VEHICLE ARRANGEMENT WITH A RADAR SENSOR AND A LOGO-FORMING LAYER ARRANGEMENT

Description

[0001] The present invention relates to a vehicle assembly. It finds a particular but non-limiting application in motor vehicles.

[0002] A vehicle assembly comprises, in a manner known to those skilled in the art: a radar sensor configured to emit radar waves, and an arrangement of layers arranged opposite said radar sensor.

[0003] The layered arrangement forms an illuminated logo. The radar sensor is thus positioned behind the illuminated logo and meets the needs of detecting an object in the vehicle's external environment.

[0004] A disadvantage of this state of the art is that when a radar wave is emitted by the radar sensor, it travels to the layer arrangement and is reflected on the layer arrangement. This generates two reflected waves, one of which has been reflected on the outer face of the layer arrangement and the other inside the layer arrangement. The two reflected waves are so-called first-order reflected waves which return to the radar sensor. This hinders the propagation of the radar waves. This reduces the signal-to-noise ratio of said radar sensor and thus causes disturbances for the detection by the radar sensor. The radar sensor loses detection range. Consequently, this can lead to a detection error or no detection of an object while the latter is present in the environment outside the vehicle. Documents DE 10 2011 115829A1, EP 3 644 087A1 and US 2018 / 351274A1 describe examples of the state of the art.

[0005] In this context, the present invention aims to provide a vehicle assembly which makes it possible to solve the mentioned drawback.

[0006] For this purpose, the invention proposes a vehicle assembly for a vehicle, said vehicle assembly comprising: one or more light sources a radar sensor configured to emit radar waves over a range of wavelengths, and an arrangement of layers arranged opposite said radar sensor, comprising a first subset of layers configured to perform an optical function, each layer having a refractive index and a thickness, and a second subset of layers configured to provide protection for said first set of layers, each layer having a refractive index and a thickness, characterized in that the total thickness of the second subset of layers is dimensioned such that the total thickness of the arrangement of layers is equal to m times a wavelength of said range divided by twice the equivalent refractive index of the first subset of layers and the second subset of layers, times the cosine of a refracted angle corresponding to the angle of incidence of the radar waves, with m being an integer.

[0007] According to non-limiting embodiments, said vehicle assembly may further comprise one or more additional characteristics taken alone or in all technically possible combinations, among the following.

[0008] According to a non-limiting embodiment, said radar sensor is a millimeter wave or hyperfrequency or microwave radar sensor.

[0009] According to a non-limiting embodiment, said radar waves are emitted on a frequency band between 100 MHz and 5 GHz.

[0010] According to a non-limiting embodiment, if the angle of incidence is equal to zero, then the total thickness of the second subset of layers is dimensioned such that the total thickness of the arrangement of layers is equal to said wavelength divided by twice the equivalent refractive index of the first subset of layers and the second subset of layers.

[0011] According to a non-limiting embodiment, the total thickness is defined with an angle of incidence equal to arctan(d1 / (2e4)), with e4 the distance between said radar sensor and said arrangement of layers and d1 the distance between a transmitting antenna and receiving antennas of said radar sensor.

[0012] According to a non-limiting embodiment, the second subset of layers comprises an output layer and a protective layer. The protective layer is an anti-ultraviolet and / or anti-scratch layer.

[0013] According to a non-limiting embodiment, said output layer has a refractive index which has a difference with an equivalent refractive index of the first subset of layers of less than 0.1.

[0014] According to a non-limiting embodiment, said output layer has a refractive index which has a difference with an equivalent refractive index of the first subset of layers of less than 0.05.

[0015] According to a non-limiting embodiment, each layer of the first subset has a refractive index which has a difference with the refractive index of an adjacent layer of less than 0.1.

[0016] According to a non-limiting embodiment, each layer of the first subset has a refractive index which has a difference with the refractive index of an adjacent layer of less than 0.05.

[0017] According to a non-limiting embodiment, the first subset of layers comprises: a film layer, a diffusing layer, a reflective layer, and an opaque layer.

[0018] According to a non-limiting embodiment, the arrangement of layers forms a non-illuminated logo.

[0019] According to a non-limiting embodiment, the arrangement of layers forms an illuminated logo.

[0020] According to a non-limiting embodiment, the first subset of layers further comprises an optical layer.

