Electromagnetic absorbing material

Abstract

The thermally conductive electromagnetic absorbing composition comprises a particle mixture dispersed in a binder, the particle mixture comprising a first group of particles and a second group of particles, the first group of particles being a plurality of particles, and the second group of particles being conductive particles, wherein the particle size of the conductive particles is smaller than that of the plurality of particles. The plurality of particles have a particle size distribution consisting of at least three peaks, wherein at least a majority of the particles within the half-maximum half-width (HWHM) of one peak (but not the others) are at least partially coated with an electromagnetic absorbing coating.

Description

Summary of the Invention

[0001] This document discloses a thermally conductive electromagnetic absorbing composition comprising a particulate mixture dispersed in a binder, and an article comprising the thermally conductive electromagnetic absorbing composition comprising a particulate mixture dispersed in a binder. This document also discloses a fifth-generation (5G) wireless communication system.

[0002] In some embodiments, the thermally conductive electromagnetic absorbing composition comprises a particle mixture dispersed in a binder, the particle mixture comprising a first group of particles and a second group of particles, the first group of particles comprising a plurality of particles, and the second group of particles comprising conductive particles, wherein the size of the conductive particles is smaller than that of the plurality of particles. The plurality of particles have a particle size distribution comprising at least three peaks, wherein at least a majority of the particles within the half-maximum half-width (HWHM) of one peak (but not the others) are at least partially coated with an electromagnetic absorbing coating.

[0003] Articles comprising these thermally conductive electromagnetic absorbing compositions, including a mixture of particles dispersed in a binder, are also disclosed. In some embodiments, the article comprises a thermally conductive electromagnetic absorbing composition, wherein the electromagnetic absorbing composition comprises the aforementioned mixture.

[0004] A fifth-generation (5G) wireless communication system was also disclosed. In some embodiments, the fifth-generation (5G) wireless communication system includes an antenna comprising an array of differently spaced antenna elements configured to receive and transmit signals having frequencies between about 1 GHz and about 120 GHz; and an electromagnetic absorbing material disposed between at least two antenna elements in the antenna element array, wherein the electromagnetic absorbing material comprises the aforementioned particulate mixture. Attached Figure Description

[0005] This application can be more fully understood by referring to the following detailed description of various embodiments of this disclosure in conjunction with the accompanying drawings.

[0006] Figure 1 This is a graph showing the dielectric constant versus frequency data for Examples E1A-E1C.

[0007] Figure 2 This is a graph showing the dielectric loss tangent and frequency data for embodiments E1A-E1C.

[0008] Figure 3 This is a graph showing the dielectric constant versus frequency data for embodiments E2A-E2D.

[0009] Figure 4 This is a graph showing the dielectric loss tangent and frequency data for embodiments E2A-E2D.

[0010] Figure 5 This is a graph showing the EMI reflection loss versus frequency data for Examples E1A-E1C.

[0011] Figure 6 This is a graph showing the EMI reflection loss versus frequency data for embodiments E2A-E2D. Detailed Implementation

[0012] Electromagnetic interference (EMI) is interference caused by electromagnetic radiation from external sources that interferes with the operation of electronic equipment or systems. EMI can be caused by natural sources (such as lightning) or man-made sources (such as power lines, radio and TV signals, and electronic equipment).

[0013] EMI technology involves the development of techniques to mitigate or prevent the effects of electromagnetic interference. This includes designing electronic devices and systems with shielding, filtering, and grounding to reduce the impact of EMI. Techniques such as frequency hopping, spread spectrum, and coding are used to reduce the impact of interference on wireless communication systems.

[0014] In addition, there are regulatory standards that limit EMI emissions from electronic devices and systems, such as the regulations of the Federal Communications Commission (FCC) in the United States. Electronic devices and systems sold in many countries are required to comply with these standards.

[0015] Generally, reducing or eliminating unwanted electromagnetic noise can be achieved by reflecting electromagnetic waves, absorbing electromagnetic waves, or both. Most commonly, highly conductive metal sheets (called EM shielding) are used to reflect unwanted EM waves. However, in some cases, reflected waves are insufficient or may cause further problems.

