ILLUMINATED COVER FOR ELECTROMAGNETIC TRANSMITTER AND RECEIVER

An illuminated cover for an electromagnetic sensor, such as a radar sensor. The cover comprises a multilayer plate that is substantially transparent to the electromagnetic radiation emitted and/or received by the electromagnetic sensor. The plate includes a first layer of optically transparent material and a second layer on at least one surface of the first layer and having a lower refractive index than the first layer. A graphic layer is provided on the second layer. At least one light source is arranged to couple light into the first layer, which acts as a light guide. At least one surface of first layer is further provided with at least one optical element for outcoupling light from the first layer.

This nonprovisional application claims priority under 35 U.S.C. § 119(a) to European Patent Application No. 21180398.6, which was filed on Jun. 18, 2021, and which is herein incorporated by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to covers for electromagnetic transmitting and receiving elements, such as radar devices and is specifically directed to radar covers for use in vehicles as well as methods of manufacture of the same.

Description of the Background Art

Electromagnetic transmitter and receiver elements or are commonly used as a radar system in vehicles for detecting the speed and range of objects for collision avoidance and adaptive cruise control systems. These elements are typically located at the front of the vehicle but may also be present at the side or rear. They are provided with a cover, which is often domed and be referred to as a radome, which protects the emitter and receiver elements from the elements and may also serve as a decorative component, for example, by supporting an emblem of the vehicle manufacturer. The cover must be substantially transparent to the radio waves of interest and to this end is preferably of uniform thickness and devoid of discontinuities and angles to minimise reflection and absorption of radio waves.

WO 2019/130033 A1, EP3300169A2 (which corresponds to US 2018/0090832), EP3495186A1 (which corresponds to US 2020/0361399) all describe radar covers for vehicles that carry a decorative element in the form of a metal layer, foil or similar. A disadvantage with these radar covers is that the design or emblem is not always clearly distinguishable particularly at night or in conditions of low lighting. It would thus be advantageous to illuminate the emblem to better identify the car brand or to improve the overall design possibilities of the vehicle. However, providing lighting in a radar cover presents a particular challenge due to the limited product dimensions, high number of components and the requirement that the radar function not be impaired.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an illuminated cover for an electromagnetic sensor, particularly a radar sensor that provides a uniform and homogenous luminance without impairing the operation of the sensor.

The above objects are achieved in a cover for an electromagnetic sensor as well as a method for fabricating a cover as detailed below.

In an example of the invention, there is provided a cover for an electromagnetic sensor such as a radar sensor, the cover comprising a plate that is substantially transparent to electromagnetic radiation, the plate having a central portion destined to be disposed over an electromagnetic sensor and an outer rim, at least the central portion being of a substantially uniform thickness, the plate further defining an upper surface destined to face an observer and a lower surface destined to face an electromagnetic sensor, the plate comprising a first layer of an optically transparent material, at least one optical element being disposed on at least one of an upper and lower surface of the first layer for outcoupling light at least from an upper surface of the plate, a second layer being disposed on at least one of the upper and lower surfaces of the first layer, the second layer being of a second optically transparent material having a refractive index lower than that of the first layer and being substantially thinner than the first layer and a graphic layer arranged on outer surface of at least one of the second layers, the graphic layer being of an optically opaque and/or reflective material.

By providing a cover with a multilayer plate, the impact on the function of the electromagnetic sensor is minimised as air-material interfaces are not increased over conventional radome structures. A first layer can serve as a light guide providing a homogeneous background illumination by virtue of at least one outcoupling optical element. The graphic layer provides a decorative component while the second layer protects from unwanted light leakage from the first layer due to the graphic layer or impurities that may deposit on the plate.

The second layer can be arranged on both an upper and lower surface of the first layer and thus limits light leakage from both sides of the first plate.

The refractive index of the first layer is preferably between 1.3-1.6, and more preferably between 1.5-1.6, while second layer preferably has a refractive index of between 1.15-1.3.

The thickness of the second layer is preferably between 1-6 μm, and still more preferably between 2-3 μm to limit the impact on the sensor function.

The at least one optical element can comprise a light diffusing surface on the first layer. This may be a surface comprising regular or irregular microstructures, grooves, or granular elevations.

The at least one optical element may comprise a light diffusing material applied to or integrated with the first layer.

To improve the durability of the cover plate and thus maintain the look and function of this plate, it preferably comprises at least one protective outer layer. This layer may be a protective lacquer. This layer is particularly useful for protecting the graphic layer when this is on an upper surface of the second layer and hence is vulnerable to impacts and wear from the environment.

