Shielding member and radar device

Abstract

The invention relates to a shielding member and a radar device. An increase in transmission loss when a radar device having a shielding member is used is prevented. A shielding member for use in a radar device, the shielding member including: a flat plate-shaped first portion formed of a foamed resin; a second portion disposed so as to surround the first portion so as to be in contact with a side surface of the first portion, the second portion comprising a non-foamed resin; and a third portion that is disposed so as to be in contact with each of the one surface and the other surface of the first portion, the third portion comprising a non-foamed resin.

Description

Technical Field The present disclosure relates to a shielding member and a radar device. Background Art Japanese Unexamined Patent Application Publication No. 2021-099313 (Patent Document 1) discloses a vehicle lamp including: a lamp unit; a millimeter-wave radar unit having an antenna; and a shielding member covering at least a part of the front surface of the millimeter-wave radar unit provided with the antenna, the shielding member being made of a foamed resin. By using a foamed resin for the shielding member, it is possible to reduce the transmission loss of millimeter waves transmitted and received by the millimeter-wave radar unit. However, when a foamed resin is used for the shielding member, moisture in the air or the like enters the bubbles of the foamed resin during use, resulting in an increase in transmission loss and a possible reduction in the performance of the radar device. Prior Art Documents Patent Documents Patent Document 1: Japanese Unexamined Patent Application Publication No. 2021-099313 Summary of the Invention Problems to be Solved by the Invention One of the objects of the specific embodiment of the present disclosure is to prevent an increase in transmission loss when using a radar device having a shielding member. Means for Solving the Problems

[0001] A shielding member according to one embodiment of the present disclosure is a shielding member for a radar device. The shielding member includes: a flat first portion made of a foamed resin; a second portion configured to surround the first portion in contact with a side surface of the first portion, the second portion being made of a non-foamed resin; and a third portion configured to be in contact with one surface and the other surface of the first portion, the third portion being made of a non-foamed resin.

