Lighting device for a motor vehicle comprising a radar sensor

Abstract

The invention relates to a lighting device (5) for a motor vehicle, the lighting device comprising a stack of contiguous elements comprising: - a protective panel (20); - an intermediate layer (30) comprising at least one radar antenna (100) configured to emit radar waves (R1, R2), first radar waves (R1) emitted by the radar antenna propagating toward the protective panel, second radar waves (R2) emitted by the radar antenna propagating toward a conductive layer (40); - the conductive layer being suitable for partly forming a ground plane for the radar antenna, the intermediate layer being positioned between the protective panel and the conductive layer, the conductive layer comprising a first portion (44) and a second portion (45), the first portion being positioned facing the radar antenna, the first portion having a sheet resistance higher than another sheet resistance of the second portion.

Description

Lighting device for a motor vehicle including a radar sensor TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention relates generally to motor vehicle equipment fitted with a radar sensor.

[0002] In particular, the invention relates to a lighting device for a motor vehicle included in that motor vehicle and comprising a radar sensor. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] A large majority of motor vehicles today are equipped with advanced driver assistance systems (ADAS, or Advanced Driver Assistance Systems). These driver assistance systems are, for example, safety and driver assistance systems designed to help prevent potentially dangerous situations that could lead to an accident.

[0004] These driver assistance systems rely in particular on the use of detection systems equipped, for example, with radar sensors. These radar sensors include at least one radar antenna that emits radar waves.

[0005] It is particularly well known to integrate radar sensors directly into lighting or signaling devices. However, radar sensors must not be aesthetically visible and must not affect the performance of the lighting or signaling devices.

[0006] Furthermore, weather conditions can significantly hinder the proper functioning of driver assistance systems. For example, snow can cause the detection system to become blinded, thus leading to malfunctions in the driver assistance system.

[0007] It is then known to install systems, such as de-icing systems, to maintain the area facing the detection system at a relatively high temperature to ensure the proper functioning of the detection system (and therefore the driver assistance system).

[0008] However, it is not possible to effectively implement both the radar sensor and the de-icing systems simultaneously. This therefore affects the performance of the detection system, and consequently the effectiveness of the driver assistance system in assisting the driver.

[0009] The present invention proposes to improve the integration of a radar sensor into a lighting device for a motor vehicle, intended for example to implement lighting or signaling functions, in order to guarantee efficient propagation of radar waves.

[0010] One aspect of the invention relates to a lighting device for a motor vehicle, said lighting device comprising a stack of contiguous elements including:

[0011] - a protective panel,

[0012] - an intermediate layer comprising at least one radar antenna of a radar sensor configured to emit associated radar waves, with the first radar waves emitted by the radar antenna propagating towards the protective panel, and the second radar waves emitted by the radar antenna propagating towards a conductive layer, and

[0013] - the conductive layer adapted to partially form a ground plane for the radar antenna, the intermediate layer being positioned between the protective panel and the conductive layer,

[0014] the conductive layer comprising a first part and a second part, the first part of the conductive part being positioned opposite the radar antenna.

[0015] Thus, advantageously according to the invention, the two-part conductive layer ensures that, with respect to the antenna, the conductive layer behaves as a ground plane, but outside this area with respect to the radar antenna, the conductive layer can behave as a heating element. In other words, the two-part conductive layer allows the two functions (ground plane and heating) to be decoupled, yet both implemented within the same conductive layer.

[0016] This is particularly advantageous because the proper functioning of the radar antenna is guaranteed (the potential difference necessary to generate radar waves is achieved by the first part of the conductive layer), and at the same time, the efficiency of the radar sensor is also guaranteed because the second part of the conductive layer protects the sensor from the elements. Indeed, thanks to the heating function of the second part of the conductive layer, water droplets from rain, fog, snow, or frost do not interfere with the radar sensor's operation. The second part of the conductive layer thus acts as a heat diffuser.

[0017] In addition to the characteristics mentioned in the preceding paragraph, the lighting device according to the invention may have one or more additional characteristics from among the following, considered individually or in all technically possible combinations:

[0018] - the first part of the conductive layer has a surface resistance greater than another surface resistance of the second part of the conductive layer;

[0019] - the other surface resistance of the second part of the conductive layer is at least ten times smaller than the surface resistance of the first part of the conductive layer;

[0020] - the second part surrounds the first part of the conductive part;

[0021] - the first part of the conductive layer comprises a first metallic mesh;

[0022] - the second part of the conductive layer comprises indium tin oxide;

[0023] - the second part of the conductive layer includes a second metallic mesh;

[0024] - the second part of the conductive layer comprises carbon nanotubes;

[0025] - the lighting device also includes a thermally conductive layer positioned in such a way that the conductive layer is placed between the intermediate layer and the thermally conductive layer;

[0026] - the thermally conductive layer comprises indium tin oxide;

[0027] - the thermally conductive layer comprises carbon nanotubes;

[0028] - the thickness of the protective panel is less than 5 millimeters;

[0029] - the radar antenna is overmolded into the intermediate layer;

[0030] - the radar antenna is encapsulated in the intermediate layer;

[0031] - the intermediate layer comprises a flexible transparent material;

[0032] - the protective panel comprises a transparent polymer material;

[0033] - the lighting device also includes another protective panel, the conductive layer being positioned between the intermediate layer and the other protective panel;

[0034] - the other protective panel has the same thickness as the protective panel;

[0035] - the other protective panel comprises a polymer material;

[0036] - the protective panel forming an external window of the motor vehicle; the lighting device also includes a lighting module configured to implement lighting or signaling functions of the motor vehicle; and

[0037] - the lighting device also includes a light source and at least one optical element, the light source being configured to emit a light beam, the optical element being arranged to direct the light beam emitted by the light source through the stack of the lighting device. BRIEF DESCRIPTION OF THE FIGURES

[0038] Other features and advantages of the invention will become apparent from the description, which can be read in conjunction with the figures. These figures are provided for illustrative purposes only and are not intended to limit the scope of the invention.

