Lighting device for a motor vehicle including a radar sensor

Abstract

The invention relates to a lighting device (5) for a motor vehicle, said lighting device comprising a stack including: - a protective panel (20), - an intermediate layer (30) including at least one radar antenna (100) configured to emit radar waves (R1, R2), the first radar waves emitted by the radar antenna propagating towards the protective panel, the second radar waves emitted by the radar antenna propagating towards a conductive layer (40), - the conductive layer adapted to form in part a ground plane of the radar antenna, the intermediate layer being positioned between the protective panel and the conductive layer, the radar antenna including a metallic mesh comprising a repeating pattern with a predefined mesh pitch, the mesh pitch being determined so as to prevent diffraction phenomena during the propagation of a light beam through the lighting device.Figure to be published with the abbreviation: Figure 2.

Description

Title of the invention: Lighting device for a motor vehicle comprising 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 are now equipped with advanced driver assistance systems (or ADAS for "Advanced Driver Assistance Systems," according to the commonly used Anglo-Saxon acronym). These driver assistance systems are, for example, safety and driver assistance systems designed to help avoid 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, in particular, at least one radar sensor capable of emitting radar waves.

[0005] It is known, in particular, to integrate the radar sensor 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. In particular, optical phenomena such as reflection and diffraction must be avoided for the propagation of light beams used to implement the lighting or signaling functions. Summary of the invention

[0006] The present invention then proposes to improve the integration of a radar sensor in 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.

[0007] One aspect of the invention thus relates to a lighting device for a motor vehicle, said lighting device comprising a stack including:

[0008] - a protective panel,

[0009] - an intermediate layer comprising at least one radar antenna of a sensor radar configured to emit associated radar waves, with the first radar waves emitted by the radar antenna propagating towards the protective panel, the second radar waves emitted by the radar antenna propagating towards a conductive layer, and

[0010] - the conductive layer adapted to partially form a ground plane of the antenna radar (100), the intermediate layer being positioned between the protective panel (20) and the conductive layer,

[0011] the radar antenna comprising a metallic mesh including a repeated pattern with a predefined mesh pitch, the mesh pitch being determined so as to prevent diffraction phenomena during the propagation of a light beam through the light device.

[0012] Thus, advantageously according to the invention, the mesh size of the metallic mesh of the radar antenna is chosen so as to limit or even completely eliminate higher orders of diffraction. More particularly, the mesh size is advantageously determined so as to allow only 0th-order propagation (in order to avoid observing diffraction phenomena after the propagation, for example, of a light beam through the radar antenna in the form of the metallic mesh).

[0013] Furthermore, the use of the conductive layer optimizes the transmission of radar waves in the light-emitting device, thereby improving the performance of the radar sensor. Moreover, this conductive layer forms a ground plane for the radar sensor (and more specifically for the antennas), which is necessary for the proper functioning of this radar sensor (in particular, by creating a potential difference that generates the radar waves).

[0014] 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:

[0015] - the mesh size of the metallic mesh is less than a value depending of a wavelength of the light beam, of a refractive index of the intermediate layer, of a refractive index of the conducting layer and of an angle of incidence of the light beam at the level of the intermediate layer;

[0016] - the mesh size of the metallic mesh is less than 500 nanometers;

[0017] - an angle of incidence of the light beam at the level of the intermediate layer is less than 60 degrees;

[0018] - the intermediate layer has a refractive index of less than 2, preferably between 1.4 and 1.95;

[0019] - the protective panel is provided with an outer face and an opposite inner face On the outer face, the first radar waves are partially reflected by the outer face of the protective panel to form second reflected radar waves; the first radar waves are partially reflected by the inner face of the protective panel to form third reflected radar waves; the panel of protection having a determined thickness such that the second reflected radar waves and the third reflected radar waves are in opposite phase;

[0020] - the thickness of the protective panel is less than 5 millimeters;

[0021] - the conductive layer comprises indium tin oxide;

[0022] - the conductive layer comprises another metallic mesh;

