WO2024022813A1

WO2024022813A1 - Vehicle part, sensor assembly, motor vehicle, and method and film set for improving the degree of transmission of a vehicle part

Info

Publication number: WO2024022813A1
Application number: PCT/EP2023/069283
Authority: WO
Inventors: Thomas Albrecht
Original assignee: Merck Patent Gmbh
Priority date: 2022-07-25
Filing date: 2023-07-12
Publication date: 2024-02-01

Abstract

The invention relates to a vehicle part (4) comprising a support part (6) which is made of a polymer material and which has a first surface (7) and a second surface (8) that is substantially parallel thereto; a first coating (9) which is applied onto the first surface (7) of the support part (6) and which has a first degree of reflection R1 for electromagnetic waves (5) of a specified frequency spectrum, in particular radar waves (5a, 5b); and a second coating (10) which is applied onto the second surface (8) of the support part (6) and which has a second degree of reflection R2 for electromagnetic waves (5) of the specified frequency spectrum. The second degree of reflection R2 matches the first degree of reflection R1 such that the support part (6), the first coating (9), and the second coating (10) form a resonator (11) for the electromagnetic waves (5). The invention additionally relates to a sensor assembly, to a motor vehicle, and to a method for improving the degree of transmission of a vehicle part.

Description

Vehicle part, sensor arrangement, motor vehicle and method and film set for improving a transmittance of a vehicle part

The invention relates to a vehicle part comprising a carrier part, a sensor arrangement comprising a vehicle chassis, at least one transmitter and detector arranged on the vehicle chassis and a vehicle part attached in the area of the transmitter and/or detector, a motor vehicle with at least one radar-based distance sensor and a method and a Set of foils for improving a transmittance for electromagnetic waves of a predetermined frequency, in particular radar waves.

From DE 10 2009 029 763 A1 a body plastic component for a motor vehicle is known which has a support body with a base body made of plastic. A varnish, in particular with at least two effect varnish layers, can be applied to the base body. The body plastic component has an attenuation for radiation in a radar frequency range between 75 GHz and 85 GHz, at least in a radar transparency section, the absolute value of which is less than 3 dB in a single pass.

It is an object of the present invention to describe alternative, preferably particularly simply constructed vehicle parts, sensor arrangements and methods for their production, which allow electromagnetic waves of a predetermined frequency, in particular radar waves, to be transmitted through a vehicle part with as little loss as possible.

According to a first aspect of the disclosure, a vehicle part is described. The vehicle part includes: a support member made of a polymer material having a first surface and a second surface substantially parallel thereto; a first coating applied to the first surface of the carrier part, which has a first reflectance R1 for electromagnetic waves of a predetermined frequency spectrum, in particular radar waves; and a second coating applied in at least a portion of the second surface of the carrier part, which has a second reflectance R2 for electromagnetic waves of the predetermined frequency spectrum, the second reflectance R2 being matched to the first reflectance R1 such that the carrier part, the first coating and the second coating forms a resonator for the electromagnetic waves.

The first coating can be a layer of lacquer or a painted or colored plastic film. The plastic film can, for example, be colored with effect pigments. The film is usually self-adhesive and is simply stuck onto the corresponding vehicle part.

The inventor has recognized, among other things, that by applying an additional, reflective layer to a second surface of a vehicle part, in particular a back of a carrier part painted or foiled on the front, such as a bumper, a resonator for electromagnetic waves, in particular radar waves, is formed can, and that this can lead to an increased degree of transmission or reduced degree of reflection of the vehicle part for the electromagnetic waves in a predetermined frequency spectrum or in a range around a given working or center frequency. For this purpose, the reflectance R2 is used Coating on the second surface is matched to the reflectance R1 of the first coating on the first surface, for example for a given working or center frequency or the entire frequency spectrum.

