough while suppressing the transmission of visible light, is composed of a black coating film layer, and is in close contact with the decorative layer  35  and the uneven surface  27 . 
     A heater unit  41  for melting snow is provided on a rear surface  29  of the rear base member  26 . In the present embodiment, as the heater unit  41 , a heater film  43  having a linear heating element (heater wire)  42  that generates heat by energization is used, and the heater film  43  is laminated on the rear surface  29 . The heater film includes a heating element  42  and a pair of transparent base members that sandwich the heating element  42  from both the front and rear sides. 
     The heating element  42  is formed of a metal such as silver or copper, a metal oxide-based conductive material such as indium tin oxide (ITO) or tin oxide, a carbon heating element, a conductive paste, or the like. The heating element  42  has a linear shape, and includes, for example, a plurality of straight portions extending in parallel with each other and a plurality of connecting units that connect end portions of adjacent straight portions Both transparent base members are formed of a transparent resin material such as PC. 
     Instead of the heater film  43 , the heating element  42  may be formed on the rear surface  29  of the rear base member  26  as the heater unit  41 . In this case, the heating element  42  is formed by applying the same material as above to a part of the rear surface  29  by sputtering, printing, or using a dispenser (liquid quantitative discharge device) or the like. As a conductive paste, for example, a paste in which silver particles or the like are dispersed as a filler in a resin material is used. 
     Depending on a type of resin material forming the rear base member  26 , the rear base member  26  and the heating element  42  may not be compatible with each other, and adhesion therebetween may be low. In this case, it is preferable that an undercoat layer be formed on the rear surface  29  and the heating element  42  be formed on the undercoat layer. In this mariner, the heating element  42  can be brought into close contact with the rear base member  26  and peeling of the heating element  42  from the rear base member  26  can be suppressed, as compared with a case where the heating element  42  is formed in a state of being in contact with the rear base member  26 . It is needless to say that such an undercoat layer is unnecessary when the compatibility between the rear base member  26  and the heating element  42  is good and there is no problem in the adhesion therebetween. 
     Further, a protective film formed by curing a paint such as acrylic or urethane may be formed on the undercoat layer and a rear surface of the heating element  42  in order to enhance durability of the heating element  42 . On a rear surface of the heater unit  41  when the undercoat layer or the protective film is not provided, a reflection suppressing layer (also called an AR coat)  45  made of a transparent thin film that suppresses reflection of the near-infrared ray IR transmitted from the near-infrared ray sensor  11  is formed. When the undercoat layer or the protective film is provided, a reflection suppressing layer  45  is formed on a rear surface thereof. The reflection suppressing layer  45  has a function of reducing the reflection of the near-infrared ray IR on the rear surface of the cover main body portion  21  by interference of the near-infrared ray IR, and suppressing reduction of an amount of the near-infrared ray IR transmitted through the cover main body portion  21  due to the reflection. The reflection suppressing layer  45  is formed by using a dielectric such as MgF 2  (magnesium fluoride) and performing vacuum vapor deposition, sputtering, WET coating, or the like. 
     The reflection suppressing layer  45  may be composed of a single-layer thin film or a multi-layer thin film. In the latter case, as multi pie thin films, those having different refractive indexes and thicknesses may be used. By doing so, it is possible to reduce the reflection of the near-infrared ray IR for a wide range of wavelengths. 
     Further, as the reflection suppressing layer  45 , a layer in which a metal oxide such as TIO 2  (titanium dioxide) or SiO 2  (silicon dioxide) is laminated may be used. A hydrophilic film  46  is formed on a rear side of the reflection suppressing layer  45 . Nano-order fine particles (nanoparticles) made of a metal oxide are uniformly dispersed in the hydrophilic film  46 . As the metal oxide, for example, SiO 2  (silica) can he used. Furthermore, in the present embodiment, the hydrophilic film  46  is formed such that a contact angle with respect to water is 10 degrees or less. The hydrophilic film  46  may be formed by mixed adsorption (alternate adsorption) of nano-order fine particles (nanoparticles) made of a metal oxide. 