The lower surface of the plate may be provided with an optically reflective layer. This improves the efficiency of the plate and the homogeneity of the illumination perceived by an observer at the upper surface of the plate, particularly when the graphic layer is on an upper surface of the second layer, i.e. on an outwardly facing surface.

The cover may further comprise at least one light source disposed adjacent the outer rim of the first layer and arranged to couple light into the first layer. By positioning a light source at the edge of the plate, this source will be effectively hidden from view, so reducing glare for the observer.

The obscuring of the light source from the view of an observer is improved in which the cover comprises a frame coupled to the outer rim of the plate, the frame being of a light blocking material and adapted to accommodate the at least one light source. In this way, the light source and accompanying electronics are also protected.

The frame can be arranged to extend under the plate to enclose a space, the frame being substantially transparent to electromagnetic radiation. The frame and plate thus together enclose a space for protecting the light sources and accompanying electronics, while the cover as a whole is designed to limit the attenuation of the electromagnetic waves to and/or from the sensor.

The frame can be arranged to extend under the plate to enclose a space adapted to accommodate an electromagnetic sensor. Thus, the sensor may also be located within the cover, i.e., between the plate and the frame, which reduces the number of elements the electromagnetic waves must pass through and hence minimises the impact on the sensor function, while simultaneously being protected.

The plate can be substantially curved in cross section, preferably domed with a substantially uniform angle of curvature in cross section at least in the central portion. Preserving a uniform angle of curvature limits the interference sustained by the electromagnetic radiation.

The present invention further relates to a method of fabricating a cover for an electromagnetic sensor as described previously. This method includes the steps of: providing a first layer of a first refractive index, forming at least one optical element on one of an upper or lower surface of the first layer, the optical element being adapted to outcouple light at least from an upper surface of the plate, providing a second layer at least on an upper surface of the first layer, the second layer being of a lower refractive index than the first layer, at least partially covering the second layer with a graphic layer.

Preferably, the step of providing the first layer includes moulding a plastic material, such as PC or PMMA, for example by injection moulding.

The at least one optical element may be formed by applying an optically diffusing material and preferably by moulding a diffusing material together with the plastic material in a 2K process. Additionally or alternatively, the at least one optical element may be formed by forming light diffusing microstructures on a surface of the first plate.

Preferably, the method includes the step of applying an optically reflective layer to a lower surface of the plate.

The method may also include the application of a protective layer to an upper and lower surface of the plate.

Further steps of the method may include: attaching a frame to the rim of the first layer, where the attachment may be mechanical, such as by screws, rivets, clips, deformation of the frame, adhesive tape adhesion, or alternatively chemically, such as glue, lacquer, electromagnetic force using magnets, electric charge; arranging at least one light source adjacent a rim of the first layer.

DETAILED DESCRIPTION

FIG.1shows a cover1, also referred to as a radome, for a radar sensor in accordance with the present invention. The cover1comprises a plate10that is arranged over a radar sensor20, which comprises one or more radio transmitters and/or receivers or antennas in the conventional manner. The radio waves emitted and/or received are depicted as a cone R inFIG.1. The whole assembly can be attached to the front of a vehicle, for example, to a facia or grille of a vehicle.

The plate10is a multilayer structure with a substantially even and constant thickness to ensure good radar performance. The geometry of the plate10is also devoid of abrupt changes or discontinuities for the same reason. In the illustrated example, the plate10is domed with a substantially uniform degree of curvature at least in a central portion that coincides with a radar cone R. It will be understood, however, that the plate may be substantially planar, over its whole structure, or at least in the central portion located above the radar cone R.

As shown inFIG.1, the plate10includes a first layer100that serves as a light guide. Two light sources130are arranged at the outer rim of this first layer and arranged such that the light is coupled into the first layer100. These light sources130preferably comprise one or more LEDs provided with associated power supply and control circuitry. The LEDs may be configured to generate white light or light of a specific colour. Two light sources130are illustrated in the figures, but it will be appreciated that a single light source or more than two light sources may be used.

