Vehicle assembly comprising a radar sensor and an arrangement of layers

Abstract

Disclosed is a vehicle comprising: - a radar sensor (10), and - an arrangement of layers (11) placed facing said radar sensor and configured to perform a lighting function, comprising a first sub-set (S1) of at least one layer (110) that is reflective in the visible domain, each layer (110) having a primary refractive index (n10) and a primary thickness (e10), and a second sub-set (S2) of at least one layer (112) that is transparent in the visible domain, each layer (112) having a secondary refractive index (n20), said primary refractive index (n10) being high with respect to said secondary refractive index (n20), wherein the total thickness (e1) of said first sub-set (S1) of layers (110) is dimensioned so that there is a phase shift of 7t modulo 271 between the waves (R11) of the radar waves (R1) incident on the exterior face (S1.1) of said first sub-set (S1) and the waves (R12) reflected from the interface (J12) between said first sub-set (S1) and said second sub-set (S2) as they exit said first sub-set.

Description

Description Title of the invention: Vehicle assembly comprising a radar sensor and a layer arrangement [1] The present invention relates to a vehicle assembly. It finds a particular but not limiting application in motor vehicles. [2] A vehicle combination comprises, in a manner known to a person skilled in the art: - a radar sensor configured to emit radar waves, and - an arrangement of layers arranged opposite said radar sensor, including a reflective layer with a high refractive index for radar waves compared to the other layers of the layer arrangement. [3] The layer 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 external environment of the vehicle. [4] One drawback of this prior art is that when a radar wave is emitted by the radar sensor, it travels to the layer arrangement and is reflected back. This generates three reflected waves, one of which is reflected off the outer surface of the layer arrangement and two others on the inner surface. These three reflected waves are first-order reflected waves that return to the radar sensor. This hinders the propagation of radar waves. It reduces the signal-to-noise ratio of the radar sensor and thus interferes with its detection capabilities. The radar sensor's detection range decreases. Consequently, this can lead to a detection error or a failure to detect an object even though it is present in the vehicle's surroundings. [5] In this context, the present invention aims to provide a vehicle assembly that solves the aforementioned problem. [6] To this end, the invention proposes a vehicle assembly for a vehicle, said vehicle assembly comprising: - a radar sensor configured to emit radar waves over a range of wavelengths, and - an arrangement of layers disposed opposite said radar sensor and configured to perform a light function, said arrangement of layers comprising a first subset of at least one reflective layer in the visible range, each layer having a primary refractive index and a primary thickness, and a second subset of at least one transparent layer in the visible range, each layer having a secondary refractive index, said primary refractive index being high relative to said secondary refractive index in the radar domain, characterized in that: - The total thickness of said first subset of layers is dimensioned such that there is a phase shift of 7t modulo 271 between the incident radar waves on the outer surface of said first subset and the waves reflected at the interface between said first subset and said second subset as they emerge from said first subset. According to non-limiting embodiments, said vehicle assembly may further comprise one or more additional features, taken alone or in any technically feasible combination, from among the following. [7] According to a non-limiting embodiment, the total thickness of said second subset of layers is dimensioned so that there is a phase shift of 7t modulo 271 between the incident waves of radar waves on the outer face of said first subset and the waves reflected on the outer face of said second subset when they emerge from said first subset. [8] According to a non-limiting embodiment, the total thickness of said second subset of layers is dimensioned by modifying the thickness of only one of the layers of said second subset. [9] According to a non-limiting embodiment, each layer of said first subset has a refractive index which has a difference with the refractive index of another layer of said first adjacent subset of less than 0.1 in the radar domain.

[0010] According to a non-limiting embodiment, each layer of said second subset has a refractive index which has a difference with the refractive index of another adjacent layer of said second subset of less than 0.1 in the radar domain.

[0011] According to a non-limiting embodiment, each layer of said second subset has a refractive index which has a difference with the refractive index of a layer of said first subset greater than 0.1 in the radar domain.

[0012] According to a non-limiting embodiment, said vehicle assembly includes at least one light source configured to emit visible light which enters said layer arrangement through a slice of one of the layers of said second subset of said layer arrangement.

[0013] According to a non-limiting embodiment, said at least one reflective layer in the visible range is composed of titanium particles.

[0014] According to a non-limiting embodiment, the layer arrangement forms an illuminated logo or an illuminated front panel grid or is part of a projector.

[0015] According to a non-limiting embodiment, said radar sensor is a millimeter wave or microwave or microwave radar sensor.

[0016] According to a non-limiting embodiment, said radar waves are emitted on a frequency band between 100MHz and 5GHz.

[0017] According to a non-limiting embodiment, the lighting function is a lighting and / or signaling function.

[0018] In a non-limiting embodiment, the second subset of layers comprises: - an output layer that forms an outlet ice from the layer arrangement, - a protective layer.

[0019] According to a non-limiting embodiment, the first subset of layers is diffusing reflective white.

[0020] According to a non-limiting embodiment, the total thickness of said first subassembly is determined for an angle said angle of incidence which is equal to arctan(dl / (2e4)), with e4 the distance between said radar sensor and said layer arrangement and dl the distance between a transmitting antenna and receiving antennas of said radar sensor.

[0021] A layer arrangement is further proposed, positioned opposite a radar sensor, said radar sensor being configured to emit radar waves over a range of wavelengths, said layer arrangement being configured to perform a light function and comprising a first subset of at least one reflective layer in the visible range, each layer having a primary refractive index and a primary thickness, and a second subset of at least one transparent layer in the visible range, each layer having a secondary refractive index, said primary refractive index being high compared to said secondary refractive index, characterized in that: - the total thickness of said first subset of layers is dimensioned so that there is a phase shift of 7t modulo 271 between the incident waves of radar waves on the outer face of said first subset and the waves reflected on the interface between said first subset and said second subset when they emerge from said first subset.