[0023] - one pitch of the metallic mesh of the radar antenna is smaller than another pitch of the other metallic mesh of the conductive layer;

[0024] - the radar antenna is overmolded in the intermediate layer;

[0025] - the radar antenna is encapsulated in the intermediate layer;

[0026] - the intermediate layer comprises a flexible transparent material;

[0027] - the protective panel comprises a transparent polymer material;

[0028] - the lighting device also includes another protective panel, the conductive layer being positioned between the intermediate layer and the other protective panel;

[0029] - the other protective panel has the same thickness as the panel of protection;

[0030] - the other protective panel comprises a polymer material;

[0031] - the protective panel forming an external window of the motor vehicle, the The lighting device also includes a lighting module configured to implement lighting or signaling functions for the motor vehicle; and

[0032] - the lighting device also includes a light source and at least an 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 light device. BRIEF DESCRIPTION OF THE FIGURES

[0033] 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.

[0034] [Fig. 1] Fig. 1 represents a partial schematic view of a motor vehicle within the scope of the present invention,

[0035] [Fig.2] Fig.2 represents a schematic cross-sectional view of a first example for the creation of a lighting device for a motor vehicle according to the invention,

[0036] [Fig.3] Fig.3 represents a schematic view in functional form of a radar sensor included in the lighting device according to the invention,

[0037] [Fig.4] Fig.4 represents a schematic view of a radar antenna included in the radar sensor of [Fig.3],

[0038] [Fig. 5] Fig. 5 represents a schematic cross-sectional view of the radar antenna represented in [Fig.4], according to a section plane AA,

[0039] [Fig. 6] Fig. 6 represents a schematic cross-sectional view of a second example of the implementation of the lighting device according to the invention,

[0040] [Fig. 7] Fig. 7 represents a schematic cross-sectional view of a third example of the implementation of the lighting device according to the invention,

[0041] [Fig.8] Fig.8 represents a schematic cross-sectional view of a fourth embodiment of the lighting device according to the invention, and

[0042] [Fig.9] Fig.9 represents a schematic cross-sectional view of a fifth example of the realization of the lighting device according to the invention.

[0043] For clarity, identical or similar elements are identified by identical reference symbols throughout the figures. DETAILED DESCRIPTION

[0044] The present invention aims to provide a lighting device for a motor vehicle (referred to as the "lighting device" in the remainder of this description) comprising a radar sensor enabling efficient propagation of radar waves. More specifically, the lighting device has a structure that improves the integration of radar antennas within a radar sensor, in particular to avoid multiple reflections that could occur and degrade the performance of the radar sensor.

[0045] Figure 1 shows 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" means any type of motorized vehicle. Hereafter, the terms "vehicle" and "motor vehicle" are used to describe the vehicle relevant to the present invention.

[0046] In a conventional manner, 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 more detail in the following.

[0047] As can be seen in [Fig. 1], a forward direction Z of movement of vehicle 1 is defined. This direction Z 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.

[0048] As shown in [Fig. 1], the motor vehicle 1 also includes a lighting device 5; 6; 7; 8; 9. This lighting device 5; 6; 7; 8; 9 is more particularly represented in [Fig.2]. This lighting device is for example a headlight or a rear light of motor vehicle 1.

[0049] The lighting device 5; 6; 7; 8; 9 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; 8; 9 comprises a stack of 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; 8; 9 according to the invention are bonded together.

[0050] The overall thickness of the stack formed 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.

[0051] The radar sensor 10 is configured to emit and receive RI, R2 radar waves.

[0052] In practice, the radar sensor 10 is a millimeter-wave radar sensor (with frequencies between 24 Gigahertz (GHz) and 300 GHz). Alternatively, the radar sensor is a microwave radar sensor (with frequencies between 300 Megahertz (MHz) and 81 GHz). As a further alternative, the radar sensor is a microwave radar sensor (between 1 GHz and 300 GHz).

[0053] Preferably in the present invention, the radar sensor 10 operates at a radar frequency between 76 GHz and 81 GHz. The RI radar waves 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 RI radar waves are therefore emitted over the frequency range of 76.5 GHz to 77.5 GHz, corresponding to a wavelength range I1 of between 3.87 millimeters (mm) and 3.92 mm.