In at least one embodiment, the vehicle part has a transmittance of more than 50 percent, preferably more than 80 percent, for example in a frequency spectrum between 60 and 100 GHz, in particular between 75 and 85 GHz. This frequency spectrum is used, among other things, for radar-based anti-collision radars and/or adaptive cruise control systems.

In at least one embodiment, the carrier part can be made from a plastic material and have a thickness in a range of 1.5 to 5 mm. Such material thicknesses achieve the rigidity required in vehicle construction and are at the same time on the order of the wavelength of radar waves.

In at least one embodiment, the first coating comprises an effect lacquer layer with effect pigments, which, for example, has a thickness between 12 and 20 μm. Together with other paint layers, for example an underlying primer and a base coat layer and an overlying clear coat layer, the first coating can have a total thickness in a range between 80 and 130 μm. Such paint layers and thicknesses achieve an appearance desired in vehicle construction and have a degree of reflection that enables the construction of a resonator.

In at least one embodiment, the second coating has a similar structure to the first coating. By applying a coating on the back, the equivalence of the two coatings can be ensured particularly easily, for example by applying the same paint in the same thickness to the second side of the vehicle part.

In at least one alternative embodiment, the second coating has a thin metallized plastic film or metal film glued to the back of the vehicle part. Such a vehicle part can be produced particularly easily and inexpensively by gluing on a film section with the required degree of reflection. The use of preferably self-adhesive films also enables simple retrofitting of existing vehicle parts, for example after determining a degree of reflection of an existing paint finish on the first surface.

Such a vehicle part is particularly suitable for producing a sensor arrangement, in which at least one transmitter for transmitting electromagnetic waves of a predetermined frequency, in particular radar waves, and at least one arranged detector for detecting electromagnetic waves of the predetermined frequency, in particular reflected radar waves, are arranged on a vehicle chassis and are covered by the vehicle part.

Such a vehicle part or such a sensor arrangement is particularly suitable for use in a motor vehicle with a radar-based sensor.

According to a further aspect of the disclosure, a method for improving a transmittance of a vehicle part for electromagnetic waves of a predetermined frequency, in particular radar waves, is disclosed. The procedure includes the steps: Determining a reflectance of a first coating of a first surface of a vehicle part, in particular a paint layer applied to an outside of the vehicle part; and

Applying a second coating in at least a portion of a second surface of the vehicle part opposite the first surface, wherein a reflectance of the second coating is adapted to the reflectance of the first coating.

According to a further aspect of the disclosure, a set of films for improving a transmittance for electromagnetic waves of a predetermined frequency, in particular radar waves, is disclosed. The film set comprises a plurality of self-adhesive sections of a metal film or a metallized plastic film, the sections differing in their degree of reflectance and, optionally, in their thickness. Such a film set makes it possible to produce a vehicle part or a sensor arrangement of the type mentioned above in a simple manner, in particular by selecting a film section with suitable physical properties.

Further refinements and advantages of the disclosed invention are disclosed in the following description of exemplary embodiments and the appended patent claims.

The invention is described in detail below using different exemplary embodiments with reference to the figures. Show in it:

Figure 1 is a schematic representation of a sensor arrangement;

Figure 2 shows a cross section through a vehicle part according to an embodiment of the disclosure; Figures 3A to 4B different samples for determining a transmittance and reflectance of coated polymer materials;

Figures 5A to 7B measurement protocols for the differently coated samples; and

Figure 8 shows schematically the steps of a method for improving a transmittance of a vehicle part.

The vehicle parts described below are particularly suitable for covering radar-based sensors. For example, radar-based distance sensors are increasingly being installed in motor vehicles to prevent accidents, improve driving comfort and ultimately enable self-driving cars. Other applications, such as radar-based sensors for detecting seeds or liquids in commercial vehicles such as trucks or agricultural machinery, are also possible. In order to protect the radar wave transmitters and detectors required for this from environmental influences and/or not to negatively influence the design of a vehicle front aerodynamically or aesthetically, radar-based sensors are usually installed behind vehicle parts or covers made of a polymer material, for example bumpers in the form of an integrated bumper of a motor vehicle or in Panels of commercial vehicles, arranged.