[0002] A radar device according to one embodiment of the present disclosure includes: the shielding member described in 1 above; and a radar wave transmitter disposed with a gap between the shielding member. According to the above structure, it is possible to prevent an increase in transmission loss when using a radar device having a shielding member. Brief Description of the Drawings Figure 1 is a diagram schematically showing the internal structure of a vehicle lamp according to an embodiment. Figure 2 (A) thereof is a schematic cross-sectional view for explaining the arrangement of the millimeter-wave radar unit and the shielding member.Figure 2 (B) is a schematic top view of the millimeter-wave radar unit and the shielding member as viewed from the side of the shielding member. Figure 3 It is a partial enlarged view of the shielding member. Figure 4 It is a diagram showing a calculation example of the attenuation amount based on the incident angle of millimeter waves to the shielding member. Figure 5 It is a diagram showing the measurement result of the transmission loss of the shielding member of the embodiment. Description of Reference Numerals 10: Vehicle lamp, 11: Base, 12: Transparent cover, 14: Headlamp unit, 15: Millimeter-wave radar unit, 16: Light-emitting unit, 18: Shielding member, 18a: First part, 18b: Second part, 18c: Third part, 18d: Boundary Detailed Description of the Embodiment Figure 1 It is a diagram schematically showing the internal structure of a vehicle lamp according to an embodiment. The vehicle lamp 10 is mounted on a vehicle and is used for irradiating light to the periphery of the vehicle. For example, it is a headlamp. Figure 1 It schematically shows a cross section of a horizontal plane (or a plane parallel to the road surface) in the case of the vehicle lamp 10 (left headlamp) mounted on the left front of the vehicle as viewed from the upper surface. The vehicle lamp 10 is configured to include a base 11, a transparent cover 12 held by the base 11, a headlamp unit 14, a millimeter-wave radar unit (radar wave transmitter) 15, a light-emitting unit 16, a shielding member 18, and an extension 19. The shielding member 18 is a kind of extension member for making it difficult to visually recognize the millimeter-wave radar unit 15 from the outside. A frame (housing) is formed by the base 11 and the transparent cover 12, and the headlamp unit 14, the millimeter-wave radar unit 15, the light-emitting unit 16, the shielding member 18, and the extension 19 are provided in the frame. In addition, in the present embodiment, the radar device is configured to include the millimeter-wave radar unit 15 and the shielding member 18. The headlamp unit 14 is configured to have a light source such as an LED (Light Emitting Diode) and a lens or a reflector for distributing and irradiating the light from the light source. The headlamp unit 14 irradiates the irradiation light LB of low beam (low beam) and high beam (high beam) in the forward direction of the vehicle. The millimeter-wave radar unit 15 has a transceiver surface on its front surface, and a transceiver antenna for millimeter waves (radar waves) is provided on the transceiver surface. In this specification, the transceiver surface of the millimeter-wave radar unit 15 (the front surface of the millimeter-wave radar unit 15) is also referred to as the antenna surface. Specifically, the millimeter-wave radar unit 15 has a transmitting antenna and a receiving antenna on its transceiver surface (electromagnetic wave radiation surface). The millimeter-wave radar unit 15 radiates millimeter waves (radar waves) as electromagnetic waves from the transmitting antenna and receives the reflected waves reflected by the object through the receiving antenna. By performing signal processing using the received reflected waves, the distance, angle, and speed to the object can be detected. In the millimeter-wave radar unit 15, for example, millimeter waves in the 76 GHz - 81 GHz band, especially millimeter waves in the 79 GHz band, are used, but it is not limited to this band. In addition, the antenna can also have both transmitting and receiving functions. The light-emitting unit 16 has a light source 16a and a light guide 16b, and the light guide 16b is composed of at least one light guide member that guides the light from the light source 16a. The light-emitting unit 16 functions as, for example, DRL (Daytime Running Lights) or a turn signal. The light source 16a has, for example, an LED, an incandescent lamp, etc., and supplies its light to the light guide 16b. The millimeter-wave radar unit 15 is configured such that the normal direction of the antenna surface is inclined in the outward direction of the vehicle (i.e., the left direction in the case of the left headlight) relative to the optical axis of the headlight unit 14. A shielding member 18 is arranged at a gap from the antenna surface of the millimeter-wave radar unit 15. In addition, at least one extension 19 is provided in the lamp housing. The extension 19 is an exterior member provided for reflecting light, guiding light, or making it difficult to visually recognize the internal structure from the outside. In addition, in Figure 1 , the shielding member 18 and the millimeter-wave radar unit 15 are provided in the housing together. However, it can also be a radar device in which the millimeter-wave radar unit 15 is provided in a different housing composed of a housing different from the base 11 and the shielding member 18. In this case, the shielding member 18 forms the exterior of the vehicle in the same way as the Figure 1 transparent cover 12. Figure 2 The (A) of Figure 2 is a schematic cross-sectional view for explaining the arrangement of the millimeter-wave radar unit 15 and the shielding member 18. In addition, Figure 2 The cross-sectional view of the (A) of Figure 2 corresponds to the cross-section in the direction of the A - A line shown in the (B) of As shown in the (A) of Figure 2 and the (A) of Figure 2As shown in (B) of , the shielding member 18 is configured, for example, as a flat plate with a substantially constant thickness, and is arranged such that one of its surfaces faces the antenna surface of the millimeter-wave radar unit 15. The shielding member 18 is preferably arranged perpendicular to the central axis or reference axis of the radiation pattern of the antenna. In addition, the radiation