[0021] According to a non-limiting embodiment, the first subset of layers further comprises: another opaque layer, another reflective layer.

[0022] According to a non-limiting embodiment, the first subset of layers further comprises a protective layer.

[0023] There is further provided an arrangement of layers arranged opposite a radar sensor, said radar sensor being configured to emit radar waves over a range of wavelengths, said arrangement of layers comprising a first subset of layers configured to perform an optical function, each layer having a refractive index and a thickness, and a second subset of layers configured to perform protection for the first set of layers, each layer having a refractive index and a thickness, - characterized in that the total thickness of the second subset of layers is dimensioned such that the total thickness of the arrangement of layers is equal to m times a wavelength of said range divided by twice the equivalent refractive index of the first subset of layers and the second subset of layers, times the cosine of a refracted angle corresponding to the angle of incidence of the radar waves, with m being an integer.

[0024] The invention and its various applications will be better understood by reading the following description and examining the accompanying figures: [ Fig. 1 ] is a schematic view of a vehicle assembly, said vehicle assembly comprising a radar sensor and a layer arrangement, according to a non-limiting embodiment of the invention, [ Fig. 2 ] is a schematic view of a radar wave emitted by the radar sensor of the vehicle assembly of the figure 1 which is partially reflected in the layer arrangement of the vehicle assembly of the figure 1 , according to a non-limiting embodiment, [ Fig. 3 ] is a schematic view of the layers of the vehicle assembly layer arrangement of the figure 1 , said arrangement of layers comprising a first subset of layers and a second subset of layers, according to a non-limiting embodiment.

[0025] Identical elements, by structure or function, appearing in different figures retain, unless otherwise specified, the same references.

[0026] The vehicle assembly 1 of a vehicle 2 according to the invention is described with reference to figures 1 à 3 . The vehicle assembly 1 is otherwise called vehicle system 1. In a non-limiting embodiment, the vehicle 2 is a motor vehicle. By motor vehicle is meant any type of motorized vehicle. This embodiment is taken as a non-limiting example in the remainder of the description. In the remainder of the description, the vehicle 2 is thus otherwise called motor vehicle 2. In a non-limiting embodiment, the vehicle assembly 1 is arranged in the grille of the motor vehicle 2. In another non-limiting embodiment, the vehicle assembly 1 can be integrated into a body part located at the rear of the motor vehicle 2.

[0027] As illustrated on the figure 1 , the vehicle assembly 1, otherwise called vehicle arrangement 1, comprises: a radar sensor 10 configured to emit radar waves R1, and an arrangement of layers 11 arranged opposite said radar sensor 10.

[0028] These elements are described below.

[0029] The radar sensor 10 is described below. As illustrated in the figure 1 , the radar sensor 10 is arranged opposite the layer arrangement 11. In a non-limiting embodiment, the radar sensor 10 is a millimeter wave radar sensor (between 24GHz and 300GHz) or hyperfrequency (between 300MHz and 81GHz) or microwave (between 1GHz and 300GHz). In a non-limiting variant embodiment, the radar sensor 10 operates at a radar frequency between 76GHz and 81GHz. The radar waves R1 are emitted over a range Δ1 of wavelengths λ. In a non-limiting embodiment, the radar waves R1 are emitted over a frequency band between 100MHz and 5GHz. Thus, in a non-limiting example, if the sensor operates at a radar frequency of 77 GHz, i.e. a wavelength λ of 3.95 mm, with a frequency band of 1 GHz, the radar sensor 10 will operate on a frequency band of 76.5 GHz to 77.5 GHz. The radar waves R1 will thus be emitted over the frequency range 76.5 GHz to 77.5GHz, i.e. a range Δ1 of wavelengths λ of 3.87mm to 3.92mm. Thus, in another non-limiting example, if the radar sensor 10 operates at a radar frequency of 78.5GHz with a frequency band of 5GHz, the radar sensor 10 will operate on a frequency band of 76GHZ to 81GHz. The radar waves R1 will thus be emitted on the frequency range 76GHZ to 81GHz, i.e. a range Δ1 of wavelengths λ of 3.701mm to 3.945mm.

