VEHICLE ARRANGEMENT WITH A RADAR SENSOR AND A GRADE INDEX LENS

Description

[0001] The present invention relates to a vehicle assembly. It finds a particular, but not limiting, application in motor vehicles.

[0002] A vehicle combination comprises, in a manner known to those skilled in the art: a radar sensor having a field of view and configured to emit radar waves over a range of wavelengths in said field of view, and a lens disposed opposite said radar sensor.

[0003] The vehicle's radar system is positioned at the front or rear of the vehicle to meet the needs of the radar sensor for detecting objects in the vehicle's surroundings. The lens is curved to adapt the radar sensor's field of view. Specifically, it allows the radar sensor's field of view to be enlarged or reduced. For example, reducing the radar sensor's field of view increases its range, while enlarging it provides wider detection of objects to the sides of the vehicle. The lens thus allows the radar sensor's field of view to be adjusted according to the manufacturer's requirements.

[0004] One drawback of this prior art is that such a curved lens is bulky, heavy, and expensive. Furthermore, the lens material absorbs some of the radar waves emitted by the radar sensor, thereby reducing its detection performance. This results in a loss of detection range for the radar sensor. Consequently, this leads to false detection or no detection of an object even when it is present in the vehicle's surroundings.

[0005] We know of documents EP 2 573 872 A1, DE 10 2011 115829 A1, EP 3 644 087 A1, US 2018 / 351274 A1, which have among other drawbacks the failure to eliminate internal reflections of radar waves on the lens.

[0006] In this context, the present invention aims to provide a vehicle assembly that solves the aforementioned problem.

[0007] To this end, the invention proposes a vehicle-to-vehicle assembly, according to claim 1, as well as a lens according to claim 13.

[0008] According to non-limiting embodiments, said vehicle assembly may further comprise one or more additional features taken alone or in all technically possible combinations, from among the following.

[0009] According to a non-limiting embodiment, said radar sensor is a millimeter wave or microwave or microwave radar sensor.

[0010] According to a non-limiting embodiment, said radar waves are emitted on a frequency band between 100MHz and 5GHz.

[0011] According to a non-limiting embodiment, said pattern repetition period is less than one tenth of said wavelength.

[0012] According to a non-limiting embodiment, the lens is composed of unit cells each comprising a motif and the local density of said motifs in said layer at a given point of the lens is equal to the weighted average of all the filling factors obtained for each unit cell located at a distance from the point considered on the lens less than a given value on the order of one of the wavelengths of the wavelength range used.

[0013] According to a non-limiting embodiment, the fill factor of each unit cell is equal to a volume of material in said unit cell divided by the repetition period of said patterns times a maximum height in the pattern of said unit cell.

[0014] In a non-limiting embodiment, the local density is equal to the width times the length of a motif, divided by the repetition period of said motifs. This is valid for a cubic or rectangular motif.

[0015] According to a non-limiting embodiment, the local refractive index is composed of two effective refractive indices that are a function of said local density and the permittivity of the patterns and the permittivity of the air.

[0016] According to a non-limiting embodiment, said motifs are cylindrical, rectangular, pyramidal, cubic prisms, or portions of tori.

[0017] According to a non-limiting embodiment, a motif includes dimensions less than 0.4mm.

[0018] According to a non-limiting embodiment, if the angle of incidence is equal to zero then the total thickness is equal to said wavelength divided by twice the equivalent refractive index.

[0019] According to a non-limiting embodiment, the total thickness is defined with an angle of incidence equal to arctan(d1 / (2e4)), with e4 the distance between said radar sensor and said lens and d1 the distance between a transmitting antenna and receiving antennas of said radar sensor.

[0020] The invention and its various applications will be better understood by reading the following description and examining the accompanying figures: [ Fig. 1 ] is a schematic view of a vehicle assembly, said vehicle assembly comprising a radar sensor and a lens, according to a non-limiting embodiment of the invention, [ Fig. 2 [ ] is a schematic view of a radar wave emitted by the radar sensor of the vehicle assembly of the figure 1 which is partially reflected on the lens of the vehicle assembly figure 1 , according to a non-limiting embodiment, [ Fig. 3 ] is a schematic view of the lens of the vehicle assembly of the figure 1 said lens comprising a sub-coating and a pattern layer, according to a non-limiting embodiment, [ Fig. 4 ] is a perspective view of a local area of ​​the patterns in the pattern layer of the lens of the figure 3 , according to a non-limiting embodiment of the invention.

