Gradient Dielectric Film

Abstract

A gradient dielectric constant film is described. Specifically, the gradient dielectric constant film includes a first continuous matrix of first components having a first dielectric constant and a second component having a second dielectric constant disposed within the continuous matrix. The first dielectric constant is greater than the second dielectric constant for at least one wavelength between 20 GHz and 300 GHz. Such a film may be useful for improving the signal-to-noise ratio of transmitting and receiving units behind a protective cover.

Description

[Background technology]

[0001] Radio waves can be reflected at sharp boundaries between air and materials with relatively high dielectric constants. Such reflections can be undesirable in certain applications. Summary of the Invention

[0002] In one embodiment, the present disclosure relates to a gradient dielectric constant film having a first major surface and an opposing second major surface separated by a thickness. The gradient dielectric constant film has a first relative dielectric constant ε r1 and a first continuous matrix of first components having a second relative dielectric constant ε r2 and a second component having ε r1 is ε for at least one wavelength range r2 and the wavelength range is from 20 GHz to 300 GHz. The dielectric constant of the first half of the gradient dielectric constant film including half of the thickness closest to the first major surface is at least 10% lower than the dielectric constant of the second half of the gradient dielectric constant film including half of the thickness closest to the second major surface for at least one wavelength in the wavelength range. The gradient dielectric constant film has a visible haze greater than 50% or a visible light transmittance less than 50%, and both the first major surface and the second major surface are predominantly the first component. [Brief description of the drawings]

[0003] [Figure 1] FIG. 2 is a side elevation cross-sectional view of a gradient dielectric constant film. [Diagram 2] FIG. 13 is a cross-sectional side elevation view of another gradient dielectric constant film. [Diagram 3] FIG. 2 is a side elevation cross-sectional view of a nonwoven component of a gradient dielectric film. [Figure 4] FIG. 2 is a side elevation cross-sectional view of a multi-layer gradient dielectric tape. [Diagram 5] FIG. 1 is a cross-sectional side elevation view of a single layer gradient dielectric constant film attached to a surface. [Figure 6]1 is a graph of a radar signal plot from Comparative Example 1. [Figure 7] 1 is a graph of a radar signal plot from Example 1. [Figure 8] 1 is a graph of a radar signal plot from Example 2. [Figure 9] 13 is a graph of a radar signal plot from Example 3. [Figure 10] 1 is a graph of a radar signal plot from Comparative Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0004] Radio wave generating and receiving units, such as radar (radio detection and ranging) units, may be useful in a diverse and growing application space. For example, as automobiles increasingly incorporate sensors to improve driver safety, sense and warn about vehicle surroundings and conditions, and enable partial or full autonomous driving capabilities, one or more radar units may be incorporated. Automotive radar applications may use microwave generating and receiving units, and thus, for the purposes of this application, "radar" and "radio wave" shall also include frequencies in the microwave range. For power consumption, safety, and regulatory reasons, these radar units may be relatively low power compared to those used in air traffic monitoring applications, as an example. Thus, the signal-to-noise ratio of these low power units may be more sensitive to interference or attenuation.

[0005] To protect these radar units from dirt accumulation or weather elements such as snow and rain, or in the case of rotating or moving components, to protect people from injury or accidental damage, the units are typically protected with a cover. In some cases, this protective cover is called a radome. Alternatively or in addition, these units are sometimes embedded within the body of the vehicle. In some embodiments, these units are placed behind or within a bumper fascia or another vehicle fascia that acts as a protective cover. Depending on the target orientation, these radar units can be placed anywhere on the vehicle. Typically, they are configured such that a minimal amount of material is placed between the radar unit and its potential or intended detection target.