[0054] 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 on a frequency band from 76 GHz to 81 GHz. In this case, the RI radar waves are thus emitted on the frequency range of 76 GHz to 81 GHz, corresponding to a wavelength range IA of wavelengths between 3.701 mm and 3.945 mm.

[0055] The radar sensor 10 is configured to scan the external environment of the motor vehicle 1, by means of the emission of radar waves RI, R2.

[0056] For this purpose, as shown in [Fig. 3], the radar sensor 10 comprises:

[0057] - at least one transmitting antenna 100 configured to emit first waves RI radar and second-wave R2 radar, and

[0058] - 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.

[0059] In practice, the radar sensor 10 also includes at least one transmitter 103 configured to generate the RI, R2 radar waves. It also includes at least one receiver 104 configured to process the radar waves received in return.

[0060] In one embodiment, a single electronic component can be used to implement both the transmission and reception functions. The lighting device then comprises one or more transmitter / receivers (also called "transceivers" according to the commonly used Anglo-Saxon term).

[0061] In practice, the transmitter 103 generates radar waves RI, 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 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.

[0062] In one embodiment, the radar waves RI, R2 and the radar waves received in return are radio frequency waves.

[0063] Alternatively (not shown), the radar sensor may comprise a plurality of transmitters and a plurality of receivers.

[0064] In practice, the transmitting antenna 100 (also referred to as the radar antenna 100 in this description) is configured to transmit the radar waves RI, 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.

[0065] In practice here, the antennas 100, 101 are offset from the other elements of the radar sensor 10 (shown in dotted lines in [Fig. 2] to illustrate this "offset" characteristic). The transmitter 103 and the receiver 104 are then arranged on a printed circuit board 105. The printed circuit board 105 is then connected to the antennas 100, 101 but positioned at a distance from these antennas 100, 101 (the antennas 100, 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 may be a flexible printed circuit board (or "Flexboard" according to the commonly used Anglo-Saxon terminology).

[0066] The radar sensor 10 further includes an electronic control unit 106 configured to control the transmitter 103 and the receiver 104.

[0067] In practice, antennas 100, 101 are, for example, so-called "patch antennas" (or "patch antennas" according to the commonly used Anglo-Saxon terminology). Alternatively, the antennas may be so-called "slot antennas" (or "slot antennas" according to the commonly used Anglo-Saxon terminology).

[0068] Preferably, the antennas 100 and 101 are in the form of a metallic mesh. The radar antenna 100 (transmitting) is described in more detail in the following description, but the principles presented also apply to the antenna 101 (receiving).

[0069] Figure 4 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.

[0070] Advantageously, the radar antenna 100 is made so as to obtain a horizontal polarization direction of the wave (i.e. in the horizontal plane of the motor vehicle 1).

[0071] As can be seen in [Fig. 4], the radar antenna 100 here has an overall zigzag shape. This overall shape optimizes the antenna's performance. Alternatively, any other shape may be used.

[0072] 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.

[0073] 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.

[0074] Advantageously, these metallic strips 110 are micrometric, that is, they form metallic patterns of micrometric dimensions. In other words, by defining a mesh size d (visible in [Fig. 5]), that is, a 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 metallic grid formed is barely visible to the naked eye. Moreover, such a structure makes it possible to obtain very good performance of the radar antenna 100. In addition, 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, not too small, facilitate the manufacture of the radar antenna 100.

[0075] Preferably, the width b (visible in [Fig. 5]), 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 (pm). Even more preferably, this thickness is less than 10 pm, or even less than 8 pm. These thickness values ​​are particularly easy to obtain by screen printing. This process is notably inexpensive and simple to implement.

[0076] Within the scope of the present invention, the thickness of each metal strip 110 can also be between 200 nm and 5 pm, for example, between 200 nm and 2 pm. 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; 8; 9 described below.