[0016] EMI absorption is the process by which electromagnetic interference (EMI) energy is dissipated by materials through absorption and conversion into heat. This process is important in applications requiring EMI absorption and dissipation, such as in electronic equipment, power distribution systems, and communication equipment. EMI absorbing materials are typically used in the form of sheets, coatings, or composites, and their effectiveness is measured by their shielding effectiveness, which is the ratio of energy transmitted through the material to the energy incident on it. The effectiveness of EMI absorbing materials can be optimized through material design, including the use of appropriate fillers, surface modification features, and adjustments to material thickness and composition.

[0017] Current EMI composites used in the high GHz band are based on high-load (28% to 70% volume or 60% to 90% wt%) dielectric and magnetic filler materials. However, such high loads tend to reduce the mechanical properties of the composites, and extrusion is troublesome during production. In addition, the particles are often abrasives, and extruding large quantities of these abrasive particles can damage the extrusion equipment.

[0018] Therefore, there is a desire to develop new fillers that can replace current fillers. These alternative fillers have a wide range of performance requirements, including the ability to be used at lower concentrations without reducing absorbance over a wide wavelength range. Using fillers at lower concentrations offers the desired characteristics of lower cost, better mechanical properties, ease of manufacture, and reduced damage to extrusion equipment.

[0019] This document discloses hybrid fillers. These hybrid fillers are filler mixtures used as EMI absorbers. These fillers include a first group of particles and a second group of particles. The first group of particles comprises a plurality of particles, wherein at least some of these particles are at least partially coated with an electromagnetic absorption coating. The second group of particles comprises conductive particles with a particle size smaller than the plurality of particles. Articles comprising particle mixtures and fifth-generation (5G) wireless communication systems comprising particle mixtures are also disclosed.

[0020] The terms silicone resin or siloxane are used interchangeably and refer to a unit having a repeating dialkyl or diarylsiloxane (-SiR2O-) unit.

[0021] The terms “room temperature” and “ambient temperature” are used interchangeably, referring to temperatures in the range of 20°C to 25°C.

[0022] As used in this article, the term "adjacent" in the context of two floors means that the two floors are adjacent to each other and there is no intervening opening space between them. They may be in direct contact with each other (e.g., laminated together) or there may be an intervening floor.

[0023] As used herein, the terms “polymer” and “macromolecule” are consistent with their common usage in chemistry. Polymers and macromolecules are composed of many repeating subunits. As used herein, the term “macromolecule” is used to describe a group having multiple repeating units attached to a monomer. The term “polymer” is used to describe the material obtained by a polymerization reaction.

[0024] The term "alkyl" refers to a monovalent group that is an alkane group, where the alkane is a saturated hydrocarbon. Alkyl groups can be straight-chain, branched, cyclic, or combinations thereof, and typically have 1 to 20 carbon atoms. In some embodiments, the alkyl group contains 1 to 18, 1 to 12, 1 to 10, 1 to 8, 1 to 6, or 1 to 4 carbon atoms. Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, cyclohexyl, n-heptyl, n-octyl, and ethylhexyl.

[0025] The term "aryl" refers to a monovalent group consisting of an aromatic ring and a carbocyclic ring. An aryl group can have one to five rings attached to or fused with an aromatic ring. Other ring structures can be aromatic, non-aromatic, or combinations thereof. Examples of aryl groups include, but are not limited to, phenyl, biphenyl, terphenyl, anthryl, naphthyl, acenaphthenic, anthraquinone, phenanthryl, anthracenyl, pyrene, peryl, and fluorenyl.

[0026] This document discloses thermally absorbing and electromagnetically absorbing compositions. In some embodiments, the composition comprises a particle mixture dispersed in a binder. The particle mixture comprises a first group of particles and a second group of particles. The first group of particles comprises a plurality of particles. The plurality of particles have a particle size distribution comprising at least three peaks, wherein at least a majority of the particles within the half-maximum half-width (HWHM) of one peak (but not the others) are at least partially coated with an electromagnetically absorbing coating. The second group of particles comprises conductive particles with a particle size smaller than that of the plurality of particles.

