Radar retroreflective products

Abstract

The present disclosure generally relates to radar retroreflective articles that include one or more dielectric layers adjacent to a reflective layer, wherein the one or more dielectric layers contribute to increasing a radar cross section of the radar retroreflective article.

Description

[0001] The present disclosure generally relates to radar retroreflective articles that include one or more dielectric layers adjacent to a reflective layer, wherein the one or more dielectric layers contribute to increasing a radar cross section of the radar retroreflective article. Background Art

[0002] Radar-based systems are widely used in automotive and autonomous driving applications such as adaptive cruise control, parking assist, lane change assist, and blind spot monitoring. Currently, there is a need for automotive radar systems that can distinguish objects on the road with higher accuracy and in more challenging weather conditions than optical camera systems or simply serve as a redundant data source. The inventors have also recognized a need to increase the detectability of workers who are not wearing visible retroreflective personal protective clothing and equipment. The present disclosure provides articles that address the needs described in this paragraph by providing radar reflective articles with improved radar reflective performance. Summary of the invention

[0003] Generally speaking, the present disclosure relates to reflective articles, which include a dielectric layer and a reflective structure capable of reflecting radar signals. Examples of useful reflective articles include marking tapes, traffic cones or barrels, road signs, guardrails, automotive parts, and wearable articles such as clothing articles, helmets, badges, and other similar articles.

[0004] In one embodiment, the radar reflective structure includes a retroreflective layer capable of reflecting radar signals, which in turn may include cube corner elements (e.g., having side dimensions of 2 mm to 65 mm) and a metal layer coated on the cube corner elements. In other embodiments, the radar reflective structure may include multiple antennas that create a radar reflective surface, or may even be a reflector that includes one or more metal layers capable of reflecting radar signals.

[0005] In some embodiments, the dielectric layer can be a single layer that diffracts an incident radar signal so that the angle of incidence of the signal on the reflective layer is increased relative to the angle of incidence on the surface of the dielectric layer. For radar signals with low angles of incidence relative to the plane of the reflective article, the radar signal refraction allows the radar signal to be reflected by the reflective article in the general direction of the signal source. In other embodiments, the dielectric layer can be a plurality of layers, each layer having a dielectric constant value that decreases from a high dielectric constant in a layer adjacent to the radar reflective structure to a low dielectric constant in an outermost layer that is typically in contact with the air. Alternatively, in other embodiments, the dielectric layer may have a dielectric constant gradient having a high dielectric constant in a portion of the layer adjacent to the radar reflective structure and a low dielectric constant in an outermost portion that is typically in contact with the air.

[0006] Unless otherwise indicated, all scientific and technical terms used herein have the meaning commonly used in the art. The definitions given herein are intended to facilitate understanding of certain terms frequently used in this application and are not intended to exclude reasonable interpretations of those terms in the context of this disclosure.

[0007] Unless otherwise indicated, all numerical values ​​in the specification and claims expressing characteristic dimensions, quantities and physical properties used in the specification and claims should be understood to be modified by the term "about" in all cases. Therefore, unless otherwise indicated, the numerical parameters listed in the above specification and the attached claims are approximate values, which can vary according to the desired characteristics sought to be obtained by those skilled in the art using the teachings disclosed herein. At the very least, and without attempting to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be interpreted according to the reported significant digits and by applying the usual rounding method. Although the numerical ranges and parameters shown in the broad scope of the present invention are approximate values, the numerical values ​​shown in the specific embodiments are reported as accurately as possible. However, any numerical value inherently contains certain errors, which must be caused by the standard deviations present in their corresponding experimental measurements.

[0008] The recitation of numerical ranges by endpoints includes all numbers subsumed within that range (eg, a range of 1 to 5 includes, for example, 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5) and any range within that range.

[0009] As used in this specification and the appended claims, the singular forms "a," "an," and "the" encompass embodiments having plural referents, unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term "or" is generally employed in its sense including "and / or," unless the content clearly dictates otherwise.

[0010] The words "preferred" and "preferably" refer to embodiments of the present invention that may provide certain benefits in certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. In addition, the description of one or more preferred embodiments does not imply that other embodiments are not applicable, and is not intended to exclude other embodiments from the scope of the present invention.

[0011] The term "radar signal" refers to electromagnetic radiation having a frequency in the range of 1 GHz to 120 GHz. Radar signals include, but are not limited to, electromagnetic radiation having a nominal frequency of 24 GHz (which is considered to be within the range of 21 GHz to 27 GHz in this disclosure), a signal nominally having a frequency of 77 GHz (which is considered to be within the range of 76 GHz to 81 GHz in this disclosure), and a signal nominally having a frequency of 110 GHz (which is considered to be within the range of 105 GHz to 115 GHz in this disclosure).

[0012] The term "opaque" refers to the property of an article, such as a layer in a film construction, that allows less than 80% visible light transmission of the article. Visible light in this disclosure refers to electromagnetic radiation with a wavelength in the range of 400 nm to 740 nm.

[0013] The term "cube corner element" refers to a structure that is capable of retroreflecting electromagnetic radiation. Cube corner elements include arrays of truncated cube corners in which the bases of adjacent cube corner elements are generally coplanar. See, e.g., FIG. 3a. Other cube corner element structures described as "full cubes" generally include at least two non-dihedral edges that are not coplanar. See, e.g., FIG. 3b. Such structures generally exhibit higher total light return than truncated cube corner elements. Examples of cube corner elements are described in PCT Patent Application No. WO2004 / 081619, which is incorporated herein in its entirety.

[0014] As understood by the context in which it appears, the term "adjacent" refers to the relative position of two elements (such as, for example, two layers) that are close to each other, and may or may not necessarily need to be in contact with each other or may have one or more layers separating the two elements.

[0015] The term "immediately adjacent" refers to a relative position where two elements (such as, for example, two layers) are immediately adjacent to each other and in contact with each other and have no intermediate layer separating the two elements. However, the term "immediately adjacent" encompasses the case where one or both elements (e.g., layers) have been treated with a primer, or their surfaces have been modified by, for example, etching, embossing, etc. to affect their properties or have been modified by surface treatments such as corona or plasma treatments, etc. that may improve adhesion or provide diffusion of incident electromagnetic radiation.

[0016] The term "radar cross section" (RCS) is a measure of an object's ability to reflect radar signals in the direction of a radar receiver. In the present disclosure, RCS is calculated as shown in the following Examples section.

[0017] The terms "retroreflect", "retroreflected" or "retroreflection" refer to the use of a retroreflective article (e.g., an article including three right-angle pyramid layers) to reflect a signal back in the direction of a source. As used herein, the term "retroreflection" is a subset of the term "reflection".

[0018] The above summary of the invention is intended only to provide a rough overview of the subject matter of the present disclosure and is not intended to describe each disclosed embodiment or each implementation of the present invention. The following description more specifically illustrates exemplary embodiments. In several places throughout this application, guidance is provided by lists of examples, which can be used in various combinations. In each case, the cited lists are only used as representative groups and should not be interpreted as exclusive lists. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a schematic diagram of an optical metal retroreflector.

[0020] 2(A) is a schematic diagram of a radar signal scattered by a retroreflective article, such as a cube corner element, having a solid angle dimension that is smaller than the wavelength of the incoming radar signal.

[0021] 2(B) is a schematic diagram of a radar signal retroreflected by a retroreflective article, such as a cube corner element, having a solid angle dimension suitable for reflecting the wavelength of an incoming radar signal.

[0022] 3(A)-3(D) are graphical representations of retroreflective elements with: (a) truncated cube corners, (b) full cube corners, (c) flat two-sided grooves, and (d) concave two-sided grooves.

[0023] Figure 4 The construction of a dielectric layer with a relatively low dielectric constant is shown to reflect back radar signals.

[0024] Figure 5 The construction of a dielectric layer with a suitable (high) dielectric constant is shown for the reflection of radar signals.

[0025] Figure 6 A dielectric layer with a suitable (high) dielectric constant is shown and the construction of the prismatic layer is clearly shown to reflect back the radar signal.

[0026] Figure 7 The reflection of a radar signal by a construction having two dielectric layers is shown.

[0027] FIG. 8A to FIG. 8F Different examples of composite dielectric layers are shown.

[0028] Fig. 9The reflection of a radar signal is shown for a construction having more than one dielectric layer, wherein the dielectric constant value of each layer decreases in the direction from the outermost layer (adjacent to air) to the layer adjacent to the reflective layer.

[0029] Fig.10 The reflection of a radar signal by a construction having a dielectric layer having a gradient of dielectric constant value decreasing in a direction from an outermost portion (adjacent to air) to a portion adjacent to the reflective layer is shown.

[0030] Fig.11 A cross section of an optical retroreflector without a dielectric layer is shown.

[0031] Fig.12 A plan view of an optical retroreflector without a dielectric layer is shown.

[0032] Fig.13 A cross section of an optical retroreflector having a dielectric layer with a dielectric constant of 4.8 is shown.

[0033] Fig.14 A cross section of an optical retroreflector having a dielectric layer with a dielectric constant of 8 is shown.

[0034] Fig.15A A cross section of an optical retroreflector having a dielectric layer with a dielectric constant of 4.8 is shown.

[0035] Fig. 15B A cross section of an optical retroreflector having a dielectric layer with a dielectric constant of 4.8 and an additional layer stack with a dielectric constant of 1.98 is shown.