The polymer materials used to produce such vehicle parts have only a relatively low degree of reflectance and a low degree of absorption for radar waves. However, for aesthetic reasons, such vehicle parts are usually covered with a layer of paint or a painted, preferably self-adhesive, plastic film, or an already pigmented, preferably self-adhesive, plastic film, which correspond to the paintwork of the rest of the vehicle. Such plastic films or lacquer layers, which in particular contain metallic effect pigments, have a higher degree of reflection and therefore hinder the transmission and reception of reflected radar waves.

Figure 1 shows a schematic cross section through a sensor arrangement 4 of a motor vehicle, which is otherwise not shown, in particular a car or truck.

The sensor arrangement 1 comprises a part of a vehicle chassis 2, a radar-based sensor in the form of a distance sensor 3 and a vehicle part 4 covering the distance sensor 3. For example, the part of the chassis 2 is a front vehicle front, which is made of a metal material. In the exemplary embodiment described, the vehicle part 4 is a bumper made essentially from a polymer material, in particular a plastic material, in the form of an integrated bumper. Alternatively, the vehicle part 4 can also be a pure cover part for a radar-based sensor. Such covers are also known as radomes.

The distance sensor 3 includes a transmitter 3a for emitting electromagnetic waves 5 of a predetermined frequency spectrum. A frequency spectrum represents a coherent frequency range, for example between a maximum frequency and a minimum frequency or a range with a predetermined bandwidth around a given frequency. In particular, the transmitter 3a emits radar waves 5a in a frequency spectrum between 70 and 80 GHz. Such electromagnetic radar waves 5a are reflected by vehicles in front or other obstacles and are considered reflected electromagnetic radar waves 5b are transmitted back to a detector 3b of the distance sensor 3. The electromagnetic waves 5 pass through the vehicle part 4 twice. In a further embodiment, the transmitter and detector can also be one and the same component.

Although the vehicle part 4 typically has a complex, rounded shape, it has surfaces that are essentially parallel to one another, at least in the area in which the radar waves 5a and 5b penetrate the vehicle part 4. If the outer surface of the vehicle part 4 on the right in FIG - The noise ratio of the distance sensor 3 is significantly reduced. In particular, the part of the outgoing radar waves that is reflected back inwards can disrupt or even completely saturate the sensor.

Figure 2 shows an enlarged section of the vehicle part 4 according to Figure 1. It should be noted that the illustration in FIG. 2 only serves as an explanation and does not reflect the actual dimensions of vehicle part 4.

The vehicle part 4 according to Figure 2 has a support part 6 with two mutually parallel surfaces 7 and 8. In the exemplary embodiment shown, the surface 7 on the right in Figure 2 points away from a distance sensor 3, not shown in Figure 2, and the second surface 8 opposite it points towards it the distance sensor 3. The first surface 7 is therefore typically an outside of the vehicle part 4 and the second surface 8 is an inside of the vehicle part 4. A first coating 9 is arranged on the first surface 7. For example, this is a lacquer layer or film 12, which includes a large number of effect pigments 13. The effect pigments 13 in particular ensure an aesthetically pleasing effect (for example metallic effect, brightness and/or color flop, possibly glitter) of the lacquer layer 12. The effect pigments 13 are, for example, metallic effect pigments in the form of microscopic aluminum plates a thickness of less than 1 pm. Such aluminum flakes can be produced, for example, by flat-rolling small aluminum spheres and stirring them into suitable carrier lacquers. In addition to metallic effect pigments, non-metallic effect pigments are also known. Such effect pigments are based on platelet-shaped substrates, such as natural or synthetic mica, talc, SiO2 platelets, A Os platelets, glass platelets, iron oxide platelets, graphite platelets, which are completely coated with one or more metal oxides. Conductive primers are also often used for the paint layer 12, which reflect a further portion of the electromagnetic radiation. Without further measures, the coating 12 and in particular the effect pigments 13 contained therein as well as a primer significantly increase the degree of reflection of the first coating 9. A significant proportion of electromagnetic waves 5 that hit the vehicle part 4 would thus be reflected.