[0021] Identical elements, whether structural or functional, appearing on different figures retain the same references unless otherwise specified.

[0022] The vehicle assembly 1 of a vehicle 2 according to the invention is described with reference to figures 1 à 4 Vehicle assembly 1 is also referred to as vehicle system 1. In a non-limiting embodiment, vehicle 2 is a motor vehicle. A motor vehicle is defined as any type of motorized vehicle. This embodiment is taken as a non-limiting example in the following description. In the following description, vehicle 2 is thus also referred to as motor vehicle 2. In a non-limiting embodiment, vehicle assembly 1 is located behind a logo integrated into the grille of motor vehicle 2 or into a body panel located at the rear of motor vehicle 2. In another non-limiting embodiment, vehicle assembly 1 is located within a lighting or signaling device.

[0023] As illustrated on the figure 1 The vehicle assembly 1, also known as vehicle arrangement 1, comprises: a radar sensor 10 having a field of view FOV and configured to emit radar waves R1, otherwise called primary radar waves R1, in said field of view FOV, and a lens 11 disposed opposite said radar sensor 10.

[0024] These elements are described below.

[0025] The radar sensor 10 is described below. As illustrated on the figure 1 The radar sensor 10 is positioned opposite the lens 11. In a non-limiting embodiment, the radar sensor 10 is a millimeter-wave radar sensor (between 24 GHz and 300 GHz), a microwave radar sensor (between 300 MHz and 81 GHz), or a microwave radar sensor (between 1 GHz and 300 GHz). In a non-limiting variant, the radar sensor 10 operates at a radar frequency between 76 GHz and 81 GHz. The radar waves R1 are emitted over a range Δ1 of wavelengths λ. In a non-limiting embodiment, the radar waves R1 are emitted over a frequency band between 100 MHz and 5 GHz. Thus, in a non-limiting example, if the sensor operates at a radar frequency of 77 GHz, i.e., a wavelength λ of 3.95 mm, with a frequency band of 1 GHz, the radar sensor 10 will operate on a frequency band from 76.5 GHz to 77.5 GHz. The radar waves R1 will therefore be emitted on the frequency range of 76.5 GHz to 77.5 GHz, i.e., a range Δ1 of wavelengths λ of 3.87 mm to 3.92 mm. Thus, in another non-limiting example, if radar sensor 10 operates at a radar frequency of 78.5 GHz with a frequency band of 5 GHz, radar sensor 10 will operate on a frequency band from 76 GHz to 81 GHz. The radar waves R1 will therefore be emitted on the frequency range of 76 GHz to 81 GHz, i.e., a range Δ1 of wavelengths λ from 3.701 mm to 3.945 mm.

[0026] As illustrated on the figure 2 The emitted radar waves R1 arrive at an angle of incidence θ on lens 11. In a non-limiting embodiment, the angle of incidence θ is between 0° and ±30°. The field of view (FOV) thus varies between -30° and +30°. The center of the FOV is at an angle of 0° with respect to the longitudinal axis of the vehicle, also known as the vehicle axis. In another non-limiting embodiment, the FOV varies between -90° and +45°. The center of the FOV is at an angle of -45° with respect to the vehicle axis, and the angle of incidence θ of the radar waves R1 on lens 11 remains close to 0° (the vehicle assembly 1 being then positioned at approximately 45° to the vehicle axis).

[0027] The radar sensor 10 is configured to scan the external environment of the motor vehicle 2, through the emission of radar waves R1. As illustrated on the figure 1 The radar sensor 10 thus comprises: at least one transmitting antenna 100 configured to transmit R1 radar waves, otherwise called primary R1 radar waves, at least two receiving antennas 101 configured to receive R2 radar waves, otherwise called secondary R2 radar waves or R2 return radar waves.

