Snow melting radome

Abstract

To provide a snow melting radome reliably melting snow with further low power consumption while securing electromagnetic wave permeability required for the radome, and exhibiting a stable snow melting function over a long period of time.SOLUTION: A snow melting radome 1 is so configured that an electromagnetic wave permeable first base material 3 and an electromagnetic wave permeable second base material 4 are respectively formed of a solid synthetic resin, a heater wire 5 wired between the first base material 3 and the second base material 4 disposed on a visible side is sealed by the first base material 3 and the second base material 4, and electromagnetic wave permeable insulation materials such as a resin foam material 7 are laminated and fixed on a surface opposite to the visible side of the second base material 4.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a radome, such as a radome for an on-board radar system, which is provided on the front side of an on-board radar system, and more particularly to a snow-melting radome having a snow-melting function. [Background technology]

[0002] Conventionally, radomes with a snow-melting function, which are wired with heater wires, have been known for use in vehicle-mounted radar systems, and one such radome is disclosed in Patent Document 1.

[0003] This radome is constructed by laminating and fixing together a first substrate made of synthetic resin and a second substrate made of synthetic resin. A groove is formed on the side of the first substrate that is fixed to the second substrate, and a heater wire is fitted into the groove and wired along the groove. Patent Document 1 discloses that foamed resin may be used for the synthetic resin of the first substrate and the synthetic resin of the second substrate (see paragraphs

[0007] and

[0025] of Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2021-170006 [Overview of the project] [Problems that the invention aims to solve]

[0005] Incidentally, in the radome described in Patent Document 1, when the second base material, which is positioned on the side opposite to the viewing side, is formed from foamed resin, the heat insulating properties of the foamed resin allow the radome to be heated to a high temperature with lower power consumption, thereby reliably melting snow and ice attached to the viewing side of the radome. However, the second base material formed from foamed resin is inferior in waterproofness and durability compared to the second base material formed from solid synthetic resin, making it difficult to provide a stable snow-melting function over a long period of time. Therefore, there is a need for a radome that can perform the required snow-melting with lower power consumption and provide a stable snow-melting function over a long period of time.

[0006] This invention is proposed in view of the above problems, and aims to provide a snow-melting radome that can reliably melt snow with lower power consumption while ensuring the electromagnetic wave permeability required for a radome, and that can exhibit a stable snow-melting function over a long period of time. [Means for solving the problem]

[0007] The snow-melting radome of the present invention is characterized in that a first electromagnetic wave-permeable substrate and a second electromagnetic wave-permeable substrate are each formed from a solid synthetic resin, a heater wire is wired between the first substrate and the second substrate which are positioned on the viewing side and is sealed by the first substrate and the second substrate, and an electromagnetic wave-permeable heat insulating material is laminated and fixed to the surface of the second substrate opposite to the viewing side. According to this, while ensuring the electromagnetic wave permeability required for the radome, the thermal insulation properties of the electromagnetic wave permeable insulation material allow the radome to be heated to a high temperature with lower power consumption, and snow and ice adhering to the viewing side of the radome can be reliably melted. Furthermore, temperature unevenness in the radome can be suppressed, the radome can be heated more uniformly, and snow melting with higher uniformity can be achieved in the electromagnetic wave irradiation area. In addition, by sealing the heater wire with a first base material and a second base material formed of solid synthetic resin, the waterproofness and durability of the heating structure by the heater wire can be stably ensured over a long period of time, and a stable snow melting function can be exhibited over a long period of time. Moreover, by fixing the electromagnetic wave permeable insulation material to the second base material without spacing it relative to the second base material, the number of interfaces between the electromagnetic wave permeable insulation material and the second base material is reduced, which can further enhance the electromagnetic wave permeability of electromagnetic waves incident on the radome from the radar device in a perpendicular or oblique direction, and it is possible to prevent a decrease in thermal insulation due to air convection or exchange between the electromagnetic wave permeable insulation material and the second base material.

[0008] The snow-melting radome of the present invention is made of 1 m of the electromagnetic wave-permeable heat insulating material. 2 It is characterized by having a thermal resistance of 0.0055 K / W or more per unit area. According to this, compared to a structure in which electromagnetic wave-permeable insulation material is not laminated on the second base material, the power consumption required to obtain the same snow-melting effect can be reduced by about 10%.