[0077] The metallic mesh includes, for example, copper. Alternatively, it may include silver, platinum, aluminum, or nickel. In practice, the metallic strips are formed, for example, by nanolithography.

[0078] In practice, the radar antenna 100 is, for example, formed by cutting, here in a zigzag shape, from a plate comprising 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.

[0079] As can be seen in particular in [Fig. 1], the lighting device 5; 6; 7; 8; 9 is intended to be positioned in the path of a light beam coming, for example, from a lighting device. However, given the regular pattern of the metallic mesh forming the radar antenna 100 and the dimensions of the metallic mesh, this metallic mesh forms a diffraction grating for the light beam passing through the radar antenna 100.

[0080] In order to limit or even completely eliminate higher orders of diffraction, the mesh pitch d is advantageously chosen in the present invention. More particularly, the mesh pitch 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 through the radar antenna 100 in the form of the metallic mesh). In other words, the pitch mesh size d is predefined and determined in such a way as to prevent diffraction phenomena during the propagation of a light beam L; through the light device 5.

[0081] Fig. 5 represents a cross-sectional view of the radar antenna 100 shown in Fig. 4, along a section plane AA.

[0082] 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: db + a.

[0083] 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. The refractive index n2 of the intermediate layer 30 is less than 2. 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).

[0084] It is noted here that the light beam L; 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 noted 0;. It should be noted here that the first medium corresponds, for example, in the case of [Fig.2], to the conductive layer 40.

[0085] In practice, by arrangement of the different elements (lighting device, luminous device 5; 6; 7; 8; 9) in the motor vehicle 1, this angle of incidence 0; is, in absolute value, less than 60 degrees (°).

[0086] Thus, by application of the classical formula for transmission gratings, and in order to obtain only 0th order propagation (therefore no diffraction phenomena), the mesh size d must satisfy the following inequality (X here corresponds to the wavelength of the light beam L):

[0087]

[0088] In other words, the mesh size d is less than a value depending on the wavelength X of the light beam L;, 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 0; of the light beam L; at the level of the intermediate layer 30.

[0089] In practice in the present invention, the mesh pitch 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; (corresponding to a wavelength of the visible spectrum).

[0090] For example, considering a light beam L; 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).

[0091] 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 on the intermediate layer. The resulting expression would then be combined with the classical formula for transmission gratings 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 X of the light beam L, the refractive indices of the different layers passed through, and the angle of incidence of the light beam L on the light device.

[0092] Furthermore, and as discussed later with regard to 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).

[0093] As can be seen in [Fig.2], the light device 5 also includes the protective panel 20.

[0094] 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.

[0095] Whatever the use considered, the protective panel 20 is particularly suitable for protecting the radar antenna 100.

[0096] In the example shown in [Fig.2], the protective panel 20 is positioned opposite the radar antenna 100. The protective panel 20 has a refractive index ni on the wavelength scale / ., of the range Al of wavelengths introduced previously.

[0097] 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.

[0098] Advantageously, the protective panel 20 comprises a material transparent to wavelengths I, of radar waves RI emitted by the radar antenna 100 and transparent to the wavelength of a light beam L from a lighting or signaling device. In other words, the protective panel 20 comprises a material transparent to radar waves and to a light beam with a wavelength in the visible spectrum.

[0099] Here, the protective panel 20 comprises a polymer material. Preferably, this is polycarbonate (PC). Alternatively, the protective panel may comprise poly(methyl methacrylate) (PMMA). Alternatively still, the protective panel may comprise polyurethane (PUR).

[0100] In order to comply with the dimensioning requirements associated with the integration of the lighting device 5 into the motor vehicle 1, a thickness ei (i.e., a dimension along the Z-axis) of the protective panel 20 is less than 5 millimeters (mm). Preferably, this thickness ei is between 300 µm and 4 mm.

[0101] The radar sensor 10 (and more specifically the radar antenna 100) emits the first RI radar waves, 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 RI radar waves are partially reflected. The reflection of some of the first RI radar waves 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 RI radar waves by the outer face 21 of the protective panel 20 forms third reflected radar waves R21, which also propagate towards the intermediate layer 30.