[0036] Fig.16 Shown is an experimental setup for measuring the radar cross section (RCS) of a material, as described in the Examples.

[0037] Fig.17 An example of a manufacturing process for embedding a reflector array into a substrate is shown.

[0038] Reference numerals list

[0039]

[0040] DETAILED DESCRIPTION

[0041] Autonomous vehicles and automated driver assistance systems (ADAS) can use various sensors, including radar systems, to sense the environment, infrastructure, and other objects around the vehicle. A radar system typically includes a radar signal transmitting device (radar transmitter) and a radar radiation detecting device (radar detector) for detecting, for example, reflected radar signals redirected from other vehicles, obstacles, or road infrastructure. The radar transmitter is typically mounted less than a meter above the ground, and the reflected radar signal originates from an element at a distance typically measured from a few feet to tens of feet to hundreds of feet. The detected reflected signal can then be processed to provide additional information about the location of the object that reflected the radar signal.

[0042] Due to the nature of their operation, radar systems require that the items to be detected have surfaces that are not only capable of reflecting radar signals but are also oriented in such a way that the reflected signals are directed toward the radar detector.

[0043] For typical vehicle radar systems that focus on scanning the environment in front of the vehicle, the radar signal has a relatively small angle of incidence relative to road surface markings (such as centerline markings and lane dividers), making it difficult for the radar system to detect this type of item. The same problem exists for moving objects where the angle of the reflecting surface is changing, such as in the case of moving people or moving / turning micro-mobility vehicles (such as scooters, motorcycles, bicycles, etc.).

[0044] In one aspect of the present disclosure, the radar reflective articles of the present disclosure are targeted to facilitate detection and identification of those objects where the angle of incidence of the radar signal is relatively low relative to the plane containing the object to be detected. Those radar reflective articles can be part of pavement markings and wearable items such as vests or helmets that do not contain typical vertical flat surfaces that are preferably used to reflect radar signals back to the radar detector. However, in other aspects, the reflective articles described herein can also be used to improve detection of other permanent or semi-permanent road infrastructure, such as guardrails, posts, signs (e.g., stop signs, yield signs, other information signs, etc.), concrete guardrails, temporary traffic signs (e.g., traffic cones or barrels), mile markers, license plates, stickers, or similar articles attached to vehicles, etc.

[0045] Generally speaking, the radar reflective articles of the present disclosure increase the radar signal reflected back to the radar detector by increasing the angle of incidence of the radar signal relative to the radar reflective surface. The angle of incidence of the radar signal is increased by refracting the radar signal through a dielectric layer with a relatively high dielectric constant. For example, Figure 6As shown, radar signal 603 has a relatively low incident angle (θ1) relative to the surface of dielectric layer 605, but has a higher incident angle relative to the plane of reflective layer 607. In other words, the reflective article of the present disclosure can substantially increase the radar cross section of the radar reflective structure by adding a suitable dielectric layer as described herein.

[0046] In some embodiments, the radar reflective article is a reflective article that includes a reflective layer capable of reflecting radar signals and a dielectric layer adjacent to the reflective layer, wherein the dielectric layer has a dielectric constant of 4 to 100. Unless otherwise specified, the term "dielectric constant" in this disclosure refers to the relative dielectric constant (ε r ), which is the dielectric constant of the material divided by the dielectric constant of a vacuum (ε0). In other embodiments, the dielectric constant of the dielectric layer is 4 to 50, 4 to 30, 4 to 25, 2 to 20, 2 to 15, 4 to 10, and 4 to 8.

[0047] In certain preferred embodiments, the dielectric layer is not transparent to visible light, but opaque. The thickness of the dielectric layer can vary depending on its dielectric constant value. For example, for a higher dielectric constant, the thickness of the dielectric layer can be lower than the thickness of a dielectric layer with a lower dielectric constant. In some embodiments, the thickness of the dielectric layer is 0.2 mm to 25 mm, 0.2 mm to 20 mm, 0.2 mm to 15 mm, 0.2 mm to 10 mm, 0.2 mm to 5 mm, 0.2 mm to 3 mm, 0.2 mm to 1 mm.

[0048] In certain embodiments, the reflective layer is a retroreflective layer comprising a cube corner element layer and a metal layer coated on the cube corner elements. In some cases, the cube corner element layer may include a body portion that generally has a substantially planar front surface and a structured rear surface comprising a plurality of cube corner elements. The cube corner elements may be truncated cube corner arrays (e.g., FIG. 3( a) ) or full cube corner elements (e.g., FIG. 3( b) ). Regardless of the type, each cube corner element includes three substantially mutually perpendicular optical faces to retroreflect incident radiation.

[0049] In some embodiments, the lateral dimensions of the cube corner elements are 2 mm to 65 mm, 2 mm to 50 mm, 2 mm to 40 mm, 2 mm to 30 mm, 2 mm to 20 mm, 2 mm to 10 mm, and 2 mm to 5 mm. In other embodiments, the lateral dimensions of the cube corner elements are 5 mm to 65 mm, 5 mm to 50 mm, 5 mm to 40 mm, 5 mm to 30 mm, 5 mm to 20 mm, and 5 mm to 10 mm.

[0050] In other embodiments, the reflective layer includes a radar reflective structure, such as a suitable antenna that causes the reflected radar radiation to send energy back to the radar transceiver. For example, the radar reflective structure may include a plurality of antennas spaced apart on a planar surface to receive incident radar waves and reflect the radar waves in the direction from which the radar waves were received. The spacing of the antennas may be determined based on the angle of incidence and the expected frequency of the radar. In this embodiment, the antenna may be a linear slot antenna, a U-shaped antenna, or an antenna of other shapes.

[0051] In other embodiments, the reflective layer comprises a continuous metal layer. Suitable metals for the metal layer include copper, aluminum, silver, gold, iron, or a combination or alloy thereof. Continuous metal layers can be beneficial because these are easy to apply and can provide reliable reflection of radar signals.

[0052] Similarly, in some embodiments, the reflective layer may include an element that is conductive or makes the layer conductive, such as at least one discrete metal element. Likewise, suitable metals for the metal element may include copper, aluminum, silver, iron, gold, or a combination or alloy thereof. The discrete metal element may be formed of a metal. Alternatively, the discrete metal element may be formed of a non-metallic material (e.g., a non-metallic carrier comprising ceramic, carbon fiber, glass fiber, epoxy resin, and combinations thereof) having a metal coating thereon. Such discrete metal elements may be beneficial because they may help save material compared to a continuous metal layer.

[0053] However, in other embodiments, the reflective layer includes a conductive layer including a conductive material, such as a bulk metal layer, a foil, and a conductive coating. In such examples, the reflective layer can be formed by etching or otherwise removing portions of the conductive layer. In other words, the reflective layer can include a conductive layer where portions of the conductive layer have been removed in the shape of the radar reflective structure such that the radar reflective structure forms an open or empty area in the conductive material.

[0054] In other embodiments, the reflective layer may include a conductive material placed on or embedded in a non-conductive dielectric layer or sheet. The conductive material may be copper or other metallic material etched on a non-conductive substrate. In another example, the conductive material may include any metal or conductive material deposited on a non-conductive substrate via masked vapor deposition, micro-contact printing, conductive ink, or other suitable processes. In other words, the reflective layer may be formed by depositing a conductive material on another layer rather than removing the conductive material from the conductive layer.

[0055] In general, the reflective layer may be configured to reflect radar radiation of specific wavelengths, such as radiation with a nominal frequency of 24 GHz in the range of 21 GHz to 27 GHz, signals with a nominal frequency of 77 GHz in the range of 76 GHz to 81 GHz, and signals with a nominal frequency of 110 GHz in the range of 105 GHz to 115 GHz. It should be understood that the wavelengths are exemplary wavelengths only, and other ranges of wavelengths are possible.

[0056] To simplify the disclosure and description of the following figures, the description may refer to pavement markings. However, the radar reflective articles of the present disclosure may be equally applicable to examples where the reflective articles are part of: wearable articles, such as vests and helmets; and other planar structures attached to vehicles (e.g., license plates, decals, or similar articles) or other planar structures attached to other road substrates (such as guardrails, traffic lights, temporary traffic control articles) and all other articles previously described.

[0057] Figure 1 Refers to a typical retroreflective sheeting for retroreflecting visible light (105 and 107), which generally includes a retroreflective layer (101) and a metal layer (103). The figure shows two types of visible light rays, namely, rays 105 with a relatively high angle of incidence and rays 107 with a lower angle of incidence. In both cases, the refraction of the visible light is small compared to the refraction by the relatively high dielectric constant dielectric layer of the reflective article of the present invention.

[0058] FIG. 2 shows a retroreflective sheeting for retroreflecting visible light ( FIG. 2( a) ) and for retroreflecting radar signals ( FIG. 2( b) ). The retroreflective sheeting includes a retroreflective layer ( 201 ) and a metal layer ( 203 ). FIG. 2( a) shows two types of radar signals: (1) a radar signal 205 having a relatively high angle of incidence, and (2) a radar signal 207 having a relatively low angle of incidence. Since the size of the cube corner elements is not suitable for the wavelength of the radar signal, none of the radar signals are retroreflected. FIG. 2( b) shows two types of radar signals: (1) a radar signal 209 having a relatively high angle of incidence, and (2) a radar signal 211 having a relatively low angle of incidence. In this case, only the radar signal having a relatively high angle of incidence is retroreflected, while the signal having a relatively low angle of incidence is reflected only in a direction different from the direction of the radar signal source. In this case, in contrast to the reflective article of the present disclosure, the retroreflective sheeting of FIG. 2( b) does not contain a dielectric layer having a suitable dielectric constant.