[0027] As described above, the thermal absorption and electromagnetic absorption compositions of this disclosure include a first group of particles, which comprises a plurality of particles. These particles are described in PCT Publication WO 2021 / 198849 or U.S. Patent Publication US 2023 / 0119856.

[0028] Thermally conductive electromagnetic absorbing particles are prepared by coating thermally conductive non-conductive particles with a thin layer of metal (e.g., tungsten). However, it is difficult to achieve high thermal conductivity using monodisperse or nearly monodisperse particles. A multimodal distribution of particles with a high volumetric loading (e.g., at least about 50% or at least about 60% volumetric loading) can be used to increase the thermal conductivity of compositions of these particles. However, it has been found that when using a multimodal distribution of thermally conductive electromagnetic absorbing particles with a high volumetric loading to increase thermal conductivity, electromagnetic absorption decreases. Not intended to be theoretically limited, it is believed that this is at least partly due to increased reflectivity, resulting in less electromagnetic energy propagating into the absorbable material. However, it has been found that high thermal conductivity (e.g., at least about 2 W / (mK)) and high electromagnetic absorption (e.g., at least about 5 dB / mm over a predetermined frequency range) can be achieved when only a small fraction of the thermally conductive particles (e.g., less than 1% of the total number of particles) includes an electromagnetic absorbing coating. By including an electromagnetic absorbing coating on only a small fraction of the particles, the real part of the relative permittivity can be reduced compared to the case where all or even most of the particles are coated. This reduced relative true permittivity can lead to a decrease in surface reflections from the thermally conductive electromagnetic absorbing material.

[0029] In some embodiments, the thermally conductive particles include at least one of metal oxides, metal carbides, metal hydrates, or metal nitrides. In some embodiments, the thermally conductive particles include at least one of alumina (e.g., one or more of α-alumina particles, substantially spherical alumina particles, or polyhedral alumina), boron nitride, magnesium oxide, zinc oxide, aluminum nitride, silicon carbide, or aluminum hydroxide.

[0030] In some embodiments, the electromagnetic absorbing coating of the thermally conductive particles comprises a metal or a semiconductor. In some embodiments, the electromagnetic absorbing coating comprises one or more of tungsten, aluminum, titanium, steel, chromium, or nickel. Particularly suitable electromagnetic absorbing coatings are those comprising tungsten. It is generally desirable that when the electromagnetic absorbing coating is metallic, it is thin enough to produce significant electromagnetic absorption in the desired frequency range (e.g., through dielectric relaxation as described by Bowler in IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 13, No. 4, pp. 703–711, August 2006, “Designing Dielectric Loss at Microwave Frequencies using Multi-Layered Filler Particles in a Composite”). When a metal layer is sputtered onto the particles, metals such as tungsten, which tend to form a monolayer, are generally preferred.

[0031] In some embodiments, the particles coated with the electromagnetic absorption coating are further coated with an electrically insulating material. The electrically insulating material may be a non-conductive metal oxide such as aluminum oxide.

[0032] The particles can have any suitable shape (e.g., at least one of flakes, plates, spheres, globules, ellipsoids, or irregularly shaped particles). In some embodiments, at least most of the particles are substantially spherical. A particle can be considered substantially spherical if its profile lies within an intermediate space between two concentric, truly spherical profiles whose diameters differ by up to about 30% of the diameter of the larger of these profiles. In some embodiments, at least most of the particles each lie within an intermediate space between two concentric, truly spherical profiles whose diameters differ by up to about 20% or 10% of the diameter of the larger of these profiles.