[0102] Advantageously, according to the invention, the thickness ei 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 ei of the protective panel 20 is determined here so as to obtain destructive interference between the second reflected radar waves R22 and the third reflected radar waves R21.

[0103] In practice, the thickness ei is chosen so as to introduce a phase shift of ir / 2 between the second reflected radar waves R22 and the third reflected radar waves R21.

[0104] This condition for determining the thickness ei 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 ei 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.

[0105] As can be seen in [Fig. 2], the lighting 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 I, R2, of the radar waves emitted by the radar antenna 100 and 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 has the ability to deform (for example, to bend) without breaking or cracking. Thanks to this flexibility, the intermediate layer is not necessarily flat but can have a curved shape (depending on its position).

[0106] Preferably, the intermediate layer 30 comprises a polymer material. This is, for example, polyethylene terephthalate (PET). Alternatively, the intermediate layer 30 may comprise silicone.

[0107] 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 (or OCA for "Optically Clear Adhesive," according to the commonly used Anglo-Saxon acronym). Alternatively, the intermediate layer 30 can be laminated to the protective panel 20.

[0108] 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).

[0109] According to a first example shown in [Fig.2], the radar antenna 100 is positioned on a first face 31 of the intermediate layer 30. In other words, in this first example, the radar antenna 100 is positioned directly between the protective panel 20 and the intermediate layer 30.

[0110] In this case, the radar antenna 100 is, for example, bonded 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 mounting of the radar antenna 100 on the first face 31 of the intermediate layer 30 is particularly easy and inexpensive to implement.

[0111] According to a second example shown in Figures 6, 7, and 8, 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 so as 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 (in particular from impacts).

[0112] 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.

[0113] This second example introduces a symmetry advantage in the structure of the light device 6; 7; 8, thereby optimizing the performance of the radar sensor 10 and the efficiency of the light device 6; 7; 8.

[0114] Advantageously according to the invention, the lighting device 5; 6; 7; 8; 9 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.

[0115] The conductive layer 40 is here adapted to form a ground plane of the radar sensor 10 (more particularly of the antennas 100, 101 included in the radar sensor 10). In other words, this conductive layer 40 forms a reflective surface for radar waves and has dimensions (of the elements forming this conductive layer 40) large compared to the wavelength λ of the radar waves.

[0116] As shown in Figures 2, 6 and 7, the radar sensor 10 (and more particularly 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.

[0117] The first face 41 of the conductive layer 40 is turned 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 first example shown in [Fig.2], the distance e2 corresponds to the thickness of the intermediate layer 30. In the case of the second example shown in Figures 6, 7 and 8, the distance e2 corresponds to the thickness of the second part 35 of the intermediate layer 30.

[0118] Advantageously, according to the invention, this distance e2 is optimized so that the first RI radar waves 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 RI radar waves and the other reflected radar waves R41.

[0119] In practice, the distance e2 is chosen so as to introduce a phase shift of ir between the first radar waves RI and the other reflected radar waves R41.

[0120] 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; 6; 7; 8; 9. 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.

[0121] In practice, in order to obtain this condition of constructive interference, the distance e2 is proportional to a quarter of the wavelength / ., of the radar waves RI, R2 emitted by the radar antenna 100 or to half of this wavelength Xr.

[0122] For radar frequencies, for example, between 76 and 81 GHz (corresponding to a wavelength of RI, R2 radar waves 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).

[0123] The conductive layer 40 has a thickness of a few micrometers. Preferably, this thickness is less than 5 pm. Even more preferably, the thickness of the conductive layer 40 is between 200 nm and 2 pm. Generally, the intermediate layer 30 is thick enough to withstand the mechanical stresses that the lighting device 5, 6, 7, 8, 9 might experience. It is also thin enough to retain its supple and flexible nature. Its thickness is therefore determined by satisfying this compromise.

[0124] 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.

[0125] In a first embodiment of the conductive layer 40, the latter comprises indium tin oxide (or ITO for "Indium tin oxide" according to the original Anglo-Saxon name). In this example, the conductive layer 40 is then formed as a single block.