[0009] The snow-melting radome of the present invention is made of 1 m of the electromagnetic wave-permeable heat insulating material. 2 It is characterized by having a thermal resistance of 0.020 K / W or more per unit area. According to this, compared to a structure in which electromagnetic wave-permeable insulation material is not laminated on the second base material, the power consumption required to obtain the same snow-melting effect can be reduced by approximately 29%.

[0010] The snow-melting radome of the present invention is characterized in that the electromagnetic wave-permeable heat insulating material is a foamed resin material. According to this method, it is possible to reliably obtain a radome with higher electromagnetic wave transmission and thermal insulation properties.

[0011] The snow-melting radome of the present invention is characterized in that the foaming ratio of the foamed resin material is 2 times or more, and the thickness of the foamed resin material in the lamination direction in the electromagnetic wave irradiation area is 1 mm or more. According to this method, it is possible to ensure the electromagnetic wave transmission required for the radome while reliably improving heat insulation and reliably increasing the power consumption reduction effect necessary to obtain the same snow melting effect.

[0012] The snow-melting radome of the present invention is characterized in that the plate thickness d3 (mm) in the lamination direction of the foamed resin material satisfies the following formula (1). (λ0×N) / 2n3-0.5(mm)≦d3≦(λ0×N) / 2n3+0.5(mm)···(1) [In equation (1), λ0 is the wavelength of the electromagnetic waves from the radar device irradiated onto the snow-melting radome, n3 is the refractive index of the foamed resin material, and N is a positive integer.] According to this method, it is possible to achieve extremely high electromagnetic wave transmission in the radome, and to reliably obtain a radome with superior electromagnetic wave transmission and thermal insulation properties. [Effects of the Invention]

[0013] The snow-melting radome of the present invention ensures the electromagnetic wave permeability required for a radome, while reliably melting snow with lower power consumption and exhibiting a stable snow-melting function over a long period of time. [Brief explanation of the drawing]

[0014] [Figure 1] Front view of a snow-melting radome according to an embodiment of the present invention. [Figure 2] Enlarged cross-sectional view AA of Figure 1. [Figure 3] Graphs showing experimental results regarding the relationship between the density of foamed resin and the dielectric loss tangent, and the relationship between the density of foamed resin and the real part of the complex relative permittivity of foamed resin. [Figure 4]A graph showing the experimental results of the relationship between the plate thickness of the foamed resin material and the electromagnetic wave transmittance.

Embodiments for Carrying out the Invention

[0015] 〔Snow-melting Dome of the Embodiment〕 The snow-melting dome 1 of the embodiment according to the present invention is a dome for an in-vehicle radar device used, for example, as a bumper cover attached to a bumper of a vehicle. As shown in FIGS. 1 and 2, it includes an electromagnetic wave-transmissive substrate 2. The substrate 2 is composed of a first base material 3 disposed on the visual recognition side, which is the outer surface side of the snow-melting dome 1, a second base material 4 disposed on the rear side, which is the side opposite to the visual recognition side of the first base material 3, and a foamed resin material ⑦ corresponding to an electromagnetic wave-transmissive heat insulating material disposed on the rear side, which is the side opposite to the visual recognition side of the second base material. The first base material 3 and the second base material 4 are laminated and fixed, and the second base material 4 and the foamed resin material ⑦ are laminated and fixed. The first base material 3, the second base material 4, and the foamed resin material ⑦ are each formed of an insulating and electromagnetic wave-transmissive synthetic resin. The snow-melting dome 1 is irradiated with electromagnetic waves from the foamed resin material ⑦ side by a radar device such as an in-vehicle radar device (not shown).

[0016] The first base material 3 and the second base material 4 are each formed of a solid synthetic resin. Different or the same synthetic resins can be used for the first base material 3 and the second base material 4. When the first base material 3 and the second base material 4 are formed of materials with refractive indices n defined based on the complex dielectric constant that match each other, or the refractive indices n are substantially the same or close to each other, it is preferable from the viewpoint of improving the transmission performance of electromagnetic waves. As the numerical range of the refractive indices of the first base material 3 and the second base material 4 that are close to each other, it is good if the difference in the refractive indices of the first base material 3 and the second base material 4 is within the range of 0 to 10%.