[0028] The radar sensor 10 further comprises at least one transmitter 103 configured to generate the primary radar waves R1 and at least one receiver 104 configured to process the secondary radar waves R2 received in return. In a non-limiting embodiment, a single electronic component can be used for both transmission and reception functions. This results in one or more transmitter / receivers, referred to as "transceivers" in English. The transmitter 103 generates primary radar waves R1, which are subsequently emitted by the transmitting antenna 100. When these waves encounter an object 3 (here, a pedestrian in the illustrated non-limiting example) in the external environment of the motor vehicle 2, they are reflected by said object 3. The reflected radar waves are transmitted back to the radar sensor 10. These are the secondary radar waves R2 received by the receiving antennas 101.These are radar waves retransmitted towards the radar sensor 10. In a non-limiting embodiment, the primary radar waves R1 and the secondary radar waves R2 are radio frequency waves. In a non-limiting embodiment, the radar sensor 10 comprises a plurality of transmitters 103 and a plurality of receivers 104.

[0029] The transmitting antenna 100, also called antenna 100, is configured to transmit the primary radar waves R1 generated by the transmitter 103. The receiving antennas 101, also called antennas 101, are configured to receive the secondary radar waves R2 and transmit them to the receiver 104, which then processes them. There is a phase shift between the secondary radar waves R2 received by the receiving antennas 101, which allows the angular position of object 3 relative to the motor vehicle 2 to be deduced. Object 3 is located in the external environment of the motor vehicle 2. In non-limiting embodiments, the antennas 100 and 101 are patch antennas or slot antennas.

[0030] In a non-limiting embodiment, the antennas 100, 101, the transmitter 103 and the receiver 104 are arranged on a printed circuit board 105. In a non-limiting embodiment, the printed circuit board is a rigid printed circuit board, also called a PCBA (Printed Circuit Board Assembly), or a flexible printed circuit board, also called a Flexboard.

[0031] The radar sensor 10 further includes an electronic control unit 106 configured to control the transmitter 103 and the receiver 104. A radar sensor being known to a person skilled in the art, it is not described in more detail here.

[0032] Lens 11 is described below. Lens 11 is a graded-index lens. In other words, lens 11 is flat and has an equivalent refractive index neq on the wavelength scale λ of the wavelength range Δ1. It is variable on the scale of said wavelengths λ because the refractive index n1 (of layer 13) is variable, while the refractive index n2 (of sublayer 12) is constant.

[0033] The lens 11 allows the field of view (FV) of the vehicle assembly 1 to be adapted by varying the equivalent refractive index neq accordingly, using the density and size of the patterns 130 (described later). This results in a vehicle assembly 1 with a field of view (FV) different from the field of view (FOV) of the radar sensor 10. In particular, a wide field of view (FV) can be obtained from a long-range radar sensor 10 (reduced FOV) or a reduced field of view (FV) from a short-range radar sensor 10 (wide FOV), depending on the manufacturers' requirements. The lens 11 is positioned between the radar sensor 10 and the exterior of the vehicle 2.

[0034] As illustrated on the figures 2 et 3 The lens 11 comprises a sublayer 12 and a layer 13 of motifs 130. The sublayer 12 is configured to support the layer 13 of motifs 130. It has a refractive index n2. In non-limiting embodiments, the sublayer 12 is made of a plastic, glass, or ceramic material. In one non-limiting example, the plastic is polycarbonate. The layer 13 of motifs 130 forms a structured sub-wavelength dielectric element. It has a refractive index n1 that depends on the motifs 130 and their spacing, also called the local refractive index n1. In non-limiting embodiments, the dielectric element is made of a plastic, glass, or ceramic material. In one non-limiting example, the plastic is polycarbonate. It should be noted that a dielectric material is non-conductive and therefore allows radar waves R1 to pass through, unlike a conductive material.

[0035] By structured, we mean that layer 13 comprises the 130 motifs, also called structures. By sub-wavelength, we mean that the structured dielectric material is on a scale smaller than the wavelengths λ of the said range Δ1. The fact that the 130 motifs of layer 13 are sub-wavelength allows this layer 13 to be modeled as a variable-index layer. Otherwise, layer 13 would have to be considered a diffractive optical element.