[0033] For example, particle size distribution can be characterized by number distribution or volume distribution. Volume distribution is often useful when there are far fewer, much larger particles and far more, much smaller particles. The cumulative particle size distribution function V(S) can be defined such that V(S) is the fraction (or percentage) of the total volume of particles provided by particles of size not exceeding S, where particle size is the particle diameter or equivalent diameter (the diameter of a sphere with the same volume as the particle). For example, the particle size distribution function can be defined on linear or logarithmic scales. Logarithmic scales are often useful when there are particles of substantially different sizes. The particle size distribution f(S) can be defined as proportional to dV(S) / dLog(S) such that the area under the curve of f(S) versus Log(S) between Log(S1) and Log(S2) is proportional to the fraction (or percentage) of the total volume of particles provided by particles of size between S1 and S2. The distribution function f(S) is normalized such that for large particle sizes, the cumulative distribution function V(S) approaches 1 or 100%. f(S) can be determined by laser scattering techniques, for example, as known in the art. The number distribution of particle size n(S) can be similarly defined such that the area under the curve of n(S) relative to Log(S) between Log(S1) and Log(S2) is proportional to the fraction (or percentage) of the total number of particles provided by particles of size between S1 and S2. Unless otherwise stated, the particle size distribution described herein can be understood as a volume distribution, and the graph of the particle size distribution can be understood as a linear logarithmic graph (the distribution function values ​​are on the linear y-axis, and the particle size is on the logarithmic x-axis).

[0034] The particle size distribution includes peaks at three particle sizes d1, d2, and d3, where d1 > d2 > d3, wherein at least a majority of the particles within the half-maximum half-width (HWHM) of the peak corresponding to particle size d1 (but not d2 and d3) are at least partially coated with an electromagnetic absorbing coating. In some embodiments, at least 20% of at least a majority of the particles within the HWHM of at least one of the at least three peaks that are at least partially coated with an electromagnetic absorbing material are only partially coated with an electromagnetic absorbing coating.

[0035] The particle size range of each of d1, d2, and d3 can vary. In some embodiments, d1 is in the range of about 50 micrometers to about 100 micrometers, d2 is in the range of about 5 micrometers to about 20 micrometers, and d3 is in the range of about 1 micrometer to about 3 micrometers.

[0036] The amount of the first group of particles in the thermal absorption and electromagnetic absorption composition can vary. Typically, the first group of particles accounts for 15% to 50% by volume or 40% to 79% by weight of the composition.

[0037] The thermal absorption and electromagnetic absorption composition also includes a second set of particles, which includes conductive particles. In some embodiments, the conductive particles include carbon black particles, carbon nanotube particles, or graphene particles.

[0038] Typically, the size of conductive particles ranges from 5 nanometers to 20 micrometers, and more typically from 5 nanometers to 500 nanometers in average particle size.

[0039] The amount of the second group of particles in the thermal absorption and electromagnetic absorption composition can vary. Typically, the second group of particles accounts for 0.05% to 1.5% by weight of the composition.

[0040] The composition also includes a binder. Various binders are suitable. Typically, the binder is a polymer binder. In some embodiments, the binder includes at least one of nylon, polyolefin (e.g., thermoplastic polyolefin (TPO)), epoxy resin, silicone resin, or (meth)acrylate. The binder is present in a sufficient amount to effectively disperse the first group of particles and the second group of particles. In some embodiments, the binder is a curable two-component silicone resin composition.

[0041] In some particularly suitable thermal and electromagnetic absorption compositions of this disclosure, the first group of particles accounts for 15% to 50% by volume or 40% to 79% by weight of the composition, and the second group of particles accounts for 0.05% to 1.5% by weight of the composition.

[0042] The thermal and electromagnetic absorbing compositions disclosed herein possess a variety of desirable properties and can be used in a variety of articles. In some embodiments, the thermal and electromagnetic absorbing compositions have electromagnetic interference mitigation capabilities in a frequency range from about 1 GHz to about 120 GHz.

[0043] In some embodiments, the heat-absorbing and electromagnetic-absorbing composition forms a component of a notch filter for EMI suppression. In other embodiments, the heat-absorbing and electromagnetic-absorbing composition is present as a component of a flexible EMI shielding layer. In still other embodiments, the heat-absorbing and electromagnetic-absorbing composition is present as a component of an EMI shielding layer that at least partially surrounds one or more conductive lines of a cable comprising one or more conductive lines. In some embodiments, the heat-absorbing and electromagnetic-absorbing composition is in the form of a rigid body with a contoured shape.