In order to reduce or completely prevent this effect, a second coating 10 is arranged on the second surface 8. In the exemplary embodiment, the second layer 10 is, for example, a glued-on film, in particular a self-adhesive metal film or metallized plastic film 14. When using a metallized plastic film 14, a controlled shift in the resonance frequency can also be brought about by controlling its thickness. 2, the second coating 10 does not necessarily cover the entire second surface 8 of the vehicle part 4. It is sufficient if the second coating 10 is arranged at least in a section 15 of the second surface 8 which is affected by the electromagnetic waves 5 is to be penetrated, for example an area of the vehicle part 4 behind which a distance sensor 3 is arranged. Alternatively, the second coating 10 can also cover the entire second surface 8.

The reflectance of the second coating 10 is closely matched to the reflectance of the first coating 9. Thus, the first coating 9, the carrier part 6 and the second coating 10 together form a resonator 11.

If the dimensions of the resonator 11 are matched to the frequency of the electromagnetic waves 5, the resonator 11 as a whole has a significantly reduced degree of reflection compared to the degrees of reflection of the individual layers 9 and 14. This means that the electromagnetic waves 5 can penetrate the vehicle part 4 essentially undamped. In other words, the vehicle part 4 is largely transparent to the electromagnetic waves 5 in the resonance range.

In the exemplary embodiment, the carrier part 6, which is made of a polymer material, has, for example, a thickness D of 2 to 3 mm. The first layer 9 or the second coating 10 have thicknesses of approximately 20 pm and have a reflectance of approximately 10 to 20 percent for the frequencies of 70 to 80 GHz that are typical for radar-based distance sensors. This corresponds to a wavelength in air of approximately 4.28 to 3.75 mm. This corresponds to a thickness D of the carrier part 6 of approximately 2 mm in approximately half the wavelength of the electromagnetic waves 5.

The resonator 11 essentially represents a relatively weak Fabry-Perot interferometer, for example with a quality of the resonator of less than 100, in particular less than 20, for example 15 or 10. The quality Q of a resonator with resonance frequency fo and bandwidth applies Af:

Transmission maxima are found at a multiple of half the wavelength X:

Where n is the refractive index of the material used and m is a positive natural number.

The transmittance T of a Fabry-Perot interferometer depends, among other things, on the first reflectance R1 of the first coating 9 and the second reflectance R2 of the second coating 10. Neglecting absorption losses, the following applies to the maximum transmission of the resonator in the case of resonance:

Above and below the resonance frequency, the transmittance T drops accordingly. If both surfaces 7 and 8 of the carrier part 6 have the same degree of reflection for the distance sensor 3 used electromagnetic waves 5, that is, when R1 = R2, a maximum of the transmittance T of theoretically 100 percent is achieved. In practice, the actual transmittance T is further reduced by absorption losses, for example of the polymer material of the carrier part 6 and other components of the coatings 9 and 10. However, in practice these losses are sufficiently small to not significantly affect the functionality of the distance sensor 3.

One way to coordinate the reflectances R1 and R2 of the coatings 9 and 10 is to first determine a reflectance R1 of the coating 12. For this purpose, the vehicle part 4 that has already been painted on one side can first be measured. Subsequently, for example, a film can be selected from metallized plastic films 14 of possibly different thicknesses, the reflectance R2 of which comes closest to the reflectance R1 of the first coating 9. Optionally, a desired shift in the resonance range can be achieved by selecting its thickness. The selected film 14 is then glued to the back 8 of the carrier part 6.