     The above is a basic configuration (layer configuration) of the cover main body portion  21 . As described above, the base member of the present embodiment is composed of the rear base member  26  and the front base member  22  having refractive indexes n 1  and n 2  different from each other. In general, when light (near-infrared ray IR) passes through a boundary surface between different substances, refraction occurs, which is a phenomenon in which a direction in which light (near-infrared ray IR) travels changes. In the present embodiment, on the premise that such refraction occurs, it is devised that the near-infrared ray sensor  11  can detect the position of the object OB outside the vehicle with the same accuracy as that when the near-infrared ray sensor cover  20  is not arranged in front of the near-infrared ray sensor  11 . The device will be described below. 
     In addition, the near-infrared ray IR also is refracted on a boundary surface between the rear base member  26  and the black presser layer  36 , a boundary surface between the decorative layer  35  and the front base member  22 , and a boundary surface between the black presser layer  36  and the decorative layer  35 . However, a thickness of the decorative layer  35  and the like is extremely small compared to a thickness of the rear base member  26  and the front base member  22 . Therefore, influence of the refraction of the near-infrared ray IR on the decorative layer  35  and the black presser layer  36  on the overall refraction of the cover main body portion  21  is negligibly small. Therefore, when considering the refraction that occurs when the near-infrared ray IR propagates through the members configuring the cover main body portion  21 , the cover main body portion  21  is composed of only the rear base member  26  and the front base member  22 . 
     Here, as illustrated in  FIG.  1   , the rear surface  29  of the rear base member  26  is used as an incident surface of the near-infrared ray IR in the cover main body portion  21 , and the front surface  23  of the front base member  22  is used as an emission surface of the near-infrared ray IR. In addition, the angles x, y, α, β, δ, and θ are defined as follows. 
     x: An angle formed by the incident surface and the emission surface 
     y: An angle formed by the boundary surface between the rear base member  26  and the front base member  22  and the emission surface 
     α: An angle (refraction angle) formed by the near-infrared ray IR refracted when passing through the incident surface and a normal line  51  with respect to the incident surface 
     β: An angle formed by the near-infrared ray IR incident on the boundary surface and a normal line  52  with respect to the boundary surface (incident angle) 
     γ: An angle (refraction angle) formed by the near-infrared ray IR refracted when passing through the boundary surface and the normal line  52   
     δ: An angle (incident angle) formed by the near-infrared ray IR, which is refracted when passing through the boundary surface and is incident on the emission surface, and a normal line  53  with respect to the emission surface 
     θ: An angle (refraction angle) formed by the near-infrared ray IR refracted when passing through the emission surface and the normal line  53   
     As described above, the uneven surface  24  and the uneven surface  27  correspond to the boundary surface between the front base member  22  and the rear base member  26 . Further, an angle γ can be obtained by δ−y. 
     When defined as described above, the following (Equation 1) to (Equation 4) are established between the angles x, y, α, β, δ, and θ. (Equation 1) to (Equation 3) are applied to Snell&#39;s law Snell&#39;s law is a law that expresses a relationship between a propagation speed of a traveling wave in two media in a general refraction phenomenon of waves, the incident angle, and the refraction angle, and is also called refraction law. 
       sin(θ+ x )= n 1 sin α  (Equation 1)
 
         n 1 sin β= n 2 sin(δ− y )   (Equation 2)
 
         n 2 sin δ=sin θ  (Equation 3)
 
         x+y−α−β= 0 or  x+y−α+β= 0   (Equation 4)
 
     The angle y in the above (Equation 1) 10  (Equation 4) is determined by an uneven shape of the uneven surface  24  on the front base member  22  and an uneven shape of the uneven surface  27  on the rear base member  26 . 
     Then, in the cover main body portion  21 , the incident surface (rear surface  29 ) is inclined with respect to the emission surface (front surface  23 ) by the angle x defined based on the above (Equation 1) to (Equation 4). 
     In addition, which of the equations in the above (Equation 4) is selected is determined by a magnitude relationship between the angle γ and the angle β. When the angle γ is smaller than the angle β (this corresponds to  FIG.  1   ), x+y−α−β=0 is selected as (Equation 4). When the angle γ is larger than the angle β, x+y−α+β=0 is set as (Equation 4). 