[0006] However, because protective covers are typically necessary or desirable for use with these radar units, the radio waves generated by the radio wave generating unit and received by the radio wave receiving unit must pass through an interface that includes an abrupt increase in electrical permittivity. As used herein, the relative permittivity for a given frequency is the ratio of the dielectric constant of a material to the dielectric constant of a vacuum, and represents the resistance of the material to forming an electric field within the material itself. This abrupt change in value, such as would be encountered by a radio wave traveling through air at an interface with a non-air material, such as a plastic vehicle fascia, will cause at least a portion of the radio wave to be reflected at the interface. Because these interfaces occur twice each time the vehicle fascia is crossed (once as it enters the material and once as it exits the material) (back toward the radio wave generating unit for the radio waves generated by the radio wave generating unit, and back away from the radio wave receiving unit for the radio waves to be received by the radio wave receiving unit), the losses exhibited by reflections in undesired directions can become significant and cause the signal to not work effectively. In particular, this may occur either because the return signal is significantly attenuated before being detected by the radio receiving unit, because the transmitted signal is reflected and detected, giving a strong false signal, or any other mechanism that reduces the ability to distinguish the desired signal from noise.Similarly, antennas for telecommunications, or indeed antennas for any electronic device that includes a transmitting and receiving unit, may encounter the same or similar problems, i.e., signal loss or noise increase due to abrupt transitions between media dielectric constants.

[0007] A gradient dielectric film provides a smooth or step change in dielectric constant from a first medium to a second medium (as opposed to the smooth or step change in refractive index of an antireflective film), similar to an antireflective film or coating at an optical interface. Typically, the dielectric constant of a gradient dielectric film changes from a value closest to the dielectric constant of the first medium to a value closest to the dielectric constant of the second medium. For example, a gradient dielectric film can have a changing dielectric constant that starts close to the dielectric constant of air on one side (to be attached to the plastic vehicle fascia) and transitions to the dielectric constant of the plastic vehicle fascia on the other side. This smooth or step transition can significantly reduce dielectric boundary reflections that would otherwise occur at these abrupt transitions.

[0008] Previous gradient dielectric constant films typically use various bulk three-dimensional shapes, such as cones or pyramids. However, in typical use environments where these films may be exposed to dirt accumulation and weather conditions, these films may become contaminated and no longer work effectively because they rely on the presence of air to provide the dielectric gradient. The films described herein may be less susceptible to ingress of debris and contaminants because only a limited portion of the air or gas portion is exposed to the outside elements, or in some embodiments, the gas volume fraction is completely sealed within the film. In other words, both major surfaces of the gradient dielectric constant film are primarily continuous matrix components.

[0009] FIG. 1 is a side elevation cross-sectional view of a gradient dielectric constant film. The gradient dielectric constant film 100 includes a first half 110A closest to a first major surface 112, a second half 110B closest to a second major surface 114, and a continuous matrix of first components 110, with a second component 120 disposed within the continuous matrix and disposed within a third component 130. The thickness of the film is indicated by t and includes both halves of the gradient dielectric constant film. The gradient dielectric constant film 100 represents a simple embodiment of a gradient dielectric constant film. In the embodiment of FIG. 1, the continuous matrix is ​​the bulk volume of the first component. In some embodiments, this first component may be a resin, plastic, polymeric material, or any other suitable material selected for its dielectric constant, mechanical properties, thermal or environmental stability, ease of processing, or any combination of the foregoing. In some embodiments, the continuous matrix of the first component is selected to match the dielectric constant and / or composition of the material to which it is intended to be attached for its designed application.

[0010] The first continuous matrix of the first component has a first relative dielectric constant ε r1 The second component has a second relative dielectric constant ε r2 and ε r1 is ε for at least one wavelength in the wavelength range. r2 In some embodiments, the wavelength range may be any wavelength range within the radio wavelength range and the microwave wavelength range. In some embodiments, the wavelength range may be 20 GHz to 300 GHz. In some embodiments, the wavelength range may be 20 GHz to 100 GHz. In some embodiments, the wavelength range may be 20 GHz to 81 GHz. In some embodiments, the wavelength range may be 20 GHz to 30 GHz.