[0022] The invention and its various applications will be better understood by reading the following description and examining the accompanying figures:

[0023] [Fig. 1] is a schematic view of a vehicle assembly, said vehicle assembly comprising a radar sensor and a layer arrangement, said layer arrangement comprising a first subset of layers and a second subset of layers, according to a non-limiting embodiment of the invention,

[0024] [Fig. 2] is a front view of a vehicle assembly of Figure 1, according to a non-limiting embodiment, said vehicle assembly further comprising a light-decoupling relief structure, according to a non-limiting embodiment,

[0025] [Fig. 3] is a schematic view of a radar wave emitted by the radar sensor of the vehicle assembly of Figure 1 or Figure 2, which generates reflected waves that are reflected off one face of the layer arrangement of the vehicle assembly of Figure 1 or Figure 2 and within said layer arrangement, according to a non-limiting embodiment,

[0026] [Fig. 4] is a schematic view of a radar wave emitted by the radar sensor of the vehicle assembly in Figure 1 or Figure 2, of reflected waves that reflect off two faces of the layer arrangement of the vehicle assembly in Figure 1 or Figure 2, according to a non-limiting embodiment,

[0027] [Fig. 5] is a schematic view of the layers of the layer arrangement of the vehicle assembly in Figure 1 or Figure 2, said layer arrangement comprising a first subset of layers and a second subset of layers, according to a non-limiting embodiment,

[0028] [Fig. 6] is a first results diagram on which are represented two relative reflectivity curves to a radar wave of the radar sensor of Figure 1, when the second subset of the layer arrangement of Figure 1 is optimized so as to minimize the reflected waves of Figure 3, according to a non-limiting embodiment,

[0029] [Fig. 7] is a first results diagram on which are represented two curves of relative reflectivity to a radar wave of the radar sensor of Figure 1, when the second subset of the layer arrangement of Figure 1 is optimized so as to minimize the reflected waves of Figure 3, and when the first subset of layers of the layer arrangement of Figure 1 is optimized so as to minimize the reflected waves of Figure 4, according to a non-limiting embodiment.

[0030] Identical elements, whether structural or functional, appearing on different figures retain the same references unless otherwise specified.

[0031] The vehicle assembly 1 of a vehicle 2 according to the invention is described with reference to Figures 1 to 7. The vehicle assembly 1 is also referred to as vehicle system 1. In a non-limiting embodiment, the vehicle 2 is a motor vehicle. A motor vehicle is understood to mean any type of motorized vehicle. This embodiment is taken as a non-limiting example in the following description. In the following description, the vehicle 2 is thus also referred to as 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.

[0032] As illustrated in Figure 1, vehicle assembly 1, also known as vehicle arrangement 1, comprises: - a radar sensor 10 configured to emit RI radar waves, and - an arrangement of layers 11 arranged opposite said radar sensor 10.

[0033] These elements are described below.

[0034] The radar sensor 10 is described below. As illustrated in Figure 1, the radar sensor 10 is positioned opposite the layer arrangement 11. In a non-limiting embodiment, the radar sensor 10 is a millimeter-wave (between 24 GHz and 300 GHz), microwave (between 300 MHz and 81 GHz), or microwave (between 1 GHz and 300 GHz) radar sensor. In a non-limiting variant, the radar sensor 10 operates at a radar frequency between 76 GHz and 81 GHz. The RI radar waves are emitted over a range of wavelengths X. In a non-limiting embodiment, the RI radar waves are emitted over a frequency band between 100 MHz and 5 GHz. Thus, in a non-limiting example, if radar sensor 10 operates at a radar frequency of 77GHz, i.e. an X wavelength of 3.95mm, with a frequency band of 1GHz, radar sensor 10 will operate on a frequency band from 76.5GHZ to 77.5GHz.The RI radar waves will thus be emitted in the frequency range of 76.5 GHz to 77.5 GHz, corresponding to a wavelength range of 3.87 mm to 3.92 mm. Therefore, in another non-limiting example, if radar sensor 10 operates at a radar frequency of 78.5 GHz with a frequency band of 5 GHz, radar sensor 10 will operate in a frequency band of 76 GHz to 81 GHz. The RI radar waves will thus be emitted in the frequency range of 76 GHz to 81 GHz, corresponding to a wavelength range of 3.701 mm to 3.945 mm.

[0035] As illustrated in Figures 3 and 4, the emitted IR radar waves arrive at an angle of incidence 0° on the layer arrangement 11. In a non-limiting embodiment, the angle of incidence 0° is between 0° and ±30°. Thus, the radar sensor 10 comprises a field of view (FOV) that varies between -30° and +30°. The center of the FOV is at an angle of 0° with respect to the longitudinal axis of the vehicle Ox, also called the vehicle axis Ox. In another non-limiting embodiment, the The field of view (FOV) varies between -90° and +45°. The center of the FOV is at an angle of -45° relative to the vehicle axis Ox, and the angle of incidence 0 of the RI radar waves on the layer arrangement 11 remains close to 0° (the vehicle assembly 1 being positioned at approximately 45° to the vehicle axis Ox).

[0036] The radar sensor 10 is configured to scan the external environment of the motor vehicle 1 by emitting radar waves (RI). As illustrated in Figure 1, the radar sensor 10 comprises: - at least one transmitting antenna 100 configured to emit RI radar waves, otherwise known as primary RI radar waves, - at least two receiving antennas 101 configured to receive R2 radar waves, otherwise known as secondary R2 radar waves or R2 return radar waves.

[0037] The radar sensor 10 further comprises at least one transmitter 103 configured to generate the primary radar waves RI 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 transmission and reception functions. This results in one or more transmitter / receiver units, referred to as "transceivers." The transmitter 103 generates primary radar waves RI, which are subsequently emitted by the transmitting antenna 100. When these waves encounter an object 3 (here, a pedestrian in the illustrated non-limiting example) in the external environment of the motor vehicle 2, they are reflected by said object 3. The reflected radar waves are transmitted back 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 RI 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.