[0126] In a second embodiment of the conductive layer 40, shown for example in [Fig. 7] (which represents a third embodiment of the lighting device 7), the conductive layer 40 comprises another metallic mesh 40a. This other metallic mesh 40a is, for example, formed in the XY plane (orthogonal to the horizontal plane of the motor vehicle 1). Advantageously, the other metallic mesh 40a is formed parallel to a direction of radar polarization. As can be seen in [Fig. 7], the conductive layer 40 here comprises a substrate 40b forming a support for the other metallic mesh 40a.

[0127] The length of the other metallic mesh 40a, 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.

[0128] As in the case of the radar antenna 100 described previously, this other metallic mesh 40a is visible. It also comprises metallic strips arranged to form a metallic grid. In the case where a regular metallic grid is formed, the other metallic mesh 40a has characteristics similar to those described for the radar antenna 100 previously (they are therefore not described in detail again here).

[0129] Essentially, the metal strips of this other metal mesh 40a are, for example, micrometric, that is to say, with a mesh size of one micrometer. Preferably, the mesh size of the metal mesh of the radar antenna 100 is smaller than the mesh size of the other mesh 40a of the conductive layer 40. This makes it easier to manufacture this other metal mesh 40a (because the conductive layer 40 has fewer constraints to meet than the radar antenna 100).

[0130] The width, in the XY plane, of each metal strip of this other metal mesh 40a is on the order of a few tens to hundreds of nanometers. Each metal strip of this other metal mesh 40a 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 this other metal mesh. Preferably, this thickness is less than 20 micrometers (pm). Even more preferably, this thickness is less than 10 pm, or even less than 8 pm. These thickness values ​​are particularly easy to obtain by screen printing. This process is notably inexpensive and simple to implement.

[0131] In the context of the present invention, the thickness of each metal strip of this other metal mesh 40a is between 200 nm and 2 pm. These thickness values ​​are obtained, for example, by lithography. This makes it possible to obtain very thin thicknesses for each metal strip of this other metal mesh, guaranteeing transparency of the lighting device according to the invention.

[0132] The other metallic mesh 40a comprises, for example, copper. Alternatively, it may comprise silver, platinum, aluminum, or nickel. In practice, the metallic strips are formed, for example, by nanolithography.

[0133] In practice, the other metal mesh 40a is, for example, formed by cutting from a plate comprising the metal strips. Alternatively, the metal strips can be selectively deposited to form the other metal mesh. As a further alternative, the metal strips can be produced by engraving the different metal patterns side by side.

[0134] Alternatively, for the conductive layer 40, whose important characteristic is to form a ground plane for the radar sensor 10 (and therefore a reflective surface for RI, R2 radar waves), the other metallic mesh 40a can be irregular. In other words, the metallic strips can have random shapes. Put another way, no periodicity of patterns is observed in this irregular structure. The use of this irregular structure makes it possible to avoid diffraction phenomena for the light beam from the signaling and / or lighting device.

[0135] Thus, the use of the conductive layer 40 makes it possible to optimize the transmission of radar waves in the light device 5; 6; 7; 8; 9, thereby improving the performance of the radar sensor 10. Furthermore, this conductive layer 40 forms a ground plane for the radar sensor 10 (and more particularly for the antennas 100, 101), necessary for the proper functioning of this radar sensor 10 (making it possible in particular to create a potential difference which is the origin of the generation of radar waves).

[0136] Furthermore, the conductive layer 40 also has the advantage of being able to act as a heating element directly integrated into the light device 5; 6; 7; 8; 9. This is particularly advantageous because, in addition to improving the performance of the radar sensor thanks to the positioning of the conductive layer 40 relative to this radar sensor 10, the conductive layer acting as a heating element 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).

[0137] In this regard, optionally (represented only in the example in [Fig. 9]), the lighting device may include a thermally conductive layer, 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). This thermally conductive layer improves the homogeneity of the heating effects from the conductive layer 40.

