EP3709440A1

EP3709440A1 - Radome for vehicles and method for manufacturing said radome

Info

Publication number: EP3709440A1
Application number: EP20162890.6A
Authority: EP
Inventors: Augusto Mayer Pujadas; Benjamín IZQUIERDO FERNANDEZ; Santiago BUITRAGO VENTURA; Jordi Romeu Robert
Original assignee: Zanini Auto Grup SA
Current assignee: Zanini Auto Grup SA
Priority date: 2019-03-13
Filing date: 2020-03-13
Publication date: 2020-09-16

Abstract

The radome for vehicles comprises a frontal layer (1) made from thermoplastic material, the radome also comprising a foamed core (2) on which the frontal layer (1) is adhered.The method for manufacturing said radome comprises the following steps: forming a foamed core (2); thermoforming a frontal layer (1); and adhering the frontal layer (1) to the foam core (2).It permits to provide a radome with a pleasant aesthetic and functional solution that can be easily manufactured.

Description

The present invention refers to a radome for vehicles, such as a decorative radome used as an emblem, especially for radomes disposed in front of a radar in the front grill of a vehicle. The present invention also refers to a method for manufacturing said radome.

Background of the invention

Vehicles with sensors able to sense their surroundings are the key enablers to decrease of road fatalities. Through sensors, driver assistance functions are implemented, minimizing risks and increasing the probability of avoiding collisions.
Vehicles are designed to offer an aesthetically pleasant impression. Therefore, sensors must be integrated within the vehicle behind covers enabling their function, concealing them from the public view and harmonized with the aesthetic design of the vehicle.
In case of a radar sensor, such covers are known as radomes. As mentioned above, radomes must minimize the impact its presence offers to radar emitted and received waves.
Current radomes possess a 3D appearance effect by superposition of several articles, which have complimentary recesses so that, once assembled together, have a performance like a dielectric lens.
These radomes are expensive due to the different articles being manufactured separately and then assembled. Typically, two injections are involved: one for the front part, one for the rear part. Decoration layers are added to one or both articles as inks, thermo-adhesives, or metallic decoration by Physical Vapor Deposition, for instance.
Sometimes, additional articles between front and rear layers are also included, such as other molded articles, or decorated foils which are thermoformed and over-injected. Additionally, other processes may be necessary for each part, such as sprue cutting, lasering, masking, etc. on each part. Finally, all components are attached together by chemical (glue), physical (welding) or mechanical (hooks) means.
The market growth on automotive radars has been steadily increasing in the last few years. Specifically, front radars are concealed behind plastic elements such as the vehicle logo, to avoid issues with paints added to bumpers which can severely deteriorate corner radar performance.
The cost of such radome logo is high due to the number of elements and processes involved in its manufacturing. In order to speed up the introduction of such sensors across all vehicle manufacturers and platforms, cost reduction is required.
The performance of such radomes can also compromise the detection function executed by the radar, as they are composed of thick lossy materials, typically 2-8 mm of PC, ASA, ABS, ABS-PC, etc. whose dielectric properties are not ideal for transparency of radar waves.
Even if substrate materials for the molded articles are chosen carefully, typical tangent losses, which determine energy absorption of radar waves in the material, are on the order of 0.01 at radar frequencies. Therefore, between 20% and 50% of the radar wave energy is absorbed in the radome.
Decoration layers may also introduce further radar wave absorption, if their composition contains conductive elements such as metallic particles.
Facets on the inner surfaces of the radomes, between front and rear articles, also affect radar performance. These facets are needed to faithfully reproduce the manufacturer brand and, on its surfaces, electromagnetic waves scatter in different directions, introducing errors in the direction of arrival of radar waves detected by the sensor.
Moreover, radar waves go through several changes of media along its propagation path when crossing the radome. Even when attaching two parts together as close as possible, a small air gap will be present between both parts. Hence, radar waves emitted by the radar transition from air to plastic to enter the radome rear part, from plastic to the air gap, from air to plastic to enter the radome front part, and finally from plastic to air to exit the radome.
The same occurs in opposite direction for radar echoes reflected by the scene. At each interface, part of the radar energy is reflected back, which can blind the radar and decrease the amount of energy transmitted to the other side of the radome.
US9114760B2 , of the same applicant than the present application, describes a radome composed of a radio transmissive resin with a metalloid-based metallic looking decoration layer. An issue of this invention is the absorption of the employed radio transmissive resin, although it offers a solution for a decorated radome. When the resin is molded, it will have a minimum thickness that will introduce significant absorption to radar waves.
Therefore, the objective of the present invention is to provide a pleasantly aesthetic radome for automotive applications, where the brand logo is frequently used as a radome.
Therefore, a foamed-based decorated radome can improve current solutions and increase radar performance in automotive applications.
The aim of this invention is solving these problems while providing a pleasant aesthetic and functional solution that can be easily manufactured.

