Article for electromagnetic wave attenuation

Abstract

An interface article for attenuating electromagnetic frequency radiation includes a multilayer structure having a first layer with a low refractive index and a second layer with a high refractive index. The article includes ceramic fillers, metal fillers, graphite fillers, or combinations thereof dispersed in a polymer matrix. The interface article is adjustable to exhibit a reduction of at least 75% in the reflection of incident electromagnetic radiation at target frequencies of 0.3–100 GHz.

Description

Technical Field

[0001] This invention relates to electromagnetic frequency attenuation materials and methods for preparing the same, and particularly to materials that effectively reduce reflections of electromagnetic frequencies between 0.3 and 100 GHz (which cover most 4G and 5G communication applications). Background Technology

[0002] Mobile communication systems using 5G standards currently operate at frequencies below 6 GHz and employ 8 to 24 radio frequency (RF) components in a single radio unit using active multiple-input multiple-output (MIMO) technology. Communication infrastructure is expected to transition to higher frequencies (below 40 GHz) using millimeter-wave technology, which will require an increase in the number of RF components in a single radio unit from 16 to 1,024 or more. This significant increase in component density necessitates the management of generated electromagnetic interference (EMI) to prevent unwanted signal interference. EMI interferes with the electromagnetic energy transmitted between electronic devices, leading to circuit performance degradation and even malfunctions. Examples of harmful effects of EMI include signal distortion or blockage between communication devices, power fluctuations and power outages, electrical fast transients (EFTs), electric shocks, and shortened device lifespan. EMI-sensitive devices include, for example, mobile phones, laptops, servers, ECUs, ADAS sensors, inverters / converters, transceivers, RRUs, and other high-power electronic devices. Currently, EMI shielding is the preferred solution to address these issues.

[0003] Most traditional EMI shielding solutions are based on highly conductive materials, which reflect almost all electromagnetic waves. Some solutions employ electromagnetic radiation absorbing materials, such as high-permeability magnetic materials, including magnetic metal powders, magnetic metal alloy powders, magnetic ceramics, high-dielectric-constant dielectric materials, and combinations thereof. The attenuation provided by these EMI shielding materials stems from both absorption and reflection mechanisms. However, as frequencies increase to the GHz range, the permeability of magnetic materials decreases significantly, while dielectric materials behave more like conductors at high frequencies. Therefore, in the frequency range commonly used in advanced communication systems, the effectiveness of magnetic EMI shielding materials is greatly reduced, and traditional magnetic, dielectric, and conductive EMI shielding materials can reflect up to 50% or more of the total electromagnetic energy, causing secondary pollution or resonant interference.

[0004] Therefore, there is a need for an electromagnetic radiation attenuation device with anti-reflective properties for high-frequency incident radiation. A combined device with both anti-reflective and absorption properties can effectively suppress or even eliminate electromagnetic interference commonly found at high application frequencies. Anti-reflective structured interfaces are widely used in optical lenses, solar photovoltaic cells, microelectronic lithography, and other optical components, as well as in near-infrared applications. However, the use of anti-reflective devices is not common for radio and electromagnetic wave frequencies, mainly because the wavelengths of radio or electromagnetic waves at destructive interference frequencies are too long, typically several meters to several kilometers. Such setups require enormous anti-reflective devices. As communication applications move towards higher frequencies (<40 GHz), the wavelengths of electromagnetic radiation in many materials are on the order of centimeters or millimeters. Effective anti-reflective interfaces with thicknesses ranging from a few millimeters to hundreds of micrometers become feasible for suppressing such electromagnetic radiation. Therefore, this invention relates to a highly efficient radiation suppression device placed near an electromagnetic energy conversion device. Summary of the Invention

[0005] This invention describes a device for attenuating electromagnetic waves, comprising a cross-linked polymer matrix filled with ceramic fillers, metal fillers, graphite, or combinations thereof. In a typical embodiment, polymer composites of different refractive indices form a multilayer device capable of absorbing electromagnetic waves in the millimeter to centimeter range and suppressing reflections at or near specific frequencies within a given frequency range. The refractive index of the polymer composite in the first layer may be lower than that of the polymer composite in the second layer. Preferably, the refractive index of the first layer is proportional to the square root of the refractive index of the second layer. The second layer may contain an electromagnetic radiation suppressing material and thus can be used as an electromagnetic radiation absorber.

[0006] In an exemplary embodiment, an article for attenuating electromagnetic radiation includes: a first layer having a first thickness defined between its incident surface and a transition surface, a first polymer matrix, and a first filler within the first polymer matrix. The first layer exhibits a first refractive index to electromagnetic radiation. The article also includes a second layer located at the transition surface of the first layer, wherein the second layer comprises a second polymer matrix and a second filler within the second polymer matrix, the second filler being adapted to absorb at least a portion of the electromagnetic radiation propagating into the second layer. The second layer exhibits a second refractive index to electromagnetic radiation, wherein the first refractive index is less than the second refractive index by an amount that effectively reduces the emission and reflection of electromagnetic radiation incident on the incident surface by at least 75%, and wherein the frequency of the incident electromagnetic radiation is between 0.3 and 100 GHz.

[0007] In some embodiments, the first thickness is between 0.1 mm and 20 mm, and preferably between 0.5 mm and 4 mm.

[0008] In some embodiments, the electromagnetic radiation exhibits a first wavelength in the first layer, and the first thickness is the product of the first wavelength and a destructive interference frequency factor between 0.2 and 0.3. In some embodiments, the destructive interference frequency factor is between 0.22 and 0.28.