pattern of the antenna referred to here means the angular distribution of the electromagnetic wave intensity transmitted from the antenna surface of the millimeter-wave radar unit 15, and generally has the following distribution: the normal direction of the antenna surface has the maximum intensity, and the electromagnetic wave intensity decreases as the angle with the normal direction increases. The angle at which the intensity becomes -3 dB from the maximum intensity is called the half-value width of the antenna pattern, and is, for example, 80°. The shielding member 18 includes a flat plate-like first portion 18a made of a foamed resin and a second portion 18b made of a non-foamed resin. The first portion 18a is arranged at the center of the shielding member 18 when viewed from above. The second portion 18b is provided in contact with the side surface of the first portion 18a and is arranged in a ring shape surrounding the first portion 18a when viewed from above. In addition, as Figure 3 shown in the partial enlarged view of , third portions 18c are provided on both the one surface and the other surface of the first portion 18a so as to be in contact with the one surface and the other surface, respectively. These third portions 18c are made of a non-foamed resin in the same manner as the second portion 18b. In the present embodiment, the second portion 18b and each of the third portions 18c are integrally formed. As a result, the first portion 18a is in a state where it is entirely sealed with a non-foamed resin around it. The shielding member 18 can be set to a thickness of about 2.9 mm, for example. In addition, each of the third portions 18c can have a thickness of 100 μm or less (a thickness smaller than that of the first portion 18a). In the present embodiment, the total thickness of the first portion 18b and each of the third portions 18c is 2.9 mm, and the thickness of the second portion 18b is also 2.9 mm. That is, the shielding member 18 has a substantially uniform thickness as a whole. In addition, in the present embodiment, the second portion 18b and the third portions 18c are made of a non-foamed resin using the same material. And the first portion 18a is made of a foamed resin obtained by mixing air bubbles into the same material as the constituent materials of the second portion 18b and the third portions 18c. Here, the "foamed resin" and "non-foamed resin" in this embodiment will be described. The "foamed resin" refers to a resin formed by mixing a gas (foaming gas) generated by a chemical reaction (chemical reaction) or a physical change with a polymer or oligomer as a raw material. Specifically, for example, it refers to a resin in which bubbles are mixed into a transparent resin such as polycarbonate, acrylic, polyimide, or epoxy resin by encapsulating carbon dioxide or the like. The foamed resin can reduce the dielectric constant by encapsulating gas in the resin, and thus can greatly reduce the influence on electromagnetic waves. The bubble ratio (the ratio of bubbles to the total volume) of the foamed resin is preferably 50% or more. In addition, the "non-foamed resin" refers to a resin in which no bubbles are provided without performing the above-described active foaming molding. In addition, in this embodiment, a resin in which a small amount of unwanted bubbles are mixed during manufacturing is not a "foamed resin" but a "non-foamed resin". As an example, the dielectric constant and the attenuation amount at an incident angle of 0° were measured for the shielding member of the example having the structure according to this embodiment and the shielding member of the comparative example made of a foamed resin. In the example, as described above, it was assumed that the combined thickness of the first part 18a and each third part 18c was 2.9 mm, and each third part 18c was 100 μm to manufacture the shielding member. In the comparative example, the foamed resin was formed into a flat plate with a thickness of 2.9 mm to manufacture the shielding member. As the resin, polycarbonate was used in both the example and the comparative example. In the comparative example, the initial dielectric constant was 1.658 and the attenuation amount was 0.035 dB, but after the water wetting test, the dielectric constant changed to 1.631 and the attenuation amount changed to 0.65 dB. In the example, there was no change before and after the water wetting test, the dielectric constant was 1.83, and the attenuation amount was 0.11 dB. Refer again to Figure 2 (A) of, and the arrangement of the millimeter-wave radar unit and the shielding member will be described in detail. As shown in Figure 2 (A) of, the shielding member 18 has a boundary 18d between the first part 18a and the second part 18b. This boundary 18d is as shown in Figure 2As shown in (B), it is circular (rectangular). In the present embodiment, the boundary 18d is provided at least in the A-A cross section at a position where the incident angle of the millimeter wave radiated from the millimeter wave radar unit 15 to the shielding member 18 is 60°. The position where the incident angle is 60° means, for example, when the entire surface of the millimeter wave radar unit 15 facing the shielding member 18 is the antenna surface, as shown in the figure, the angle formed by the line connecting the outer edge portion of the antenna surface and the boundary 18d and the normal line of the surface of the shielding member 18 facing the antenna surface is 60°. That is, in the present embodiment, the first portion 18a is arranged corresponding to the range where the incident angle of the millimeter wave is 0° or more and 60° or less (a relatively small range), and the second portion 18b is arranged corresponding to the range where the incident angle of the millimeter wave is greater than 60° (a relatively large incident angle range). In addition, considering errors during manufacturing, etc., it is preferable to set the boundary 18d within a range of ±5° with respect to the preferred value of the incident angle (60° in the above example). Figure 4 It is a diagram showing a calculation example of the attenuation amount based on the incident angle of the millimeter wave to the shielding member. This calculation example is calculated using the Fresnel formula under the conditions of a frequency of 76.5 GHz, a horizontally polarized wave, a dielectric constant of 2.7, and a dielectric