[0059] 3 shows different examples of retroreflective elements: FIG. 3( a ) shows a truncated solid corner, FIG. 3( b ) shows a full solid corner, FIG. 3( c ) shows a flat two-sided groove, and FIG. 3( d ) shows a concave two-sided groove.

[0060] Figure 4 A retroreflective sheeting suitable for retroreflecting radar signals is shown. However, the sheeting is either completely free of a dielectric layer or includes a dielectric layer having a relatively low dielectric constant. The results are similar to those of FIG. 2( b ). The retroreflective sheeting is only capable of retroreflecting radar signals ( 401 ) having a relatively high angle of incidence. Radar signals ( 403 ) having a relatively low angle of incidence are reflected, but not in the direction of the signal source (i.e., not retroreflected).

[0061] Figure 5 A retroreflective sheeting according to the present disclosure is shown having a relatively high dielectric constant value. In this case, two radar signals (501 and 503) are retroreflected, including a radar signal having a relatively low angle of incidence.

[0062] Figure 6 Retroreflective sheeting according to the present disclosure is shown in more detail. Figure 6 Retroreflective sheeting is similar to Figure 5 6, except that it shows a prism layer 609 and an optional adhesive layer 611. In this case, both radar signals 601 and 603 are properly retroreflected back to the signal source.

[0063] Figure 7 A retroreflective sheeting is shown that includes at least two different dielectric layers (705 and 707) in contact with each other, wherein layer (705) has a lower dielectric constant than (707). As can be seen, even for low incident angle signals, each dielectric layer is able to refract the radar signal to a certain extent, so that the specular reflection of the signal is reduced. The substrate layer (not shown in the figure) is generally adjacent to both the reflective layer and the first dielectric layer 707. That is, the substrate layer is between the reflective layer and the first dielectric layer.

[0064] These types of step gradient dielectric constant configurations provide a smooth or stepped change in dielectric constant from a first layer to a second layer so that the dielectric constant of an individual layer does not have to be as high as that of other individual layers necessary to achieve the same level of overall refraction.

[0065] In this embodiment, the reflective article includes a first dielectric layer (707) including a first continuous matrix of a first material having a first relative dielectric constant (ε1) and a second dielectric layer (705) adjacent to the first dielectric constant layer having a second relative dielectric constant (ε2). In this case, the first dielectric layer has a first thickness (T1); and the second dielectric layer has a second thickness (T2). In this case, the first dielectric constant ε1 is greater than the second dielectric constant ε2.

[0066] Figure 8 shows different embodiments of dielectric layers, where components made of a material with a high dielectric constant are embedded in a resin matrix (801, 813, 805, 817, and 823) with a low dielectric constant. Referring to Figure 8(a), the pure resin layer 801 is optional, and the composite layer 803 contains particles of a high dielectric constant material in a resin matrix.

[0067] Figure 8(b) shows a similar configuration to Figure 8(a), except that the high dielectric constant material is in the form of plates or rods to form composite layer 807. Figure 8(c) shows two separate composite layers (809 and 811), each with a different type (different composition or different shape or both) of high dielectric constant material. In this embodiment, layer 811 includes two types of high dielectric constant materials.

[0068] FIG. 8( d ) shows a configuration similar to that of FIG. 8( a ), except that the composite layer 815 includes two different types (different compositions or different shapes or both) of high dielectric constant materials.

[0069] Figure 8(e) shows three separate layers (817, 819 and 821). Layer 817 is composed of a resin without a high dielectric constant element, while composite layers 819 and 821 each have a different type (different composition or different shape or both) of high dielectric constant material.

[0070] FIG. 8( f ) shows a configuration similar to that of FIG. 8( c ), except that the composite layer 825 includes only one type of high dielectric constant material, unlike the two-component composite layer 815 of FIG. 8( c ).

[0071] Fig. 9 Shown with Figure 7 The structure is similar to the step gradient dielectric constant structure, except that Fig. 9 Three separate dielectric layers are shown, each with a different dielectric constant. In this embodiment, the dielectric constant increases from the lowest dielectric constant value at the outermost layer (in contact with air) to the highest dielectric constant value in the layer adjacent to the reflective layer. The premix layer shown on this figure is equivalent to the premix layer shown above for Figure 7 In some embodiments, the premix layer (base layer) refers to a pavement marking composition or layer (or a group of layers corresponding to a pavement marking).

[0072] Fig.10 Shown with Fig. 9 The construction is similar to the construction of Fig. 9 The configuration in shows a single dielectric layer with a relatively continuous dielectric constant gradient, rather than a dielectric layer with a step gradient.

[0073] Generally speaking, the dielectric constant of the dielectric layer changes from the dielectric constant closest to the first medium to the dielectric constant closest to the second medium. For example, the dielectric layer may have a changing dielectric constant that starts close to the dielectric constant of air (low dielectric constant) on one side and transitions toward a portion with a high dielectric constant at a portion adjacent to the reflective layer. Such a smooth or stepped transition can significantly reduce dielectric boundary reflections that would otherwise occur at these boundary transitions.

[0074] Potential uses for reflective articles of the present disclosure include, as described above, reflective articles made in the form of pavement marking tapes that can be used to mark lanes, center lines, edges, or other features of vehicle lanes. In such examples, the size of the tape can conform to appropriate standards. For example, for pavement markings used to mark lanes, the material can be between about 7.5 centimeters and 30 centimeters (between 3 inches and 12 inches) wide and 30 centimeters (12 inches) long or longer. In the United States, pavement marking tapes are about 4 inches, about 6 inches, or about 8 inches wide (about 10 cm-about 20 cm). In Europe, pavement marking tapes are typically about 15 centimeters or about 30 centimeters wide.

[0075] In other embodiments, the reflective article may include an adhesive layer adjacent to or in close proximity to the reflective layer and a pad adjacent to or in close proximity to the adhesive layer. For example, in some embodiments, and independently of other features described herein, the radar reflective article can be manufactured in the form of an adhesive tape or a self-adhesive tape. The adhesive tape includes an adhesive layer, such as, for example, a hot melt adhesive layer, a pressure-sensitive adhesive layer, a UV curable adhesive layer, a silicone-based adhesive layer, a polyurethane-based adhesive layer, or a combination of any other suitable adhesive layers or adhesives, through which the band can be permanently or temporarily attached to the surface of a road, a wearable article, or attached to other surfaces. The tape material for temporary attachment to the road surface may be removable from the road surface. The self-adhesive tape may include a pressure-sensitive adhesive layer for attachment to the road surface or to another surface, and a suitable pad.

[0076] The reflective article may also include a backing or liner. The backing / liner may include any suitable film or layer to protect the adhesive properties of the adhesive layer and also prevent the article from accidentally adhering to an undesirable surface. Suitable materials for the backing layer include plastic film, coated or uncoated paper, etc. Generally speaking, the backing / liner may be selected so that it does not have a strong adhesion to the adhesive layer itself and is therefore easily removed by hand or with limited tools.

[0077] In some embodiments, the backing layer may include a compliant layer that may enable the radar reflective article to remain substantially planar when attached to a rough surface, such as by conforming to an uneven surface in a vehicle lane or other material to which the lane article may be applied. In other words, the compliant layer may allow the reflective article applied to a rough surface to conform to and adhere to the surface while ensuring that the rough surface does not substantially deform the radar reflective layer.

[0078] In some embodiments, the reflective article may include a thin, highly abrasion resistant and / or dust resistant coating applied to the top surface of the reflective article to protect the reflective article from traffic wear and dirt accumulation. In some preferred embodiments, the protective layer may be radar and light transparent.

[0079] In other embodiments, the skid control particles may be partially embedded in the protective layer or in a layer on top of the protective layer.The skid control particles may be referred to as anti-skid particles and may be included in the upper surface of a pavement marking tape to improve vehicle traction.

[0080] The protective layer can be a single layer or multiple layers, for example, also including a top film covering the underlying layers. In some examples, aliphatic polyurethanes can be used for the top film because aliphatic polyurethane properties can include transparency, resistance to dirt accumulation, sufficient flexibility to conform to the road surface, bonding to inorganic anti-skid particles, and resistance to discoloration due to exposure to ultraviolet radiation.

[0081] In some embodiments, in addition to radar reflection, the reflective articles of the present disclosure may also include other human or machine detectable features. For example, the reflective article may include a colored (e.g., yellow, white, etc.) surface that can be detected by a human or machine vision system. That is, at least a portion of the reflective article may be colored in the human visible spectrum so that the reflective article can be perceived by humans. In other embodiments, a combination of opaque and light-transmissive colorants may be used. In this way, the reflective article will have effective daytime and nighttime colors. The colored elements may be selected to avoid interfering with the function of the radar reflective layer.

[0082] As another example, at least a portion of the reflective article may include text, images, or other visual information. Similarly, the reflective article may include a machine-perceivable surface. For example, at least a portion of the reflective article may be detected via an infrared camera.