     Next, the operation of the present embodiment configured as described above will be described. In addition, the effects caused by the operation will also be described. 
     As illustrated in  FIGS.  2  and  3   , when the near-infrared ray IR is transmitted from the transmitting unit  13 , the hydrophilic film  46  of the cover main body portion  21  is irradiated with the near-infrared ray IR. At this time, the reflection of the near-infrared ray IR transmitted through the hydrophilic film  46  by the reflection suppressing layer  45  is suppressed by the reflection suppressing layer  45 . An amount of the near-infrared ray IR transmitted through the reflection suppressing layer  45  increases by an amount of this suppression. 
     The near-infrared ray IR transmitted through the reflection suppressing layer  45  passes through the heater unit  41 , the rear base member  26 , the black presser layer  36 , the decorative layer  35 , the front base member  22 , the hard coat layer  31 , and the water-repellent layer  32  in this order. In this manner, the near-infrared ray IR passes through the cover main body portion  21 . 
     The near-infrared ray IR transmitted through the cover main body portion  21  is reflected by hitting the object OB (refer to  FIG.  1   ), such as a preceding vehicle or a pedestrian. The reflected near-infrared ray IR again passes through the water-repellent layer  32 , the hard coat layer  31 , the front base member  22 , the decorative layer  35 , the black presser layer  36 , the rear base member  26 , the heater unit  41 , the reflection suppressing layer  45 , and the hydrophilic film  46  on the cover main body portion  21  in order. The near-infrared ray IR transmitted through the cover main body portion  21  is received by the receiving unit  14 . The near-infrared ray sensor  11  detects the position of the object OB based on the transmitted and received near-infrared ray IR, and also measures a distance between the vehicle  10  and the object OB, a relative speed, and the like. 
     Here, as illustrated in  FIG.  1   , the rear surface  29  of the rear base member  26  configuring the incident surface is inclined by the angle x defined based on the above (Equation 1) to (Equation 4) with respect to the front surface  23  of the front base member  22  configuring the emission surface. Therefore, when the near-infrared ray IR is transmitted from the near-infrared ray sensor  11  such that an angle formed by the normal line  53  with respect to the front surface  23  is θ, the near-infrared ray is incident on the rear surface  29  at an angle (θ+x). The near-infrared ray IR is refracted at the angle α when passing through the rear surface  29 , and then is incident on the uneven surface  24  and the uneven surface  27  configuring the boundary surface at the angle β. The near-infrared ray IR refracted at the angle γ(=δ−y) when passing through the uneven surface  24  and the uneven surface  27  is incident on the front surface  23  at the angle δ and is refracted at the angle θ when passing through the front surface  23 . In this manner, an angle of the near-infrared ray IR when transmitted from the near-infrared ray sensor  11  and the angle θ refracted when passing through the front surface  23  are the same. In other words, an angle of the near-infrared ray IR before passing through the cover main body portion  21  and an angle of the near-infrared ray IR after passing through are the same. As a result, the near-infrared ray sensor  11  can detect the position of the object OB with the same accuracy as that when the near-infrared ray sensor cover  20  is not provided. In other words, the near-infrared ray IR passes through the near-infrared ray sensor cover  20 , and accordingly, it is possible to suppress the deterioration of the performance of the near-infrared ray sensor  11  that detects the position of the object OB. 
     Further, as described with reference to  FIG.  3   , the amount of the near-infrared ray IR transmitted through the cover main body portion  21  is increased by an amount that the reflection of the near-infrared ray IR is suppressed by the reflection suppressing layer  45 , and the transmittance is increased. Therefore, the cover main body portion  21  is unlikely to interfere with the transmission of the near-infrared ray IR. Of the near-infrared ray IR, an amount attenuated by the cover main body portion  21  can be kept within an allowable range. Therefore, the near-infrared ray sensor  11  tends to exert a function of detecting the position of the object OB and a function of measuring the distance, the relative speed, and the like. 