[0039] The diagram represents a partial schematic view of a motor vehicle within the scope of the present invention.

[0040] This represents a schematic cross-sectional view of a first example of the implementation of a lighting device for a motor vehicle according to the invention,

[0041] The diagram represents a schematic view in functional form of a radar sensor included in the lighting device according to the invention.

[0042] This represents a schematic view of a radar antenna included within the radar sensor of the,

[0043] Figure 1 represents a schematic cross-sectional view of the radar antenna shown on the diagram, along a section plane AA.

[0044] Lare represents a schematic cross-sectional view of a second example embodiment of the lighting device according to the invention, and

[0045] Lare represents a schematic cross-sectional view of a third example of an embodiment of the lighting device according to the invention.

[0046] For clarity, identical or similar elements are identified by identical reference symbols across all figures. DETAILED DESCRIPTION

[0047] The present invention aims to provide a lighting device for a motor vehicle (hereinafter referred to as the "lighting device") comprising a radar sensor that enables efficient propagation of radar waves. More specifically, the lighting device features a structure that improves the integration of radar antennas within a radar sensor, thereby preventing any degradation in the radar sensor's performance.

[0048] Figure 1 represents a partial schematic view of a vehicle 1 relevant to the invention. In this description, the vehicle 1 considered is a motor vehicle. "Motor vehicle" is understood to mean any type of motorized vehicle. In the following, the terms "vehicle" and "motor vehicle" are used interchangeably to describe the vehicle relevant to the present invention.

[0049] Typically, the motor vehicle 1 includes, in particular, a signaling device 2 and a lighting device 3. Here, the motor vehicle 1 also includes a lidar 4. As these elements do not constitute the core of the invention, they are not described in further detail below.

[0050] As can be seen in the diagram, a forward Z direction of movement for vehicle 1 is defined. This Z direction also corresponds to a longitudinal axis of vehicle 1 (this longitudinal axis can also be called the "vehicle axis"). An XZ plane here corresponds to the horizontal plane of vehicle 1.

[0051] As shown in Figure 1, the motor vehicle 1 also includes a lighting device 5; 6; 7. This lighting device 5 is more specifically represented in Figure 1. This lighting device is, for example, a headlight or a taillight of the motor vehicle 1.

[0052] The lighting device 5; 6; 7 comprises a radar sensor 10, a protective panel 20, an intermediate layer 30, and a conductive layer 40. Here, the lighting device 5; 6; 7 comprises a stack of contiguous layers. This stack includes the protective panel 20, the intermediate layer 30, and the conductive layer 40. It is important to note here that this stack of layers is achieved without any air gaps between the different layers. In other words, the various layers comprising the lighting device 5; 6; 7 according to the invention are assembled together, in contact, in a contiguous manner.

[0053] The overall thickness of the resulting stack is, for example, less than 20 millimeters (mm). Preferably, this overall thickness is between 1 and 15 mm, and even more preferably between 1 and 12 mm.

[0054] Radar sensor 10 is configured to emit and receive R1, R2 radar waves.

[0055] In practice, radar sensor 10 is a millimeter-wave radar sensor (with frequencies between 24 GHz and 300 GHz). Alternatively, the radar sensor is a microwave radar sensor (with frequencies between 300 MHz and 81 GHz). As a further alternative, the radar sensor is a microwave radar sensor (between 1 GHz and 300 GHz).

[0056] Preferably in the present invention, the radar sensor 10 operates at a radar frequency between 76 GHz and 81 GHz. The radar waves R1 are, for example, emitted over a frequency band between 100 MHz and 3 GHz. Thus, in a preferred example, if the sensor operates at a radar frequency of 77 GHz with a frequency band of 1 GHz, the radar sensor 10 operates over a frequency band from 76.5 GHz to 77.5 GHz. The radar waves R1 are therefore emitted over the frequency range of 76.5 GHz to 77.5 GHz, corresponding to a range Δ1 of wavelengths λ r between 3.87 millimeters (mm) and 3.92 mm.

[0057] In another embodiment, if the radar sensor 10 operates at a radar frequency of 78.5 GHz with a frequency band of 5 GHz, the radar sensor 10 operates over a frequency band from 76 GHz to 81 GHz. In this case, the radar waves R1 are thus emitted over the frequency range of 76 GHz to 81 GHz, corresponding to a range Δ1 of wavelengths λ r between 3,701 mm and 3,945 mm.

[0058] The radar sensor 10 is configured to scan the external environment of the motor vehicle 1, through the emission of radar waves R1, R2.

[0059] For this purpose, as shown in the diagram, radar sensor 10 comprises:

[0060] - at least one transmitting antenna 100 configured to emit first radar waves R1 and second radar waves R2, and

[0061] - at least two receiving antennas 101 configured to receive radar waves (not shown) received by reflection from the external environment of the motor vehicle 1.

[0062] In practice, the radar sensor 10 also includes at least one transmitter 103 configured to generate the radar waves R1, R2. It also includes at least one receiver 104 configured to process the radar waves received in return.

[0063] In one example, a single electronic component can be used to implement both the transmission and reception functions. The lighting device then comprises one or more transmitters / receivers (also called "transceivers" according to the commonly used Anglo-Saxon terminology).

[0064] In practice, the transmitter 103 generates radar waves R1 and R2, which are subsequently emitted by the transmitting antenna 100. When these waves encounter an object (not visible in the figures) in the external environment of the motor vehicle 1, they are reflected back by that object. The reflected radar waves are transmitted back to the radar sensor 10. These are the radar waves received by the receiving antennas 101. They correspond to the radar waves retransmitted towards the radar sensor 10.