[0138] In practice, this thermally conductive layer comprises indium tin oxide. Alternatively, the thermally conductive layer may comprise carbon nanotubes. Alternatively still, this thermally conductive layer may comprise graphene.

[0139] Furthermore, in order to ensure transparency properties for the lighting device, the thermally conductive layer comprises a material transparent to the wavelength of a light beam L from a lighting or signaling device. In other words, the thermally conductive layer comprises a material transparent to a light beam with a wavelength in the visible spectrum.

[0140] 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 above.

[0141] The thermally conductive layer has a thickness on the order of a few hundred micrometers. For example, this thickness is between 40 and 200 pm.

[0142] In practice, the thermally conductive layer 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 can be laminated onto the conductive layer 40.

[0143] Fig. 8 represents a cross-sectional view of a lighting device 8 according to a fourth embodiment of the invention.

[0144] In this fourth embodiment, the lighting device 8 also includes another protective panel 50. The conductive layer 40 is here situated between the intermediate layer 30 and the other protective panel 50.

[0145] This other protective panel 50 is introduced here to give structural symmetry to the lighting device 8. This structural symmetry makes it possible to give stability to the lighting device, thus ensuring efficient operation.

[0146] For this purpose, the other protective panel 50 has structural characteristics similar to the protective panel described above. In particular, the other protective panel 50 has a thickness similar 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.

[0147] In order to comply with the dimensioning requirements associated with the integration of the lighting device 8 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.

[0148] 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). Alternatively still, the other protective panel may comprise polyurethane (PUR).

[0149] Advantageously, the other protective panel 50 comprises a material transparent to the wavelength of a light beam from a lighting or signaling device. It is not necessary for this material to be transparent to the wavelengths of the radar waves emitted by the radar sensor 10, since these radar waves do not propagate through this other protective panel 50.

[0150] Although not shown in the figures, the light device 6; 7 shown in figures 6 and 7 may of course include such another protective panel.

[0151] Optionally (not shown) in this fourth 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.

[0152] Fig. 9 represents a cross-sectional view of a lighting device 9 according to a fifth embodiment of the invention.

[0153] In this embodiment, the conductive layer 40 has a first part 44 and a second part 45. The first part 44 of the conductive layer 40 is positioned opposite the radar antenna 100. The second part 45 of the conductive layer 40 surrounds the first part 44. In other words, the second part 45 of the conductive layer 40 is positioned around the radar antenna 100.

[0154] 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 of origin) between these two parts.

[0155] More particularly, 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.

[0156] Preferably, the surface resistance of the second part 45 of the conductive layer 40 is ten times smaller than the surface resistance of the first part 44 of the conductive layer 40.

[0157] Thus, this difference in surface resistance 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) makes it possible to decouple the two functions (ground plane and heating) but to implement them nonetheless within the same conductive layer.

[0158] 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 light-emitting device from the elements. Indeed, thanks to the heating function of the second part of the conductive layer, water droplets, which would be due to rain, fog, snow, or frost, do not impede the proper functioning of the radar sensor. The second part of the conductive layer thus acts as a heat diffuser.

[0159] 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.

[0160] 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.

[0161] For example, when the 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).

[0162] In a defrosting mode, the radar antenna 100 is switched off while an electric current flows in the first part 44 and the second part 45 of the conductive layer 40 in order to implement the heating function.

[0163] In practice, each of the first part 44 and the second part 45 of the conductive layer 40 comprises, for example, indium tin oxide.

[0164] According to a preferred embodiment, 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 then different. of the metallic mesh of the second part 45 of the conductive layer 40. This difference is observed from the point of view of the mesh spacing and also from the point of view of the mesh pattern. This implementation is advantageous because the same deposition technology is used and makes it possible to obtain the two different functions, ground plane and heating. Moreover, this implementation is particularly easy to implement and inexpensive.

[0165] 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).

[0166] In this case, and in order to comply with 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.

[0167] Alternatively, the second part 45 may comprise carbon nanotubes so as to provide the desired heating function. Alternatively, the second part 45 of the conductive layer 40 may comprise graphene.