[0036] As illustrated on the figure 4 which is a view of a local area Z1 of the 130 patterns of layer 13, the 130 patterns have dimensions a1 (width), a2 (width), h1 (height). In non-limiting embodiments, the 130 patterns are cylindrical prisms (also called cylinder pillars), or rectangular prisms (also called rectangular pillars), or pyramidal prisms (also called pyramidal pillars), or cubic prisms (also called square pillars), the latter case being illustrated on the figure 4 or portions of tori. They can also have any other parallelepiped shape. In a non-limiting embodiment, a motif 130 comprises dimensions a1, a2 less than 0.4 mm. This value is very small compared to the wavelengths λ of said range Δ1. For example, a wavelength λ of said range Δ1 is 4 mm for a frequency of 77 GHz; in this case, the value of a1, a2 is approximately equal to λ / 10.

[0037] As illustrated on the figure 4 The lens 11 is composed of unit cells 132, each comprising a motif 130 and an air portion surrounding said motif 130. In a non-limiting embodiment not shown, the motifs 130 are contiguous (adjacent) on the boundary surface between the layer 13 and the sublayer 12. This non-limiting embodiment is applicable for motifs 130 in the shape of pyramids or portions of tori. The unit cell 132 is defined by the repetition period A of the structures 130, also called the repetition period Λ of the motifs 130 or the lattice period A, with A = A1 x A2. A1 is the lattice period along a first direction Ax (illustrated in the figure 4 ), and A2 is the period of the network along a second direction Ay (illustrated on the figure 4 Ax and Ay are arbitrary, non-parallel directions. In a non-limiting embodiment, the second direction Ay is perpendicular to the first direction Ax. In another non-limiting example, the unit cell 132 is a square, a hexagon, a parallelogram, or any other shape that allows the boundary surface between layer 13 and sublayer 12 to be tiled periodically. We will denote Az as a third direction perpendicular to the first direction Ax and the second direction Ay, the whole forming a coordinate system Ax, Ay, Az.

[0038] In a first, non-limiting embodiment, the sub-wavelength structured dielectric element, layer 13, is a sub-wavelength structured periodic dielectric element. The dimensions a1, a2 of the motifs 130 change along layer 13 to vary the refractive index of lens 1, while A1 and A2 remain constant. In other words, the motifs 130 are spaced identically from each other along a first direction Ax (illustrated in the figure 4 ) and are spaced identically along a second direction Ay (illustrated on the figure 4 ) perpendicular to the first direction Ax. In other words, layer 13 comprises identical 131x spacings along the first direction Ax, and identical 131y spacings along the second direction Ay (illustrated on the figure 4 ) between the 130 motifs, namely there is the same proportion of air between the 130 motifs.

[0039] In another non-limiting embodiment illustrated on the figure 3 The sub-wavelength structured dielectric element, layer 13, is not periodic. A1 and A2 change along layer 13 to vary the refractive index of lens 1, while the dimensions a1, a2 of the motifs 130 are constant. Layer 13 includes variable spacings 131x, 131y between the motifs 130; that is, there are different air proportions between the motifs 130. A1 and A2, as well as the dimensions a1, a2 of the motifs 130, can also be varied to change the refractive index of lens 1.

[0040] By sub-wavelength, we mean that the period of the grating A1, A2 is less than one-quarter of a wavelength λ in the range Δ1 of wavelengths λ. In a non-limiting example, the wavelength λ considered is the smallest wavelength in the range Δ1. Thus, A1 < λ / 4 and Λ2 < λ / 4. In a non-limiting embodiment, the period of the grating A1, A2 is less than one-tenth of the wavelength λ. Thus, Λ1 < λ / 10 and Λ2 < λ / 10. Note that this wavelength λ is chosen from the range Δ1 and will be used for the formulas below.