[0038] The transmitting antenna 100, also called antenna 100, is configured to transmit the primary radar waves RI generated by the transmitter 103. The receiving antennas 101, also called antennas 101, are configured to receive the secondary radar waves R2 and transmit them to the receiver 104, which then processes them. There is a phase shift between the secondary radar waves R2 received by the receiving antennas 101, which allows the angular position of object 3 relative to the motor vehicle 2 to be deduced. Object 3 is located in the external environment of the motor vehicle 2. In non-limiting embodiments, the antennas 100 and 101 are patch antennas or slot antennas.

[0039] 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, also called a PCBA (Printed Circuit Board Assembly), or a flexible printed circuit board, also called a Flexboard.

[0040] The radar sensor 10 further includes an electronic control unit 106 configured to control the transmitter 103 and the receiver 104. A radar sensor being known to a person skilled in the art, it is not described in more detail here.

[0041] The layer arrangement 11 is described below. As illustrated in Figure 1 or Figures 3 to 5, it comprises: - a first SI subset of at least one 110 reflective layer in the visible range, and - a second subset S2 of at least one layer 112.

[0042] The layer arrangement 11 is configured to perform a lighting function. The first subset SI and the second subset S2 collaborate to perform this lighting function. In a non-limiting embodiment, the lighting function is a lighting and / or signaling function. It is a regulatory lighting function.

[0043] Note that Figure 1 being a schematic view, only two layers 110 have been illustrated in Figure 1 and only two layers 112 have been illustrated in Figure 1. In the following description, the first subset SI of layers 110 is otherwise called first subset SI, and the second subset S2 of layers 112 is otherwise called second subset S2.

[0044] In non-limiting embodiments, the layer arrangement 11 forms an illuminated logo or an illuminated front grille, or is part of a spotlight. In these cases, the vehicle assembly 1 includes one or more light sources 12. Thus, the logo, the front grille, or the decoupling relief structure 13 (described later) is illuminated by a plurality of light sources 12. Therefore, in one non-limiting embodiment, said vehicle assembly 1 includes at least one light source 12 configured to emit visible light Lx, also called Lx light or light, which enters said layer arrangement 11 edge-on. In the non-limiting example shown in Figure 2, the light sources 12 are arranged around the perimeter of said layer arrangement 11 at the level of the layers 112 of the second subassembly S2.In this non-limiting example, the layer arrangement 11 is part of a projector 5 which also includes a light module 50 which also has one or more light sources (not shown).

[0045] The light sources 12 generate light rays (not shown) and produce the light Lx which is injected into the transparent layers 112 and reflected on said at least one layer 110. It will be noted in particular that one of the transparent layers 112 is configured to serve as a light guide for said light Lx, and the other layers 112 are style or protection layers (against corrosion in a non-limiting example).

[0046] In one non-limiting embodiment, the light sources 12 are semiconductor light sources. In another non-limiting embodiment, the semiconductor light sources are part of a light-emitting diode (LED). Light-emitting diode is understood to mean any type of LED, including, but not limited to, LEDs (Light Emitting Diodes), OLEDs (Organic LEDs), AMOLEDs (Active-Matrix Organic LEDs), and FOLEDs (Flexible OLEDs). In yet another non-limiting embodiment, the light source 12 is a bulb with a filament.

[0047] As illustrated in Figure 1, the first SI subset of layers 110 is arranged opposite the radar sensor 10, while the second S2 subset of layers 112 is adjacent to the first SI subset of layers 110 and is arranged opposite the exterior of the motor vehicle 2.

[0048] In a first non-limiting embodiment, the first subset S1 is a diffusing reflective subset, namely said at least one layer 110 is diffusing reflective, and the second subset S2 is transparent in the visible range, namely the layers 112 are transparent to visible light.

[0049] In a second non-limiting embodiment, the first subset S1 is a transparent subset in the visible domain with a light-decoupling relief structure 13, namely said at least one layer 110 is transparent to visible light and includes a light-decoupling relief structure 13, and the second subset S2 is transparent in the visible domain, namely the layers 112 are transparent to visible light.

[0050] The light decoupling relief structure 13 is configured to decouple the Lx light produced by the light sources 12. The reliefs 130 of the light decoupling relief structure 13 are local modifications of the relief of the face on which they are located, namely here one of the layers 110 opposite the radar sensor 10.

[0051] It should be noted that if layer 110 is white, reflective, and diffusive, the light Lx does not propagate within this layer 110; it is reflected directly outwards from the motor vehicle 2 by the light-decoupling relief structure 13. This light-decoupling relief structure 13 is arranged to reflect the light Lx along the vehicle axis Ox of the motor vehicle 2, thus ensuring the lighting function. In non-executive embodiments limiting, the light decoupling relief structure 13 comprises a plurality of: - minidisks, also known as laser-impact optical micros, and / or - micro-cones, and / or - micro-cones-prisms, and / or - mini-prisms, and / or - of the graining.

[0052] Thus, the 130 reliefs are minidisks and / or microcones, and / or micro-cone prisms and / or miniprisms and / or graining. Such a surface is often described as a scattering or micro-optical surface.

[0053] The first subset of layer SI is configured to reflect the light Lx produced by the light sources 12 outwards from the motor vehicle 2. Each layer 110 of the first subset SI has a primary refractive index nlO, also called the refractive index nlO, and a primary thickness elO, also called the thickness elO. The first subset SI comprises a total thickness el composed of all the thicknesses elO. Each layer 110 has a refractive index nlO very close to the refractive index nlO of another adjacent layer 110. In a non-limiting embodiment, each layer 110 has a refractive index nlO that differs from the refractive index nlO of an adjacent layer 110 of said first subset SI by less than 0.1. This threshold also makes it possible to make negligible the internal reflected waves between the 110 layers of the first SI subset.In a non-limiting embodiment variant of this non-limiting embodiment, the difference is less than 0.05.