[0017] For the foamed resin material 7, which corresponds to an electromagnetic wave permeable thermal insulation material, it is preferable from the viewpoint of improving electromagnetic wave transmission performance to use a material whose refractive index n, defined based on the complex dielectric constant, is mutually compatible with both the first base material 3 and the second base material 4, or whose refractive index n is approximately the same or close in value. A good numerical range for the close refractive index of the first base material 3 and the foamed resin material 7 is when the difference in refractive index between the first base material 3 and the foamed resin material 7 is within the range of 0 to 10%. Similarly, a good numerical range for the close refractive index of the second base material 4 and the foamed resin material 7 is when the difference in refractive index between the second base material 4 and the foamed resin material 7 is within the range of 0 to 10%.

[0018] Here, the refractive index n is a quantity defined by Equation 1, which is derived from the real part ε'r and the imaginary part ε”r of the relative permittivity. From the viewpoint of transmittance, it is preferable that the magnitude of the dielectric loss tangent tanδ, defined by Equation 2 from the ratio of the imaginary and real parts at the applicable frequency, be 0.1 or less. It is also preferable that the magnitude of the real part of the relative permittivity be 3 or less. By keeping the magnitudes of the dielectric loss tangent and the real part of the non-dielectric constant below these values, it is possible to reliably reduce the reflectivity and internal loss required for the radome.

[0019]

number

[0020]

number

[0021] For the solid synthetic resin of the first base material 3 and the solid synthetic resin of the second base material 4, it is possible to use synthetic resins appropriate within the scope of the present invention. For example, it is preferable to use one of the following, either alone or in combination of two or more, for the first base material 3 or the second base material 4: acrylic resins such as polymethyl methacrylate (PMMA), polycarbonate (PC), acrylonitrile-butadiene-styrene copolymer (ABS), acrylonitrile-styrene-acrylate copolymer (ASA), acrylonitrile-ethylenepropyl rubber-styrene copolymer (AES), polypropylene (PP), polyphenylene ether (PPE), modified polyphenylene ether (m-PPE), etc. Additives may also be included.

[0022] The foamed resin material 7, which corresponds to an electromagnetic wave permeable heat insulating material, can use any synthetic resin appropriate within the scope of the present invention. For example, polyphenylene ether (PPE), modified polyphenylene ether (m-PPE), polyurethane (PUR), polyethylene (PE), polypropylene (PP), phenolic resin (PF), polyvinyl chloride (PVC), urea resin (UF), silicone (SI), polyimide (PI), melamine resin (MF), polystyrene resin (PS), polyamide resin (PA), acrylic resin, fluororesin, polyester resin, etc. are preferred, and additives may also be included. Among the synthetic resins used in the foamed resin material 7, it is preferable to use a resin with low polarity from the viewpoint of reducing the complex refractive index of the foamed resin material 7. Examples include polyolefin resins, polystyrene resins, polyphenylene ether resins, polyimide resins, and fluororesin. Among these, polyolefin resins, polystyrene resins, and polyphenylene ether resins are preferred from the viewpoints of processability, cost, and flame retardancy.

[0023] The electromagnetic wave permeable insulation material or equivalent foamed resin material 7 contains 1 m 2Using a material with a thermal resistance of 0.0055 K / W or more per unit area is preferable because, compared to a structure in which the foamed resin material 7 is not laminated on the second base material 4, the power consumption required to obtain the same snow-melting effect can be reduced by approximately 10% or more. Furthermore, 1m 2 Using a material with a thermal resistance of 0.020 K / W or higher per unit area is preferable because it can reduce the power consumption required to obtain the same snow-melting effect by approximately 29% or more. 2 The greater the thermal resistance per unit area, the better the insulation, and therefore the greater the effect of reducing power consumption. However, as shown in equation 3 below, increasing thermal resistance requires either increasing the thickness or decreasing the thermal conductivity. Since thermal conductivity is a value inherent to the material, increasing the thickness can increase the thermal resistance. However, due to practical constraints, the strong correlation between thickness and electromagnetic wave permeability as shown in equation (1) above, and the fact that generally, increasing the thickness increases the absorption rate of electromagnetic waves and worsens electromagnetic wave permeability, it is difficult to increase the thickness. From the above perspective, 1m 2 The thermal resistance value per unit area is 0.0055 K / W or higher, preferably 0.010 K / W or higher, more preferably 0.015 K / W or higher, and even more preferably 0.020 K / W or higher. There is no particular upper limit, but it is preferably 2.000 K / W or lower, more preferably 1.5000 K / W or lower, and even more preferably 1.000 K / W or lower.