[0011] In some embodiments, the second component is air or another inert gas. In some embodiments, the second component is a partial vacuum. Given the low relative dielectric constant of air, gas, or partial vacuum, the inclusion of the second component in the gradient dielectric constant film reduces the effective dielectric constant of that portion of the film. Averaged over the volume of that portion of thickness, a half or portion of the gradient dielectric constant film 100 that includes more of the second components 120 will have a lower effective dielectric constant than a half or portion of the gradient dielectric constant film 100 that includes less or none of the second components 120. In some embodiments, this difference in dielectric constant is at least 10%. The first half 110A, which is designed to have a lower dielectric constant than the second half 110B, includes the second components 120 arranged in a continuous matrix of the first components 110, while the second half 110B does not include the second components 120.

[0012] It should be noted that in the illustration of Figure 1, gradient dielectric constant film 100 is depicted as a single layer. Through certain fabrication methods (described in more detail elsewhere herein), it is possible to achieve a single layer film with a dielectric constant gradient.

[0013] 1, the second component 120 is disposed within the third component 130. In some embodiments, the second component 120 is disposed freely within the continuous matrix of the first component, such as in the form of air or bubbles. In some embodiments, nanoparticles, such as silsesquioxane nanoparticles, can be used to add porosity to a polymer layer, such as an epoxy or silicone layer.

[0014] However, in some embodiments, the second component 120 is disposed within a different material. For example, in some embodiments, the second component 120 is disposed within glass to form the spheres, glass bubbles, or microbubbles of FIG. 1. Glass microbubbles are generally formed by simultaneous fusion of glass-forming components and expansion of the fused mass. See generally U.S. Pat. No. 4,767,726 (Marshall). Similarly, polymer or plastic microbubbles (polyethylene, polypropylene, poly(methyl methacrylate), etc.) may be used, filled with an inert gas or air. In some embodiments, cenospheres (lightweight spheres typically formed from silica or alumina, filled with air or other inert gas, and produced as a by-product of coal combustion) may be used. In some embodiments, ceramic particles may be used. These ceramic particles may be porous and may contain air or another inert gas. In some embodiments, any of the particles described herein may be coated with or include an absorber composite. The absorber composite may include at least one of a ceramic filler, a conductive filler, or a magnetic filler. The conductive filler may include, for example, carbon black, carbon bubbles, carbon foam, graphene, carbon fibers, graphite, carbon nanotubes, metal particles, metal nanoparticles, metal alloy particles, metal nanowires, polyacrylonitrile fibers, or conductive coating particles. The ceramic material filler may include, for example, copper oxide or titanium monoxide. The magnetic filler may include, for example, sendust, carbonyl iron, permalloy, ferrite, or garnet. The third component may have a third dielectric constant ε r3 and for wavelengths in the wavelength range, ε r2 ≦ε r3 Any combination or blend of particles and free voids or bubbles can be used within the continuous matrix of the first component.

[0015] The thickness t may be any suitable value, taking into consideration physical robustness and environmental stability (such as resistance to thermal cooling cycle warping). In addition, the suitable thickness may also be ranged as being greater than the minimum thickness, such that the wave encounters and interacts with an intermediate change in dielectric constant. If the thickness is too thin, the incident electromagnetic wave will not interact with the gradient dielectric constant film. Alternatively, in the case of a multi-layer gradient dielectric constant film, the electromagnetic wave will interact with the multi-layer gradient dielectric constant film as if it were a single layer of blended effective dielectric constant, instead of as a film of graded dielectric constant, as desired. If the film is too thick, it may not effectively attach or remain attached to the surface, or may be less flexible or conformable than desired.

[0016] The distribution of the second component or its volume fraction within the continuous matrix may vary along one or more non-thickness directions of the film. In some embodiments, the variation may be monotonic. In some embodiments, due to the required size and distribution of the second component within the continuous matrix of the first component, the gradient dielectric constant films described herein may have high visible haze or low visible light transmittance. In some embodiments, the visible haze may be greater than 50%. In some embodiments, the visible light transmittance may be less than 50%.