[0065] In one example implementation, the radar waves R1, R2 and the radar waves received in return are radio frequency waves.

[0066] Alternatively (not shown), the radar sensor may include a plurality of transmitters and a plurality of receivers.

[0067] In practice, the transmitting antenna 100 (also called radar antenna 100 in this description) is configured to transmit the radar waves R1 and R2 generated by the transmitter 103. The receiving antennas 101 (also referred to as antennas 101) are configured to receive the returning radar waves and transmit them to the receiver 104, which then processes them. There is a phase shift between the radar waves received by the receiving antennas 101, which allows the position of the object in question to be deduced relative to the motor vehicle 1, an object located in the external environment of the motor vehicle 1.

[0068] In practice, the antennas 100 and 101 are offset from the other elements of the radar sensor 10 (the dotted lines on the diagram illustrate this "offset" characteristic). The transmitter 103 and the receiver 104 are then mounted on a printed circuit board 105. The printed circuit board 105 is connected to the antennas 100 and 101 but positioned at a distance from them (the antennas 100 and 101 are therefore offset from the printed circuit board 105). The printed circuit board is, for example, a rigid printed circuit board, also called a PCBA (for "Printed Circuit Board Assembly" according to the commonly used Anglo-Saxon terminology). Alternatively, the printed circuit board can be a flexible printed circuit board (or "Flexboard" according to the commonly used Anglo-Saxon terminology).

[0069] The radar sensor 10 further includes an electronic control unit 106 configured to control the transmitter 103 and the receiver 104.

[0070] In practice, antennas 100 and 101 are, for example, so-called "patch antennas" (or "patchantenna" according to the commonly used Anglo-Saxon terminology). Alternatively, the antennas can be so-called "slot antennas" (or "slotantenna" according to the commonly used Anglo-Saxon terminology).

[0071] Preferably, antennas 100 and 101 are presented here in the form of a metallic mesh. In the following description, radar antenna 100 (transmitting) is described in more detail, but the principles presented also apply to antenna 101 (receiving).

[0072] Figure 1 schematically represents the radar antenna 100 according to the present invention. The radar antenna 100 therefore comprises a metallic mesh. This metallic mesh is, for example, formed in the XY plane (orthogonal to the horizontal plane of the motor vehicle 1). This metallic mesh is conductive.

[0073] Advantageously, the radar antenna 100 is designed to obtain a horizontal polarization direction of the wave (i.e. in the horizontal plane of the motor vehicle 1).

[0074] As can be seen in the image, the radar antenna 100 here has an overall zigzag shape. This overall shape optimizes the antenna's performance. Alternatively, any other shape can be used.

[0075] The length of the radar antenna 100, along the X direction, is on the order of a few centimeters (cm). For example, this length is between 3 and 6 cm, preferably on the order of 5 cm.

[0076] In this overall zigzag shape, the metal mesh is visible, but its arrangement and dimensions make it almost transparent to the naked eye. It comprises 110 metal strips arranged to form a metal grid.

[0077] Advantageously, these 110 metallic strips are micrometric, meaning they form metallic patterns with micrometric dimensions. In other words, by defining a mesh size d (visible on the diagram), that is, the dimension of a repeated pattern in the metallic mesh, this mesh size d has a micrometric dimension. A micrometric metallic grid is thus formed. These micrometric dimensions are particularly advantageous because the resulting metallic grid is barely visible to the naked eye. Moreover, such a structure allows for very good performance of the 100 radar antenna. Furthermore, the metallic mesh does not affect the performance of a lighting or signaling device that emits a light beam passing through this metallic mesh. Finally, such dimensions, which are not too small, facilitate the manufacture of the 100 radar antenna.

[0078] Preferably, the width b (visible on the diagram), in the XY plane, of each metal strip 110 is on the order of a few tens to hundreds of nanometers (nm). Each metal strip 110 has a thickness (along the Z-axis) ranging from a few nanometers to a few micrometers. This thickness depends in practice on the manufacturing process used to produce the metal mesh. Preferably, this thickness is less than 20 micrometers (µm). Even more preferably, this thickness is less than 10 µm, or even less than 8 µm. These thickness values ​​are particularly easy to obtain by screen printing. This process is notably inexpensive and simple to implement.

[0079] Within the framework of the present invention, the thickness of each metal strip 110 can also be between 200 nm and 5 µm, for example, between 200 nm and 2 µm. These thickness values ​​are obtained, for example, by lithography. This makes it possible to obtain very thin strips for each metal strip 110, ensuring the transparency of the luminous device 5, 6, 7 described below.

[0080] The metallic mesh may contain copper, for example. Alternatively, it may contain silver, platinum, aluminum, or nickel. In practice, the metallic strips are formed, for example, by nanolithography.

[0081] In practice, the radar antenna 100 is formed, for example, by cutting, in this case into a zigzag shape, a plate containing the metal mesh. Alternatively, the metal strips 110 can be selectively deposited to form the metal mesh and the overall shape of the radar antenna 100. As a further alternative, the metal strips 110 can be produced by engraving the different metal patterns side by side.

[0082] As can be seen in the figure, the lighting device 5, 6, and 7 is designed to be positioned in the path of a light beam originating, for example, from a lighting device. However, given the regular pattern of the metallic mesh forming the radar antenna 100, as well as the dimensions of the metallic mesh, this mesh forms a diffraction grating for the light beam passing through the radar antenna 100.

[0083] In order to limit or even completely eliminate higher orders of diffraction, the mesh size d is advantageously chosen in the present invention. More particularly, the mesh size d is advantageously determined so as to allow only 0th-order propagation (so as not to observe diffraction phenomena after the propagation of the light beam L). i through the radar antenna 100 in the form of the metallic mesh).