[0024] If the foaming ratio of the foamed resin material 7 is 2 times or more, and the thickness of the foamed resin material 7 in the lamination direction in the electromagnetic wave irradiation area is 1 mm or more, it is preferable to reliably improve the heat insulation and reliably increase the power consumption reduction effect required to obtain the same snow melting effect. Furthermore, from the viewpoint of practicality, improving mechanical strength, improving heat insulation, and improving electromagnetic wave permeability, the foaming ratio of the foamed resin material 7 is preferably 20 times or less, more preferably 15 times or less. Furthermore, from the same viewpoint, it is preferable to set the thickness of the foamed resin material 7 in the lamination direction in the electromagnetic wave irradiation area to 50 mm or less, more preferably 30 mm or less.

[0025] Furthermore, regarding the thickness in the electromagnetic wave transmission direction of the first base material 3, the second base material 4, and the foamed resin material 7 which corresponds to an electromagnetic wave permeable heat insulating material in the snow-melting radome 1, the ratio of the thickness of the first base material 3, the thickness of the second base material 4, and the thickness of the foamed resin material 7, the thickness of the first base material 3, the thickness of the second base material 4, the thickness of the foamed resin material 7, and the thickness (total thickness) of the base body 2 composed of the first base material 3, the second base material 4, and the foamed resin material 7 can be set within an appropriate range as long as the required electromagnetic wave permeability can be ensured as a radome such as a radome for an in-vehicle radar device.

[0026] Furthermore, it is preferable to provide the foamed resin material 7, which corresponds to an electromagnetic wave permeable heat insulating material, so that it overlaps the entire electromagnetic wave irradiation area R in the direction of electromagnetic wave irradiation, in order to reliably obtain the necessary electromagnetic wave permeability. Moreover, it is even more preferable to provide the foamed resin material 7 over the entire wiring area of ​​the heater wire 5 in the base 2 and over an area larger than the entire electromagnetic wave irradiation area R.

[0027] In the snow-melting radome 1, heater wires 5 are wired in the planar direction of an electromagnetic wave-transparent substrate 2. The conductive material constituting the heater wires 3 can be any conductive material suitable within the scope of the present invention. For example, copper, silver, silver-plated copper, copper-silver alloy, copper-nickel alloy, nickel-chromium alloy, iron-chromium alloy, transparent conductive films such as ITO films, or carbon fibers are suitable. Furthermore, the form of the heater wire is not limited; wire, conductive ink, conductive filler, etc., can be used.

[0028] In the illustrated example, the heater wire 5 is formed by meandering and folding along the direction in which the plate-shaped base body 2 expands, extending in a continuous line. The straight sections of the heater wire 5 are arranged side by side with spacing along the plane direction of the base body 2 in and outside the electromagnetic wave irradiation area R of the radar device on the base body 2, and the direction of the current flowing through the straight sections of adjacent heater wires 5 is set to be approximately antiparallel or antiparallel to each other.

[0029] Furthermore, the heater wire 5 is embedded between the first base material 3 and the second base material 4, and is sandwiched between the first base material 3 and the second base material 4, and is installed and sealed within the base body 2 composed of the first base material 3 and the second base material 4. In this embodiment, a groove 31 is formed on the side of the first base material 3 that is fixed to the second base material 4, and another groove 41 is formed on the side of the second base material 4 that is fixed to the first base material 3, opposite to the groove 31. The heater wire 5 is fitted into the groove 31 of the first base material 3 and the other groove 41 of the second base material 4 and wired along the groove 31 and the other groove 41. As a modified example, a resin film on which the heater wire is wired may be provided between the first base material and the second base material, and the heater wire may be sealed by the first base material and the second base material by fixing the first base material and the second base material via the resin film.