[0009] In some implementations, the first refractive index is within 25% of the square root of the second refractive index, and may be within 10% of the square root of the second refractive index.

[0010] For electromagnetic frequencies between 12 and 18 GHz, the first refractive index can be between 1 and 7, while the second refractive index can be between 5 and 16.

[0011] In some embodiments, the first filler may be selected from alumina, aluminum nitride, boron nitride, magnesium oxide, alumina trihydrate, titanium dioxide, zinc oxide, aluminum hydroxide, zinc nitride, silicon carbide, silicon nitride, and combinations thereof.

[0012] In some embodiments, the second filler may be selected from silicon carbide, titanium dioxide, barium titanate, zinc oxide, aluminum powder, silver powder, magnetic metal powder, magnetic metal alloy powder, carbon fiber, graphite, carbon nanotubes, magnetic ceramics, iron, carbonyl iron, iron oxide, iron alloy, zinc alloy, and combinations thereof.

[0013] In some embodiments, the first polymer matrix and the second polymer matrix are selected from silicone, polyethylene, polybutadiene, acrylics, epoxy resins, polyurethanes, polysulfides, polyisobutylene, polyvinyl polymers, or polyolefin polymers and combinations thereof. The first polymer matrix may be a different polymer or combination of polymers than the second polymer matrix.

[0014] In some embodiments, the first polymer matrix accounts for less than 10% by weight of the first layer.

[0015] Another exemplary embodiment includes an article of article for attenuating electromagnetic radiation, wherein the article includes a first layer having a first thickness defined between an incident surface and a transition surface. The first layer also includes a first polymer matrix and a first filler within the first polymer matrix. The electromagnetic radiation in the first layer exhibits a first wavelength, wherein the first thickness is the product of the first wavelength and a destructive interference frequency factor between 0.2 and 0.3, and the first thickness is between 0.1 mm and 20 mm. The article also includes a second layer having a first surface located at the transition surface of the first layer, wherein the second layer comprises a second polymer matrix.

[0016] In some embodiments, the second filler may be dispersed in the second polymer matrix and is adapted to absorb at least a portion of the electromagnetic radiation propagating into the second layer.

[0017] The second layer exhibits a second refractive index, and the first layer exhibits a first refractive index, which is within 25% of the square root of the second refractive index.

[0018] In some embodiments, a reflector element may be disposed on a second surface of the second layer, wherein the reflector element can effectively reflect electromagnetic radiation propagating from the first layer through the second layer.

[0019] The electronic device according to the invention comprises an electronic device capable of emitting electromagnetic radiation in the frequency range of 0.3-100 GHz. The device also includes an attenuating article located near the electronic device for attenuating the electromagnetic radiation.

[0020] In some embodiments, at least the first layer of the attenuation article exhibits a Young's modulus of less than 1 MPa at 25°C. In some embodiments, both the first and second layers of the attenuation article exhibit a Young's modulus of less than 1 MPa at 25°C. Brief description of the attached diagram

[0021] Figure 1 This is a cross-sectional view of the electromagnetic radiation attenuation product of the present invention;

[0022] Figure 2 This is a schematic diagram of traditional electromagnetic interference shielding;

[0023] Figure 3 This is a schematic diagram of the electromagnetic radiation attenuation product of the present invention;

[0024] Figure 4 This is a cross-sectional view of the electromagnetic radiation attenuation product of the present invention;

[0025] Figure 5 This is a cross-sectional view of the electromagnetic radiation attenuation product of the present invention;

[0026] Figure 6 This is a cross-sectional view of the electronic device of the present invention;

[0027] Figure 7 A graph showing the effect of filler weight fraction on the refractive index of silicon carbide-filled polymer composites;

[0028] Figure 8 This is a chart showing the effect of different filler systems on the refractive index of polymer composites;

[0029] Figure 9 It is a chart showing the effect of different filler systems on the electromagnetic wavelength in filled polymer composites;

[0030] Figure 10 This is a graph showing the radiation return loss tested on the electromagnetic radiation attenuation article of the present invention;

[0031] Figure 11 It is a graph showing the radiation reflection tested on a single-layer filled polymer composite material;

[0032] Figure 12 This is a graph showing the radiation reflection tested on the electromagnetic radiation attenuation article of the present invention;

[0033] Figure 13 It is a graph showing the radiation absorption tested on a single-layer filled polymer composite material;

[0034] Figure 14 This is a graph showing the radiation absorption tested on the electromagnetic radiation attenuation article of the present invention;

[0035] Figure 15 This is a graph showing the radiation reflection tested on the electromagnetic radiation attenuation article of the present invention;

[0036] Figure 16 This is a graph showing the radiation absorption tested on the electromagnetic radiation attenuation article of the present invention;

[0037] Figure 17 This is a graph showing the radiation reflection tested on the electromagnetic radiation attenuation article of the present invention;

[0038] Figure 18 This is a graph showing the radiation absorption tested on the electromagnetic radiation attenuation article of the present invention;

[0039] Figure 19 This is a graph showing radiation reflection tested on the electromagnetic radiation attenuation article of the present invention; and

[0040] Figure 20 This is a graph showing the radiation absorption tested on the electromagnetic radiation attenuation article of the present invention. Detailed Implementation

[0041] The objectives and features listed above, as well as other objectives, features, and advancements embodied in this invention, will now be described in detail with reference to the accompanying drawings. Other aspects of this invention should be understood by those skilled in the art.