Description of the invention

With the radome and the method according to the present invention it is possible to solve said drawbacks, providing other advantages that are described below.
According to a first aspect, the present invention refers to a radome for vehicles, comprising a frontal layer made from thermoplastic material, wherein the radome also comprises a foamed core on which the frontal layer is adhered.
Advantageously, the frontal layer and the foamed core can have protrusions and/or recesses for reproducing a 3D image, such as a logo.
According to an embodiment, the radome can also comprise a rear layer adhered to the foamed core.
Advantageously, the foamed core and the frontal layer are curved, defining a cavity.
The foamed core can be made from any suitable material, such as Polyurethanes (PU), Polyvinyl chloride (PVC), and Polypropylene (PP) among others or most preferably Polymethacrylimide composites.
Advantageously, the frontal layer is decorated, comprising on its outer surface ink, thermo-adhesive and/or metallic luster.
Moreover, in order to protect it, from chemicals, mechanical impacts or UV radiation damages, the frontal layer comprises preferably an additional UV-curable hard coat.
The radome for vehicles according to the present invention also comprises a case and said case can be frontally open and attached at its frontal portion to the frontal layer, or alternatively, said case can be placed behind the frontal layer and the foamed core and it can be closed by a sealing surface.
According to a second aspect, the present invention refers to a method for manufacturing a radome for vehicles as described previously, wherein the method comprises the following steps:

forming a foamed core;
thermoforming a frontal layer;
adhering the frontal layer to the foam core.

Advantageously, during the forming step of the foamed core protrusions and/or recesses are formed for reproducing a 3D image, such as a logo, and during the thermoforming of the frontal layer protrusions and/or recesses are also formed for reproducing the same 3D image.
Preferably, the thermoforming of the frontal layer is made from a thermoplastic extruded foil material.
The method for manufacturing a radome for vehicles according to the present invention also comprises the step of decorating the frontal layer such as, e.g., by means of inks, thermo-adhesives and/or metallic luster by physical vapor deposition (PVD).
If necessary, the method can also comprise the step of applying a UV-curable hard coat completely overlying the frontal layer.
Preferably, the step of adhering the frontal layer to the foam core is made by means of glue, heat-curable fluid resin, temperature or pressure.
According to an embodiment, the method can also comprise the step of attaching a case, which is frontally open, at its frontal portion to said frontal layer.

Brief description of the drawings

For a better understanding the above explanation and for the sole purpose of providing an example, some non-limiting drawings are included that schematically depict a practical embodiment.
Figs. 1-8 show in a diagrammatical section view eight different embodiments of the radome for vehicles according to the present invention.

Description of preferred embodiments

In its base form, the radome for vehicles according to the present invention comprises a frontal layer 1 made from thermoplastic material and a foamed core 2 on which the frontal layer 1 is adhered.
Foamed materials have dielectric properties similar to air. The reason is their physical nature is porous and have large air content inside. This fact has several advantages from a radar point of view.
Their relative permittivity lies between 1.1 and 1.5, depending on their density. That of air is 1. Therefore, reflections at the interfaces between air and material are much smaller. For instance, when compared with typical PC, ABS-PC, PMMA, ABS or ASA values, reflections due to the change of media can be 13% smaller, as summarized in table 1. Thus, the improvement on the radar performance will come from the fact that most of the energy propagates to objects present far away from the radar and, being reflections due to the radome almost inexistent, no distortion of the echoes of such objects will occur. The radar will be able to see the scene in the most accurate way. Table 1: reflection coefficient for different cores

Core material Resin (PC, ABS-PC, PMMA, ASA) Foam

Reflection coefficient ∼23% 10%
Loss tangent of foamed materials is also very low, typically one order of magnitude smaller than PC, ABS, ABS-PC, PMMA, or ASA, as shown in Table 2. Therefore, even if similar thickness compared to traditional radomes described above is employed in foamed radomes, losses due to the absorption will be much smaller. Radar waves will reach objects on the scenario farther end with more energy, and echoes from these objects will be stronger. So, for identical radar sensitivity and receiver noise level, a foamed radome will improve the radar detection range with respect to traditional radomes. Table 2: loss tangent for different cores