[0030] Furthermore, a positioning recess 32 is formed on the fixing surface side of the first base material 3 so as to be connected to the groove 31, and at least a part of the wire harness connection part 6, which is electrically connected to the heater wire 5, is housed in the positioning recess 32. The connection terminal 61 of the wire harness connection part 6 and the end 51 of the heater wire 5 are arranged to overlap, for example, at a position corresponding to the groove 31, with the connection terminal 61 of the wire harness connection part facing the second base material 4 side, and are electrically connected.

[0031] In this embodiment, the second base material 4 is made of an injection-molded material that is injection-molded to overlap the first base material 3, and the second base material 4 of the injection-molded material is fixed to the first base material 3 by molding and welding. A heater wire 5 is embedded and sealed inside the second base material 4 of the injection-molded material and the first base material 3, and a wire harness connection part 6 is also embedded and sealed inside. An electrical cable 62 extending from the wire harness connection part 6 is led out from the base body 2 made up of the first base material 3 and the second base material 4. In addition to molding and welding, the first base material 3 and the second base material 4 can be fixed by any appropriate method within the scope of applicability, for example, by bonding via an adhesive layer or by heat fusion, but from the viewpoint of more reliably preventing a decrease in electromagnetic wave permeability, it is preferable to directly fix the first base material 3 and the second base material 4 together by welding or heat fusion.

[0032] Furthermore, the foamed resin material 7, which corresponds to the electromagnetic wave permeable heat insulating material in this embodiment, is directly fixed to the second base material 4 by welding or heat fusion, etc., from the viewpoint of more reliably preventing a decrease in electromagnetic wave permeability. It should be noted that the foamed resin material 7 can also be fixed to the second base material 4 by bonding, for example, via an adhesive layer.

[0033] According to the snow-melting radome 1 of this embodiment, while ensuring the electromagnetic wave permeability required for the radome, the thermal insulation properties of the foamed resin material 7, which corresponds to an electromagnetic wave permeable thermal insulation material, allow the radome to be heated to a high temperature with lower power consumption, and snow and ice adhering to the visible side of the radome can be reliably melted. Furthermore, temperature unevenness in the radome can be suppressed, allowing the radome to be heated more uniformly, and snow melting with higher uniformity can be achieved in the electromagnetic wave irradiation area. In addition, by sealing the heater wire 5 with the first base material 3 and the second base material 4 formed of solid synthetic resin, the waterproofness and durability of the heating structure by the heater wire 5 can be stably ensured over a long period of time, and a stable snow-melting function can be exhibited over a long period of time.

[0034] Furthermore, by fixing the foamed resin material 7, which corresponds to the electromagnetic wave permeable thermal insulation material, to the second base material 4 without spacing it relative to the second base material 4, the number of interfaces between the foamed resin material 7 and the second base material 4 is reduced, thereby further improving the electromagnetic wave permeability of electromagnetic waves incident from the radar device to the radome in a perpendicular or oblique direction, and preventing a decrease in thermal insulation due to air convection or exchange between the foamed resin material 7 and the second base material 4. In addition, by using the foamed resin material 7 as the electromagnetic wave permeable thermal insulation material, it is possible to reliably obtain a radome with higher characteristics in both electromagnetic wave permeability and thermal insulation.

[0035] [Scope of the invention disclosed herein] The inventions disclosed herein include, in addition to the inventions and embodiments listed herein, those specified by modifying some of these to the extent applicable, or by adding other to these, or by deleting some of these to the extent that some effects are obtained and defining them as broader concepts. Furthermore, the inventions disclosed herein also include the modifications and additions listed below.

[0036] For example, the electromagnetic wave-permeable heat insulating material in the snow-melting radome of the present invention is appropriate within the scope of the present invention, and in addition to the foamed resin material 7 of the above embodiment, it may be, for example, cork material. Furthermore, the snow-melting radome of the present invention is suitable for use as a radome for an on-board radar device, and when the snow-melting radome of the present invention is used as a radome for an on-board radar device, it can be made into an appropriate type of vehicle mounting component, and is not limited to a bumper cover, but is also suitable as, for example, an emblem-shaped radome. Furthermore, the snow-melting radome of the present invention is also suitable for use as a radome other than an on-board radar device radome to protect an appropriate radar device. In addition, the method of wiring the heater wire 5 in the planar direction of the electromagnetic wave-permeable base 2 is appropriate, such as wiring in concentric circles in addition to meandering wiring.