[0044] Thermally absorbing and electromagnetically absorbing compositions can be in various forms and can be delivered in various ways. In some embodiments, the composition is provided in the form of moldable granules, molded articles, or films. For example, the composition can be formed by mixing particles with a binder at a high temperature (e.g., above the melting point of the binder). For example, the composition can then be extruded into a film or multilayer film, or formed into granules, for example, by extrusion granulation. Alternatively, granules can be formed from materials extruded or otherwise formed by grinding or otherwise granulating the material. For example, the granules can be used to form articles by injection molding. In other embodiments, the composition is in the form of ink for mitigating electromagnetic interference and is suitable for printing on workpieces.

[0045] This document also discloses articles comprising a thermally conductive electromagnetic absorbing composition. In some embodiments, the thermally conductive electromagnetic absorbing composition comprises the above-described particulate mixture. The particulate mixture comprises a first group of particles and a second group of particles. The first group of particles comprises a plurality of particles. The plurality of particles have a particle size distribution comprising at least three peaks, wherein at least a majority of the particles within the half-maximum half-width (HWHM) of one peak (but not the others) are at least partially coated with an electromagnetic absorbing coating. The second group of particles comprises conductive particles, the particle size of which is smaller than the particle size of the plurality of particles. The particles have been described in detail above.

[0046] Articles typically include antireflective films or coatings or antireflective injection molded articles. These types of articles each have their own advantages and disadvantages. Regardless of the type of article, in some embodiments, the thermally conductive and electromagnetically absorbing composition in the article results in a first group of particles comprising 15% to 50% by volume or 40% to 79% by weight. In other embodiments, the thermally conductive and electromagnetically absorbing composition in the article results in a second group of particles comprising 0.05% to 1.5% by weight. In some particularly suitable embodiments, the first group of particles comprises 15% to 50% by volume or 40% to 79% by weight, and the second group of particles comprises 0.05% to 1.5% by weight.

[0047] In some embodiments, the article includes an antireflective film that reflects at least one frequency in the range of about 1 GHz to about 120 GHz. In some embodiments, the thickness of the film or multilayer film is from 0.1 mm to 1.5 mm.

[0048] This document also discloses a fifth-generation (5G) wireless communication system. In some embodiments, the fifth-generation (5G) wireless communication system includes an antenna comprising an array of differently spaced antenna elements configured to receive and transmit signals having frequencies between about 1 GHz and about 120 GHz; and an electromagnetic absorbing material disposed between at least two antenna elements in the antenna element array, wherein the electromagnetic absorbing material comprises: a particle mixture dispersed in a binder, the particle mixture comprising: a first set of particles comprising a plurality of particles having a particle size distribution comprising at least three peaks, wherein at least a majority of the particles within the half-maximum half-width (HWHM) of one peak (but not the others) are at least partially coated with an electromagnetic absorbing coating; and a second set of particles comprising conductive particles, wherein the particle size of these conductive particles is smaller than that of the plurality of particles.

[0049] Example

[0050] These embodiments are for illustrative purposes only and are not intended to limit the scope of the appended claims. Unless otherwise specified, all parts, percentages, ratios, etc., in the embodiments and the remainder of the specification are by weight. The following abbreviations are used: mm = millimeter; cm = centimeter; nm = nanometer; rpm = revolutions per minute; Pa = Pascal; kW = kilowatt; GHz = gigahertz; kg = kilogram. The terms "weight%", "by weight%", and "wt%" are used interchangeably.

[0051] Abbreviation Table

[0052] Preparation of particulate mixtures

[0053] The particle size distribution of BAK-70 and BAK-10 particles was measured by laser scattering using a laser particle size analyzer (LS-POP (6) available from OMEC Instruments, Guangdong, China).

[0054] Tungsten coating on BAK-70 alumina particles

[0055] Alumina particles coated with a W film were produced using a 5-inch × 12-inch (13cm × 30cm) rectangular tungsten (W) sputtering target. The apparatus for preparing particles coated with a W film is described in U.S. Patent 8,698,394 (McCutcheon et al.). 5786.29 g of BAK-70 alumina particles were loaded into a particle stirrer assembly positioned inside a vacuum chamber. The vacuum chamber was evacuated to reduce the pressure to [a certain value]. The reference pressure was 0.133 mPa. Tungsten was sputtered at 1.0 kW for 6 hours under an argon sputtering gas pressure of 5 mPa (0.67 Pa). The chamber was backfilled with argon to remove a small portion of the tungsten-coated alumina particles, and the powder resistivity was measured to be 150 ohm-cm. The estimated thickness of the W coating was 6 nm to 7 nm.