[0042] This document describes an apparatus for suppressing or eliminating electromagnetic wave reflection and a method for manufacturing the same. Exemplary application frequencies may be between 0.3 and 100 GHz, preferably between 2.1 and 86 GHz, a range that covers most 4G and 5G communication application frequencies.

[0043] For the purposes of this document, the terms “electromagnetic radiation,” “electromagnetic interference,” “electromagnetic waves,” and “EMI” are intended to refer to radiation with wavelengths in the millimeter or centimeter range (0.001–0.1 m) that can interfere with the normal operation of electronic components (e.g., processors, transmitters, receivers, etc.). The frequencies of such radiation are typically in the range of 0.3–100 GHz, preferably in the range of 2.1–86 GHz. The terms listed above, and other similar terms, are intended to refer to radiation within this frequency range and are therefore used interchangeably to define radiative transmission affected by the materials of this invention (absorption, reflection, inclusion, etc.).

[0044] In an exemplary embodiment, the electromagnetic radiation attenuation device for suppressing electromagnetic radiation reflection includes a multilayer article having a low-refractive-index layer and a high-refractive-index layer. Referring to the accompanying drawings, Figure 1 This is a cross-sectional view of the article 10 of the present invention. Article 10 includes a first layer 12 and a second layer 14. The first layer 12 has a first thickness “T1”, defined between an incident surface 22 and a transition surface 24. The second layer 14 includes a first surface 32 and a second surface 34. The second layer 14 may be disposed at the transition surface 24 of the first layer 12.

[0045] As described herein, article 10 can effectively attenuate electromagnetic radiation, particularly electromagnetic radiation incident on article 10 at the incident surface 22 of the first layer 12. The attenuation of electromagnetic radiation incident on article 10 at the incident surface 22 is facilitated by an anti-reflection effect, which can be tuned to the electromagnetic frequency range of interest to suppress or eliminate the emission and reflection of incident electromagnetic radiation.

[0046] Figure 2 illustrates a conventional EMI shielding device 50, schematically demonstrating the shielding of incident electromagnetic waves 52. The shielding device 50 can be configured to absorb a portion of the incident electromagnetic radiation 52, denoted by absorption loss “A”. The remaining portion of the incident electromagnetic radiation 52 may be redirected due to reflection loss “R” and secondary reflection loss after internal reflection of the incident radiation 52, both of which together constitute emitted reflection 56. The transmitted wave 54 and the re-reflected radiation represent the degree of transmitted electromagnetic radiation passing through the shielding device 50. Shielding effectiveness (SE) is represented by the following relationship: SE = R + A + B Where B = multiple reflection factor.

[0047] As described above, the radiation attenuation device of this invention aims to reduce emitted reflections from incident radiation and transmitted radiation through the device to maximize SE. Conventional EMI shielding devices exhibit insufficient radiation attenuation, particularly in the 0.3-100 GHz frequency range.

[0048] The attenuation effect provided by the present invention within the target frequency range is partly achieved by suppressing or eliminating reflections at the interface between the ambient medium and the incident surface. Figure 3 The article 10 of the present invention is schematically shown, wherein electromagnetic radiation can be significantly attenuated by adjusting the refractive indices of the first layer 12 and the second layer 14 to the frequency of the incident radiation, causing the reflected radiation from the incident surface 22 and the transition surface 24 to be out of phase and to produce destructive interference with each other. Figure 3 As shown, the destructive interference between "reflected wave 1" and "reflected wave 2" can be controlled by the relationship between the electromagnetic radiation wavelength (λ), the thickness (T1) of the first layer 12, and the relative refractive index (n1) of the first layer 12 and the relative refractive index (n2) of the second layer 14.

[0049] In some embodiments, the reflected radiation from the incident surface 22 is out of phase with the reflected radiation from the transition surface 24, resulting in destructive interference between the two reflected electromagnetic waves. This destructive interference can be induced at least in part by constructing a first layer 12 with a thickness (T1) according to the electromagnetic radiation wavelength (λ) in the first layer 12. The destructive interference frequency factor (F) is determined by the following relationship: F = T1 / λ.

[0050] To maximize the destructive interference effect, the factor (F) is preferably within a specific range. In some embodiments, the factor (F) ranges from 0.1 to 0.4. In some embodiments, the factor (F) ranges from 0.2 to 0.3. In some embodiments, the factor (F) ranges from 0.22 to 0.28. In some embodiments, the factor (F) is approximately 0.25.

[0051] In this manner, the article 10, particularly the first layer 12, can be configured with a first thickness T1, which is proportional to the wavelength of electromagnetic radiation in the first layer 12. Therefore, it can be understood that the dimensions of the article 10 of the present invention can be adjusted according to the wavelength (λ) of electromagnetic radiation in the first layer 12 to optimally achieve destructive interference of the reflected wave. This destructive interference improves the anti-reflection performance of the article 10 of the present invention.

[0052] The applicant discovered that for incident electromagnetic radiation frequencies from 0.3 to 100 GHz, the first thickness T1 can be between 0.1 and 20 mm. In some embodiments, the first thickness T1 can be between 0.1 and 10 mm. In some embodiments, the first thickness T1 can be at least 0.1, 0.2, 0.3, 0.4, or 0.5 mm, and not greater than 5, 6, 7, 8, 9, or 10 mm. In some embodiments, the first thickness T1 can be between 0.5 and 4 mm.