[0037] [Experimental results on the power consumption reduction effect of the snow melting radome in the example] Next, experimental results regarding the power consumption reduction effect of the snow melting radome of the embodiment and the snow melting radome of the comparative example according to the present invention will be described. In this experiment, the snow melting radome 1 of the embodiment was defined as having a structure in which heater wires 5 were routed along a groove 31 formed in the first base material 3 of the above embodiment and another groove 41 in the second base material 4, the first base material 3 and the second base material 4 were bonded together, and an electromagnetic wave permeable heat insulating material of foamed resin 7 or cork material was laminated and bonded to the second base material 4. The comparative example was defined as a snow melting radome of a structure in which heater wires 5 were routed along a groove 31 formed in the first base material 3 of the above embodiment and another groove 41 in the second base material 4, the first base material 3 and the second base material 4 were bonded together, and an electromagnetic wave permeable heat insulating material of foamed resin 7 or cork material was not laminated and bonded to the second base material 4.

[0038] In each example and comparative example, a rectangular snow-melting area measuring 110 mm x 50 mm was set up, and the heater wires 5 were routed in a meandering pattern within the snow-melting area. The wire width of the heater wires 5 was 0.06 mm, and the pitch between the parallel-arranged heater wires 5 was 7.00 mm. Copper was used as the material for the heater wires 5.

[0039] In each example and comparative example, the first substrate 3 and the second substrate 4 were formed from ABS resin having a relative permittivity real part ε'r = 2.67 and tanδ = 0.005, respectively. The thickness of the first substrate 3 and the second substrate 4 were both 1.2 mm, and the total thickness of the laminated first substrate 3 and second substrate 4 was 2.4 mm.

[0040] Furthermore, the foamed resin material 7 corresponding to the electromagnetic wave permeable heat insulating material in Examples 1-1 to 1-5 and Examples 2-1 to 2-4 was formed from modified polyphenylene ether (m-PPE resin, manufactured by Asahi Kasei Corporation, product name: Sunforce BE). In Examples 1-1 to 1-5, the thickness of the foamed resin material 7 was 2 mm, and the foaming ratios of the foamed resin material 7 were 10 times, 8 times, 6 times, 4 times, and 2 times, respectively. In Examples 2-1 to 2-4, the foaming ratio of the foamed resin material 7 was 4 times, and the thickness of the foamed resin material 7 was 1 mm, 2 mm, 3 mm, and 4 mm, respectively. In addition, for the cork material corresponding to the electromagnetic wave permeable heat insulating material in Example 3, a cork material manufactured by JEJ Astage, with a sheet of medium grain, a real dielectric constant ε'r = 1.75, and tanδ = 0.029 was used, and its thickness was 2 mm.

[0041] Then, electromagnetic waves (frequency: 76.5 GHz, wavelength: 3.92 mm) were irradiated onto the radomes of each example and comparative example from the electromagnetic wave permeable insulation material or the second substrate 4 side using a radar device, and the electromagnetic wave transmittance was measured.

[0042] Furthermore, the temperature of the surface (front of the radome) of the first substrate 3 was evaluated under conditions where the ambient temperature was -5°C and a wind speed of 100 km / h struck the front of the radome of each example and comparative example. After a sufficient amount of time had elapsed under the aforementioned conditions and the surface temperature reached a steady state of 15°C, the power consumption of each example and comparative example was determined from the voltage applied to the heater wire 5 and the current value of the heater wire 5, and the power consumption reduction effect (%) compared to the comparative example without electromagnetic wave permeable insulation material was calculated.

[0043] Furthermore, the thermal conductivity (W / mk) of the foamed resin material 7 of Examples 1-1 to 1-5 and Examples 2-1 to 2-4, which correspond to electromagnetic wave permeable insulation materials, and the cork material of Example 3 were measured in accordance with JIS A1412, and 1m 2 The thermal resistance per unit area (K / W) was calculated using the following formula 3. In formula 3, R is the thermal resistance of the electromagnetic wave permeable insulation material, t is the thickness of the electromagnetic wave permeable insulation material, λ is the thermal conductivity of the electromagnetic wave permeable insulation material, and S is the area of ​​the electromagnetic wave permeable insulation material. However, for generality, S is set to 1 m in this case. 2 The results of these experiments are shown in Tables 1 and 2 below.