For example, a film set with several film sections with different physical properties can be used for this purpose. For example, the film sections can be arranged and marked in the form of a matrix, with film sections in a column having different degrees of reflection and the same thicknesses and film sections in a row having the same degrees of reflection and different thicknesses.

Another way to set the reflectances R1 and R2

Matching coatings 9 and 10 consists of:

Carrier part 6 is to be provided on both sides with comparable layers of paint. How Beforehand, the painting can only be done in the area 15 of the sensor 3 or over the entire surface.

To confirm the above effect, a total of five different samples are prepared. The structure of four of the five samples is shown in Figures 3A to 4B.

The sample 0F0R consists of a plastic plate that is not shown in the figures and is uncoated on both sides. In particular, this is a 3 mm thick plate made of a polycarbonate with the trade name Makrolon®, which has the electromagnetic properties of plastics that are used, for example, for bumpers.

The sample 2F0R according to Figure 3A only has a one-sided, simple lacquer layer 12 with a thickness of approximately 13 μm on the first surface 7. Such a thickness is typical for a painted motor vehicle part 4. The lacquer used comprises approximately 18 percent mass concentration of aluminum pigments in the solid paint (18 percent PMC aluminum effect pigments), which corresponds to a very high pigmentation of a metallic paintwork on motor vehicles. This sample is used, among other things, to demonstrate the reflection or transmission behavior of a conventional vehicle part 4 that is only painted on one side.

The sample 2F2R according to FIG. 3B is coated on both sides with a simple lacquer layer 12 approximately 13 μm thick. For this purpose, both surfaces 7 and 8 of the carrier part 6 are painted with the same vehicle paint including metallic effect pigments 13.

4A and 4B show two further samples 4F0R and 4F4R, the surfaces 7 and 8 of which are provided with a double layer of lacquer 12 with a total thickness of approximately 27 μm. This is done at In the sample 4F0R according to FIG. 4A, only the first surface 7 is again painted, while in the sample 4F4R according to FIG. 4B, the first surface 7 and the second surface 8 are painted in the same way.

5A and 5B first show the transmission and reflection behavior of the uncoated plastic plate according to sample 0F0R and of the plastic plate 2F0R coated on one side according to FIG. 3A as a percentage value or as the corresponding signal attenuation in decibels. As can be seen in particular in FIG. 5A, the uncoated plastic material has a reflectance of 0 to 20 percent and a transmittance of approximately 75 to 95 percent in the relevant frequency spectrum between 60 and 90 GHz. The lowest reflectance is in a frequency spectrum that is typically not used by radar sensors below 65 GHz. The values missing from 100 percent can be explained in particular by absorption by the plastic material.

By applying a simple lacquer layer 12, as shown in FIG. 3A, a minimum of the reflection is shifted to approximately 83 GHz. In contrast, there is a maximum in the range between 64 and 77 GHz, with reflectances of around 30 to 40 percent, while the transmittance decreases to around 55 to 65 percent.

In Figures 6A and 6B, the measured transmission and reflectance values for the two samples 2F0R and 2F2R according to Figures 3A and 3B are compared with one another. As can be seen in Figures 6A and 6B, the transmittance has a maximum of over 85 percent near a frequency of 77 GHz. Accordingly, the reflection at this frequency has a minimum of almost 0 percent (-24 dB). The vehicle part 4 therefore causes practically no disturbing reflections in a frequency spectrum typical of radar sensors. In addition, the transmitted Signal proportion is significantly increased, so that a signal-to-noise ratio is significantly improved.

In Figure 6A it can be seen, among other things, that there is a coherent frequency range in which the reflection of the double-painted sample 2F2R is significantly lower than the reflection minimum of the single-painted sample 2F0R. Equivalently, the transmission is significantly greater in this area. Radar-based distance sensors can be operated reliably in this hatched range between 74 and 79 GHz.