[0053] For incident electromagnetic radiation frequencies between 0.3 and 100 GHz, in some embodiments, the second thickness T2 of the second layer 14 can be between 0.1 and 5 mm. In some embodiments, the second thickness T2 can be between 0.2 and 3 mm. In some embodiments, the second thickness T2 can be between 0.25 and 2 mm.

[0054] Destructive interference can be further optimized by aligning the relative refractive indices (n1, n2) of the first layer 12 and the second layer 14 in a specific relationship. In some embodiments, the first refractive index n1 of the first layer 12 is less than the second refractive index n2 of the second layer 14. The presence of two layers with unequal refractive indices is beneficial for internal reflection characteristics at the transition surface 24, which is out of phase with the incident radiation in the first layer 12. Figure 3 As shown, the out-of-phase reflected wave 2 causes destructive interference, thereby reducing the total emission reflection 56.

[0055] In some embodiments, the first refractive index n1 is less than the second refractive index n2, and the amount by which it effectively reduces the emitted reflection 56 of incident radiation 52 at frequencies between 0.3 and 100 GHz by at least 75%. In some embodiments, the first refractive index n1 is less than the second refractive index n2, and the amount by which it effectively reduces the emitted reflection 56 of incident radiation 52 at frequencies between 0.3 and 100 GHz by at least 85%. In some embodiments, the first refractive index n1 is less than the second refractive index n2, and the amount by which it effectively reduces the emitted reflection 56 of incident radiation 52 at frequencies between 0.3 and 100 GHz by at least 90%. In some embodiments, the first refractive index n1 is less than the second refractive index n2, and the amount by which it effectively reduces the emitted reflection 56 of incident radiation 52 at frequencies between 0.3 and 100 GHz by at least 95%.

[0056] The applicant has determined that, for optimal suppression of electromagnetic reflection, an ideal relationship can be established between the first and second refractive indices (n1, n2), wherein the first refractive index n1 approaches the square root of the second refractive index n2. This relationship is expressed as:

[0057] This relationship is particularly applicable when the ambient medium of the incident radiation 52 is air (refractive index 1.0). In this document, the term "ambient medium" refers to the medium immediately adjacent to the first layer 12 reflective surface 22. For applications where the ambient medium is not air, the optimal relationship between refractive indices is: Where n0 = the refractive index of the surrounding medium.

[0058] In some embodiments, the first refractive index n1 is within 25% of the square root of the second refractive index n2. In some embodiments, the first refractive index n1 is within 10% of the square root of the second refractive index n2. In some embodiments, the first refractive index n1 is within 5% of the square root of the second refractive index n2. In some embodiments, for electromagnetic frequencies between 12 and 18 GHz, the first refractive index n1 is between 1 and 7. In some embodiments, for electromagnetic frequencies between 12 and 18 GHz, the second refractive index n2 is between 5 and 16.

[0059] The refractive indices of the first layer 12 and the second layer 14 can be controlled by their material composition, including the polymer matrix material, the filler material, and their respective weight concentrations (including their relative concentrations). In this regard, the antireflective properties of the first layer 12 can be adjusted by appropriately setting the thickness T1 and the first refractive index n1 according to the relationships and guidelines described herein to optimize the effect on the intended electromagnetic radiation exposure. In other words, the antireflective properties of the first layer 12 can be customized to match the target incident radiation frequency by changing the first refractive index n1 (e.g., based on the filler material and filler concentration) and / or the first thickness T1.

[0060] One or more thermoplastic and thermosetting resins are envisioned for use in the polymer matrix of the first layer 12 and the second layer 14. Exemplary resins used in the first layer 12 and the second layer 14 include silicone, acrylics, polyurethanes, epoxy resins, polysulfides, polyisobutylene, polyvinyl polymers, or polyolefin polymers and combinations thereof. In some embodiments, the first polymer matrix of the first layer 12 is less than 60% by weight of the first layer 12. In some embodiments, the first polymer matrix of the first layer 12 is less than 50% by weight of the first layer 12. In some embodiments, the first polymer matrix of the first layer 12 is less than 40% by weight of the first layer 12. In some embodiments, the first polymer matrix of the first layer 12 is less than 30% by weight of the first layer 12. In some embodiments, the first polymer matrix of the first layer 12 is less than 20% by weight of the first layer 12. In some embodiments, the first polymer matrix of the first layer 12 is less than 10% by weight of the first layer 12. In some embodiments, the first polymer matrix of the first layer 12 is less than 5% by weight of the first layer 12. The first polymer matrix may comprise one or more polymer resins.

[0061] Similarly, the second polymer matrix of the second layer 14 may be less than 60% by weight of the second layer 14. In some embodiments, the second polymer matrix of the second layer 14 is less than 50% by weight of the second layer 14. In some embodiments, the second polymer matrix of the second layer 14 is less than 40% by weight of the second layer 14. In some embodiments, the second polymer matrix of the second layer 14 is less than 30% by weight of the second layer 14. In some embodiments, the second polymer matrix of the second layer 14 is less than 20% by weight of the second layer 14. In some embodiments, the second polymer matrix of the second layer 14 is less than 10% by weight of the second layer 14. In some embodiments, the second polymer matrix of the second layer 14 is less than 5% by weight of the second layer 14. The second polymer matrix may comprise one or more polymer resins. The second polymer matrix may employ one or more polymer resins different from those used in the first layer 12.