[0056] Alumina (AlOx) coating on tungsten-coated BAK-70 alumina particles

[0057] As generally described in U.S. Patent 5,389,434 (Chamberlain et al.), an aluminum oxide coating was prepared to encapsulate a W film to prevent oxidation. A 5-inch × 8-inch (13 cm × 20 cm) aluminum target was used in the same sputtering machine, and aluminum was sputtered. An AlOx layer was coated on top by supplying oxygen at a rate of 25 sccm (standard cubic centimeters per minute) in addition to sputtering argon. The total pressure was maintained at 10 mTorr (0.13 Pascals). A cathode power of 5.00 kW was applied for 5 hours with particle agitation at 15 rpm. At the end of 5 hours, the chamber was ventilated to ambient conditions, and the particles were removed from the agitator. The final aluminum oxide coating had a powder resistivity >30 x 10⁻⁶. 6 Ohm-centimeter range.

[0058] The aluminum oxide particles coated with W metal and AlOx oxide films (a combination of BAK-70, BAK-30, BAK-10 and TM-1250) are referred to as CP in the table above.

[0059] Test methods

[0060] Determine EM characteristics

[0061] To determine the EM properties of the composite material samples, the following procedure was used:

[0062] Cut a silicone sample (smooth and uniform) to fit a coaxial transmission line fixture and sized it to have the smallest possible air gap inside the transmission line.

[0063] Using an Agilent E8363C network analyzer coupled to a Damaskos Inc. M07T air coaxial test fixture, complex dielectric and magnetic properties were calculated from the obtained S-parameters in the frequency range of 0.1 GHz to 18 GHz using a toroidal sample at room temperature.

[0064] For measurements from 18 GHz to 40 GHz, the complex permittivity and magnetic properties were calculated from the S-parameters obtained using an Agilent E8363C network analyzer (from Agilent Technologies, Santa Clara, California). The rectangular waveguide was made of the silicone composite material described in the example.

[0065] The data is represented by the real part (ε') and the imaginary part (ε”) of the dielectric constant.

[0066] Calculation of dielectric loss tangent

[0067] The dielectric loss tangent (tanδ = ε” / ε’) and frequency are calculated using the EM characteristic data described above. ε’ is the real part of the dielectric constant; ε” is the imaginary part of the dielectric constant.

[0068] Calculation of reflection loss

[0069] A known model, called the radar absorption or reflection loss model, assumes that electromagnetic waves are incident perpendicularly on a single-layer composite absorber adhered to a highly conductive metal plate (to prevent transmission), and that the EM wave absorption performance can then be evaluated based on the reflection loss (RL) in decibels (dB). In this model, lower reflection loss indicates higher electromagnetic absorption performance. In this case, the EM wave absorption performance is studied based on the following equation:

[0070] Where Z0 is the impedance in free space, t is the thickness of the absorber, and c is the speed of light. As indicated by equation (a), the input impedance of the absorber depends on six parameters: complex permeability (µF). r =µ'-jµ'') value and complex permittivity (ε r The real and imaginary parts of ε'-jε'', the thickness (t) of the absorber, and the operating frequency (f).

[0071] Reference: "Structural and high GHz frequency EMI (Electromagnetic Interference) properties of carbonyl iron and boron nitride hybrid composites", Materials Research Express 6(10), 106305, 2019

[0072] Using this radar absorption model, the microwave absorber performance of the sample composite material was calculated. An absorber composite material with a thickness of 1.0 mm (t) was used.