[0044] [Number]

[0045] [Table [1]]

[0046] [Table [2]]

[0047] From the experimental results of Table [1] and Table [2] above, it can be seen that both the domes of the examples and the comparative examples clear the electromagnetic wave transmittance of -1.0 dB required for, for example, a dome for an in-vehicle radar device. And in the snow-melting dome of each example having a laminated structure of the first base material 3, the second base material 4, and the electromagnetic wave-transparent heat insulating material, when a material having a thermal resistance of 0.020 K / W or more per 1 m is used for the electromagnetic wave-transparent heat insulating material, it can be seen that the power consumption required to obtain the same snow-melting effect can be reduced by 29% or more compared with the comparative example. 2 When the foaming ratio of the foamed resin material 7 is 2 times or more and the plate thickness in the lamination direction of the electromagnetic wave-transparent heat insulating material composed of the foamed resin material 7 or the cork material is 1 mm or more, it can be seen that the heat insulation performance can be surely improved and the power consumption reduction effect required to obtain the same snow-melting effect can be surely enhanced.

[0048] Also, when the foaming ratio of the foamed resin material 7 is 2 times or more and the plate thickness in the lamination direction of the electromagnetic wave-transparent heat insulating material composed of the foamed resin material 7 or the cork material is 1 mm or more, it can be seen that the heat insulation property can be surely improved and the power consumption reduction effect required to obtain the same snow-melting effect can be surely enhanced.

[0049] [Preferred Plate Thickness Range of Electromagnetic Wave-Transparent Heat Insulating Material in Snow Melting of the Present Invention] Next, a suitable plate thickness range for the foamed resin material corresponding to the electromagnetic wave permeable heat insulating material in the snow melting radome of the present invention will be described. Figure 3 is a graph showing experimental results of the relationship between the density of the foamed resin and the dielectric loss tangent, and the relationship between the density of the foamed resin and the real part of the complex relative permittivity of the foamed resin material. In this experiment, a foamed resin material of m-PPE resin was closely laminated on the back surface of an ABS resin plate with a thickness of 2.4 mm, corresponding to the plate thickness of the laminated state of the first base material and the second base material. Electromagnetic waves of 76.5 GHz were irradiated onto this laminate from the foamed resin material side in a perpendicular direction, and the value of the complex relative permittivity of the foamed resin material was obtained from the transmitted and reflected waves using the Nicholson-Ross method. In Figure 3, the black dots indicate the measured values ​​of the real part of the complex relative permittivity of the foamed resin material, and the white dots indicate the measured values ​​of the dielectric loss tangent of the foamed resin material.

[0050] The fitting function for the complex relative permittivity in Figure 3 is given by Equation 4 below. In Equation 4 below, εf is the complex relative permittivity of the foamed resin, ε'f is the real part of the complex relative permittivity of the foamed resin, ε”f is the imaginary part of the complex relative permittivity of the foamed resin, εp is the complex relative permittivity before foaming, and εg is the complex relative permittivity of the gas constituting the foamed resin. The dotted line at the top of Figure 3 is the fitting result of the real part of the complex relative permittivity calculated using Equation 4 from the experimental results. In this case, the complex relative permittivity of air, εg = 1 + i0, was substituted for εg in the calculation.

[0051]

number

[0052] Similarly, the imaginary part ε”f of the relative permittivity of the foamed resin material is calculated using Equation 4. Furthermore, by using Equation 5, the dielectric loss tangent tanδ in the foamed resin is calculated, and the fitting result shown by the dotted line at the bottom of Figure 3 is obtained.

[0053]

number

[0054] The refractive index n3 of the foamed resin material is given by equation 6 below, and the plate thickness d3 of the foamed resin material at which electromagnetic wave transmittance is minimized (electromagnetic wave transmission loss is minimized) is given by equation 7 below. In equation 7 below, λ0 is the wavelength of the irradiated electromagnetic wave, and N is a positive integer, with λ0 being approximately 3.92 mm for electromagnetic waves at 76.5 GHz.