[0054] The second subset of layers S2 is configured to propagate visible light Lx into the layers 112, thereby increasing the efficiency of the light function. Each layer 112 of the second subset S2 has a secondary refractive index n20 and a secondary thickness e20. The second subset 52 comprises a total thickness e2, which is composed of all the e20 thicknesses. Each layer 112 has a refractive index n20 very close to the refractive index n20 of an adjacent layer 112. In a non-limiting embodiment, each layer 112 has a refractive index n20 that differs from the secondary refractive index n20 of an adjacent layer 112 in the second subset 52 by less than 0.1.This threshold also makes negligible the internal reflected waves between the layers 112 of the second subset 52. In the non-limiting example shown, the second subset 52 comprises two layers 112a and 112b, of which layer 112a serves as a waveguide. light for the Lx light, and layer 112b, which is a protective layer. The output layer 112a has a secondary refractive index n20a that differs from the secondary refractive index n20b of the adjacent protective layer 112b by less than 0.1 in the radar domain. In a non-limiting embodiment of this non-limiting design, the difference is less than 0.05. In the illustrated non-limiting example, the secondary refractive index n20a is 1.6 and the secondary refractive index n20b is 1.62.

[0055] The layer arrangement 11 thus comprises a total thickness e0=el+e2 as illustrated in Figure 5.

[0056] The primary refractive index n10 is high compared to the secondary refractive index n20 in the radar domain. By "high," we mean that layers 110 and 112 cannot be considered equivalent layers. Thus, in a non-limiting embodiment, each layer 112 of the second subset 52 has a refractive index n20 that differs from the refractive index n10 of a layer 110 of said first subset SI by more than 0.1. This results in a refractive index delta greater than 0.1 in the radar domain.

[0057] In a non-limiting embodiment illustrated in Figure 5, the first SI subset of layers 110 comprises a single layer 110. In this non-limiting embodiment, layer 110 is a layer of white reflective material. Thus, the first SI subset of layers 110 is white diffusing reflective material. This maximizes the efficiency of the light sources 12; otherwise, half of the visible light Lx would be lost. In a non-limiting variant, the material is composed of titanium dioxide (TiO2) particles. In a non-limiting example, it is a plastic with titanium dioxide dopant. It should be noted that the higher the titanium dioxide doping, the more optically reflective the material, and therefore the higher the refractive index in the radar range. In a non-limiting embodiment, the doped plastic is polycarbonate (PC). Titanium doping has the following advantages: - to use a controlled process that allows for homogeneous distribution over large parts such as a front grille, unlike a layer of paint, - to be able to vary the reflectivity and thus control the refractive index, unlike a paint layer. The titanium oxide-doped plastic layer 110 contributes to the luminous function. Furthermore, it should be noted that the titanium protects the titanium-doped plastic. Layer 110 is transparent to radar waves RI, R2, but not to visible light Lx; that is, it allows radar waves RI to pass through, but not visible light Lx, since the latter is largely reflected by layer 110 (particularly by the J12 interface described later). In a non-limiting embodiment, its thickness elO is a few millimeters. In a non-limiting embodiment, the primary refractive index nlO of this layer 110 is equal to 2. It should be noted that as the concentration of titanium particles (TiO2) increases, the layer 110 becomes more reflective and its primary refractive index nlO increases. This non-limiting embodiment of a single layer 110 is taken as a non-limiting example in the remainder of the description.

[0058] In a non-limiting embodiment illustrated in Figure 5, the second subset S2 of layers 112 comprises: - an outlet layer 112a which forms an outlet ice of the layer arrangement 11, - a protective layer 112b which prevents the plastic of the exit glass 112a from yellowing by stopping ultraviolet rays.

[0059] In a non-limiting embodiment, the protective layer 112b may also be a scratch-resistant layer. In a non-limiting embodiment, the output layer 112a is made of PC. It is transparent to both radar waves (RI, R2) and visible light (Lx). In a non-limiting embodiment, the protective layer 112b has a thickness e20b of approximately 50 micrometers. In a non-limiting embodiment, the protective layer 112b is a protective varnish coating.

[0060] As illustrated in Figures 3 to 5, when a radar wave RI is emitted by the radar sensor 10, it travels to the layer arrangement 11. The radar wave RI is reflected off the layer arrangement 11 and generates four reflected waves R11, R12, R13, R14, of which: - Rll, a wave reflected on the outer face Sl.l of the first subset SI, - R12, a wave reflected within the layer arrangement 11 and on the interface J12 between said first subset SI and said second subset S2, - R13 (illustrated in Figure 5 drawing (a)), a wave reflected inside the layer arrangement 11 and on the interface J22 between the two layers 112a and 112b of the second subset, - R14, a wave reflected on the outer face S2.1 of the second subset S2.

[0061] It should be noted that the reflected waves R12, R13 and R14 include before reflection an incident part which passes through layers 110 for R12, 110 and 112a for R13, and 110, 112a and 112b for R14.

[0062] In other words, there are reflected waves at each interface defined between two different adjacent layers. The four reflected waves R11 to R14 are first-order reflected waves that return to the radar sensor 10. These are parasitic reflections that disturb the radar wave RI. Figures 3 and 4 show the radar wave RI', which is the radar wave emerging from the layer arrangement 11. Due to these parasitic reflections, the radar wave RI is greatly attenuated compared to the radar wave RI entering the layer arrangement 11. The efficiency of the radar sensor 10 is thus reduced. To overcome this problem, as we will see below, we successively optimize the thicknesses el and then e2.