[0073] Example

[0074] Examples E1-E2

[0075] Preparation of composite matrix

[0076] A series of composite matrices were prepared using CP, CB, and silicone resin according to the amounts shown in Table 1. First, CB was added to a plastic cup, followed by CP filler, where CB was added at a concentration of 0.5% to 1.0% by weight relative to the CP filler. For example, 1% by weight CB in Example E1A refers to adding 1% by weight CB relative to the CP particles (71% by weight), thus the added CB was 0.71% by weight. The cup was sealed, and the mixture was manually mixed by shaking the cup for 20 to 30 seconds. The desired amount of silicone resin component A was added. The desired amount of silicone resin component B, i.e., the curing agent, was added to component A. The plastic cup was covered with a lid configured to allow rapid mixing for 2 minutes and 15 seconds under vacuum (100 mbar, 10,000 Pa). The mixture was then poured onto a stainless steel plate. A second stainless steel plate was placed on top of the mixture. A smooth-surface composite was prepared using Teflon sheets. Appropriate spacers were used between the two plates to separate them to the desired thickness (1.0 mm). The board containing the mixture was hot-pressed at 118°C and 3 tons (2700 kg) of pressure for 45 to 60 minutes. The board was then allowed to cool for 30 to 45 minutes before the cured composite sheet was removed. Table 1

[0077] Testing of polymer composites

[0078] The EM properties of the polymer composite material samples were tested using the above-described test methods.

[0079] Figure 1 The EM characteristics (dielectric constant and frequency) of embodiments E1A-E1C are shown. Figure 1 In the middle: ε' and ε are shown. Figure 2 The calculation of dielectric loss tangent for embodiments E1A-E1C is shown in the figure.

[0080] Figure 3 The EM characteristics (dielectric constant and frequency) of embodiments E2A-E2D are shown. Figure 3 In the middle: ε' and ε are shown. Figure 4The calculation of dielectric loss tangent for embodiments E2A-E2D is shown in the figure.

[0081] Calculation of reflection loss

[0082] Calculate Examples E1A-E1C using the method described above (e.g.) Figure 5 (as shown) and Examples E2A-E2D (as shown) Figure 6 The reflection loss is shown in the figure.

[0083] Data Analysis

[0084] As the loading of hybrid fillers (CP and CB) increases, dielectric polarization also increases, thus increasing the dielectric constant. Consequently, the value of the dielectric loss tangent (tanδ = ε” / ε’) also increases.

[0085] As the loading of the EMI hybrid filler increases, the RL peak shifts to lower frequencies. They also show a significant increase in EMI performance with increasing loading (e.g., -24 dB minimum RL peak at ~26 GHz for a 40 vol% filler composite, -22 dB minimum RL peak at ~30 GHz for a 30 vol% filler composite, and -9.5 dB minimum RL peak at ~36 GHz for a 20 vol% filler composite), as shown in Table 2 below. Table 2

[0086] As the loading of EMI hybrid fillers increases, the RL peak shifts to lower frequencies. They also show a significant increase in EMI performance with increasing loading (e.g., -42 dB minimum RL peak at ~28 GHz for a 40 vol% load composite, compared to -18 dB minimum RL peak at ~32 GHz for a 30 vol% load composite), as shown in Table 3 below. Table 3

Claims

1. A thermally conductive electromagnetic absorbing composition, the thermally conductive electromagnetic absorbing composition comprising a particulate mixture dispersed in a binder, the particulate mixture comprising: A first group of particles, comprising a plurality of particles, wherein the plurality of particles have a particle size distribution including at least three peaks, wherein at least a majority of the particles within the half-maximum half-width (HWHM) of one peak but not the others are at least partially coated with an electromagnetic absorption coating; and The second group of particles includes conductive particles, wherein the particle size of the conductive particles is smaller than that of the plurality of particles.

2. The thermally conductive electromagnetic absorption composition according to claim 1, wherein the conductive particles include carbon black particles, carbon nanotube particles, or graphene particles.

3. The thermally conductive electromagnetic absorbing composition according to claim 1, wherein the thermally conductive electromagnetic absorbing composition has electromagnetic interference mitigation capability in a frequency range of about 1 GHz to about 120 GHz.