[0030] As illustrated on the figure 2 , the emitted radar waves R1 arrive with an angle of incidence θ on the arrangement of layers 11. In a non-limiting embodiment, the angle of incidence θ is between 0° and +-30°. Thus, the radar sensor 10 comprises a field of view FOV which thus varies between -30° and +30°. °. The center of the field of view FOV is an angle of 0° relative to the longitudinal axis of the vehicle, otherwise called the vehicle axis. In another non-limiting embodiment, the field of view FOV varies between -90° and +45°. The center of the field of view FOV is an angle of -45° relative to the vehicle axis and the angle of incidence θ of the radar waves R1 on the arrangement of layers 11 remains close to 0° (the vehicle assembly 1 then being positioned at approximately 45° from the vehicle axis).

[0031] The radar sensor 10 is configured to scan the external environment of the motor vehicle 2, by emitting radar waves R1. As illustrated in the figure 1 , the radar sensor 10 thus comprises: at least one transmitting antenna 100 configured to transmit radar waves R1, otherwise called primary radar waves R1, at least two receiving antennas 101 configured to receive radar waves R2, otherwise called secondary radar waves R2 or return radar waves R2.

[0032] The radar sensor 10 further comprises at least one transmitter 103 configured to generate the primary radar waves R1 and at least one receiver 104 configured to process the secondary radar waves R2 received in return. In a non-limiting embodiment, a single electronic component can be used for both the transmission and reception functions. There will thus be one or more transmitters / receivers called "transceivers" in English language. Said transmitter 103 generates primary radar waves R1 which are subsequently emitted by the transmitting antenna 100, which when they encounter an object 3 (here a pedestrian in the non-limiting example illustrated) in the external environment of the motor vehicle 2 are reflected on said object 3. The radar waves thus reflected are waves transmitted in return to the radar sensor 10. These are the secondary radar waves R2 received by the receiving antennas 101.These are radar waves retransmitted towards the radar sensor 10. In a non-limiting embodiment, the primary radar waves R1 and the secondary radar waves R2 are radio frequency waves. In a non-limiting embodiment, the radar sensor 10 comprises a plurality of transmitters 103 and a plurality of receivers 104.

[0033] The transmitting antenna 100, otherwise called antenna 100, is configured to transmit the primary radar waves R1 generated by the transmitter 103. The receiving antennas 101, otherwise called antennas 101, are configured to receive the secondary radar waves R2 and communicate them to the receiver 104 which subsequently processes them. There is a phase shift between the secondary radar waves R2 received by the receiving antennas 101 which makes it possible to deduce therefrom the angular position of the object 3 relative to the motor vehicle 2, object 3 which is located in the external environment of the motor vehicle 2. In non-limiting embodiments, the antennas 100, 101 are patch antennas or slot antennas.

[0034] In a non-limiting embodiment, the antennas 100, 101, the transmitter 103 and the receiver 104 are arranged on a printed circuit board 105. In a non-limiting embodiment, the printed circuit board is a rigid printed circuit board otherwise called PCBA (“Printed Circuit Board Assembly” in English language or a flexible printed circuit board, otherwise called “Flexboard” in English language.

[0035] The radar sensor 10 further comprises an electronic control unit 106 configured to control the transmitter 103 and the receiver 104. Since a radar sensor is known to those skilled in the art, it is not described in further detail here.

[0036] The layer arrangement 11 is described below. As illustrated in the figure 1 or the figure 3 , it includes: a first subset S1 of layers 110 configured to perform an optical function, and a second subset S2 of layers 112 configured to perform protection for said first set S1 of layers 110.

[0037] It should be noted that the figure 1 being a schematic view, only two layers 110 have been illustrated on the figure 1 . In the remainder of the description, the first subset S1 of layers 110 is otherwise called first subset S1, and the second subset S2 of layers 112 is otherwise called second subset S2. In non-limiting embodiments, the arrangement of layers 11 forms an illuminated logo or a non-illuminated logo. In the case of an illuminated logo, the vehicle assembly 1 comprises one or more light sources 12. The non-limiting embodiment of an illuminated logo is taken as an example in the remainder of the description.