[0083] The reflective articles of the present disclosure having radar reflective properties combined with other sensible elements may provide additional advantages over other types of marker tapes or wearable items. For example, these items may be detected by other sensor systems (such as magnetic detectors) mounted on the vehicle to provide additional redundancy. This redundancy may enable the use of sensors to provide greater confidence in the detection of pavement markings or wearable items under a wider range of conditions, and enable the articles of the present disclosure to be distinguished from other radar reflective objects in the field of view.

[0084] Exemplary embodiments including a reflective layer and multiple dielectric layers or a single dielectric layer with a dielectric constant gradient

[0085] 1. A reflective article, comprising:

[0086] a reflective layer that reflects radar signals,

[0087] A substrate layer adjacent to the reflective layer, the substrate layer having a dielectric constant ε s ,

[0088] a first dielectric layer adjacent to the base layer, the first dielectric layer having a first dielectric constant ε1, and

[0089] a second dielectric layer adjacent to the first dielectric layer, the second dielectric layer having a second dielectric constant ε2,

[0090] The first dielectric constant ε1 is greater than the second dielectric constant ε2, and the dielectric constant ε s Greater than the first dielectric constant ε1.

[0091] 2. A reflective article, comprising:

[0092] a reflective layer that reflects radar signals,

[0093] A substrate layer adjacent to the reflective layer, the substrate layer having a dielectric constant ε s ,

[0094] A first dielectric layer adjacent to the base layer, the first dielectric layer having a first dielectric constant ε1 of 2 to 5, and

[0095] a second dielectric layer adjacent to the first dielectric layer, the second dielectric layer having a second dielectric constant ε2 of 1 to 2.5, and

[0096] The first dielectric constant ε1 is greater than the second dielectric constant ε2, and the dielectric constant ε s Greater than the first dielectric constant ε1.

[0097] 3. A reflective article, comprising:

[0098] a reflective layer that reflects radar signals,

[0099] A substrate layer adjacent to the reflective layer, the substrate layer having a dielectric constant ε of 1.5 to 5 s ,

[0100] A first dielectric layer adjacent to the base layer, the first dielectric layer having a first dielectric constant ε1 of 2 to 5, and

[0101] a second dielectric layer adjacent to the first dielectric layer, the second dielectric layer having a second dielectric constant ε2 of 1 to 2.5, and

[0102] The first dielectric constant ε1 is greater than the second dielectric constant ε2.

[0103] 4. A reflective article, comprising:

[0104] a reflective layer that reflects radar signals,

[0105] A substrate layer adjacent to the reflective layer, the substrate layer having a dielectric constant ε of 1.5 to 5 s ,

[0106] A first dielectric layer adjacent to the base layer, the first dielectric layer having a first dielectric constant ε1 of 2.5 to 5, and

[0107] a second dielectric layer adjacent to the first dielectric layer, the second dielectric layer having a second dielectric constant ε2 of 1.5 to 3, and

[0108] a third dielectric layer adjacent to the second dielectric layer, the third dielectric layer having a third dielectric constant ε3 of 1 to 2.5, and

[0109] The first dielectric constant ε1 is greater than the second dielectric constant ε2, and the second dielectric constant ε2 is greater than the third dielectric constant ε3, and the dielectric constant ε s Greater than the first dielectric constant ε1.

[0110] 5. A reflective article, comprising:

[0111] a reflective layer that reflects radar signals,

[0112] A substrate layer adjacent to the reflective layer, the substrate layer having a dielectric constant ε of 1.5 to 5 s ,

[0113] a first dielectric layer adjacent to the reflective layer, the first dielectric layer having a first dielectric constant ε1 of 2 to 5 and a first thickness of 0.4 mm to 0.8 mm, and

[0114] a second dielectric layer adjacent to the first dielectric layer, the second dielectric layer having a second dielectric constant ε2 of 1 to 2.5 and a second thickness of 0.5 mm to 0.9 mm, and

[0115] The first dielectric constant ε1 is greater than the second dielectric constant ε2, and the dielectric constant ε s Greater than the first dielectric constant ε1.

[0116] 6. A reflective article, comprising:

[0117] a reflective layer that reflects radar signals,

[0118] A substrate layer adjacent to the reflective layer, the substrate layer having a dielectric constant ε s ,

[0119] A first dielectric layer adjacent to the base layer, the first dielectric layer having a first dielectric constant ε1 of 2 to 5, and

[0120] a second dielectric layer adjacent to the first dielectric layer, the second dielectric layer having a second dielectric constant ε2 of 1 to 2.5,

[0121] The first dielectric constant ε1 is greater than the second dielectric constant ε2, and the dielectric constant ε s is greater than the first dielectric constant ε1, and

[0122] At least one of the first dielectric layer or the second dielectric layer is opaque.

[0123] 7. A reflective article, comprising:

[0124] a reflective layer that reflects radar signals,

[0125] A substrate layer adjacent to the reflective layer, the substrate layer having a dielectric constant ε s ,

[0126] a first dielectric layer adjacent to the base layer, the first dielectric layer having a first dielectric constant ε1, and

[0127] a second dielectric layer adjacent to the first dielectric layer, the second dielectric layer having a second dielectric constant ε2,

[0128] The first dielectric constant ε1 is greater than the second dielectric constant ε2, and the dielectric constant ε s is greater than the first dielectric constant ε1, and

[0129] wherein the reflective layer has a first major surface and an opposing second major surface, and the first major surface defines a plane of the reflective article,

[0130] The combined effect of the first dielectric layer and the second dielectric layer refracts a radar signal having an incident angle of 5 degrees relative to the plane of the reflective article by at least 60 degrees (30 degrees relative to the normal to the surface).

[0131] 8. A reflective article, comprising:

[0132] a reflective layer that reflects radar signals,

[0133] A substrate layer adjacent to the reflective layer, the substrate layer having a dielectric constant ε s ,

[0134] a dielectric layer adjacent to the base layer and having a first major surface and an opposing second major surface,

[0135] wherein the first major surface of the dielectric layer is adjacent to the base layer,

[0136] wherein the dielectric layer has a dielectric constant gradient from a dielectric constant ε1 on its first major surface to a dielectric constant ε2 on its second major surface, and

[0137] The dielectric constant ε1 is greater than the dielectric constant ε2, and the dielectric constant ε s Greater than the first dielectric constant ε1.

[0138] 9. A reflective article, comprising:

[0139] a reflective layer that reflects radar signals,

[0140] A substrate layer adjacent to the reflective layer, the substrate layer having a dielectric constant ε s ,

[0141] a dielectric layer adjacent to the base layer and having a first major surface and an opposing second major surface,

[0142] wherein the first major surface of the dielectric layer is adjacent to the base layer,

[0143] wherein the dielectric layer has a dielectric constant gradient from a dielectric constant ε1 on its first major surface to a dielectric constant ε2 on its second major surface,

[0144] wherein the dielectric constant 1 is 2 to 5, and the dielectric constant ε2 is 1 to 2.5, and

[0145] The dielectric constant ε1 is greater than the dielectric constant ε2, and the dielectric constant ε s Greater than the first dielectric constant ε1.

[0146] 10. A reflective article, comprising:

[0147] a reflective layer that reflects radar signals,

[0148] A substrate layer adjacent to the reflective layer, the substrate layer having a dielectric constant ε of 1.5 to 5 s ,

[0149] a dielectric layer adjacent to the base layer and having a first major surface and an opposing second major surface,

[0150] wherein the first major surface of the dielectric layer is adjacent to the base layer,

[0151] wherein the dielectric layer has a dielectric constant gradient from a dielectric constant ε1 on its first major surface to a dielectric constant ε2 on its second major surface,

[0152] wherein the dielectric constant 1 is 2 to 5, and the dielectric constant ε2 is 1 to 2.5, and

[0153] The dielectric constant ε1 is greater than the dielectric constant ε2, and the dielectric constant ε s Greater than the first dielectric constant ε1.

[0154] 11. A reflective article, comprising:

[0155] a reflective layer that reflects radar signals,

[0156] A substrate layer adjacent to the reflective layer, the substrate layer having a dielectric constant ε of 1.5 to 5 s ,

[0157] a dielectric layer adjacent to the base layer and having a first major surface and an opposing second major surface,

[0158] wherein the first major surface of the dielectric layer is adjacent to the base layer,

[0159] wherein the dielectric layer has a dielectric constant gradient from a dielectric constant ε1 on its first major surface to a dielectric constant ε2 on its second major surface,

[0160] wherein the dielectric constant 1 is 2 to 5, and the dielectric constant ε2 is 1 to 2.5, and

[0161] The dielectric constant ε1 is greater than the dielectric constant ε2, and the dielectric constant ε s Greater than the first dielectric constant ε1,

[0162] The dielectric layer has a thickness of 0.4 mm to 2 mm.

[0163] 12. A reflective article, comprising:

[0164] a reflective layer that reflects radar signals,

[0165] A substrate layer adjacent to the reflective layer, the substrate layer having a dielectric constant ε s ,

[0166] a dielectric layer adjacent to the base layer and having a first major surface and an opposing second major surface,

[0167] wherein the first major surface of the dielectric layer is adjacent to the base layer,

[0168] wherein the dielectric layer has a dielectric constant gradient from a dielectric constant ε1 on its first major surface to a dielectric constant ε2 on its second major surface,

[0169] wherein the dielectric constant 1 is 2 to 5, and the dielectric constant ε2 is 1 to 2.5, and

[0170] The dielectric constant ε1 is greater than the dielectric constant ε2, and the dielectric constant ε s Greater than the first dielectric constant ε1.