4. The thermally conductive electromagnetic absorbing composition according to claim 1, wherein the particle size distribution of the first group of particles includes peaks at three particle sizes d1, d2 and d3, d1 > d2 > d3, wherein at least a majority of the particles are at least partially coated with an electromagnetic absorbing coating within the half-maximum half-width (HWHM) of the peak corresponding to the particle size d1 but not d2 and d3.

5. The thermally conductive electromagnetic absorbing composition of claim 1, wherein at least 20% of the at least majority of the particles within the HWHM of at least one of the at least three peaks of the electromagnetic absorbing material are only partially coated with the electromagnetic absorbing coating.

6. The thermally conductive electromagnetic absorbing composition according to claim 1, wherein the first group of particles comprises 15% to 50% by volume or 40% to 79% by weight.

7. The thermally conductive electromagnetic absorbing composition according to claim 6, wherein the second group of particles accounts for 0.05% to 1.5% by weight.

8. The thermally conductive electromagnetic absorbing composition according to claim 1, wherein the first group of particles accounts for 15% to 50% by volume or 40% to 79% by weight, and the second group of particles accounts for 0.05% to 1.5% by weight.

9. The thermally conductive electromagnetic absorption composition according to claim 1, wherein the composition forms a component of a notch filter for EMI suppression.

10. The thermally conductive electromagnetic absorption composition according to claim 1, wherein the composition is present in the form of a component of a flexible EMI shielding layer.

11. The thermally conductive electromagnetic absorption composition of claim 1, wherein the composition is present in the form of a component of an EMI shielding layer, the EMI shielding layer at least partially surrounding the one or more conductive lines of a cable comprising one or more conductive lines.

12. The thermally conductive electromagnetic absorbing composition according to claim 1, wherein the composition is in the form of a rigid body having a contoured shape.

13. The thermally conductive electromagnetic absorbing composition according to claim 1, wherein the precursor composition is in the form of ink, the ink being applied to a workpiece and cured to form the thermally conductive electromagnetic absorbing composition.

14. An article comprising a thermally conductive electromagnetic absorbing composition, wherein the electromagnetic absorbing composition comprises: A particulate mixture dispersed in a binder, the particulate mixture comprising: A first group of particles, comprising a plurality of particles, wherein the plurality of particles have a particle size distribution including at least three peaks, wherein at least a majority of the particles within the half-maximum half-width (HWHM) of one peak but not the others are at least partially coated with an electromagnetic absorption coating; and The second group of particles includes conductive particles, wherein the particle size of the conductive particles is smaller than the particle size of the plurality of particles.

15. The article of claim 14, wherein the conductive particles comprise carbon black particles, carbon nanotube particles, or graphene particles.

16. The article of claim 14, wherein the article comprises a multilayer antireflective film or an antireflective injection molded article.

17. The article of claim 16, wherein the article of claim 16 includes electromagnetic interference mitigation capability in a frequency range of about 1 GHz to about 120 GHz.

18. The article of claim 16, wherein the first group of particles comprises 15% to 50% by volume or 40% to 79% by weight.

19. The article of claim 16, wherein the second group of particles comprises 0.05% to 1.5% by weight.

20. The article of claim 16, wherein the first group of particles comprises 15% to 50% by volume or 40% to 79% by weight, and the second group of particles comprises 0.05% to 1.5% by weight.

21. The article of claim 16, wherein the thickness of the film is from 0.1 mm to 1.5 mm.

22. A fifth-generation (5G) wireless communication system, the fifth-generation (5G) wireless communication system comprising: The antenna comprises an array of differently spaced antenna elements configured to receive and transmit at least one of signals having frequencies between about 1 GHz and about 120 GHz. and An electromagnetic absorbing material disposed between at least two antenna elements in the antenna element array, wherein the electromagnetic absorbing material comprises: A particulate mixture dispersed in a binder, the particulate mixture comprising: A first group of particles, comprising a plurality of particles, wherein the plurality of particles have a particle size distribution including at least three peaks, wherein at least a majority of the particles are at least partially coated with an electromagnetic absorption coating within the half-maximum half-width (HWHM) of one peak but not the others; and The second group of particles includes conductive particles, wherein... The particle size of the conductive particles is smaller than the particle size of the plurality of particles.

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