Measurement results for samples 4F0R and 4F4R according to FIGS. 4A and 4B are shown in FIGS. 7A and 7B. As can be seen therein, the transmission maximum or the reflection minimum shifts by doubling the lacquer layer 12 towards lower working frequencies, in particular in the range of 72 GHz. Despite the significantly increased reflectivity of the double layer of paint, the minimum reflection in the range around 72 GHz is only a few percent and is therefore also suitable for radar-based distance sensors 3. In addition, the reflected signal component of the sample 4F4R, which is painted on both sides, is around -14 dB, around 10 dB below the only Sample 4F0R painted on one side with a reflected signal component of approximately -4 dB.

6A to 7B, it can be seen that by adjusting the thickness of the paint layers 12, the resonance frequency of the vehicle part 4 can be adapted to the frequency of the electromagnetic waves 5 used, in particular radar waves 5a and 5b. The thickness D of the carrier part 6 is available as a further optimization parameter. The degree of reflection or transmittance of the coated vehicle part 4 can be further optimized if the degree of reflection R2 of the second coating 10 is chosen to be slightly smaller than the degree of reflection R1 of the first coating 9 in order to at least partially compensate for the absorption caused by the carrier part 6. For example, the reflectance R2 of the second coating 10 is approximately 80 to 99 percent, preferably 90 to 98 percent, for example 95 percent, of the reflectance R1 of the first coating 9.

Figure 8 shows schematically the steps of a method for improving a transmittance of a vehicle part 4.

As shown in FIG. 8, in a first step S1 a reflectance R1 of a first coating 9 is first determined.

This can be done, as described above, by measuring a vehicle part 4 that has already been painted on one side or based on knowledge of the relevant parameters used for production, in particular the transmission, reflection and absorption behavior of the materials used, the thickness of the carrier part 6 and the first coating 9 , take place. In this case, the reflectance R1 of the vehicle part 4 can be determined using appropriate theoretical models or based on known series of measurements. Finally, only the parameters used for painting can be recorded without explicitly recording the first reflectance R1.

In a further step S2, a second coating 10 is applied to an opposite surface 8, the reflectance R2 of the second coating 10 being chosen so that it essentially corresponds to the first reflectance R1. As already shown above, this can be done either by sticking a corresponding film section onto the second surface 8, in particular a self-adhesive metallized plastic film 14, or by painting at least a section 15 of the second surface 8. If essentially the same parameters are selected for painting, such as a layer thickness of a paint layer, the explicit determination of the degree of reflectance can be dispensed with in practice, since the type of reflection of such paint layers 12 largely corresponds.

Reference symbols

1 sensor arrangement

2 chassis

3 distance sensor

3a transmitter

3b detector

4 vehicle part

5 electromagnetic waves

5a (emitted) radar waves

5b (reflected) radar waves

6 carrier part

7 first surface

8 second surface

9 first coating

10 second coating

11 resonator

12 coats of varnish

13 effect pigment

14 metallized plastic film

15 section (the second surface 8) S1, S2 process steps

D Thickness of the support part

Claims

Patent claims

1 . Vehicle part (4), comprising: a support part (6) made of a polymer material with a first surface (7) and a second surface (8) substantially parallel thereto; a first coating (9) applied to the first surface (7) of the carrier part (6), which has a first reflectance R1 for electromagnetic waves (5) of a predetermined frequency spectrum, in particular radar waves (5a, 5b); and a second coating (10) applied in at least one section (15) of the second surface (8) of the carrier part (6), which has a second reflectance R2 for electromagnetic waves (5) of the predetermined frequency spectrum, the second reflectance R2 being such the first reflectance R1 is coordinated so that the carrier part (6), the first coating (9) and the second coating (10) form a resonator (11) for the electromagnetic waves (5).

2. Vehicle part (4) according to claim 1, wherein the first reflectance R1 and the second reflectance R2 differ from each other in magnitude by a maximum of 20 percent, preferably less than 10 percent.