[0017] FIG. 2 is a side elevation cross-sectional view of another gradient dielectric constant film. The gradient dielectric constant film 200 includes a first half 210A closest to the first major surface 212, a second half 210B closest to the second major surface 214 and laminated together by an adhesive 270, and a continuous matrix of first components 210, the second components disposed within the continuous matrix and, optionally, within a third component 230. The gradient dielectric constant film 200 of FIG. 2 is similar to and generally corresponds to the gradient dielectric constant film 100 of FIG. 1. However, FIG. 2 shows two portions of the film, the first halves 210A and 210B, laminated together by an adhesive 270 instead of the unitary structure of FIG. 1. Additionally, FIG. 2 illustrates that the second component 220 may be freely disposed within the continuous matrix of the first components 210 and not within the third component. In the gradient dielectric films described herein, the volume fraction of the second component may be varied across any portion of the thickness of the gradient dielectric film by varying either the size, shape, or density of bubbles, voids, or other components, such as glass microbubbles or cenospheres, present in the continuous matrix. In some embodiments, this difference in the volume fraction of the second component is at least 10% between the two halves.

[0018] Any suitable adhesive may be used as adhesive 270. For example, a pressure sensitive adhesive, a UV curable adhesive, a silicone based adhesive, a urethane based adhesive, or any other suitable adhesive or combination of adhesives may be used to adhere the halves of gradient dielectric constant film 200 to one another.

[0019] FIG. 3 is a side elevation cross-sectional view of a nonwoven component 300 of a gradient dielectric constant film. The nonwoven component 300 has an inherent porosity and has at least some inert gas (e.g., air) volume fraction provided within the continuous matrix of the nonwoven component. A gradient dielectric constant film can use a nonwoven component as part of a multi-layer laminate, where the effective dielectric constant is varied by controlling or selecting the porosity of the various layers of the nonwoven component. In some embodiments, the porosity of a single nonwoven layer can be controlled along the thickness direction such that a gradient of dielectric constant exists. Suitable nonwoven components can include spunbond nonwovens, flashspun nonwovens, meltblown nonwovens, staple nonwovens, and may include glass or plastic fibers. In some embodiments, the glass or plastic fibers can themselves contain an inert gas or air component, which can help to further tailor or control the dielectric constant gradient along the thickness direction or possibly one or more non-thickness directions as well. The nonwoven component may be used in combination with any other layer described herein, including one or more layers of a resin matrix having voids or bubbles (plastic or glass or free) disposed therein. Alternatively, particularly in the case of glass or polymeric fibers containing voids or microbubbles, such fibers may be woven or arranged to form a gradient dielectric constant film.

[0020] FIG. 4 is a side elevation cross-sectional view of a multi-layer gradient dielectric tape. Gradient dielectric tape 400 includes a first layer 410, a second layer 420, a third layer 430, a fourth layer 440, a fifth layer 450, an adhesive layer 460, and a backing layer 470. Gradient dielectric tape 400 of FIG. 4 illustrates a multi-layer laminate design in which first layer 410, second layer 420, third layer 430, and fourth layer 440 each have a different effective dielectric constant, representing a step change moving along the thickness of the gradient dielectric tape (up and down in the reference frame of FIG. 4). Each of the layers of FIG. 4 may be formed and attached separately by separate processes such as adhesive or thermal lamination, or they may be formed sequentially by various process conditions or input materials (e.g., different resins with different loadings of glass or plastic microbubbles). 4 is a simplified diagram and the boundaries between each of the layers are not necessarily as defined in a flat and real-world article of manufacture. In some embodiments, the continuous matrix of each layer is the same material.

[0021] The gradient dielectric tape also includes an adhesive layer 460 and a backing layer 470. The adhesive layer 460 may include any suitable adhesive, including a pressure sensitive adhesive, a repositionable adhesive, or a stretch release adhesive. The adhesive layer 460 may be of any suitable thickness to provide a secure contact to the surface to which it is attached. The adhesive layer 460 may alternatively include a curable component, such as a UV curable component or a heat curable component. In some embodiments, the adhesive layer 460 may also include one or more of an inert gas or air containing component, such as glass or plastic microbubbles, cenospheres, ceramic particles, or free voids, to further control the dielectric gradient.