[0084] Lare represents a cross-sectional view of radar antenna 100 shown on the, according to a cross-sectional plane AA.

[0085] As can be seen in Figure 5, three characteristic dimensions are introduced to define the metallic mesh of the radar antenna 100: the width b of each metallic strip 110, a spacing a between two adjacent metallic strips 110, and the mesh pitch d (corresponding to the dimension of the repeated pattern to form the metallic grid structure of the radar antenna 100). By definition, the following relationship is observed between these three characteristic dimensions: .

[0086] As will be described later, the radar antenna 100 is in practice overmolded or encapsulated in the intermediate layer 30. This intermediate layer 30 has a refractive index denoted n2. Preferably, it is between 1.4 and 1.95. It should be noted here that the intermediate layer 30 includes the antennas 100, 101 of the radar sensor 10 and that the other elements of this radar sensor 10 are offset from the antennas 100, 101 (in other words, the other elements of the radar sensor 10 are positioned outside the intermediate layer 30).

[0087] It is noted here that the light beam L i propagates in a first medium with refractive index n3, then is incident on the intermediate layer 30 comprising the radar antenna 100. At the level of this intermediate layer 30, the angle of incidence is denoted θ i It should be noted here that the first medium corresponds, for example, in the case of the, to the conductive layer 40.

[0088] In practice, by arranging the different elements (lighting device, luminous device 5; 6; 7) in the motor vehicle 1, this angle of incidence θ i is, in absolute value, less than 60 degrees (°).

[0089] Thus, by applying the classical formula for transmission gratings, and in order to obtain only zero-order propagation (i.e., no diffraction phenomena), the mesh size d must satisfy the following inequality (λ here corresponds to the wavelength of the light beam L). i ) :

[0090]

[0091] In other words, the mesh size d is less than a value that depends on the wavelength λ of the light beam L i , the refractive index n2 of the intermediate layer 30, the refractive index n3 of the first medium (here the conducting layer 40) and the angle of incidence θ i of the light beam L iat the intermediate layer 30.

[0092] In practice, in the present invention, the mesh size d is less than a few hundred nanometers, for example less than 500 nanometers, in order to prevent the metallic mesh of the radar antenna 100 from behaving like a diffraction grating for a light beam L i (corresponding to a wavelength of the visible spectrum).

[0093] For example, considering a light beam L i with a wavelength of the order of 550 nm, the mesh pitch d is less than 230 nm in order to avoid the presence of diffraction phenomena (which would be due to the regular metallic mesh forming the radar antenna 100).

[0094] In practice, if the light beam were to pass through several layers before the first medium with refractive index n3, it would be possible to modify the inequality presented above by applying, for all the layers passed through before the first medium, a succession of Snell's law of refraction to express the angle of incidence θ i on the intermediate layer. The resulting expression would then be combined with the classical formula for transmission networks to obtain the inequality concerning the mesh size d. In general, the mesh size d is less than a quantity that depends on the wavelength λ of the light beam L i , the refractive indices of the different layers traversed and the angle of incidence of the light beam L i on the lighting device.

[0095] Furthermore, as discussed later regarding the conductive layer, the metallic mesh can also be adapted to perform a defrosting function, for example, when an electric current passes through it. This is particularly advantageous when the lighting device is exposed to variable weather conditions (rain, snow, ice).

[0096] As can be seen on the diagram, the lighting device 5 also includes the protective panel 20.

[0097] This protective panel 20 corresponds, for example, here to an exit lens of the lighting device of the motor vehicle 1. In practice, the protective panel 20 forms an outer layer of the lighting device 5, that is to say, a layer which is in direct contact with the external environment of the motor vehicle 1.

[0098] Whatever the intended use, the protective panel 20 is particularly suitable for protecting the radar antenna 100.

[0099] In the example shown, the protective panel 20 is positioned opposite the radar antenna 100. The protective panel 20 has a refractive index n1 on the wavelength scale λ r of the Δ1 range of wavelengths introduced previously.

[0100] Here, the protective panel 20 is in the form of a layer and comprises an outer face 21 and an inner face 22, opposite the outer face 21. The outer face 21 is here directly in contact with the external environment of the motor vehicle 1.

[0101] Advantageously, the protective panel 20 comprises a material transparent to wavelengths λ r R1 radar waves emitted by radar antenna 100 and transparent to the wavelength of a light beam L ioriginating from a lighting or signaling device. In other words, the protective panel 20 comprises a material transparent to radar waves and to a beam of light with a wavelength within the visible spectrum.

[0102] Here, the protective panel 20 comprises a polymer material. Preferably, this is polycarbonate (PC). Alternatively, the protective panel may comprise poly(methyl methacrylate) (PMMA). As another alternative, the protective panel may comprise polyurethane (PUR).

[0103] In order to comply with the sizing requirements associated with the integration of the lighting device 5 into the motor vehicle 1, a thickness e1 (i.e., a dimension along the Z-axis) of the protective panel 20 is less than 5 millimeters (mm). Preferably, this thickness e1 is between 300 µm and 4 mm.

[0104] The radar sensor 10 (and more specifically the radar antenna 100) emits the first radar waves R1, which propagate towards the protective panel 20. Due to the differences in refractive indices and the interfaces formed by the inner face 22 and the outer face 21 of the protective panel 20, the first radar waves R1 are partially reflected. The reflection of some of the first radar waves R1 by the inner face 22 of the protective panel 20 forms second reflected radar waves R22, which propagate towards the intermediate layer 30. Furthermore, the reflection of some of the first radar waves R1 by the outer face 21 of the protective panel 20 forms third reflected radar waves R21, which also propagate towards the intermediate layer 30.