Core material Resin (PC, ABS-PC, PMMA, ASA) Foam

Loss tangent ∼0.01-0.02 <0.005

Losses due to absorption (∼3.6mm) 0.3dB 0.015dB
There are drawbacks, however, when using foamed materials in decorative radomes, such as automotive logos. Given their porous nature, foam surfaces cannot be smooth or polished-like, so only irregular aspect, with spots and valleys, will be attained, even when thick paint layers are used to try to level the surface inhomogeneity. This is not attractive for end customers of automobiles. Hence, a solution needs to be found.
Moreover, radomes are articles that are subject to very demanding tests, as they have to have high resistance to chemical products, abrasion, corrosion, impact, weather conditions, etc. Foamed materials may not be able to withstand such variety of conditions, so it makes sense having a suitable layer of another material protecting them from the outer environment
The solution is adding the frontal layer 1, and if necessary, a rear layer 4, of thermoplastic materials, as PC, ABS, PMMA, ASA or ABS-PC. These materials can withstand demanding tests for exteriors, sometimes requiring a hard coat layer, and they possess high quality surfaces that can be decorated with ease, so they are ideal to reproduce an automobile manufacturer logo.
The selected layer thickness will depend on the material properties and on the foam density of the foamed core 2, as for such thin layer the foam material will be the core of the radome that will provide the mechanical resistance of the whole. Ideally, the layer(s) will be as thin as possible in order to introduce lower absorption losses.
Given typical values of relative permittivity and loss tangents for thermoplastic materials, such as PC, ABS, ABS-PC, ASA or PMMA, which lie between 2.5-3 and 0.005-0.02 respectively at automotive radar frequencies, they offer a resonant behavior as a function of their thickness.
The ideal layer thickness for such materials should be selected so that minimal attenuation and reflection is achieved. Optimal thicknesses can be therefore very small (about 0.1-0.3 mm) or around 1-1.5 mm, 2-2.5 mm and thicker resonant points. As the foamed material will be the bulk of the radome thickness, the layer thickness will be selected as thin as possible among the previous resonance thickness points. Moreover, there are certain limitations from an injection point of view if large, thin layers from the materials mentioned above are needed. For such large, thin layers, around 1 mm thick, defects on the surface will appear due to the resistance and cooling the melted material will suffer during the injection process inside tool cavity. The lower thickness limit for large layers depends on the material viscosity, but typically a value of 1.5 mm is enough to be able to inject such layers without defects on their surfaces.
However, at such thicknesses, absorption is high, and for the next resonant thickness (around 2-2.5 mm) there are no extruded layers. To get such thicknesses, an injection tool is needed. Therefore, product cost is increased.
In order to use thin, large layers of such materials, commercial thermoplastic foils of extruded, non-injected materials are available with high surface quality. There is also a wide range of thicknesses available, so the most suitable for the purpose herein described can be selected.
The thermoplastic layer(s) 1, 4 needs to be adhered to the foamed core 2 by means of temperature, glue, heat curable fluid resin, pressure or a combination of the above, in order to obtain a solid monolithic block that will allow the passing of radar waves.
The main requirement in case other consumables are needed is that they are transparent to radar waves.
Decoration can be applied on the surface of the frontal layer 1, and this process can take place before or after the adhesion with the foamed core 2. In case the decoration occurs before the adhesion step, suitable protection might be necessary to protect the decoration during the adhesion process.
Different kinds of decoration can be applied to the surface of the frontal layer 1: color inks, thermo-adhesive, metallic-looking decoration by means of PVD, etc. The selected decorations will be determined by the appearance of the vehicle manufacturer's logo.
Additionally, a last layer of UV-curable hard coat might be needed depending on the layer material to withstand the different testing scenarios required by the vehicle manufacturer. The list of test extends, but is not limited to: abrasion, corrosion, scratching, aging resistance, chemical, climatic, etc.
Some embodiments are shown in Figs. 1-8.
In the first and third embodiments shown in Figs. 1 and 3, a foamed core 2 is cured in a tool producing a curved foamed core 2 defining a cavity that possesses a curvature but not protrusions or recesses for reproducing a 3D image.
A thermoplastic resin frontal layer 1 of extruded material chosen among PC, PMMA, ABS, ABS-PC or ASA, thermoformed in a tool adapted to the foamed core 2 curvature.
The thermoformed frontal layer 1 is decorated with inks, thermo-adhesives, and/or metallic luster via PVD deposition, to reproduce a vehicle manufacturer logo.
The frontal layer 1 is protected with UV-curable hard coat (not shown in the drawings).
The decorated frontal layer 1 is adhered to the foamed core 2 by means of glue, resin, temperature, or pressure. The frontal layer 1 is placed in the radome surface farther from the motor engine.
The second and fourth embodiments, shown in Figs. 2 and 4 are very similar to the previous embodiments, with the difference of a second thermoplastic resin layer, rear layer 4, of extruded material, thermoformed in a tool adapted to the foamed core 2 curvature.
This rear layer 4 is also adhered to the foamed core 2 by means of glue, resin, temperature, or pressure, and it is placed in the radome surface closer from the motor engine.
The fifth and seventh embodiments, shown in Figs. 5 and 7 are very similar to the first and third embodiments, with the difference that the foamed core 2 and the frontal layer 1 have protrusions and recesses to reproduce a 3D image.
The sixth and eighth embodiments, shown in Figs. 6 and 8 are very similar to the second embodiment, with the difference that the foamed core 2 and the frontal layer 1 have protrusions and recesses to reproduce a 3D image.
Furthermore, the radome for vehicles according to the present invention comprises a case 5 and said case 5 can be frontally open and attached at its frontal portion to the frontal layer 1, as shown in the first, second, fifth and sixth embodiments. I.e. in these embodiments, the frontal layer 1 and the foamed core 2 are used as a primary surface.
In the third, fourth, seventh and eighth embodiments, said case is placed behind the frontal layer 1 and the foamed core 2 and being closed by a sealing surface 7. I.e. in these embodiments, the frontal layer 1 and the foamed core 2 are used as a secondary surface.
This case 5 houses a radar circuit and antennas 6.
As primary surface means the radar cover, which is non decorated, that seals the radome, preventing any water or dust leaking into the radar circuits, offering better thermal isolation with respect to the environment and providing a robust packaging to the assembly.
In this case, when the frontal layer 1 and the foamed core 2 are used as a primary surface, the frontal layer 1 would be attached to the radar case 5 on the perimeter by glue, welding or any other suitable means, thus preventing and leaks from the outside towards the radar circuitry and offering an integrated, compact and robust enclosure for the whole radar and decorative radome.
When the frontal layer 1 and the foamed core 2 are used as a secondary surface, there is a sealing element 7 in front of the radar antennas 6.
Even though reference has been made to a specific embodiment of the invention, it is obvious for a person skilled in the art that the radome and method described herein is susceptible to numerous variations and modifications, and that all of the details mentioned can be substituted for other technically equivalent ones without departing from the scope of protection defined by the attached claims.