[0038] Indeed, as illustrated on the figure 3 , in a non-limiting embodiment, the logo is illuminated by two light sources 12. In the non-limiting example illustrated, the light sources 12 are arranged on the sides of the first subset S1 of layers 110. A total reflection optical device 12' makes it possible to inject the light emitted by the light sources 12 into a layer 110c described later. In a non-limiting embodiment, the light sources 12 are semiconductor light sources. In a non-limiting embodiment, the semiconductor light sources are part of a light-emitting diode. By light-emitting diode, we mean any type of light-emitting diode, whether in non-limiting examples LEDs ("Light Emitting Diodes"), OLEDs ("organic LEDs"), AMOLEDs (Active-Matrix-Organic LEDs), or FOLEDs (Flexible OLEDs).In another non-limiting embodiment, the light sources 12 is a bulb with a filament.

[0039] As illustrated on the figure 1 , the first subset S1 of layers 110 is arranged facing the radar sensor 10, while the second subset S2 of layers 112 is adjacent to the first subset S1 of layers 110 and is arranged facing the exterior of the motor vehicle 2.

[0040] As illustrated on the figure 3 , each layer 110 of the first subset S1 has a refractive index n10 and a thickness e10. The first subset S1 comprises a total thickness e1 composed of all the thicknesses e10. Each layer 112 of the second subset S2 has a refractive index n20 and a thickness e20. The second subset S2 comprises a total thickness e2 composed of all the thicknesses e20. The layer arrangement 11 thus comprises a total thickness e0=e1+e2.

[0041] In a non-limiting embodiment, the first subset S1 of layers 110 comprises an optical layer 110c. The optical layer 110c is located opposite the radar sensor 10. The optical layer 110c makes it possible to transmit the light rays from the light sources 12. The optical layer 110c is a layer transparent to both radar waves R1, R2 and visible light. In non-limiting embodiments, the optical layer 110c may be a light guide or a lens with prisms.

[0042] As illustrated on the figure 3 , in a non-limiting embodiment, the first subset S1 of layers 110 comprises the following successive layers 110: 110c optical layer, 110d film layer, 110e diffusing layer, 110f reflective layer, 110g opaque layer.

[0043] All layers 110 except the reflective layer 110f are dielectric layers, which allows them to be transparent to radar waves R1, R2. The reflective layer 110f is more absorbent, but very thin, which allows radar waves R1 to pass through it as well. In a non-limiting embodiment, the reflective layer 110f is made of indium. In non-limiting embodiments, a dielectric layer is formed of a plastic, glass, or ceramic material. In a non-limiting example, the plastic is polycarbonate (PC). It is recalled that a dielectric material is non-conductive and therefore allows radar waves R1 to pass through, unlike a conductive material.

[0044] In this non-limiting embodiment, the optical layer 110c serves as a support for the film layer 110d. The film layer 110d is disposed between the optical layer 110c and the reflective layer 110f. The film layer 110d is in a non-limiting example made of PC-IML (polycarbonate In Mold Labeling).

[0045] The diffusing layer 110e is arranged between the film layer 110d and the opaque layer 110g. The diffusing layer 110e makes it possible to create a secondary source located at the level of said diffusing layer 110e. This thus makes it possible to perceive the design of the illuminated logo at the location of said diffusing layer 110e. In a non-limiting embodiment, the diffusing layer 110e is arranged opposite the opening 111 made in the opaque layer 110g. The opening 111 makes it possible to produce the design of the logo.

[0046] The opaque layer 110g is arranged opposite the second set S2 of layers 112. The opaque layer 110g makes it possible to mask and illuminate a specific area. It makes it possible to create a pattern for the illuminated logo.

[0047] The 110f reflective layer allows the logo to appear metallic in visible light when viewed from the outside. The 110f reflective layer can extend under the entire 110g opaque layer.

[0048] As illustrated on the figure 3 , in a non-limiting embodiment, the first subset S1 of layers 110 further comprises: another opaque layer 110a, another reflective layer 110b.

[0049] This other opaque layer 110a when it exists is arranged opposite the radar sensor 10 and is adjacent to this other reflective layer 110b. It prevents light leaks behind the illuminated logo which would be seen from the outside of the motor vehicle 2. It absorbs the light from the light sources 12.

[0050] This other reflective layer 110b when it exists is arranged between the opaque layer 110a and the optical layer 110c. This other reflective layer 110b is in a non-limiting embodiment white paint. It allows the light rays emitted by the light sources 12 to be reflected towards the center of the arrangement of layers 11.