[0062] In some embodiments, the first layer 12 may include a filler material to help adjust the first layer 12 to the desired refractive index characteristics, thereby making it suitable for attenuating target electromagnetic radiation. Various filler materials can be used as the first filler in the first layer 12. In some embodiments, the first filler may be selected from alumina, aluminum nitride, boron nitride, magnesium oxide, alumina trihydrate, titanium dioxide, zinc oxide, aluminum hydroxide, zinc nitride, silicon carbide, silicon nitride, and combinations thereof.

[0063] In some embodiments, the first filler may constitute at least 40% by weight of the first layer 12. In some embodiments, the first filler may constitute at least 50% by weight of the first layer 12. In some embodiments, the first filler may constitute at least 60% by weight of the first layer 12. In some embodiments, the first filler may constitute at least 70% by weight of the first layer 12. In some embodiments, the first filler may constitute at least 80% by weight of the first layer 12. In some embodiments, the first filler may constitute at least 90% by weight of the first layer 12. In some embodiments, the first filler may constitute at least 95% by weight of the first layer 12.

[0064] In some embodiments, the second layer 14 may include a filler material to assist in adjusting the second layer 14 to the desired refractive index characteristics, thereby making it suitable for attenuating target electromagnetic radiation. In some embodiments, the second filler material may be suitable for obtaining a second refractive index higher than the first refractive index. In some embodiments, the second filler material may be selected from filler materials with a refractive index higher than that of the filler material in the first layer 12. Suitable filler materials include silicon carbide, boron carbide, titanium dioxide, barium titanate, zinc oxide, aluminum powder, silver powder, magnetic metal powder, magnetic metal alloy powder, carbon fiber, graphite, carbon nanotubes, magnetic ceramics, iron, carbonyl ion, iron oxide, iron alloys, zinc alloys, and combinations thereof.

[0065] In some embodiments, the second layer 14 may comprise one or more electromagnetic radiation suppressing filler materials that effectively absorb electromagnetic radiation. Examples of such filler materials include silicon carbide, boron carbide, titanium dioxide, barium titanate, zinc oxide, aluminum powder, silver powder, magnetic metal powder, magnetic metal alloy powder, carbon fiber, graphite, carbon nanotubes, magnetic ceramics, iron, carbonyl ions, iron oxide, iron alloys, zinc alloys, and combinations thereof. The above filler materials are merely examples and are not limited to the use of various anti-reflection and EMI interference suppressing materials known in the art. The filler materials in both the first layer 12 and the second layer 14 may be dispersed in their respective polymer matrices.

[0066] In some embodiments, the second filler may constitute at least 40% by weight of the second layer 14. In some embodiments, the second filler may constitute at least 50% by weight of the second layer 14. In some embodiments, the second filler may constitute at least 60% by weight of the second layer 14. In some embodiments, the second filler may constitute at least 70% by weight of the second layer 14. In some embodiments, the second filler may constitute at least 80% by weight of the second layer 14. In some embodiments, the second filler may constitute at least 90% by weight of the second layer 14. In some embodiments, the second filler may constitute at least 95% by weight of the second layer 14.

[0067] The highly filled polymer composite material of the first layer 12 and the second layer 14 may comprise filler packages containing different types of fillers, or the same filler containing different particle sizes, or a combination of both. In some embodiments, the filler package may comprise a multimodal particle mixture, wherein the average particle size of the first mode (d) 50 The first mode has a refractive index of 100-500 micrometers, the second mode has a refractive index of 1-100 micrometers, and the third mode has a submicrometer size. Highly filled polymer composites offer exceptional flexibility in adjusting the refractive index and electromagnetic wavelength by modifying the filler type and weight fraction, and allow for a variety of filler combinations in multifunctional material designs, such as in thermal management and EMI shielding. Because the polymer matrix may constitute only a small, or even very small, portion of the total composition, the refractive index of the polymer composite is closer to that of the filler material itself. The filler material in both the first and second layers can be granular, flake-like, powdered, filamentous, fiber, or a combination thereof.

[0068] Traditional EMI suppression materials used for electromagnetic or optical frequencies, especially those used as antireflectors, tend to be relatively rigid. The electromagnetic radiation attenuation articles of this invention exhibit good flexibility due to the resin component in their composition. This flexibility is particularly useful in interface applications for electronic devices, such as thermal management applications between radiating emitters and heat sinks. Good flexibility allows for better wetting and contact of materials at the interface, and reduces air gaps and thermal barriers.

[0069] In some embodiments, the Young's modulus of at least the first layer 12 of the article 10 at 25°C is less than 1 MPa, in some embodiments less than 0.5 MPa, and in some embodiments less than 0.2 MPa. In some embodiments, the Young's modulus of both the first layer 12 and the second layer 14 at 25°C is less than 1 MPa, in some embodiments less than 0.5 MPa, and in some embodiments less than 0.2 MPa.