loss tangent of 0.01. As shown in the calculation example, in the case of a plate thickness of 2.4 mm with the least attenuation amount at a vertical incidence with an incident angle of 0°, the attenuation amount becomes a relatively large value exceeding 4 dB at an incident angle of 80°. If the plate thickness is set to 2.9 mm, the attenuation amount under vertical incidence is -1.4 dB, which becomes a relatively large attenuation amount. Here, it is known that if the dielectric constant of the shielding member is reduced by using a foamed resin, the influence on the attenuation amount becomes smaller even for a relatively large incident angle. Therefore, for the shielding member, the portion where the incident angle exceeds 60° (the above-mentioned second portion 18b) is made of a non-foamed resin with a plate thickness of 2.9 mm, and the portion where the incident angle is within 60° (the above-mentioned first portion 18a) is made of a foamed resin, thereby reducing the overall attenuation amount of the measurement range (field of view: FOV) of the shielding member 18. In addition, in order to make the overall thickness of the shielding member 18 uniformly 2.9 mm, it is necessary to determine the dielectric constant of the foamed resin in such a way that the attenuation amount is the least when the plate thickness of the first portion 18a, which is the portion of the foamed resin, is 2.9 mm. The dielectric constant of the foamed resin is represented by the following relational expression. Therefore, by using this relational expression, the dielectric constant can be determined in such a way that the transmission loss is minimized. Dielectric constant of the foamed resin = (1 / (plate thickness / wavelength of the millimeter wave radar)) 2 For example, in the case where the plate thickness is 2.9 mm and the wavelength of the millimeter-wave radar is 3.92 mm (equivalent to 76.5 GHz), if the foaming ratio is set such that the dielectric constant of the foamed resin portion becomes 1.83, the optimal foamed resin can be obtained with a plate thickness of 2.9 mm. In addition, third portions 18c serving as surface layers are formed on both the front surface and the back surface of the first portion 18a made of the foamed resin. Therefore, pores such as those for moisture absorption are not formed on the front surface and the back surface of the first portion 18a. Moreover, since the second portion 18b is formed around (on the side surface of) the first portion 18a, moisture absorption from the side surface of the first portion 18a can also be suppressed. In addition, the formation of the second portion 18b and the third portion 18c on the front surface, the back surface, and the periphery of the first portion 18a can be achieved, for example, by insert molding. Figure 5 This is a graph showing the measurement results of the transmission loss of the shielding member according to the embodiment. Here, a shielding member of an embodiment is used in which the total plate thickness of the first portion 18a and each third portion 18c is 2.9 mm, and the plate thickness of the second portion 18b is also 2.9 mm. In the shielding member of this embodiment, the dielectric constant of the portion combining the first portion 18a and each third portion 18c is 1.83, the tangent of the dielectric loss angle is 0.002, the dielectric constant of the second portion 18c is 2.7, and the tangent of the dielectric loss angle is 0.01. As shown by the characteristic line a in the figure, regarding the shielding member of the embodiment, when millimeter waves are irradiated from the millimeter-wave radar unit 15 to the first portion 18a (including the third portion 18), in the range where the incident angle is 0 or more and 65° or less, the attenuation amount is lower than that of the second portion 18b shown by the characteristic line b. On the other hand, in the range where the incident angle exceeds 65°, the attenuation amount of the second portion 18b is lower than that of the first portion 18a. Based on the results of the attenuation amount caused by such an incident angle, in the present embodiment, the boundary 18d between the first portion 18a and the second portion 18b can be determined at the position where the incident angle is 65°. Considering the manufacturing error as described above, the boundary 18d can be determined within the range of 65° ± 5°. According to the above-described embodiments and examples, since countermeasures against moisture absorption in the case of using a foamed resin are adopted, in various devices such as a radar device and a vehicle lamp using the radar device, an increase in transmission loss can be prevented as a whole for the shielding member. In addition, since the entire shielding member has a simple flat plate-like structure, an improvement in the strength of the shielding member can also be achieved. In addition, the present disclosure is not limited to the content of the above-described embodiments, and various modifications can be made within the scope of the gist of the present disclosure. For example, the specific numerical values and other conditions listed in the embodiments and the like are examples for helping to understand the present disclosure, and do not limit the application scope of the present disclosure to these conditions. Specifically, for example, the method for determining the position of the above-mentioned boundary 18d (corresponding to the incident angle of 60° as an example in the embodiment) is an example, and the preferred value can vary according to various conditions such as the material and thickness of the foamed resin and non-foamed resin used to form the shielding member 18. That is, Figure 5 similar to the example shown, find the range of the incident angle at which the transmission loss in the foamed resin is smaller than the transmission loss in the non-foamed resin, and determine the boundary 18d between the first portion 18a and the second portion 18b based on this. In addition, in the above-described embodiment, a headlamp is listed as an example of a vehicle lamp, but it is not limited thereto, and the vehicle lamp may also be a taillight, a backlight, or the like. In addition, as an example of the place where the radar device is provided, the inside of the frame of the vehicle lamp is cited, but it is not limited thereto, and the radar device can be provided at any place.