[0022] Backing layer 470 may include any suitable film or layer to protect the adhesive properties of adhesive layer 460 and prevent accidental adhesion to undesirable surfaces of gradient dielectric tape 400. Suitable materials for backing layer 470 include plastic films, coated or uncoated papers, and the like. Backing layer 470 may be selected such that it does not itself have strong adhesion to adhesive layer 460, and thus is easily removable by hand or with limited tools.

[0023] FIG. 5 is a side elevation cross-sectional view of a single layer gradient dielectric film attached to a surface. The gradient dielectric tape includes a single layer gradient dielectric film 510 disposed on a substrate 520 and attached to a surface 540 via an adhesive layer 530. The gradient dielectric 510 in FIG. 5 is a single layer gradient dielectric film. In some embodiments, a single layer gradient dielectric film may be formed by disposing different sizes or shapes of microbubbles (glass or plastic), cenospheres, air or other inert gas bubbles, or combinations thereof, in an uncured flowable material. Such flowable materials may be disposed or coated on the substrate 520 by any suitable method, such as dip coating, spin coating, spraying or conformal coating, or even printing. If the particles or bubbles are allowed to flow within the material, then on average, the particles or bubbles with a larger air or gas volume fraction will rise to the top of the material, while those with a smaller air or gas volume fraction will stay where they were or sink towards the bottom. It is therefore possible to form a gradient dielectric constant along the thickness within a single layer. Similar to the gradient dielectric constant film 100 of Figure 1, the difference in dielectric constant between the top and bottom halves of the gradient dielectric constant film 510 may be at least 10%.

[0024] The gradient dielectric constant film of Figure 5 is attached to the surface 540 via an adhesive layer 530. In some embodiments, the gradient dielectric constant film 510 may be configured as a tape, with an adhesive layer disposed on the gradient dielectric constant film prior to attachment to the surface 540, as described and shown in Figure 4. In some embodiments, the gradient dielectric constant film 510 is attached to the surface 540 by applying an adhesive layer 530 at or before or after attachment. Any suitable adhesive may be used.

[0025] Surface 540 may be a vehicle fascia in some embodiments. Surface 540 may be a radome. In some embodiments, surface 540 may be a different protective cover or casing, such as an antenna cover or the exterior surface of an electronic device. In some embodiments, while FIG. 5 shows one gradient dielectric constant film attached to a surface, more than one gradient dielectric constant tape may be attached to the surface in the same or similar manner. In some embodiments, a second gradient dielectric constant film is attached to the opposite side of surface 540, one half of which has a lower dielectric constant and is positioned away from surface 540. Surface 540 may be curved or non-planar, and the gradient dielectric constant film or tape including such film may be similarly shaped, flexible, or pliable to closely adhere to the shape of surface 540.

[0026] In some embodiments, at the location of attachment of the gradient dielectric constant film to the surface, the dielectric constant of the surface is within 10% of the dielectric constant of the continuous matrix. In particular, when different layers in the gradient dielectric constant film have different continuous matrix materials, the continuous matrix closest to the surface is the one that is within 10% of the dielectric constant of the surface. In some embodiments, the dielectric constant of the surface may be within 5% of the dielectric constant of the continuous matrix.

[0027] The gradient dielectric constant films described herein may be post-processed to further tailor the properties and performance of these films. For example, the gradient dielectric constant films described herein may be heated or thinned to selectively change the properties at a particular point or points on the film. In some embodiments, the gradient dielectric constant films described herein may be perforated to selectively change the dielectric properties at a particular point on the film. In some embodiments, the perforations have a regular shape and / or size. In some embodiments, the perforations are of different sizes or shapes. In some embodiments, the perforations are circular. In some embodiments, the perforations vary in size, shape, or density across one or more non-thickness directions. EXAMPLES

[0028] The four-layered samples were coated to facilitate radar penetration measurements, and for the test configuration, the samples were fixed to either bare or painted 1.7 mm polypropylene plates to simulate automotive bumper materials. The air volume in each layer of the three four-layered examples was provided in the form of hollow glass beads (3M Glass Bubbles K1) embedded in a matrix of 55% silicone acrylate (Sartomer CN990) and 45% tetrahydrofurfuryl acrylate (Sartomer SR285). In each example, each layer of the structure was 250 μm thick for a total thickness of 1 mm.