[0171] wherein the reflective layer has a first major surface and an opposing second major surface, and the first major surface defines a plane of the reflective article,

[0172] The dielectric layer refracts a radar signal having an incident angle of 5 degrees relative to the plane of the reflective article by at least 60 degrees (30 degrees relative to the normal to the surface).

[0173] 13. A reflective article, comprising:

[0174] a reflective layer that reflects radar signals,

[0175] A substrate layer adjacent to the reflective layer, the substrate layer having a dielectric constant ε s ,

[0176] a dielectric layer adjacent to the base layer and having a first major surface and an opposing second major surface,

[0177] wherein the first major surface of the dielectric layer is adjacent to the base layer,

[0178] wherein the dielectric layer has a dielectric constant gradient from a dielectric constant ε1 on its first major surface to a dielectric constant ε2 on its second major surface,

[0179] wherein the dielectric constant 1 is 2 to 5, and the dielectric constant ε2 is 1 to 2.5, and

[0180] The dielectric constant ε1 is greater than the dielectric constant ε2, and the dielectric constant ε s Greater than the first dielectric constant ε1,

[0181] The dielectric layer is opaque.

[0182] 14. The reflective article according to any one of the preceding embodiments, wherein the substrate layer has a dielectric constant ε of 1.5 to 5. s .

[0183] 15. The reflective article according to any one of the preceding embodiments, wherein the substrate layer has a dielectric constant ε of 2 to 5. s .

[0184] 16. The reflective article according to any one of the preceding embodiments, wherein the substrate layer has a dielectric constant ε of 2.5 to 5. s .

[0185] 17. The reflective article according to any of the preceding embodiments, wherein the first dielectric constant ε1 is in the range of 2 to 5, and the second dielectric constant ε2 is in the range of 1 to 2.5.

[0186] 18. The reflective article according to any of the preceding embodiments, wherein the thickness of the gradient dielectric layer is in the range of 0.4 mm to 2 mm.

[0187] 19. A reflective article according to any of the preceding embodiments, wherein the first thickness is in the range of 0.4 mm to 0.8 mm (or 0.45 mm to 0.75 mm or 0.5 mm to 0.7 mm), and the second thickness is in the range of 0.5 mm to 0.9 mm (or 0.6 mm to 0.85 mm or 0.65 mm to 0.8 mm).

[0188] 20. A reflective article according to any of the preceding embodiments, wherein the first dielectric constant ε1 is in the range of 2 to 5, and the second dielectric constant ε2 is in the range of 1 to 2.5, and wherein the first thickness is in the range of 0.4 mm to 0.8 mm (or 0.45 mm to 0.75 mm or 0.5 mm to 0.7 mm), and the second thickness is in the range of 0.5 mm to 0.9 mm (or 0.6 to 0.85 mm or 0.65 to 0.8 mm).

[0189] 21. The reflective article according to any of the preceding embodiments, wherein at least one of the first dielectric layer or the second dielectric layer is opaque.

[0190] 22. The reflective article according to any of the preceding embodiments, further comprising a third dielectric layer adjacent to the second dielectric layer, the third dielectric layer having a third dielectric constant ε3, wherein the second dielectric constant ε2 is greater than the third dielectric constant ε3.

[0191] 23. The reflective article according to any of the preceding embodiments, further comprising a third dielectric layer adjacent to the second dielectric layer, the third dielectric layer having a third dielectric constant ε3 in the range of 1.5 to 3, wherein the second dielectric constant ε2 is greater than the third dielectric constant ε3.

[0192] 24. The reflective article according to any of the preceding embodiments, further comprising a third dielectric layer adjacent to the second dielectric layer and having a third dielectric constant ε3, wherein the first dielectric constant ε 1is is 2.5 to 5, the second dielectric constant ε2 is 1.5 to 3, and the third dielectric constant ε3 is 1 to 2.5.

[0193] 25. A reflective article according to any one of the preceding embodiments, wherein the reflective article further comprises a third dielectric layer, which is adjacent to the second dielectric layer and has a third dielectric constant ε3, wherein the first dielectric constant ε1 is 2.5 to 5, the second dielectric constant ε2 is 1.5 to 3, and the third dielectric constant ε3 is 1 to 2.5, wherein the second dielectric constant ε2 is greater than the third dielectric constant ε3, and wherein the third dielectric layer has a thickness in the range of 0.4 mm to 0.8 mm.

[0194] 26. A reflective article according to any of the preceding embodiments, wherein the reflective layer has a first major surface and an opposing second major surface, and the first major surface defines the plane of the reflective article, wherein the combined effect of the first dielectric layer and the second dielectric layer refracts a radar signal having an incident angle of 5 degrees relative to the plane of the reflective article by at least 60 degrees (30 degrees relative to the normal to the surface).

[0195] 27. A reflective article according to any of the preceding embodiments, wherein the reflective layer has a first major surface and an opposing second major surface, and the first major surface defines the plane of the reflective article, wherein the dielectric layer refracts a radar signal having an incident angle of 5 degrees relative to the plane of the reflective article by at least 65 degrees (25 degrees relative to the normal to the surface).

[0196] 28. A reflective article according to any of the preceding embodiments, wherein the reflective layer has a first major surface and an opposing second major surface, and the first major surface defines the plane of the reflective article, wherein the dielectric layer refracts a radar signal having an incident angle of 5 degrees relative to the plane of the reflective article by at least 70 degrees (20 degrees relative to the normal to the surface).

[0197] 29. The reflective article according to any of the preceding embodiments, further comprising a fourth dielectric layer adjacent to the third dielectric layer, the fourth dielectric layer having a fourth dielectric constant ε4, wherein the third dielectric constant ε3 is greater than the fourth dielectric constant ε4.

[0198] 30. The reflective article according to any one of the preceding embodiments, wherein the radar signal is between 76 GHz and 81 GHz.

[0199] 31. The reflective article according to any of the preceding embodiments, wherein the radar signal is between 21 GHz and 27 GHz.

[0200] 32. The reflective article according to any of the preceding embodiments, wherein the radar signal is between 105 GHz and 115 GHz.

[0201] 33. The reflective article of any preceding embodiment, wherein the reflective layer is immediately adjacent to the dielectric layer.

[0202] 34. The reflective article according to any one of the preceding embodiments, wherein the reflective layer comprises:

[0203] a. a retroreflective layer capable of reflecting radar signals, the retroreflective layer comprising cube corner elements having side dimensions of 2 mm to 65 mm, and

[0204] b. A metal layer coated on the cube corner elements.

[0205] 35. The reflective article according to any of the preceding embodiments, wherein the reflective layer comprises a metal layer.

[0206] 36. The reflective article of any preceding embodiment, wherein the reflective layer comprises a plurality of antennas.

[0207] 37. The reflective article of any preceding embodiment, wherein the reflective layer comprises a plurality of antennas including a first antenna, a second antenna partially surrounding the first antenna, and a third antenna partially surrounding the first antenna and the second antenna.

[0208] 38. A reflective article according to any of the preceding embodiments, wherein any of the dielectric layers independently comprises poly(methyl methacrylate), polyethylene terephthalate, polycarbonate, polyurethane, PVC, polyethylene, polypropylene, silicone, acrylates including trimethylolpropane and poly(ethylene glycol) acrylate, and combinations thereof.

[0209] 39. The reflective article according to any of the preceding embodiments, wherein any one of the dielectric layers independently of one another comprises two or more phases.

[0210] 40. A reflective article according to any one of the preceding embodiments, wherein any one of the dielectric layers is independently a composite material comprising at least one material having a low dielectric constant of 1.5 to 3.5 and at least one material having a dielectric constant of 20 to 50.

[0211] 41. A reflective article according to any of the preceding embodiments, wherein any one of the dielectric layers independently comprises particles selected from barium titanate, glass, ABO3 type oxides, AB(Ox,N1-x)3 type oxynitrides and combinations thereof, wherein A is selected from ions Ba, Sr, Pb, Ca, Ln, lanthanide groups, and B is selected from ions Ti, Nb, Cr, Bi, Nd, Zr, Cu.

[0212] 42. A reflective article according to any of the preceding embodiments, wherein any one of the dielectric layers independently comprises particles having a shape selected from spherical, elongated, plate-shaped, rod-shaped, and wherein the particles comprise a material selected from barium titanate, glass, ABO3 type oxide, AB(Ox,N1-x)3 type oxynitride and combinations thereof, wherein A is selected from ions Ba, Sr, Pb, Ca, Ln, lanthanide groups, and B is selected from ions Ti, Nb, Cr, Bi, Nd, Zr, Cu.

[0213] 43. The reflective article according to any of the preceding embodiments, wherein any of the dielectric layers independently of one another have a dielectric constant of 4 to 100.

[0214] 44. The reflective article according to any of the preceding embodiments, wherein any one of the dielectric layers independently of one another has a dielectric constant of 4 to 50.

[0215] 45. The reflective article according to any of the preceding embodiments, wherein any one of the dielectric layers independently of one another has a dielectric constant of 4 to 30.

[0216] 46. ​​The reflective article according to any of the preceding embodiments, wherein any one of the dielectric layers independently of one another has a dielectric constant of 4 to 20.

[0217] 47. The reflective article according to any of the preceding embodiments, wherein any one of the dielectric layers independently of one another has a dielectric constant of 4 to 15.