[0063] The reflection intensity varies from one reflected wave to another. In the illustrative, non-limiting example, the reflection intensity of R13 is negligible because the difference in reflection index between n20a and n20b is very small, and the Fresnel reflections are therefore negligible. Its reflection intensity is less than 0.5% of the RI radar wave, while the reflection intensity of the reflected waves R11, R12, and R14 varies between 3 and 8% in a non-limiting example. The reflected wave R13 has very little effect on the transmission of the RI radar wave, while the reflected waves R11, R12, and R14 disrupt the RI radar wave.

[0064] If the first subset of layers 110 comprises several layers 110, it should be noted that it is possible to consider that the set of layers 110 of the first subset SI is equivalent to a single equivalent layer of total thickness e1 with an equivalent refractive index n eqi(illustrated in Figures 1, 3, and 4) when the 110 layers each have a refractive index nlO very close to the refractive index nlO of another adjacent, or contiguous, 110 layer. As a reminder, in the non-limiting example given, there is a refractive index delta of less than 0.1.

[0065] It should be noted that it is possible to consider that the set of layers 112 of the second subset S2 is equivalent to a single equivalent layer of total thickness e2 with an equivalent refractive index n eq 2 (illustrated in Figures 1, 3, and 4) when the 112 layers each have a refractive index n20 very close to the refractive index n20 of an adjacent, or contiguous, 112 layer. As a reminder, in the non-limiting example given, there is a refractive index delta of less than 0.1.

[0066] It should be noted that these two secondary refractive indices, n20a and n20b, are far removed from the primary refractive index, n10, in terms of value. There is a large jump in refractive index. Therefore, we cannot have equivalent refractive indices between the two subsets SI and 82 unless the 110 layer(s) have a thickness e10 significantly less than the RI radar wave and negligible compared to the thickness e2 of the 112 layer(s), which is not the case. By significantly less, we mean that e10 = X / 10.

[0067] Furthermore, since n1O is significantly greater than n20, there cannot be an equivalent refractive index between the two subsets SI and S2.

[0068] Note that we could have an equivalent refractive index if nlO were very close to or equal to n20, which is also not the case. Thus, because of the large index jump between nlO and n20, it is not possible to have an equivalent refractive index between the first subset SI and the second subset S2 and to optimize the thickness eO.

[0069] However, as illustrated in Figures 1, 3 and 4, the second subset S2 has an equivalent refractive index n eq 2 equals:

[0070] [Math 1]

[0072] The same principle applies to the first SI subset if it comprises a plurality of layers with very similar refractive indices nlO. It will have an equivalent index n eq i. 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.

[0073] With the calculation of the equivalent index n eq 2. The reflected wave R13, which is negligible due to its very low reflection intensity, is no longer considered. Thus, as illustrated in diagram (b) of Figure 5, only the reflected waves R11, R12, and R13 remain, interfering with the radar sensor 10. The radar wave RI is reflected by the layer arrangement 11 and generates three reflected waves R11, R12, and R13, which have significant reflection intensities; a large portion of their energy returns to the radar sensor 10. In this case, there exists a reflection intensity value equal to:

[0074] [Math 2]

[0075] / (M) = Rll + R12 + R14 + 2 R11R12 cos A <p(Rll,R12) + 2VRllR14cos A<p(Rll,R14) + 2 R12R14 cos A<p(R12, R14)

[0076] With : - A(p(R11, R12) the phase difference between the reflected waves R11, R12, - A(p(R11, R14) the phase difference between the reflected waves R11, R14, - - A(p(R12, R14) the phase difference between the reflected waves R12, R14.

[0077] A minimum reflection intensity value l(M) is obtained when the different layers of the two subsets SI, S2 are optimized to separately induce a phase shift of 7t modulo 271, resulting in destructive interference between the terms R11 & R14 and R11 & R12, respectively. Thus, to minimize the spurious waves R11, R12, and R14, R11 and R12 must be in opposite phase to create destructive interference, and R11 and R14 must also be in opposite phase to create destructive interference. This optimizes the interference phenomena due to the most significant reflections, namely R11 and R14. Note that the term R12 & R14 will remain in constructive phase, but it is significantly less impactful than the sum of the other two terms because the term R12&R14 is lower in intensity than the terms R11&R14 and R11&R12.

[0078] To this end, in order to reduce spurious waves and improve the transmission of RI radar waves, since the 112 layers of the second subset S2 can be considered an equivalent layer because there is a small refractive index difference between the different 112 layers, this equivalent layer will be dimensioned to have a phase shift of 7t modulo 271 between R11 and R14. However, in the case of a large refractive index difference between two successive layers, they cannot be considered an equivalent layer. This is the case with layer 110 and the equivalent layer formed by layers 112a and 112b. In this case, each non-equivalent layer must be optimized separately to reduce spurious waves and improve the transmission of RI radar waves. In this case, each non-equivalent layer must induce a phase shift of 7t modulo 27t.

[0079] The following is now described how destructive interference between R11 and R12 is achieved. As we will see, for this purpose, the thickness el is optimized.

[0080] The total thickness el of the first SI subset of layers 110 is dimensioned such that there is a phase shift of 7t modulo 271 between R11 and R12. In other words, the total thickness el of the first SI subset of layers 110 is dimensioned such that there is a phase shift of 7t modulo 271 between the incident waves R11 of the RI radar waves on the outer face Sl.1 of the first SI subset and the reflected waves R12 on the interface J12 between said first SI subset and said second S2 subset when they emerge from said first SI subset.

[0081] When the angle of incidence 0 is different from 0°, the corresponding refracted angle referenced r is also different from 0°.