     Furthermore, in the near-infrared ray sensor cover  20 , the hard coat layer  31  enhances impact resistance of the cover main body portion  21 . Therefore, the hard coat layer  31  can suppress damage to the cover main body portion  21 , which is caused by flying stones or the like. Further, the hard coat layer  31  enhances weather resistance of the cover main body portion  21 . Therefore, the hard coat layer  31  can suppress degeneration or deterioration of the cover main body portion  21  due to sunlight, wind and rain, temperature changes, and the like. In this respect as well, the near-infrared ray sensor  11  tends to exert the function of detecting the position of the object OB and the function of measuring the distance, the relative speed, and the like. 
     Further, since the front surface of the cover main body portion  21  is composed of the water-repellent layer  32 , even when water adheres to the front surface of the cover main body portion  21 , water is repelled. The cover main body portion  21  is unlikely to get wet, and it is possible to suppress formation of a water film on the front surface of the cover main body portion  21 . 
     Meanwhile, the heating element  42  in the heater unit  41  generates heat when energized. A part of this heat is transferred to the front surface of the cover main body portion  21 . Therefore, even when snow adheres to the front surface of the cover main body portion  21 , the heating element  42  generates heat by energization, and the snow is melted by the heat transferred from the heating element  42 . Even when it snows, the near-infrared ray sensor  11  can exert the function of detecting the position of the object OB and a function of measuring the distance, the relative speed, and the like. 
     Further, when the near-infrared ray sensor  11  arranged behind the cover main body portion  21  becomes hot due to the operation, there is a concern that the heat causes dew condensation on the rear surface of the cover main body portion  21  to cause cloudiness. However, in the present embodiment, the rear surface of the cover main body portion  21  is composed of the hydrophilic film  46 , and the contact angle with respect to water is 10 degrees or less. Condensed water spreads on the hydrophilic film  46 . Therefore, cloudiness of the rear surface of the cover main body portion  21  is suppressed. Therefore, the reflection suppressing layer  45  can sufficiently exert a function of suppressing the reflection of the near-infrared ray IR. 
     Incidentally, when the cover main body portion  21  is irradiated with visible light from the front side, the visible light passes through the water-repellent layer  32 , the hard coat layer  31 , and the front base member  22 , and is reflected by the decorative layer  35 . When the near-infrared ray sensor cover  20  is seen from the front of the vehicle  10 , the decorative layer  35  appears to be positioned on the rear side (back side) of the front base member  22  through the water-repellent layer  32 , the hard coat layer  31 , and the front base member  22 . As for the colored decorative layer in the decorative layers  35 , the color of the colored decorative layer can be seen. Further, as for the bright decorative layer in the decorative layers  35 , the bright decorative layer appears to be brilliant like metal. In this manner the near-infrared ray sensor cover  20  is decorated with the decorative layer  35 , and the appearance of the near-infrared ray sensor cover  20  and the peripheral part thereof is improved. 
     In particular, the rear surface of the front base member is composed of the uneven surface  24 . The decorative layer  35  is formed on the uneven surface  24  and has irregularities. Therefore, when the near-infrared ray sensor cover  20  is seen from the front of the vehicle  10 , the part of the decorative layer  35  that protrudes forward appears to be positioned on the front side (front side), and the part other than this appears to be positioned on the rear side (back side). In other words, the decorative layer  35  appears three-dimensionally, that is, in a three-dimensional shape in the front-rear direction. Therefore, the appearance of the near-infrared ray sensor cover  20  and the peripheral part thereof is further improved. It is difficult to obtain such an effect with a near-infrared ray sensor cover in which the rear surface of the front base member  22  is composed of a single flat surface and a decorative layer is formed on the flat surface. 
     The reflection of visible light on the decorative layer  35  is performed on the front side of the near-infrared ray sensor  11 . The decorative layer  35  has a function of covering and hiding the near-infrared ray sensor  11 . Therefore, the near-infrared ray sensor  11  is unlikely to be seen from the front side of the near-infrared ray sensor cover  20 . Therefore, the near-infrared ray sensor cover  20  is not used, and the near-infrared ray sensor  11  is incorporated into the vehicle body in an exposed state, and the appearance of the near-infrared ray sensor  11  is improved compared to that when the near-infrared ray sensor  11  is seen through the near-infrared ray sensor cover  20 . 