[0218] 48. The reflective article according to any of the preceding embodiments, wherein any one of the dielectric layers independently of one another has a dielectric constant of 4 to 10.

[0219] 49. The reflective article according to any of the preceding embodiments, wherein any one of the dielectric layers independently of one another has a dielectric constant of 4 to 8.

[0220] 50. The reflective article according to any of the preceding embodiments, wherein the reflective article is a pavement marking.

[0221] 51. The reflective article according to any of the preceding embodiments, wherein the reflective article is a traffic barrel.

[0222] 52. The reflective article according to any of the preceding embodiments, wherein the reflective article is a road marking.

[0223] 53. The reflective article according to any of the preceding embodiments, wherein the reflective article is a traffic cone.

[0224] 54. The reflective article according to any of the preceding embodiments, wherein the reflective article is a guard rail.

[0225] 55. The reflective article according to any of the preceding embodiments, wherein the reflective article is an automotive part.

[0226] 56. A wearable article comprising the reflective article according to any one of the preceding embodiments.

[0227] 57. An article of clothing comprising the reflective article according to any of the preceding embodiments.

[0228] 58. A helmet comprising the reflective article according to any one of the preceding embodiments.

[0229] 59. A badge comprising the reflective article according to any one of the preceding embodiments.

[0230] 60. The reflective article of any preceding embodiment, further comprising a protective layer adjacent to or in close proximity to the dielectric layer.

[0231] 61. The reflective article of any preceding embodiment, further comprising an anti-corrosion layer adjacent to or in close proximity to the reflective layer.

[0232] 62. The reflective article of any preceding embodiment, further comprising a substrate adjacent to or in close proximity to the reflective layer.

[0233] 63. The reflective article of any preceding embodiment, further comprising a substrate adjacent or proximate to the dielectric layer.

[0234] 64. The reflective article of any preceding embodiment, further comprising an adhesive layer adjacent to or proximate to the reflective layer.

[0235] 65. The reflective article according to any one of the preceding embodiments, further comprising: an adhesive layer and a liner, wherein the adhesive layer is adjacent to or in close proximity to the reflective layer; and the liner is adjacent to or in close proximity to the adhesive layer.

[0236] 66. The reflective article according to any of the preceding embodiments, further comprising an adhesive layer adjacent to or in close proximity to the reflective layer, wherein the adhesive is selected from the group consisting of a thermoplastic adhesive and a pressure sensitive adhesive.

[0237] Exemplary embodiments including a retroreflective layer and a dielectric layer to diffract radar signals

[0238] 1. A retroreflective article, comprising:

[0239] A retroreflective layer, which is capable of reflecting radar signals, and includes:

[0240] O cube corner elements having side dimensions of 2 mm to 65 mm, and

[0241] O metal layer, which is coated on the cube corner elements,

[0242] A dielectric layer adjacent to the retroreflective layer and having a dielectric constant of 4 to 100.

[0243] 2. A retroreflective article, comprising:

[0244] A retroreflective layer, which is capable of reflecting radar signals, and includes:

[0245] O cube corner elements having side dimensions of 2 mm to 65 mm, and

[0246] O metal layer, which is coated on the cube corner elements,

[0247] a dielectric layer adjacent to the retroreflective layer and having a dielectric constant of 4 to 50, and

[0248] The dielectric layer is opaque.

[0249] 3. A retroreflective article, comprising:

[0250] A retroreflective layer, which is capable of reflecting radar signals, and includes:

[0251] O cube corner elements having side dimensions of 2 mm to 65 mm, and

[0252] O metal layer, which is coated on the cube corner elements,

[0253] a dielectric layer adjacent to the retroreflective layer and having a dielectric constant of 4 to 50, wherein the dielectric layer is opaque, and

[0254] The thickness of the dielectric layer is 0.2 mm to 25 mm.

[0255] 4. A retroreflective article, comprising:

[0256] A retroreflective layer, which is capable of reflecting radar signals, and includes:

[0257] O cube corner elements having side dimensions of 2 mm to 65 mm, and

[0258] O metal layer, which is coated on the cube corner elements,

[0259] a dielectric layer adjacent to the retroreflective layer and having a dielectric constant of 4 to 30,

[0260] The dielectric layer is opaque.

[0261] The thickness of the dielectric layer is 0.2 mm to 15 mm.

[0262] wherein the retroreflective layer has a first major surface and an opposing second major surface, and the first major surface defines a plane of the retroreflective article, and

[0263] Wherein, when the radar signal has an incident angle of 5 degrees relative to the plane of the retroreflective article, a ratio of the radar cross section with the dielectric layer to the radar cross section without the dielectric layer is greater than 3.

[0264] 5. A retroreflective article, comprising:

[0265] A retroreflective layer, which is capable of reflecting radar signals, and includes:

[0266] O cube corner elements having side dimensions of 2 mm to 65 mm, and

[0267] O metal layer, which is coated on the cube corner elements,

[0268] a dielectric layer adjacent to the retroreflective layer and having a dielectric constant of 4 to 30,

[0269] The dielectric layer is opaque.

[0270] The thickness of the dielectric layer is 0.2 mm to 15 mm.

[0271] wherein the retroreflective layer has a first major surface and an opposing second major surface, and the first major surface defines a plane of the retroreflective article,

[0272] wherein the ratio of the radar cross section with the dielectric layer to the radar cross section without the dielectric layer is greater than 3 when the radar signal has an angle of incidence of 5 degrees relative to the plane of the retroreflective article, and

[0273] The dielectric layer refracts a radar signal having an incident angle of 5 degrees relative to the plane of the retroreflective article by at least 60 degrees (30 degrees relative to the normal to the surface).

[0274] 6. A retroreflective article, comprising:

[0275] A retroreflective layer, which is capable of reflecting radar signals, and includes:

[0276] O cube corner elements having side dimensions of 2 mm to 65 mm, and

[0277] O metal layer, which is coated on the cube corner elements,

[0278] a dielectric layer adjacent to the retroreflective layer and having a dielectric constant of 4 to 30,

[0279] The dielectric layer is opaque.

[0280] The thickness of the dielectric layer is 0.2 mm to 15 mm.

[0281] wherein the retroreflective layer has a first major surface and an opposing second major surface, and the first major surface defines a plane of the retroreflective article,

[0282] wherein the ratio of the radar cross section with the dielectric layer to the radar cross section without the dielectric layer is greater than 3 when the radar signal has an angle of incidence of 5 degrees relative to the plane of the retroreflective article, and

[0283] The radar signal is from 76GHz to 81GHz.

[0284] 7. The retroreflective article of any preceding embodiment, wherein the dielectric layer is opaque.

[0285] 8. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 0.2 mm to 25 mm.

[0286] 9. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 0.2 mm to 20 mm.

[0287] 10. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 0.2 mm to 15 mm.

[0288] 11. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 0.2 mm to 10 mm.

[0289] 12. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 0.2 mm to 5 mm.

[0290] 13. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 0.2 mm to 3 mm.

[0291] 14. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 0.2 mm to 1 mm.

[0292] 15. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 0.3 mm to 25 mm.

[0293] 16. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 0.3 mm to 20 mm.

[0294] 17. The retroreflective article of any of the preceding embodiments, wherein the dielectric layer has a thickness of 0.3 mm to 15 mm.

[0295] 18. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 0.3 mm to 10 mm.

[0296] 19. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 0.3 mm to 5 mm.

[0297] 20. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 0.3 mm to 3 mm.

[0298] 21. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 0.3 mm to 1 mm.

[0299] 22. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 0.5 mm to 25 mm.

[0300] 23. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 0.5 mm to 20 mm.

[0301] 24. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 0.5 mm to 15 mm.

[0302] 25. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 0.5 mm to 10 mm.

[0303] 26. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 0.5 mm to 5 mm.

[0304] 27. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 0.5 mm to 3 mm.

[0305] 28. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 0.5 mm to 1 mm.

[0306] 29. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 1 mm to 25 mm.

[0307] 30. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 1 mm to 20 mm.

[0308] 31. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 1 mm to 15 mm.

[0309] 32. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 1 mm to 10 mm.

[0310] 33. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 1 mm to 5 mm.

[0311] 34. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 1 mm to 3 mm.

[0312] 35. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 1.5 mm to 25 mm.

[0313] 36. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 1.5 mm to 20 mm.

[0314] 37. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 1.5 mm to 15 mm.

[0315] 38. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 1.5 mm to 10 mm.

[0316] 39. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 1.5 mm to 5 mm.

[0317] 40. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a thickness of 1.5 mm to 3 mm.

[0318] 41. The retroreflective article of any of the preceding embodiments, wherein the retroreflective layer has a first major surface and an opposing second major surface, and the first major surface defines a plane of the retroreflective article,

[0319] Wherein, when the radar signal has an incident angle of 5 degrees relative to the plane of the retroreflective article, a ratio of the radar cross section with the dielectric layer to the radar cross section without the dielectric layer is greater than 3.

[0320] 42. The retroreflective article of any of the preceding embodiments, wherein the retroreflective layer has a first major surface and an opposing second major surface, and the first major surface defines a plane of the retroreflective article,

[0321] Wherein, when the radar signal has an incident angle of 5 degrees relative to the plane of the retroreflective article, a ratio of the radar cross section with the dielectric layer to the radar cross section without the dielectric layer is greater than 5.