[0051] As illustrated on the figure 3 , in a non-limiting embodiment, the first subset S1 of layers 110 further comprises a protective layer 110h to prevent oxidation of the other layers 110, in particular the reflective layer 110f. This protective layer 110h is arranged between the opaque layer 110g and the second set S2 of layers 112.

[0052] In a non-limiting embodiment, the second subset S2 of layers 112 comprises an output layer 112a which forms an output glass of the illuminated logo, and a protective layer 112b which makes it possible to prevent the yellowing of the plastic of the output glass 112a in particular and also of the protective layer 110h, by stopping ultraviolet rays. In a non-limiting embodiment, the protective layer 112b may also be an anti-scratch layer. In a non-limiting embodiment, the output layer 112a is made of PC. It is a layer transparent to both radar waves R1, R2 and visible light. In a non-limiting embodiment, the protective layer 112b comprises a thickness e20b of 50 micrometers. In a non-limiting embodiment, the protective layer 112b is a deposit of a protective varnish.

[0053] It will be noted that it is possible to consider that all the layers 110 of the first subset S1 are equivalent to a single equivalent layer of total thickness e1 with an equivalent refractive index n eq1 when the layers 110 each have a refractive index n10 very close to the refractive index n10 of another adjacent, in other words contiguous, layer 110. Thus, in a non-limiting embodiment, each layer 110 has a refractive index n10 which has a difference with the refractive index n10 of an adjacent layer 110 of less than 0.1. This threshold also makes it possible to make the internal reflected waves between the layers 110 of the first subset S1 negligible. In a non-limiting variant of this non-limiting embodiment, the difference is less than 0.05.

[0054] Similarly, it will be noted that it is possible to consider that all of the layers 112 of the second subset S2 are equivalent to a single equivalent layer of total thickness e2 with an equivalent refractive index n eq2 when the layers 112 each have a refractive index n20 very close to the refractive index n20 of an adjacent, in other words contiguous, layer 112. Thus, in a non-limiting embodiment, each layer 112 has a refractive index n20 which has a difference with the refractive index n20 of an adjacent layer 112 of less than 0.1. This threshold also makes it possible to make the internal reflected waves between the layers 112 of the second subset S2 negligible. In other words, the output layer 112a has a refractive index n20a which has a difference with the refractive index n20b of the protective layer 112b which is adjacent to it of less than 0.1.In a non-limiting alternative embodiment of this non-limiting embodiment, the difference is less than 0.05.

[0055] The first subset S1 has an equivalent refractive index n eq1 . To calculate the equivalent refractive index n eq1 , we calculate it step by step. Thus, we start by calculating the equivalent refractive index n eqa for the first two adjacent layers 110a, 110b, i.e.: n eqa = n 10 a n 10 b e 10 a + e 10 b n 10 b e 10 a + n 10 a e 10 b = n 10 a n 10 b 1 + e 10 b e 10 a n 10 b + n 10 a e 10 b e 10 a

[0056] The two layers 110a and 110b are thus replaced by a single layer with a total thickness ea = e10a + e10b identical to the two layers. The equivalent refractive index between this layer obtained with equivalent index n eqa and the next adjacent layer, namely here 110c, is then calculated, and so on.

[0057] Thus, the first subset S1 has an equivalent refractive index n eq1 equal to: n eq 1 = n eqe n 10 h e e + e 10 h n 10 h e e + n eqe e 10 h = n eqe n 10 h 1 + e 10 h e e n 10 h + n eqe e 10 h e e

[0058] With ee the total thickness of layers 110a to 110g, and n eqe the equivalent index of layers 110a to 110g.

[0059] The second subset S2 has an equivalent refractive index n eq2 equal to: n eq 2 = n 20 a n 20 b e 20 a + e 20 b n 20 b e 20 a + n 20 a e 20 b = n 20 a n 20 b 1 + e 20 b e 20 a n 20 b + n 20 a e 20 b e 20 a

[0060] We therefore obtain the equivalent refractive index n eq0 of the first subset S1 and the second subset S2: n eq 0 = n eq 1 n eq 2 e 1 + e 2 n eq 2 e 1 + n eq 1 e 2 = n eq 1 n eq 2 1 + e 2 e 1 n eq 2 + n eq 1 e 2 e 1

[0061] It should be noted that a refractive index n can be calculated from the permittivity of a layer. This calculation being known to those skilled in the art, it is not described here.