[0041] As illustrated on the figure 2 When a radar wave R1 is emitted by the radar sensor 10, it travels to the lens 11, which has a thickness e0. The radar wave R1 arrives at the lens 11 at an angle of incidence θ, corresponding to a refracted angle r. The radar wave R1 is reflected by the lens 11 and generates two reflected waves, one R11, which is reflected off the outer surface of the sub-layer 12 of the lens 11, and the other inside the lens 11. The two reflected waves, R11 and R12, are first-order reflected waves that return to the radar sensor 10. These are spurious reflections. When the angle of incidence θ is not 0°, the corresponding refracted angle r is also not 0°. The phase difference Δφ, also called the phase shift Δφ, between these two reflected waves R11 and R12 is equal to: Δφ = n eq δ γ + π − 2 e 0 tan r sin θ λ

[0042] With : n eq , the equivalent refractive index for sub-layer 12 and layer 13, δ the path of the reflected wave R12 in the material equal to 2e0 / cos(r), nδ / λ the phase shift due to the path in the material, π the phase shift due to internal reflection in sub-layer 12 and layer 13 of motifs 130, - ((2e0 tan(r) sin(θ)) / λ) the phase shift in air due to the difference between the reflection point Pt1 of the reflected wave R11 and the emergence point Pt2 of the reflected wave R12.

[0043] Since sin(θ) = n eq x sin(r), we obtain: − 2 e 0 tan r sin θ λ = − 2 e 0 n eq sin r 2 λcos r

[0044] Either : Δφ = π + 2 n eq e 0 λcos r 1 − sin r 2 = π + 2 n eq e 0 cos r λ and this is true regardless of the value of the refracted angle r.

[0045] As the reflected waves R11 and R12 return towards the radar sensor 10, they cause disturbances on the radar sensor 10, namely an attenuation of the signal-to-noise ratio. In order to eliminate these disturbances, the total thickness e0 of the lens 11 will be defined such that the reflected waves R11 and R12 are out of phase to create destructive interference. To obtain destructive interference, the phase difference Δφ between the two reflected waves R11 and R12 must be equal to π modulo 2π. Thus, we have Δφ = (2m+1)*π, where m is a natural number. We therefore obtain: 2 m + 1 π = π + 2 n eq e 0 cos r λ

[0046] Let: Let e0 = mm λ / (2n eq cos (r)).

[0047] It should be noted that the equation e0 = m λ / (2n eq cos (r)) is applied regardless of the value of the angle r. Thus, this total thickness e0 is dimensioned so that it is equal to m times the wavelength λ, divided by twice the equivalent refractive index n eq of the pattern layer 13 and sublayer 12, times the cosine of a refracted angle r corresponding to the angle of incidence θ of the radar waves R1, where m is an integer. Therefore, from the equivalent refractive index n eq and the wavelength λ used over the operating frequency range of the radar sensor 10, the total thickness e0 can be determined such that the reflected waves R11 and R12 cancel each other out. In a non-limiting embodiment, the wavelength used is that which lies in the middle of the allowed Δ1 range.

[0048] An ideal total thickness e0 is defined when the angle of incidence is equal to 0° and m is equal to 1. When θ = 0, r = 0. Consequently, for m = 1, the ideal total thickness e0 of lens 11 is therefore e0 = λ / (2n eq). When r = 0°, that is, cos(r) = 1.

[0049] In a non-limiting embodiment, the lens 11 has a total thickness e0 that is between 0.8 and 1.2 times the ideal total thickness e0. This range of values ​​takes into account the possible emission angles of the radar sensor 10. The possible values ​​of the angle of incidence θ are defined in the technical specifications of the radar sensor 10, meaning that the possible values ​​of the angle of incidence θ are within the field of view (FOV) of the radar sensor 10. In a non-limiting example, the angle of incidence θ is between 0° and ±30°. This range of 0.8 to 1.2 allows for the manufacturing tolerances of the total thickness e0.

[0050] It should be noted that there is a value for the angle of incidence θ for which the reflected radar waves R11 and R12 cause maximum disturbance to the receiving antennas 101 of the radar sensor 10. This angle of incidence θ is called the critical angle of incidence θ. In a non-limiting embodiment, this value is equal to θ = arctan(d1 / (2e4)), where d1 is the distance between the transmitting antenna 100 and the receiving antennas 101, and e4 is the distance between the radar sensor 10 and the lens 11 as illustrated in the figure 2 Note that in a non-limiting example, the midpoint of the receiving antennas 101 is taken to calculate d1.