[0070] As shown in Figure 4, the article 10 may further include a reflector element 40 for reflecting electromagnetic radiation incident on the incident surface 22, which is not attenuated by destructive interference or absorption in the first layer 12 and the second layer 14. Therefore, the reflector element 40 may be arranged, for example, on the second surface 34 of the second layer 14. Figure 4 schematically shows incident radiation 52a reflected as reflected radiation 52b by the reflector element 40. This reflection effectively doubles the absorption distance that the radiation must pass through the article 10 before leaving it, thereby enhancing the overall radiation attenuation performance of the article 10. The reflector element 40 preferably has high conductivity to substantially block electromagnetic radiation waves from passing through as transmitted waves 54. The reflector element may be formed as a continuous or discontinuous plate, sheet, foil, fabric, mesh, or combination structure capable of effectively reflecting electromagnetic radiation in at least the range of 0.3 to 100 GHz. Examples of materials that may be used in reflector element 40 include aluminum foil, aluminum mesh, copper mesh, nickel-plated copper taffeta fabric, stainless steel, metal-filled polymer composites, carbon-coated aluminum foil, carbon-filled polymer composites, graphite sheets, and other metal, carbon-based, or intrinsically conductive polymers (ICPs), such as poly(3,4-ethylenedioxythiophene) (PEDOT), poly(p-phenylene sulfide) (PPS), polyacetylene (PAC), polyaniline (PANI), polypyrrole (PPY), polythiophene (PTH) materials, poly(p-phenylene acetylene) (PPV), and combinations thereof.

[0071] In some embodiments, the thickness (T3) of the reflector element 40 can be between 1 micrometer and 1 millimeter. In some embodiments, the thickness T3 of the reflector element 40 can be between 5 micrometers and 500 micrometers. In some embodiments, the thickness T3 of the reflector element 40 can be between 10 micrometers and 200 micrometers.

[0072] As shown in Figure 5, the article 10 may further include a functional layer 60 for adding one or more properties to the article 10. The functional layer 60 may be one or more of the following: thermal conductivity, viscosity, low modulus, electrical insulation, mechanical reinforcement, etc.

[0073] The electronic device 100 of the present invention includes an electronic device 170 that is operatively capable of emitting electromagnetic radiation. In some embodiments, the electronic device is operatively capable of emitting electromagnetic radiation in the frequency range of 0.3-100 GHz. In some embodiments, the electronic device 170 may be a transmitter, a processor, an antenna, etc. Figure 6The illustrated electronic device 100 includes a substrate 180, a bottom filler layer 190 for securing an electronic device 170 to the substrate 180, and an attenuating article 110 comprising a first layer 112 and a second layer 114, wherein the first layer 112 is located near the electronic device 170 for attenuating electromagnetic radiation. In some embodiments, a heat sink and / or EMI shielding element 195 may be attached to the attenuating article 110 and the substrate 180 to impart additional beneficial characteristics to the electronic device 170. Example

[0074] The following examples illustrate the materials and methods used in manufacturing exemplary embodiments of the electromagnetic radiation attenuation articles of the present invention. However, the examples described herein should not be construed as any limitation on the materials, structure, or manufacturing methods of the articles of the present invention. Example 1

[0075] The first anti-reflective layer comprises the following components:

[0076] The first layer was prepared as follows: Filler material and silicone resin were placed in a container. The silicone resin comprised a silicone polymer containing vinyl functional groups, hydrogen functional groups, and a dispersant. These materials were then placed in a high-speed mixer and mixed at 800 rpm for 15 seconds under vacuum, followed by mixing at 1200 rpm for 90 seconds under vacuum. After cooling to room temperature, catalyst and inhibitor were added, and the sample was placed in the high-speed mixer and mixed at 800 rpm for 15 seconds, followed by mixing at 1000 rpm for 60 seconds. The mixed sample was then poured into an 80 mil thick rectangular stainless steel mold. Typically, an FEP liner was placed between the sample and the mold surface to facilitate easy demolding of the cured sample. A top plate was placed on the mold, and the sample in the mold was manually flattened. The mold and sample were placed in a hot press and heated at 120°C for 60 minutes at a pressure of 5 tons of force per square inch. After removing the mold from the hot press, the cured sample was demolded.

[0077] The second absorption layer comprises the following components:

[0078] The second layer is prepared using the same method described in the preparation method for the first layer. A 1 mm fully cured first layer is placed on a 120 mil thick rectangular mold. The composition of the second layer is then poured onto the first layer, and an FIP liner is placed between the mold surface and the first layer. A top plate is placed on the mold, and the sample is gently pressed flat to flatten it. The mold is then placed in a thermopress and subjected to a pressure of 5 tons of force per square inch at 120°C for 60 minutes. The mold is removed from the thermopress, and the cured sample is demolded. When using silicone resin to prepare both the first and second layers, the second layer typically adheres firmly to the first layer. Alternatively, a 1 mm second layer can be prepared first, and then the first layer can be added on top of it. test

[0079] Electromagnetic reflection, absorption, dielectric constant, and permeability were measured using a vector network analyzer (VNA) according to the standard test method ASTM D5568. The VNA measured the electrical network parameters (S-parameters), including S11, S12, S21, and S22. Absorption and reflection were calculated based on the S-parameters.

[0080] The refractive index and wavelength of the composite polymer material can be determined using a vector network analyzer (VNA) test apparatus. A coaxial fixture suitable for the target waveguide size is selected, and a test sample of appropriate size is cut using a steel ruler die matched to the waveguide size. The test sample is then inserted into and pressed into the waveguide fixture, ensuring complete contact between the test sample and the entire inner surface of the fixture. The waveguide fixture is then mounted on the test equipment and calibrated within the frequency range corresponding to the selected waveguide size (e.g., X-band 8.2–12.4 GHz, Ku-band 12.4–18.0 GHz). The VNA test apparatus measures the electrical network parameters (S-parameters), including S11, S12, S21, and S22.