[0062] As illustrated on the figure 2 , when a radar wave R1 is emitted by the radar sensor 10, it travels to the layer arrangement 11 which has an equivalent refractive index n eq0 , and a total thickness e0.

[0063] The radar wave R1 is reflected on the layer arrangement 11 and generates two reflected waves, one of which R11 has been reflected on the outer face of the first subassembly S1 and the other inside the layer arrangement 11. The two reflected waves R11 and R12 are so-called first-order reflected waves which return to the radar sensor 10. These are parasitic reflections. When the angle of incidence θ is different from 0°, the corresponding refracted angle referenced r is also different from 0°.

[0064] The phase difference Δϕ, otherwise called phase shift Δϕ, between these two reflected waves R11 and R12 is equal to: Δφ = n eq 0 δ λ + π − 2 e 0 tan r sin θ λ

[0065] With : n eq0 , the total equivalent refractive index for the first subsets S1 and the second subsets S2, δ the path of the reflected wave R12 in the material equal to 2e0 / cos(r), nδ / λ the phase shift due to the path in the material, π the phase shift due to internal reflection in the first subset S1 and the second subset S2, - - ((2e0 tan(r) sin(θ)) / λ) the phase shift in the air due to the difference between the reflection point Pt1 of the reflected wave R11 and the emergence point Pt2 of the reflected wave R12.

[0066] As sin(θ) = n eq0 x sin(r), we obtain: − 2 e 0 tan r sin θ λ = − 2 e 0 n eq 0 sin r 2 λcos r

[0067] Either : Δφ = π + 2 n eq 0 e 0 λcos r 1 − sin r 2 = π + 2 n eq 0 e 0 cos r λ and this whatever the value of the refracted angle r.

[0068] As the reflected waves R11 and R12 return towards the radar sensor 10, they cause disturbances on the radar sensor 10, namely an attenuation of the signal-to-noise ratio. In order to eliminate these disturbances, the total thickness e0 of the layer arrangement 11 will be defined so that the reflected waves R11 and R12 are in phase opposition to create destructive interference. To obtain destructive interference, the phase difference Δϕ between the two reflected waves R11 and R12 must be equal to π modulo 2π. Thus, we have Δϕ = (2m+1)*π, with m a natural integer. We therefore obtain: 2 m + 1 π = π + 2 n eq 0 e 0 cos r λ

[0069] Either : Soit e 0 = mλ / 2 n eq 0 cos r .

[0070] It will be noted that the equation e0 = m λ / (2n eq cos (r)) is applied whatever the value of the angle r. Thus, this total thickness e0 is dimensioned so that it is equal to m times a wavelength λ of said range Δ1 all divided by twice an equivalent refractive index n eq0 of the first subset S1 of layers 110 and of the second subset S2 of layers 112, times the cosine of a refracted angle r corresponding to the angle of incidence θ of the radar waves R1, with m integer. Thus, from the total equivalent refractive index n eq0 and the wavelength λ used over the operating frequency range of the radar sensor 10, the total thickness e0 of the layer arrangement 11 can be determined so that said reflected waves R11 and R12 cancel each other out. In a non-limiting embodiment, the wavelength λ chosen is that of the middle of said range Δ1.

[0071] An ideal total thickness e0 is defined when the angle of incidence is equal to 0; and m is equal to 1. When θ = 0, r = 0. Consequently for m=1, the ideal total thickness e0 of the layer arrangement 11 is therefore e0 = λ / (2n eq0 ). When r = 0°, namely cos (r) = 1.

[0072] The arrangement of layers 11 comprises a total thickness e0 formed by the total thickness e1 of the first subset S1 of layers 110 and by the total thickness e2 of the second subset S2 of layers 112. Since it is preferable not to play on the total thickness e1 in order not to modify the optical performances of the illuminated logo, the total thickness e2 will be adapted to obtain ideal e0 = λ / (2n eq0 ) when θ = 0 or to obtain e0 = m λ / (2n eq0 cos (r)) when θ ≠ 0. Playing on the total thickness e2 does not modify the optical performances of the illuminated logo. Note that in the case of a non-illuminated logo, we can also play on the total thickness e1, in particular by modifying the thickness e10d of the film layer 110d.