FIG.2shows detailed view of the layered structure of the plate10. As is visible inFIG.2, on both the upper and lower surfaces of the first layer100are arranged second layers, specifically optical insulating layers110. These optical insulating layers110have a lower refractive index than the first layer100and thus ensure that light coupled into the first layer100is subjected to total internal reflection at the upper and lower surfaces of this layer100and thus propagates through it. The reflected light beams are illustrated inFIGS.1and2as L. The optical insulating layer110serves to protect the light guide100from light leakage due to impurities that might deposit on the surface or graphic elements that could otherwise alter the refractive index boundary at the surface of the light guide100. The second layer thus prevents unwanted glare for an observer and instead ensures that the cover10provides a homogenous background illumination. While the optical insulating layers102are shown on both the upper and lower surfaces of the light guide100, it may be sufficient to provide such an insulating layer only on the upper surface of the light guide100, i.e. on the surface that is directly outwardly and is thus open to the elements, providing that the light guide100has a refractive index that is higher than air, i.e. higher than1. The light guide100is made of a material that is substantially transparent to both light and to the radio waves used by the radar sensors. Suitable materials include thermoplastic polymers, such as polycarbonate (PC) or PMMA (Poly(methyl methacrylate)). The thickness of the light guide100depends on the application but is preferably within the range of 1 to 5 mm. Preferably, the light guide100has a refractive index of between 1.3 and 1.6, preferably around 1.5. The optical insulating layer110is a thin film of depth between 1-6 μm, preferably between 2-3 μm and has a refractive index of less than 1.3, preferably 1.15-1.3. The optical insulating layer110is preferably substantially transparent to light and optically clear and also substantially transparent to the radio waves used by the radar sensors. Suitable materials include siloxane resins. The insulating layer or layers110may be spray-coated or otherwise deposited on the underlying layer100, or alternatively bonded to this layer by adhesive or heat treatment.

As shown in bothFIGS.1and2, a number of optical elements120are provided on the bottom surface of the first layer100. These optical elements120serve to outcouple light from the light guide100by diffusing light, that is, by causing a refraction, reflection and/or diffraction of the light at the surface of first layer which causes it to leak out of the light guide100. As a consequence, the plate10is perceived as illuminated, although the light sources130are not visible. These optical elements120may be composed of diffractive surface relief structures such as microstructures or a roughened or granular surface formed on the lower surface of the light guide, for example, by chemical or mechanical etching of the light guide surface. The optical elements120may alternatively be formed by applying a diffusing material to the light guide surface, or alternatively by incorporating a light-diffusing material in the light guide100by using a 2K injection moulding process. The optical elements120shown inFIGS.1and2are provided only on the lower surface of the light guide100, however, it will be understood that they may instead be provided on the upper surface, or equally on both the lower and upper surfaces of the light guide100. The optical elements120may be provided as several discrete elements arranged in a regularly spaced pattern on the upper and/or lower surface of the light guide100to provide an even distribution of light over the surface of the cover plate10. Alternatively, the optical elements120may formed as a single dispersing surface at a desired location on the light guide100. The optical elements120may further be arranged to form a desired design, such as an emblem or logo, or the negative of a desired design, so that the observer will see an illuminated design or a shaded design.

On the underside of the lower optical insulating layer110there is provided a graphic layer140, comprising a film or foil, for example a metallic film or a foil on which a design is applied or that may be arranged to display a desired design such as the emblem or logo of a manufacturer. This film is preferably very thin, of the order of a few pm so that changes in thickness of the cover10between areas where the graphic layer is present and those where graphic material is absent have a negligible effect on the radiation emitted and/or received by the radar sensor20. The material of the film140is substantially opaque and/or reflective to visible light, but substantially transparent to the electromagnetic radiation used by sensor20. The design is visible through the multilayer structure of the light guide100and insulating layer110. The graphic layer140may alternatively be formed on the upper surface of cover plate10, i.e. on the outer surface of the upper insulating layer110(seeFIG.5), or even on the outer surface of both the upper and lower insulating layers110. In all cases, the graphic layer140is separated from the first layer100by the optically insulating layer110to preclude the risk of light leakage that may otherwise occur on the boundary between the graphic layer140and first layer100. When the optical elements120are formed in a specific design as described above, the graphic layer140may advantageously be arranged to occupy the spaces between the optical elements120so that the design is visible not only by the presence of the graphic layer but also by the illuminated portions between the graphic elements. In this way, a desired shape may be displayed as an illuminated design or alternatively as the negative of an illuminated design.

As shown in the detailed section illustrated inFIG.2, the cover plate100may also include an outer protective layer150applied to the upper and/or lower surface. This protective layer150is preferably a varnish or resin of sufficient hardness to protect the surface of the cover, and particularly the graphic layer140, from wear and scratches. In addition, the protective layer150may be used to compensate for differences in thickness caused by the application or removal of the graphic layer. The protective layer150is omitted from the remaining figures in the interests of clarity.