[0168] Alternatively, it is possible that the first part 44 and the second part 45 of the conductive layer 40 are formed differently. For example, the first part 44 of the conductive layer 40 may comprise a metallic mesh while the second part 45 of the conductive layer 40 may comprise indium tin oxide or carbon nanotubes or graphene.

[0169] Optionally (shown in dashed lines in [Fig. 9]), the lighting device 9 may include the thermally conductive layer 60, positioned on a second face 42 of the conductive layer 40. 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 heat diffusion from the second part 45 to the first part 44.

[0170] Although described in the context of this fourth embodiment example, this two-part conductive layer can of course be integrated into the embodiment examples of the lighting device described previously.

[0171] Regardless of the embodiment considered, the lighting device 5; 6; 7; 8; 9 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 is thus possible to fulfill a lighting, signaling, or aesthetic function, simultaneously with an antenna function for a radar application.

[0172] In order to effectively implement the lighting or signaling functions of the motor vehicle 1, the lighting device 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, enabling the implementation of lighting and / or signaling functions.

[0173] The optical element is adapted to direct the light beam L; emitted by the light source through the stack of the light device 5; 6; 7; 8; 9. More particularly, the optical element is arranged to direct the light beam Li in such a way that the latter propagates from the conductive layer 40 towards the protective panel 20.

[0174] The optical element is for example an optical lens, a light guide, a diffuser or a reflector.

[0175] In practice, as can be seen in [Fig.1], the lighting device 5; 6; 7; 8; 9 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

Demands

1. Lighting device (5; 6; 7; 8; 9) for a motor vehicle (1), said lighting device (5; 6; 7; 8;9) comprising a stack including: - a protective panel (20), - an intermediate layer (30) including at least one radar antenna (100) of a radar sensor (10) configured to emit associated radar waves (RI, R2), the first radar waves (RI) 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 of the radar antenna (100), the intermediate layer (30) being positioned between the protective panel (20) and the conductive layer (40), the radar antenna (100) having a metallic mesh comprising a repeating pattern with a predefined mesh pitch (d), the mesh pitch (d) being determined so as to prevent diffraction phenomena during beam propagation luminous (L;) through the luminous device.;

2. Light device (5; 6; 7; 8; 9) according to claim 1, wherein the mesh pitch (d) of the metallic mesh is less than a value depending on a wavelength (X) of the light beam (L;), a refractive index (n2) of the intermediate layer (30), a refractive index (n3) of the conductive layer (40) and an angle of incidence (00) of the light beam (Li) at the level of the intermediate layer (30).

3. Light device (5; 6; 7; 8; 9) according to claim 1 or 2, wherein the mesh pitch (d) of the metallic mesh is less than 500 nanometers.

4. Light device (5; 6; 7; 8; 9) according to any one of claims 1 to 3, wherein an angle of incidence (00) of the light beam (LO) at the level of the intermediate layer (30) is less than 60 degrees.

5. A lighting device (5; 6; 7; 8; 9) according to any one of claims 1 to 4, wherein the intermediate layer (30) has a refractive index (n2) less than 2, preferably between 1.4 and 1.

95.

6. Light device (5; 6; 7; 8; 9) according to any one of claims 1 to 5, wherein the radar antenna (100) is overmolded in the intermediate layer (30).

7. Light device (5; 6; 7; 8; 9) according to any one of claims 1 to 5, wherein the radar antenna (100) is encapsulated in the intermediate layer (30).

8. Light device (5; 6; 7; 8; 9) according to any one of claims 1 to 7, wherein the protective panel (20) comprises a transparent polymer material.

9. Lighting device (5; 6; 7; 8; 9) according to any one of claims 1 to 8, wherein the protective panel (20) forming an external window of the motor vehicle (1), the lighting device (5; 6; 7; 8; 9) also includes a lighting module configured to implement lighting functions or signaling functions of the motor vehicle (1).

10. A light device (5; 6; 7; 8; 9) according to any one of claims 1 to 9, also comprising 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 light device (5; 6; 7; 8; 9).

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