[0051] Thus, depending on the value of the local refractive index n1 and the wavelength λ used over the operating frequency range of the radar sensor 10 (between 76 GHz and 81 GHz in the non-limiting example), the value of the total thickness e0 can be determined so that the first-order reflected waves R11 and R12 cancel each other out. The reflected radar waves R11 and R12 are reflected by the lens 11 within a limited area. As a result, the receiving antennas 101 receive less noise, leading to a better signal-to-noise ratio.

[0052] The lens 11 comprises a total thickness e0 formed by the height h1 of the motifs 130 and the thickness e2 of the sub-layer 12. To dimension the total thickness e0, the height h1 of the motifs 130 or the thickness e2 is adjusted so that e0 = m λ / (2n eq cos (r)) for a given r. In a non-limiting embodiment, the given r corresponds to the critical angle of incidence θ.

[0053] The equivalent refractive index neq is equal to: n eq = n 1 n 2 e 1 + e 2 n 2 e 1 + n 1 e 2 = n 1 n 2 1 + e 2 e 1 n 2 + n 1 e 2 e 1

[0054] With n1 the local refractive index of layer 13 of motifs 130, n2 the refractive index of sublayer 12, e1 equal to the height h1 of motifs 130, and e2 the thickness of sublayer 12. Note that n1 is a function of the position of the local zone Z1 of motifs 130 on layer 13 where the calculation is performed. Thus, the equivalent refractive index neq is a function of the position of the local zone Z1 on layer 13.

[0055] It should be noted that the layer 13 of motifs 130 has a local refractive index n1 which is calculated as a function of the local density τ r of said motifs 130 in the layer 13. The local density τ r at a point of the lens 11 is the weighted average of the filling factor τ r132 of each cell 132 located at a distance from the point considered less than a given value on the order of one of the wavelengths λ of the range Δ1 of wavelengths used.The local refractive index n1, also called the effective refractive index neff, is composed of two effective refractive indices neffTE and neffTM, which depend on the polarization of the incident wave, namely the primary radar wave R1, and which can be expressed as a function of the local density τr (also called the filling factor τr), which represents the portion of matter occupied by the medium with a high refractive index n1, in this case the 130 motifs, as opposed to the medium with a low refractive index n0, in this case air. It should be noted that the local density τr represents the portion of matter occupied by the medium with a high refractive index n1 over an area with a dimension on the order of one of the wavelengths λ of the range Δ1 of wavelengths used. Thus, we have: n effTE = ε effTE = τ r ε max + 1 − τ r ε min n effTM = ε effTM = 1 τ r ε max + 1 − τ r ε min

[0056] With the term TE denoting the polarization of the incident wave, namely the radar wave R1 arriving at the lens 11, perpendicular to the plane of the substrate, namely the sublayer 12, TM the polarization parallel to the plane of the substrate, and εmax the permittivity of the medium with the highest refractive index, namely the motifs 130, and εmin for the one with the lowest refractive index, namely air. In another non-limiting embodiment, air can be replaced by a plastic material with a very low refractive index.

[0057] It should be noted that when the incident wave, here the radar wave R1, illuminates the structured dielectric element, namely the lens 11, and has a wavelength λ (of said range Δ1) much greater than the repetition period A1, A2 of the structures 130 (λ>>Λ1, and λ>>Λ2), this is a propagation regime called static limit.