Turning now toFIG.3there is shown an arrangement of the cover1, which includes a frame160that extends downwards from the lower rim of cover plate10and under the cover plate10to enclose a space bordered by cover plate10and frame160. The light sources130and associated electronics are located within this space. The frame160serves to block unwanted light and also protect the one or more light sources130and associated electronics. The frame160may also be provided with coupling elements, such as clips, screw holes or the like, that enable the cover1to be mounted over a radar sensor20on a vehicle, for example. The frame160is of a substantially optically opaque material, preferably of moulded plastic formed by injection moulding. The frame160may be fixed to the outer rim of the cover plate10mechanically with, for example, screws, rivets, clips, deformation of the frame160, adhesive tape, or the like, chemically, such as with glue or lacquer, electromagnetic force using magnets, electric charge, or similar or by any other suitable fixing method.

As shown inFIG.3, the cover1including the cover plate10and frame160may be arranged over a radar sensor20, such that the radio waves illustrated by the cone R must pass through both the frame160and the cover plate10. In this case, the frame160must be substantially transparent to the radio waves transmitted and/or received by the sensor20. In addition, the spacing between the frame160and the cover plate10, at least in the central area of the cover1that corresponds to the radio wave cone R, is chosen to minimise the attenuation of radio waves. In an alternative arrangement, the frame160does not extend over the whole space occupied by the plate10as shown inFIG.3, but instead covers only part of the way under the cover plate10such that the space is not enclosed, but the light sources130are protected and light leakage from the light sources130at the edge of the plate10are precluded or minimised.

FIG.4shows a further example of the cover1. In this figure, the radar sensor20is accommodated between the frame160and the cover plate10, i.e. frame160and plate10together form a housing enclosing a protective space within which the radar sensor20light sources130and other electronic components may be accommodated. This arrangement reduces the attenuation of the radar signal as these pass through only two boundaries, namely the two outer surfaces of the cover plate10.

The frame160can be essentially annular with an outer edge that essentially corresponds to that of the plate10or extends slightly beyond this, and an inner edge that extends inside the outer rim of the plate10to provide an essentially annular place serving as a protective housing for the light sources130and associated electronics. This annular space may be closed. In such an arrangement, the frame does not impact on the performance of the radar sensor20as it is not traversed by the conde R.

Turning now toFIG.5there is shown a further example of the cover1. The cover1illustrated inFIG.5is similar to that shown inFIG.4with the notable difference that a graphic layer140is provided on the upper side of the cover plate10, i.e. on the outer surface of the upper optically insulating layer110. As discussed above, a hardened protective layer150is preferably applied over the graphic layer, although this is not shown inFIG.5.FIG.5also includes an optically reflective layer170that is applied to a lower surface of the cover plate, specifically on the outer surface of the lower optically insulating layer110. If a graphic layer140is present on the underside of the cover plate10, the optically reflective layer170is applied over that layer, i.e. on the outside of that layer, such that an observer can perceive the graphic layer140on top of the optically reflective layer170. The optically reflective layer170serves to improve the efficiency and homogeneity of the illumination of the cover plate10by reflecting all light out of the cover plate10. The layer170is preferably a white or pale film or coating, e.g. paint or pigmented lacquer of a few pm in thickness that is applied to the remaining structure of the cover plate10by adhesion or thermal bonding or another suitable manner. The optically reflective layer may also serve as a protective layer, or alternatively be coated with a protective layer150

FIG.6shows the steps of a process for manufacturing a cover plate10according to the examples described above. In a first step designated a) the first light guide layer100is formed by injection moulding into the desired domed or planar shape of the cover plate10. At step b) one or more optical elements are provided at the lower or upper surface of the light guide layer100. These optical elements may be formed by mechanical or chemical etching to create structured or roughened diffusing surfaces, or by application of a diffusing material to the surface of the layer100. Alternatively, the optical elements may be formed integrally with the light guide100, for example by 2K injection moulding of a diffusing material and thus be formed simultaneously with step a). At step c) optical insulating layers110are applied to the upper and/or lower surfaces of the light guide layer100. These optical insulating layers110may be applied directly to the surface of the light guide100and optionally hardened or cured, or applied as a separate film that is bonded to the surface of the light guide100chemically or mechanically. At step d) a graphic layer is applied to at least one of the outer surfaces formed by the optical insulating layers110. This graphic layer140may be a metallization layer which is then partially removed to form the desired design by use of a laser or chemical etching. Alternatively, the graphic layer may be a foil on which a design is applied. The foil is then hot stamped to the optical insulating layer110.

The process may include further steps, for example the application of a protective layer150in the form of a lacquer, for example can be applied to the outer surface of the plate, but particularly over the graphic layer140to protect this and possibly compensate for variations in thickness. An optically reflective layer170may be applied prior to this step on the lower surface of the plate10, i.e. on the surface that faces the radar sensor20and is directed away from the observer.

It will be understood that the examples and embodiments described herein can be used in various combinations and sub-combinations.