[0082] The phase difference A(p), also called the phase shift A(p), between these two reflected waves R11 and R12 is equal to:

[0083] [Math 3]

[0085] With : - n eq i, the equivalent refractive index for the first SI subset, here equal to nlO because there is only one layer 110 in the non-limiting example taken, - the path of the reflected wave R12 in the material equal to 2el / cos(r), - nô / X the phase shift due to the path through the material, - 7i the phase shift due to internal reflection in the first SI subset, - - ((2el tan(r) sin(0)) / X) the phase shift in air due to the difference between the reflection point Ptl of the reflected wave Rll and the emergence point Pt2 of the reflected wave R12 illustrated in figure 3.

[0086] Since sin(0) = n eqi x sin(r), we obtain:

[0087] [Math 4] -2eltcm(r)sm(0) > -2eln 8] eqlsin(r') [8 2 A.cos(r)

[0089] Either :

[0090] [Math 5]

[0092] and this is true regardless of the value of the refracted angle r.

[0093] 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, we will define the total thickness e1 of the first SI subset such that the reflected waves R11 and R12 are out of phase to create destructive interference. To obtain destructive interference, the phase difference A(p) between the two reflected waves R11 and R12 must be equal to 7t modulo 27t. Thus, we have A(p) = (2m+l)*7t, where m is a natural number. We therefore obtain:

[0094] [Math 6] r . . 2 M,,,,, elcosM

[0095] (2m + 1) Ti = Ti + A - —

[0096] Either :

[0097] Let el = m A / (2n eqi cos (r)).

[0098] Note that the equation el = m X / (2n eqi cos(r)) is applied regardless of the value of the angle r. Thus, this thickness el is dimensioned so that it is equal to m times a wavelength X of said range Al, all divided by twice an equivalent refractive index n eqi of the first SI subset of layers 110, times the cosine of a refracted angle r corresponding to the angle of incidence 0 of the RI radar waves, with m an integer. Thus, from the equivalent refractive index n eqi and the wavelength X used over the operating frequency range of the radar sensor 10, the thickness el of the first subset SI can be determined so that said waves The reflected R11 and R12 cancel each other out. In a non-limiting embodiment, the chosen wavelength X is that of the middle of said range Al.

[0099] An ideal total thickness el is defined when the angle of incidence is equal to 0 and m is equal to 1. When 0 = 0, r = 0. Consequently, for m = l, the ideal total thickness el of the first SI subset is therefore el = X / (2n eq i), when r = 0°, namely cos (r) = 1. In other words, here in the non-limiting example of a single layer el = X / (2nl0).

[0100] We will thus adjust the total thickness el to obtain the ideal total thickness el = X / (2n eq i) when 0 = 0 or to obtain el = m X / (2n eqi cos (r)) when 0 * 0.

[0101] In a non-limiting embodiment, the first set of SI layers comprises a total thickness el that is between 0.8 and 1.2 times the ideal total thickness el. This range of values ​​takes into account the possible emission angles of the radar sensor 10. The possible values ​​of the angle of incidence 0 are defined in the technical specifications of the radar sensor 10, meaning that the possible values ​​of the angle of incidence 0 are within the field of view of the radar sensor 10. In a non-limiting example, the angle of incidence 0 is between 0° and ±30°. This range of 0.8 to 1.2 allows for the manufacturing tolerances of the total thickness eO. It should be noted that in the non-limiting example given, the thickness elO of the layer 110 of white reflective material, which is composed of titanium TiO2 particles, is easily controlled in terms of industrial processes.

[0102] It should be noted that there exists a value for the angle of incidence θ for which the reflected radar waves R11 and R12 cause maximum disturbance to 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(dθ / (2e4)), where dθ is the distance between the transmitting antenna 100 and the receiving antennas 101, and e4 is the distance between the radar sensor 10 and the layer arrangement 11 as illustrated in Figure 3. Thus, in a non-limiting embodiment, the value of the total thickness εl is determined for an angle of incidence θ equal to arctan(dθ / (2e4)). Note that in a non-limiting example, the midpoint of the receiving antennas 101 is taken to calculate dθ.

[0103] Thus, depending on the value of the total equivalent refractive index n eqiFrom the wavelength X used over the operating frequency range of radar sensor 10 (between 76 GHz and 81 GHz in the non-limiting example), the value of the total thickness el can be determined so that the first-order reflected waves R11 and R12 cancel each other out. Thus, the receiving antennas 101 see less noise. A better signal-to-noise ratio is achieved.

[0104] Thanks to the optimization of the thickness el, and since layers 110 and 112 are parallel, the path traveled within the thickness el between the radar wave RI and the reflected wave R14 is the same. Therefore, the radar wave RI arrives at the same angle of incidence at the interface Sl.l, and the reflected wave R14 arrives at the interface J1.2. Consequently, there is also a phase shift of 7t modulo 271 between the incident portion of the reflected wave R14 that passes through the first subset SI on the way forward (i.e., layer 110) and the portion of the reflected wave R14 that passes through the first subset on the way back (i.e., layer 110). These two portions therefore cancel each other out. For the next step, it is sufficient to have destructive interference between the reflected wave R1ll and the reflected wave R14 at the level of the second subset S2. The method for achieving destructive interference between R1ll and R14 is described below.As we will see, for this purpose, we optimize the thickness e2 (after having therefore optimized the thickness el).

[0105] The total thickness e2 of the second subset S2 of layers 112 is dimensioned such that there is a phase shift of 7t modulo 271 between R11 and R14. In other words, the total thickness e2 of the second subset S2 of layers 112 is dimensioned such that there is a phase shift of 7t modulo 271 between the incident waves R11 of the radar waves RI on the outer face Sl.1 of the first subset SI and the reflected waves R14 on the outer face S2.1 of the second subset S2 when they emerge from said first subset SI.

[0106] When the angle of incidence 0 is different from 0°, the corresponding refracted angle referenced r is also different from 0°.