[0322] 43. The retroreflective article of any of the preceding embodiments, wherein the retroreflective layer has a first major surface and an opposing second major surface, and the first major surface defines a plane of the retroreflective article,

[0323] Wherein, when the radar signal has an incident angle of 5 degrees relative to the plane of the retroreflective article, the ratio of the radar cross section with the dielectric layer to the radar cross section without the dielectric layer is greater than 10.

[0324] 44. The retroreflective article of any of the preceding embodiments, wherein the retroreflective layer has a first major surface and an opposing second major surface, and the first major surface defines a plane of the retroreflective article,

[0325] Wherein, when the radar signal has an incident angle of 5 degrees relative to the plane of the retroreflective article, the ratio of the radar cross section with the dielectric layer to the radar cross section without the dielectric layer is 3 to 100.

[0326] 45. The retroreflective article of any of the preceding embodiments, wherein the retroreflective layer has a first major surface and an opposing second major surface, and the first major surface defines a plane of the retroreflective article,

[0327] Wherein, when the radar signal has an incident angle of 5 degrees relative to the plane of the retroreflective article, the ratio of the radar cross section with the dielectric layer to the radar cross section without the dielectric layer is 3 to 50.

[0328] 46. ​​The retroreflective article of any of the preceding embodiments, wherein the retroreflective layer has a first major surface and an opposing second major surface, and the first major surface defines a plane of the retroreflective article,

[0329] Wherein, when the radar signal has an incident angle of 5 degrees relative to the plane of the retroreflective article, the ratio of the radar cross section with the dielectric layer to the radar cross section without the dielectric layer is 3 to 20.

[0330] 47. The retroreflective article of any preceding embodiment, wherein the dielectric layer refracts a radar signal having an incident angle of 5 degrees relative to the plane of the retroreflective article by at least 60 degrees (30 degrees relative to the normal to the surface).

[0331] 48. The retroreflective article of any preceding embodiment, wherein the dielectric layer refracts a radar signal having an incident angle of 5 degrees relative to the plane of the retroreflective article by at least 65 degrees (25 degrees relative to the normal to the surface).

[0332] 49. The retroreflective article of any preceding embodiment, wherein the dielectric layer refracts a radar signal having an incident angle of 5 degrees relative to the plane of the retroreflective article by at least 70 degrees (20 degrees relative to the normal to the surface).

[0333] 50. The retroreflective article of any preceding embodiment, wherein the radar signal is between 76 GHz and 81 GHz.

[0334] 51. The retroreflective article of any preceding embodiment, wherein the radar signal is between 21 GHz and 27 GHz.

[0335] 52. The retroreflective article of any preceding embodiment, wherein the radar signal is between 105 GHz and 115 GHz.

[0336] 53. The retroreflective article of any preceding embodiment, wherein the reflective layer is immediately adjacent to the dielectric layer.

[0337] 54. The retroreflective article of any preceding embodiment, wherein the retroreflective layer comprises a metallic material.

[0338] 55. The retroreflective article of any preceding embodiment, wherein the retroreflective layer comprises a metal selected from silver, gold, copper, or combinations thereof.

[0339] 56. A retroreflective article according to any of the preceding embodiments, wherein the dielectric layer comprises poly(methyl methacrylate), polyethylene terephthalate, polycarbonate, polyurethane, PVC, polyethylene, polypropylene, silicone, acrylates including trimethylolpropane and poly(ethylene glycol) acrylate, and combinations thereof.

[0340] 57. The retroreflective article of any preceding embodiment, wherein the dielectric layer and the cube corner elements are made of the same material.

[0341] 58. The retroreflective article of any preceding embodiment, wherein the dielectric layer comprises two or more phases.

[0342] 59. The retroreflective article of any preceding embodiment, wherein the dielectric layer is a composite material comprising at least one material having a dielectric constant of 1.5 to 3.5 and at least one material having a dielectric constant of 10 to 50.

[0343] 60. The retroreflective article of any preceding embodiment, wherein the dielectric layer is a composite material comprising at least one material having a dielectric constant of 1.5 to 3.5 and at least one material having a dielectric constant of 20 to 50.

[0344] 61. A retroreflective article according to any of the preceding embodiments, wherein the dielectric layer comprises a dielectric selected from barium titanate, glass, ABO3 type oxide, AB(O x ,N 1-x )3 type nitride materials and their combinations, wherein A is selected from ions Ba, Sr, Pb, Ca, Ln, lanthanide elements, and B is selected from ions Ti, Nb, Cr, Bi, Nd, Zr, Cu.

[0345] 62. A retroreflective article according to any of the preceding embodiments, wherein the dielectric layer comprises particles having a shape selected from spherical, elongated, plate-shaped, rod-shaped, and wherein the particles comprise a material selected from barium titanate, glass, ABO3 type oxide, AB(O x ,N 1-x )3 type nitride materials and their combinations, wherein A is selected from ions Ba, Sr, Pb, Ca, Ln, lanthanide elements, and B is selected from ions Ti, Nb, Cr, Bi, Nd, Zr, Cu.

[0346] 63. The retroreflective article of any preceding embodiment, wherein the dielectric layer comprises particles of a material having a dielectric constant of 10 to 50.

[0347] 64. The retroreflective article of any of the preceding embodiments, wherein the dielectric layer has a structure and / or composition as shown in FIG. 8.

[0348] 65. The retroreflective article of any of the preceding embodiments, wherein the side dimensions of the cube corner elements are from 2 mm to 50 mm.

[0349] 66. The retroreflective article of any of the preceding embodiments, wherein the side dimensions of the cube corner elements are from 2 mm to 40 mm.

[0350] 67. The retroreflective article of any of the preceding embodiments, wherein the side dimensions of the cube corner elements are from 2 mm to 30 mm.

[0351] 68. The retroreflective article of any of the preceding embodiments, wherein the side dimensions of the cube corner elements are from 2 mm to 20 mm.

[0352] 69. The retroreflective article of any of the preceding embodiments, wherein the side dimensions of the cube corner elements are from 2 mm to 10 mm.

[0353] 70. The retroreflective article of any preceding embodiment, wherein the cube corner elements have a side dimension of 2 mm to 15 mm.

[0354] 71. The retroreflective article of any of the preceding embodiments, wherein the side dimensions of the cube corner elements are from 2 mm to 5 mm.

[0355] 72. The retroreflective article of any of the preceding embodiments, wherein the side dimensions of the cube corner elements are from 2 mm to 4 mm.

[0356] 73. The retroreflective article of any of the preceding embodiments, wherein the side dimensions of the cube corner elements are from 3 mm to 15 mm.

[0357] 74. The retroreflective article of any of the preceding embodiments, wherein the side dimensions of the cube corner elements are from 3 mm to 10 mm.

[0358] 75. The retroreflective article of any of the preceding embodiments, wherein the side dimensions of the cube corner elements are from 3 mm to 5 mm.

[0359] 76. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a dielectric constant of 4 to 100.

[0360] 77. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a dielectric constant of 4 to 50.

[0361] 78. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a dielectric constant of 4 to 30.

[0362] 79. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a dielectric constant of 4 to 20.

[0363] 80. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a dielectric constant of 4 to 15.

[0364] 81. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a dielectric constant of 4 to 10.

[0365] 82. The retroreflective article of any preceding embodiment, wherein the dielectric layer has a dielectric constant of 4 to 8.

[0366] 83. The retroreflective article of any preceding embodiment, wherein a surface of the dielectric layer not adjacent to the retroreflective layer has an increased surface roughness relative to an untreated dielectric layer surface.

[0367] 84. The retroreflective article of any preceding embodiment, wherein the retroreflective article is a pavement marking.

[0368] 85. The retroreflective article of any preceding embodiment, wherein the retroreflective article is a traffic barrel.

[0369] 86. The retroreflective article of any preceding embodiment, wherein the retroreflective article is a traffic cone.

[0370] 87. The retroreflective article of any preceding embodiment, wherein the retroreflective article is a road marking.

[0371] 88. The retroreflective article of any preceding embodiment, wherein the retroreflective article is a guard rail.

[0372] 89. The retroreflective article of any preceding embodiment, wherein the retroreflective article is an automotive part.

[0373] 90. A wearable article comprising the retroreflective article according to any of the preceding embodiments.

[0374] 91. An article of clothing comprising the retroreflective article according to any of the preceding embodiments.

[0375] 92. A helmet comprising the retroreflective article according to any of the preceding embodiments.

[0376] 93. A badge comprising the retroreflective article according to any of the preceding embodiments.

[0377] 94. The retroreflective article of any preceding embodiment, further comprising a protective layer adjacent to or proximate to the dielectric layer.

[0378] 95. The retroreflective article of any preceding embodiment, further comprising an anti-corrosion layer adjacent to or in close proximity to the metal layer.

[0379] 96. The retroreflective article of any preceding embodiment, further comprising a substrate adjacent or proximate to the retroreflective layer.

[0380] 97. The retroreflective article of any preceding embodiment further comprising a substrate adjacent or proximate to the metal layer.

[0381] 98. The retroreflective article of any preceding embodiment further comprising an adhesive layer adjacent or proximate to the retroreflective layer.

[0382] 99. The retroreflective article of any of the preceding embodiments, further comprising: an adhesive layer and a liner, the adhesive layer being adjacent or proximate to the retroreflective layer; the liner being adjacent or proximate to the adhesive layer.

[0383] 100. The retroreflective article of any preceding embodiment, further comprising an adhesive layer adjacent or proximate to the retroreflective layer, wherein the adhesive is selected from the group consisting of a thermoplastic adhesive and a pressure sensitive adhesive.