[0029] The three examples differ from each other in that the density of glass beads in volume percent is different for each of the four layers of the structure. For relative measurements, Comparative Example 1 (CE-1) is provided as a bare 1.7 mm polypropylene plate (no film) and Comparative Example 2 is provided as the same 1.7 mm polypropylene plate with a metallic gray paint layer of sufficient thickness so as to be visually opaque. The metallic gray paint mixture is 25% DBC9700 (black) and 25% Nissan Silver (KYO Nissan equivalent available from Dupont P2929) commercially available from PPG and 50% DT885 reducer / solvent also from PPG.

[0030] [Table 1]

[0031] As shown in the table above, the percent bead density by volume of each layer is expected to directly affect the dielectric constant of the layer. The expected dielectric constant as a function of glass bead volume % is shown in Table 2.

[0032] [Table 2]

[0033] Radar Attenuation Test Method The test setup included three essential parts: (A) the radar test unit, (B) the sample located approximately 20 mm from the radar unit, and (C) the detection target.

[0034] The radar test unit was a commercially available INRAS RadarBook with a MIMO 77GHz front end. This unit provides a measure, Rx Signal [dBV], which is a measure of the relative measurement of the detected radar signal reflected by the combined sample and detection targets. The output from the test unit provides a signature of the measured signal versus distance from the test head. This is simply reported as "Radar Signal Plot" in the measurement results section in the form of a diagram showing a graph of Rx versus distance from the radar test unit.

[0035] The proximity of the sample to the radar unit and the mounting of the multiple layers to a 1.7 mm thick polypropylene plate was designed to mimic the effect of a bumper / fascia on the radar signal. The distance from the radar unit to the plate was nominally 20 mm, but this was adjusted slightly between measurements to obtain both maximum and minimum target signals. A typical slight adjustment was less than about 2 mm from the nominal distance of 20 mm. This adjustment was expected to demonstrate measurement variability due to delicate positioning of the sample relative to the radar source. In the ideal case, the difference in target signal between the minimum and maximum values ​​would be minimized. In the example shown, this reduction in variation is seen to be about 5 dB compared to the variation seen with only a bare plate. It is observed that as the sample becomes less visible to the radar source, the variation due to sample adjustment becomes less.

[0036] A copper plate was placed approximately 3.5 m from the radar unit as a detection target. This target distance appears as a peak in the Rx radar unit output versus distance.

[0037] Measurement results In some measurements, samples were mounted on bare polypropylene plates (1-3), and in other measurements, samples were mounted on polypropylene plates painted gray (with metal flakes) to increase the reflection from the plate. Figure 6 shows the radar signal plot from Comparative Example 1 (baseline bare polypropylene plate). Figure 7 shows the radar signal plot from Example 1 on a bare polypropylene plate. Figure 8 shows the radar signal plot from Example 2 on a bare polypropylene plate. Figure 9 shows the radar signal plot from Example 3 on a painted polypropylene plate (corresponding to Comparative Example 2). Figure 10 shows the radar signal plot from Comparative Example 2 (polypropylene plate painted with gray paint containing metal flakes).