[0107] The phase difference A(p), also called the phase shift A(p), between these two reflected waves R11 and R14 is equal to:

[0108] [Math 7]

[0110] With : - n e q2, the total equivalent refractive index for the second subset S2, - the path of the reflected wave R14 in the material equal to 2e2 / cos(r), - nô / X the phase shift due to the path through the material, - 7t the phase shift due to internal reflection caused by the passage of the RI radar wave from a low index medium (air) to a high index medium (neql), - - ((2e2 tan(r) sin(0)) / X) the phase shift in air due to the difference between the reflection point Ptl of the reflected wave Rll and the emergence point Pt4 of the reflected wave R14 illustrated in figure 4.

[0111] Since sin(0) = n eq 2 x sin(r), we obtain:

[0112] [Math 8] 1- , -2e2tan(r)sin(_9) _ -2e2n eq2 sin(r) 2 1 J A “ Âcos(r)

[0114] Either :

[0115] [Math 9]

[0117] and this is true regardless of the value of the refracted angle r.

[0118] As the reflected waves R11 and R14 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 e2 of the second subset S2 will be defined such that the reflected waves R11 and R14 are out of phase to create destructive interference. To obtain destructive interference, the phase difference A(p) between the two reflected waves R11 and R14 must be equal to 7t modulo 27t. Thus, we have A(p) = (2m+l)*7t, where m is a natural number. We therefore obtain:

[0119] [Math 10]

[0121] Either :

[0122] Let e2 = m A / (2n eq 2 cos (r)).

[0123] Note that the equation e2 = m X / (2n eq2 cos(r)) is applied regardless of the value of the angle r. Thus, this total thickness e2 is dimensioned so that it is equal to m times a wavelength X of said range Al, all divided by twice an equivalent refractive index n eq 2 of the second subset S2 of layers 112, times the cosine of a refracted angle r corresponding to the angle of incidence 0 of the RI radar waves, with m an integer. Thus, from the total equivalent refractive index n eq 2 and the wavelength X used over the operating frequency range of the radar sensor 10, the total thickness e2 of the second subset S2 can be determined such that said reflected waves R11 and R14 cancel each other out. In a non-limiting embodiment, the chosen wavelength X is that of the midpoint of said range A11.

[0124] An ideal total thickness e2 is defined when the angle of incidence is equal to 0 and m is equal to 1. When 0 = 0, r = 0. Consequently, for m = l, the ideal total thickness e2 of the second subset S2 is therefore e2 = X / (2n eq 2). When r = 0°, i.e. cos (r) = 1.

[0125] We will therefore adjust the total thickness e2 to obtain the ideal e2 = X / (2n eq 2) when 0 = 0 or to obtain e2 = m A / (2n eq 2 cos (r)) when 0 * 0. Playing with the total thickness e2 does not change the optical performance of the illuminated logo.

[0126] Thus, the total thickness e2 of the second subset of layers 112 is dimensioned such that the total thickness e2 is equal to said wavelength X divided by twice the equivalent refractive index n eq 2 of the second subset S2 of layers 112, for an angle of incidence 0 equal to zero. If the angle of incidence 0 is not zero, we obtain e2 = m X / (2neq 2 cos (r)). This equation is applied regardless of the value of the angle of refraction r.

[0127] In a non-limiting embodiment, to optimize e2, the thickness of only one of the layers 112 of said second subset S2 is modified. This simplifies the optimization process. In a non-limiting embodiment, it is the layer into which the light Lx is injected, and which serves as a light guide for said light Lx, that will be modified. Thus, it should be noted that in practice, the thickness e20a of the output layer 112a will be adjusted. Indeed, since the protective layer 112b is already very thin, its thickness e20b cannot be altered. Thus, in practice, the thickness e20 of only one layer 112 is changed, namely the one that is easiest to inject or the one made of the least expensive material.

[0128] In a non-limiting embodiment, the second subassembly S2 comprises a total thickness e2 that is between 0.8 and 1.2 times the ideal total thickness e2. This range of values ​​takes into account the possible emission angles of the radar sensor 10. The possible values ​​of the angle of incidence 0 are defined in the technical specifications of the radar sensor 10, meaning that the possible values ​​of the angle of incidence 0 are within the field of view of the radar sensor 10. In a non-limiting example, the angle of incidence 0 is between 0° and ±30°. This range of 0.8 to 1.2 allows for the manufacturing tolerances of the total thickness e2.

[0129] It should be noted that there exists a value for the angle of incidence θ for which the reflected radar waves R11 and R14 cause maximum disturbance to 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(dθ / (2e4)), where dθ is the distance between the transmitting antenna 100 and the receiving antennas 101, and e4 is the distance between the radar sensor 10 and the layer arrangement 11 as illustrated in Figure 4. Thus, the value of the total thickness e2 is determined for an angle of incidence θ equal to arctan(dθ / (2e4)). Note that in a non-limiting example, the midpoint of the receiving antennas 101 is taken to calculate dθ.

[0130] Thus, depending on the value of the total equivalent refractive index n eq2 and the X wavelength used over the operating frequency range of radar sensor 10 (between 76 GHz and 81 GHz in (This is a non-limiting example.) We can determine the value of the total thickness e2 so that the first-order reflected waves R11 and R14 cancel each other out. Thus, the receiving antennas 101 see less noise, resulting in a better signal-to-noise ratio.

[0131] Figure 6 illustrates a diagram of the results following an optimization of the second subset S2 of the layer arrangement 11 to minimize the effects of reflected waves R11 and R14 on the RI radar wave, but without optimization of the first subset SI of the layer arrangement 11; the effects of reflected waves R11 and R12 on the RI radar wave are still present. Thus, R11 and R14 produce destructive interference with each other, while R11 and R12 produce constructive interference. The x-axis represents the angle of incidence θ, and the y-axis represents the reflected intensity IRL in decibels (dB). There are two curves, C1 and C2, for two angles of incidence θ of 76 GHz and 77 GHz, respectively.