[0384] 101. The retroreflective article of any of the preceding embodiments, further comprising a set of dielectric layers (or a single dielectric layer having a dielectric constant gradient) as described in any of the embodiments preceding this embodiment section.

[0385] Example

[0386] Unless otherwise indicated or readily apparent from the context, all parts, percentages, ratios, etc. in the examples and the remainder of the specification are by weight.

[0387] Computational modeling of prismatic retroreflectors with metal coatings was performed and baseline samples where air was adjacent to the radar source side of the prismatic layer were compared to samples of the present invention where different dielectric layers were adjacent to the prismatic layer. The model simulated radar signals incident on the sample at various angles when calculating the RCS of the sample. Sample parameters that were varied included: dielectric constant of the dielectric layer, thickness of the dielectric layer, element size of the retroreflector. Some models included a weathered layer adjacent to the dielectric layer, where the weathered layer had a dielectric constant value similar to a dust or dirt layer, to determine the impact on RCS performance.

[0388] Computational modeling part

[0389] Testing methods for computational modeling

[0390] Modeling was performed using the electromagnetic modeling tool CST Microwave studio. The RSC (radar cross section) of samples with and without dielectric layers was calculated.

[0391] a. First sample without dielectric layer

[0392] The size of the sample is 25 mm × 25 mm, and the size of the retroreflector is Fig.12 and the incident radar signal comes from an axis at an angle of 85° relative to the axis perpendicular to the plane of the retroreflector ( Fig.11 ).

[0393] b. Second sample with dielectric layer (dielectric constant = 4.8)

[0394] See also Fig.13 .

[0395] c. The third sample with a dielectric layer (dielectric constant = 8)

[0396] See also Fig.14 .

[0397] Here are the calculated RCS results for 3 samples with an 85° incident radar signal.

[0398] At 78 GHz <![CDATA[RCS[mm 2 ]]]> Air 1,724 Dielectric constant = 4.8 16,560 Dielectric constant = 8 28,010

[0399] d. Additional layer stacking due to weather and dust

[0400] For practical applications, retroreflective performance degradation should take into account rain, snow, dust, etc. If there is no dielectric layer on top of the retroreflector, then this additional layer stack will directly cause EM wave refraction, which will critically change the retroreflective performance. However, with a dielectric layer on top, the incident angle at the retroreflector surface will not change due to rain, snow, dust, etc., regardless of any additional layer stack on the dielectric layer, as shown in Figure 15.

[0401] e. Different thickness of dielectric layer (dielectric constant = 8): 500μm / 1mm / 2mm

[0402] Dielectric layer thickness <![CDATA[RCS at 78 GHz (mm 2 )]]> 500μm 16,300 1mm 18,000 2mm 28,010

[0403] Hypothetical Embodiment Section

[0404] Test methods for hypothetical experiments

[0405] For RCS measurements, a set of standard antennas at 77 GHz is used. One acts as a transmitter antenna (Tx) and the other acts as a receiver antenna (Rx). Fig.16The antennas are located near each other, facing the sample, thereby presenting the same angle to the sample. The transmitter antenna is connected to a radio frequency signal generator, and the receiver antenna is connected to a spectrum analyzer. The sample is placed on a flat surface that is non-reflective to the radar signal.

[0406] The RCS is calculated by measuring the transmitted power and the received power by calculating the power loss by subtracting the transmitted power and the received power at the terminals. This power reduction is partly due to losses in the connecting cables and in free space, which depends on the cable properties and the distance between the sample and the antenna. If the transmitting antenna and cable are the same as those on the receiving side, the ratio of the received power and the transmitted power gives the RCS.

[0407] Preparative Hypothetical Example

[0408] One sample consisted of a silicone prismatic substrate with a vapor-coated silver metal layer on top of the prismatic layer. This sample did not have a dielectric layer and was used as a comparative sample. The other sample had a silicone prismatic substrate and a vapor-coated silver metal layer, but also included a dielectric layer on top of the silver layer.

[0409] The silicon prism substrate is replicated by 3D printing a mold. Then, a silver conductive layer is coated on top of the silicon substrate. After the silver is applied, a dielectric layer is applied.

[0410] Fig.17 is an example of a manufacturing process where the reflector array is embedded in a substrate. Depending on the application, the substrate can be flexible.

[0411] The preparation of the various dielectric layers is described below.

[0412] 1: One continuous phase and one discontinuous high dielectric constant dielectric material

[0413] The first granular high dielectric low loss material with a maximum particle size of about 100 microns-200 microns is dispersed into a relatively low viscosity (10,000cP or less) continuous phase until uniformly mixed. The continuous phase can be a mixture of low-loss carbon-based or silicon-based monomers / oligomers, or a solution of a polymer, or a combination thereof, and has a dielectric constant lower than the discontinuous phase. The high dielectric material has a density higher than the continuous phase. The mixture is applied to the metallized layer by a suitable method (e.g., slit die, gravure coating, overcoating). Provide enough residence time before the coating solution becomes solid so that the dense high dielectric phase settles toward the cavity in the metallized layer, thereby producing a dielectric constant gradient from a lower value at the air interface to a higher value at the metallized interface. The curing of the coating can be achieved by drying in an oven, curing the reaction material in an oven, being exposed to actinic radiation, or a certain combination of all three processes. The composition may also include a homogenizing agent, a dispersant, and a desiccant.

[0414] Another example of a continuous phase having a discontinuous high dielectric constant dielectric material includes a discontinuous phase, wherein at least one discontinuous phase has a shape having a width-to-thickness ratio greater than 10. The phase may exhibit (i) a rod-like or (ii) a plate-like morphology. The high aspect ratio discontinuous phase has a higher density than the continuous phase. Both the continuous and discontinuous phases can be deposited by the same process (see the above embodiments), and after coating, the discontinuous plate phase is given sufficient residence time to settle and form an aligned structure having a long direction roughly parallel to the air-dielectric surface.

[0415] 2. One continuous phase, two discontinuous dielectrics

[0416] Following the same procedure as described immediately above in 1, but the composition also includes particles in the same size range that are less dense and have a lower dielectric constant than the continuous phase (e.g., glass bubbles)

[0417] 3. A continuous phase, an added discontinuous dielectric and a discontinuous dielectric added by a process

[0418] The same procedure as described above in 1 is followed, except that the composition may also include a surfactant and the composition is lightly foamed prior to coating so that the bubbles rise and create air gaps in the cured coating while the denser particles settle.

[0419] 4. A continuous phase, an added discontinuous dielectric and a discontinuous dielectric added by a process

[0420] Two-layer coextrusion where 1) is coated as the bottom layer and 2) or the foamed layer has no dielectric added as the layer closest to the air interface

Claims

1. A retroreflective article, comprising: A retroreflective layer, which is capable of reflecting radar signals, and includes: O cube corner elements having side dimensions of 2 mm to 65 mm, and O metal layer, the metal layer is coated on the cube corner elements, a dielectric layer adjacent to the retroreflective layer and having a dielectric constant of 4 to 30, wherein the dielectric layer is opaque, The thickness of the dielectric layer is 0.2 mm to 15 mm, and wherein the retroreflective layer has a first major surface and an opposing second major surface, and the first major surface defines a plane of the retroreflective article, The retroreflective article further comprises: an adhesive layer and a liner, wherein the adhesive layer is adjacent to or closely adjacent to the retroreflective layer; the liner is adjacent to or closely adjacent to the adhesive layer, The dielectric layer comprises a composite layer in which components made of a material with a high dielectric constant are embedded in a resin matrix with a low dielectric constant.

2. The retroreflective article of claim 1, wherein the dielectric layer has a thickness of 0.2 mm to 10 mm.

3. The retroreflective article of claim 1 , wherein the retroreflective layer has a first major surface and an opposing second major surface, and the first major surface defines a plane of the retroreflective article, wherein when the radar signal has an incident angle of 5 degrees relative to the plane of the retroreflective article, a ratio of a radar cross section with the dielectric layer to a radar cross section without the dielectric layer is greater than 3.

4. The retroreflective article of claim 1, wherein the dielectric layer refracts a radar signal having an incident angle of 5 degrees relative to the plane of the retroreflective article by at least 60 degrees.

5. The retroreflective article of any one of the preceding claims, wherein the radar signal is 76 GHz to 81 GHz. The retroreflective article of claim 1 , wherein the radar signal is between 21 GHz and 27 GHz.

7. The retroreflective article of claim 1, wherein the radar signal is between 105 GHz and 115 GHz.

8. The retroreflective article of claim 1, wherein the retroreflective layer is immediately adjacent to the dielectric layer.

9. The retroreflective article of claim 1, wherein the retroreflective layer comprises a metallic material.

10. The retroreflective article of claim 1, wherein the dielectric layer comprises polymethyl methacrylate, polyethylene terephthalate, polycarbonate, polyurethane, pvc, polyethylene, polypropylene, silicone, acrylates including trimethylolpropane and polyethylene glycol acrylate, and combinations thereof.

11. The retroreflective article of claim 1 wherein the cube corner elements have a side dimension of 2 mm to 20 mm.

12. The retroreflective article of claim 1, wherein the dielectric layer has a dielectric constant of 4 to 20.

13. The retroreflective article of claim 1, wherein the retroreflective article is a pavement marking.

Images