Claims

1. A shielding component, which is a shielding component for a radar device, wherein: The shielding component comprises: A flat plate-shaped first portion, which is made of foamed resin; a second portion configured to surround the first portion in a manner in contact with a side surface of the first portion, the second portion being made of a non-foamed resin; as well as The third portion is arranged to be in contact with one surface and the other surface of the first portion, respectively, and the third portion is made of a non-foamed resin.

2. The shielding member according to claim 1, wherein: The total thickness of the first portion and the third portion is substantially the same as the thickness of the second portion.

3. The shielding member according to claim 1, wherein: The second portion and the third portion are integrally formed.

4. The shielding member according to claim 1, wherein: The thickness of the third portion is smaller than the thickness of the first portion.

5. The shielding member according to claim 1, wherein: The second portion and the third portion are made of the same material.

6. The shielding member according to claim 1, wherein: The first region is formed of a foamed resin in which air bubbles are mixed into the same material as that of the second region and the third region.

7. A radar device, comprising: The shielding member according to claim 1; and A radar wave transmitter is arranged with a gap provided between the radar wave transmitter and the shielding member.

8. The radar device according to claim 7, wherein: The shielding member is disposed at a first portion within a range where an incident angle of the radar wave is relatively small, and is disposed at a second portion within a range where the incident angle is relatively large.

9. The radar device according to claim 8, wherein: The boundary between the first portion and the second portion is determined based on the range of the incident angle in which the transmission loss in the foamed resin is smaller than the transmission loss in the non-foamed resin.

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