[0105] Advantageously, according to the invention, the thickness e1 of the protective panel 20 is optimized so that the second reflected radar waves R22 and the third reflected radar waves R21 are out of phase. In other words, the thickness e1 of the protective panel 20 is determined here to produce destructive interference between the second reflected radar waves R22 and the third reflected radar waves R21.

[0106] In practice, the thickness e1 is chosen so as to introduce a phase shift of π / 2 between the second reflected radar waves R22 and the third reflected radar waves R21.

[0107] This condition for determining the thickness e1 of the protective panel 20 makes it possible to reduce or even eliminate the reflected radar waves R21, R22 on the protective panel 20, which would degrade the efficiency (and in particular the range) of the radar sensor 10. This optimization of the thickness e1 of the protective panel 20 improves the signal-to-noise ratio of the radar sensor 10 because the parasitic reflections are eliminated (or greatly reduced so that they do not reduce the signal-to-noise ratio associated with the radar sensor). The performance of the radar sensor 10 is therefore considerably improved.

[0108] As can be seen in the figure, the luminous device 5 also includes the intermediate layer 30. This intermediate layer 30 comprises a transparent, flexible material. As with the protective panel 20, the intermediate layer 30 is transparent to wavelengths λ rRadar waves R1 and R2 are emitted by radar antenna 100 and are transparent to the wavelength of a light beam from a lighting or signaling device. In this description, the term "flexible material" refers to a material that can deform (e.g., bend) without breaking or cracking. Due to this flexibility, the intermediate layer does not necessarily lie in a plane but can have a curved shape (depending on its position).

[0109] Preferably, the intermediate layer 30 comprises a polymer material. This is, for example, polyethylene terephthalate (PET). Alternatively, the intermediate layer 30 may comprise silicone.

[0110] In practice, the intermediate layer 30 is, for example, bonded to the protective panel 20. The adhesive used here is, for example, an optically clear adhesive (OCA, or "Optically Clear Adhesive," according to the commonly used Anglo-Saxon acronym). Alternatively, the intermediate layer 30 can be laminated to the protective panel 20.

[0111] As previously stated, this intermediate layer 30 includes the radar antenna 100. Here, the intermediate layer 30 forms, for example, a support substrate for the radar antenna 100 (in particular for a metallic mesh forming the radar antenna 100).

[0112] According to the example shown in Figure 1, the intermediate layer 30 comprises a first part 34 and a second part 35. The first part 34 and the second part 35 of the intermediate layer 30 are arranged to sandwich the radar antenna 100. The second part 35 of the intermediate layer 30 forms, for example, a support substrate for the radar antenna 100 (in particular for a metallic mesh forming the radar antenna 100). In other words, in this second example, the radar antenna 100 is encapsulated within the intermediate layer 30. This positioning example is particularly advantageous because it provides an assembly in which the radar antenna is protected from external elements (especially from impacts).

[0113] Here, the first part 34 of the intermediate layer 30 is positioned between the protective panel 20 and the radar antenna 100. In practice, the first part 34 of the intermediate layer 30 is, for example, glued to the protective panel 20. Alternatively, the first part 34 can be laminated onto the protective panel 20.

[0114] This example introduces a symmetry advantage in the structure of the light device 5, thereby optimizing the performance of the radar sensor 10 and the efficiency of the light device 5.

[0115] Alternatively (not shown), the radar antenna can be positioned on a first face 31 of the intermediate layer 30. In other words, in this variant, the radar antenna is positioned directly between the protective panel 20 and the intermediate layer 30.

[0116] In this case, the radar antenna 100 is, for example, glued to the first face 31 of the intermediate layer 30. Alternatively, the radar antenna 100 can be overmolded onto the first face 31 of the intermediate layer 30. This placement of the radar antenna 100 on the first face 31 of the intermediate layer 30 is particularly easy and inexpensive to implement.

[0117] Advantageously according to the invention, the lighting device 5 also includes the conductive layer 40. This conductive layer 40 is arranged in such a way that the intermediate layer 30 is positioned between the protective panel 20 and the conductive layer 40.

[0118] The conductive layer 40 is adapted here to form, in part, a ground plane of the radar sensor 10 (more specifically of the antennas 100, 101 included in the radar sensor 10). In other words, this conductive layer 40 forms, in part, a reflective surface for radar waves and has dimensions (of the elements forming this conductive layer 40) that are large compared to the wavelength λ r radar waves.

[0119] As shown in the diagram, the radar sensor 10 (and more specifically the radar antenna 100) emits the second radar waves R2, which propagate towards the conductive layer 40. Given the ground plane functionality formed by the conductive layer 40, the second radar waves R2 are partly reflected by a first face 41 of the conductive layer 40 so as to form other reflected radar waves R41, which propagate towards the intermediate layer 30.

[0120] The first face 41 of the conductive layer 40 is oriented towards the radar antenna 100. In other words, the first face 41 of the conductive layer 40 is the face of the conductive layer 40 that is closest to the radar antenna 100. The radar antenna 100 is positioned at a distance e2 from the first face 41 of the conductive layer 40. According to the example shown in Figure 1, the distance e2 corresponds to the thickness of the second part 35 of the intermediate layer 30. Alternatively (not shown), if the radar antenna is positioned on the first face 31 of the intermediate layer 30, the distance e2 corresponds to the thickness of the intermediate layer 30.

[0121] Advantageously, according to the invention, this distance e2 is optimized so that the first radar waves R1 and the other reflected radar waves R41 are in phase. In other words, the distance e2 between the radar antenna 100 and the conductive layer 40 is determined here so as to obtain constructive interference between the first radar waves R1 and the other reflected radar waves R41.

[0122] In practice, the distance e2 is chosen so as to introduce a phase shift of π between the first radar waves R1 and the other reflected radar waves R41.