[0073] Thus, the total thickness e2 of the second subset of layers 112 is dimensioned so that the total thickness e0 of the arrangement of layers 11 is equal to said wavelength λ divided by twice the equivalent refractive index n eq0 of the first subset S1 of layers 110 and of the second subset S2 of layers 112, for an angle of incidence θ equal to zero. If the angle of incidence θ is different from zero, we obtain e0 = m λ / (2n eq0 cos (r)). This equation is applied regardless of the value of the angle of refraction r. It will be noted that in practice we will adjust the thickness e20a of the output layer 112a. Indeed, the protective layer 112b being already very thin, we cannot play on its thickness e20b.

[0074] In a non-limiting embodiment, the layer arrangement 11 comprises a total thickness e0 which is between 0.8 and 1.2 times said ideal total thickness e0. This range of values ​​takes into account the possible emission angles of the radar sensor 10. The possible values ​​of the angle of incidence θ are defined in the technical specifications of the radar sensor 10, which means that the possible values ​​of the angle of incidence θ are in the field of view of the radar sensor 10. In a non-limiting example, the angle of incidence θ is between 0° and +-30°. This range value of 0.8 to 1.2 makes it possible to take into account the manufacturing tolerances of the total thickness e0.

[0075] It will be noted that the values ​​of the angle of incidence θ are included in the possible emission angles of the radar sensor 10. The possible values ​​of the angle of incidence θ are defined in the technical specifications of the radar sensor 10. It will be noted that there is a value of the angle of incidence θ for which the reflected radar waves R11 and R12 cause a maximum disturbance of the receiving antennas 101 of the radar sensor 10. This angle of incidence θ is called the critical angle of incidence θ. In a non-limiting embodiment, this value is equal to θ = arctan(d1 / (2e4)), with d1 the distance between the transmitting antenna 100 and the receiving antennas 101, e4 the distance between the radar sensor 10 and the layer arrangement 11 as illustrated in the figure 2. Thus, the value of the total thickness e0 is determined for an angle of incidence θ equal to arctan(d1 / (2e4)). It will be noted that in a non-limiting example, the midpoint of the receiving antennas 101 is taken to calculate d1.

[0076] Thus, depending on the value of the total equivalent refractive index n eq0 and the wavelength λ used over the operating frequency range of the radar sensor 10 (between 76GHZ to 81GHZ in the non-limiting example taken), it is possible to determine the value of the total thickness e0, more particularly the value of the total thickness e2 of the second sub-assembly S2 so that the reflected waves R11 and R12 of order 1 cancel each other out. Thus, the receiving antennas 101 see less noise. This results in a better signal-to-noise ratio.

[0077] It will be noted that to avoid the existence of internal reflected waves between the output layer 112a and the first subset S1 of layers 110, in a non-limiting embodiment, the output layer 112a has a refractive index n20a which has a difference with an equivalent refractive index neq1 of the first subset S1 of layers 110 of less than 0.1. In a non-limiting embodiment, the difference is less than 0.05.

[0078] Of course, the description of the invention is not limited to the embodiments described above and to the field described above. Thus, in another non-limiting embodiment, the radar sensor 10 comprises more than one transmitting antenna 100 and more than two receiving antennas 101. Thus, in another non-limiting embodiment, the light sources 12 are integrated in a cavity of the layer 110c. Thus, in the non-limiting embodiment of a non-illuminated logo, the first subassembly S1 does not comprise the layers 110a to 110c and possibly 110d.

[0079] Thus, the invention described has in particular the following advantages: it makes it possible to eliminate the reflected waves R11, R12, of order 1 which are reflected in the direction of the radar sensor 10. The signal-to-noise ratio of said radar sensor 10 is thus no longer reduced. The transmission of the radar waves R1 is improved, it makes it possible to just adjust the total thickness e2 (in particular the thickness e20a of the output layer 112a) of the second subassembly S2 without touching the total thickness e1 of the first subassembly S1 so that the optical performances of the illuminated logo are not modified.