[0038] Descriptions of elements in the figures should be understood to apply equally to corresponding elements in other figures unless otherwise indicated. The above-described embodiments have been described in detail to facilitate the explanation of various aspects of the present invention, and therefore the present invention should not be considered limited to the specific examples and embodiments described above. Rather, the present invention should be understood to encompass all aspects of the present invention, including various modifications, equivalent processes, and alternative devices, that fall within the scope of the present invention as defined by the appended claims and their equivalents. In the following, exemplary embodiments are presented. [Item 1] 1. A gradient dielectric constant film having a first major surface and an opposing second major surface separated by a thickness, First relative permittivity ε r1 a first continuous matrix of first components having A second dielectric constant ε disposed within the continuous matrix r2 and a second component having Equipped with ε r1 is ε for at least one wavelength in the wavelength range. r2 and the wavelength range is 20 GHz to 300 GHz; a dielectric constant of a first half of the gradient dielectric film including half of the thickness closest to the first major surface is at least 10% lower than a dielectric constant of a second half of the gradient dielectric film including half of the thickness closest to the second major surface for the at least one wavelength in the wavelength range; the gradient dielectric film having a haze greater than 50% or a visible light transmission less than 50%; Both the first major surface and the second major surface are predominantly of the first component. Gradient dielectric constant film. [Item 2] The second component has a third relative dielectric constant ε r3 and for the at least one wavelength in the wavelength range, r2 ≦ε r3 2. The gradient dielectric constant film of item 1, wherein [Item 3] Item 3. The gradient dielectric film of item 2, wherein the third component is glass and the second component is air. [Item 4] 4. The gradient dielectric film of claim 3, wherein the glass is coated with a broadband absorber. [Item 5] 3. The gradient dielectric constant film of claim 2, wherein the third component is a polymer and the second component is a gas. [Item 6] 6. The gradient dielectric film of claim 5, wherein the polymer is coated with a broadband absorber. [Item 7] Item 3. The gradient dielectric film of item 2, wherein the third component is a ceramic and the second component is a gas. [Item 8] 8. The gradient dielectric film of claim 7, wherein the ceramic is porous. [Item 9] 6. The gradient dielectric film of claim 5, wherein the ceramic is coated with a broadband absorber. [Item 10] 2. The gradient dielectric film of claim 1, wherein the first component comprises a polymer material. [Item 11] Item 1. The gradient dielectric film of item 1, wherein the continuous matrix is ​​a nonwoven material. [Item 12] Item 2. The gradient dielectric film of item 1, wherein the second component is a gas. [Item 13] Item 2. The gradient dielectric film of item 1, wherein the second component is air. [Item 14] The fourth dielectric constant ε r4 Item 10. The gradient dielectric film of item 1, further comprising a second continuous matrix of a fourth component having a first continuous matrix and a second continuous matrix disposed on the first continuous matrix. [Item 15] Item 15. The gradient dielectric constant film of item 14, wherein the first component and the fourth component are the same material. [Item 16] Item 15. The gradient dielectric film of item 14, wherein the second continuous matrix has a volume percentage of the second component within the second continuous matrix that differs from the first continuous matrix by at least 10%. [Item 17] The fifth dielectric constant ε r5 Item 17. The gradient dielectric film of item 16, further comprising a third continuous matrix of a fifth component having a volume percentage of the second component within the third continuous matrix that differs from either the first continuous matrix or the second continuous matrix by at least 10%. [Item 18] Item 18. The gradient dielectric constant film of item 17, wherein the fifth component, the fourth component, and the first component are the same material. [Item 19] Item 2. The gradient dielectric film of item 1, wherein the gradient dielectric film is a single layer. [Item 20] Item 1. The gradient dielectric film of item 1, disposed on a substrate, the substrate being a solid layer that does not include the second component. [Item 21] Item 1. A gradient dielectric constant tape comprising the gradient dielectric constant film of item 1 and an adhesive layer. [Item 22] 22. The gradient dielectric constant tape of claim 21, further comprising a backing layer disposed on the adhesive layer opposite the gradient dielectric constant film. [Item 23] 22. An assembly comprising the gradient dielectric tape of item 21 attached to a vehicle bumper fascia. [Item 24] 24. The assembly of claim 23, wherein at an attachment location of the gradient dielectric constant tape to the vehicle bumper fascia, the dielectric constant of the vehicle bumper fascia is within 10% of the first dielectric constant. [Item 25] 25. The assembly of claim 24, wherein the dielectric constant of the vehicle bumper fascia is within 5% of the first dielectric constant. [Item 26] 22. An assembly comprising the gradient dielectric tape of item 21 attached to an automotive radome. [Item 27] Item 27. The assembly of item 26, wherein at an attachment location of the gradient dielectric constant tape and the automotive radome, the dielectric constant of the automotive radome is within 10% of the first dielectric constant. [Item 28] Item 28. The assembly of item 27, wherein the dielectric constant of the automotive radome is within 5% of the first dielectric constant. [Item 29] Item 1 . The gradient dielectric film of item 1 , wherein the volume fraction of the second component varies across one or more non-thickness directions of the gradient dielectric film. [Item 30] 30. The gradient dielectric film of claim 29, wherein the change in the one or more non-thickness directions is a monotonic change. [Item 31] Item 10. The gradient dielectric film of item 1, wherein the gradient dielectric film is non-planar. [Item 32] Item 2. The gradient dielectric film of item 1, wherein the first continuous matrix of the first component comprises fibers. [Item 33] 2. The gradient dielectric film of claim 1, comprising perforations. [Item 34] Item 34. The gradient dielectric film of item 33, wherein the perforations are circular. [Item 35] Item 34. The gradient dielectric film of item 33, wherein the perforations are of different sizes. [Item 36] Item 34. The gradient dielectric film of item 33, wherein the perforations vary in size, shape, or density across one or more non-thickness directions. [Item 37] 2. The gradient dielectric constant film according to item 1, wherein the wavelength range is 20 GHz to 120 GHz. [Item 38] 2. The gradient dielectric constant film according to item 1, wherein the wavelength range is 20 GHz to 100 GHz. [Item 39] 2. The gradient dielectric constant film according to item 1, wherein the wavelength range is 20 GHz to 81 GHz. [Item 40] 2. The gradient dielectric constant film according to item 1, wherein the wavelength range is 20 GHz to 30 GHz.