[0132] Figure 7 illustrates a diagram of the results following an optimization of the second subset S2 of the layer arrangement 11 to minimize the effects of reflected waves R11 and R14 on the RI radar wave, and an optimization of the first subset SI of the layer arrangement 11 to minimize the effects of reflected waves R11 and R12 on the RI radar wave. Thus, R11 and R14 produce destructive interference with each other, and R11 and R12 also produce destructive interference with each other. The x-axis represents the angle of incidence θ, and the y-axis represents the reflected intensity IRL in decibels (dB). There are two curves, C1 and C2, for two angles of incidence θ of 76 GHz and 77 GHz, respectively.

[0133] In the diagram in Figure 6, the average IRL reflection intensity is -1 dB when only the disturbances due to reflected waves R11 and R14 are considered, while in the diagram in Figure 7, the average IRL reflection intensity is -16 dB when the disturbances due to reflected waves R11 and R12 are considered in addition to those due to reflected waves R11 and R14. This results in a gain of 6 dB in decibels when considering both the disturbances due to reflected waves R11 and R12 and those due to reflected waves R11 and R14.

[0134] Of course, the description of the invention is not limited to the embodiments and the scope 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 a non-limiting embodiment, the thickness e2 can be dimensioned before or in parallel with the thickness el.

[0135] Thus, the described invention offers the following advantages in particular: - It minimizes the first-order reflected waves R11, R12, and R14 that reflect towards the radar sensor 10. The signal-to-noise ratio of said radar sensor 10 is thus no longer reduced. Transmission of RI radar waves is improved, - it allows minimizing the reflected waves R11, R12, and R14 by modifying the total thickness 110 and the total thickness e2, therefore by modifying the white reflective diffusing layer 110 and by modifying the transparent layers 112, - it allows minimizing the reflected waves R11 and R12 between two non-equivalent layers with a significant difference in refractive indices.

Claims

Demands

1. Vehicle assembly (1) for vehicle (2), said vehicle assembly (1) comprising: - a radar sensor (10) configured to emit radar waves (RI) over a range (Al) of wavelengths (X), and - a layer arrangement (11) disposed opposite said radar sensor (10) and configured to perform a lighting function, said layer arrangement (11) comprising a first subset (S1) of at least one layer (110) reflective in the visible range, each layer (110) having a primary refractive index (n10) and a primary thickness (e10), and a second subset (S2) of at least one layer (112) transparent in the visible range, each layer (112) having a secondary refractive index (n20), said primary refractive index (n10) being high compared to said secondary refractive index (n20) in the radar range, characterized in that: - the total thickness (el) of said first subset (SI) of layers (110) is dimensioned so that there is a phase shift of 7t modulo 271 between the incident waves (Rll) of the radar waves (RI) on the outer face (Sl.l) of said first subset (SI) and the reflected waves (R12) on the interface (J12) between said first subset (SI) and said second subset (S2) when they emerge from said first subset (SI).

2. Vehicle assembly (1) according to claim 1, wherein the total thickness (e2) of said second subassembly (S2) of layers (112) is dimensioned so that there is a phase shift of 7t modulo 271 between the incident waves (R11) of the radar waves (RI) on the outer face (S1.1) of said first subassembly (SI) and the reflected waves (R14) on the outer face (S2.1) of said second subassembly (S2) when they emerge from said first subassembly (SI).

3. Vehicle assembly (1) according to the preceding claim, wherein the total thickness (e2) of said second sub-assembly (S2) of layers (112) is dimensioned by modifying the thickness of only one of the layers (112) of said second sub-assembly (S2).

4. Vehicle assembly (1) according to any one of the preceding claims, wherein each layer (110) of said first subassembly (SI) has a refractive index (nlO) which has a difference with the refractive index (nlO) of another adjacent layer (110) of said first subassembly (SI) of less than 0.1 in the radar domain.

5. Vehicle assembly (1) according to any one of the preceding claims, wherein each layer (112) of said second subassembly (S2) has an index of refraction (n20) which has a difference with the refractive index (n20) of another adjacent layer (112) of said second subset (S2) of less than 0.1 in the radar domain.

6. Vehicle assembly (1) according to any one of the preceding claims, wherein each layer (112) of said second subassembly (S2) has a refractive index (n20) which has a difference with the refractive index (n10) of a layer (110) of said first subassembly (S1) greater than 0.1 in the radar domain.

7. Vehicle assembly (1) according to any one of the preceding claims, wherein said vehicle assembly (1) comprises at least one light source (12) configured to emit visible light (Lx) which enters said layer arrangement (11) through a slice of one of the layers (112) of said second sub-assembly (S2) of said layer arrangement (11).

8. Vehicle assembly (1) according to any one of the preceding claims, wherein said at least one visible-reflective layer (110) is composed of titanium (Tio2) particles.

9. Vehicle assembly (1) according to any one of the preceding claims, wherein the layer arrangement (11) forms an illuminated logo or an illuminated front grille or forms part of a projector.

10. A layer arrangement (11) disposed opposite a radar sensor (10), said radar sensor (10) being configured to emit radar waves (RI) over a range (A1) of wavelengths (X), said layer arrangement (11) being configured to perform a light function and comprising a first subset (S1) of at least one layer (110) reflective in the visible range, each layer (110) having a primary refractive index (n1O) and a primary thickness (e1O), and a second subset (S2) of at least one layer (112) transparent in the visible range, each layer (112) having a secondary refractive index (n2O), said primary refractive index (n1O) being high compared to said secondary refractive index (n2O), characterized in that: - the total thickness (el) of said first subset (SI) of layers (110) is dimensioned so that there is a phase shift of 7t modulo 271 between the incident waves (Rll) of the radar waves (RI) on the outer face (Sl.l) of said first subset (SI) and the reflected waves (R12) on the interface between said first subset (SI) and said second subset (S2) when they emerge from said first subset (SI).

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