[0081] Where Γ is the reflection coefficient and T is the transmission coefficient. Magnetic permeability µ r and dielectric constant ε r The S-parameters are calculated using the Nicolson-Ross-Weir transformation method shown below:

[0082] in λ 0 It is the wavelength in free space. λ cIt is the cutoff wavelength. The refractive index n and wavelength of a material at a specific frequency. λ The calculation is as follows: Where c is the speed of light in free space, and f It is the target frequency.

[0083] All samples were measured using rectangular waveguide sections in the X-band (8.2–12.4 GHz) and Ku-band (12.4–18.0 GHz). Post-processing TRL calibration was employed, incorporating a 12-term error model that corrects for reflections and crosstalk associated with two-port systems. Samples were cut using steel ruler molds to fit each waveguide sample holder. Radiated return loss (R0) was measured on the samples. L ) and insertion loss (I L Tests were conducted, measured in dB. Multiple samples of identical composition were measured, and the results were averaged. The return loss of the material is directly related to the measured reflection coefficient (Γ), as shown below: R L = 20 log 10 (Г) .

[0084] Insertion loss is determined using a similar method by measuring the transmission coefficient. The measured reflection coefficient includes reflections from both sides of the sample. Generally, the closer the return loss is to 0 dB, the more energy is reflected.

[0085] Shielding effectiveness (SE) is a well-known metric in the field used to measure the effectiveness of a material in shielding electromagnetic radiation. SE originates from: SE = SE R + SE A + SE B = -20 log T i / I o Where SE represents the total shielding effectiveness, SE R For electromagnetic energy loss caused by reflection, SE A To absorb the electromagnetic energy loss, and SE B This refers to the loss of electromagnetic energy caused by multiple reflections. (Similar to SE) R and SE A Compared to the scale, SE B This is usually negligible. i For transmitted radiation, I o = Incident radiation. SE A (dB) and SE B (dB) can be calculated based on the S parameters: and and

[0086] The reflection and absorption of electromagnetic radiation can be calculated using the following formula:

[0087] The effect of filler addition amount (by weight %) on the refractive index (n) of the cured polymer composite material, and the effect of different filler materials on the refractive index (n) of the cured polymer composite material are shown in the table below.

[0088] Figure 6 The effect of filler loading weight fraction on the refractive index of silicon carbide-based cured polymer composites is shown in the figure. The samples listed in Table 3 are samples 1-6. Within the test frequency range, the refractive index of silicon carbide is higher than that of silicone resin. With increasing silicon carbide filler weight fraction, the refractive index of the polymer composite at 15 GHz increases significantly. Figure 7 The effect of filler materials on the refractive index of polymer composites in the 12-18 GHz frequency range is also shown, with samples 3 and 7-11 in Table 3 also showing the effect. Figure 7 middle.

[0089] Figure 8 shows the effect of filler material on the wavelength of intralayer incident radiation in the 12-18 GHz frequency range, where samples 3 and 7-11 in Table 3 are also shown. Figure 8 The applicant discovered that by adjusting the composition of the filler package, a wide refractive index range (e.g., 1.0–12.0) and a wide wavelength range (e.g., 0.2–3 mm) can be achieved using the same resin system in the 12–18 GHz frequency range. Therefore, the term “dominant filler” in Table 3 refers to the dominant filler used in the composition. The dominant filler typically accounts for 70%, 80%, or 90% by weight of the total filler used in the polymer composite. No single sample in the current sample must necessarily contain 100% of the same type of filler.

[0090] The following table shows the effect of the thickness of the first layer on the destructive interference frequency (f) of the cured polymer composite when used in conjunction with the second layer, as shown in the table below.

[0091] The table below lists the composition and thickness of the second layer used in conjunction with the first layer shown in the table above.

[0092] Figure 9 shows the return loss (Ro) of electromagnetic radiation tested on the electromagnetic radiation attenuation device in the 11–19 GHz frequency range. L The unit is dB. This device comprises an alumina-based first-layer polymer composite material with thicknesses of 1.25 mm, 1.50 mm, 1.75 mm, and 2.00 mm (samples 12-15), and a silicon carbide-based second-layer polymer composite material with a constant thickness of 1 mm. Both layers contain a silicone polymer matrix. The silicon carbide polymer composite second layer can also be used as a dielectric electromagnetic absorber for purely experimental purposes, but the second layer does not need to have electromagnetic suppression properties. As shown in Figure 9, R... L The significant decrease corresponds to the destructive interference frequency of each sample. As the thickness of the first layer increases, the wavelength of the electromagnetic radiation also needs to increase accordingly, such that approximately one-quarter of the wavelength (1 / 4λ) equals the thickness of the first layer. The amplitude difference in return loss may include artifacts caused by improper sample preparation, placement, and deformation of the test fixture.

[0093] Figure 10 The S11 reflectance data of the single-layer device using only samples 6 and 7 are shown. Figure 11 The S11 reflection data of a double-layer electromagnetic attenuation device, comprising samples 12-15 as the first layer and the second layer shown in Table 5, are displayed. By comparison... Figure 10 and Figure 11 As can be seen, when using the device of the present invention, reflection decreases from approximately 60-70% to near 0%. Absorption results are similar, as... Figure 12 and Figure 13 The comparison shows that the absorption increases from a maximum of about 40% when using a single-layer device to about 90% in the multi-layer device of the present invention.