[0123] This condition for determining the distance e2 between the radar sensor 10 and the conductive layer 40 then makes it possible to optimize the transmission of radar waves in the light device 5. This optimization of the distance e2 between the radar antenna 100 and the conductive layer 40 also makes it possible to improve the signal-to-noise ratio of the radar sensor 10 and therefore the performance of the radar sensor 10.

[0124] In practice, to obtain this condition of constructive interference, the distance e2 is proportional to one quarter of the wavelength λ r radar waves R1, R2 emitted by radar antenna 100 or at half this wavelength λ r .

[0125] For radar frequencies, for example between 76 and 81 GHz (corresponding to a wavelength λ rradar waves R1, R2 between 3.7 and 4 mm), the distance e2 is on the order of a few millimeters, more particularly between 0.9 and 4 mm for refractive indices n2 of the intermediate layer 30 between 1.4 and 1.95 (the radar antenna 100 being overmolded or encapsulated in this intermediate layer 30).

[0126] The conductive layer 40 has a thickness of a few micrometers. Preferably, this thickness is less than 5 µm. Even more preferably, the thickness of the conductive layer 40 is between 200 nm and 2 µm. Generally, the intermediate layer 30 is thick enough to withstand the mechanical stresses that the lighting device 5 might experience. It is also thin enough to retain its supple and flexible nature. Its thickness is therefore determined by satisfying this compromise.

[0127] In practice, the conductive layer 40 comprises a material transparent to the wavelength of a light beam from a lighting or signaling device. For example, the conductive layer 40 comprises a material transparent to wavelengths in the visible spectrum while retaining its conductive character.

[0128] Advantageously, according to the present invention, the conductive layer 40 comprises a first portion 44 and a second portion 45. The first portion 44 of the conductive layer 40 is positioned opposite the radar antenna 100. The second portion 45 of the conductive layer 40 surrounds the first portion 44. In other words, the second portion 45 of the conductive layer 40 is positioned around the radar antenna 100.

[0129] In practice, the distinction between the first part 44 and the second part 45 of the conductive layer 40 is based on a difference in surface resistance (or "sheet resistance" according to the commonly used Anglo-Saxon term) between these two parts.

[0130] More specifically, in order to ensure the ground plane function for the radar antenna 100, the surface resistance of the first part 44 of the conductive layer 40 is greater than the surface resistance of the second part 45 of the conductive layer 40.

[0131] This difference in surface resistance between the two parts of the conductive layer 40 ensures that, with respect to the antenna, the conductive layer 40 behaves as a ground plane, but that outside this area, with respect to the radar antenna, the conductive layer 40 can behave as a heating element. In other words, the formation of the conductive layer in two parts with different surface resistances (and with a difference of an order of magnitude) allows the two functions (ground plane and heating) to be decoupled, while still enabling them to be implemented within the same conductive layer.

[0132] This is particularly advantageous because the proper functioning of the radar antenna 100 is guaranteed (the potential difference necessary to generate the radar waves is obtained thanks to the first part of the conductive layer), and at the same time, the efficiency of the radar sensor is also guaranteed because the second part of the conductive layer protects the sensor from the elements. Indeed, thanks to the heating function of the second part of the conductive layer, water droplets from rain, fog, snow, or frost do not interfere with the proper functioning of the radar sensor. The second part of the conductive layer thus acts as a heat diffuser.

[0133] Preferably, the surface resistance of the second part 45 of the conductive layer 40 is at least four times smaller, more preferably ten times smaller than the surface resistance of the first part 44 of the conductive layer 40.

[0134] Thanks to the two-part conductive layer according to the present invention, the radar (with the generation of radar waves) and heating functions can be implemented simultaneously in the lighting device.

[0135] In particular, the first part 44 and the second part 45 of the conductive layer 40 are not electrically connected. In other words, the first part 44 and the second part 45 of the conductive layer 40 are electrically driven independently.

[0136] For example, when radar antenna 100 is in operation, only the second part 45 has a heating function (so as to heat around the radar antenna but not opposite it).

[0137] In defrost mode, the radar antenna 100 is switched off while an electric current flows through the first section 44 and the second section 45 of the conductive layer 40 to activate the heating function. Thus, when the vehicle is started in defrost mode, both sections 44 and 45 are activated. The proximity of the conductive layer 40 to the protective element 20 ensures low thermal resistance, enabling more efficient and rapid defrosting, on the order of a few minutes. Then, when the radar function is activated, the activation of the second section 45 prevents the exposed face of the stack from frosting again while the vehicle is in motion or simply from exposure to the elements, including in front of the radar antenna 100, due to the thermal continuity of the layers and sections 44 and 45.

[0138] In practice, each of the first part 44 and the second part 45 of the conductive layer 40 includes, for example, indium tin oxide (or ITO for "Indium tin oxide" according to the Anglo-Saxon original name).

[0139] According to a preferred variant, each of the first part 44 and the second part 45 of the conductive layer 40 comprises a metallic mesh. The metallic mesh of the first part 44 of the conductive layer 40 is thus different from the metallic mesh of the second part 45 of the conductive layer 40. This difference is observed in terms of both the mesh spacing and the mesh pattern. This implementation is advantageous because the same deposition technology is used and allows for the achievement of two different functions: ground plane and heating. Furthermore, this embodiment is particularly easy to implement and inexpensive.

[0140] In practice, the metallic mesh of the first part 44 of the conductive layer 40 is made parallel to a direction of polarization of the radar wave (so as to be able to reflect this radar wave).

[0141] In this case, and in order to respect the constraint on the surface resistance, the mesh size of the first part 44 of the conductive layer 40 is less than the mesh size of the second part 45 of the conductive layer 40.

[0142] In practice, the first part 44 of the conductive layer 40 comprises, for example, a first metallic mesh. The second part 45 of the conductive layer 40 comprises, for example, a second metallic mesh. In what follows, the characteristics of the first and second metallic meshes are described together for the sake of brevity, but it should be noted that they can be considered separately (i.e., the characteristics of the first metallic mesh on the one hand and those of the second metallic mesh on the other).