[0058] For 130 two-dimensional structures, such as those illustrated on the figure 4 The effective refractive index neff2D of a 2D structure can be approximated by taking the root mean square of the effective refractive indices according to the two polarizations TM and TE in one dimension to order 0, which corresponds to the static limit. The filling factor τr132 of a unit cell 132 is, in this particular case: τ r 132 = a 1 . a 2 Λ 1 . Λ 2

[0059] And we have: n eff 2 D = 1 2 n effTE 2 + n effTM 2 1 2

[0060] In the more general case, for any pattern shape 130 where A1, A2 are arbitrary, with a basic rectangular unit cell 132, the filling factor τ r132 for a unit cell 132 will be: τ r 132 = V 132 Λ 1 . Λ 2 . hmax

[0061] This corresponds to a ratio of the volume of material (V 132) in the unit cell 132 to an encompassing empty volume (A1 A2hmax), with hmax being the maximum height of the motif 130 in the unit cell 132 (i.e., the highest height in the motif 130), and V 132 = ∫ 0 hmax ∫ X 132 X 132 + Λ 1 ∫ Y 132 Y 132 + Λ 2 M X Y Z dXdYdZ

[0062] With (X 132 , Y 132 , 0), the coordinates of a corner C1 of unit cell 132 and M(X, Y, Z) = 1 if the point with coordinates (X, Y, Z) is in the material and M(X, Y, Z) = 0 if it is not, that is, if the point with coordinates (X, Y, Z) is in the air. Note that when it is in the material, the point is located within pattern 130 of unit cell 132, and when it is in the air, the point may or may not be inside a pattern 130 (a pattern 130 may indeed contain air pockets in a non-limiting example). Note that in the non-limiting example of the figure 4 , hmax = h1 described previously.

[0063] It should be noted that this formula for the volume of matter V 132 is valid for any rectangular unit cell 132, regardless of the shape of the motif 130 within said unit cell 132. Thus, since A1 and A2 can change from one unit cell 132 to another, as well as the maximum height hmax from one motif 130 to another, each unit cell 132 can have a different volume of matter and consequently a different filling factor τ r132. To obtain the filling factor τ r of the entire layer 13 of motifs 130 at a given point on the lens 11, a weighted average of the filling factors τ r132 of each cell 132 located at a distance from the point considered on the lens 11 less than a given value on the order of one of the wavelengths λ in the range Δ1 of wavelengths used is performed. This definition is valid for all points of lens 11.In a non-limiting embodiment, the points belong to the surface of the sublayer 12 with coordinate Z=0. Thus, we have: τ r = ∑ n Λ 1 n . Λ 2 n . hmax n . τ rn ∑ n Λ 1 n . Λ 2 n . hmax n

[0064] Where n denotes any one of the unit cells 132 located at a distance from the point considered on the lens 11 less than a given value on the order of one of the wavelengths λ of the range Δ1 of wavelengths used.

[0065] It should be noted that low-cost manufacturing technologies, such as injection molding, are used to produce lens 11. Specifically, the sub-layer 12 and the pattern layer 130 are made from the same material and injected simultaneously, which significantly reduces manufacturing costs. Additive manufacturing technologies, also known as 3D printing, are also used as a manufacturing method.

[0066] Of course, the description of the invention is not limited to the embodiments and the field described above. Thus, in another non-limiting embodiment, the radar sensor 10 comprises more than one transmitting antenna 100 and more than two receiving antennas 101.

[0067] Thus, the described invention offers, in particular, the following advantages: It allows the range of the radar sensor 10 to remain unchanged, it allows the overall size of the vehicle assembly 1 to be reduced by replacing a curved lens with a flat lens, it allows the cost and weight of the vehicle assembly 1 to be reduced by replacing a curved lens with a flat lens, it allows the absorption of some of the radar waves R1 emitted by the radar sensor 10 to be considerably reduced, like a curved lens it allows the field of view of the radar sensor 10 to be adapted to the manufacturers' requirements, it allows the elimination of the reflected waves R11, R12, of order 1 which are reflected towards the radar sensor 10. The signal-to-noise ratio of said radar sensor 10 is therefore no longer reduced.