[0094] As can be seen from these exemplary embodiments, the article of the present invention exhibits a reduction of at least 75%, 85%, or 95% in the reflection of incident electromagnetic radiation at the destructive interference frequency, and in some embodiments, the article of the present invention exhibits a reduction of at least 98.0%, 98.5%, 99.0%, or 99.5% in the reflection at the destructive interference frequency.

[0095] Figure 14-19 Further examples of the effectiveness of the electromagnetic radiation attenuation device of the present invention are demonstrated by using different filler systems in the first layer, including magnesium oxide-based polymer composites with thicknesses of 1.75 mm and 2.0 mm (samples 16-17); boron nitride-based polymer composites with thicknesses of 2.50 mm and 3.00 mm (samples 18-19); and aluminum nitride-based polymer composites with thicknesses of 1.5 mm, 1.75 mm, and 2.0 mm (samples 20-22), and their reflection and absorption results.

Claims

1. An article for attenuating electromagnetic radiation, the article comprising: A first layer, the first layer having a first thickness defined between its incident surface and its transition surface, a first polymer matrix, and a first filler in the first polymer matrix, wherein the first layer exhibits a first refractive index to electromagnetic radiation; and A second layer is disposed at the transition surface of the first layer. The second layer has a second polymer matrix and a second filler within the second polymer matrix. The second filler is adapted to absorb at least a portion of the electromagnetic radiation propagating into the second layer. The second layer exhibits a second refractive index to the electromagnetic radiation. The first refractive index is less than the second refractive index by such a amount that the reflected electromagnetic radiation incident on the incident surface is effectively reduced by at least 75%, wherein the frequency of the incident electromagnetic radiation is between 0.3 and 100 GHz.

2. The article of claim 1, wherein the first thickness is between 0.1 mm and 20 mm.

3. The article of claim 2, wherein the first thickness is between 0.5 mm and 4 mm.

4. The article of claim 1, wherein the electromagnetic radiation exhibits a first wavelength in the first layer, and the first thickness is the product of the first wavelength and a destructive interference frequency factor, wherein the destructive interference frequency factor is between 0.2 and 0.

3.

5. The article of claim 4, wherein the destructive interference frequency factor is between 0.22 and 0.

28.

6. The article of claim 1, wherein the first refractive index is within 25% of the square root of the second refractive index.

7. The article of claim 6, wherein the first refractive index is within 10% of the square root of the second refractive index.

8. The article of claim 1, wherein the first refractive index is between 1 and 7 for an electromagnetic radiation frequency between 12 and 18 GHz.

9. The article of claim 8, wherein the second refractive index is between 5 and 16 for an electromagnetic frequency between 12 and 18 GHz.

10. The article of claim 1, wherein the first filler is selected from alumina, aluminum nitride, boron nitride, magnesium oxide, alumina trihydrate, titanium dioxide, zinc oxide, aluminum hydroxide, zinc nitride, silicon carbide, silicon nitride, and combinations thereof; and the second filler is selected from silicon carbide, boron carbide, titanium dioxide, barium titanate, zinc oxide, aluminum powder, silver powder, magnetic metal powder, magnetic metal alloy powder, carbon fiber, graphite, carbon nanotubes, magnetic ceramics, iron, iron carbonyl, iron oxide, iron alloy, zinc alloy, and combinations thereof.

11. The article of claim 1, wherein the first polymer matrix and the second polymer matrix are selected from silicone, polyethylene, polybutadiene, acrylics, epoxy resins, polyurethanes, polysulfides, polyisobutylene, polyvinyl polymers or polyolefin polymers and combinations thereof.

12. The article of claim 11, wherein the first polymer matrix is ​​a polymer or combination of polymers different from the second polymer matrix.

13. The article of claim 1, wherein the first polymer matrix comprises less than 10% by weight of the first layer.

14. An article for attenuating electromagnetic radiation, said article comprising: A first layer, the first layer having a first thickness defined between its incident surface and its transition surface, a first polymer matrix, and a first filler in the first polymer matrix, wherein electromagnetic radiation exhibits a first wavelength in the first layer, the first thickness is the product of the first wavelength and a destructive interference frequency factor, wherein the destructive interference frequency factor is between 0.2 and 0.3, and the first thickness is between 0.1 mm and 20 mm; and The second layer has a first surface disposed at the transition surface of the first layer, and the second layer has a second polymer matrix.

15. The article of claim 14, comprising a second filler in the second polymer matrix, the second filler being adapted to absorb at least a portion of electromagnetic radiation propagating into the second layer.

16. The article of claim 15, wherein the second layer exhibits a second refractive index and the first layer exhibits a first refractive index, the first refractive index being within 25% of the square root of the second refractive index.

17. The article of claim 14, comprising a reflector element disposed on a second surface of the second layer, the reflector element effectively reflecting electromagnetic radiation propagating from the first layer through the second layer.

18. An electronic device comprising: Electronic devices capable of operably emitting electromagnetic radiation in the frequency range of 0.3-100 GHz; and The attenuation article of claim 14, located near the electronic device, is used to attenuate electromagnetic radiation.

19. The electronic device of claim 18, wherein at least the first layer of the attenuation article exhibits a Young's modulus of less than 1 MPa at 25°C.

20. The electronic device of claim 19, wherein both the first and second layers of the attenuation article exhibit a Young's modulus of less than 1 MPa at 25°C.

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