[0055]

number

[0056]

number

[0057] Figure 4 shows the experimental results regarding the relationship between the thickness of the foamed resin material and the electromagnetic wave transmittance. In this experiment, a foamed m-PPE resin material was closely laminated on the back surface of an ABS resin sheet with a thickness of 2.4 mm, corresponding to the thickness of the laminated state of the first and second substrates. Electromagnetic waves at 76.5 GHz were irradiated perpendicularly from the foamed resin material side, and the electromagnetic wave transmittance of the foamed resin material in the laminate was measured to obtain the experimental results. Foamed resin materials with foaming ratios of 2x, 4x, 6x, 8x, and 10x were used, and the electromagnetic wave transmittance of laminates with foamed resin materials of each foaming ratio was measured. From Figure 4, it can be seen that, depending on the foaming ratio of the foamed resin material, the thickness of the foamed resin material that satisfies the conditions of Equation 6 above results in the minimum electromagnetic wave transmittance (minimum electromagnetic wave transmission loss).

[0058] Based on the above experimental results, in a snow-melting radome 1, which is positioned on the viewing side and consists of a first electromagnetic wave-transmitting substrate 3 made of solid synthetic resin, a second electromagnetic wave-transmitting substrate 4 made of solid synthetic resin, and a foamed resin material 7 equivalent to an electromagnetic wave-transmitting heat insulating material, it is preferable to set the plate thickness d3 of the foamed resin material to satisfy the condition (λ0×N) / 2n3-0.5(mm)≦d3≦(λ0×N) / 2n3+0.5(mm) (λ0: wavelength of electromagnetic waves from the radar device irradiated onto the snow-melting radome 1, n3: refractive index of the foamed resin material, N: positive integer). Furthermore, it is even more preferable to set the plate thickness d3 of this foamed resin material to satisfy the condition (λ0×N) / 2n3-0.25(mm)≦d3≦(λ0×N) / 2n3+0.25(mm). [Industrial applicability]

[0059] This invention can be used, for example, as a radome for a radar device such as a radome for an in-vehicle radar system. [Explanation of symbols]

[0060] 1…Snow melting radome 2…Base 3…First substrate 31…Recess 32…Positioning recess 4…Second substrate 41…Another recess 5…Heater wire 51…End 6…Wire harness connection 61…Connection terminal 62…Electrical cable 7…Foamed resin material R…Electromagnetic wave irradiation area

Claims

1. A first electromagnetic wave-transmitting substrate and a second electromagnetic wave-transmitting substrate are each formed from a solid synthetic resin. A heater wire is wired between the first substrate, which is positioned on the viewing side, and the second substrate, which is positioned on the rear side opposite to the viewing side of the first substrate, and is sealed by the first substrate and the second substrate. An electromagnetic wave permeable heat insulating material is laminated and fixed to the side of the second substrate opposite to the visible side. The electromagnetic wave permeable heat insulating material is a foamed resin material, A snow-melting radome characterized in that the electromagnetic wave-permeable insulating material has mutually matched refractive indices defined based on the complex dielectric constant for both the first substrate and the second substrate.

2. 1 m of the aforementioned electromagnetic wave permeable insulation material ２ The snow-melting radome according to claim 1, characterized in that the thermal resistance per unit area is 0.0055 K / W or more.

3. 1 m of the aforementioned electromagnetic wave permeable insulation material ２ The snow-melting radome according to claim 2, characterized in that the thermal resistance per unit area is 0.020 K / W or more.

4. A snow-melting radome according to any one of claims 1 to 3, characterized in that the foaming ratio of the foamed resin material is 2 times or more, and the thickness of the foamed resin material in the lamination direction in the electromagnetic wave irradiation area is 1 mm or more.

5. The thickness d of the foamed resin material in the lamination direction ３ The snow-melting radome according to claim 1, characterized in that (mm) satisfies the following formula (1). (λ ０ ×N) / 2n ３ -0.5(mm)≦d ３ ≦(λ ０ ×N) / 2n ３ +0.5(mm)・・・(1) 〔In formula (1), λ ０ is the wavelength of the electromagnetic wave of the radar device irradiated on the snow melting dome, n ３ is the refractive index of the foamed resin material, and N represents a positive integer〕

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