Claims

1. Vehicle assembly (1) for a vehicle (2), said vehicle assembly (1) comprising: - a radar sensor (10) having a field of vision (FOV) and configured to emit radar waves (R1) over a range (A1) of wavelengths (λ) in said field of vision (FOV), and - a lens (11) arranged facing said radar sensor (10), said lens (11) being a gradient-index lens, and comprising a sublayer (12) and a layer (13) of patterns (130) forming a sub-wavelength structured dielectric element with a repetition period (A1, A2) of the patterns (130) that is less than a quarter of a wavelength (λ) of said range (A1), the layer (13) of patterns (130) having a local refractive index (n1) that is calculated based on a local density (tr) of said patterns (130) in said layer (13), characterized in that said lens (11) comprises a total thickness (e0) formed by the height (h1) of said patterns (130) and by the thickness (e2) of said sublayer (12), said total thickness (e0) being dimensioned so that it is equal to m times said wavelength (λ) all divided by twice the equivalent refractive index (neq) of the layer (13) of patterns (130) and of the sublayer (12) times the cosine of a refracted angle (r) corresponding to an angle of incidence (0) of the radar waves (R1), with m being an integer.

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

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

4. Vehicle assembly (1), according to any one of the preceding claims, wherein said repetition period (A1, A2) of the patterns (130) is less than one-tenth of said wavelength (λ).

5. Vehicle assembly (1) according to any one of the preceding claims, wherein the lens (11) is composed of unit cells (132) each comprising a pattern (130) and the local density (tr) of said patterns (130) in said layer (13) at a given point of the lens (11) is equal to the weighted average of all the filling factors (Tr132) obtained for each unit cell (132) located at a distance from the considered point on the lens (11) less than a given value of the order of one of the wavelengths (λ) of the range (A1) of wavelengths used.

6. Vehicle assembly (1) according to the preceding claim, wherein the filling factor (Tr132) of each unit cell (132) is equal to a volume of material (V132) in said unit cell (132) all divided by the repetition period (A1, A2) of said patterns (130) times a maximum height (hmax) in the pattern (130) of said unit cell (132).

7. Vehicle assembly (1) according to any one of the preceding claims, wherein the local density (tr) is equal to the width (a1) times the length (a2) of a pattern (130) all divided by the repetition period (A1, A2) of said patterns (130).

8. Vehicle assembly (1) according to any one of the preceding claims, wherein the local refractive index (n1) is composed of two effective refractive indices (neffTe, NeffTM) as a function of said local density (tr) and the permittivity (&max) of the patterns (130) and the permittivity of air (&min).

9. Vehicle assembly (1) according to any one of the preceding claims, wherein said patterns (130) are cylindrical, or rectangular, or pyramidal, or cubic prisms, or portions of toruses.

10. Vehicle assembly (1), according to any one of the preceding claims, wherein a pattern (130) comprises dimensions (a1, a2) less than 0.4mm.

11. Vehicle assembly (1) according to any one of the preceding claims, wherein if the angle of incidence (0) is equal to zero then the total thickness (e0) is equal to said wavelength (λ) divided by twice the equivalent refractive index (neq).

12. Vehicle assembly (1) according to any one of the preceding claims, wherein the total thickness (e0) is defined with an angle of incidence (0) equal to arctan(d1 / (2e4)), with e4 being the distance between said radar sensor (10) and said lens (11) and d1 being the distance between a transmitting antenna (100) and receiving antennas (101) of said radar sensor (10).

13. Lens (11) configured to adapt a field of vision (FOV) of a radar sensor (10) of a vehicle (2) configured to emit radar waves (R1), said lens (11) being arranged facing said radar sensor (10), characterized in that: - said lens (11) being a gradient-index lens, and comprising a sublayer (12) and a layer (13) of patterns (130) forming a sub-wavelength structured dielectric element with a repetition period (A1, A2) of the patterns (130) that is less than a quarter of a wavelength (λ) of a range (A1) of wavelengths (λ) on which said radar waves (R1) are emitted, and whose layer (13) of patterns (130) has a local refractive index (n1) that is calculated based on a local density (τr) of said patterns (130) in said layer (13), characterized in that said lens (11) comprises a total thickness (e0) formed by the height (h1) of said patterns (130) and by the thickness (e2) of the sublayer (12), said total thickness (e0) being dimensioned so that it is equal to m times said wavelength (λ) all divided by twice the equivalent refractive index (neq) of the layer (13) of patterns (130) and of the sublayer (12) times the cosine of a refracted angle (r) corresponding to an angle of incidence (0) of the radar waves (R1), with m being an integer.