Claims

Radome for vehicles, comprising a frontal layer (1) made from thermoplastic material, characterized in that the radome also comprises a foamed core (2) on which the frontal layer (1) is adhered.
Radome for vehicles according to claim 1, wherein the frontal layer (1) and the foamed core (2) have protrusions (3) and/or recesses.
Radome for vehicles according to claim 1 or 2, wherein the radome also comprises a rear layer (4) adhered to the foamed core (2).
Radome for vehicles according to anyone of the previous claims, wherein the foamed core (2) and the frontal layer (1) are curved.
Radome for vehicles according to anyone of the previous claims, wherein the foamed core material (2) is made from Polyurethane (PU), Polyvinyl chloride (PVC), Polypropylene (PP) or alike and, most preferably, Polymethacrylimide composites.
Radome for vehicles according to anyone of the previous claims, wherein the frontal layer (1) comprises on its outer surface ink, thermo-adhesive and/or metallic cluster.
Radome for vehicles according to anyone of the previous claims, wherein the frontal layer (1) comprises an UV-curable hard coat.
Radome for vehicles according to anyone of the previous claims, wherein the radome comprises a case (5), said case (5) being frontally open and attached at its frontal portion to the frontal layer (1).
Radome for vehicles according to anyone of claims 1-7, wherein the radome comprises a case (5) that houses a radar circuit and antennas (6), said case (5) being placed behind the frontal layer (1) and the foamed core (2) and being closed by a sealing surface (7).
Method for manufacturing a radome for vehicles according to anyone of the previous claims, characterized in that the method comprises the following steps:
- forming a foamed core (2);

- thermoforming a frontal layer (1),

- adhering the frontal layer (1) to the foam core (2).
Method for manufacturing a radome for vehicles according to claim 10, wherein during the forming step of the foamed core (2) protrusions and/or recesses are formed for reproducing a 3D image.
Method for manufacturing a radome for vehicles according to claim 10, wherein during the thermoforming of the frontal layer (1) protrusions and/or recesses are formed for reproducing a 3D image.
Method for manufacturing a radome for vehicles according to claim 10 or 12, wherein the thermoforming of the frontal layer (1) is made from a thermoplastic extruded foil material.
Method for manufacturing a radome for vehicles according to claim 10, wherein the method also comprises the step of decorating the frontal layer (1) by means of inks, thermo-adhesives and/or metallic luster by physical vapor deposition (PVD).
Method for manufacturing a radome for vehicles according to claims 10 or 14, wherein the method also comprises the step of applying a UV-curable hard coat completely overlying the frontal layer (1).
Method for manufacturing a radome for vehicles according to claim 10, wherein the step of adhering the frontal layer (1) to the foam core (2) is made by means of glue, heat-curable fluid resin, temperature or pressure.
Method for manufacturing a radome for vehicles according to claim 10, wherein the method also comprises the step of attaching a case (5), which is frontally open, at its frontal portion to said frontal layer (1).