3. Vehicle part (4) according to claim 1 or 2, wherein the predetermined frequency spectrum is in the range between 60 and 100 GHz, in particular between 75 and 85 GHz.

4. Vehicle part (4) according to at least one of claims 1 to 3, wherein the vehicle part (4) has a transmittance of more than 50 percent, preferably more than 80 percent, for the predetermined Frequency spectrum and / or has a reflectance of less than 10 percent, preferably less than 5 percent. Vehicle part (4) according to at least one of claims 1 to 4, wherein the carrier part (6) has a thickness (D) in a range between 1.5 and 5.0 mm, in particular in the range of 1.85 to 2.15 mm or from 3.70 to 4.3 mm. Vehicle part (4) according to at least one of claims 1 to 5, wherein the first coating (9) is a lacquer layer or a painted or colored plastic film. Vehicle part (4) according to at least one of claims 1 to 6, wherein the first coating (9) and/or the second coating (10) has a thickness in a range between 80 and 130 pm. Vehicle part (4) according to at least one of claims 1 to 7, wherein the first coating (9) contains effect pigments (13), in particular metallic effect pigments. Vehicle part (4) according to at least one of claims 1 to 8, wherein the second coating (10) has essentially the same structure, composition and thickness as the first coating (9). Vehicle part (4) according to at least one of claims 1 to 9, wherein the second coating (10) has a metal foil or metallized plastic film (14). Vehicle part (4) according to at least one of claims 1 to 10, wherein the vehicle part is designed as a bumper and / or cover of a sensor arrangement. Sensor arrangement (1), comprising:

- a vehicle chassis (2);

- at least one transmitter (3a) arranged on the vehicle chassis (2) for sending electromagnetic waves (5) of a predetermined frequency spectrum, in particular radar waves (5a);

- at least one detector (3b) arranged on the vehicle chassis (2) for detecting electromagnetic waves (5) in the predetermined frequency spectrum, in particular reflected radar waves (5b); and

- a vehicle part (4) mounted in the area of the transmitter (3a) and/or detector (3b) according to one of claims 1 to 11. Motor vehicle with at least one radar-based sensor, in particular distance sensor (3), the radar-based sensor being behind a vehicle part ( 4) is arranged according to one of claims 1 to 11, and wherein the first coating (9) of the vehicle part (4) has a paint layer (12) applied to an outside of the vehicle and the second coating of the vehicle part (4) faces the radar-based sensor is. Method for improving a transmittance of a vehicle part (4) for electromagnetic waves (5) of a predetermined frequency spectrum, in particular radar waves (5a, 5b), comprising:

- Determining (S1) a reflectance R1 of a first coating (9) of a first surface, in particular a lacquer layer or colored or painted plastic film (12) applied to an outside of the vehicle part (4); and

- Applying (S2) a second coating (10) in at least one section (15) of one of the first surfaces (7) opposite second surface (8) of the vehicle part (4), a reflectance R2 of the second coating (10) being adapted to the reflectance R1 of the first coating (9). The method according to claim 14, wherein the step of determining (S1 ) comprises:

- Determining a layer thickness of the first coating (9); and or

- Measuring a reflectance R1 of a first coating (9) applied to a carrier part (6) of the vehicle part (4). A method according to claim 14 or 15, wherein the applying step (S2) comprises:

- Painting the at least one section (15) of the second surface (8), in particular an inside of the vehicle part (4), in particular with a paint with effect pigments (13); and or

- Sticking a film, in particular a self-adhesive metal film or metallized plastic film (14), onto the at least one section (15). Film set for improving a transmittance for electromagnetic waves (5) of a predetermined frequency spectrum, in particular radar waves (5a, 5b), the film set comprising a plurality of self-adhesive sections of a metal film or a metallized plastic film (14), the sections differing in their degree of reflectance and , optionally, differ in terms of their thickness.