Claims

1. 1. A gradient dielectric constant film having a first major surface and an opposing second major surface separated by a thickness, First relative dielectric constant ε ｒ１ a first continuous matrix of first components having a second contiguous matrix of the first components disposed on the first contiguous matrix; A second dielectric constant ε disposed within the first and second continuous matrices ｒ２ and a second component having Equipped with the volume percentages of the second component in the first and second continuous matrices differ by at least 10%, thereby providing a gradual change in the dielectric constant of the gradient dielectric film across a thickness of the gradient dielectric film; ε ｒ１ is ε for at least one frequency in the frequency range. ｒ２ greater, the frequency range being 20 GHz to 300 GHz; a dielectric constant of a first half of the thickness of the gradient dielectric film closest to the first major surface is at least 10% lower than a dielectric constant of a second half of the thickness of the gradient dielectric film closest to the second major surface for the at least one frequency in the frequency range; the gradient dielectric film having a haze greater than 50% or a visible light transmission less than 50%; both the first major surface and the second major surface are predominantly of the first component; Gradient dielectric constant film.

2. The second component has a third relative dielectric constant ε ｒ３ and for the at least one frequency in the frequency range, ｒ２ ≦ε ｒ３ 2. The gradient dielectric film of claim 1 , wherein

3. 3. The gradient dielectric film of claim 2 wherein said third component is glass and said second component is air.

4. 3. The gradient dielectric film of claim 2 wherein said third component is a polymer and said second component is a gas.

5. 3. The gradient dielectric film of claim 2 wherein said third component is a ceramic and said second component is a gas.

6. The gradient dielectric film of claim 2 wherein the third component is coated with a broadband absorber.

7. The gradient dielectric film of claim 1 , wherein the first component comprises a polymeric material.

8. 10. The gradient dielectric film of claim 1 wherein said continuous matrix is ​​a nonwoven material.

9. The gradient dielectric film of claim 1 wherein the second component is a gas.

10. 10. The gradient dielectric film of claim 1 wherein said second component is air.

11. 11. An assembly comprising the gradient dielectric tape of any of claims 1 to 10 attached to a vehicle bumper fascia or an automotive radome.

12. 10. The gradient dielectric film of claim 1, wherein a volume fraction of the second component varies across one or more non-thickness directions of the gradient dielectric film.

13. 10. The gradient dielectric film of claim 1 comprising perforations.

14. 10. The gradient dielectric film of claim 1, wherein the frequency range is from 20 GHz to 120 GHz.

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