Claims

1. Vehicle assembly (1) for a vehicle (2), said vehicle assembly (1) comprising: - one or more light sources (12); - a radar sensor (10) configured to emit radar waves (R1) over a range (Δ1) of wavelengths (A); and - an arrangement of layers (11) disposed facing said radar sensor (10), comprising a first subset (S1) of layers (110) configured to perform an optical function, with each layer (110) having a refractive index (n10) and a thickness (e10), and a second subset (S2) of layers (112) configured to provide protection for said first set (S1) of layers (110), with each layer (112) having a refractive index (n20) and a thickness (e20); - characterized in that the total thickness (e2) of the second subset (S2) of layers (112) is dimensioned so that the total thickness (e0) of the arrangement of layers (11) is equal to m times a wavelength (λ) of said range (Δ1) divided by twice the equivalent refractive index (neq0) of the first subset (S1) of layers (110) and of the second subset (S2) of layers (112), times the cosine of a refracted angle (r) corresponding to the angle of incidence (θ) of the radar waves (R1), where m is an integer.

2. Vehicle assembly (1) according to Claim 1, wherein said radar sensor (10) is a millimetre wave or a hyperfrequency wave or a microwave radar sensor.

3. Vehicle assembly (1) according to the preceding claim, wherein said radar waves (R1) are emitted over a frequency band ranging between 100 MHz and 5 GHz.

4. Vehicle assembly (1) according to any one of the preceding claims, wherein, if the angle of incidence (θ) is equal to zero, then the total thickness (e2) of the second subset (S2) of layers (112) is dimensioned so that the total thickness (e0) of the arrangement of layers (11) is equal to said wavelength (λ) divided by twice the equivalent refractive index (neq0) of the first subset (S1) of layers (110) and of the second subset (S2) of layers (112).

5. Vehicle assembly (1) according to any one of the preceding claims, wherein the total thickness (e0) is defined with an angle of incidence (θ) equal to arctan (d1 / (2e4)), with e4 being the distance between said radar sensor (10) and said arrangement of layers (11) and d1 being the distance between an emitter antenna (100) and receiver antennas (101) of said radar sensor (10).

6. Vehicle assembly (1) according to any one of the preceding claims, wherein the second subset (S2) of layers (112) comprises an output layer (112a) and a protective layer (112b).

7. Vehicle assembly (1) according to the preceding claim, wherein said output layer (112a) has a refractive index (n20a) that has a difference with an equivalent refractive index (neq1) of the first subset (S1) of layers (110) of less than 0.1.

8. Vehicle assembly (1) according to the preceding claim, wherein said output layer (112a) has a refractive index (n20a) that has a difference with an equivalent refractive index (neq1) of the first subset (S1) of layers (110) of less than 0.05.

9. Vehicle assembly (1) according to any one of the preceding claims, wherein each layer (110) of the first subset (S1) has a refractive index (n10) that has a difference with the refractive index (n10) of an adjacent layer (110) of less than 0.1.

10. Vehicle assembly (1) according to the preceding claim, wherein each layer (110) of the first subset (S1) has a refractive index (n10) that has a difference with the refractive index (n10) of an adjacent layer (110) of less than 0.05.

11. Vehicle assembly (1) according to any one of the preceding claims, wherein the first subset (S1) of layers (110) comprises: - a film layer (110d); - a scattering layer (110e); - a reflective layer (110f); and - an opaque layer (110g).

12. Vehicle assembly (1) according to any one of the preceding claims, wherein the arrangement of layers (11) forms a non-illuminated logo.

13. Vehicle assembly (1) according to any one of the preceding Claims 1 to 11, wherein the arrangement of layers (11) forms an illuminated logo.

14. Vehicle assembly (1) according to the preceding claim, wherein the first subset (S1) of layers (110) further comprises an optical layer (110c).

15. Arrangement of layers (11) disposed facing a radar sensor (10), said radar sensor (10) being configured to emit radar waves (R1) over a range (Δ1) of wavelengths (A), said arrangement of layers (11) comprising a first subset (S1) of layers (110) configured to perform an optical function, with each layer (110) having a refractive index (n10) and a thickness (e10), and a second subset (S2) of layers (112) configured to provide protection for the first set (S1) of layers (110), with each layer (112) having a refractive index (n20) and a thickness (e20), - characterized in that the total thickness (e2) of the second subset (S2) of layers (112) is dimensioned so that the total thickness (e0) of the arrangement of layers (11) is equal to m times a wavelength (λ) of said range (Δ1) divided by twice the equivalent refractive index (neq0) of the first subset (S1) of layers (110) and of the second subset (S2) of layers (112), times the cosine of a refracted angle (r) corresponding to the angle of incidence (θ) of the radar waves (R1), where m is an integer.