[0143] This first metallic mesh and this second metallic mesh are, for example, formed in the XY plane (orthogonal to the horizontal plane of the motor vehicle 1). Advantageously, the first metallic mesh and the second metallic mesh are made parallel to a direction of polarization of the radar wave.

[0144] The length of the first metal mesh, along the X direction, is on the order of a few centimeters. For example, this length is at least greater than the length of the radar antenna 100. The length of the second metal mesh, along the X direction, is on the order of a few centimeters. For example, this length is at least greater than the length of the radar antenna 100.

[0145] It should be noted that the length of the first metal mesh and the length of the second metal mesh are not necessarily identical.

[0146] As with the previously described 100 radar antenna, the first and second metal meshes are visible. Each also comprises metal strips arranged to form a metal grid. In the case where a regular metal grid is formed, the first and second metal meshes exhibit characteristics similar to those described for the 100 radar antenna previously (they are therefore not described in detail again here).

[0147] Essentially, the metal strips of this first and second metal meshes are, for example, micrometric, meaning they have a mesh size of one micrometer. Preferably, the mesh size of the metal mesh of radar antenna 100 is smaller than the mesh size of the first metal mesh of the first part 44 and the mesh size of the second metal mesh of the second part 45 of the conductive layer 40. This simplifies the fabrication of this first and second metal meshes (since the conductive layer 40 has fewer constraints to meet than the radar antenna 100).

[0148] The width, in the XY plane, of each metal strip in the first and second metal meshes is on the order of tens to hundreds of nanometers. Each metal strip in the first and second metal meshes has a thickness (along the Z-axis) ranging from a few nanometers to a few micrometers. This thickness depends in practice on the manufacturing process used to produce the first and second metal meshes. Preferably, this thickness is less than 20 micrometers (µm). Even more preferably, this thickness is less than 10 µm, or even less than 8 µm. These thickness values ​​are easily obtained by screen printing. This process is particularly inexpensive and straightforward to implement.

[0149] In the context of the present invention, the thickness of each metal strip in the first and second metal meshes is between 200 nm and 2 µm. These thickness values ​​are obtained, for example, by lithography. This makes it possible to obtain very thin strips for each metal strip in the first and second metal meshes, ensuring the transparency of the lighting device according to the invention.

[0150] The first and second metal meshes include, for example, copper. Alternatively, they may include silver, platinum, aluminum, or nickel. In practice, the metal strips are formed, for example, by nanolithography.

[0151] In practice, the first and second metal meshes are formed, for example, by cutting from a sheet containing the metal strips. Alternatively, the metal strips can be selectively deposited to form the second metal mesh. Another alternative is to create the metal strips by engraving the different metal patterns side by side.

[0152] Alternatively, for the conductive layer 40, whose key characteristic is to form a ground plane for the radar antenna 100 (and thus a reflective surface for radar waves R1, R2), the first and second metallic meshes can be irregular. In other words, the metallic strips can have random shapes. Put another way, no pattern period is observed in this irregular structure. The use of this irregular structure avoids diffraction phenomena for the light beam from the signaling and / or lighting device.

[0153] Thus, the use of the conductive layer 40 optimizes the transmission of radar waves in the light device 5, thereby improving the performance of the radar sensor 10. Furthermore, this conductive layer 40, thanks to the presence of the first part 44, forms a ground plane for the radar sensor 10 (and more specifically for the antennas 100, 101), which is necessary for the proper functioning of this radar sensor 10 (in particular, creating a potential difference that generates the radar waves). Moreover, the conductive layer 40 also has the advantage, thanks to the presence of the second part 45, of acting as a heating element directly integrated into the light device 5.This is particularly advantageous because, in addition to improving the performance of the radar sensor by positioning the first part 44 of the conductive layer 40 relative to this radar sensor 10, the conductive layer (through its second part 45) acts as a heating element which will prevent the deposition of water or frost in front of the radar sensor (these deposits altering the detection functionalities of the radar sensor because the water droplets also disrupt the radar sensor, the water partially absorbing the radar waves used for detection).

[0154] Alternatively, the second part 45 may comprise carbon nanotubes to provide the desired heating function. Alternatively still, the second part 45 of the conductive layer 40 may comprise graphene.

[0155] Alternatively, the first part 44 and the second part 45 of the conductive layer 40 may be formed differently. For example, the first part 44 of the conductive layer 40 may comprise a metallic mesh (here the first metallic mesh described previously) while the second part 45 of the conductive layer 40 may comprise indium tin oxide, carbon nanotubes, or graphene.

[0156] Lare represents a cross-sectional view of a lighting device 6 according to a second embodiment of the invention

[0157] In this second embodiment, the lighting device 6 also includes a thermally conductive layer 60, positioned on a second face 42 of the conductive layer 40 (i.e., on the face of the conductive layer 40 furthest from the radar antenna 100). In other words, the thermally conductive layer 60 is positioned such that the conductive layer 40 is placed between the intermediate layer 30 and the thermally conductive layer 60.

[0158] This thermally conductive layer 60 improves the homogeneity of the heating effects from the conductive layer 40. In particular, this thermally conductive layer 60 will allow better diffusion of heat from the second part 45 to the first part 44.

[0159] In practice, this thermally conductive layer comprises indium tin oxide. Alternatively, the thermally conductive layer may comprise carbon nanotubes. As a further alternative, this thermally conductive layer may comprise graphene.

[0160] Furthermore, in order to ensure transparency properties for the lighting device, the thermally conductive layer 60 comprises a material transparent to the wavelength of a light beam L i originating from a lighting or signaling device. In other words, the thermally conductive layer 60 comprises a material transparent to a beam of light with a wavelength within the visible spectrum.