     In addition, the above embodiment can also be implemented as a modification example in which the embodiment is modified as follows. The above embodiment and the following modification examples can be implemented in combination with each other within a technically consistent range. 
     A reflection suppression structure unit may be provided instead of the reflection suppressing layer  45 . 
     In this case, the heater unit  41  made of the linear heating element  42  is formed on the rear surface  29  of the rear base member  26 . The reflection suppression structure unit is formed at a rear portion including the rear surface  29  of the rear base member  26 , which is at least a part of a place different from the place where the heater unit  41  is provided. 
     The reflection suppression structure unit has a moth-eye structure having a fine uneven shape. The moth-eye structure is an uneven structure having an average period shorter than a wavelength of light ray (near-infrared ray IR), as seen on a surface of moth eyes. The uneven shape has a reflection suppressing surface that is inclined with respect to the front-rear direction and suppresses the reflection of near-infrared ray. 
     In this modification example, when the near-infrared ray IR is transmitted from the transmitting unit  13  of the near-infrared ray sensor  11 , the rear surface of the cover main body portion  21  is irradiated with the near-infrared ray IR. At this time, the near-infrared ray IR with which the reflection suppression structure unit is irradiated is suppressed by the reflection suppressing surface. 
     Also in this case, as in the above embodiment, the amount of the near-infrared ray IR transmitted through the cover main body portion  21  is increased by an amount that the reflection of the near-infrared ray IR is suppressed by the reflection suppression structure unit, and the transmittance is increased. Therefore, the cover main body portion  21  is unlikely to interfere with the transmission of the near-infrared ray IR. Of the near-infrared ray IR, the amount attenuated by the cover main body portion  21  can be kept within an allowable range. Therefore, the near-infrared ray sensor  11  tends to exert various detection functions such as the position detection. 
     As described above, when the heater unit  41  and the reflection suppression structure unit are provided on the rear surface of the rear base member  26 , at least the reflection suppression structure unit of the heater unit  41  and the reflection suppression structure unit may be covered from the rear side by the above-described hydrophilic film  46 . 
     The reflection suppressing layer  45  or the reflection suppression structure unit may be omitted as long as the reflection on the rear surface of the cover main body portion  21  of the near-infrared ray IR transmitted from the transmitting unit  13  of the near-infrared ray sensor  11  is acceptable. 
     The near-infrared ray sensor cover  20  can he applied even when the near-infrared ray sensor  11  is installed at a place different from the front portion of the vehicle  10 , for example, at the rear portion. In this case, the near-infrared ray sensor  11  transmits the near-infrared ray IR toward the rear part of the vehicle  10 . The near-infrared ray sensor cover  20  is arranged in front of the transmitting unit  13  in the transmission direction of the near-infrared ray IR, that is, at the rear part of the vehicle  10  with respect to the transmitting unit  13 . 
     The near-infrared ray sensor cover  20  is also applicable when the near-infrared ray sensor  11  is installed on both side portions of the front portion or the rear portion of the vehicle  10 , that is, on the diagonal front side portion or the diagonal rear side portion. 
     REFERENCE SIGNS LIST 
       11  . . . Near-infrared ray sensor 
       20  . . . Near-infrared ray sensor cover 
       21  . . . Cover main body portion 
       22  . . . Front base member (second resin layer) 
       23  . . . Front surface (emission surface) 
       24  . . . Uneven surface (boundary surface) 
       26  . . . Rear base member (first resin layer) 
       27  . . . Uneven surface (boundary surface) 
       29  . . . Rear surface (incident surface) 
       35  . . . Decorative layer 
       51 ,  52 ,  53  . . . Normal line 
     IR . . . Near-infrared ray 
     n 1 , n 2  . . . Refractive index 
     x, y, α,β, δ, θ, γ . . . Angle