[0161] In the case of a thermally conductive layer comprising indium tin oxide, a light transmission rate for the visible spectrum is greater than 85%, guaranteeing the transparency properties mentioned previously.

[0162] The thermally conductive layer 60 has a thickness on the order of a few hundred micrometers. For example, this thickness is between 40 and 200 µm.

[0163] In practice, the thermally conductive layer 60 is, for example, bonded to the conductive layer 40. The adhesive used here is, for example, an optically transparent adhesive (or OCA). Alternatively, the thermally conductive layer 60 can be laminated onto the conductive layer 40.

[0164] Figure 1 represents a cross-sectional view of a lighting device 7 according to a third embodiment of the invention.

[0165] In this third embodiment, the lighting device 7 also includes another protective panel 50. The conductive layer 40 is here situated between the intermediate layer 30 and the other protective panel 50.

[0166] This additional protective panel 50 is introduced here to provide structural symmetry to the lighting device 7. This structural symmetry provides stability to the lighting device, thus ensuring efficient operation.

[0167] For this reason, the other protective panel 50 has similar structural characteristics to the protective panel described previously. In particular, the other protective panel 50 has a similar thickness to that of the protective panel 20. By "similar," it is understood here that a difference of less than 5% can be observed between the thickness of the other protective panel and the thickness of the protective panel.

[0168] In order to comply with the dimensioning requirements associated with the integration of the lighting device 7 into the motor vehicle 1, the thickness of the other protective panel 50 is less than 5 mm. Preferably, this thickness is between 1.8 and 4 mm.

[0169] Here, the other protective panel 50 comprises a polymer material. Preferably, this is polycarbonate (PC). Alternatively, the other protective panel may comprise poly(methyl methacrylate) (PMMA). As a further alternative, the other protective panel may comprise polyurethane (PUR).

[0170] Advantageously, the other protective panel 50 comprises a material transparent to the wavelength of a light beam from a lighting or signaling device. This material need not be transparent to wavelengths λ rradar waves emitted by radar sensor 10 since these radar waves do not propagate through this other protective panel 50.

[0171] Although not shown on the diagram, the lighting device 6 shown on the diagram may of course include such another protective panel.

[0172] Thus, optionally (not shown) in this third embodiment, the lighting device may also include the thermally conductive layer. This thermally conductive layer is positioned here between the conductive layer 40 and the other protective panel 50.

[0173] Regardless of the specific embodiment considered, the lighting device 5, 6, or 7 is integrated into automotive equipment. It includes, in particular, a lighting module configured to perform lighting or signaling functions for the motor vehicle 1. It thus enables the vehicle to fulfill a lighting, signaling, or aesthetic function, simultaneously with an antenna function for a radar application.

[0174] In order to effectively implement the lighting or signaling functions of the motor vehicle 1, the lighting system also includes a light source (not shown) and at least one optical element (not shown in the figures). The light source is configured to emit the light beam L i enabling the implementation of lighting and / or signaling functions.

[0175] The optical element is adapted to direct the light beam Li emitted by the light source through the stack of the light device 5; 6; 7. More specifically, the optical element is arranged so that it directs the light beam L i in such a way that the latter propagates from the conductive layer 40 to the protective panel 20.

[0176] An optical element is, for example, an optical lens, a light guide, a diffuser, or a reflector.

[0177] In practice, as can be seen in the figure, the light device 5; 6; 7 according to the invention can be arranged in front of the lighting device 3 and / or in front of the signaling device 2 and / or in front of the lidar 4.

Claims

A lighting device (5; 6; 7) for a motor vehicle (1), said lighting device (5; 6; 7) comprising a stack of contiguous elements including: - a protective panel (20), - an intermediate layer (30) comprising at least one radar antenna (100) of a radar sensor (10) configured to emit associated radar waves (R1, R2), the first radar waves (R1) emitted by the radar antenna (100) propagating towards the protective panel (20), the second radar waves (R2) emitted by the radar antenna (100) propagating towards a conductive layer (40), and - the conductive layer (40) adapted to partially form a ground plane for the radar antenna (100), the intermediate layer (30) being positioned between the protective panel (20) and the conductive layer (40), the conductive layer (40) comprising a first part (44) and a second part (45), the first part (44) of the conducting part (40) being positioned opposite the radar antenna (100). Light device (5; 6; 7) according to claim 1, wherein the first part (44) of the conductive layer (40) has a surface resistance greater than another surface resistance of the second part (45) of the conductive layer (40). Light device (5; 6; 7) according to claim 1 or 2, wherein the first part (44) of the conductive layer (40) comprises a first metallic mesh. Light device (5; 6; 7) according to any one of claims 1 to 3, wherein the second part (45) of the conductive layer (40) comprises indium tin oxide. Light device (5; 6; 7) according to any one of claims 1 to 3, wherein the second part (45) of the conductive layer (40) comprises a second metallic mesh. Light device (5; 6; 7) according to any one of claims 1 to 3, wherein the second part (45) of the conductive layer (40) comprises carbon nanotubes. Light device (6) according to any one of claims 1 to 6, also comprising a thermally conductive layer (60) positioned such that the conductive layer (40) is placed between the intermediate layer (30) and the thermally conductive layer (60). Light device (6) according to claim 7, wherein the thermally conductive layer (60) comprises indium tin oxide. Light-emitting device (6) according to claim 7, wherein the thermally conductive layer (60) comprises carbon nanotubes. Lighting device (5; 6; 7) according to any one of claims 1 to 9, wherein the protective panel (20) forming an external window of the motor vehicle (1), the lighting device (5; 6; 7) also includes a lighting module configured to implement lighting functions or signaling functions of the motor vehicle (1).

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